Refractory Zinc Oxide Ore Sulfide Roasting-flotation Theory And Technology Research

Zinc oxide ore,as an important kind of zinc resource,is very rich in China.At present,it is very difficult to achieve an effective processing for this kind of ore using conventional mineral processing methods,especially for the low-grade zinc oxide ore.Until today,most of the ore was not exploited.In order to effectively recovery zinc from low-grade zinc oxide ore,a method to dispose the zinc oxide ore by sulfurization roasting-flotation was proposed and investigated in this paper.The sulfur was used for vulcanizing agent in this paper.The zinc oxide phase was converted into the zinc sulfide with a quality of better floatability than zinc oxide,and then the zinc was recovered by the conventional method for zinc sulfide flotation.In this paper,the sample comes from Lanpin county,Yunnan province,China,which contains 7.84%zinc,and the oxidation degree of Zn reach to 55.13%.The main conclusions are as follows:（1）The main reactions of zinc oxide with sulfur was investigated by thermodynamic analysis,and the favorable conditions for forming the zinc sulfide in the sulfurization roast process were found out.Zinc oxide can be transformed to zinc sulfide at a certain temperature,high-temperature can favor sulfurization reactions both thermodynamically and kinetically.The addition of carbon not only promotes these sulfurization reactions but also can increase sulfur utilization rate and eliminate the generation of SO₂.The thermodynamic analysis also indicates that the gangue ore in the sample has no influence with the sulfurization of zinc oxide,so the zinc oxide can be sulfured selectively.（2）The experimental results of the sulfurization roast-flotation indicate that sulfur dosage,temperature,coal powder dosage,time and grinding fineness have a significant effect on the flotation behavior of roasted product.The optimum conditions for the roasting process were determined as:1%of sulfur dosage,650℃of temperature,1%of coal powder dosage,60min of time,and 85%below 74μm of grinding fineness.Under these conditions,a zinc concentrate assaying 28.81%Zn with 86.83%recovery was produced from a sample open-circuit flotation of the roasted product,and then a zinc concentrate assaying 32.05%Zn with 91.29%recovery was produced from the closed-circuit flotation,which indicates the roasted product can be floated easily.（3）In order to investigate the phase and morphology of the roasted product,The XRD,SEM-EDS and EPMA was conducted.Before roasted,the sample shows complex associated relations,which is go against the flotation separation of zinc and gangue.The zinc was concentrated as zinc sulfide,and the zinc sulfide be proved to be in a good crystalline form and coarse grains,in addition,the concentrations of S and Zn at the surface were approximately close to that of sphalerite,all that is beneficial to separate zinc by flotation.（4）Based on the crystal structure of ZnO,the sulfurization mechanism of ZnO involving the interaction between S₂ and zincite（10 1^—0）surface was investigated by density functional theory（DFT）calculations at an atomic level.The S₂ could easily adsorb on the surface of zincite with an adsorption energy of-2.27eV,followed by dissociation of Zn-O bond.The density of sate（DOS）analyses presented that the S 3p orbital from the S₂ and O 2p orbital at the mineral surface layer were obviously overlapped near the Fermi energy,suggesting that an intensive hybridization occurred between them.The Mulliken population results showed that both S atoms in S₂ could not only be oxidized,but also be reduced,resulting in the generation of SO₂ and ZnS.In conclusion,sulfurization roasting-flotation can significantly improve floatability of zinc oxide ore,so the flowsheet can be simplified and the index can be improved,which should be conducive to the utilization of low-grade zinc oxide ore.The results achieved from this research may provide a deeper understanding of the sulfurization reaction mechanism and give a theory reference for further improving the roasting process.