Abstract Rare-earth (RE) extraction activities in Malaysia produce an average of 75000 tonnes of Water Leach Purification (WLP) residue containing an estimated 106 tonnes of thorium that leads to negative perception and concern among the public especially related to the environmental and radiological aspects. The main challenge to separate thorium from the WLP residues is the formation of insoluble thorium pyrophosphate (ThP2O7) due to the treatment process during rare-earth extraction. Therefore, the objectives of this study are to verify the thorium composition in WLP residue as well as to investigate the possibility of separating thorium from WLP. The characterizations using FTIR, SEM-EDS, XRD, and XPS verified the presence of ThP2O7 along with other thorium phosphate compounds (Th(PO3)4) and (Th3(PO4)4) in WLP residue. The digestion study using sulphuric acid (H2SO4) at various molarity ranging from 3 to 18 mol/L showed that thorium in WLP can be dissolved in acid. The dissolution of thorium up to 50% was achieved at 6 mol/L H2SO4 and further increase to 90% with the increase of acid molarity at 150 °C within an hour of the leaching time. This research showed promising findings on the separating thorium from WLP residue through the acid digestion process that might open up the possibility of recycling rare-earth residue as sustainable thorium resources.

中文翻译：

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稀土加工残渣作为可持续钍资源的前沿展望：对钍化学成分和分离的洞察

摘要 马来西亚的稀土 (RE) 开采活动平均产生 75000 吨水浸提净化 (WLP) 残留物，其中估计含有 106 吨钍，这导致公众产生负面看法和担忧，尤其是与环境和放射性方面相关的问题。 . 从 WLP 残留物中分离钍的主要挑战是由于稀土提取过程中的处理过程而形成不溶性焦磷酸钍 (ThP2O7)。因此，本研究的目的是验证 WLP 残留物中的钍成分，并研究从 WLP 中分离钍的可能性。使用 FTIR、SEM-EDS、XRD 和 XPS 的表征证实了 WLP 残留物中存在 ThP2O7 以及其他磷酸钍化合物 (Th(PO3)4) 和 (Th3(PO4)4)。使用 3 至 18 mol/L 不同摩尔浓度的硫酸 (H2SO4) 进行的消化研究表明，WLP 中的钍可以溶解在酸中。在 6 mol/L H2SO4 下，钍的溶解度高达 50%，随着酸摩尔浓度的增加，在 150°C 的浸出时间一小时内，钍的溶解度进一步增加到 90%。这项研究显示了通过酸消化过程从 WLP 残渣中分离钍的有希望的发现，这可能开辟了将稀土残渣回收为可持续钍资源的可能性。