Study On The Leaching Kinetics Of Copper Ores And The Leaching Of Oxidized Copper/Zinc Ores In The Ammoniacal Solution

Tangdan low-grade oxidized copper ore and Nanping low-grade oxidized zinc ore are Chinese massive oxidized copper/zinc ores, respectively. Both of the ores are processed and concentrated difficultly by traditional flotation methods, and are not fitted with the acid leaching technique. In view of these defects, ammonia-ammonium sulfate solution was introduced to dissolve the oxidized copper/zinc ores. The leaching kinetics of several copper ores and leaching technology of oxidative ammonia leaching for oxidized copper/zinc ores are investigated in ammonium solution. All the results will provide the theoretical foundation and basic dates for the hydrometallurgy process of copper/zinc ores.The behavior of non-oxidative and oxidative ammonia leaching of several copper ores in ammonia-ammonium sulfate solution was investigated. A new technology of oxidative ammonia leaching for low-grade copper ore with sulphide copper was put forward and another new technology of catalytic-oxidative leaching of low-grade oxidized copper/zinc mixed ores was proposed. The main conclusions were made as follows:1. The dissolution kinetics of malachite was investigated systematically in ammonia-ammonium sulfate solution.Comparison of the leaching behavior of malachite in ammonia solution and ammonia-ammonium sulfate solution was made. The results show that the dissolution of malachite is favored in the ammonia-ammonium solution. The important factors for the leaching process in ammonia-ammonium sulfate solution are reaction temperature, particle size, concentration of ammonia and ammonium sulfate. The dissolution behavior of malachite coincides with the mixed kinetic shrinking core model, which is based on the interface transfer and diffusion across the solid layer. The activation energy is determined to be26.75kJ/mol and the kinetic equation can be expressed as follows:2. The oxidative leaching behavior of bornite was investigated systematically in ammonia-ammonium sulfate solution. The results show that the reaction time, temperature, particle size, concentration of ammonia and ammonium sulfate and the dosage of sodium persulfate are the main factors to the oxidative leaching process. The dissolution kinetics of bornite is controlled by the mixed kinetic shrinking core model which is affected by both the interface transfer and diffusion across the solid layer. The activation energy is calculated to be15.63kJ/mol and the dissolution kinetics of bornite can be written as follows:The dissolution mechanism of bornite in ammonia solution with persulfate is drawn according to the results of XRD analysis of the residue and can be expressed as follows:3. The non-oxidative ammonia leaching of low-grade oxidized copper ore was studied in ammonia-ammonium solution. The main factors for the leaching contain the concentration of ammonia and ammonium sulfate, temperature, the liquid-to-solid ratio and particle size. The results of the chemical phase analysis and SEM-EDS detection show that malachite is mostly dissolved, sulphide copper ore is dissolved partly and chrysocolla is extracted difficultly. The extraction of copper of low-grade copper ore is determined mainly by the dissolution of chrysocolla.The non-oxidative leaching behavior of low-grade oxidized copper ore can be described by diffusion shrinking model, and the leaching process is controlled by diffusion across the solid layer. The leaching kinetics with an activation energy of25.54kJ/mol can be presented as:4. The oxidative ammonia leaching of low-grade oxidized copper ore was investigated in ammonia-ammonium sulfate solution. The leaching process is determined to be controlled by mixed kinetic shrinking core model, which is affected by both interface transfer and diffusion across solid layer. The leaching kinetics with an activation energy of22.91kJ/mol can be expressed as: A new technique of the oxidative ammonia leaching of low-grade oxidized copper ore with sulphide copper is put forward based on the above results. It is found that sulphide copper ore in the low-grade oxidized copper ore can be oxidized by persulfates including sodium, potassium and ammonium persulfates and the oxidation efficiency of ammonium persulfate is the highest. The extraction percentage of copper by oxidative ammonia leaching is at least9%higher than that of copper by non-oxidative ammonia leaching. The results of chemical phase analysis and SEM-EDS detection show that bornite can be oxidized by persulfate and dissolved in ammoniacal solution.5. The catalytic-oxidative leaching of low-grade oxidized zinc ore was investigated by the catalysis of Cu(NH3)42+produced from low-grade oxidized copper ore in ammonia-ammonium sulfate solution. The dissolution mechanism of ZnS in the zinc ore with the oxidization of persulfate by the catalysis of Cu(NH3)42+is proposed as follows:A new technique of catalytic-oxidative ammonia leaching of low-grade oxidized copper/zinc mixed ores is proposed for the first time.Leaching temperature, the mass ratio of copper ore to zinc ore, liquid-to-solid ratio, the concentration of ammonia, ammonium sulfate and ammonium persulfate are the important factors that affect the leaching process of the mixed ore. The extraction percentage of zinc is lower than that of copper. The results of SEM-EDS analysis of the residue of the mixed ore show that Zn2SiO4is dissolved in ammonia solution and the dissolution of Zn2SiO4is further blocked owing to the adsorption of the precipitated SiO2on the surface of ore. ZnFeO2can not be extracted in ammonia solution.The optimal leaching conditions with a maximum extraction percentage of Cu92.6%and Zn87.5%were determined as follows:the mass ratio of copper ore to zinc ore4/10, temperature50℃, reaction time6h, stirring speed500r/min, liquid-to-solid3.6/1mL/g, concentration of ammonia2.0mol/L, concentration of ammonium sulfate1.0mol/L and concentration of ammonium persulfate0.3mol/L.