铁砷共沉淀中水铁矿转化及其对砷稳定性的影响机制

Large quantities of arsenic were accumulated in soils or sediments due to discharging arsenic-containing waters and/or waste solids which were generated from mining and metallurgical industries. This will cause severe environmental problems and subsequently pose significant threat to human health. Coprecipitation of As(V) with iron(III) is the industrial method of choice for the removal and immobilization of arsenic from mineral processing solutions and effluents considering the cost-effectiveness and the easiness of operation. Two-line ferrihydrite is the major arsenic-bearing solid in the generated Fe(III)-As(V) coprecipitates. This solid is thermodynamically metastable and may transform to more crystalline products such as goethite or hematite. However, the fate of arsenic during this process is still unknown. In this research, the transformation process of ferrihydrite under oxic conditions and its effect on the long-term stabilities of Fe(III)-As(V) coprecipitates were systematically studied. The redistribution of arsenic as well as the crystallinities of the produced iron oxyhydroxides were investigated by chemical extraction method combined with solid phase characterizations. A comprehensive understanding of the stabilities of Fe(III)-As(V) coprecipitates could be obtained from this project which in turn may useful for the prevention of the secondary pollution caused by arsenic-containing solid wastes.

近年来，由于采矿、冶金等行业产生的含砷废水废渣的排放，导致砷在环境中大量积累，严重威胁人类健康及生态安全。铁砷共沉淀工艺由于具有成本低、操作简便等经济技术方面的优势而被广泛应用于有色冶金工业的废液除砷过程。2-线水铁矿是铁砷共沉淀中主要的固砷载体，在自然环境条件下是一种亚稳态物质，可以向结晶程度更高的铁氧化物(针铁矿或赤铁矿等)进行转化。然而，水铁矿转化对其固持砷的环境行为的影响目前还缺乏清晰认识。本项目将对无定形水铁矿在有氧环境中的转化及其对共沉淀长期稳定性的影响展开深入研究，利用化学提取与现代结构分析手段相结合的方法，搞清铁砷共沉淀中不同结晶程度铁氧化物的分布规律以及砷在各相中的分配，揭示水铁矿转化过程及其对砷再分配的影响机制。项目的成功实施对预测共沉淀含砷废渣的稳定性及预防二次砷污染的发生具有重要意义。

采矿和冶金工业中排放的含砷废水废渣是自然环境中人为砷污染最主要的来源之一，铁砷共沉淀是冶金工业中常见的除砷固砷技术之一，其中主要的固砷载体是水铁矿，在一定条件下这种亚稳态物质可以向结晶程度更高的铁氧化物转化，从而引起砷在固液相之间以及固相内部不同结晶程度铁氧化物之间的再分配。本项目主要研究了水铁矿在不同条件下的结晶转化情况以及水铁矿结晶转化对铁砷共沉淀的长期稳定性所产生的影响。研究发现，偏酸性pH值时，水铁矿在不同反应介质中转化为不同的结晶态铁氧化物，硫酸盐介质中产物为针铁矿，而硝酸盐介质中产物则主要为赤铁矿并伴有少量的针铁矿，而在偏碱性pH值时，不同反应介质的转化产物均以赤铁矿为主，但是固相钙离子的存在会大大降低转化速率。水铁矿的结晶转化对铁砷共沉淀中砷的再分配的影响主要取决于砷的赋存形态。偏酸性pH值时，砷几乎不会重新释放到液相中，固相中也并没有出现砷再吸附到结晶程度更高的铁氧化物上的现象，而在中性pH值时，水铁矿结晶程度稍有改变，便会导致液相中砷含量大幅度升高。此外，本项目还就含砷废渣中砷的赋存形态进行了研究，结果表明砷可以介入到废渣中大量存在的硫酸钙晶体中，并影响其形貌。