Use of hydraulic binders for reducing sulphate leaching

Environmental Science and Pollution Research https://doi.org/10.1007/s11356-018-2376-5

RESEARCH ARTICLE

Use of hydraulic binders for reducing sulphate leaching: application to gypsiferous soil sampled in Ile-de-France region (France) Vincent Trincal 1,2 & Vincent Thiéry 1,2 & Yannick Mamindy-Pajany 1,2 & Stephen Hillier 3,4 Received: 31 January 2018 / Accepted: 22 May 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018

Abstract Polluted soils are a serious environmental risk worldwide and consist of millions of tons of mineral waste to be treated. In order to ensure their sustainable management, various remediation options must be considered. Hydraulic binder treatment is one option that may allow a stabilisation of pollution and thus offer a valorisation as secondary raw materials rather than considering them as waste. In this study, we focused on sulphate-polluted soil and tested the effectiveness of several experimental hydraulic binders. The aim was to transform gypsum into ettringite, a much less soluble sulphate, and therefore to restrict the potential for sulphate pollutant release. The environmental assessment of five formulations using hydraulic binders was compared to the gypsiferous soil before treatment (contaminated in sulphate). The approach was to combine leaching tests with mineralogical quantifications using among others thermogravimetric and XRD methods. In the original soil and in the five formulations, leaching tests indicate sulphate release above environmental standards. However, hydraulic binders promote ettringite formation, as well as a gypsum content reduction as observed by SEM. The stabilisation of sulphates is, however, insufficient, probably as a result of the very high content of gypsum in the unusual soil used. The mineralogical reactions highlighted during the hydration of hydraulic binders are promising; they could pave the way for the development of new industrial mixtures that would have a positive environmental impact by allowing reuse of soils that would otherwise be classified as waste. Keywords Sulphate leaching . Gypsiferous soils . Mineralogical quantifications . Sulphoaluminate ALPENAT® binder . SEM observations

Introduction The reuse of excavated soils in civil engineering projects as materials strongly depends on their geo-mechanical and Responsible editor: Philippe Garrigues Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11356-018-2376-5) contains supplementary material, which is available to authorized users. * Vincent Trincal [email protected] 1

Institut Mines-Télécom Lille Douai, LGCgE-GCE, 941 rue Charles Bourseul, 59500 Douai, France

2

Université Lille Nord de France, 1 bis Georges Lefèvre, 59044 Lille, France

3

The James Hutton Institute, Craigiebuckler, Aberdeen AB15 8QH, United Kingdom

4

Department of Soil and Environment, Swedish University of Agricultural Sciences (SLU), 75007 SE-Uppsala, Sweden

environmental characteristics, especially regarding the potential release of any contaminants they may contain. During road construction, excavated soils are often categorised as waste that must be analysed, managed and if possible valorised. France has edited a guide that defines the procedure to assess the acceptance of wastes, including excavated soils, as alternative road construction materials (SETRA 2011). It uses the leaching limits for inert wastes as starting point for general use. However, if any chemical parameters are not in compliance with the standard criteria, the waste stream must be treated before reuse or stored at landfills. Soil stabilisation, with lime or cement, is a widely used technique to improve their valued properties, for example as building materials. The use of these additives is particularly suitable for clay soils, which generally have inadequate mechanical properties in terms of plasticity, handling and loadbearing capacity (Guney et al. 2007; Lin et al. 2007; Göktepe et al. 2008). Ca2+ ions, from the addition of lime, can amalgamate clay particles and improve the properties of the soil by providing a more granular structure, a greater permeability and a reduced plasticity (Kinuthia et al. 1999; Lin et al.

Environ Sci Pollut Res

2007). The stabilisation of a soil depends, among other things, on its mineralogy, the choice of the additive and the curing conditions (Misra et al. 2005; Yarbaşı et al. 2007; Göktepe et al. 2008). Ordinary Portland cement is usually recommended, for example, because it contains the necessary oxides (SiO2, Al2O3 and CaO) and it acts quickly (Wild et al. 1998; Degirmenci et al. 2007). In this study, gypsiferous soil that can generate high sulphate leaching was investigated. Gypsum is the most abundant of all sulphate minerals occurring in extensive bedded sedimentary deposits, sometimes of considerable thickness, and in association with limestone, shale and marls, particularly in rocks of Permian and Triassic age (Deer et al. 1962). It also occurs in evaporite sequences giving rise to considerable deposits in saline lakes and salt pans (Charola et al. 2007). In arid and semiarid environments, gypsum can also be a major soil component (Herrero et al. 2009). The reaction of calcium, aluminium and silicon with sulphate in the presence of water causes expansive minerals formation, the most common in civil engineering contexts being ettringite [Ca6Al2(SO4)3(OH)12 · 26H2O] (Crammond 2002; Nobst and Stark 2003; Ciliberto et al. 2008; Norman et al. 2013). Expansive effects of sulphates in lime stabilised clay soils have been reported by many authors (e.g. Wild et al. 1999 and references therein). Ettringite, also known as hydrated calcium sulphoaluminate, is the most important solid phase of the AFt group of cement terminology (e.g. Taylor 1997), where AFt stands for alumina, ferric oxide and tri-sulphate (e.g. Thiéry et al. 2017). Ettringites can also incorporate other oxi-anions like chromate (Hillier et al. 2003). For Seco et al. (2016), the mechanisms of ettringite formation are not well established (Mohamed 2000), although the conditions that promote its formation are known (Ouhadi and Yong 2003) and include (1) high pH, (2) presence of soluble Al, (3) presence of soluble Ca, (4) presence of soluble sulphate, and (5) availability of water. It is also known that the rate of ettringite formation is accelerated by high temperatures (Rajasekaran 2005). The crystallisation rate, the shape and the size of the crystals vary according to the different reagents from the pozzolanic cements and any additives used (Talero 2005; Rahhal and Talero 2014). Substitution of lime/cement by blast furnace slags or magnesium binders will inhibit the formation of ettringite in favour of less expansive calcium silicate hydrate (C-S-H) gels (Xeidakis 1996a, b; Wild et al. 1998; Tasong et al. 1999; Obuzor et al. 2012; Celik and Nalbantoglu 2013). The objective of the research described herein was to find a hydraulic binder that will reduce sulphate releases from gypsiferous soil. One way to accomplish this would be to modify the mineralogical composition of the soil, in particular by transforming the gypsum into ettringite (a mineral much less soluble than gypsum and therefore with less potential to release sulphate pollution). Various mixtures between gypsiferous clay soil and experimental hydraulic binders were tested. Chemical leaching tests were carried out 28 days after mixing in order to evaluate environmental suitability,

according to European standard (NF EN 12457-2 2002). Mineralogical and petrological characterizations were also carried out using scanning electron microscopy (SEM), Xray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), and thermogravimetric analysis coupled with mass spectrometry (TGA-MS). The confrontation between the chemical data, physical analyses and the microscopic observations makes it possible to better understand the chemical processes and the mineralogical reactions that took place during the hydration of the hydraulic binder mixed with polluted soil. The results obtained in this study are encouraging for the treatment of sulphate waste and their possible reuse as raw material. At a time when the preservation of natural resources and the treatment of waste become important economic and environmental issues, the development of new hydraulic binders seems to be a promising solution in civil engineering.

Material and setting Samples Mineralogical and geochemical studies were performed on the initial gypsiferous soil from the Paris Basin near Monthyon (France) and then on the same material 28 days after mixing with hydraulic binders for sulphate stabilisation. The aim of this stabilisation is to transform gypsum (CaSO4·2H2O, also called selenite) into ettringite (Ca6Al2(SO4)3(OH)12·26H2O) to reduce sulphate leaching. For that, it is necessary to provide a source of water, aluminium and calcium following Eq. (1): 3½CaSO4
2H2 0 þ 32H2 0 þ 2Al   þ 3Ca→ Ca6 Al2 ðSO4 Þ3 ðOHÞ12
26H2 0 þ 12H

ð1Þ

Assuming 100 g of dry soil contains around 30 g of gypsum (cf. ‘Results and discussion’ section), then according to Eq. (1), 33.5 ml of water (H2O), 3.1 g of aluminium (Al), and 7.0 g of calcium (Ca) must be added to completely transform the gypsum into 61.7 g of ettringite. To provide the required elements to drive this reaction, several additives were tested (Table 1): –

–

Calcium sulphoaluminate ALPENAT®, a hydraulic blend produced by Vicat mainly composed of ye'elimite (Ca4Al6O12SO4), larnite ‘C2S’ (Ca2SiO4), perovskite (Ca3Fe2TiO9) and brownmillerite a ‘C4AF’ ferrite phase (Ca4Al2Fe2O10) (e.g. Ambroise et al. 2009; Fig. 1) Fine clayey-limestone dust from quarry exploitation (FAC) provided by the Carrières du Boulonnais Company and composed of quartz, calcite and clay minerals (Fig. 1)

Environ Sci Pollut Res Table 1

F1 to F5 formulations and expected gypsum and quartz content following the cure

Name

Formulations Dry soil

Expected gypsum

ALPENAT®

CaO

F1

50.66

13.81

F2

50.02

13.69

1.00

F3

49.62

4.26

0.99

F4 F5

53.33 38.28

4.03

Canitrate

Mixture 1

FAC

9.50 5.17

4.31

38.28

Expected quartz

H2O

35.54

➜

21.6

3.4

35.30

➜

21.3

3.4

35.63

➜

19.7

3.4

37.47 19.14a

➜ ➜

20.7 15.1

4.7 6.2

Maximum expected gypsum was calculated from its concentration in the soil coupled with sulphur introduced by the binders. Maximum expected quartz was calculated from the amount of quartz in both soil and binder a

Water content probably varied by exchanges with the ambient air (first cure step in an open system)

–

An experimental hydraulic binder (mixture 1) composed of metakaolin, quartz, amorphous phases from slag, hatrurite (Ca3SiO5) and minor Portland cement phases (brownmillerite, larnite and calcium aluminium oxide (CaAl4O7) (Fig. 1)

Additionally, lime (CaO) and Ca-nitrate (CaN2O6·4H2O) were also added in some formulations (Table 1). Five formulations were tested: four using core (i.e. bottles filled with a mixture of soil with additives) and one other which consisted of 0–10 mm granules (Table 1). For cores (F1 to F4 samples), the mixture between oven dried (60 °C) crushed soil (0–4 mm) and hydraulic binder was made manually, then poured into sealed plastic flasks and stored at room temperature (~ 25 °C). For the granulated sample (F5), the dry soil was reduced to powder and then mixed with binder using an Eirich intensive mixer, then placed 1 week in an oven at 60 °C in a moist atmosphere. The granules were then stored in sealed plastic bags for a further 21 days. Samples were prepared for microscopy, dried, and ground to perform mineralogical and geochemical analyses. Most observations and analyses were performed at the Civil and Environmental Engineering Department, LGCgE of IMT Lille-Douai. Microscopy Petrographic characteristics of soil samples were studied on carbon-coated raw samples and on standard polished sections using optical and electronic microscopies. Optical microscopy was carried out using a Zeiss Axiozoom macroscope (stereomicroscope observations under white light) and a Leica DMRXP polarising/ reflecting microscope. SEM observations were performed on a Hitachi S-4300 SE/N (Schottky FEG in Douai) and a JEOL JSM-7800F LV at the Centre Commun de Microscopie (CCM) of Lille, both equipped with an EDS detector. Images were obtained with backscattered electrons at 10 to 20 kV.

