Soy-Based Adhesive Cross-Linked by Phenol-Formaldehyde ... - MDPI

metals Article

Diatoms and Their Capability for Heavy Metal Removal by Cationic Exchange Juan Hernández-Ávila 1 , Eleazar Salinas-Rodríguez 1, *, Eduardo Cerecedo-Sáenz 1 , Ma. Isabel Reyes-Valderrama 1 , Alberto Arenas-Flores 1 , Alma Delia Román-Gutiérrez 2 and Ventura Rodríguez-Lugo 1 1

2

*

Área Académica de Ciencias de la Tierra y Materiales, Universidad Autónoma del Estado de Hidalgo, Carretera Pachuca–Tulancingo, Km 4.5 s/n, Mineral de la Reforma, Hidalgo C.P. 42184, Mexico; [email protected] (J.H.-Á.); [email protected] (E.C.-S.); [email protected] (M.I.R.-V.); [email protected] (A.A.-F.); [email protected] (V.R.-L.) Área Académica de Química en Alimentos, Universidad Autónoma del Estado de Hidalgo, Carretera Pachuca–Tulancingo, Km 4.5 s/n, Mineral de la Reforma, Hidalgo C.P. 42184, Mexico; [email protected] Correspondence: [email protected]; Tel.: +52-771-717-2000 (ext. 2280)

Academic Editors: Seung-Mok Lee and Jae-Kyu Yang Received: 23 February 2017; Accepted: 8 May 2017; Published: 12 May 2017

Abstract: This work shows the physicochemical behavior of two different diatoms from the country of Mexico (State of Jalisco and Hidalgo) with similar compositions. These were used to eliminate toxic cations from a synthetic solution containing 5.270 mg As3+ /L; 4.280 mg Ag+ /L; 3.950 mgNi2+ /L; 4.090 mg Cr6+ /L; and 4.081 mg Pb2+ /L. These diatoms were used as filters, and the quantity of cations remaining in the solution after filtering was measured. According to the most important results found, for the recovery of metals, both minerals achieved arsenic, silver, lead, and nickel recoveries up to 95%, and lower than 10% for chromium. This could be due to the absence of an environment to reduce Cr6+ to Cr3+ . On the other hand, it was observed that there was no selectivity during the recovery of the other cations present in the solution. According to efficiency of interchange, the mineral from Hidalgo is slightly better than the mineral from Jalisco for the removal of arsenic, lead, and silver. For nickel, and particularly Cr6+ , the efficiency is higher for the sample from Jalisco. Keywords: diatomite; ionic exchange; metals removal; heavy metals

1. Introduction Diatomite is a siliceous rock of sedimentary origin that is inert and of low toxicity that shows small quantities of associated inorganic compounds, such as aluminum, iron, ammonium, alkali metals and other minor constituents [1]. It is also formed by crystalline aluminum silicates of tetrahedral structure linked among them, which share oxygen atoms. The elemental cell structure consists of tetrahedral molecules of SiO4 and AlO4 arranged in such a way that each oxygen atom is distributed between two adjacent tetrahedrons. Diatomite is also composed mostly of the fossilized fragments of diatom algae [2,3]. It is basically microscopic unicellular marine algae with varied shapes and sizes. The algae are composed by a transparent cellular wall, with a translucent outer layer of crystal-like silica [4], and an inner layer of pectin, with a chemical composition of the diatoms’ walls of 96.5 wt. % of silica and 1.5 wt. % of sesqui-oxides. The minerals also have properties similar to clay, where in some cases the thermodynamic swelling could be related to the tendency of the charge-balancing counterions to hydrate the hydrophilic interaction between the clay surface and water, and the strength of the interaction between the clay surface and the counterion [5]. On the other hand, some researchers have disclosed that for clay Metals 2017, 7, 169; doi:10.3390/met7050169

