ABSTRACT

Increasing disruption in the rare earth supply chain creates an urgency to develop alternative resources, in which utilization of coal-based materials presents great potential. Nevertheless, environmental control is a significant challenge in rare earth extraction processes. This study was conducted to contribute to the limited information on removing thorium and uranium from rare earths while coal-based products are used as feedstock. The laboratory studies suggested that the selective precipitation and solvent extraction approach yields the most favorable separation performance. Complete thorium precipitation was achieved around a pH value of 4.8. Due to the close precipitation pH ranges of uranium and rare earths, further separation by solvent extraction was applied to achieve an enhanced separation. Based on a Box-Behnken experimental design, the effect of extractant concentration, pH, strippant concentration, and O/A ratio was investigated. Best separation performance was achieved using 50 v% TBP at a pH of 3.5 with an O/A ratio of 3 and 1 mol/L H₂SO₄, which resulted in 1.8% uranium and 73.4% rare earth extraction. The extraction and precipitation behavior of the elements were further assessed with the distribution ratio, separation factor, thermodynamic parameters, and species distribution diagrams to provide a thorough understanding of the separation mechanisms. The results were statistically analyzed, and a model was developed to predict uranium recovery. The developed experimental protocol was validated using a rare earth oxalate sample produced at the pilot-scale processing facility. Finally, a conceptual process flowsheet was developed to effectively separate radionuclides while producing rare earth oxide products.

摘要

稀土供应链的日益中断导致开发替代资源的紧迫性，其中煤基材料的利用具有巨大的潜力。然而，环境控制是稀土提取过程中的重大挑战。进行这项研究的目的是提供有关以煤基产品为原料时从稀土中去除钍和铀的有限信息。实验室研究表明，选择性沉淀和溶剂萃取方法可产生最有利的分离性能。pH 值约为 4.8 时，钍完全沉淀。由于铀和稀土的沉淀pH范围接近，因此采用溶剂萃取进一步分离以实现强化分离。基于 Box-Behnken 实验设计，研究了萃取剂浓度、pH、汽提剂浓度和 O/A 比的影响。使用 50 v% TBP、pH 3.5、O/A 比为 3 和 1 mol/LH 实现最佳分离性能₂ SO ₄，导致1.8%的铀和73.4%的稀土提取。通过分配比、分离因子、热力学参数和物种分布图进一步评估元素的萃取和沉淀行为，以全面了解分离机制。对结果进行统计分析，并开发了一个模型来预测铀回收率。使用中试规模加工设施生产的稀土草酸盐样品对所开发的实验方案进行了验证。最后，开发了一个概念工艺流程，以在生产稀土氧化物产品的同时有效分离放射性核素。