XRF—chemistry Bulk rock chemical analyses were performed by X-ray fluorescence spectrometry (XRF) using a Bruker S4 Pioneer spectrometer and a 4-kW wavelength dispersive X-ray fluorescence spectrometer equipped with a rhodium anode. Measurements were performed at 60 keV and 40 mA on powdered rock-compressed tablets. The integrated standardless evaluation of the machine allows the fast and easy semi-quantitative determination of element concentrations down to the part per million level without performing a calibration. XRD—mineralogy Powders (thoroughly dry micronised by grinding in an agate mortar and pestle) were analysed using a Bruker D8 Advance diffractometer system using Co-Kα radiation equipped with a fast LynxEye position sensitive detector (WL = 1,54,060). The diffractometer was operated at 35 kV and 40 mA. Scans were run from 5° to 80°2θ, with a step interval of 0.02°2θ and a time acquisition of 96 s per step. The identification of minerals was performed using BrukerAXS DiffracPlus EVA software and the International Centre for Diffraction Data (ICDD) Powder Diffraction File 2015 database. Mineral quantification of the soil sample was made by Rietveld analysis (e.g. Rietveld 1969; Snyder and Bish 1989; Bish and Post 1993) with the DIFFRACplus TOPAS software, version 4.2 (Bruker-AXS). The Rietveld method consists of minimising the difference between an experimental diffractogram and a diffractogram calculated for a given starting model. Crystal structure data were taken from the ICDD PDF and Bruker Structure Database. Rietveld refined parameters used in this study are the same as described in Trincal et al. (2014). Mineral content standard deviations were obtained by the multiplication of the standard deviation given by Topas software by the goodness of fit (GOF) in order to provide a more realistic approximation of error (Taylor and Hinczak 2006; Trincal et al. 2014). The formulations were deemed too complex to quantify by Rietveld due to large numbers of minerals in the sample and due to the presence of amorphous and complex solid solution

Environ Sci Pollut Res

Fig. 1 X-ray diffractograms of disoriented powdered samples. a Soil and F1 to F5 formulations showing gypsum, quartz, calcite, ferroan-dolomite, ettringite and Ca-Al-nitrate hydrate. b M1, FAC and ALPENAT®

sulphoaluminate binders/additives showing quartz (Q), ye'elimite (Y), larnite (L), perovskite (P), calcite (C), ferroan-dolomite, hatrurite and minor brownmillerite and calcium aluminium oxide (CaAl4O7)

phases (such as C-S-H). Thus, the reference intensity ratio (RIR) method was used with added internal standard to quantify specific minerals only. When carefully applied, the RIR method is capable of accurate quantitative results (e.g. Hubbard and Snyder 1988). It is based on the relationship between the abundance of a mineral in the sample and the intensity of its corresponding diffraction pattern peaks (e.g. Klug and Alexander 1974; Hillier 2000; Hillier 2003; Supplementary material 1).

The percentage of amorphous vs crystallised minerals can be estimated by many techniques (e.g. Shah et al. 2006). The simple qualitative method used herein as advocated in the Bruker Eva software (Bruker 2011) uses the following formulas (2 and 3):

%Amorphous ¼

Global area−Reduced area  100 Global area

ð2Þ

Environ Sci Pollut Res

%Crystallinity ¼ 100−%Amorphous

ð3Þ

where the global area includes all peaks and the ‘hump’ due to any X-ray amorphous material and the reduced area is the background subtracted scan, the subtraction including the amorphous ‘hump’ (Bruker 2011). XRD—clay mineralogy Following the removal of carbonate and gypsum by weak hydrochloric heated (at ~ 70 °C) acid, particles smaller than 2 μm were separated via sedimentation by sampling the upper 2 cm of the clay suspension after 100 min without agitation. Three XRD runs were performed on the oriented mounts of the clay-size particles following airdrying, ethylene-glycol solvation and heating at 550 °C for 2 h (Moore and Reynolds 1997; Thiry et al. 2013). Identification of the clay minerals was performed according to the position of the (00 l) series of basal reflections on the three XRD diagrams. Scans were run from 5° to 60°2θ, with a step interval of 0.02°2θ and a time acquisition of 192 s per step. TGA-MS—carbonate quantification To cross-check and validate the Rietveld data, thermogravimetry coupled with mass spectrometry (TGA-MS) (e.g. Kulp et al. 1951) was used as an additional independent method to identify and quantify the carbonates in the soil sample. Analyses were conducted using a Netzsch STA 449F3 Jupiter thermal analyser coupled with a Netzsch QMS 403 D Aëlos quadrupole mass spectrometer. This configuration allows measurement of gas and mass changes of a powdered sample under the effect of temperature. Setup was configured for a temperature increase of 3 °C/min from 40 to 1000 °C under an argon stream. Sample mass variation measurement was quantitative during analyses, while gas estimation was qualitative. Environmental acceptability To evaluate the environmental impact of the proposed hydraulic formulations, leaching tests according to European standard EN 12457-2 (2002) were performed on crushed samples after 28 days. The leaching tests were carried out with a liquid-to-solid ratio L/S = 10. After adding distilled water, the samples were automatically shaken with an end-over-end shaker at room temperature (20 °C) for 24 h. After filtration through a 0.45-μm cellulose acetate membrane, the supernatants were divided into several flasks to calculate the soluble fraction and to determine the concentrations of leached inorganic substances such as sulphates and heavy metals by ion chromatography and inductively coupled plasmaatomic emission spectrometry (ICP-AES). Ion chromatography was carried out using a Dionex ICS 3000 on two aliquots of fluid diluted 20 times. ICP-AES analyses were performed on two duplicates previously acidified with HNO3 then stored at 4 °C, using a Varian 720 ES. The

precision of the measurements depends on the standards used for each element; it is given in the ‘Results and discussion’ section. Additional analyses A density measurement was carried out on a few milligram of soil powder using a helium pycnometer (Micromeritics AccuPyc 1330) according to the standard NF EN ISO 8130-2 (2011). Methylene blue dye test was used to determine the specific surface area (SS) and the cation exchange capacity (C.E.C.) of the soil (Santamarina et al. 2002). It was carried out by the halo method following standard NF P 94-068.

Results and discussion Soil characterisation Petrography and mineralogy of the soil Mainly composed of gypsum, calcite, dolomite, quartz, clay minerals and rutile, the studied soil presents an interesting mineralogy. According to quantitative XRD analyses (Fig. 1), the crystalline minerals comprise 35 ± 5 wt% of gypsum, 28 wt% of calcite, 13 wt% of dolomite (a ferroan variety), 12 wt% of quartz, 11 wt% of clay minerals and less than 1 wt% of rutile. The quantitative results were cross-validated using modal calculation from XRF data (Table 2) following the method used in Trincal et al. (2014). For example, 5.6 wt% of sulphur (S) measured in soil can be attributed to 30 wt% of gypsum. The results of the Rietveld analysis on the soil were also confirmed by the RIR method (Table 3) for gypsum and quartz, as well as by thermogravimetry coupled with mass spectrometry (as in Moreau et al. 2018) for carbonates. In this respect, dehydration of 35 g of gypsum would generate 7.32 g of H2O, a value that is very close to the mass loss of 7.85 wt% measured on the TGA spectrum before 200 °C (Fig. 2). Similarly, heating from 600 to 900 °C of 28 g of calcite and 13 g of dolomite produces a total of 18.53 g of CO2. A value compatible with the loss of 19.11 wt% was measured by thermogravimetry (Fig. 2). More detailed analysis of the clay mineral assemblage (from the decarbonated < 2 μm fraction) indicates mainly palygorskite (Mg,Al)2Si4O10(OH) · 4(H2O) and possibly minor sepiolite Mg4Si6O15(OH)2 · 6H2O minerals, together with minor illite, chlorite and possibly some kaolinite (Fig. 3). XRF analyses also shows a significant amount of aluminium in soil presumably hosted mainly in the clay minerals (Table 2). These observations are confirmed by the spot EDS analyses in the SEM which indicate the presence of Al-bearing clays and supporting the XRD evidence that palygorskite rather than sepiolite is predominant. However, there are solid solutions between these two fibrous minerals that can also be present here (Singer et al. 2011). The spectrum obtained by

Environ Sci Pollut Res Table 2

XRF analyses (expressed on an anhydrous basis) of the bulk soil, binders and F1 to F5 formulations following the cure Σ