www.mdpi.com/journal/metals

Metals 2017, 7, 169

2 of 10

swelling to occur, water molecules must pass from external regions (i.e., external surfaces, internal surfaces, and micropores) to the interlayer gallery, passing between all clay edges. It has been determined that, in contrast to the chemically-inert basal plane, the edges of particles are extremely reactive [6–9], containing both Brönsted acid and base groups. Other authors [9–11] have reported that the reactive nature of clay layer edges has been implicated in catalysis reactions, such as polymerization. Other studies have evaluated different types of materials, such as fibrous absorbents, resins, polymeric anion exchangers, ligand-doped conjugate absorbents, mesoporous absorbents, among others, for the removal of arsenic [12,13], phosphorous [14,15], and lead [16–19]. This has led to good results, not only for removal of these metals, but also in the reuse of exchangers. This last point is of importance for the cost efficiency of the method and material to be used in the removal process. Industrially, diatomite is used in a variety of fields, and has different names depending on its purity or the region of origin. Diatoms are widely used as filters in diverse branches of industry, such as in water filters, filters for the elaboration of beer and wine [2], filler additive, absorbent additive, and as a soft abrasive. There are few research works related to the use of diatoms for the treatment of wastes for the recovery of metals. This work will evaluate the capacity of this material to remove heavy metals from solution. 2. Methodology The material used in this work was sampled in the mining region of “El Barqueño” in the state of Jalisco, and the other in the community of “Loma Larga” in the county of “Acatlán”, in the state of Hidalgo, both in the country of Mexico. For characterization techniques, it was necessary to prepare the sample to particle sizes lower than 100 µm, and then characterize by the following analytical methods: X-ray diffraction conducted with an INEL Diffractometer model Equinox 2000 located at the Autonomous University of the State of Hidalgo (UAEH), Mexico. The MATCH database was used to index the spectra. The quantification of elements contained in samples was carried out by inductively-coupled plasma spectrophotometry using a Perkin Elmer model 2100 (located at UAEH). The morphology of samples was obtained using a scanning electron microscope, JEOL model JMS 6300 (located at UAEH) with a voltage of 30 keV and equipped with an Energy Dispersive Spectrometer of X-ray EDS detector. For the analysis of particle size, a 0.3 g sample was dissolved in 125 mL of water, and then analyzed in a particle size analyzer by laser diffraction; model LS-13320 (located at UAEH). The porosity was measured using porosity measuring equipment by BET Micrometrics, model ASAP 2020, carried out with 1 g of sample. Finally, IR spectrophotometry was obtained with Perkin Elmer Flouries equipment. In addition, water content was calculated by difference in weight, using a 100 g sample and then placing it in a furnace at 350 ◦ C for one hour. After that, the sample was removed from the furnace, it was cooled until it reached a temperature of 25 ◦ C, and was finally reweighed to calculate the difference and the percentage of water content. An atomic absorption spectrophotometer (AAS) was used to evaluate the exchange capacity of metals during absorption proofs. Samples included nitrates of Ag+ , Ni2+ , Pb2+ , As3+ , and Cr6+ . To determine if there was ionic exchange with the clay present in the diatoms, the sodium concentration in the water–diatom mixture was measured. Results indicated if sodium was present, and was compared with a pattern. A solution containing the mentioned metals was added in an average concentration of approximately 4 mg/L. For each test set, a calibration curve with patterns from 0.1 to 10 mg/L (including blank) was conducted to evaluate the amount of cation in solution before and after each proof. The two solutions having 5.270 mg As3+ /L; 4.280 mg Ag+ /L; 3.950 mg Ni2+ /L; 4.090 mg Cr6+ /L; and 4.081 mg Pb2+ /L were added to both diatoms separately (Diatom from Jalisco and diatom from Hidalgo), and left for one week to allow for permanent contact and exchange. At the end of the reaction time, the solution was filtered, and the corresponding measurements by AAS were made to obtain the concentration of each cation remaining in solution [20].

Metals 2017, 7, 169

3 of 10

Metals 2017, 7, 169

3 of 10

The removal efficiency (Er, amount of cation removed from solution) was calculated using the following formula: The removal efficiency (Er, amount of cation removed from solution) was calculated using the Er = 100 (Co − Cf)/Co (1) following formula: where, Co is defined as the initialEconcentration metal of interest, and Cf is the (1) metal r = 100 (Co − Cof o f )/Cthe concentration once exposed to diatom. The two samples were taken and the liquid was evaporated, where, Co is defined as the initial concentration of the metal of interest, and Cf is the metal concentration adding 100 mL of water to the first sample and 100 mL of HCl at 0.1 mol/L to the second sample. It once exposed to diatom. The two samples were taken and the liquid was evaporated, adding 100 mL was allowed to stand for 5 days, and the concentration of the metal was measured. of water to the first sample and 100 mL of HCl at 0.1 mol/L to the second sample. It was allowed to stand for 5 days, and the concentration of the metal was measured. 3. Results and Discussion 3. Results and Discussion The principal mineral species identified in the diatoms studied by X-ray diffraction are shown inThe Table 1. Results showspecies that theidentified majority in species found was quartz. Otherdiffraction mineral species wereinalso principal mineral the diatoms studied by X-ray are shown present in different amounts (Figure 1 for diatom from Hidalgo state). In Figure 2 (diatom form Table 1. Results show that the majority species found was quartz. Other mineral species were also Jalisco), the diffraction pattern natural diatom (D), calcined flux diatom (D-C) and calcined present in different amounts (Figurefor 1 for diatom from Hidalgo state).with In Figure 2 (diatom form Jalisco), without flux diatom (D-S) can be observed. the diffraction pattern for natural diatom (D), calcined with flux diatom (D-C) and calcined without flux diatom (D-S) can be observed.

Table 1. Mineral species identified in the materials studied.

