Comparison of compost with biochar versus technosol

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Comparison of compost with biochar versus technosol with biochar in the reduction of metal pore water concentrations in a mine soil ⁎

R. Forján , A. Rodríguez-Vila, B. Cerqueira, E.F. Covelo Department of Plant Biology and Soil Science, Faculty of Biology, University of Vigo, As Lagoas-Marcosende, 36310 Vigo, Pontevedra, Spain

A R T I C LE I N FO

A B S T R A C T

Keywords: Compost Technosol Biochar Water Metal Mine soil

Mining activities cause serious impacts on the environment, one of these impacts is the contamination of aquatic systems by metals carried by the leachates of these soils. In order to try to reduce the leached metals on mine soil waters different amendments made from residues are being applied to this type of soils. At present to enhance the characteristics of amendments made from waste and minimize their deficiencies, these amendments are being combined with biochar. Phytoremediation can be applied alone or in support of techniques such as the application of amendments made from waste. The type of phytoremediation that best adapts to large surfaces and especially to mine soils is phytostabilization. The objective of this study is to compare the ability of compost combined with biochar and Brassica juncea L. versus tecnosol combined with biochar and Brassica juncea L to reduce Cu, Ni, Pb and Zn concentrations in the pore water of a mine soil. The combination of compost + biochar + Brassica juncea L. is the best combination to reduce the concentrations of metals in a soil of this type.

1. Introduction One of the most important problems arising from mining activities is the contamination of aquatic systems by metals carried by the leachates of these soils (Antunes et al., 2016; Batsaikhan et al., 2017). These leachates cause the transport of metals which contaminates entire ecosystems (Ghosh and Singh, 2005; Rinklebe et al., 2016). In order to try to reduce the leached metals on mine soil waters, different amendments made from residues such as compost or technosols are being applied to this type of soils. One of the most important objectives of these amendments is to fix the metals so that they are not dispersed (Macías-García et al., 2009; Moreno-Jiménez et al., 2017). However, technosols and compost are elaborated with residues that can contain metals that can be filtered by leaching (Alvarenga et al., 2016; Sáez et al., 2016; Yao et al., 2009). At present to enhance characteristics of amendments made from waste and minimize their deficiencies, these amendments are being combined with biochar (Fowles, 2007; Kammann et al., 2015). Biochar has a high capacity to retain metals due to its high pH, carbon content, cation exchange capacity and a large specific surface area due to its porous microstructure and active functional groups, which implies a high capacity to complex metals in its surface (Beesley and Marmiroli, 2011; Lu et al., 2012). The ability of biochar to reduce the concentrations of metals in pore water has already been demonstrated by authors such as Ahmad et al. (2014) or Lu

⁎

et al. (2017). Phytoremediation is an environmentally friendly technique that is booming in the recovery of contaminated soils (Prelac et al., 2016). Phytoremediation can be applied alone or in support of techniques such as the application of amendments made from waste. The type of phytoremediation that best adapts to large surfaces and especially to mine soils is phytostabilization (Cunningham et al., 1995). The phytostabilization could be defined as a partial prevention of contaminant transfer from contaminated soil to adjacent areas or groundwater (Clemente et al., 2004). The objective of this study is compare the ability of compost combined with biochar and Brassica juncea L. versus tecnosol combined with biochar and Brassica juncea L to reduce Cu, Ni, Pb and Zn concentrations in the pore water of a mine soil. With the obtained results, we will try to know which type of amendment is most appropriate to apply in this soil. As discussed previously, these amendments can reduce metal concentrations in leachates but also could add metals to the soil, so special attention will be given to this problem. The experiment was carried out for eleven months. The soil used belongs to the settling pond soil of an old copper mine located in Touro (Galicia, north-west Spain). We put the settling pond soil into 50-cm cylinders, in order to reproduce as closely as possible the first few centimetres of the settling pond in the field. In the cylinders rhizon samples were placed at three different depths (15 cm, 30 cm, and 45 cm) to better know the

Corresponding author. E-mail address: [email protected] (R. Forján).

https://doi.org/10.1016/j.gexplo.2018.06.007 Received 9 August 2017; Accepted 15 June 2018 0375-6742/ © 2018 Elsevier B.V. All rights reserved.

Please cite this article as: Forján, R., Journal of Geochemical Exploration (2018), https://doi.org/10.1016/j.gexplo.2018.06.007


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2. Material and methods

lead and zinc was extracted with 0.01 M CaCl2 in soil solution (Houba et al., 2000). Pseudototal metal contents were extracted with aqua regia by acid digestion in a microwave oven (Milestone ETHOS 1, Italy). Metal concentrations were determined by ICP-AES (Optima 4300 DV; Perkin-Elmer).

