风化壳淋积型稀土矿浸出液草酸沉淀稀土母液去除草酸的研究

通过草酸沉淀回收风化壳淋积型稀土矿浸出液中稀土后的沉淀母液，含有大量的浸取剂硫酸铵和过量草酸，直接排放不仅浪费浸取剂，而且会引起氨氮废水污染；直接用于回浸稀土矿，会由于草酸含量高而影响稀土的浸出，因此必须去除草酸后再复用。本文筛选了去除草酸的钙类去除剂，探讨了不同去除剂用量和陈化时间条件下草酸的去除效果，探索了去除草酸后回浸液对稀土浸出率的影响。对比氯化钙、氢氧化钙和碳酸钙对沉淀稀土后母液中残留草酸的去除率发现，氢氧化钙效果最好。生产上通常沉淀稀土母液草酸质量浓度都在0.8 g/L以下，较佳的去除草酸工艺参数为氢氧化钙与草酸的物质的量之比为2，陈化时间为3 h，得到回浸液中草酸质量浓度在0.08 g/L以下。回浸液中补加硫酸铵使其质量分数达到2%后再用于风化壳淋积型稀土矿的浸出，稀土的浸出率达93%以上，表明回浸液对稀土的浸出率影响很小，完全可以循环使用。本研究实现了稀土浸出液沉淀稀土后母液的循环使用，提高了风化壳淋积型稀土矿开采的经济效益。

Removal of Oxalic Acid from Rare Earth Oxalate Precipitation Mother Liquor of Weathered Crust Elution-Deposited Rare Earth Ore Leachate

Rare earth oxalate precipitation mother liquor after recovering the rare earth in the weathered crust elution-deposited rare earth ore leachate by the oxalic acid precipitation method still contains a large amount of leaching agent ammonium sulfate and excess oxalic acid. Discharging mother liquor will cause waste and ammonia-nitrogen pollution. When the precipitation mother liquor which still contains oxalic acid was directly used as the leaching liquor，the residual oxalic acid， especially with high concentration，may decrease the leaching efficiency of rare earth. Therefore oxalic acid must be removed before the recycle. In this paper，the screening of calcium-based removal agents for oxalic acid was carried out. The effects of removal agent dosage and aging time on oxalic acid removal rate were discussed and the effect of the precipitation mother liquor after removal of oxalic acid on the leaching rate of rare earth was investigated. Comparing the removal rates of excess oxalic acid by calcium chloride，calcium hydroxide and calcium carbonate，it was found that calcium hydroxide showed the better performance. The oxalic acid mass concentration of the rare earth oxalate precipitation mother liquor during the production is generally below 0.8 g/L. The optimized oxalic acid removal process is that the ratio of calcium hydroxide to oxalic acid is 2 and the aging time is 3 h. After removing excess oxalic acid by calcium hydroxide，the reused leaching liquor is obtained with the low mass concentration of oxalic acid below 0.08 g/L. Ammonium sulfate was added to the reused leaching liquor to a mass fraction of 2%，and then used as the leaching agent for the weathered crust elution-deposited rare earth ore. The leaching efficiency of rare earth from weathered crust elution-deposited rare earth ore is above 93%. It is indicated that the precipitation mother liquor after removal of oxalic acid has little effect on the leaching efficiency of rare earth and can be recycled in the mines completely. These results realize the recycling of rare earth oxalate precipitation mother liquid，and can improve the economic benefits of weathered crust elution-deposited rare earth ore mining.