C O (calc) Na

Mg

Al

Si

Soil

98%

P 55.2

0.1

4.5

2.1

8.2

ALPENAT®

99%

– 41.7

< 0.1% 0.4

13.0

4.7

< 0.1% 0.2 30.1 0.6 6.1

< 0.1%

Mixture 1 FAC

102% P 50.7 101% – 53.8

0.2 1.3 < 0.1% 0.7

10.4 5.3

18.1 < 0.1% 0.5 < 0.1% 0.3 16.4 0.5 1.4 8.7 < 0.1% < 0.1% – 0.9 28.4 0.2 1.7

< 0.1% < 0.1%

F1 F2

97% 98%

P 54.7 P 54.4

< 0.1% 2.5 < 0.1% 2.4

4.6 4.7

6.0 5.6

< 0.1% 6.0 – 5.6

< 0.1% 0.3 23.1 0.2 2.2 < 0.1% 0.3 23.8 0.2 2.2

0.2 0.4

F3

101% P 56.7

< 0.1% 2.9

2.5

5.5

< 0.1% 5.6

< 0.1% 0.3 24.2 0.1 1.3

0.7

F4 F5

96% P 54.1 100% P 55.2

< 0.1% 3.1 < 0.1% 2.1

1.9 4.6

6.9 8.1

< 0.1% 6.4 < 0.1% 2.7

< 0.1% 0.3 25.0 0.1 1.0 < 0.1% 0.6 24.4 0.2 1.9

1.0 0.1

Soil soluble fraction precipitate 97.5

49.3

0.2

P

S –

5.6

< 0.1% 2.8

< 0.1% < 0.1% 0.2

21.5

Cl

K –

Ca

Ti

Fe

0.5 22.0 0.1 1.3

0.1

0.1 28.3

Sr 0.2

< 0.1% 0.2

Soil soluble < 0.45 μm fraction leachate was added in this table. It consists of the precipitate obtained by the leachate evaporation in an oven at 60 °C

thermogravimetric analysis on the decarbonated < 2-μm clay fraction shows four H2O degassing peaks at about 100, 125, 225 and 450 °C (Fig. 4). These peaks also correspond to those of palygorskite and are not representative of sepiolite (Földvári 2011). Palygorskite therefore appears to be the main crystallised clay phase of the soil, as observed on backscattered images obtained with SEM (Fig. 5). It occurs as isolated fibres of a few microns length or in slightly larger homogeneous lumps. Formerly named attapulgite, this fibrous clay has very interesting properties which are necessary to study for soil stabilisation (e.g. Molard et al. 1987). Indeed, its physical, chemical and mechanical behaviours will certainly be very different from more common layered clay minerals. Commonly formed in brackish-water environments in an association with sepiolite, palygorskite tends to have high surface area of 100–200 m2 g−1 (300–400 m2 g−1 for sepiolite). This determination is based on BET analyses not taking into account the surface area of the internal channels (Le Berre 1989; Lindgreen et al. 2008). This high surface is mainly related to the existence of micropores between the fibres, of Table 3

the order of 15 to 20 Å. It gives these clays a high capacity for adsorption and desorption. Thus, in their natural state, they can absorb water up to 200 to 250% of their weight (Le Berre 1989) and even 373 wt% (Lindgreen et al. 2008). Their cation exchange capacity is relatively low, in the order of 20 to 30 mg/100 g (Molard et al. 1987; Le Berre 1989). Palygorskite has a strong thixotropy, between that of kaolinite and that of montmorillonite. Palygorskite Atterberg’s liquidity, plasticity and shrinkage limits are much more important than those of kaolinite and montmorillonite (at least two times higher) (Molard et al. 1987). Due to these specific properties, palygorskite is exploited in many countries and is used in many industrial fields (e.g. Le Berre 1989; Gueye et al. 2017). The SEM observations coupled with the EDS analyses provide additional granulometric and textural information on the soil minerals present. Gypsum, quartz and calcite vary considerably in particle size ranging from a few micrometres to several centimetres diameter (Fig. 5). On the other hand, dolomite forms homogeneous hollow spheres approximately 5 μm in diameter (Fig. 5e, f). Dolomite appears to be

Quartz and gypsum estimation using RIR XRD method

Sample

Gypsum content in dry Quartz content in dry Evaporated sample by RIR sample by RIR water at method method 50 °C

Soil F1 F2 F3 F4 F5 FAC M1 ALPENAT®

38 24 16 21 26 17 0 0 0

7 5 5 5 7 11 9 20 0

18 30 31 27 23

Evaporated water at 100 °C

Equivalent gypsum content in wet sample

Equivalent quartz content in wet sample

% crystallinity in dry sample

36 43 39 38 26

20 13 16 20 13

4 4 4 6 9

84 78 73 75 77 88

Evaporated waters were measured by gravimetry before and after evaporation; the percentage of crystallinity form XRD data was evaluated qualitatively using Bruker EVA software. All data in wt%

Environ Sci Pollut Res

Fig. 2 Thermogravimetry coupled with mass spectrometry (TGA-MS) of soil sample. Note a H2O mass loss of 6.6 wt% before 200 °C, a CO2 mass loss of 19.1 wt% between 600 and 900 °C and a CO2+SO2 mass loss of

4.2 wt% up to 900 °C. The attribution of the various losses and emissions to different minerals is indicated

intimately associated with clay; these two minerals are probably cogenetic. According to Folk and Siedlecka (1974), several hypotheses may explain similar dolomite crystallisations which they studied in Norway in schizohaline environments (i.e. alternating hypersaline waters and fresh waters). The element originally in the centre of the dolomite, the nucleus, could be a pellet (faecal?), a Mg-rich calcite or a protodolomite which would have served as a support for the growth of the dolomite. Later, a change in the chemistry of the environment (diagenesis?) may have caused its dissolution or replacement without affecting the external dolomitic zone. It is also possible that the central zone was once occupied by an evaporitic crystal (a grain of salt for example) and that it was dissolved by a change in the salinity of the environment. The presence of these hollow dolomites could therefore indicate a schizohaline-type formation environment, which is compatible with the precipitation of gypsum (evaporitic mineral) and even palygorskite (Weaver 1975).

liquid/solid ratio ≈ 10) (Table 4). The soluble fraction level is above the 0.4% threshold for classification as inert waste but less than 10% for hazardous waste. So the gypsiferous soil used in this study is considered as a non-hazardous waste (European Council 2002). However, as anticipated, an important sulphate pollution is observed (≈ 18,200 mg kg−1 instead of 1000 mg kg−1 for inert waste), whilst fluoride (≈ 6 mg kg−1) and chloride (≈ 64 mg kg−1) in the soluble fraction are below their respective thresholds (Table 4, European council 2002). No other pollutants were detected.

Chemical behaviour of the soil The leaching test of the soil indicates a pH of 8–9 and a soluble fraction ≈ 2.4% (g L−1) (i.e. ≈ 24,000 mg kg−1 with a

Physical properties of the soil Soil density measured by helium pycnometer is 2.53 g cm−3. Soil methylene blue (MB) dye test indicates a methylene blue solution volume VTotal = 0.110 l to saturate a dry mass of soil sample ms = 28.36 g. In the soil, the 0/5 mm fraction (C) was estimated between 75 and 100%. The VBS is the methylene blue value of a soil. It is expressed in grams of blue for 100 g of the 0/50 mm fraction of the studied soil. The VBS was estimated between 2.9 and 3.9 g/100 g of dried soil using Eq. (4) (NF P 94-068 1998):

Environ Sci Pollut Res

Fig. 3 X-ray diffractograms on the oriented mounts of the clay-size particles of decarbonated soil, following air-drying (natural), ethyleneglycol solvation and heating at 550 °C for 2 h. Key: C for chlorite and

10  V Total C ms

possible trace of kaolinite (?), I for illite and other micas (muscovite), P for palygorskite and minor amount of sepiolite (?), Q for quartz

Specific surface area (SS) was estimated at 95 m2 g−1 following Eq. (5) (Santamarina et al. 2002):

VBs ðg=100 gÞ 319:87 cBlue 100 g C:E:C:ðmEq=100g Þ ¼ V Total   319:87 ms

mMB 1  AV  AMB  SS ¼ 319:87 ms

with a dry mass of soil sample ms = 28.36 g, a methylene blue solution volume VTotal = 0.110 l and a methylene blue solution concentration cBlue of 10 g L−1.

VBS ¼ 100 

ð4Þ

ð5Þ

where the mass of the absorbed MB mMB = VTotal × cBlue, AV is Avogadro’s number (6.02 · 1023 mol−1) and AMB is the area covered by one MB molecule (typically assumed to be 130 Å2 or 130 · 10−20 m2). The coefficient of 319.87 is the anhydrous MB (C16H18ClN3S) molecular weight (g mol−1). For comparison, the SS of pure attapulgite (palygorskite) is estimated at 140–170 m3 g−1, that of illite at 80–100 m3 g−1 and that of kaolinite of 10–20 m3 g−1 (Santamarina et al. 2002). The cation exchange capacity (C.E.C.) of soil was estimated at between 9 and 12 mEq/100 g according to the following formula (6) (Clément 1988; Lasledj 2009) and close to 12 using formula (7) (Cokca and Birand 1993; Santamarina et al. 2002; Yukselen and Kaya 2008; Chahal 2013):

C:E:C:ðmeq=100gÞ ¼ 1000 

ð6Þ ð7Þ

Characterisation of soil-binder mixtures Mineralogy Soil-binder mixtures were cured within just a few hours (i.e. they became solid) suggesting mineralogical transformations, with the single exception of the sample F3 which remained soft over the entire 28 days. Newly formed ettringite was identified 28 days after mixing in all F1 to F5 samples using both SEM observations and XRD analyses (Fig. 1a). In addition, calcium aluminium oxide nitrate hydrate (Ca6Al2O6(NO3)6 · xH2O) was identified in sample F3. Conversely, all the cementitious phases from the binders disappeared during hydration, i.e. ye'elimite, larnite, brownmillerite and hatrurite.

