Purification mechanism of fluoride-containing sludge from different sources by hydrometallurgy

Abstract

The rapid development of electronic technology and the new energy industry accelerates the production of fluoride-containing sludge (FCS), mainly composed of CaF2. Meanwhile, fluorite is suffering shortage. Therefore, recycling FCS is a win-win way. In this study, the components of four FCS from different factories were analyzed and their mechanism of purification by hydrometallurgy was explored. The results showed that the components of FCS1 and FCS2 from different semiconductor factories were similar, and their main content was CaF2. FCS3 from a liquid crystal display (LCD) factory contained a large amount of Ca3(PO4)2 and FCS4 from a solid center contained many NaNO3, leading to different purification mechanisms. Research on acid leaching for impurity removal indicated that H2SO4 acid was not suitable for purifying FCS1, HCl acid dissolved a large amount of CaF2 and HF acid was the best. After the organic matter was removed by 500 °C calcination, the CaF2 content in the solid product reached about 90 % by 2 mol/LHF purifying FCS1 and FCS2. After HF acid leaching FCS3, the solid product contained a large amount of bonded water, therefore, only after calcination can the CaF2 content reach 96.9 %. FCS4 was purified by the calcination-HF acid leaching process of FCS1 to obtain 94.3 % CaF2 content, but it can also obtain 90.3 % CaF2 content by simple washing to remove a large amount of NaNO3 in it. To sum up, according to the fluorite grade standard and FCS compositions, different processes can be selected to purify the sludge as a fluorite substitute for the needs of different industries. Finally, the industrial process flowchart was provided, and operating costs were accounted for.