Applying the surface differences in the sulfophilic and oxyphilic affinities for reverse flotation separation of calcite from smithsonite

Abstract

This study aims to evaluate the effectiveness of sodium sulfide (Na2S) as a selective depressant in the reverse flotation of calcite from smithsonite. Additionally, the objective is to gain insights into the underlying mechanism driving this selectivity. The findings of flotation experiments showed that Na2S can strongly depress smithsonite but not depress calcite when a fatty acid collector was used. The presence vs. absence of Na2S produced a significant difference in Gaudin's selectivity index value (1.08 vs. 81.21), showing a significant impact of Na2S in selectively depressing smithsonite during the flotation process. The results of the contact angle measurement provided strong support for the flotation test findings. The results from attenuated total reflectance-Fourier transform infrared spectroscopy analysis and NaOL adsorption measurements indicated that Na2S prevented NaOL adsorption on the smithsonite surface but not on the calcite surface. Furthermore, the results from X-ray photoelectron spectroscopy and field-emission scanning electron microscopy revealed that the sulfide species dissolved from Na2S exhibited a strong affinity for the smithsonite surface but not for the calcite surface. Based on these findings, a selective depression mechanism was proposed. When the concentration of Na2S is sufficient, the formed ZnS nanoparticles cover the smithsonite with high density, thereby limiting the diffusion of residual sulfide species to the smithsonite surface. Thus, an interfacial boundary layer containing residual sulfide species forms, hindering the adsorption of NaOL on the smithsonite surface. In contrast, the dissolved sulfide species cannot form specific bonds with the calcite surface, thus having no significant effect on the adsorption of NaOL on the calcite surface. In conclusion, the mineral surface differences in the sulfophilic and oxyphilic affinities contribute the high selectivity and strong depression performance of Na2S during the reverse flotation separation of calcite from smithsonite, when using fatty acid as a collector.