氧化钙沉淀硫酸稀土过程中杂质的分布与去除

Impurities Distributions and Removal during Precipitation of Rare Earth Sulfate with Calcium Oxide

针对离子型稀土矿传统工艺采用碳酸氢铵或草酸沉淀富集稀土过程中产生大量氨氮或草盐废水，严重污染环境的问题，本文提出采用氧化钙和／或碳酸钠沉淀富集低浓度硫酸稀土浸出液中的稀土。研究表明，以碳酸钠为沉淀剂，所得沉淀为碳酸稀土，经焙烧后REO含量可达92％以上；以氧化钙为沉淀剂，所得沉淀为氢氧化稀土，经焙烧后REO含量低于82％。沉淀及焙烧产物的物相分析表明，以氧化钙为沉淀剂，焙烧产物中的硫酸根主要以碱式硫酸稀土的形式存在，表明硫酸根在沉淀过程中进入了氢氧化稀土的晶格。为了在保证沉淀产物稀土纯度的同时，避免高盐废水排放造成环境污染，降低生产成本，进一步采用氧化钙与碳酸钠复合沉淀的方式处理硫酸稀土浸出液，所得沉淀经焙烧后，REO含量可达89％左右，而SO3含量降至7．22％，基本满足生产需求，实现了低浓度硫酸稀土浸出液的高效绿色低成本回收。

In order to solve the problems of large amounts of ammonia or oxalate wastewater generated during the precipitation of rare earth using ammonium bicarbonate/oxalic acid in the conventional rare earth enrichment process for the treatment of the ion-absorbed rare earth ore, a new precipitation method using calcium oxide and/or sodium carbonate was developed for the treatment of low concen- tration rare earth sulfate solution. Experimental data showed that rare earth carbonate formed when sodium carbonate was used as pre-cipitant, and the REO content of the roasted precipitate higher than 92%. While for calcium oxide, rare earth hydroxide was formed and the REO content of the roasted precipitate was lower than 82%. X-ray diffraction （XRD） analyses of the precipitate and the roasted precipitate addressed that sulfate ion existed mainly in the form of basic rare earth sulfates and entered into the crystal lattice of rare earth hydroxide when using calcium oxide as precipitant. Composite precipitation using calcium oxide and sodium carbonate were em- ployed for the treatment of rare earth sulfate solution to improve the purity of rare earth, and avoid the environmental pollution arising from the discharge of high salnity waste water and reduce the production cost. The REO content of the obtained roasted precipitate was 88.99% , while the SO3 content decreased to 7.22% , which could basically meet the requirements for industrial production and ensure low cost recovery of the low concentration rare earth sulfate solution by an efficient and green process.