Extraction of Li, K, and Rb from zinnwaldite by chlorination roasting with CaCl2

Abstract

The extraction of lithium, potassium, and rubidium from lithium mica zinnwaldite was investigated using high-temperature roasting with solid calcium chloride, followed by water leaching of the resulting sinters. This study examined the impact of roasting temperature, heating rate, roasting time, and the calcium chloride content within the roasting mixture on the extraction efficiency of alkali metals. Based on the observed phenomena, a comprehensive reaction mechanism for alkali metals chlorination was proposed.The crucial factors of the roasting process are the roasting temperature and the calcium chloride content within the roasting mixture. The optimal results were achieved when a mixture containing four times the stoichiometric amount of calcium chloride was roasted at 1000 °C for 20 min with a heating rate of 10 °C/min. Under these conditions, 77 % of lithium, 90 % of potassium, and 90 % of rubidium were successfully extracted.The proposed chlorination mechanism of zinnwaldite roasting involves three successive stages:a)Chlorination of alkali metals between 500 and 650 °C primarily via the surface reaction of calcium chloride with zinnwaldite before the mineral decomposition initiates.b)Decomposition of zinnwaldite between 650 and 850 °C, with a preferential chlorination of potassium and rubidium due to their better accessibility for the chlorinating agent after the structural disruption of the original mineral.c)Chlorination of lithium as a result of the reaction between calcium chloride andβ-spodumene, a decomposition product of zinnwaldite.During the roasting process, the emission of fluorinated gaseous compounds was observed, along with the reaction of chlorine with iron. This reaction consumes the chlorinating agent and eventually leads to the generation of chlorine gas as a result of the decomposition of chlorinated iron compounds.