硫脲—盐酸体系从稀土抛光粉废料中浸出回收稀土氧化物

基于稀酸溶液中Ce(Ⅳ)难溶而Ce(Ⅲ)易溶的特点，采用硫脲-稀盐酸体系还原浸出稀土抛光粉废料中稀土氧化物。考察了浸出温度、浸出时间、液固比(L/S)、盐酸浓度和硫脲用量对稀土抛光粉废料中铈浸出率的影响。结果表明：在盐酸浓度为4 mol/L、L/S为4.2、浸出温度90 ℃、浸出时间60 min、硫脲用量0.04 g/g给料的优选条件下，铈浸出率达99.37%。然后对浸出液采用草酸沉淀法分离和回收稀土氧化物，经氨水调pH至1.8~2.0，草酸沉淀，氧化焙烧，得到稀土氧化物产物，总REO含量约为97%，其中CeO2 78.00%、La2O3 18.93%，回收率分别为91.66%和68.44%。激光粒度分析、XRD、SEM等研究表明，稀土氧化物产物粒度分布均匀，主要为CeO2晶体，方形颗粒表面平整，棱角分明。

The Leaching Technology of Rare Earth Polishing Powder Waste in Thiourea-Hydrochloric Acid System and Recovery of Rare Earth Oxides from the Lixivium Through Oxalic Acid Precipitation

The solubility of Ce(Ⅲ) is far greater than that of Ce(Ⅳ). Thus, the thiourea was used to reduce Ce(Ⅳ) into Ce(Ⅲ) in dilute hydrochloric acid solutions to promote the recovery of rare earth oxides from a rare earth polishing powder waste. The effects of leaching temperature, leaching time, liquid-to-solid ratio (L/S), hydrochloric acid concentration and thiourea dosage on the leaching ratio of cerium from the rare earth polishing powder waste were investigated. The results showed that under the optimal technologies, hydrochloric acid concentration of 4 mol/L, L/S of 4.2, leaching temperature of 90 ℃, leaching time of 60 min, and thiourea dosage of 0.04 g/g, the cerium leaching ratio reached 99.37%. Then, the rare earth ions in leaching solutions were separated and recovered by oxalic acid precipitation approach. After adjusting pH to 1.8-2.0 by ammonia water, oxalic acid was added to deliver rare earth oxalate precipitates which were subsequently roasted under air to obtain the rare earth oxide (REO) product. The total REO content in the REO product was about 97% with 78.00% CeO₂ and 18.93% La₂O₃, and their recovery ratio was 91.66% and 68.44%, respectively. In addition, the findings of laser particle size analysis, XRD and SEM showed that the rare earth oxide products were mainly composed by CeO₂ square particles, and exhibited a narrow particle size distribution with a flat and angular surface.