Origin

Table 1. Mineral species identified in the materials studied. Mineral Species

Jalisco Origin Hidalgo Jalisco

Silica, Albite, Muscovite, Potassium Feldspar, Mineral Species Mogonita, and Andesite Silica, Albite, Muscovite, Potassium Feldspar, Mogonita, and Andesite Silica, Albite, Muscovite, Potassium Feldspar, Mogonita, and Andesite Silica, Albite, Muscovite, Potassium Feldspar, Mogonita, and Andesite

Hidalgo 600

D-S

500

Q

Intensity (counts)

400

Or

300

D-C

200

Or

100

D 0 10

20

30

40

50

60

70

80

90

2theta

Figure 1. X-ray spectrum of diatom from the state of Hidalgo, Mexico (where Q is quartz and Or Figure 1. X-ray spectrum of diatom from the state of Hidalgo, Mexico (where Q is quartz and Or is is Orthoclase). Orthoclase).

From thethe chemical analysis results, Al, K, K,Na, Na,Ca, Ca,Fe, Fe,and From chemical analysis results,the theprincipal principalelements elementspresent present are are Si, Si, Al, andMg. Mg.Values Valuesthat that are associated to their respective oxides (Table 2) represent normal values for are associated to their respective oxides (Table 2) represent normal values for highhigh-quality diatoms. quality diatoms.

Metals 2017, 7, 169 Metals 2017, 7, 169 Metals 2017, 7, 169

4 of 410of 10 4 of 10

Table 2. Chemical compositions for the diatoms studied. Table 2. Chemical compositions for the diatoms studied. Table 2. Chemical compositions for theElement diatoms studied. % wt Element % wt Treatment Treatment SiOSiO 2 O 2OCaO 2Al2O Al3 2OK 3 2O K2ONa2Na CaOFeOFeOMgO MgOTiOTiO

Origin Origin Origin

Treatment Natural Natural SiO2

Element % wt

70.070.0 11.63 11.632.412.41 6.106.10 0.850.85 1.951.95 1.791.790.500.50 Al2 O3

K2 O

Na2 O

CaO

FeO

MgO

Hidalgo without fluxflux81.50 HidalgoCalcined Calcined without 81.5012.00 12.002.102.10 1.451.45 0.100.10 1.441.44 0.480.48 0 Hidalgo

TiO

0

Natural 70.0 11.63 2.41 6.10 0.85 1.95 1.79 0.50 Calcined without flux 81.50 12.00 2.10 1.961.96 1.45 1.44 0.48 Calcined withwith flux 2.822.820.10 0.130.131.646 Calcined flux 82.00 82.0011.15 11.15 1.6460.51 0.51 0 00 Calcined with flux 82.00 11.15 1.96 2.82 0.13 1.646 0.51 0

Natural Natural

93.58 93.58 3.033.03 0.920.92 0.240.24 0.110.11 1.811.81 0.400.40 0

Natural 93.58 3.03 0.92 0.24 0.11 1.81 0.40 Calcined without flux 0.230.230.0 0.0 0.0 00 0 0.08 Calcined without flux96.39 96.39 3.253.25 0.08 0 Jalisco Calcined without flux 96.39 3.25 0.05 0.050.05 0.23 0.08 JaliscoJalisco Calcined with flux 94.49 2.90 0.7 1.75 0.07 0 0.09 Calcined withwith fluxflux 94.49 Calcined 94.49 2.902.90 0.7 0.7 1.751.75 0.070.07 0 0 0.090.09 0

0

0

00 00

600 600

D-SD-S Q Q

400 400

Intensity (counts)

Intensity (counts)

500 500

Or Or

300 300

D-CD-C

200 200

Or Or

100 100

D D 0

0 10 10

20 20

30 30

40 40

50 50

60 60

70 70

80 80

90 90

2theta 2theta

Figure 2. X-ray spectrum of diatom from the state of Jalisco, Mexico (where Q is quartz and Or Figure 2. X-ray spectrum of diatom from the the state of Jalisco, Mexico (where Q isQquartz andand Or is Figure 2. X-ray spectrum of diatom from state of Jalisco, Mexico (where is quartz Or is is Orthoclase). Orthoclase). Orthoclase).

TheThe average sizesize of diatom pores waswas alsoalso measured, where values vary from 1.5 1.5 µm to 7toµm as as µmµm µm average of diatom pores measured, where values vary from 7 µm determined by electron microscopy (SEM) for both diatoms. The morphology of this material determined byscanning scanning electron microscopy (SEM) for for both diatoms. TheThe morphology of this determined by scanning electron microscopy (SEM) both diatoms. morphology of this can be observed in observed Figuresin3–5. material cancan be observed Figures 3–5.3–5. material be in Figures

(a) (a)

(b) (b)

Figure 3. ofofdiatoms: (a) (a) natural diatom from Jalisco; (b) (b) natural diatom from Figure 3. Photomicrography ofdiatoms: diatoms: (a) natural diatom from Jalisco; diatom from Figure 3. Photomicrography Photomicrography natural diatom from Jalisco; (b)natural natural diatom Hidalgo. Hidalgo. from Hidalgo.

