Dissolution kinetics of malachite in ammonia/ammonium carbonate leaching

The leaching of oxide copper ore containing malachite, which is the unique copper mineral in the ore, by aqueous ammonia solution has been studied. The effect of leaching time, ammonium hydroxide, and ammonium carbonate concentration, pH, [NH₃]/[NH₄⁺] ratio, stirring speed, solid/liquid ratio, particle size, and temperature were investigated. The main important parameters in ammonia leaching of malachite ore are determined as leaching time, ammonia/ammonium concentration ratio, pH, solid/liquid ratio, leaching temperature, and particle size. Optimum leaching conditions from malachite ore by ammonia/ammonium carbonate solution are found as ammonia/ammonium carbonate concentrations: 5 M NH₄OH+0.3 M (NH₄)₂CO₃; solid/liquid ratio: 1:10 g/mL; leaching times: 120 min; stirring speed: 300 rpm; leaching temperature: 25 °C; particle size finer than 450 μm. More than 98% of copper was effectively recovered. During the leaching, copper dissolves as in the form of Cu(NH₃)₄⁺² complex ion, whereas gangue minerals do not react with ammonia. It was determined that interface transfer and diffusion across the product layer control the leaching process. The activation energy for dissolution was found to be 15 kJ mol⁻¹.     

Leaching kinetics of malachite in ammonium carbonate solutions

Leaching of malachite was conducted with ammonium carbonate as lixiviant and with temperature, lixiviant concentration, and particle size as variables. Two stages of reaction were found. In Stage I, the initial dissolution of malachite proceeds rapidly, but after about 10 pct reaction the rate is reduced by surface blockage due to the presence of a needle-structured intermediate, presumably Cu(OH)₂. Subsequently, malachite and the intermediate dissolve concurrently. In Stage II, after 90 pct reaction, essentially all of the malachite has dissolved and only the intermediate remains. It dissolves in Stage II. The activation energy is 64 kJ/mole (15.3 kcal/mole) for Stage I and 75 kJ/mole (18 kcal/mole) for Stage II. The rate of reaction in Stage I is proportional to the reciprocal of particle size and is 0.8 order with respect to the concentration of ammonium carbonate. The structures of leaching residues were studied using a scanning electron microscope. The kinetic data (activation energy and entropy), particle size and concentration dependence, residue morphology, and general leaching behavior evident from microscopic monitoring during leaching were used to develop the geometric equation for leaching in Stage I. The equation, based on a heterogeneous reaction with geometric rate control, is: 1 − (1 − α^1/3 = K₀₁/r₀/[(NH₄)₂C0₃]^0.8 exp(-64,000/RT)t. It was deduced that initial steps in reaction were: (1) release of Cu²⁺ from malachite; (2) initial complexing with ammonia to form Cu(NH₃)²⁺; and (3) subsequent complexing to produce Cu(NH₃) ₄ ²⁺ which is stable in solution at pH 8.8, the buffered pH of reaction. Stage II appears to be a similar reaction except that the reaction obeys cylindrical geometry instead of spherical geometry as in Stage I.     

Leaching Kinetics of Willemite in Ammonia-Ammonium Chloride Solution

The leaching kinetics of willemite in ammonia-ammonium chloride solution was investigated. The effects of the ammonia-ammonium ratio, particle size, temperature, and total ammonia concentration on the leaching rate of willemite were determined. The results show that the optimum ammonia-ammonium ratio is 1:2 over the studied range. The zinc extraction increases with the reduction of particle size and with the increase of temperature and the total ammonia concentration. Leaching kinetics indicate that the grain pore model could be adopted to describe the leaching process, and diffusion is the main rate-controlling step. The apparent activation energy was determined to be 54.47 ± 6.39 kJ/mol and a reaction order with respect to NH₃(aq) was 3.16 ± 0.40, both of which are likely a result of the parallel nature of the chemical reaction and diffusion in porous solids, even if the chemical reaction is not the rate-controlling step.     

Catalytic-Oxidative Leaching of Low-Grade Complex Zinc Ore by Cu (II) Ions Produced from Copper Ore in Ammonia-Ammonium Sulfate Solution

The catalytic-oxidative leaching of a mixed ore, which consists of low-grade oxide copper ore and oxide zinc ore containing ZnS, was investigated in ammonia-ammonium sulfate solution. The effect of the main parameters, such as mass ratio of copper ore to zinc ore, liquid-to-solid ratio, concentration of lixivant, leaching time, and temperature, was studied. The optimal leaching conditions with a maximum extraction of Cu 92.6?pct and Zn 85.5?pct were determined as follows: the mass ratio of copper ore to zinc ore 4/10?g/g, temperature 323.15?K (50?°C), leaching time 6?hours, stirring speed 500?r/min, liquid-to-solid ratio 3.6/1?cm³/g, concentration of lixivant including ammonia 2.0?mol/dm³, ammonium sulfate 1.0?mol/dm³, and ammonium persulfate 0.3?mol/dm³. It was found that ZnS in the oxide zinc ore could be extracted with Cu(II) ion, which was produced from copper ore and was used as the catalyst in the presence of ammonium persulfate.     