Environ Sci Pollut Res

Fig. 4 Thermogravimetry coupled with mass spectrometry (TGA-MS) of decarbonated < 2 μm soil sample. Note four H2O peaks allocated to palygorskite at 100, 125, 225 and 450 °C. No significant CO2 and SO2 emission was detected

The percentage of crystallinity was estimated in the soil samples before and after treatment with hydraulic binder using the Bruker XRD method (Table 3). While it was estimated at 84% in soil, it varied from 73 to 88% in the formulated samples. Although only qualitative, these results suggest the formation of amorphous phases or poorly crystallised minerals in most formulations most probably C-S-H gels formed during hydration. In the case of gypsum, it is always still present in all five formulations (Fig. 1). This indicates that it has not been completely transformed into ettringite (or another sulphate) and also that the action of the hydraulic binders is not sufficient or pervasive enough for complete transformation. However, mineralogical observations and quantifications are necessary in order to determine the efficiency of each binder and therefore to refine formulations for sulphate stabilisation. Mineralogical quantification with RIR method Due to the large number of mineralogical phases as well as the presence of amorphous or poorly crystallised C-S-H as previously mentioned, Rietveld analyses were not carried out on treated soil. Quartz and gypsum contents were nevertheless estimated using the reference intensity ratio (RIR) method

(Table 3 and Supplementary material 1). The XRD patterns of samples F1 to F5 are very complex and many overlaps are suspected. Therefore, following the recommendations of Hillier (2003), peaks giving the lowest intensities following scaling by relative peak intensities were chosen as the most reliable basis for quantification. The concentration of gypsum and quartz in the samples spiked with 50 wt% of corundum (XCor) is obtained by equation (c) in Supplementary material 1. In dry samples F1 to F4, the gypsum content varies from 16 to 26 wt% and the quartz content varies from 5 to 7 wt% (Table 3). In F5, there is 17 wt% of gypsum and 11 wt% of quartz. RIR gypsum quantifications were compared to the maximum expected amount of gypsum calculated from XRF data (Table 2). Elemental sulphur concentration is 5.6 to 6 wt% in samples F1 to F4 and 2.7 wt% in F5 (Table 2); thus, the maximum content of gypsum in F1 to F4 is 30 to 34 wt%, and in F5, it is 15 wt%. However, the presence of ettringite in all samples must mean that the true gypsum content is lower (sulphur must be distributed in these two minerals), which is consistent with our RIR estimates (Table 3). RIR results were also compared to the amounts of gypsum and quartz introduced into the formulations prior to hydration. For this, we used the quartz and gypsum

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Fig. 5 Backscattered images of initial soil showing gypsum crystals covered by fibrous clay (palygorskite) and white crystals of dolomite (a–d). Panel b is a zoom of a. Quartz and calcite are also visible in

polished section, in addition to gypsum, palygorskite and dolomite (d). Panel f is a zoom of e. Note the holes in the small dolomite crystals in the matrix (e). Key: C: calcite; D: dolomite; P: Palygorskite; Q: quartz

content of the soil and the additives, all weighted according to their concentrations (Eq. (8))

calculations, 3 to 5 wt% of quartz and 20 to 22 wt% of gypsum would be expected in the F1 to F4 formulations before the hydration reaction and 6 wt% of quartz and 15 wt% of gypsum in the F5 (Table 1). In these cases, the addition of ALPENAT® acts as a diluent of the quartz and gypsum contents of the soil, while the addition of mixture 1 and FAC increases the quartz content. In contrast to the sulphates, quartz does not react during hydration because it is insoluble and it cannot be newly formed under these conditions. The comparison between the calculated quartz content (with Eq. (8)) and that estimated by the RIR method thus seems to be a good indicator of the validity of the RIR results. However,

n

X Mineral ¼ ∑ mi  X i i¼1

ð8Þ

with X for concentration of gypsum or quartz, m for mass and i for mixture element (soil, binder and water). In ALPENAT®, there is no quartz, while it is present in mixture 1 and FAC (Table 3 and Fig. 1b). Gypsum is absent in the three additives (Table 3 and Fig. 1b), but there is elemental sulphur in ALPENAT® and in mixture 1 which can be transformed into gypsum during hydration (Table 2). According to our

Environ Sci Pollut Res Table 4

Leachate analyses on soil and F1 to F5 formulations by ion chromatography and ICP-AES

Eluate

Units

Temperature

°C

Hazardous wastea

Non-hazardous wastea

Inert wastea

pH

SOIL

F1

F2

F3

F4

F5

24.5

21.5

21.5

21.5

21.5

21.5

7.8

11.4

11.1

9.2

12.8

10.9

Conductivity Soluble fraction

mS/cm %

10

6

0.4

2.6 2.42

2.8 2.42

2.8 2.30

11.4 11.47

6.5 3.54

2.8 2.60

Chlorides (Cl) Fluorides (F)

mg/kg mg/kg

25,000 500

15,000 150

800 10

63.8 6.4

< 200 < 50

< 200 < 50

< 200 < 50

< 200 < 50

< 200 < 50

Nitrates (N)

mg/kg mg/kg

18,285

14,905

14,925

~ 60,000 10,365

12,625

16,075

0.5

< 0.11

< 0.1 < 0.06

< 0.1 < 0.06

40.42 < 0.07

41.24 < 0.08

0.57 < 0.09

20

1.16 6415

1.49 6229

4.20 25,106

3.66 19,208

1.01 6447

0.04 0.5

1.47 8034b < 0.003 < 0.01

< 0.003 8.39

< 0.004 8.00

< 0.005 1.39

< 0.006 1.41

< 0.007 1.91

50

2

0.14

0.2

0.01

0.05 0.07 < 0.08

0.06 0.06 < 0.09

0.01 0.13 < 0.10

0.16 0.19 < 0.11

0.05 0.05 < 0.12

10

0.5

0.12

142.39 0.74 0.56

165.52 0.81 0.45

107.98 8.76 0.06

98.96 8.94 0.08

104.31 0.61 0.20

40 50

10 10

0.4 0.5

< 0.02 < 0.06

93.69 < 0.01 < 0.05

112.04 < 0.01 < 0.05

76.89 < 0.01 < 0.05

86.14 0.33 < 0.05

58.85 < 0.01 < 0.05

mg/kg mg/kg

5 7

0.7 0.5

0.06 0.1

< 0.17 < 0.14

< 0.12 < 0.07

< 0.12 < 0.07

< 0.12 < 0.07

< 0.12 < 0.07

< 0.12 < 0.07

mg/kg mg/kg

200

50

4

0.95

206.18 < 0.03

178.57 < 0.04

190.67 < 0.05

133.55 < 0.06

141.53 < 0.07

Sulphates (SO4) Al As

mg/kg mg/kg

50,000

20,000

25

2

Ba Ca Cd Cr

mg/kg mg/kg mg/kg mg/kg

300

100

5 70

1 10

Cu Fe Hg

mg/kg mg/kg mg/kg

100 2

K Mg Mo

mg/kg mg/kg mg/kg

30

Na Ni Pb

mg/kg mg/kg mg/kg

Sb Se Si Zn

1000

Values in italics highlight values above the inert waste criteria a

Authorized threshold classes with L/S = 10 for the acceptance of waste at landfills (from European Council 2002)

b

Concentration calculated from XRF data on the solid leach residue (Table 2)

XRD analyses for the RIR method were performed on dry samples. There was therefore a loss of mass during drying at 50 °C (Table 3). The subtraction of water increases the concentration of estimated minerals in the sample (by changing the total mass of the closed system). The values of gypsum and quartz estimated by RIR were therefore converted to a percentage in the wet sample before drying (Table 3). Quartz data obtained by the RIR method give similar results to those expected for F1 to F4 samples (within measurement errors) but differ slightly for sample F5. The F5 difference is possibly due to the amount of atmospheric water captured or evaporated during the cure (open system). Gypsum RIR results are different to the expected level (Tables 1 and 3). When lower (samples F2 and F3), the gypsum of the soil has been partially transformed into carbonate and/or ettringitic minerals. Conversely, when both results are quite similar (samples F1, F4 and F5), this suggests that the

gypsum of the soil has not been transformed into ettringite and that the binder has been the main source of sulphur to form ettringite. Chemical behaviour The leaching of all five samples indicates a soluble fraction well above the threshold of inert waste of 0.4% (g L−1) (i.e. ≈ 4000 mg kg−1 with a liquid/solid ratio ≈ 10) and sulphate content well above the 1000-mg kg −1 level (Table 4; European Council 2002). Note that chlorides and fluorides remain below the inert waste threshold with less than 200 mg kg −1 and less than 50 mg kg −1 , respectively. Chloride presence was confirmed by the observation of spectacular mineralisation on the F1 sample during SEM analyses (Fig. 6). These are dendritic salt efflorescence, rich in potassium, sodium and chloride (Supplementary material 2) and

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Fig. 6 Backscattered images of polished section of treated soil (F1 formulation) showing spectacular efflorescence of dendritic salt mineralisation formed at the surface of the sample (positive reliefs on the plane samples). Blue point in a corresponds to EDS analyse location reported in Supplementary material 2

formed at the surface of the sample. They have thus crystallised after the ethanol polishing step (otherwise, it would not form positive reliefs on the plane samples), possibly during as the vacuum is applied in the SEM chamber. Indeed, pressure variations of the sample under SEM can induce fluid circulations and precipitation/dissolution of salt (e.g. Podor et al. 2012). An important pollution in sulphate is thus observed, suggesting that stabilisation was not effective irrespective of the formulation tested. Additionally, the relatively weak decrease in sulphate content compared to the initial soil could be explained by its dilution with binder or by its stabilisation. In sample F3, the addition of Ca-nitrate in the blend elevated nitrate contents to almost 60.000 mg kg−1 the soluble fraction value more than 11% (Table 4). However, in this F3 sample, the sulphate value is lower than in the other samples. This could be explained by a competition between nitrate and sulphate, meaning that the solubility of the sulphates would be decreased by the increase of the nitrates in solution. Mineralogical reactions In F1 and F2 formulations, ALPENAT® blend was added to gypsiferous soil in order to provide enough aluminium and calcium to transform all of the gypsum present but also to form ettringite with the elemental sulphur that it contains (Table 2). In the same way, added water was optimised for the moisture content of the soil and for the gypsum-ettringite

reaction. Since the hydration reaction is taking place in a closed system, all water should thus be incorporated into the newly formed minerals and should not end up in porosity. The quantity of water located in porosity was measured by mass loss during heating at 50 °C (Table 3). It confirms that all the water was not consumed, and thus the expected mineralogical reactions did not take place completely. However, the addition of ~ 1 wt% of lime in F2 seems to have a significant effect on the hydration reaction. Indeed, in the sample without lime (F1), the water content is 18% while it is 30% in the limed one (F2) (Table 3). SEM observations confirm partial dissolution of gypsum and carbonate recrystallizations (Figs. 7 and 8). The hydration of the lime releases OH− ions which increase the pH to about 12.4. Under these conditions, pozzolanic reactions take place in the soil: aluminium and silicon of the clay matrix are solubilised and combined with the available calcium and sulphates, generating AFt minerals (e.g. ettringite) and/or hydrated cementitious compounds like C-S-H (Figs. 9 and 10; Nalbantoğlu 2004; Gartner 2004; Guney et al. 2007; Yong and Ouhadi 2007; Chen and Lin 2009). The kinetics of the pozzolanic reactions depend on the quantity and the accessibility of the oxides concerned; it can last from several hours to several years (Wild et al. 1998). According to our results, gypsum content in F1 is more important than in F2 (Table 3). In F1, soil gypsum has not been transformed to ettringite but it was partially transformed to Ca- and

