Extraction of Lithium into Solution from Lithium-Containing Hydroxide Precipitates Formed by Chemisorption Precipitation

This paper presents the results of lithium extraction from a lithium-containing precipitate obtained by the sulfation roasting of rare-metal production tailings, leaching of the sulfate roast product, and subsequent precipitation. Unlike the conventional sulfuric acid process, in the present study, lithium is chemisorbed from the solution obtained after leaching the sulfate calcine onto freshly precipitated aluminum hydroxide, which is subsequently calcined, followed by lithium desorption (aqueous leaching). During the preparation of the precipitate for the formation of the freshly precipitated aluminum hydroxide sorbent, the aluminum impurity naturally present in the solution was utilized, while the lithium to be recovered was present in the solution in the form of a sulfate compound. Data were obtained on the leaching (desorption) of lithium from freshly precipitated precipitates in which lithium was present in the form of a sulfate compound. Aqueous leaching was investigated for the precipitate in the wet state, after drying at 105 °C, and after calcination at 275–350 °C under atmospheric pressure in a thermostatic cell at 30 °C, as well as under autoclave conditions at 200 °C. The results showed that calcination significantly enhanced lithium extraction, while autoclave leaching further improved recovery. The effects of the solid-to-liquid (S:L) ratio, leaching time, and temperature on lithium extraction from the calcined precipitate were evaluated. The optimum conditions were aqueous leaching of the precipitate calcined at 275–350 °C with an S:L ratio of 1:10–1:15, a leaching time of 0.5–1 h, and a temperature of 55–98 °C. Autoclave leaching was also effective for precipitates dried at 105 °C and calcined at 350 °C. Under the optimum conditions, lithium extraction reached 92–96% during atmospheric leaching and approximately 98–100% under autoclave conditions. Concentration of the lithium-bearing solution produced a lithium-containing carbonate precipitate with 1.43 wt.% Li, corresponding to 3.07 wt.% Li2O.