QUANTUM CHEMICAL MECHANISM ON THE SURFACE OXIDATION AND FLOTATION OF SULPHIDE MINERALS

The surfaces of galena and pyrite,the adsorption of oxygen,and the reactions of ethyl xanthate on the sulfides were studied using quantum chemical calculations.In addition,the surface electron structures of the minerals were discussed.According to the results,the mechanisms of ionic exchange reaction and dixanthogen adsorption for the xanthate notation of galena and pyrite were explained.The important role of oxygen in collector and collectorless flotation processes was also investigated.

Mineral sulphide-lime reactions and effect of CaO/C mole ratio during carbothermic reduction of complex mineral sulphides

Mineral sulphide （MS）-lime （CaO） ion exchange reactions （MS ＋ CaO = MO ＋ CaS） and the effect of CaO/C mole ratio during carbothermic reduction （MS ＋ CaO ＋ C = M ＋ CaS ＋ CO（g）） were investigated for complex froth flotation mineral sulphide concentrates. Phases in the partially and fully reacted samples were characterised by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The primary phases during mineral sulphide-lime ion exchange reactions are Fe304, CaSO4 Cu2S, and CaS. A complex liquid phase of Ca2CuFeO3S forms during mineral sulphide-lime exchange reactions above 1173 K. The formation mechanisms of Ca2CuFeO3S liquid phase are determined by characterising the partially reacted samples. The reduction rate and extent of mineral sulphides in the presence of CaO and C increase with the increase in CaO/C ratio. The metallic phases are surrounded by the CaS rich phase at CaO/C 〉 1, but the metallic phases and CaS are found as separate phases at CaO/C 〈 1. Experimental results show that the stoichiometric ratio of carbon should be slightly higher than that of CaO. The reactions between CaO and gangue minerals （SiO2 and A1203） are only observed at CaO/C 〉 1 and the reacted samples are excessively sintered.

Physical chemistry mechanisms of CDR system in sulphide mineral flotation

The flotation tests, zeta potential measurements, and Fourier transform infrared spectroscopy （FTIR） analysis on galena, sphalerite, and pyrite were studied in a collecting-depressing-reactivating （CDR） system. In this system, sulphide minerals were first collected and acti- vated by the collector, and then depressed strongly by Ca（OH）2 in a strong alkaline solution. Finally, they were reactivated by H2SO4. The flotation tests of pure minerals showed that in the Ca（OH）2 depressing process sulphide minerals had similar flotation characteristics because they had already been influenced by the collector. Hence, the flotability differences between them were reduced. However, in the H2SO4 re- activating process considerable differences in the flotability between galena and sphalerite/pyrite were produced. That is to say, galena was relatively easy to be reactivated by H2SO4, but sphalerite and pyrite were not reactivated at pH 〉 11. The zeta potentials of sulfide minerals measured by the Zeta Plus presented irreversible characteristics on the change of pH values. The results of the FTIR spectra analysis indi- cated that the collectors already adsorbed on the mineral surface were removed partially by Ca（OH）〉

Central composite design for optimization and formulation of desulphurization of iron ore concentrate using atmospheric leaching process

Owing to the negative effects of sulphur in iron ore on steelmaking process and environment, a tank leaching process was performed in atmospheric conditions to remove the sulphur from the iron ore concentrate and simultaneously to transform sulphide minerals into useful by-products. To achieve desirable sulphur removal rate and efficiency, central composite design was adopted as a response surface methodology for the optimization and evaluation of the process. A full-quadratic polynomial equation between the sulphur removal and the studied parameters was established to assess the behaviour of sulphur removal as a function of the factors and to predict the results in various conditions. The optimum conditions were obtained based on the variance tests and response surface plots, from which the optimized ranges for each factor resulting in the best response （corresponding to the highest percentage of desulphurization） could be then achieved. The results show that most desirable conditions are atmospheric leaching in 1.39 mol/dm3 nitric acid and 0.88 mol/dm3 sulphuric acid for 47 h. The designed process under the optimized desulphurization conditions was applied to a real iron ore concentrate. More than 75% of the total sulphur was removed via the leaching process. In addition to the desulphurization, the conversion of sulphide-bearing minerals into useful by-products, extraction of valuable metals, and executing the process under atmospheric conditions are the other advantages of the proposed method.