Metals 2017, 7, 169

5 of 10

Metals 2017, 7, 169 Metals 2017, 7, 169

5 of 10 5 of 10

(a) (b) (a) (b) Figure 4. Photomicrography of diatoms: (a) calcined with flux from Jalisco; (b) calcined with flux from Figure Photomicrographyofofdiatoms: diatoms:(a)(a) calcined with from Jalisco; (b) calcined flux Figure 4. 4. Photomicrography calcined with fluxflux from Jalisco; (b) calcined with with flux from Hidalgo. from Hidalgo. Hidalgo.

(a) (b) (a) (b) Figure 5. Photomicrography of diatoms: (a) calcined without flux from Jalisco; (b) calcined without Figure 5. 5. Photomicrography Photomicrography of of diatoms: diatoms: (a) (a) calcined calcined without without flux flux from from Jalisco; Jalisco; (b) (b) calcined calcined without without Figure flux from Hidalgo. flux from Hidalgo. flux from Hidalgo.

In the study of particle size, a bimodal granulometric curve was observed, and the maximum In the study of particle size, a bimodal granulometric curve was observed, and the maximum the study of percentage particle size, bimodal granulometric curve observed, and12.99 the maximum rangeIn shows a major of aretained material in particle sizeswas ranging between and 22.73 range shows a major percentage of retained material in particle sizes ranging between 12.99 and 22.73 range shows a major percentage of retained material in particle sizes ranging between 12.99 and µm for the diatom from Jalisco and from 12.87 to 22.51 µm for the diatom from Hidalgo, showing a µm for the diatom from Jalisco and from 12.87 to 22.51 µm for the diatom from Hidalgo, showing a 22.73 µmweight for theranging diatom from andand from 12.87 to 22.51 respectively. µm for the diatom from Hidalgo, retained fromJalisco 4–4.49% from 4–4.48%, An average particleshowing size of retained weight ranging from 4–4.49% and from 4–4.48%, respectively. An average particle size of a retained ranging from 4–4.49% and from 4–4.48%, respectively. An average particle size of 17.18 µm forweight diatom from Jalisco, and 17.23 µm for diatom from Hidalgo was observed. Particle size 17.18 µm for diatom from Jalisco, and 17.23 µm for diatom from Hidalgo was observed. Particle size 17.18maximum µm for diatom from Jalisco, andmaterials 17.23 µmclearly for diatom from Hidalgo wasminerals observed. Particle size with percentages for both demonstrates that the correspond to with maximum percentages for both materials clearly demonstrates that the minerals correspond to maximum percentages for bothanother materials clearly demonstrates that the material minerals correspond to a awith clay/silt material. Additionally, maximum range of retained was observed a clay/silt material. Additionally, another maximum range of retained material was observed clay/siltparticle material. Additionally, another range of retained material wasinobserved between sizes ranging from 39.78maximum to 63.41 µm, showing a retained weight the rangebetween of 2.33 between particle sizes ranging from 39.78 to 63.41 µm, showing a retained weight in the range of 2.33 particle ranging fromJalisco. 39.78 to 63.41 µm, from showing a retained weight in the39.58 rangetoof63.23 2.33 to 2.96% to 2.96% sizes for diatom from For diatom Hidalgo, the data showed µm for to 2.96% for diatom from Jalisco. For diatom from Hidalgo, the data showed 39.58 to 63.23 µm for for diatom For diatom Hidalgo, theWe data showed 39.58 to 63.23 µm forshow particle size, particle size,from withJalisco. a retained weight from of 2.30 to 2.92%. can see that studied diatoms mostly particle size, with a retained weight of 2.30 to 2.92%. We can see that studied diatoms show mostly withtextures, a retainedand weight of 2.30 toin2.92%. Wesizes can see studied finethat textures, and fine principally particle notthat larger thandiatoms 40 µm.show It ismostly possible residual fine textures, and principally in particle sizes not larger than 40 µm. It is possible that residual principally in particle sizes larger than 40 µm. It (Figure is possible material shows silicified andnot agglomerated particles 6). that residual material shows silicified material shows silicified and agglomerated particles (Figure 6). and According agglomerated particles (Figurefor 6). the determination of water content in the studied diatoms, it to results obtained According to results obtained for the determination of water content in the studied diatoms, it According to results obtained thefor determination water content the for studied diatoms, was found that water amounted to for 4.2% the material of from Jalisco and in 5.4% diatom from was found that water amounted to 4.2% for the material from Jalisco and 5.4% for diatom from it was found that water amounted to 4.2% the material from Jalisco and 5.4% for diatom from Hidalgo. This is favorable because with low for values, the diatoms have a higher absorption capacity. Hidalgo. This is favorable because with low values, the diatoms have a higher absorption capacity. Hidalgo. Thisisisan favorable because low values, the diatoms have a higher absorption capacity. Water content important factor with that promotes liquid absorption capacity in diatoms. Water content is an important factor that promotes liquid absorption capacity in diatoms. Water is an important factor that promotes absorption in diatoms. Oncontent the other hand, when diatom is calcined, theliquid hydroxyl groupscapacity on the mineral surface are lost On the other hand, when diatom is calcined, the hydroxyl groups on the mineral surface are lost theofother hand, diatom is calcined, the groups hydroxyl on (Si-OH). the mineral are lost in theOn form water, andwhen a greater quantity of silanol aregroups exposed Thissurface improves its in the form of water, and a greater quantity of silanol groups are exposed (Si-OH). This improves its in the form of water, and adue greater quantity of silanol groups are diatoms. exposed (Si-OH). This improves its capacity to absorb liquids, to the increasing pore size in both capacity to absorb liquids, due to the increasing pore size in both diatoms. capacity to absorb liquids, due to the increasing pore size in both diatoms.

