Activation mechanism of calcium hydrolysate on the spodumene surface and its effect on the adsorption of collector

•The interaction of H2O and spodumene surface reduces the collector adsorption strength.•The weak adsorption of Ca2+ makes spodumene difficult to be activated at neutral pH.•The bonding of OH with Al sites improves the adsorption of Ca(OH)+ and Ca(OH)2.•Ca(OH)+ effectively improved the adsorption strength of collector.•Ca(OH)2 has great hindrance to the adsorption of collector on Al sites. Calcium chloride is an important activator for spodumene flotation; however, its mechanism has been controversial. In this study, density functional theory (DFT) calculation was taken to investigate the adsorption of reagents from the atomic and electronic microscopic perspective, and the activation mechanism of calcium was discovered. Results show that the reaction of the O in the H2O with the Al on the mineral surface reduces the bonding strength between the collector and the Al sites, making spodumene recovery by flotation impossible in the absence of active ions. The Ca2+ can bond with two adjacent O atoms of the spodumene surface. However, the weak adsorption strength makes spodumene difficult to be activated effectively at neutral pH. The hydroxyl group in Ca(OH)+ and Ca(OH)2 strongly bonds with Al sites on the surface, significantly improving the adsorption strength of these components, and the adsorption strength of Ca(OH)2 is the highest. However, the Ca(OH)2 have a greater steric hindrance effect on the adsorption of the collector on the Al sites, resulting in the collector adsorbing on the Ca site of the spodumene surface in the bidentate adsorption form. Hence, Ca(OH)2 cannot effectively improve the flotation recovery effect of spodumene. After the Ca(OH)+ treatment, the O atoms of the collector bond with Ca and Al atoms on the surface, resulting in the great increase of collector adsorption strength. Thus, the species of Ca(OH)+ is the sole effective active component in spodumene flotation.