Environ Sci Pollut Res

Fig. 7 Backscattered images of polished section of treated soil showing gypsum crystals from F1 to F3 formulations. Gypsum appears partially transformed in Ca- or CaMg-carbonate (a, b), dissolved and supporting ettringite rim (c zoomed in d) or serving as nuclei for carbonate formation

(e zoomed in f). Blue points correspond to EDS analyse locations reported in Supplementary material 2. Key: AFt: mineral group with alumina, ferric oxide and tri-sulphate

CaMg-carbonates (Fig. 7 and Supplementary material 2). Elemental sulphur from the binder is probably hydrated into gypsum and ettringite minerals. In contrast, a proportion of gypsum was probably transformed into ettringite in F2, while elemental sulphur formed only ettringite (Figs. 7, 8 and 9). However, gypsum content remains elevated and generates excessive sulphates during leaching. This is probably due to pH buffering up to 11.1 after hydration

(Table 4), suggesting that the amount of lime in F2 was insufficient to maintain pozzolanic reactions conditions. In F3, Ca-nitrate was added to dry soil, ALPENAT®, lime and water in order to supply all the necessary calcium for the transformation of gypsum into ettringite. Indeed, calcite and dolomite are poorly soluble in basic pH and gypsum alone does not contain enough calcium to form ettringite according to Eq. (1). For dolomite, the dissolution rates decrease with

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Fig. 8 Backscattered images of polished section of treated soil showing gypsum crystals from F2 to F5 formulations. Gypsum appears partially dissolved with ghosts at the extremities (a zoomed in b); associated with hydrates ettringite in porosity (b), newly formed as microcrystals with

box-work (c zoomed in d); recrystallised in carbonates (as in Fig. 7) (e) or enriched in iron along cleavage plans (f). Blue points correspond to EDS analyse locations reported in Supplementary material 2. Key: AFt: mineral group with alumina, ferric oxide and tri-sulphate; G: gypsum

increasing pH at pH > 8 and ΣCO2 > 10−3 M (Pokrovsky and Schott 2001). In the alkaline pH region, carbonate and bicarbonate ions significantly inhibit dolomite dissolution rates at far from equilibrium conditions. Dissolved calcium was found to be a strong inhibitor of dolomite dissolution at pH above 7, whereas dissolved magnesium has no effect on the dissolution rate (Pokrovsky and Schott 2001). Furthermore, the solubility of calcium carbonate in

aqueous solutions is influenced by temperature, by the partial pressure of carbon dioxide in the system and by the presence of other salts (Frear and Johnston 1929). Solubility of calcite at 25 °C is less important in gypsum saturated water than in pure water (Frear and Johnston 1929). Thus, a lack of available calcium could explain why stabilisation was not complete in F1 and F2, but this is considered unlikely. Indeed, as in F3, gypsum was

Environ Sci Pollut Res

Fig. 9 Backscattered images of polished section of treated soil showing hydrate phases from F2 to F4 formulations. Complex hydration halo/ crown around cementitious phase with non-hydrated clinker residues (a zoomed in b). Ettringite needles are locally visible in porosity (b).

Ettringite hydration halo around clinker grains of ye'elimite and larnite (c to f). Clinker can be totally hydrated and replaced by hydrates and porosity (e) or remain visible (f). Blue points correspond to EDS analyse locations reported in Supplementary material 2. Key: G: gypsum

partially replaced by carbonate suggesting that it is not the limiting component (Fig. 7). Gypsum estimation by the RIR method in F3 indicates that the quantity of gypsum is greater than in F2. This result suggests that the partial replacement of ALPENAT® by Canitrate did not favour the transformation of gypsum into ettringite. However, Ca-nitrate does not contain aluminium, which could also become the limiting reagent. Furthermore,

the pH was close to 9 after hydration (Table 4), which does not allow the pozzolanic reaction to proceed and will also increase the deficit of the required aluminium. Finally, calcium aluminium oxide nitrate hydrate crystallisation identified by XRD (Fig. 1) may also inhibit ettringite formation, as is the case for some phosphonates (Cody et al. 2001). In F4, ALPENAT® is replaced by mixture 1, a ternary binder mainly composed of metakaolin, slag minerals and

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Fig. 10 Backscattered images of polished section of treated soil showing hydrate phases from F4 to F5 formulations. Complex hydration phases can be observed in sample matrix, as calcite or portlandite rim around lime grain and ettringitic products (a zoomed in b). Other phases, from

soil, additive or hydration reactions highlight the important complexity of the material (c zoomed in d; e; f). Locally, framboidal pyrite and its iron pseudomorphosis are observed in F5 sample (f). Blue points correspond to EDS analyse location reported in Supplementary material 2

cementitious phases. Mixture 1 content was calculated to provide all the aluminium required for the reaction of Eq. (1). Since this binder was not rich enough in calcium (Table 2), the amount of lime in the blend was increased. This lime addition maintains the pH above 12 after hydration (Table 4), which is favourable for pozzolanic reaction. Particles of lime are still visible; they are surrounded by a rim of calcite or portlandite suggesting only partial hydration (Fig. 10). Metakaolin has

pozzolanic properties (Frías et al. 2000; Sha and Pereira 2001; Gartner 2004; Nadeem et al. 2013). It is more reactive than silica fumes, which are in turn more reactive than slags (Largent 1978; Zhang et al. 2012; Palou et al. 2016). Water is required to activate the pozzolanic activity (Wild et al. 1996), which may weaken the mechanical strength of the material (Boháč et al. 2016). In the presence of lime and water, metakaolin forms C-S-H and a variety of calcium aluminate

Environ Sci Pollut Res

phases ‘C4AH13’, ‘C2ASH8’ and ‘C3AH6’ (Gruyaert et al. 2010; Palou et al. 2016). The formation of these crystalline products depends mainly on the ‘AS2’/lime ratio and the temperature (Morsy 2005; Li and Ding 2003; Cassagnabère et al. 2009; Nadeem et al. 2013; Boháč et al. 2016; Palou et al. 2016). The hydration of ternary binders (Portland cement + blast furnace slag + metakaolin) determined the important role of metakaolin in the formation of AFt (Ettringite) in the presence of gypsum and calcium hydroxide (Zemlicka et al. 2015; Palou et al. 2016; Boháč et al. 2014; Frías et al. 2000). Alkaline activation of slags has been widely studied (Li et al. 2010; Palou et al. 2016). Mineralogical content estimation by RIR method indicates that the gypsum was not further reacted into ettringite compared to the F1 to F3 samples. This suggests a failure of stabilisation which does not appear to be due to pH or to a lack of available water, calcium or aluminium. In contrast, the size of the particles could have a role as well as the kinetics of the reactions. Indeed, there is evidence of gypsum dissolution and recrystallization (Fig. 8) as well as AFt and/or C-S-H formation (Figs. 8, 9 and 10). Crystallisation is a complex and therefore delicate operation. Indeed, under the influence of supersaturation, transfers of matter and heat, mechanical factors (such as those related to kinetic phenomena: nucleation, growth, agglomeration) compete for the ettringite crystallisation among other mineralogical phases. In F5, the last formulation, a dry and powdered soil, was mixed with ALPENAT®, FAC and water to form granules. Grinding the soil before mixing with the hydraulic binder will reduce the size of the gypsum grain and thus increase its contact area and its reactivity. Moreover, the fact that soil is mixed with FAC changes its mechanical properties, especially its permeability. The amount of added ALPENAT® in this mixture is insufficient to convert all the gypsum into ettringite, but calcium and aluminium were present in clays and calcite, and ALPENAT® should form an external surface, or coating, on the pellets created by the intensive mixer. As for F1 and F2, sample pH for F5 is close to 11. This is not sufficient to promote pozzolanic reaction, which could explain why the gypsum was apparently not transformed into ettringite (Table 3). The gypsum decrease observed between the initial soil and the mixture would be due solely to the dilution by the FAC. However, it is difficult to calculate the theoretical quantity of gypsum in F5 because the amount of water captured as moisture from air or evaporated during the cure was not measured. Only an estimate can be made by measuring the amount of water injected before the cure and the amount of water evaporated at 50 °C in the sample 28 days old (Table 3). However, evidence of gypsum dissolution was observed by SEM, together with various minerals, hydrous products and clinker particles (Figs. 8, 9 and 10 and Supplementary material 2) suggesting complex mineralogical reactions. Pyrite was locally observed as well as his iron pseudomorphosis (Fig. 10f). Decomposition of pyrite in pyrrhotite (Fe0.8-1S) then haematite (Fe2O3) may be related to significant heating (Thiéry

et al. 2015) and would indicate that the pyrite comes from the ALPENAT® binder. However, if the pyrite came from the soil or from the FAC, this would indicate fluid-mineral interactions, i.e. a leaching of the elemental sulphur during the cure. Sulphate solubility The solubility of a mineral is measured by the concentration of the solution which is in final equilibrium with the solid and is independent of the rate at which this equilibrium is established (Hulett 1905). At 25 °C, the solubility of gypsum is close to 2.08 g CaSO4/kg of water, i.e. approximately 0.015 mol L−1 (Hulett and Allen 1902; Seidell and Smith 1904; Shternina 1960; Bock 1961). Gypsum solubility is temperature dependant; in distilled water, it reaches a maximum close to 2.14 g L−1 at 40 °C, decreasing with further temperature increase thereafter (Hulett and Allen 1902; Ostroff and Metler 1966; Carlberg and Matthews 1973). The solubility product constant, Ksp, is the equilibrium constant for a solid substance dissolving in an aqueous solution (Eq. (9)). K sp ¼ Ca2þ


