Process And Mechanism Of Microwave-Aided Roasting Of Copper Sulfide Minerals

In the thesis copper sulfide minerals are roasted in air by microwave heating in the presence of calcite. The calcine is subsequently leached by ammonia. The emission of SO2 is eliminated and the roasting reaction rate is increased considerably due to the presence of calcite. The percent extraction of copper obtained is 97.4%. The advantages of this new process of extracting copper are fewer pollution, lower energy consumption and higher efficiency. It has a good prospect of application.The study on the heating characteristics of covellite-calcite and chalcopyrite-calcite systems in microwave irradiation shows that an increase in microwave irradiation power can increase the heating rate, but an increase in the content of calcite can decrease the heating rate. The temperature increases with an increase in microwave irradiation time. And for covellite-calcite system its heating rate dramatically increases at the temperature around 470K. However, for chalcopyrite-calcite system its heating rate obviously decreases at the temperature between 500K and 600K. Therefore, the equation of the heating rate of the copper sulfide minerals can be expressed aswhere Cp heat capacity, p density, T temperature, t time, w angler frequency of microwaves, dielectric constant in vacuum, effective dielectric loss factor, E electric field strength, e emission coefficient, a Stefen-Boltzman constant, A surface area of sample, V volume, n molar number in unit volume. enthalpy of reaction, A'conversion.The study on the optimum experimental conditions of roasting copper sulfide minerals by the application of microwave is carried out. It is indicated that the percent extraction of copper increases with an increase in microwave irradiation power, microwave irradiation time, the mass and particle size of the sample and air flow rate. Once percent extraction of copper reaches the maximum it decreases with the increase of the above parameters. The optimum experimental conditions are summarized as follows:According to the analysis of the experimental data, it is indicated that the oxidation of covellite-calcite and chalcopyrite-calcite systems is controlled by interface chemical reaction in conventional heating and the corresponding rate equation is developed. The oxidation kinetics of chalcopyrite with and without calcite is studied by thermogravimetry and differential thermal analysis. The results show the oxidation can be divided into two stages. Analysis of X-ray diffraction indicates that in the first stage, the phase of Cu is transformed into CuSO4 with a mass gain as well as an exothermic peak. In the second stage, CuSO4 decomposed into CuO with a mass loss and an endothermic peak. In the first stage, the activation energies for roasting of chalcopyrite with and without calcite are found to be l59.5kJ/mol and 121.1 kJ/mol, respectively. In the second stage, the corresponding activation energies are 242.2kJ/mol and 182.9 kJ/mol, respectively. It is obvious that calcite can loweractivation energies of the reaction.Compared with conventional heating, microwave heating can dramatically promote the roasting reaction. With the proceeding of the reaction, rate increase factors of covellite-calcite and chalcopyrite-calcite systems in the roasting are increased from 4.7 to 14 and from 3.5 to 10, respectively. On the basis of the comparison of their rate increase factors, it is demonstrated that the acceleration of the oxidation roasting of covellite-calcite system by microwaves is more obvious than that of chalcopytile-calcite system.