Hydrometallurgical Processing of Rare Earth Elements from Ion Adsorption Clays

ABSTRACT
The  surface mining and heap leaching of China’s ion-adsorption rare-earth  resources have caused severe environmental damage, there is a need to better  understand Rare Earth leaching from Clay ore with the use of agglomerates that  improve the permeability of the ore during heap leaching operation. The  practice of in-situ leaching has also revealed serious environmental problems  including underground contamination, mine collapses, and landslides. 
The  performance of lixiviants in extracting Rare Earth has been compared in many  studies however still this has been carried out in agitated systems and the  heap leach scenario is different from agitated systems. This limits the  understanding of poor heap permeability and post-closure stability whereas  un-agitated leaching of Rare Earth from Clay agglomerates gives a better  understanding of diffusion, heap permeability, and material balance to mimic  the heap leach scenario. A comprehensive understanding of the leaching  mechanism is crucial for achieving high extraction efficiency with low cost  and less environmental impact. 
A  series of inorganic salts with different concentrations were employed to leach  the Ion-adsorption rare earth agglomerates, and the relationship between the  leaching efficiency of rare earth and reagent type was investigated in  unagitated systems. This study showed that ammonium sulfate extracts less  aluminum content than magnesium chloride. Even when magnesium sulfate  (hydrate) extracts less aluminum (impurity in Pregnant Leach Solution) content  than the other lixiviants used in the study, magnesium sulfate extracts less Rare  Earth Elements (REE) compared to the other lixiviants in the same leaching  time, this was mainly attributed to it being a heptahydrate and magnesium  sulfate without the hydrate was much more expensive compared to the prices of  the other leaching reagents. Therefore the lixiviant of preference in terms of  REE extraction from ion adsorption clays in un-agitated systems is in the  order (NH4)2SO4 > MgCl2.6H2O  > NaCl > MgSO4.7H2O.

摘要：中国离子吸附型稀土资源的露天开采和堆浸作业已造成严重的环境破坏，有必要深入理解利用团聚体改善堆浸作业中矿石渗透性的粘土矿石稀土提取。原地浸矿的实践亦暴露出一系列严重的环境问题，包括地下污染、矿洞坍塌及滑坡。众多研究已对比了浸出剂在提取稀土元素方面的性能，然而这些研究仍主要在搅拌系统中进行，而堆浸场景与搅拌系统存在显著差异。这限制了对于堆浸渗透性差和闭坑后稳定性的理解，而原地浸矿稀土元素从粘土团聚体中的非搅拌浸出则能更好地揭示扩散、堆浸渗透性及物质平衡，以模拟堆浸场景。对浸出机理的全面理解对于实现高提取效率、低成本及降低环境影响至关重要。本研究采用了一系列不同浓度的无机盐来浸出离子吸附型稀土团聚体，并探究了在不搅拌系统中稀土提取效率与试剂类型之间的关系。研究结果表明，硫酸铵比氯化镁提取的铝含量更低。即使在硫酸镁（水合物）提取的铝（母液中的杂质）含量低于本研究中使用的其他浸出剂时，硫酸镁在相同浸出时间内提取的稀土元素（REE）相比其他浸出剂更少，这主要归因于它是七水合物，且无水硫酸镁的价格远高于其他浸出试剂。因此，在不搅拌系统中，从离子吸附型粘土中提取稀土元素的首选浸出剂顺序为：(NH4)2SO4 > MgCl2.6H2O > NaCl > MgSO4.7H2O。