2.1. Soil sampling

2.4. Pore water collection

The sample zone is located in an old copper mine at Touro, northwestern Spain (8° 20′ 12.06″ W 42° 52′ 46.18″ N). The climate in this zone is Atlantic (oceanic) with precipitation reaching 1886 mm per year (with an average of 157 mm per month) and a mean daily temperature of 12.6 °C. The average relative humidity is 77% (AEMET, 2015). In order to carry out the study, one soil and three amendments were selected: the soil chosen belongs to the settling pond (S) at the Touro mine; Compost (C) supplied by the company Ecocelta Galicia S.L. (Ponteareas, Pontevedra, Spain); technosol (T) provided by the company Tratamientos Ecológicos del Noroeste (T.E.N.) and biochar (B) provided by the company PROININSO S.A. The settling pond soil (S) was comprised of waste material resulting from the flotation of sulphides during copper processing. The settling pond has been dry for several years, and it is considered a soil according to the latest version of the FAO (2006). The technosol (T) consisted of a mixture of 60% purified sludge (from a waste water treatment plant), 10% sludge from an aluminium company (Padrón, La Coruña, Spain) 5% ash (Ence, a cellulose production plant in Pontevedra, Spain), 10% waste from the agri-food industry (canning plants and Ecogal), 5% sands from purification plants (sand fraction), plus a further 10% of materials whose contents are not precisely known due to the privacy policy of the company. The compost (C) consisted of horse and rabbit manure mixed with grass cuttings, fruit and seaweed. The biochar (B) used was made from Quercus ilex wood with a pyrolysis temperature of 400 °C for 8 h.

Pore water samples were collected monthly from the third month, by employing a non-destructive method, to portray the metal profiles in the interstitial water after dredging. Rhizon soil moisture samplers (Rhizon SMS, Rhizosphere Research Products, Netherlands) were used to extract successive pore water samples (Fig. 1). Three rhizon samples were placed in each cylinder at 15 cm, 30 cm and 45 cm to collect pore water. Pore water samples were taken once a month, with a total of nine intakes (Time 1 = 3 months, Time 2 = 4 months, Time 3 = 5 months, Time 4 = 6 months, Time 5 = 7 months, Time 6 = 8 months, Time 7 = 9 months, Time 8 = 10 months, Time 9 = 11 months). Pore water metal concentrations were determined by ICP-AES (Optima 4300 DV; Perkin-Elmer).

2.2. Greenhouse experiment

The soil from the settling pond (S) had an acidic pH, while amendments compost (C), technosol (T) and biochar (B) had higher pH values (Table 2). The biochar had the highest pH value (Table 2). Total carbon (TC) was significantly higher in the biochar compared to the compost, technosol and soil from the settling pond (Table 2). The compost had the highest total nitrogen content (TN) and the TN was undetectable in the settling pond soil (Table 2). The exchangeable cation capacity (CEC) of C, T and B was significantly higher than in the original soil (Table 2). The pseudototal concentration of Cu in the settling pond soil was higher than in the used amendments (C, T and B) (Table 2). The technosol had the highest pseudototal concentration of Pb (Table 2). The compost had the highest pseudototal concentrations of Ni and Zn (Table 2). The extractable CaCl2 concentration of Cu, Pb and Ni in S was significantly higher than in C, T and B (Table 2). The CaCl2-extractable concentration of Zn in T was higher than in S, C and B. The biochar had no detectable CaCl2-extractable concentrations of Cu and Pb (Table 2).

behaviour of leachates. The settling pond soil has been treated with compost and biochar vegetated with Brassica juncea L. or with technosol and biochar vegetated with Brassica juncea L.

