有色金属(冶炼部分)

钕铁硼废料是主要的稀土二次资源，实现其绿色高效分离是当前研究热点。以钕铁硼废料浸出液经萃取分离稀土产生的含钴氯化镁废水和石灰为原料制备氢氧化镁，然后采用CO₂碳化法制备碳酸氢镁溶液，研究钴杂质对该过程的影响。结果表明：在氯化镁转化为氢氧化镁反应过程中，钴离子对氯化镁转化的影响较小，当pH为10.5时，废水中的钴离子全部转化为氢氧化钴，镁离子的转化率为99.8%，固相为氢氧化镁和氢氧化钴混合物。碳化反应过程中，氢氧化钴浓度增加到1.4 g/L时，氢氧化镁的碳化率由98.0%降低至90.2%。氢氧化钴对氢氧化镁的碳化反应过程存在竞争性抑制归因于碳化过程中碳酸镁和碳酸钴等不溶物包覆氢氧化物，导致氢氧化物内核无法接触溶解态CO₂而难以被碳化，此时固体渣中的主要成分为碳酸镁。升高温度对氢氧化镁和氢氧化钴的碳化过程均产生不利影响，当温度从25℃升高到40℃时，氢氧化镁的碳化率从92.8%降到78.0%，氢氧化钴的碳化率从33.2%降到9.4%。研究结果为含钴氯化镁废水循环利用提供了理论和工艺指导。

Nd-Fe-B waste is the main secondary resource of rare earth, and its green and efficient separation is the current research hotspot. In this paper, magnesium hydroxide was prepared applying cobalt-containing magnesium chloride wastewater produced by extraction and separation of rare earth from Nd-Fe-B waste leaching solution and lime as raw materials, and then magnesium bicarbonate solution was prepared by CO₂ carbonization method to study the effect of cobalt impurities on the process. The results show that cobalt ions have little effect on the conversion of magnesium chloride during the conversion of magnesium chloride to magnesium hydroxide. When pH value is 10.5, 100% of cobalt in the wastewater is converted into cobalt hydroxide and 98.0% of magnesium is converted into magnesium hydroxide, generating a mixture of magnesium hydroxide and cobalt hydroxide in sediment. During the carbonization reaction, cobalt hydroxide has a competitive inhibition on the carbonization reaction of magnesium hydroxide. When the concentration of cobalt hydroxide increases to 1.4 g/L, carbonization rate of magnesium hydroxide declines from 98.0% to 90.2%. The competitive inhibition of the carbonization reaction process of magnesium hydroxide by cobalt hydroxide is attributed to the fact that the insoluble substances such as magnesium carbonate and cobalt carbonate are coated with hydroxide during the carbonization process, which prevents the core of the hydroxide from coming into contact with dissolved CO₂ and thus cannot be carbonized. Thus, the main compound in the solid slag is magnesium carbonate. Increasing of the temperature has an adverse effect on the carbonization process of both magnesium hydroxide and cobalt hydroxide. When temperature rises from 25 ℃ to 40 ℃, carbonization rate of magnesium hydroxide drops from 92.8% to 78.0%, and carbonization rate of cobalt hydroxide also drops from 33.2% to 9.44%. The research results provide theoretical and technological guidance for the recycling of cobalt-containing magnesium chloride wastewater.