eq

SO2− 4


eq

ð9Þ

where (Ca2+)eq and (SO42−)eq are the activities of the calcium and sulphate ions at equilibrium. Ksp represents the level at which a solute dissolves in solution. The more soluble a substance is, the higher the Ksp value it has. At 25 °C and in pure water, the log Ksp gypsum is equal to − 4.58, i.e. Ksp = 2.58 · 10−5 (Bennett and Adams 1972; Nordstrom et al. 1990; Möschner et al. 2008), while log Ksp is close to − 45 for ettringite (Warren and Reardon 1994; Myneni et al. 1998; Perkins and Palmer 1999; Barbarulo et al. 2007). However, the solubility product varies in the group of ettringite minerals, with log Ksp varying from − 43.13 to − 46.43 (Lothenbach and Winnefeld 2006) and for example − 44.0 for Fe-ettringite (Möschner et al. 2008). Ettringite remains therefore much less soluble than gypsum under all circumstances. The effect of the size of particles on the solubility of the solid is detectable and measurable; the smaller particles not only dissolve more rapidly but have a greater solubility (Ostwald 1900). Surface-tension plays a decided role in the solubility, and it is possible to increase gypsum solubility by about 20% by decreasing the size of the particles to 0.3 μm (Hulett and Allen 1902). However, in this case, the system obtained is not really in equilibrium. Indeed, the smaller particles become smaller and eventually disappear while the larger ones grow. This process is very slow and does not compensate the abrasion caused by stirring (during leaching test); hence, a normally saturated solution is never attained (Hulett and Allen 1902). When larger pieces of gypsum were placed

Environ Sci Pollut Res

in a flask with water and rotated in a thermostat (as is our case). the concentration became 5% greater than a normally saturated solution at the same temperature, because gypsum is a very soft mineral and is easily ground to powder (Hulett and Allen 1902). The solubility of gypsum is strongly influenced by the presence of other salts. Indeed, gypsum solubility is considerably increased in solutions containing the chlorides and nitrates of sodium, potassium and magnesium. For examples, in the presence of NaCl gypsum, solubility increases up to almost 7.3 g L−1; with MgCl2 or with KNO3 to 8.6 g L−1; with NaNO3 to 9.3 g L−1; with NH4Cl to 10.8 g L−1; and finally, in presence of Mg(NO3)2, it increases up to 15 g L − 1 (Seidell and Smith 1904; Shternina 1960). In contrast, gypsum solubility decreases with CaCl2 and Ca(NO3)2 solutions; e.g. in a solution with Ca(NO3)2 gypsum solubility decrease up to 0.35 g L−1 (Seidell and Smith 1904; Zhang and Muhammed 1989; Charola et al. 2007). Furthermore, gypsum solubility is influenced by pH, at least in aqueous NaCl solutions (Shukla et al. 2008; Bhagawati et al. 2016). The determination of the degree of gypsum-unsaturation by electrical conductivity measurement using several salts made it possible to quantify gypsum content of an aqueous soil (Lagerwerff et al. 1965). However, determination of solubility products for soil minerals is difficult because the soil and its attendant solution constitute a complex, heterogeneous, non-ideal, thermodynamic system (Bennett and Adams 1972). According to our analyses on the soluble fraction by ICPAES (Table 4), and its precipitate by XRF (Table 2), there are 0.80 g L−1 of Ca2+ and 1.83 g L−1 of SO42− in the leachate soil solution. This corresponds to 3.3 g L−1 of gypsum in solution, which exceeds its solubility of 2.08 g L−1 in pure water at 25 °C. This suggests that the formation of fine particles during 24 h stirring and the presence of some chlorides, nitrates, sodium, potassium and magnesium in the solution have increased the solubility of gypsum. It may also be suggested that the gypsum is saturated in the solution and therefore it has not completely dissolved. Molar concentrations of Ca2+ and SO42− are more or less equal for soil leachate, as well as for samples F1, F2 and F5, suggesting that gypsum is the main mineral source of these two ions in solution. On the other hand, in the F3 and F4 samples, the molar concentration of the Ca2+ is much greater than that of SO42−, indicating the dissolution of another calcium-rich source in addition to the gypsum: presumably Ca-nitrate for sample F3 and probably lime for sample F4. In F3, pH is close to 9, which may allow C-S-H and ettringite dissolution (Chatain et al. 2013). Finally, there does not seem to be any stoichiometric relationship between the contents of (1) calcium of the sample with Ca2+ in leachate; (2) gypsum of the sample with Ca2+ in leachate; (3) sulphur of the sample with SO42− in leachate; and (4) gypsum

of the sample with SO42− in leachate (Supplementary material 3). This suggests that for all samples, the gypsum has reached saturation in the leached water, but that its solubility varies from one sample to another.

Conclusions The aim of this research was to identify a hydraulic binder that would be effective in reducing sulphate release from gypsiferous soils. For this purpose, we investigated the transformation of gypsum into ettringite, a less soluble sulphate-rich mineral. Five experimental mixtures were made, each corresponding to a specific formulation based on additions of calcium sulphoaluminate cement, experimental metakaolin-rich binder, FAC (industrial waste), Ca-Nitrate and lime. The petrographic, mineralogical and geochemical analyses carried out on the formulations after curing reveal that various mineralogical reactions occurred during the hydration reactions binders; in particular, ettringite formation was demonstrated. From an environmental point of view, the sulphate releases are reduced by the hydraulic binders, but the reduction remains insufficient in relation to regulatory inert waste criteria. Additionally, the soluble fraction increased for some samples, especially for one formulation to a level for hazardous waste criteria due to its nitrate and calcium releases. To better understand the reactions that took place, mineralogical observations and quantification methods were employed and the parameters that can influence the solubility of sulphates in such materials have been discussed. In a wider context where the management of polluted soils is becoming an important commercial issue, it is hoped that the strategies pursued in this research may lead to interesting developments in civil engineering in the coming years. Acknowledgments Authors thank Johanna Caboche, Damien Betrancourt and Dominique Dubois, from the GCE department (Douai), for their contribution to mineralogical and chemical analyses; Phillipe Hauza from Colas Company for initiating this research theme and providing the soil and mixture 1 samples; and Vicat Company for the ALPENAT® and Carrières du Boulonnais Company for the FAC.

References Ambroise J, Georgin JF, Peysson S, Péra J (2009) Influence of polyether polyol on the hydration and engineering properties of calcium sulfoaluminate cement. Cem Concr Compos 31:474–482. https:// doi.org/10.1016/j.cemconcomp.2009.04.009 Barbarulo R, Peycelon H, Leclercq S (2007) Chemical equilibria between C–S–H and ettringite, at 20 and 85 °C. Cem Concr Res 37:1176– 1181. https://doi.org/10.1016/j.cemconres.2007.04.013 Bennett AC, Adams F (1972) Solubility and solubility product of gypsum in soil solutions and other aqueous solutions. Soil Sci Soc Am J 36:288–291. https://doi.org/10.2136/sssaj1972. 03615995003600020025x

Environ Sci Pollut Res Bhagawati D, Kakoty U, Saikia PP, Baruah MK (2016) Study on the effect of pH, ionic strength and pressure on the solubility of CaSO4-NaCl-H2O system. Int Res J Pure Appl Chem 11:1–10 Bish DL, Post JE (1993) Quantitative mineralogical analysis using the Rietveld full-pattern fitting method. Am Mineral 78:932–940 Bock E (1961) On the solubility of anhydrous calcium sulphate and of gypsum in concentrated solutions of sodium chloride at 25 °C, 30 °C, 40 °C, and 50 °C. Can J Chem 39:1746–1751 Boháč M, Palou M, Novotný R, Másilko J, Všianský D, Staněk T (2014) Investigation on early hydration of ternary Portland cement-blastfurnace slag–metakaolin blends. Constr Build Mater 64:333–341. https://doi.org/10.1016/j.conbuildmat.2014.04.018 Boháč M, Palou M, Novotný R, Másilko J, Šoukal F, Opravil T (2016) Influence of temperature on early hydration of Portland cement– metakaolin–slag system. J Therm Anal Calorim 127:309–318. https://doi.org/10.1007/s10973-016-5592-6 Bruker (2011) DIFFRAC.SUITE, User manual, DIFFRAC.EVALUATION PACKAGE DIFFRAC.EVA,Original Instructions. Bruker AXS GmbH, DOC-M88-156 EXX200 V2. 162p. Carlberg BL, Matthews RR (1973) Solubility of calcium sulfate in brine. In: SPE Oilfield Chemistry Symposium. Society of Petroleum Engineers Cassagnabère F, Escadeillas G, Mouret M (2009) Study of the reactivity of cement/metakaolin binders at early age for specific use in steam cured precast concrete. Constr Build Mater 23:775–784. https://doi. org/10.1016/j.conbuildmat.2008.02.022 Celik E, Nalbantoglu Z (2013) Effects of ground granulated blast furnace slag (GGBS) on the swelling properties of lime-stabilized sulfatebearing soils. Eng Geol 163:20–25. https://doi.org/10.1016/j. enggeo.2013.05.016 Chahal H (2013) Etude du comportement hydromécanique des sédiments pollués par les PCB en interaction avec les géomatériaux pour un stockage hors site. PhD Thesis, INSA de Lyon, 237 p. Charola AE, Pühringer J, Steiger M (2007) Gypsum: a review of its role in the deterioration of building materials. Environ Geol 52:339–352. https://doi.org/10.1007/s00254-006-0566-9 Chatain V, Benzaazoua M, Cazalet ML et al (2013) Mineralogical study and leaching behavior of a stabilized harbor sediment with hydraulic binder. Environ Sci Pollut Res 20:51–59. https://doi.org/10.1007/ s11356-012-1141-4 Chen L, Lin D-F (2009) Stabilization treatment of soft subgrade soil by sewage sludge ash and cement. J Hazard Mater 162:321–327. https://doi.org/10.1016/j.jhazmat.2008.05.060 Ciliberto E, Ioppolo S, Manuella F (2008) Ettringite and thaumasite: a chemical route for their removal from cementious artefacts. J Cult Herit 9:30–37. https://doi.org/10.1016/j.culher.2007.05.004 Clément C (1988) Etude de coulis hydrauliques pour la rétention de cations polluants: Pb, Cd, Hg, Sr, Cs. Phd Thesis, ENSMP, 150p. Cody RD, Cody AM, Spry PG, Lee H (2001) Reduction of concrete deterioration by ettringite using crystal growth inhibition techniques. Department of Geological and Atmospheric Sciences, Iowa State University, Ames, IA 50011. Iowa DOT TR-431. 112p. Cokca E, Birand A (1993) Determination of cation exchange capacity of clayey soils by the methylene blue test. GTJ 16:518–524. https://doi. org/10.1520/GTJ10291J Crammond N (2002) The occurrence of thaumasite in modern construction—a review. Cem Concr Compos 24:393–402. https://doi.org/10. 1016/S0958-9465(01)00092-0 Deer WA, Howie RA, Zussman J (1962) Rock-forming minerals: vol. 5: non-silicates. Longman, London. 371p. ISBN 0582462134 9780582462137 Degirmenci N, Okucu A, Turabi A (2007) Application of phosphogypsum in soil stabilization. Build Environ 42:3393–3398. https://doi. org/10.1016/j.buildenv.2006.08.010 European Council (2002) Council decision of 19 December 2002 establishing criteria and procedures for the acceptance of waste at landfills pursuant to Article 16 of and Annex II to Directive 1999/31/EC

