粉煤灰酸法提取氧化铝蒸发母液回收氯化铝工艺研究

Study on technology of recovering aluminum chloride from evaporation mother liquor in extraction of alumina from fly ash by hydrochloric acid method

在粉煤灰盐酸法提取氧化铝蒸发结晶工序中,由于氯化铝溶液多次循环蒸发,引起蒸发母液中钙、镁、硅、磷等杂质离子的富集,当母液中杂质离子的浓度达到一定程度时需将部分氯化铝蒸发母液外排,这将会造成15%~20%原料铝的损失。利用氯化氢气体盐析结晶技术对蒸发母液进行处理,通过两级盐析结晶和浓盐酸洗涤,不仅实现了回收蒸发母液中氯化铝的目的,还提高了六水氯化铝晶体的纯度,使回收的氧化铝纯度达到99.38%,同时氧化铝中氧化钙、氧化镁、五氧化二磷的质量分数分别降低至2.680×10^-5、2.849×10^-4、2.051×10^-4。提出了蒸发母液回收氯化铝工艺路线,此流程可完全并入现有粉煤灰盐酸法提取氧化铝工艺的主流程。

In the evaporation and crystallization process of extracting alumina from fly ash by hydrochloric acid method,the aluminum chloride solution was repeatedly evaporated,which caused the enrichment of impurity ions such as calcium,magnesium,silicon and phosphorus in the evaporation mother liquor.When the impurity ions in the mother liquor reached a certain degree,part of the aluminum chloride evaporation mother liquor needs to be discharged,which will cause the loss of 15%~20%of the raw aluminum.The technology of HCl gas salting-out crystallization was used to treat the evaporation mother liquor.After two-stage salting-out crystallization and concentrated hydrochloric acid washing,not only the purpose of recovering aluminum chloride in the evaporation mother liquor was realized,but also the purity of aluminum chloride crystal hexahydrate was increased,so that the purity of alumina recovered reached to 99.38%.Meanwhile,the contents of CaO,MgO and P2O5 in alumina were reduced to 2.680×10^-5,2.849×10^-4 and 2.051×10^-4 respectively.In addition,the process of recovering aluminum chloride from mother liquor was put forward,which can be completely incorporated into the existing main process of extracting aluminum oxide by hydrochloric acid method from fly ash.