Study on the depression mechanism of calcium on the flotation of high-iron sphalerite under a high-alkalinity environment

Abstract

Although numerous studies on the flotation depression of sphalerite by calcium have been reported, certain issues warrant further investigation. Previous research works did not examine the role that the iron content of iron-bearing sphalerite plays in calcium depression and did not obtain direct and convincing microscopic evidence of calcium adsorption to support the depression of calcium-containing ions on iron-bearing sphalerite’s flotation. In this paper, the effects of iron content and the presence of calcium on iron-bearing sphalerite’s flotation depression under high alkalinity environment are studied using flotation tests, adsorption amount measurements, surface extraction, zeta potential measurements, time-of-flight secondary-ion mass spectrometry (TOF-SIMS) and density functional theory (DFT) calculations. The results show that increasing iron content or the presence of calcium will lead to an increase in the degree of flotation depression and will reduce the adsorption of copper and xanthate. Increasing iron content will cause the surface of iron-bearing sphalerite to adsorb more metal hydroxides (especially iron hydroxide) and calcium. The TOF-SIMS results confirmed the trend of calcium adsorption at the atomic level. DFT calculations show that the adsorption energy of CaOH+ on the surface of iron-substituted sphalerite is lower than that on the surface of ideal sphalerite. The following conclusions can be obtained through analysis of the aforementioned: Increase in the adsorption of hydroxides (especially iron hydroxide) and calcium significantly hinder the adsorption of copper and xanthate, and increase the hydrophilicity of high-iron sphalerite surface, which ultimately leads to an increase in the degree of flotation depression of high-iron sphalerite with increasing iron content.