Faculty of Agriculture and Natural Sciences, School of Biology and Environmental Sciences, University of Mpumalanga, Mbombela, 1200, South Africa.
Department of Environmental Sciences, College of Agriculture and Environmental Sciences, University of South Africa (UNISA), P.O. Box 392, Florida, 1710, South Africa.
J Environ Manage. 2022 Nov 1;321:115866. doi: 10.1016/j.jenvman.2022.115866. Epub 2022 Aug 16.
The permeable reactive barrier has been deemed as the most prudent and pragmatic way to passively manage and remediate acid mine drainage (AMD). Herein, insights into mechanisms governing the removal of inorganic contaminants from AMD using a permeable reactive barrier (PRB), i.e. pervious concrete, were reported. In particular, the effects of varying dosages, i.e., 6, 10, 30, and 60 g, of cementitious materials comprising CEM I 52.5R with or without fly ash, hydrated lime, and gypsum were evaluated whilst the fate of chemical species was underpinned using the state-of-the-art analytical techniques, along with PHREEQC geochemical modelling. The role of gypsum, a product formed from the interaction of PRB with AMD in heavy metals attenuation was also elucidated. Findings revealed cementitious materials to play an indispensable role in the removal of inorganic contaminants from AMD. Furthermore, alkalinity from used materials increases the pH (i.e. pH ≥ 12.5) of AMD leading to the precipitation of chemical species. Specifically, the efficacy registered the following sequence: Lime ≥ CEM I ≥ 30%FA ≥ Gypsum with ≥99 for Al and Fe except for Gypsum which attained ≥98 while the performance for Zn removal registered the following sequence, 97 ≥ 98 ≥ 88.8 ≥ 45% for CEM I ≥ Lime ≥30%FA ≥ Gypsum, respectively. Chemical species exist as divalent, trivalent, oxyanions, and other complexes in solution as predicted by PHREEQC. Moreover, they were removed as metal hydroxides, oxyhydrosulphates, and gypsum hence corroborating findings from XRD, SEM-EDS, and FTIR results. Mechanisms which were responsible for the removal of chemical species were precipitation, adsorption, co-adsorption, co-precipitation, ion exchange, and complexation. Henceforth, this study explicitly demonstrated mechanisms that underpin the removal of inorganic contaminants from AMD using PRB and findings from this study will be used to develop effective PRB for the management of acid mine drainage and the receiving environment.
可渗透反应屏障被认为是被动管理和修复酸性矿山排水（AMD）的最谨慎和务实的方法。本文报道了用可渗透反应屏障（PRB），即渗透混凝土，从 AMD 中去除无机污染物的机制的见解。特别是，评估了不同剂量（即水泥基材料 6、10、30 和 60 g）的效果，这些水泥基材料包含 CEM I 52.5R 以及是否含有粉煤灰、熟石灰和石膏，同时使用最先进的分析技术以及 PHREEQC 地球化学模型来支撑化学物质的归宿。还阐明了 PRB 与 AMD 相互作用形成的石膏在重金属衰减中的作用。研究结果表明，水泥基材料在从 AMD 中去除无机污染物方面发挥了不可或缺的作用。此外，所用材料的碱度会增加 AMD 的 pH 值（即 pH≥12.5），导致化学物质沉淀。具体来说，效果的顺序为：石灰> CEM I> 30%粉煤灰>石膏，除了石膏达到≥98 外，Al 和 Fe 的去除率均≥99，而 Zn 的去除率顺序为：97>98≥88.8>45%，对于 CEM I、石灰、30%粉煤灰和石膏。根据 PHREEQC 的预测，化学物质以二价、三价、含氧阴离子和其他络合物的形式存在于溶液中。此外，它们被去除为金属氢氧化物、氧硫化物和石膏，这与 XRD、SEM-EDS 和 FTIR 结果一致。负责去除化学物质的机制是沉淀、吸附、共吸附、共沉淀、离子交换和络合。因此，本研究明确地展示了 PRB 去除 AMD 中无机污染物的机制，本研究的结果将用于开发有效的 PRB，以管理酸性矿山排水和受纳环境。