Metals 2017, 7, 169 Metals 2017, 7, 169

6 of 10 6 of 10

(a)

(b) Figure 6. 6. Particle Particle Size: Size: (a) Jalisco; (b) (b) diatom diatom from from Hidalgo. Hidalgo. Figure (a) diatom diatom from from Jalisco;

Figure 7 shows the Fourier transform infrared spectrometry spectra, where the position of the Figure 7 shows the Fourier transform infrared spectrometry spectra, where the position of the peaks was found for the natural diatom (D), calcined diatom with flux (DC), and calcined diatom peaks was found for the natural diatom (D), calcined diatom with flux (DC), and calcined diatom without flux (DS). It was observed that all are coincident, only varying slightly in their intensity. This without flux (DS). It was observed that all are coincident, only varying slightly in their intensity. This is is evidence that siloxane groups (Si-O-Si) [20–23] can be formed during the calcination of diatoms, evidence that siloxane groups (Si-O-Si) [20–23] can be formed during the calcination of diatoms, which which was verified by elimination of the water and the increase in temperature. This results in a was verified by elimination of the water and the increase in temperature. This results in a release of release of water, and the corresponding band to the vibrational modes of the OH groups (Si-OH and water, and the corresponding band to the vibrational modes of the OH groups (Si-OH and H-OH) H-OH) of 3430 cm−1 is separated into two differentiated signals (3692 cm−1 from Si-OH, and 3432 cm−1 of 3430 cm−1 is separated into two differentiated signals (3692 cm−1 from Si-OH, and 3432 cm−−11 from H-OH). In addition to losing water, the band corresponding to the Si-O group of 1098 cm from H-OH). In addition to losing water, the band corresponding to the Si-O group of 1098 cm−1 decreased in intensity due to the loss of this kind of link. Other bands that decreased correspond to decreased in intensity due to the loss of this kind of link. Other bands that decreased correspond to water (3432 cm−1 and 1638 cm−1). water (3432 cm−1 and 1638 cm−1 ). Table 3 shows the properties of the studied diatoms in their natural state, and calcined with and Table 3 shows the properties of the studied diatoms in their natural state, and calcined with without flux. It is possible to observe that properties such as porosity, density, and compressive and without flux. It is possible to observe that properties such as porosity, density, and compressive strength improve substantially after calcination versus that observed for natural mineral. strength improve substantially after calcination versus that observed for natural mineral.

Metals 2017, 7, 169

7 of 10

Metals 2017, 7, 169

7 of 10

DS

3 00

T ra ns m ita nc e (c ounts )

79 6 DC

2 00

1 07 1

4 55 79 6

D

1 00

1 0 71

455

16 40 36 3 8

690

79 6 1 07 1

0 4 00 0

3 5 00

3 0 00

2500

2 0 00

1500

455

10 0 0

50 0

W a v e num be rs c m -1-1

(a)

DS

30 0

T ra ns m ita nc e (c ounts )

796 DC

20 0

1071

455 796

D

10 0

1071

455

1640 796

3638

690

1071

0 40 00

3 50 0

3 000

25 0 0

2 00 0

150 0

455

10 0 0

5 00

W a v e num be rs c m -1 -1

(b) Figure7.7. Fourier infrared spectrometry spectrums of (a) diatom from Hidalgo; and (b) and Figure Fouriertransform transform infrared spectrometry spectrums of (a) diatom from Hidalgo; diatom from Jalisco. D: natural diatom; DC: diatom calcined with flux; DS: diatom calcined without (b) diatom from Jalisco. D: natural diatom; DC: diatom calcined with flux; DS: diatom calcined flux. without flux. Table 3. Properties of the studied diatoms.

