Remediation of Cr(VI) contaminated soil by chitosan stabilized FeS composite and the changes in microorganism community

In-suit immobilization is one of the major strategies to remediate heavy metals contaminated soil with the effectiveness largely depends on the characteristics of the added chemical reagents/materials. In this study, chitosan stabilized FeS composite (CS-FeS) was prepared to evaluate the performance of remediating the high and toxic hexavalent chromium contaminated soil from the effectiveness and microbial response aspects. The characterization analysis confirmed the successful preparation of composite, and the introduction of chitosan successfully stabilized FeS to protect it from rapid oxidation as compared to bare FeS particles. With the addition dosage at 0.1%, about 85.6% and 81.3% of Cr(VI) was reduced in 3 d based on toxicity characteristic leaching procedure (TCLP) and CaCl2 extraction, and the reduction efficiency increased to 96.6% and 94.8% in 7 d, respectively. The Cr(VI) was non-detected in the TCLP leachates with increase the CS-FeS composites to 0.5%. The percentages of HOAc-extractable Cr decreased from 25.17% to 6.12% accompanied with the increase in the residual Cr from 4.26% to 13.77% and improvement of soil enzyme activity under CS-FeS composites addition. Cr(VI) contamination reduced the diversity of microbial community in soil. Three dominate prokaryotic mi-croorganisms, namely Proteobacteria, Actinobacteria and Firmicutes, were observed in Cr-contaminated soil. The addition of CS-FeS composites increased the microbial diversity especially for that in relative lower abundance. The relative abundance of Proteobacteria and Firmicute related to Cr-tolerance and reduction increased in CS-FeS composites added soils. Taking together, these results demonstrated the potential and promising of using the CS-FeS composites for Cr(VI) polluted soil remediation.