Emission reduction treatment of chlorine-containing waste gas during the chlorination roasting process of lepidolite: thermodynamic analysis and mechanism investigation

It was vital for the chlorination roasting process to effectively reduce and avoid the production of chlorine-containing waste gas. In this paper, the chlorination roasting process of lepidolite was optimized and the reaction mechanism was studied emphatically. Thermodynamic investigations indicated that the direct interaction of calcium chloride with the alkali metal oxides in lepidolite played a dominant role in the chlorination process. The addition of calcium hydroxide achieved the goal of reducing the emission of chlorine-containing waste gas, which increased the chlorine content of the roasted product from 20% to 70% with the increase of calcium hydroxide dosage. The mechanism analysis revealed that the calcium oxide produced by the decomposition of calcium hydroxide consumed a lot of alumina and silicon dioxide in minerals, which improved the effective utilization rate of calcium chloride. Thus, the extraction efficiency of valuable metals was enhanced while the production of chlorine-containing waste gas was reduced dramatically. This study provided some theoretical guidance for the mechanism analysis of the lepidolite chlorination roasting process, and also contributed to a new method for the emission reduction treatment of chlorine-containing waste gas.