Study of copper-free activation collectors for sphalerite flotation based on halogen atom-enhanced outer orbital coordination

The development of non-activated collectors for sphalerite is aimed at eliminating the dependence of traditional flotation processes on copper sulfate, reducing mineral processing costs, and minimizing environmental pollution. Based on the surface electronic structure of sphalerite, this study establishes a molecular-level collector design strategy driven by enhanced outer-orbital coordination. Coordination chemistry analysis of Zn 2+ on the sphalerite surface demonstrates that Zn 2+ cannot form effective π-backbonding due to 3d 10 electron inertness, and enhancing σ-bonding between its outer sp orbital electrons and collectors is a viable approach to strengthen sphalerite-collector interactions. Accordingly, three novel collectors, namely 2-fluorothiophenol(2-FTP), 2-chlorothiophenol(2-CTP), and 2-bromothiophenol(2-BTP), were designed and synthesized by precisely introducing fluorine, chlorine, and bromine atoms at the ortho -position of the thiol group in thiophenol. Pure mineral flotation tests verified that the three novel collectors can efficiently recover non-activated sphalerite at low dosages. Among them, 2-BTP exhibited superior performance, with a recovery of 84.6% achieved at a dosage of 5 × 10 −6  mol/L. In actual ore flotation tests, both the grade and recovery of zinc concentrate obtained with the novel collectors under non-activated conditions were superior to those of the CuSO 4  + xanthate process. Combined with Fourier Transform Infrared Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) analyses, and Density functional theory (DFT) calculations, it is revealed that stable σ bonds are formed between the novel collectors and Zn 2+ via the thiol S atom. Notably, 2-BTP can further form a binuclear coordination structure with Zn 2+ through the bromine atom, which significantly enhances adsorption stability. The introduction of halogen substituents effectively improves the electron enrichment degree and electron transfer capacity of the thiol group, thereby optimizing the outer-orbital coordination effect.