Table 3. Properties of the studied diatoms.

Property Property

Real density (g/cm3) Real density Global density (g/cm3 ) (g/cm3) Global density Total porosity (%) (g/cm3 ) Specific surface Total(m porosity (%) 2/g) Compressive Specific surface (m2(kg/cm /g) 2) strength Compressive Color strength (kg/cm2 )

pH Color Average pore size pH (µm) Average pore size (µm)

Sample from Hidalgo Diatom Diatom Sample from Hidalgo Calcined with Calcined Diatom Diatom Flux without Flux Calcined with Flux 2.37 2.37

Calcined without 2.22 Flux 2.22

Natural Diatom

Natural Diatom

2.15

2.15

Sample from Jalisco Diatom Diatom Sample from Jalisco Natural Calcined with Calcined Diatom Diatom Diatom Flux without Flux Natural Calcined with 2.35Flux 2.35

Calcined without Flux 2.20 2.20

Diatom

2.13

0.52

0.61

0.52

0.54

89.95 0.50

81.5 0.52

77.2 0.61

89.590.52

79.850.54

71.1 0.62

16.391 89.95

17.74 81.5

22.53 77.2

16.59 89.59

17.9479.85

22.07 71.1

16.391 17.7

17.74 16.49

22.53 15.00

18.316.59

17.5117.94

17.0022.07

White 18.3

Rose17.51

White 17.7 10 White

Rose 16.49 7 Rose

710

37

7

3

Cream15.00 Grey 7 Cream-Grey 1.5 7 1.5

10White 6.7 10 6.7

8 Rose 4.6 8 4.6

0.62

2.13

0.50

Cream17.00 Grey 7 Cream-Grey 1.8

7 1.8

Metals 2017, 7, 169 Metals 2017, 7, 169

8 of 10 8 of 10

4. Exchange of Metals 4. Exchange of Metals As can be seen in Table 4, diatoms show good efficiency for the cationic exchange of metals As can be seen in Table 4, diatoms show good efficiency for the cationic exchange of metals except for Cr6+6+, where exchange corresponded to only 9%. This could be because Cr6+ in a reducing except for Cr , where exchange corresponded to only 9%. This could be because Cr6+ in a reducing 3+ to promote its elimination from solutions. However, environment can be reduced from Cr6+ to Cr environment can be reduced from Cr6+ to Cr3+ to promote its elimination from solutions. However, when Cr6+6+is present at high concentrations, it surpasses its capacity of reduction, which avoids its when Cr is present at high concentrations, it surpasses its capacity of reduction, which avoids adequate elimination [24]. Consequently, all cations have similar concentrations and there is no its adequate elimination [24]. Consequently, all cations have similar concentrations and there is no reducing environment. Cr6+ could not be reduced to Cr3+, demonstrating the low exchange efficiency reducing environment. Cr6+ could not be reduced to Cr3+ , demonstrating the low exchange efficiency of both diatoms for this cation. The similar efficiency values for other metals confirms the oxidizing of both diatoms for this cation. The similar efficiency values for other metals confirms the oxidizing environment present in solution. Accordingly, the diatomaceous material can be used favorably for environment present in solution. Accordingly, the diatomaceous material can be used favorably for treatment of residual waters both in the metallurgical industry and for municipal water. It can be treatment of residual waters both in the metallurgical industry and for municipal water. It can be seen that unlike polymerization processes where there is selectivity for the removal of cations, the seen that unlike polymerization processes where there is selectivity for the removal of cations, the diatoms studied here showed that this phenomenon does not occur because the pore walls resulting diatoms studied here showed that this phenomenon does not occur because the pore walls resulting from calcination and the formation of potential sites for the adsorption of heavy metals allows the from calcination and the formation of potential sites for the adsorption of heavy metals allows the simultaneous removal of the cations in solution. These cations can be easily discharged with weak simultaneous removal of the cations in solution. These cations can be easily discharged with weak acid solutions, which enhances their reuse. For the case of As3+3+, besides removal by cation exchange, acid solutions, which enhances their reuse. For the case of As , besides removal by cation exchange, the adsorption could play an important role. As3+ could be present in solution as HAsO42− at a pH of the adsorption could play an important role. As3+ could be present in solution as HAsO4 2− at a 8, and the removal could be due to the adsorption in some active alumina formed after the calcination pH of 8, and the removal could be due to the adsorption in some active alumina formed after the process. calcination process. Table 4. Values of cationic exchange for metals using diatoms (pH = 8). Table 4. Values of cationic exchange for metals using diatoms (pH = 8). Initial Final Concentration (in Final Concentration (in Initial Solution) Final Concentration Final Concentration (in Concentration after Filtering (inSolution) after Filtering Metal Concentration in Solution) after Filtering withSolution) Diatomafter fromFiltering with Diatom from Metal in Solution Solution with Diatom from with Diatom from (±0.004(± mg/L) (±0.004 (±0.004 mg/L) 0.004 mg/L)Hidalgo Hidalgo (±mg/L) 0.004 mg/L) Jalisco Jalisco (±0.004 mg/L) As3+ As3+ 5.27 5.27 0. 175 0. 175 0.185 0.185 Ag+ Ag+ 4.28 4.28 0.063 0.063 0.066 0.066 2+ 0.180 3.95 3.95 0.188 0.188 0.180 Ni2+ Ni6+ 4.09 3.790 3.710 Cr 4.09 4.081 3.790 0.048 3.710 Cr6+ Pb2+ 0.049 4.081 0.048 0.049 Pb2+