2.5. Statistical analysis All of the analytical determinations were performed in triplicate. The data obtained were statistically treated using version 19.0 the SPSS programme for Windows. Analysis of variance (ANOVA) and test of homogeneity of variance were carried out. In case of homogeneity, a post hoc least significant difference (LSD) test was carried out. If there was no homogeneity, Dunnett's T3 test was performed. 3. Results 3.1. General characteristics of the settling pond soil (S), compost (C), technosol (T), and biochar (B)

The greenhouse experiment was carried out in cylinders to try to reflect the top 45 cm of the soil; the cylinders were made of PVC, measuring 50 cm high with a diameter of 10 cm. A porous mesh was inserted into the cylinders, and the settling pond soil was poured inside (Fig. 1). The mesh used for the settling pond soil was not in contact with the PVC for a long period of time. The cylinders were filled with settling pond soil (S, negative control), and settling pond soil with different treatments: -Settling pond soil + Compost + biochar + vegetated with Brassica juncea L. (SCBP). -Settling pond soil + Technosol + biochar + vegetated with Brassica juncea L. (STBP). The total weight of each cylinder was 3.5 kg. The amendment ratios used are shown in Table 1. The experiment was carried out over 11 months at a controlled temperature and humidity (at a temperature of 22 ± 2 °C, and 65 ± 5% relative air humidity). A total of 18 cylinders (6 cylinders per treatment) were prepared and distributed at random (S, SCBP, STBP).

3.2. Evolution of the pore water concentrations of Cu, Pb, Ni and Zn at the three different depths over the time

2.3. Soil analysis

3.2.1. Evolution of the Cu pore water concentrations at the three different depths over the time At depth 15 cm, the settling pond soil (S) had a higher pore water concentration of Cu over the time than in the treated settling pond soil with compost, biochar and vegetated with Brassica juncea L. (SCBP) or technosol, biochar Brassica juncea L. (STBP) (Fig. 2A). Between the first and fourth month, the treatments showed no detectable pore water concentration of Cu. At depth 30 cm, the treatment STBP had the highest pore water Cu concentrations between the times 1–4 (Fig. 2B). From Time 5 the settling pond soil had higher concentrations of Cu in

The settling pond soil samples collected from the cylinders were air dried, passed through a 2 mm sieve and homogenized prior to analysis. Soil pH was determined using a pH electrode in 1:2.5 water to soil extracts (Porta, 1986). Total soil carbon (TC) and total nitrogen (TN) were determined in a LECO CN-2000 module using solid samples. Exchangeable cations were extracted with 0.1 M BaCl2 (Hendershot and Duquett, 1986) and their concentrations determined by ICP-OES (Optima 4300 DV; Perkin-Elmer). Phytoavailable content of copper, nickel, 2


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Fig. 1. Cylinder and rhizon samples design.

the pore water than the treatments (SCBP, STBP). At depth 45 cm, S had the highest pore water concentration of Cu at time 1, time 8 and time 9, but between times 2–7 the STBP treatment had the highest pore water concentration of Cu (Fig. 2C). The treatment SCBP had lower pore water concentration of Cu than the settling pond soil over the time.

Table 1 Proportions used to make the controls and the different treatments.

S STBP SCBP

Soil

Compost

100% 85% 85%

11%

Technosols

Biochar

11%

4% 4%

3.2.2. Evolution of the Pb pore water concentrations at the three different depths over the time At depth 15 cm, the treatments showed no detectable pore water concentration of Pb over the time (Fig. 3A). At depth 30 cm, the

Table 2 Selected characteristics and metal concentrations of settling pond soil (S), compost (C), technosoil (T) and biochar (B).

pH Total carbon Total nitrogen CEC Cu Pb Ni Zn Cu Pb Ni Zn

(g/kg) (mg/kg) (cmol(+)kg−1) Pseudototal (mg/kg)

CaCl2 (mg/kg)

S

C

T

B

2.73 ± 0.08d 1.93 ± 0.15d u.d 6.11 ± 0.05d 637 ± 2.08a 16.1 ± 1.00c 16.4 ± 1.10c 65.4 ± 2.51c 139 ± 2.08a 0.65 ± 0.03a 2.25 ± 0.30a 64.4 ± 1.24b

6.25 ± 0.04b 276 ± 2.66b 21.3 ± 1.02a 53.5 ± 1.07b 193 ± 1.14c 26.6 ± 0.96b 49.7 ± 1.71a 403 ± 3.33a 0.95 ± 0.04c 0.14 ± 0.01c 0.24 ± 0.03c 7.98 ± 0.05c

6.04 ± 0.05c 256 ± 2.51c 17.6 ± 0.50b 76.6 ± 4.80a 226 ± 5.13b 89.6 ± 1.52a 26.3 ± 0.57b 340 ± 5.50b 6.01 ± 0.03b 0.33 ± 0.02b 1.03 ± 0.02b 165 ± 1.63a

9.93 ± 0.02a 676 ± 4.58a 5.34 ± 0.22c 15.8 ± 0.17c 27.1 ± 1.24d u.d 25.1 ± 2.00b 62.6 ± 1.70c u.d u.d 0.33 ± 0.02c 1.24 ± 0.01d

For each row, different letters in different samples means significant differences (n = 3, ANOVA; P < 0.05). u.d. undetectable level. Typical deviation is represented by ± . 3


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Fig. 2. Evolution of the Cu pore water concentrations at the three different depths over the time. Controls (S and SS) and treatments (STBP and SCBP). For each row, differ letters in different samples means significant differences (n = 3, Student's t-test: P < 0.05). Error bars represent standard deviation. ul: under detection limit.

