污泥基生物炭用于土壤中Cr的钝化及作用机制分析

污泥基生物炭是广泛用于处理各种环境污染物的添加剂之一。然而，关于污泥基生物炭原位钝化修复Cr污染土壤的研究还较少。以污泥与棉杆为原料，通过共热解制备污泥基生物炭，并按不同比例施加到Cr含量为33.97 mg/kg的土壤中，研究了该生物炭对土壤中Cr吸附固定的效果和机制。当添加比例由1%增加到15%时，土壤中Cr含量由34.02 mg/kg增加到38.52 mg/kg，但各处理土壤Cr浓度均低于GB 15618-2018《土壤环境质量农用地土壤污染风险管控标准（试行）》中Cr的筛选值标准。BCR顺序提取实验结果表明:该生物炭促进土壤中Cr由弱酸可提取态、可还原态向可氧化态、残渣态转化，并降低了Cr的浸出毒性。此外，该生物炭提高了土壤pH、CEC，增加了有机质和有效磷含量，有利于土壤中Cr的固定。污泥基生物炭固定土壤中Cr的机制包括离子交换、沉淀、络合作用等，但污泥基生物炭对土壤中Cr价态的影响需要深入研究。

EFFECT AND POSSIBLE MECHANISM OF IMMOBILIZATION OF CHROMIUM IN THE SOIL AMENDED BY BIOCHAR DERIVED FROM SEWAGE SLUDGE

Biochar derived from sewage sludge is widely used for the treatment of various environmental contaminants. However, little is known about the effects of the biochar on remediation of Cr contaminated soil. In this study, the effects and mechanisms of the biochar prepared via co-pyrolysis of sewage sludge and cotton stalks on the immobilization of Cr in a sandy loam soil (Cr, 33.9 mg/kg) were investigated. The Cr content increased from 34.0 mg/kg to 38.5 mg/kg with the addition ratio increasing from 1% to 15%. The contents of Cr in all treatments were lower than the thresholds of China National Standard (GB 15618-2018). The results of BCR sequential extraction procedure showed that the biochar amendment promoted the transformation of Cr from the acid soluble and reducible fractions to the oxidizable and residua fractions, reducing Cr bioavailability in the soil. Meanwhile, biochar amendment effectively reduced the leaching ability of Cr. In addition, biochar amendment increased soil pH, CEC, organic matter, and available phosphorus in the soil, which were conducive to the immobilization of Cr. The possible immobilization mechanisms includes ion exchange, precipitation/co-precipitation, complexation, but the influence of the biochar on the valence of Cr in soil needs further study.