Efficiency of Efficiency of Exchange of Exchange of Diatom from Diatom from Hidalgo (%) Hidalgo (%) 96.67 96.67 98.52 98.52 95.24 95.24 7.33 7.33 98.82 98.82

Efficiency of Efficiency of of Exchange Exchange of Diatom from Diatom from Jalisco Jalisco (%)(%)

96.48 96.48 98.46. 98.46. 95.44 95.44 9.29 9.29 98.80 98.80

With respect respect to to the the exchange exchange with with arsenic arsenic using using the the studied studied diatoms, diatoms, results results show show that that once once With diatoms are saturated, a liberation of arsenic occurs (see Figure 8). diatoms are saturated, a liberation of arsenic occurs (see Figure 8).

Figure 8. Arsenic exchange using diatoms. Figure 8. Arsenic exchange using diatoms.

5. Conclusions 5. Conclusions According to the obtained chemical composition, it is concluded that diatoms are minerals According to the obtained chemical composition, it is concluded that diatoms are minerals incapable of effecting anionic exchange in a natural state. An adequate activation (calcination) can incapable of effecting anionic exchange in a natural state. An adequate activation (calcination) can improve their anionic exchange capacity. Likewise, treating diatoms increased their efficiency in improve their anionic exchange capacity. Likewise, treating diatoms increased their efficiency in filtering processes, and they can be used in the absorption of cations due to their high retention filtering processes, and they can be used in the absorption of cations due to their high retention capacity. This increased with a heat treatment. For the retention of heavy metals, these diatoms

Metals 2017, 7, 169

9 of 10

capacity. This increased with a heat treatment. For the retention of heavy metals, these diatoms showed good results, showing that the metals can be eliminated as long as they are not in very high concentration or in a too acidic solution. It can be also concluded that diatoms could be used in the treatment of wastewater contaminated with heavy metals. In the case of arsenic, it was observed that once the diatom was saturated with this element, its liberation to the solution occurred. For the case of Cr6+ , removal was not possible due to the absence of a reducing environment that can reduce Cr6+ to Cr3+ to allow its adequate removal. Acknowledgments: The authors want to thank to the PRODEP-SEP of the Mexico Government for its financial support. Author Contributions: J. Hernández and E. Salinas conceived and designed the experiments; J. Hernández and M. I. Reyes performed and reviewed the experiments; E. Cerecedo, A. Arenas and V. Rodríguez made the XRD and SEM characterization of samples and helped in discussion. J. Hernández and A. D. Román performed the infrared analysis and interpreted the results. J. Hernández and E. Salinas wrote the paper. Finally, all author contributed in the revision and correction of observations form reviewers. Conflicts of Interest: The authors declare no conflicts of interest.

References 1. 2.

3.

4. 5.

6.

7. 8. 9.

10. 11.

12. 13. 14.