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Fig. 3. Evolution of the Pb pore water concentrations at the three different depths over the time. Controls (S and SS) and treatments (STBP and SCBP). For each row, differ letters in different samples means significant differences (n = 3, Student's t-test: P < 0.05). Error bars represent standard deviation. ul: under detection limit.

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treatment SCBP had a lower pore water concentration of Pb than the settling pond soil over the time (Fig. 3B). At times 8–9, the treatments showed no detectable pore water concentration of Pb. At depth 45 cm, the treatments (SCBP, STBP) had a lower pore water concentration of Pb at times 1, 7, 8, 9 (Fig. 3C). At the end of experimental time the treatments showed no detectable pore water concentration of Pb.

concentrations in pore water than SCBP (Fig. 2C). Moreover, SCBP reduced Cu concentrations in the pore water over the time in comparison with S, with the exception of time 5.

3.2.3. Evolution of the Ni pore water concentrations at the three different depths over the time At depth 15 cm, the settling pond soil (S) had a higher pore water concentration of Cu over the time than in the treated settling pond soil with compost, biochar and vegetated with Brassica juncea L. (SCBP) or technosol, biochar Brassica juncea L. (STBP). At depths 30 cm and 45 cm, between times 3–7 in general the treatments had the highest pore water concentration of Ni. The treatments SCBP and STBP had a lower pore water concentration of Cu than the settling pond soil at times 1, 2, 8 and 9.

At depth 15 cm, the SCBP and STBP treatments reduced Pb concentrations in pore water to levels below the detection limit (Fig. 3A). This reduction in Pb concentrations is due to the high pH and TC provided by the residues used to elaborate the compost and technosol amendments. On the one hand, Weng et al. (2001) demonstrated that pH plays a crucial role in the sorption and solubility of metals. Covelo et al. (2007) proposed that soils with higher organic matter content have a greater metal retention capacity. In addition, the values of pH and TC increased by mixing compost and technosol with biochar. Authors such as Fowles (2007) have previously observed a greater positive effect on the soil properties by applying organic amendments that contained biochar amongst their components, compared with organic amendments that did not contain biochar. At depth 30 cm, at the end of the experimental time the Pb values in the pore water were not detectable in SCBP and STBP (Fig. 3B). However, during the 9 months SCBP treatment was more effective. As previously discussed, compost presented a higher pH, TC and also less phytoavailable concentration of Pb than the technosol (Table 2). As the depth increased, the treatments took longer to take effect. Therefore, in the 45 cm depth the treatments did not reduce the Pb concentrations in the pore water until the time 7 (Fig. 3C).

4.2. Evolution of the Pb pore water concentrations at the three different depths over the time

3.2.4. Evolution of the Zn pore water concentrations at the three different depths over the time At depth 15 cm, the settling pond soil had a higher pore water concentration of Zn over the time than in the treatments. At depth 30 cm and 45 cm, S had the highest pore water concentration of Zn at time 1, time 8 and time 9. In general, between times 2–7 the treatments had a higher pore water concentration of Zn than S. 4. Discussion 4.1. Evolution of the Cu pore water concentrations at the three different depths over the time