Földvári M (2011) Handbook of thermogravimetric system of minerals and its use in geological practice. Budapest. 179p. ISBN 978-963671-288-4 Folk RL, Siedlecka A (1974) The Bschizohaline^ environment: its sedimentary and diagenetic fabrics as exemplified by Late Paleozoic rocks of Bear Island, Svalbard. Sediment Geol 11:1–15. https:// doi.org/10.1016/0037-0738(74)90002-5 Frear GL, Johnston J (1929) The solubility of calcium carbonate (calcite) in certain aqueous solutions at 25. J Am Chem Soc 51:2082–2093 Frías M, de Rojas MIS, Cabrera J (2000) The effect that the pozzolanic reaction of metakaolin has on the heat evolution in metakaolincement mortars. Cem Concr Res 30:209–216. https://doi.org/10. 1016/S0008-8846(99)00231-8 Gartner E (2004) Industrially interesting approaches to Blow-CO2^ cements. Cem Concr Res 34:1489–1498. https://doi.org/10.1016/j. cemconres.2004.01.021 Göktepe AB, Sezer A, Sezer Gİ, Ramyar K (2008) Classification of time-dependent unconfined strength of fly ash treated clay. Constr Build Mater 22:675–683. https://doi.org/10.1016/j. conbuildmat.2006.10.008 Gruyaert E, Robeyst N, Belie ND (2010) Study of the hydration of Portland cement blended with blast-furnace slag by calorimetry and thermogravimetry. J Therm Anal Calorim 102:941–951. https://doi.org/10.1007/s10973-010-0841-6 Gueye RS, Davy CA, Cazaux F et al (2017) Mineralogical and physicochemical characterization of Mbodiene palygorskite for pharmaceutical applications. J Afr Earth Sci 135:186–203 Guney Y, Sari D, Cetin M, Tuncan M (2007) Impact of cyclic wetting– drying on swelling behavior of lime-stabilized soil. Build Environ 42:681–688. https://doi.org/10.1016/j.buildenv.2005.10.035 Herrero J, Artieda O, Hudnall WH (2009) Gypsum, a tricky material. Soil Sci Soc Am J 73:1757–1763. https://doi.org/10.2136/sssaj2008. 0224 Hillier S (2000) Accurate quantitative analysis of clay and other minerals in sandstones by XRD: comparison of a Rietveld and a reference intensity ratio (RIR) method and the importance of sample preparation. Clay Miner 35:291–302 Hillier S (2003) Quantitative analysis of clay and other minerals in sandstones by X-ray powder diffraction (XRPD). In: Worden RH, Morad S (eds) Clay mineral cements in sandstones. Blackwell Publishing Ltd., pp 213–251 Hillier S, Roe MJ, Geelhoed JS, Fraser AR, Farmer JG, Paterson E (2003) Role of quantitative mineralogical analysis in the investigation of sites contaminated by chromite ore processing residue. Sci Total Environ 308:195–210 Hubbard CR, Snyder RL (1988) RIR-measurement and use in quantitative XRD. Powder Diffract 3:74–77. https://doi.org/10.1017/ S0885715600013257 Hulett GA (1905) The solubility of gypsum as affected by size of particles and by different crystallographic surfaces. J Am Chem Soc 27:49– 56. https://doi.org/10.1021/ja01979a008 Hulett GA, Allen LE (1902) The solubility of gypsum. J Am Chem Soc 24:667–679 Kinuthia JM, Wild S, Jones GI (1999) Effects of monovalent and divalent metal sulphates on consistency and compaction of lime-stabilised kaolinite. Appl Clay Sci 14:27–45. https://doi.org/10.1016/S01691317(98)00046-5 Klug HP, Alexander LE (1974) X-ray diffraction procedures: for polycrystalline and amorphous materials, 2nd edition. Wiley-VCH, 992 p. ISBN 0-471-49369-4 Kulp JL, Kent P, Kerr PF (1951) Thermal study of the Ca-Mg-Fe carbonate minerals. Am Mineral 36:643–670 Lagerwerff JV, Akin GW, Moses SW (1965) Detection and determination of gypsum in soils. Soil Sci Soc Am J 29:535–540. https://doi.org/ 10.2136/sssaj1965.03615995002900050019x

Environ Sci Pollut Res Largent R (1978) Evaluation of pozzolanic activity-attempt at finding a test. Bull. Liaison Labo. P. et Ch. 93: 61-65. Lasledj A (2009) Traitement des sols argileux à la chaux: processus physicochimique et propriétés géotechniques. PhD thesis, Orléans, 370 p. Le Berre P (1989) Les attapulgites (palygorskites) et sépiolites. Bureau de Recherches Géologiques et Minières, Orléans Li Z, Ding Z (2003) Property improvement of Portland cement by incorporating with metakaolin and slag. Cem Concr Res 33:579–584. https://doi.org/10.1016/S0008-8846(02)01025-6 Li C, Sun H, Li L (2010) A review: the comparison between alkali-activated slag (Si + Ca) and metakaolin (Si + Al) cements. Cem Concr Res 40: 1341–1349. https://doi.org/10.1016/j.cemconres.2010.03.020 Lin D-F, Lin K-L, Hung M-J, Luo H-L (2007) Sludge ash/hydrated lime on the geotechnical properties of soft soil. J Hazard Mater 145:58– 64. https://doi.org/10.1016/j.jhazmat.2006.10.087 Lindgreen H, Geiker M, Krøyer H, Springer N, Skibsted J (2008) Microstructure engineering of Portland cement pastes and mortars through addition of ultrafine layer silicates. Cem Concr Compos 30: 686–699. https://doi.org/10.1016/j.cemconcomp.2008.05.003 Lothenbach B, Winnefeld F (2006) Thermodynamic modelling of the hydration of Portland cement. Cem Concr Res 36:209–226 Misra A, Biswas D, Upadhyaya S (2005) Physico-mechanical behavior of self-cementing class C fly ash–clay mixtures. Fuel 84:1410– 1422. https://doi.org/10.1016/j.fuel.2004.10.018 Mohamed AMO (2000) The role of clay minerals in marly soils on its stability. Eng Geol 57:193–203. https://doi.org/10.1016/S00137952(00)00029-6 Molard JP, Camps JP, Laquerbe M (1987) Etude de l’extrusion et de la stabilisation par le ciment d’argiles monominérales. Mater Struct 20: 44–50. https://doi.org/10.1007/BF02472726 Moore DM, Reynolds RC (1997) X-ray diffraction and the identification and analysis of clay minerals. Oxford University Press, New York (1989) 2nd impression. 400 p. Moreau J-D, Trincal V, André D et al (2018) Underground dinosaur tracksite inside a karst of southern France: early Jurassic tridactyl traces from the Dolomitic Formation of the Malaval Cave (Lozère). Int J Speleol 47(1):29–42. https://doi.org/10. 5038/1827-806X.47.1.2149 Morsy MS (2005) Effect of temperature on hydration kinetics and stability of hydration phases of metakaolin-lime sludge-silica fume system. Ceramics-Silikaty 49:237–241 Möschner G, Lothenbach B, Rose J, Ulrich A, Figi R, Kretzschmar R (2008) Solubility of Fe–ettringite (Ca6[Fe(OH)6]2(SO4)3·26H2O). Geochim Cosmochim Acta 72:1–18. https://doi.org/10.1016/j.gca. 2007.09.035 Myneni SC, Traina SJ, Logan TJ (1998) Ettringite solubility and geochemistry of the Ca(OH)2–Al2(SO4)3–H2O system at 1 atm pressure and 298 K. Chem Geol 148:1–19 Nadeem A, Memon SA, Lo TY (2013) Mechanical performance, durability, qualitative and quantitative analysis of microstructure of fly ash and Metakaolin mortar at elevated temperatures. Constr Build Mater 38:338–347. https://doi.org/10.1016/j. conbuildmat.2012.08.042 Nalbantoğlu Z (2004) Effectiveness of Class C fly ash as an expansive soil stabilizer. Constr Build Mater 18:377–381. https://doi.org/10. 1016/j.conbuildmat.2004.03.011 NF EN 12457-2 (2002) Lixiviation – Essai de conformité pour lixiviation des déchets fragmentés et des boues. Partie 2 : Essai en bâchée unique avec un rapport liquid-solide de 10 l/kg et une granularité inférieure à 4 mm NF EN ISO 8130-2 (2011) Poudres pour revêtement. Partie 2 : Détermination de la masse volumique à l’aide d’un pycnomètre à gaz (méthode de référence) NF P 94-068 (1998) Sols : Reconnaissance et essais. Mesure de la capacité d’adsorption de bleu de méthylène d’un sol ou d’un matériau rocheux

