Abstract: During the mining and metallurgy of non-ferrous heavy metals, a large number of arsenic-containing compounds are exposed to the environment, posing great environmental risks to the surrounding water and soil. Due to their good arsenate affinity, iron ions and their compounds are the main components of commonly used chemical arsenic fixation agents. Whether in arsenic pollutant solidification or arsenic-contaminated site remediation, silicate and hydration processes are important physical barriers to arsenic. Based on this, we synthesized an iron-based silicate gel and evaluated its performance for the solidification/stabilization of typical arsenic compounds [Na3AsO4, Ca3(AsO4)2, AlAsO4, and FeAsO4·2H2O] and arsenic-containing sludge from non-ferrous metallurgy, and explored the arsenic fixation mechanism. The results showed that the iron-based silicate gel with a Fe/Si molar ratio of 1:4 could effectively immobilize the arsenic-containing compounds (Na3AsO4 and FeAsO4·2H2O). However, in the process of curing Ca3(AsO4)2 and AlAsO4, due to the competitive reaction between arsenate and silicate, the toxic leaching of arsenic was higher than that in the process of uncaring. The introduction of CaO could inhibit the competitive reaction, improve the arsenic fixation rate of Ca3(AsO4)2 and AlAsO4, and reach more than 98% of the arsenic fixation efficiency. The synergistic effect of Fe and Ca co-precipitation and physical immobilization is responsible for the immobilization/stabilization of arsenic-containing compounds. The core-shell structure with arsenic-containing compounds as the core and iron-based silicate gel/C-S-H gel as the shell separated arsenic species and reduced toxic leaching when in contact with the surrounding environment. The long-term stability showed that the iron-based silicate gel-cured arsenic-containing waste remained highly stable at pH=8 for 30 days. The CaO-assisted iron-based silicate gel proposed in this work showed great potential for the immobilization of arsenic-containing wastes and arsenic-contaminated land and provided a new way to solidify arsenic-containing pollutants.

Key words: Arsenic, solidification, Iron-based silicate gel, Leaching toxicity

摘要： 有色重金属矿冶过程中，大量含砷化合物及固废暴露在环境中，给周围水土带来巨大环境危机。由于具有良好的砷酸盐亲和力，铁离子及其化合物是常用的化学固砷药剂的主要成分。无论在砷污染物固化还是砷污染场地修复，硅酸盐及水化过程是重要的砷物理阻隔手段。基于此，本工作合成了一种铁基硅酸盐凝胶，评价了其用于典型砷化合物[Na3AsO4, Ca3(AsO4)2, AlAsO4和FeAsO4·2H2O]及有色冶金炼砷污泥的固化/稳定性能，探究了固砷机制。结果表明，Si/Fe摩尔比为1:4的铁基硅酸盐凝胶能有效固化Na3AsO4和FeAsO4·2H2O。但固化Ca3(AsO4)2和AlAsO4过程中，由于砷酸盐和硅酸盐之间的竞争反应，砷的毒性浸出比未固化时高。引入CaO可以抑制竞争反应，提高Ca3(AsO4)2和AlAsO4的固砷率，达到98%以上的固砷率。Fe和Ca共沉淀以及物理封装的协同效应是固化/稳定含砷化合物及固废的原因。以含砷化合物为核心，铁基硅酸盐凝胶/C-S-H凝胶为外壳的核-壳结构，在与周围环境接触时，能有效固化含砷化合物及固废，降低浸出毒性。长期稳定性测试表明，在pH值为8时，铁基硅酸盐凝胶固化的含砷化合物及固废在30天内保持较好的稳定性。从酸性到碱性条件下，固化体的砷毒性浸出浓度均低于5 mg/L。本工作所提出的CaO辅助铁基硅酸盐凝胶在含砷固废和砷污染土地的固定化方面表现出巨大的潜力，为含砷污染物固化提供了一种新途径。

关键词: 砷, 固化, 铁基硅酸盐凝胶, 毒性浸出