4.3. Evolution of the Ni pore water concentrations at the three different depths over the time

The treatments had a greater effect on the reduction of Cu concentrations in pore water at depth 15 cm (Fig. 2A). This reduction of Cu concentrations in pore water is due to the higher pH, TC and CEC presented in the amendments used to elaborate the treatments SCBP and STBP. The high pH of the amendments (compost, technosol and biochar) is related to the decrease of the concentrations of metals in the pore water (Oustriere et al., 2017). As can be seen in Table 2 the biochar presented a high pH and TC so it will be the most influential amendment on Cu retention. This positive effect of biochar was already demonstrated by Puga et al. (2015) in a previous study. In this previous study the incorporation of sugarcane straw-derived biochar decreased the DTPA-extractable concentrations of Cd, Pb, and Zn in a Zn mining soil, Vazante (Minas Gerais, Brazil). In the case of the reduction of Cu concentrations in the pore water, previous studies demonstrated that the application of technosol combined with biochar increases the soil sorption capacity. This was demonstrated for example by Forján et al. (2016), who applied a combination of technosol and biochar on a mine soil improving the sorption capacity for copper in this soil. On the other hand, Venegas et al. (2016) concluded that the addition of compost and biochar led to a beneficial effect decreasing metal extractability in the soil. The treatments were vegetated with Brassica juncea L. which is a phytoremediating species. The Brassica juncea L. phytoremediate capacity helps reduce Cu concentrations in pore water. Authors like Blaylock et al. (1997), Lim et al. (2004), Singh and Sinha (2005) already demonstrated the phytoremediating capacity of Brassica juncea L. At depth 30 cm, the treatment made with compost and biochar significantly reduced Cu concentration in pore water from time 1 (Fig. 2B). However, the treatment made with technosol and biochar did not significantly reduce these concentrations compared to the soil of the settling pond until after seven months. The best effect of the SCBP was due to the fact that the compost presented a higher pH, TC and less phytoavailable concentration of Cu than the technosol (Table 2). pH and organic matter content plays a crucial role in metal solubility (Park et al., 2011; Temminghoff et al., 1997; Weng et al., 2001). At depth 45 cm, SCBP had a better effect on the reduction of Cu

After treating the soil Ni was the metal that presented lower concentrations in the pore water after Pb, these results coincide with those obtained by Wierzbowska et al. (2016). In the depth 15 cm both treatments had a greater effect in the reduction of the concentrations of Ni in the pore water (Fig. 4A). At depth 30 cm and 45 cm until time 8 treatments did not reduce Ni concentrations in pore water (Fig. 4B, C). Observing the behaviour of the treatments between time 1 and 7, the Ni concentrations in the pore water in the STBP treatment decrease while the Ni concentrations in the pore water in the SCBP treatment increase. This reduction of Ni concentrations in pore water is important because Ni toxicity leads to a variety of physiological disorders in plants. Ni could enter accumulate in the human body through food crops grown onto Ni contaminated soils (Rehman et al., 2016). 4.4. Evolution of the Zn pore water concentrations at the three different depths over the time The treatments were able to reduce the concentrations of Zn in the pore water in S. The concentrations of Zn in pore water were the most difficult to reduce because S had high Zn phytoavailable concentrations (64.4 ± 1.24 mg kg−1, Table 2), and the amendments which the treatments were made also contained high concentrations of Zn (compost = 7.98 ± 0.05 mg kg−1, technosol = 165 ± 1.63 mg kg−1. Table 2). The residues which the technosol was elaborated such as sewage sludge (Smith, 2009) contain high concentrations of Zn. Moreover, Zn is the element in sewage sludge-treated agricultural soil identified as the main concern in relation to potential impacts on soil microbial activity and is also the most significant metal in compost with regard to soil fertility and microbial processes (Smith, 2009). The compost used in this experiment consisted of a mixture of wastes such as horse manure (Pérez-Esteban et al., 2012) or rabbit manure (Canet et al., 2007) which may have high concentrations of Zn. For all of the above, the ability of the treatments applied to reduce Zn concentrations 6


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Fig. 4. Evolution of the Ni pore water concentrations at the three different depths over the time. Controls (S and SS) and treatments (STBP and SCBP). For each row, differ letters in different samples means significant differences (n = 3, Student's t-test: P < 0.05). Error bars represent standard deviation. ul: under detection limit.

biochar has a strong adsorptive energy for metals (Inyang et al., 2015). The best effect of the treatments reducing the concentrations of Zn in the pore water was in the depth 15 cm (Fig. 5A). In this first depth, the treatment that combined compost with biochar and Brassica juncea

on pore water is very important. The reduction of the Zn concentrations on the pore water of the soil S is improved by the biochar. Biochar has many immobilizing properties such as its microporous structure, active functional groups, high pH and cation exchange capacity. In addition, 7


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Fig. 5. Evolution of the Zn pore water concentrations at the three different depths over the time. Controls (S and SS) and treatments (STBP and SCBP). For each row, differ letters in different samples means significant differences (n = 3, Student's t-test: P < 0.05). Error bars represent standard deviation. ul: under detection limit.

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L. showed lower concentrations of Zn in the pore water than the treatment elaborated with technosol combined with biochar and Brassica juncea L. At depths of 30 cm and 45 cm the treatments took longer to reduce Zn concentrations in the pore water, however, at times 8–9 both treatments reduced those concentrations. In general, at depths 30 cm and 45 cm the SCBP showed a better behaviour reducing the concentrations of Zn in the pore water.

