Immobilization of hexavalent chromium in contaminated soils using biochar supported nanoscale iron sulfide composite

Biochar supported carboxymethyl cellulose (CMC)-stabilized nanoscale iron sulfide (FeS) composite (CMC-FeS@biochar) was prepared and tested for immobilization of hexavalent chromium Cr(Vl) in soil. Results of UV vis and transmission electron microscopy (TEM) showed that the backbone of biochar suppressed the aggregation of FeS, resulting in smaller particle size and more sorption sites than bare FeS. The composite at a dosage of 2.5 mg per gram soil displayed an enhanced Cr(VI) immobilization efficiency (a 94.7% reduction in the toxicity characteristic leaching procedure (TCLP) based leachability and a 95.6% reduction in the CaCl2 extraction) compared to plain biochar and bare FeS. Sequential extraction procedure (SEP) and X-ray photoelectron spectroscopy (XPS) analysis suggested that CMC-FeS@biochar promoted the conversion of more accessible Cr (exchangeable and carbonate-bound fractions) into the less accessible forms (iron-manganese oxides-bound, organic material-bound, and residual fractions) to reduce the toxicity of Cr(VI) and that surface sorption and reduction were dominant mechanisms for Cr(VI) immobilization. CMC-FeS@biochar greatly reduced the bioavailability of Cr(VI) to wheat and earthworms (Eisenia fetida). Moreover, the application of CMC-FeS@biochar enhanced soil organic matter content and microbial activity. This work highlighted the potential of CMC-FeS@biochar composite as a low-cost, "green", and effective amendment for immobilizing Cr(VI) in contaminated soils and improving soil properties. (C) 2017 Elsevier Ltd. All rights reserved.

制备了生物炭负载羧甲基纤维素（CMC）稳定的纳米硫化亚铁（FeS）复合材料（CMC - FeS@生物炭），并测试了其对土壤中六价铬Cr(VI)的固定效果。紫外 - 可见光谱和透射电子显微镜（TEM）结果表明，生物炭的骨架抑制了FeS的团聚，使其粒径比纯FeS更小，吸附位点更多。与纯生物炭和纯FeS相比，在每克土壤添加2.5毫克该复合材料时，对Cr(VI)的固定效率提高（基于毒性特征浸出程序（TCLP）的浸出率降低94.7%，CaCl₂萃取降低95.6%）。顺序提取程序（SEP）和X射线光电子能谱（XPS）分析表明，CMC - FeS@生物炭促进了更多可利用的Cr（可交换态和碳酸盐结合态）转化为较难利用的形态（铁锰氧化物结合态、有机物结合态和残渣态），从而降低了Cr(VI)的毒性，并且表面吸附和还原是固定Cr(VI)的主要机制。CMC - FeS@生物炭极大地降低了Cr(VI)对小麦和蚯蚓（赤子爱胜蚓）的生物有效性。此外，CMC - FeS@生物炭的应用提高了土壤有机质含量和微生物活性。这项工作强调了CMC - FeS@生物炭复合材料作为一种低成本、“绿色”且有效的改良剂，在污染土壤中固定Cr(VI)以及改善土壤性质方面的潜力。（C）2017爱思唯尔有限公司。保留所有权利。