Work

The role of Na2CO3 in the selective flotation of Ca-activated spodumene and quartz

Year: 2026

Type: article

Abstract: Spodumene separation from gangue minerals such as quartz is challenging, as both silicate minerals are activated by metal cations, naturally present in process water, like Ca2+. Research has shown that when used as a pH modifier, Na2CO3 can depress both minerals, to different degrees, in the presence of Ca2+, but the mechanisms remain unclear. We use spectroscopic and computational methods to examine the interaction of Na2CO3 with Ca-activated quartz and spodumene surfaces in the presence of sodium oleate (NaOL) and the consequences for their selective flotation. Our results indicate that adsorption competition between the collector (Ca/OL complexes) and depressant (CaCO3) species occurs on spodumene and quartz surfaces. We provide detailed mechanisms of the interactions, including with respect to the adsorbed species, their relative amounts, surface charge, and the adsorption strengths. Although both the collector and depressant were adsorbed onto both minerals, the collector had more affinity for spodumene than quartz (-296.14 kJ/mol vs -192.99 kJ/mol), unlike the depressant (-288.55 kJ/mol vs -311.59 kJ/mol), hence the soda ash induced surface deprotonation and desorption of Ca/OL complexes from quartz during conditioning, but not from spodumene. Unlike quartz, which had only Ca as the surface site for reagent adsorption, spodumene also had surface Al sites. The results explain the limited depression of spodumene and the total depression of quartz in flotation using fatty acid-based collectors. Specifically, in the presence of Ca2+, Na2CO3 treatment increased the Li2O grades from 2.53 to 4.40 %, while maintaining a high lithium recovery of 71 %. Overall, the study demonstrated that, in addition to being a pH modifier, Na2CO3 acts as a selective quartz depressant in the Ca-activated flotation of spodumene-quartz, making it a more effective pH modifier than NaOH directly prior to spodumene flotation. Since quartz is a common gangue mineral in most flotation systems, these findings can be applied to benefit other flotation systems.

Source: Minerals Engineering

DOI: 10.1016/j.mineng.2026.110618

Authors: Espoir M. Murhula, Wennie Wang, Carolyn Hill-Svehla, Gideon Lambiv Dzemua, Lebogang Babedi, Charlotte E. Gibson