MOE Key Laboratory of Groundwater Circulation and Environmental Evolution, China University of Geosciences (Beijing), Beijing, 100083, People's Republic of China.
Beijing Key Laboratory of Water Resources and Environmental Engineering, School of Water Resources and Environment, China University of Geosciences, Beijing, 100083, People's Republic of China.
Environ Sci Pollut Res Int. 2021 Jun;28(24):31885-31894. doi: 10.1007/s11356-021-13039-w. Epub 2021 Feb 22.
Recently, some new leaching agents without ammonium, such as magnesium sulfate (MgSO) and aluminum sulfate [Al(SO)], have been developed to eliminate ammonia nitrogen pollution in in situ mining process of the weathered crust elution-deposited rare earth ore (WCED-REO), but they might cause heavy metal contamination. In this study, characteristics and mechanisms of different fractions of lead (Pb) released by (NH)SO, MgSO and Al(SO) leaching agents were investigated using batch experiments and column leaching tests. The experimental results showed that the amounts of Pb released by the different leaching agents followed the trend of Al(SO) > (NH)SO > MgSO under the same total cationic charge, and both the acid extractable and reducible fractions of Pb were released. The release of acid extractable fraction Pb was related to the cation hydration radius of NH, Mg, and Al, whereas the release of reducible fraction Pb was mainly influenced by the concentration of H, especially at pH < 4.0. Furthermore, column leaching tests indicated that pH has little effect on the Pb contents of different fractions released by (NH)SO and MgSO in leaching the WCED-REO. Although Al(SO) released the largest contents of rare earth and Pb in leachate, the content of residual acid extractable fraction Pb in soil was the most after water injection (simulating the cleaning process after mining). This work can provide a scientific method and theoretical basis for comprehensively assessing the environmental impact of new leaching agents on WCED-REO mining.
最近，一些不含铵的新型浸出剂，如硫酸镁（MgSO）和硫酸铝[Al（SO）]，已被开发用于消除风化壳淋积型稀土矿（WCED-REO）原地开采过程中的氨氮污染，但它们可能会造成重金属污染。在这项研究中，采用批量实验和柱浸实验研究了（NH）SO、MgSO 和 Al（SO）浸出剂浸出时不同形态铅（Pb）的特征和机制。实验结果表明，在相同的总阳离子电荷下，不同浸出剂释放的 Pb 量遵循 Al（SO）>（NH）SO>MgSO 的趋势，并且都释放了酸可提取态和可还原态的 Pb。酸可提取态 Pb 的释放与 NH、Mg 和 Al 的阳离子水合半径有关，而可还原态 Pb 的释放主要受 H 的浓度影响，尤其是在 pH < 4.0 时。此外，柱浸实验表明，pH 值对（NH）SO 和 MgSO 浸出 WCED-REO 时释放的不同形态 Pb 含量影响不大。尽管 Al（SO）在浸出液中释放出最大量的稀土和 Pb，但在注水后（模拟采矿后的清洗过程），土壤中残留的酸可提取态 Pb 含量最高。这项工作可以为全面评估新型浸出剂对 WCED-REO 开采的环境影响提供科学方法和理论依据。
