Theoretical Study On Enhanced Sulfidation Flotation Of Smithsonite Based On Copper-ammonium Synergistic Activation

Zinc oxide mineral is an important zinc resource in China,and it may be primarily upgraded by sulfidization amine and sulfidization xanthate flotation methods.However,amine collectors have poor selectivity and are extremely sensitive to slime,and the flotation foam is extremely stable,so it is difficult to defoam,resulting in an increased difficulty in practical production.Compared with the sulfidization amine flotation method,a weaker impact by slime occurs when using the sulfidization xanthate flotation method.Therefore,the efficient recovery of zinc minerals from low-grade and complex zinc oxide resources is expected to be achieved by an in-depth study on the sulfidization xanthate flotation method.A large number of experimental studies and practice show that the desired flotation performance can be obtained after zinc oxide minerals are sulfidized with Na₂S using xanthate as collector.However,the traditional surface sulfidization has some disadvantages such as low sulfidization efficiency,low level of sulfidization products and unstable sulfidization layer,resulting in unstable adsorption of xanthate on the mineral surface and poor flotation index.Therefore,enhancing the surface sulfidization of zinc oxide minerals is the key and difficult point to realize the efficient recovery of zinc oxide resources by sulfidization xanthate flotation method.In order to solve these problems,a technical approach,i.e.,copper ions and ammonium salt（i.e.,copper–ammonium species）are utilized to enhance the surface sulfidization of zinc oxide minerals,has been proposed.In this paper,a typical zinc oxide mineral,smithsonite,is taken as the research object.Through DFT simulation calculation,Zeta potential measurement,XPS analysis,ToF-SIMS characterization and flotation tests,the interaction configuration,process and products of smithsonite surfaces with sulfide ions were studied based on multi-angles and multi-scales,which reveals the surface sulfidization characteristics and flotation mechanism using sodium sulfide as the sulfidizing reagents.The distribution regularities of active species in the system containing copper ions,and copper–ammonium species were determined by solution chemical calculation,which provided theoretical basis for the subsequent surface activation of smithsonite.By means of ICP-OES,Zeta potential,XPS and ToF-SIMS,the differences were compared and studied regarding the adsorption characteristics of copper species and activation products formed on the mineral surface in the different activation systems.Besides,the activation mechanism of active species on the surface of smithsonite was revealed.The flotation behavior,surface potential,composition and chemical state of elements,and distribution of sulfidization products in the different sulfidization system were investigated.The effect of copper ions and copper–ammonium species on the surface sulfidization characteristics of smithsonite was ascertained,and the mechanism of surface enhanced sulfidization was revealed.By means of XPS,Zeta potential,surface adsorption and FT-IR measurements,the interaction mechanism between copper ions and sulfidized smithsonite surfaces,as well as the adsorption characteristics of collector in the different sulfidization systems were compared and investigated,which revealed the adsorption mechanism of copper ions and collector on the smithsonite surface by enhanced sulfidization.Combined with the surface activation,sulfidization behavior,xanthate adsorption characteristics,flotation behavior,as well as the analysis of surface activation products and sulfidization products,the theoretical system of smithsonite enhanced sulfidization flotation based on the synergistic activation of copper–ammonium species was finally established.In the process of crushing and grinding,smithsonite was prone to fracture along the weak Zn-O bonding,leading to the exposure of abundant Zn²⁺species on the fresh mineral surface.A large number of zinc-hydroxyl complexes formed due to the complexation of the exposed Zn²⁺species in the pulp solution,resulting in enhanced hydrophilicity on the mineral surface.The adsorption of xanthate on the mineral surface was weak when it was used for direct flotation of smithsonite,and it was difficult to exist stably,thus causing a poor floatability of smithsonite.Moreover,the flotation recovery could not be significantly improved with an increase of xanthate concentrations.After treatment with sodium sulfide,the flotation recovery of smithsonite increased,but more than 45%smithsonite was still lost in the tailings.Copper ions and copper–ammonium species could greatly improve the flotation recovery of smithsonite.Under the same concentration of sodium sulfide and xanthate,the maximum flotation recovery of smithsonite increased by 19%in the activation system of copper ions,and by 32%in the synergistic activation system of copper–ammonium species.In the process of surface activation of smithsonite,copper ions mainly existed in the form of Cu²⁺and Cu（OH）⁺in the pulp solution,while copper–ammonium complexes mainly existed in the form of Cu（NH₃）₂²⁺and Cu（NH₃）₃²⁺.Thus,Cu²⁺in the pulp solution could react with O sites on the mineral surface to form the–O–Cu species.Meanwhile,the dehydration reaction between Cu（OH）⁺in the pulp solution and Zn（OH）_mⁿ⁺species on the mineral surface resulted in the formation of–Zn–O–Cu species on the mineral surface.In the synergistic activation system of copper–ammonium species,after the interaction of active Cu（NH₃）₂²⁺and Cu（NH₃）₃²⁺with smithsonite surfaces,the Cu（II）and–Cu–OH/Cu（NH₃）_n²⁺species formed on the mineral surface,which realized the surface activation of smithsonite.Compared with the copper ion activation,it was better when smithsonite was activated with copper–ammonium species because copper species formed on the mineral surface had higher content and stronger reactivity.Moreover,the adsorption efficiency of copper species on the mineral surface was higher in the synergistic activation system of copper–ammonium species,which was conducive to the subsequent adsorption of sulfide ions.Sodium sulfide could adsorb on the surface of smithsonite to form sulfide products consisting of zinc sulfide（Zn S）and zinc polysulfide（Zn S_n）.The results of DFT simulation calculation show that HS^–ions could adsorb at the Top,Bottom and Bridge sites on the（101）surface and stable Zn–S chemical bonds were formed.The adsorption stability was in the order of Top site<Bottom site<Bridge site.In addition,sodium sulfide could also adsorb on the surface of smithsonite activated by copper ions and copper–ammonium species,and copper sulfide species consisting of Cu（I）–S and Cu（II）–S could formed on the mineral surface.In other words,sulfidization products on the mineral surface were composed of zinc sulfide and copper sulfide species.The effect of smithsonite sulfidization in the different sulfidization system was in the order of copper–ammonium synergistic activation system>copper ion activation system>sodium sulfide system.Compared with copper ion activation,the sulfidization products formed on the smithsonite surface had higher content and stronger reactivity in the copper–ammonium synergistic activation system.Copper ions could adsorb on the sulfidized smithsonite surface in the system of sodium sulfide,copper ion activation or copper–ammonium synergistic activation,and activation products composed of Cu（I）–S and Cu（II）–S were generated.Compared with copper ion activation,the result of enhanced sulfidization was better when smithsonite activated in the copper–ammonium synergistic activation system,and copper sulfide species generated on the mineral surface had higher content and stronger reactivity,which was conducive to the adsorption of xanthate on the mineral surface.Under the condition of the same initial concentration of xanthate,the adsorption ability of xanthate on the sulfidized smithsonite surface in the different sulfidization system was in the order of copper–ammonium system>copper ion system>sodium sulfide system.Therefore,copper–ammonium synergistic activation not only enhanced the sulfidization of smithsonite surfaces,but also hydrophobicity of the sulfidized mineral surface,thereby greatly improving the floatability of smithsonite.It will provide a theoretical support for the efficient recovery of zinc oxide minerals using sulfidization flotation methods.