Leaching behavior of lithium slag at various pH conditions

Abstract

To explore possible safe valorization routines for lepidolite lithium slags (LS) in different cement systems, this paper investigates their fundamental composition features and dissolution mechanisms under various pH conditions. Lepidolite LS is mainly divided into two types: high calcium LS with mineral phases mainly composed of anorthite and gypsum, and low calcium LS mainly comprising nosean and leucite, together with a higher amorphous phase content ($>$ 24 %). The main reaction product of LS in NaHCO₃ solution is calcite, while the products in NaOH solution are Ca(OH)₂ and (K, N)-A-S-(H). The dissolution of the amorphous LS phase in NaOH solution occurs in 0–3 h and generates (K, N)-A-S-(H) gels in 3–8 h. The shrinking core model can be used to describe the dissolution process of LS in NaOH solution, which is controlled by a reaction product layer diffusion. The leached quantity of Be, Tl, Ni, and Mn is negatively correlated with the solution pH, and the leaching rate increases with increasing temperature. The concentration of S in the LS leachate is higher than 300 mg/L, which may pose a threat to the volume stability of cement in concrete. Based on these characterization results, dissolution models of LS in neutral, weakly alkaline, and aggressive alkaline solutions have been proposed, providing theoretical guidance for understanding the hydration of LS in different binders, further its utilization in various cases.