摘要
Phosphogypsum(PG), the main by-product of phosphoric acid production industries, is considered one of the most important secondary sources of rare earth elements(REEs). The current study focuses on the recovery of REEs content and the residual phosphate content existing in the PG with preserving on the CaSO_(4)skeleton to be used in other various applications. These attainments are carried out using citric acid leaching process via soaking technique. Several dissolution parameters for REEs using citric acid were studied, including soaking time, soaking temperature, citric acid concentration, solid-to-liquid ratio, and recycling of the citrate leaching solutions in the further REEs dissolution experiments. The best-operating conditions were 14 d of soaking time, 7.5% citric acid concentration, and the solid-toliquid ratio of 1/5 at ambient temperature. About 79.57% dissolution efficiency of REEs was achieved using the optimal conditions. Applying four soaking stages by mixing different fresh PG samples with the same citrate solution sequentially, cumulative dissolution efficiency for REEs was found to be 64.7% under optimal soaking conditions. REEs were recovered using Dowex 50X8 resin from citrate solutions with 96% extraction efficiency. Dissolution kinetics proved the pseudo-first-order nature, reversible reactions, and two activation energies for all REEs.
磷石膏(PG)是磷酸生产工业的主要副产物,被认为是稀土元素(REEs)最重要的二次来源之一。本研究重点是回收PG中存在的REEs和残留的磷酸盐的同时,保留CaSO_(4),以用于其他各种应用。这些成果是采用柠檬酸浸出工艺实现的。研究了几个参数对柠檬酸浸出回收稀土的影响,包括浸泡时间、浸泡温度、柠檬酸浓度、固液比以及柠檬酸浸出溶液在进一步的稀土溶解实验中的循环利用。最佳操作条件为室温浸泡时间14 d,柠檬酸浓度为7.5%,固液比为1/5。优化条件下稀土的溶解效率为79.57%。将不同的新鲜PG样品与相同的柠檬酸溶液依次混合浸泡4个阶段,在最佳浸泡条件下,稀土的累积溶解效率为64.7%。采用Dowex 50X8树脂从柠檬酸溶液中回收稀土,萃取效率为96%。溶解动力学证明了稀土的伪一级性质、溶解过程为可逆反应,存在两个活化能。
