Remediation And Mechanism Of Heavy Metals From Water And Soil In Mining Area By Steel-making Slag/biochar Composites

Heavy metal pollution in water and soil endangers the ecological environment and human health,and is a global problem that urgently needs solutions.Biochar has always been a research hotspot for the efficient remediation of heavy metals in water and soil due to its wide range and low cost of raw materials.This paper focuses on the feasibility of using steelmaking slag with phytoremediation plants as a raw material for biochar preparation and applying it to the remediation of heavy metal pollution of water and soil.The remediation effects of several prepared materials were compared and their remediation mechanisms for heavy metals were investigated.The results of the study are as follows:（1）Two steelmaking slags（oxide scale and blast furnace slag）and a phytoremediation plant（ramie stalk）were used to prepare several steelmaking slag/biochar composites,and the best performing ramie stalk biochar-blast furnace slag-oxide scale composite（BOS）was screened.Characterization analysis by XRD and XPS revealed that many nano-zero valent irons（n ZVI）were loaded on the carbon-based materials of BOS and ramie stalk biochar-oxide scale composite（BO）.The BO exhibited weaker performance than the BOS due to the passivation layer on the surface of the BO-loaded nano-zero valent iron,which inhibits the oxidation of zero-valent iron.BOS has high removal performance（>99%）and regeneration performance for As（V）,and the column experiments also showed its excellent removal effect for arsenic in natural water.（2）The potential environmental risks of heavy metals（Pb,As,Cu,Cd and Mn）in raw materials and BOS composites were quantitatively assessed by various risk assessment methods.The environmental risk and heavy metal toxicity of the co-pyrolysis-treated biochar were significantly reduced compared to the raw materials,and no additional contaminants were observed in the follow-up experiments.（3）This study revealed the mechanism by which n ZVI enhanced As（V）removal.The removal mechanism of As（V）by BOS is mainly attributed to the complexation and co-precipitation between Fe and As,and the hydrogen bonding between the C=O functional group of BOS and As.During the co-pyrolysis process,a protective layer of Ca₂Si O₄was formed on the surface of n ZVI to prevent the passivation of n ZVI.During the reaction process,the Ca₂Si O₄covering the surface of n ZVI is continuously separated,exposing the fresh surface of n ZVI,thereby providing more redox activity and adsorption sites for enhanced arsenic removal.（4）The stabilization effect of BOS and BO on Pb-Zn ore-contaminated soil is remarkable.It has a significant improvement effect on soil properties,moderated soil acidity,increased soil p H,and alleviated the toxicity of Pb and Zn in the soil.The bioavailable components of Pb and Zn were significantly reduced after the addition,and the treatment effect of BOS was the best.In the toxicity leaching experiment,the leaching of Pb in the remediated soil was very low（<40μg/L）.the leaching of Zn in the soil decreased by 56.4%and 59.9%after BO and BOS remediation,respectively.And the additives amount has a greater effect on the immobilization of Zn,with more additives of BO and BOS,the better the stabilization effect of Zn.