Kadey, F.L. Diatomite. In Industrial Minerals & Rocks, 4th ed.; Society for Mining, Metallurgy & Exploration: New York, NY, USA, 1975; pp. 101–115. Avila, J.H.; Moreno, F.P.; Espinoza, I.B.; Rodríguez, E.S. Caracterización De Diatomitas De Hidalgo, México. Posible Uso Como Adsorbente En La Disminución De Arsénico En Agua Potable; XL Congreso Mexicano de Química: Guadalajara, Jalisco, México, 2005; pp. 38–42. (In Spanish) Martínez, M.; Duro, L.; Rovira, M.; De Pablo, J. Sorption of cadmium and nickel (II) on a natural zeolite rich in clinoptilolite. In Natural Microporous Materials in Environmental Technology; Springer: Dordrecht, The Netherlands, 1999; pp. 327–334. Merchán, W.N.; Melo, S.G.; Sánchez, S.M. Mineralogía y geoquímica de diatomitas (Boyacá, Colombia). Geol. Colomb. 2007, 32, 77. Boulet, P.; Greenwell, H.C.; Stackhouse, S.; Coveney, P.V. Recent advances in understanding the structure and reactivity of clays using electronic structure calculations. J. Mol. Struct. TEOCHEM 2006, 762, 33–48. [CrossRef] Bickmore, B.R.; Rosso, K.M.; Nagy, K.L.; Cygan, R.T.; Tadanier, C.J. Ab initio determination of edge surface structures for dioctahedral 2:1 phyllosilicates: Implications for acid-base reactivity. Clay Clay Miner. 2003, 51, 359–371. [CrossRef] Churakov, S.V. Ab initio study of sorption on pyrophillite: Structure and acidity of the edge sites. J. Phys. Chem. B 2006, 110, 4135–4146. [CrossRef] [PubMed] Churakov, S.V. Structure and dynamics of the water films confined between edges of pyrophyllite: A first principle study. Geochim. Cosmochim. Acta 2007, 71, 1130–1144. [CrossRef] Stackhouse, S.; Coveney, P.V.; Sandre, E. Plane-wave density functional theoric study of formation of clay-polymer nanocomposite materials by self-catalyzed in situ intercalative polymerization. J. Am. Chem. Soc. 2001, 123, 11764. [CrossRef] [PubMed] Briones-Jurado, C.; Agacino-Valdés, E. Brönsted sites on acid-treated montmorillonite: A theorical study with probe molecules. J. Phys. Chem. A 2009, 113, 8994–9001. [CrossRef] [PubMed] Suter, J.L.; Kabalan, L.; Khader, M.; Coveney, P.V. Ab initio molecular dynamics study of the interlayer and micropore structure of aqueous montmorillonite clays. Geochim. Cosmoschim. Acta 2015, 169, 17–29. [CrossRef] Awal, M.R.; Urata, S.; Jyo, A.; Tamada, M.; Katakai, A. Arsenate removal from water by a weak-base anion exchange fibrous adsorbent. Water Res. 2008, 42, 689–696. [CrossRef] [PubMed] Awal, M.R.; Jyo, A. Rapid column-mode removal of arsenate from water by crosslinked poly (allylamine) resin. Water Res. 2009, 43, 1229–1236. [CrossRef] [PubMed] Awal, M.R.; Jyo, A. Assessing of phosphorous removal by polymeric anion exchange. Desalination 2011, 281, 111–117. [CrossRef]

Metals 2017, 7, 169

15. 16. 17. 18. 19. 20. 21. 22. 23.

24.

10 of 10

Awal, M.R.; Jyo, A.; Ihara, T.; Seko, N.; Tamada, M.; Lim, K.T. Enhanced trace phosphate removal from water by zirconium (IV) loaded fibrous adsorbent. Water Res. 2011, 45, 4592–4600. [CrossRef] [PubMed] Awal, M.R. Assessing of lead (III) capturing from contamined wastewater using ligand doped conjugate adsorbent. Chem. Eng. J. 2006, 289, 65–73. [CrossRef] Awal, M.R.; Hasan, M.M. A novel fine-tuning mesoporous adsorbent for simultaneous lead (II) detection and removal from wastewater. Sens. Actuators B Chem. 2014, 202, 395–403. [CrossRef] Awal, M.R.; Hasan, M.M.; Shahat, A. Functionalized novel mesoporous adsorbent for selective lead (II) ions monitoring and removal from wastewater. Sens. Actuators B Chem. 2014, 203, 854–863. [CrossRef] Awal, M.R.; Hasan, M.M. Novel conjugate adsorbent for visual detection and removal of toxic lead (II) ions from water. Microporous Mesoporous Mater. 2014, 196, 261–269. [CrossRef] Yuan, P; Wu, D.Q.; He, H.P.; Lin, Z.Y. The hydroxyl species and acid sites on diatomite surface: A combined IR and Raman study. Appl. Surf. Sci. 2004, 227, 30–39. [CrossRef] Murphy, V.; Tofail, S.A.M.; Highes, H.; McLoughlin, P. A novel study of hexavalent chromium detoxification by selected seaweed species using SEM-EDX and XPS analysis. Chem. Eng. J. 2009, 148, 425–433. [CrossRef] Murphy, V.; Hughes, H.; McLoughlin, P. Cu (II) binding by dried biomass of red, green and brown macroalgae. Water Res. 2007, 41, 731–740. [CrossRef] [PubMed] Sheng, P.X.; Ting, Y.P.; Chen, J.P.; Hong, L. Sorption of lead, copper, cadmium, zinc and nickel by marine algal biomass: Characterization of biosorptive capacity and investigation of mechanisms. J. Colloid Interface Sci. 2004, 275, 131–141. [CrossRef] [PubMed] Cervantes, C.; Campos-García, J.; Devars, S.; Gutiérrez-Corona, F.; Loza-Tavera, H.; Torres-Guzmán, J.C.; Moreno-Sánchez, R. Interactions of chromium with microorganism and plants. FEMS Microbiol. Rev. 2001, 25, 335–347. [CrossRef] [PubMed] © 2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).