磷尾矿钝化材料研制及其对土壤重金属的修复机制

The remediation mechanism of heavy metals contaminated soils by the passivator prepared from phosphate tailing

我国场地土壤面临严峻的重金属污染问题。活性钝化是一种较成熟的原位修复技术,而高效低成本钝化材料的缺乏限制了该技术应用。本研究基于磷尾矿废弃物制备的羟基磷灰石材料,探究了材料对Zn-Cd-Pb混合溶液中重金属的去除及对土壤中重金属的钝化机制。结果表明,多金属体系中羟基磷灰石材料对Pb的吸附量显著高于Zn和Cd,pH对吸附量的影响与金属元素种类和浓度有关。土壤钝化实验结果显示,添加材料可降低土壤中水溶态Zn、Cd、Pb含量,且酸性土壤中水溶态重金属含量的降幅高于中性土壤。由于羟基磷灰石溶解后可与重金属形成磷酸盐沉淀,且添加材料可使土壤pH升高,从而促进重金属形成碳酸盐和氢氧化物沉淀、增加土壤组分对重金属的吸附,钝化后土壤中重金属由可交换态向碳酸盐结合态、铁锰氧化物结合态和残渣态等稳定态转化。本研究通过磷尾矿渣废弃物研制了一种低成本高效的重金属钝化材料,有望为场地土壤重金属污染修复提供新的技术选择。

The contamination of heavy metals in soil is an important environmental issue in China.Active passivation is a commonly used technique for in situ soil remediation,but the lack of passivator with high efficiency and low cost hinders the large-scale application of this technology.With a hydroxyapatite-based material(HAPPT)prepared from low-cost phosphate tailing,in this paper,we have investigated the removal mechanism of heavy metals in the Zn-Cd-Pb mixed solution and the passivation mechanism of heavy metals in soils by the HAPPT through experiments.The results show that adsorption capacity of the HAPPT on Pb is higher than that on Zn and Cd in the Zn-Cd-Pb solution,and the effect of pH on adsorption of various metals is related to different types and concentrations of various metal elements.The results of passivation experiments of heavy metals in soils show that contents of water-soluble heavy metals including Zn,Cd and Pb in soils could be significantly reduced by the added HAPPT and the reduction efficiencies of water-soluble heavy metal contents of the acid soil are higher than those of the neutral soil.The precipitation of phosphate formed by the reaction of soluble hydroxyapatite and heavy metals in soils,and,the increase of pH values in soils due to the addition of HAPPT,had promoted the formation and precipitation of carbonates and hydroxides of heavy metals,and the increased adsorption capacitiies of heavy metals by the passivated soils.In addition,after passivation of soils by the HAPPT,the exchangeable phases of heavy metals in soils had been transformed to the stable phases,such as carbonate,Fe-Mn oxides bounded and/or residual fractions.The transformation was related to the precipitation of phosphates due to the dissolution of HAPPT in acid soils.Besides,the increase of pH in soils can stimulate the precipitation of carbonate and hydroxide and can also increase metal adsorption by soil constituents such as Fe oxides.Through this study,a low-cost and highly efficient heavy metal passivation material has been developed from phosphate ore tailings.It is expected that this will provide a new technical way for the remediation of heavy metal contaminated soils.