Understanding the role of sodium hydroxide in the selective flotation separation of spodumene from feldspar and quartz

In our latest study, surface dissolution of minerals has been found to be important in the flotation of spodumene. This study provides further information in the role of NaOH in the flotation separation of spodumene from feldspar and quartz using size distribution analysis, micro-flotation experiments, AFM imaging, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-atomic emission spectrometry (ICP-AES) measurements and density functional theory (DFT) calculations. NaOH pretreatment had no significant influence in the size distribution of minerals, while spodumene subjected to pretreatment with NaOH showed an increase in selective oleate adsorption. After being ground in NaOH solution, spodumene surface was smoother than feldspar and quartz surfaces as revealed by AFM imaging. ICP-AES results indicated that the dissolution of quartz was slight, and the concentration of dissolved species for spodumene and feldspar followed the order of Si > Al > Li, and Si > Al, respectively. The Al density at feldspar surface was smaller than that at spodumene surface. The increase in the relative concentration of Al at the feldspar surface with NaOH pretreatment was not large enough to significantly enhance oleate adsorption, and the decrease in the relative concentration of K and Na may be unfavorable for oleate adsorption. Increased relative concentrations of Al and Li at spodumene surface due to NaOH pretreatment accounted for the enhanced oleate adsorption. DFT calculation showed that elements at spodumene and feldspar surfaces were likely to dissolve, and OH- was more readily to interact with Si sites at spodumene surface and K sites at feldspar surface.