Impact of the impurities on lithium extraction from β-spodumene in the sulfuric acid process

Abstract

The H2SO4 roasting for the lithium extraction from β-spodumene concentrate has been the traditional process since the middle of the twentieth century (Ellestad and Leute, 1950) and is the preferred one for new producers due to its economic viability and high purity product to supply the growing lithium-ion batteries market. Unfortunately, very few studies have tried to determine the fundamental causes why lithium extraction is limited to 90% and the need for more than 30% stoichiometric excess of H2SO4. Acid roasting of β-spodumene was carried out in a rotary tube furnace followed by lithium leaching to complete a factorial design of experiments studying H2SO4 stoichiometric excess (30% vs 20%), roasting temperature (250 °C vs 225 °C), roasting duration (30 min vs 5 min) and mechanical stirring amplified by the use of 35 alumina beads of 6.35 mm diameter. An analysis of variance was made on lithium and impurity leaching and a principal component analysis on impurity leaching. These statistical analyses showed the dependence and independence respectively of lithium and impurity extraction on operating parameters. The extraction percentages of impurities (Al, Na, Fe, Ca, Mn and K) were quite low with a total of 0.5 at% of the spodumene concentrate being leached. H2SO4 excess, temperature, duration and mechanical stirring respectively improve the lithium recovery by 0.8%, 0.0%, 1.0% and 0.3%. Residual H2SO4 excess was estimated to be 7–13%. These observations point to negate, at least for low impurity concentrates, the hypothesis of sulfuric acid consumption by impurities as a reason for the need of stoichiometric excess as high as 30%. Nonetheless, it was demonstrated that lithium extraction decreases with the impurity content in the feed material. This suggests that lithium recovery may be limited by the impurity coating of some β-spodumene particles.