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Abstract：
The scavenging of soluble metals by iron (Fe) and aluminium (Al) oxyhydroxides is a natural process that occurs in acid mine drainage (AMD). This phenomenon is relevant to the immobilization, transport, and recovery of important natural resources such as rare earth elements (REE) and uranium (U). Furthermore, understanding the players and the reactions that govern the scavenging of REE and U by Fe and Al oxyhydroxides in aqueous systems is fundamental for natural and engineering sciences and for environmental management. In this scenario, the current work investigated the role of iron in the co-precipitation of REE and U when treating effluents by pH neutralization in an AMD system located in Brazil. The research employed water sampling, co-precipitation batch experiments, sequential extraction, X-ray diffraction and 57Fe Mössbauer spectroscopy. The results revealed that the presence and the amount of Fe in the initial solution can influence the REE removal efficiency positively. The effect of the addition of Fe over the REE removal efficiency was irrelevant when the pH of the AMD was raised to values equal to 7-8. The scavenging of U was not influenced by the addition of Fe to the AMD. The sequential extraction results showed that precipitates containing higher amounts of Fe tend to be less labile. The 57Fe Mössbauer spectra revealed that the REE can occupy iron sites in the structure of the amorphous precipitates. The findings of the current study can be extrapolated to other AMD systems and contribute to the development of novel REE recovery and hydrometallurgical techniques.
摘要：
铁（Fe）和铝（Al）的羟基氧化物清除可溶性金属是在酸性矿山排水（AMD）中发生的自然过程。这种现象与固定有关，运输,和回收重要的自然资源，如稀土元素（REE）和铀（U）。此外，了解参与者以及控制水性系统中Fe和Al羟基氧化物清除REE和U的反应是自然和工程科学以及环境管理的基础。在这种情况下，当前的工作研究了在巴西的AMD系统中通过pH中和法处理废水时，铁在REE和U共沉淀中的作用。这项研究采用了水采样，共沉淀批量实验，顺序提取，X射线衍射和57Fe穆斯堡尔谱。结果表明，初始溶液中Fe的存在和含量可以积极影响REE的去除效率。当AMD的pH升高到等于7-8的值时,添加Fe对REE去除效率的影响是不相关的。U的清除不受向AMD中添加Fe的影响。顺序提取结果表明，含有较高量Fe的沉淀物往往不太不稳定。57FeMössbauer光谱表明，REE可以占据无定形沉淀物结构中的铁位点。当前研究的结果可以外推到其他AMD系统，并有助于开发新的REE回收和湿法冶金技术。
