School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK.
Sci Total Environ. 2012 Mar 15;420:238-49. doi: 10.1016/j.scitotenv.2012.01.034. Epub 2012 Feb 11.
Reducing and Alkalinity Producing Systems (RAPS) remediate net-acidic metalliferous mine drainage by creating anoxic conditions in which bacterial sulfate reduction (BSR) raises alkalinity and drives the precipitation of iron and other chalcophilic elements as sulfides. We report chemical and stable isotopic data from a study monitoring the biogeochemical processes involved in the generation of mine waters and their remediation by two RAPS. Sulfur isotopes show that sulfate in all mine waters has a common source (pyrite oxidation), whilst oxygen isotopes show that oxidation of pyritic sulfur is mediated by Fe(III)(aq). The isotopic composition of dissolved sulfide, combined with the sulfur and oxygen isotopic composition of sulfate in RAPS effluents, proves BSR and details its dual isotope systematics. The occurrence and isotopic composition of solid phase iron sulfides indicate the removal of reduced sulfur within the RAPS, with significant amounts of elemental sulfur indicating reoxidation steps. However, only 0 to 9% of solid phase iron occurs as Fe sulfides, with approximately 70% of the removed iron occurs as Fe(III) (hydr)oxides. Some of the (hydr)oxide is supplied to the wetland as solids and is simply filtered by the wetland substrate, playing no role in alkalinity generation or proton removal. However, the majority of iron is supplied as dissolved Fe(II), indicating that acid generating oxidation and hydrolysis reactions dominate iron removal. The overall contribution of BSR to the sulfur geochemistry in the RAPS is limited and sulfate retention is dominated by sulfate precipitation, comparable to aerobic treatment systems, and show that the proton acidity resulting from iron oxidation and hydrolysis must be subsequently neutralised by calcite dissolution and/or BSR deeper in the RAPS sediments. BSR is not as important as previously thought for metal removal in RAPS. The results have practical consequences for the design, treatment performance and long-term functionality of such systems.
还原-产碱系统 (RAPS) 通过创造缺氧条件来修复净酸性含金属矿排水，在这种条件下，细菌硫酸盐还原 (BSR) 会提高碱度，并促使铁和其他亲硫元素以硫化物的形式沉淀。我们报告了一项监测生成矿水的生物地球化学过程及其通过两个 RAPS 修复的研究的化学和稳定同位素数据。硫同位素表明，所有矿水中的硫酸盐都有一个共同的来源（黄铁矿氧化），而氧同位素表明，黄铁矿硫的氧化是由 Fe(III)(aq)介导的。溶解态硫化物的同位素组成，结合 RAPS 流出物中硫酸盐的硫和氧同位素组成，证明了 BSR 的存在，并详细说明了其双重同位素系统。固相铁硫化物的出现和同位素组成表明 RAPS 内还原硫的去除，大量元素硫表明存在再氧化步骤。然而，只有 0 到 9%的固相铁以 Fe 硫化物的形式存在，大约 70%的去除铁以 Fe(III) (氢)氧化物的形式存在。一些 (氢)氧化物作为固体供应给湿地，并且只是被湿地基质过滤，在产生碱度或去除质子方面没有作用。然而，大部分铁是以溶解态 Fe(II)的形式供应的，这表明产生酸的氧化和水解反应主导了铁的去除。BSR 对 RAPS 中硫地球化学的总体贡献是有限的，硫酸盐的保留主要受硫酸盐沉淀的影响，这与好氧处理系统相当，并表明铁氧化和水解产生的质子酸度必须随后通过方解石溶解和/或 RAPS 沉积物更深部位的 BSR 来中和。BSR 对 RAPS 中金属去除的重要性不如之前认为的那么大。这些结果对这些系统的设计、处理性能和长期功能具有实际意义。
