Department of Mining and Materials Engineering, McGill University, 3610 University St., Montréal, QC H3A 0C5, Canada.
Department of Chemistry, Université de Montréal, 5155 Ave Decelles, Montréal, QC H3T 2B1, Canada.
J Hazard Mater. 2015 Jul 15;292:108-17. doi: 10.1016/j.jhazmat.2015.03.008. Epub 2015 Mar 7.
High content arsenic waste generated in the metallurgical industry can be converted into a synthetic mineral, scorodite, FeAsO4·2H2O, and deposited into a landfill site. Scorodite is most stable in weakly acidic to neutral pH range under oxic conditions. A novel way to enhance the range of stability for scorodite is to encapsulate it with an inert material. In this work, silicate gel is developed and investigated as a possible encapsulating material for scorodite. The initial method of gel formation in this study produced a silicate gel with high alkalinity (pH 10) that was incompatible with scorodite. A reverse titration method was developed producing a gel with optimum pH profile (5-6.5). This technique proved to have only marginal effect on scorodite stabilization prompting an investigation of different ageing techniques (drying; 22, 44°C and hydrothermal treatment; 110, 160°C) as a means of producing silica-like coatings with better stabilization potential. Interestingly most of these measures proved counterproductive as aged scorogels showed a higher release of As than scorodite alone. Through surface-sensitive depth profile analysis (XPS), and molecular-sensitive analysis (Raman and FTIR mapping), it was discovered that the silicate engaged into an "ion-exchange" type reaction on the surface of scorodite by bonding to iron, hence the observed release of arsenic. Development of a hydrothermally-induced iron silicate layer may lead to an effective encapsulant.
在冶金工业中产生的高含量砷废物可以转化为合成矿物砷酸铁，FeAsO4·2H2O，并沉积到垃圾填埋场中。在有氧条件下，砷酸铁在弱酸性到中性 pH 范围内最稳定。增强砷酸铁稳定性的一种新方法是用惰性材料将其包裹起来。在这项工作中，开发并研究了硅酸盐凝胶作为包裹砷酸铁的一种可能的包裹材料。本研究中最初的凝胶形成方法产生了一种高碱性（pH 值 10）的硅酸盐凝胶，与砷酸铁不相容。开发了一种反滴定法，得到了具有最佳 pH 值分布（5-6.5）的凝胶。该技术对砷酸铁的稳定化效果只有微小的影响，因此研究了不同的老化技术（干燥；22、44°C 和水热处理；110、160°C），作为产生具有更好稳定化潜力的硅类似涂层的手段。有趣的是，这些措施中的大多数都适得其反，因为老化的砷酸铁凝胶释放的砷比单独的砷酸铁释放的砷更多。通过表面敏感的深度剖面分析（XPS）和分子敏感分析（拉曼和傅里叶变换红外测绘），发现硅酸盐通过与铁结合在砷酸铁表面发生“离子交换”型反应，从而导致砷的释放。开发水热诱导的铁硅酸盐层可能会得到一种有效的包裹剂。
