Solubilities And Components Evolution For Malachite, Quartz,Dolomite, Calcite And Chrysocolla In NH₃-NH₄Cl-H₂O Systems At25℃

With growing use of Cu metal for different applications and rapid depletion of high-grade natural copper sulfide ores, worldwide effords are being made to look for low-grade copper minerals for recovering this metal. For many years these ores were not effectively utilized due to nonavailability of cost and technology effective processes. Malachite, chrysocolla, quartz, dolomite and calcite are the most common mineralogical compositions in low-grade copper oxide ores. In order to extract the valuable metals in an efficient and environmentally friendly manner, process optimizing as well as plant design, it is critical to gain the correct thermodynamic information regarding these minerals leaching. As part of the "973" project titled "Fundamental research on efficient separation and extraction of important nonferrous metals from refractory resources", the solubilities, components developing and dissolving model of Cu-NH3-NH4Cl-H2O, malachite-NH3-NH4Cl-H2O, quartz-NH3-H2O, dolomite-calcite-NH3-NH4C1-H2O and chrysocolla-NH3-NH4C1-H2O systems have been investigated systematically by experimental measure and thermodynamic modeling.(1) An innovative methodology was developed to construct predominance existence diagrams (PED) for systems involving multi-phase, multi-component and concentrated solutions. The stability diagrams for Cu(Ⅰ) and Cu(Ⅱ) were generated as an example in the presence of realistically modeled NH3-NH4C1-H2O solutions. The resulted diagrams boldly break through some inherent limitations of traditional stability diagrams due to taking the non-ideality of solution into consideration. The effects of total concentrations of copper ions, ammonia and chloride on the stability of species in system were investigated. The simulated and experimental results indicate that the predominance of a given species in solution depends strongly on the pH and the concentrations of Cu(Ⅰ) or Cu(Ⅱ) in this system. And the total concentration of ammonia and Cl-irons has minor impact on the existence area of predominance species.(2) The solubilities of malachite in the presence of aqueous NH3 solution, NH4Cl solution and their mixed solution were measured and calculated for the first time. The thermodynamic modeling rationalised the interactions between the different components and predicted the influence of changes in the concentration of ammonia and ammonium chloride on the copper solubility of malachite. The results reveal the nature of the incongruent dissolution for malachite in aqueous NH3and NH4Cl medium. For a mixed solution containing ammonia and ammonium chloride, the highest copper solubility can be achieved by adjusting the [NH3]/[NH4C1] ratio to about2:1. A quantitative estimate of copper solubility in0to3mol/kg NH4C1and NH3was calculated and represented diagrammatically as total dissolved copper concentration contour plots, together with the formation zone of secondary solids, which provides the important theoretical basis of extraction process control and allows optimum conditions to be selected to achieve higher copper recovery. Additionally, the impact of solubility product constant of malachite on the thermodynatic calculation on copper solubility was ducussed.(3) The solubility measurements of well-crystallized natural quartz sand (250-600μm) and ground quartz with particle size from45μm to75μm in the NH3-H2O system at25℃were reported and combined with thermodynamic predictions by the geochemical modeling code. And the impacts of particle size and duration on dissolved silica were investigated. The results from thrermodynamic modeling showed the evolution of phases and components. The solubilites of the both quartz as the function of concentration of ammonia were deduced by regressing analysis. The results show that the solubility of quartz was determinted by the crystallinity of particle surface.(4) To the natural composite ore containing64wt%dolomite and36wt%calcite, the solubilities were measured in NH3-H2O, NH4Cl-H2O and their mixture solutions at25℃,1atm and predicated by the geochemical modeling code. The result revealed some general regularities in the variation of phases and components. And dissolving model was also constructed. The experimental and predicted results showed the CaCO3component of dolomite dissolves faster than the MgCO3component and that dolomite dissolution is limited by MgCO3dissolution. The total dissolved Ca2+concentrations for this composite ore in0-3mol/kg NH3solutions is less than10mg/L (as CaO), while the total dissolved Mg2+almost keeps constant of less than1mg/L(as MgO). The solubilities of Ca2+and Mg2+have the same trend in0-3mol/kg NH4Cl solutions, but the Ca2+solubility is about100times compared to the figure in NH3solutions at same concentration, while the Mg2+solubility is about7times. The solubilities of Ca2+and Mg2+for this composite in their mixture solutions will increase as the increasing of NH4Cl concentration. In addition, the solubilities of sole dolomite and calcite were predicted in solution of0-3mol/kg aqueous NH4Cl and aqueous NH3, respectively.(5) Amorphous and aged chrysocolla solubilities were predicted in aqueous NH3, NH4C1and their mixture solutions at298.15K based on the optimally seltected thermodynamic data achieved from the solubility study of malachite and quartz in solutions mentioned above. And the relationship between the total dissolved copper and silica as the function of the lixiviant concentration was studied. Thermodynamic modeling retionalised the interactions between phase and components resulting in the dissolving models of these dissolution systems to be built. The total dissolved copper and silica concentration contour for the both type of chrydocolla were contructed showing the maximum solubility of copper can be achieved at near an ammonia-ammonium ratio of unite, where the pH of quenched solutions is9.0-9.5.