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5. Conclusions The applied treatments (SCBP and STBP) on the settling pond mine soil (S) were able to reduce the concentrations of Cu, Pb, Ni and Zn in the pore water. In all cases the best behaviour of the treatments occurred in depth 15 cm. The treatments took longer to take effect when deepening the soil. The metals that most reduced their concentrations in the pore water once the treatments were applied were Cu and Pb. Zn was the metal that had the worst behaviour in reducing its concentrations in the pore water once the treatments were applied. In this work can be concluded that the application of the treatment made with compost combined with biochar and Brassica juncea L. or the treatment made with technosol combined with biochar and Brassica juncea L. does not increase Cu, Pb, Ni and Zn concentrations in the pore water. The combination of compost + biochar + Brassica juncea L. is the best combination to reduce the concentrations of metals in a soil of this type. In this study the addition of amendments made from waste does not increase the contents of metals in the pore water. References AEMET, 2015. Valores Climatológicos Normales. Santiago de Compostela Aeropuerto. http://www.aemet.es/es/serviciosclimaticos/datosclimatologicos/ valoresclimatologicos?l=1428&k=gal. Ahmad, M., Rajapaksha, A.U., Lim, J.E., Zhang, M., Bolan, N., Mohan, D., Vithanage, M., Lee, S.S., Ok, Y.S., 2014. Biochar as a sorbent for contaminant management in soil and water: a review. Chemosphere 99, 19–33. Alvarenga, P., Farto, M., Mourinha, C., Palma, P., 2016. Beneficial use of dewatered and composted sewage sludge as soil amendments: behaviour of metals in soils and their uptake by plants. Waste Biomass Valoriz. 7, 1189–1201. Antunes, I.M.H.R., Gomes, M.E.P., Neiva, A.M.R., Carvalho, P.C.S., Santos, A.C.T., 2016. Potential risk assessment in stream sediments, soils and waters after remediation in an abandoned W ˃ Sn mine (NE Portugal). Ecotoxicol. Environ. Saf. 133, 135–145. Batsaikhan, B., Kwon, J.S., Kim, K.H., Lee, Y.J., Lee, J.H., Badarch, M., Yun, S.T., 2017. Hydrochemical evaluation of the influences of mining activities on river water chemistry in central northern Mongolia. Environ. Sci. Pollut. Res. 24, 2019–2034. Beesley, L., Marmiroli, M., 2011. The immobilisation and retention of soluble arsenic, cadmium and zinc by biochar. Environ. Pollut. 159, 474–480. Blaylock, M.J., Salt, D.E., Dushenkov, S., Zakharova, O., Gussman, C., Kapulnik, Y., Ensley, B.D., Raskin, I., 1997. Enhanced accumulation of Pb in Indian mustard by soil-applied chelating agents. Environ. Sci. Technol. 31, 860–865. Canet, R., Pomares, F., Cabot, B., Chaves, C., Ferrer, E., Ribó, M., Albiach, Mª., 2007. Composting olive mill pomace and other residues from rural southeasthern Spain. Waste Manag. 28, 2585–2592. Clemente, R., Walker, D.J., Bernal, M.P., 2004. Uso de enmiendas orgánicas en la fitorecuperación de suelos contaminados por metales pesados. In: Centro de Edafología y Biología Aplicada del Segura. CSIC, Murcia, España. Covelo, E.F., Vega, F.A., Andrade, M.L., 2007. Simultaneous sorption and desorption of Cd, Cr, Cu, Ni, Pb, and Zn in acid soils. I. Selectivity sequences. J. Hazard. Mater. 147, 852–861. Cunningham, S.D., Berti, W.R., Huang, J.W., 1995. Remediation of contaminated soils and sludges by green plants. In: Hinchee, R.E., Means, J.L., Burris, D.R. (Eds.), Bioremediation of Inorganics. Battelle Press, Columbus, OH. FAO, 2006. World Reference Base for Soil Resources. IUSS. ISRIC, FAO, Rome. Italy. Forján, R., Asensio, V., Rodríguez-Vila, A., Covelo, E.F., 2016. Contribution of waste and biochar amendment to the sorption of metals in a copper mine tailing. Catena 137, 120–125. Fowles, M., 2007. Black carbon sequestration as an alternative to bioenergy. Biomass Bioenergy 31, 426–432.

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