Nobst P, Stark J (2003) Investigations on the influence of cement type on thaumasite formation. Cem Concr Compos 25:899–906 Nordstrom DK, Plummer LN, Langmuir D, et al (1990) Revised chemical equilibrium data for major water—mineral reactions and their limitations. In: Chemical Modeling of Aqueous Systems II; Melchior, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC. pp 398–413 Norman RL, Dann SE, Hogg SC, Kirk CA (2013) Synthesis and structural characterisation of new ettringite and thaumasite type phases: Ca6[Ga(OH)6·12H2O]2(SO4)3·2H2O and Ca6[M(OH)6·12H2O]2(SO4)2(CO3)2, M = Mn, Sn. Solid State Sci 25:110–117. https://doi.org/10.1016/j.solidstatesciences.2013.08.006 Obuzor GN, Kinuthia JM, Robinson RB (2012) Soil stabilisation with lime-activated-GGBS—a mitigation to flooding effects on road structural layers/embankments constructed on floodplains. Eng Geol 151:112–119. https://doi.org/10.1016/j.enggeo.2012.09.010 Ostroff AG, Metler AV (1966) Solubility of calcium sulfate dihydrate in the system NaCl-MgCl2-H2O from 28° to 70°C. J Chem Eng Data 11:346–350 Ostwald W (1900) Über die vermeintliche Isomerie des roten und gelben Quecksilberoxyds und die Oberflächenspannung fester Körper. Z Phys Chem 34U:495–503. https://doi.org/10.1515/zpch-1900-3431 Ouhadi VR, Yong RN (2003) The role of clay fractions of marly soils on their post stabilization failure. Eng Geol 70:365–375. https://doi.org/ 10.1016/S0013-7952(03)00104-2 Palou MT, Kuzielová E, Novotný R, Šoukal F, Žemlička M (2016) Blended cements consisting of Portland cement–slag–silica fume– metakaolin system. J Therm Anal Calorim 125:1025–1034. https:// doi.org/10.1007/s10973-016-5399-5 Perkins RB, Palmer CD (1999) Solubility of ettringite (Ca6[Al(OH)6]2(SO4)3·26H2O) at 5–75 °C. Geochim Cosmochim Acta 63:1969–1980 Podor R, Ravaux J, Brau H-P (2012) In situ experiments in the scanning electron microscope chamber. In: Dr. Viacheslav Kazmiruk (Ed.) Scanning electron microscopy, InTech. 31-54. https://doi.org/10. 5772/36433 Pokrovsky OS, Schott J (2001) Kinetics and mechanism of dolomite dissolution in neutral to alkaline solutions revisited. Am J Sci 301: 597–626. https://doi.org/10.2475/ajs.301.7.597 Rahhal V, Talero R (2014) Very early age detection of ettringite from pozzolan origin. Constr Build Mater 53:674–679. https://doi.org/ 10.1016/j.conbuildmat.2013.10.082 Rajasekaran G (2005) Sulphate attack and ettringite formation in the lime and cement stabilized marine clays. Ocean Eng 32:1133–1159. https://doi.org/10.1016/j.oceaneng.2004.08.012 Rietveld H (1969) A profile refinement method for nuclear and magnetic structures. J Appl Crystallogr 2:65–71 Santamarina JC, Klein KA, Wang YH, Prencke E (2002) Specific surface: determination and relevance. Can Geotech J 39:233–241 Seco A, Miqueleiz L, Prieto E, Marcelino S, García B, Urmeneta P (2016) Sulfate soils stabilization with magnesium-based binders. Appl Clay Sci 135:457–464. https://doi.org/10.1016/j.clay.2016.10.033 Seidell A, Smith JG (1904) The solubility of calcium sulphate in solutions of nitrates. J Phys Chem 8:493–499 SETRA (2011) Acceptabilité de matériaux alternatifs en technique routière. Évaluation environnementale. Guide Méthodologique. Service d’études sur les transports, les routes et leurs aménagements, France Sha W, Pereira GB (2001) Differential scanning calorimetry study of ordinary Portland cement paste containing metakaolin and theoretical approach of metakaolin activity. Cem Concr Compos 23:455– 461. https://doi.org/10.1016/S0958-9465(00)00090-1 Shah B, Kakumanu VK, Bansal AK (2006) Analytical techniques for quantification of amorphous/crystalline phases in pharmaceutical solids. J Pharm Sci 95:1641–1665. https://doi.org/10.1002/jps. 20644

Environ Sci Pollut Res Shternina EB (1960) Solubility of gypsum in aqueous solutions of salts. Int Geol Rev 2:605–616. https://doi.org/10.1080/ 00206816009473496 Shukla J, Mohandas VP, Kumar A (2008) Effect of pH on the solubility of CaSO4·2H2O in aqueous NaCl solutions and physicochemical solution properties at 35 °C. J Chem Eng Data 53:2797–2800. https:// doi.org/10.1021/je800465f Singer A, Huertos EG, Galan E (2011) Developments in palygorskitesepiolite research: a new outlook on these nanomaterials. Elsevier. 529 p. ISBN 978-0-444-53607-5 Snyder RL, Bish DL (1989) Quantitative analysis. Rev Mineral Geochem 20:101–144 Talero R (2005) Performance of metakaolin and Portland cements in ettringite formation as determined by ASTM C 452-68: kinetic and morphological differences. Cem Concr Res 35:1269–1284. https://doi.org/10.1016/j.cemconres.2004.10.002 Tasong WA, Wild S, Tilley RJD (1999) Mechanisms by which ground granulated blastfurnace slag prevents sulphate attack of limestabilised kaolinite. Cem Concr Res 29:975–982. https://doi.org/ 10.1016/S0008-8846(99)00007-1 Taylor HFW (1997) Cement chemistry. Thomas Telford, 488p. ISBN 978-0-7277-2592-9 Taylor JC, Hinczak I (2006) Rietveld made easy: a practical guide to the understanding of the method and successful phase quantifications. Sietronics Pty Limited. 201 p. ISBN 0975079808 Thiéry V, Bourdot A, Bulteel D (2015) Characterization of raw and burnt oil shale from Dotternhausen: petrographical and mineralogical evolution with temperature. Mater Charact 106:442–451 Thiéry V, Trincal V, Davy CA (2017) The elusive ettringite under the high-vacuum SEM - a reflection based on natural samples, the use of Monte Carlo modelling of EDS analyses and an extension to the ettringite group minerals. J Microsc 268:84–93. https://doi.org/10. 1111/jmi.12589 Thiry M, Carrillo N, Franke C, Martineau N (2013) Technique de préparation des minéraux argileux en vue de l’analyse par diffraction des Rayons X et introduction à l’interprétation des diagrammes. Centre de Géosciences, Ecole des mines de Paris, Fontainebleau, France. Rapport No. RT131010MTHI. 38 p. Trincal V, Charpentier D, Buatier MD, Grobety B, Lacroix B, Labaume P, Sizun JP (2014) Quantification of mass transfers and mineralogical transformations in a thrust fault (Monte Perdido thrust unit, southern Pyrenees, Spain). Mar Pet Geol 55:160–175 Warren CJ, Reardon EJ (1994) The solubility of ettringite at 25°C. Cem Concr Res 24:1515–1524. https://doi.org/10.1016/0008-8846(94) 90166-X

Weaver CE (1975) Construction of limpid dolomite. Geology 3:425–428. https://doi.org/10.1130/0091-7613(1975)32.0.CO;2 Wild S, Khatib JM, Jones A (1996) Relative strength, pozzolanic activity and cement hydration in superplasticised metakaolin concrete. Cem Concr Res 26:1537–1544. https://doi.org/10.1016/0008-8846(96) 00148-2 Wild S, Kinuthia JM, Jones GI, Higgins DD (1998) Effects of partial substitution of lime with ground granulated blast furnace slag (GGBS) on the strength properties of lime-stabilised sulphate-bearing clay soils. Eng Geol 51:37–53. https://doi.org/10.1016/S00137952(98)00039-8 Wild S, Kinuthia JM, Jones GI, Higgins DD (1999) Suppression of swelling associated with ettringite formation in lime stabilized sulphate bearing clay soils by partial substitution of lime with ground granulated blastfurnace slag (GGBS). Eng Geol 51:257–277. https://doi. org/10.1016/S0013-7952(98)00069-6 Xeidakis GS (1996a) Stabilization of swelling clays by Mg(OH)2. Changes in clay properties after addition of Mg-hydroxide. Eng Geol 44:107–120. https://doi.org/10.1016/S0013-7952(96)00047-6 Xeidakis GS (1996b) Stabilization of swelling clays by Mg(OH)2. Factors affecting hydroxy-Mg-interlayering in swelling clays. Eng Geol 44:93–106. https://doi.org/10.1016/S0013-7952(96)00046-4 Yarbaşı N, Kalkan E, Akbulut S (2007) Modification of the geotechnical properties, as influenced by freeze–thaw, of granular soils with waste additives. Cold Reg Sci Technol 48:44–54. https://doi.org/ 10.1016/j.coldregions.2006.09.009 Yong RN, Ouhadi VR (2007) Experimental study on instability of bases on natural and lime/cement-stabilized clayey soils. Appl Clay Sci 35:238–249. https://doi.org/10.1016/j.clay.2006.08.009 Yukselen Y, Kaya A (2008) Suitability of the methylene blue test for surface area, cation exchange capacity and swell potential determination of clayey soils. Eng Geol 102:38–45. https://doi.org/10.1016/ j.enggeo.2008.07.002 Zemlicka M, Kuzielova E, Kuliffayova M et al (2015) Study of hydration products in the model systems metakaolin–lime and metakaolin– lime–gypsum. Ceramics-Silikáty 59:283–291 Zhang Y, Muhammed M (1989) Solubility of calcium sulfate dihydrate in nitric acid solutions containing calcium nitrate and phosphoric acid. J Chem Eng Data 34:121–124 Zhang T, Yu Q, Wei J, Gao P, Zhang P (2012) Study on optimization of hydration process of blended cement. J Therm Anal Calorim 107: 489–498. https://doi.org/10.1007/s10973-011-1531-8