Kinetics of Ammonia Leaching of Multimetal Sulphides

This paper briefly describes the studies carried out on oxidative ammonia leaching of Cu-Zn-Pb multimetal sulphides. Kinetics of zinc and copper dissolution were studied with ? 200 + 300 mesh BSS fraction and 1% solids in the slurry. It is observed that the dissolution of sphalerite proceeds by a phase boundary reaction model and that of copper via diffusion through product layer in the temperature range of 70-100°C. The rate equations for zinc and copper dissolution are given by:

1 ? (1 ? α)^1/3 = k _Zn[NH₃][pO₂]^1/2

1 ? 2/3α ? (1 2/3α )^2/3 = k^Cu[NH₃]²[pO₂]^1/2

where the symbols have the usual meanings.

Activation energies for zinc and copper dissolution reactions are estimated to be 66.5 and 55.4 kJ/mole, respectively. Activation energy values thus obtained are also comparable to those obtained using a differential approach.

The leaching results obtained with 10% solids using a wide range of particle size (? 140 + 500 mesh) indicate that copper dissolution is chemically controlled in ammonia as well as ammonia-ammonium sulphate medium in the temperature range of 115-135°C. However, at lower temperature (?55°C). the leaching reaction follows a diffusion model. Zinc dissolution data show deviations from the shrinking core model due to high extractions in the initial stages.     

The leaching kinetics of chalcopyrite (CuFeS2) in ammonium lodide solutions with iodine

The leaching kinetics of chalcopyrite (CuFeS₂) in ammonium iodide solutions with iodine has been studied using the rotating disc method. The variables studied include the concentrations of lixiviants, rotation speed, pH of the solution, reaction temperature, and reaction product layer. The leaching rate was found to be independent of the disc rotating speed. The apparent activation energy was measured to be about 50 kJ/mole from 16 °C to 35 °C, and 30.3 kJ/mole from 35 °C to 60 °C. The experimental findings were described by an electrochemical reaction-controlled kinetic model: rate =k [NH₃]^0.69[OH⁻]^0.42[I ₃ ⁻ ]^0.5.     

Solubility prediction of malachite in aqueous ammoniacal ammonium chloride solutions at 25 °C

The solubility of malachite in the presence of ammonia, ammonium chloride and their mixed solution is calculated by a geochemical modeling code and is measured in a series of dissolution experiments using synthetic malachite at 25 °C. The simulated results show a good agreement with the experimental data gained at 25 °C. The predicted and experimental results indicate that the precipitate CuO limits the copper solubility in aqueous ammonia and Cu(OH)_1.5Cl_0.5 in aqueous ammonium chloride. For a mixed solution containing ammonia and ammonium chloride, highest copper solubility can be achieved by adjusting the [NH₃]/[NH₄Cl] ratio to about 2:1. The thermodynamic model presented rationalises the interactions between the different components and predicts the influence of changes in the concentration of ammonia and ammonium chloride on the copper solubility of malachite.     

Separation of cobalt from nickel in ammonia-ammonium carbonate solutions using pressurized ion exchange

High resolution pressurized ion exchange has been used successfully to study and separate the various cobalt and nickel complexes present in commercial ammonia-ammonium carbonate solutions produced by the Caron process. Using chromatographic elution from Dowex 50W-X8 (15–25 micron) resin with ammonium carbonate solutions, three cobalt species, identified as the purple carbonato tetrammine complex, [Co(NH₃)₄CO₃]⁺, the red carbonato pentammine complex, [Co(NH₃)₅CO₃]⁺, and the yellow hexammine complex [Co(NH₃)₆]³⁺, were separated from a single nickel species. Nickel sorption was found to be a strong function of pH, whereas sorption of the cobalt complexes was essentially independent of pH over a rather wide range, extending from ～pH 7.8 to 10. Distribution ratios for all species increased significantly with decreasing ammonium carbonate concentration. With ammonium carbonate solution at pH 9.5, the complexes were eluted in the following order: [Co(NH₃)₄CO₃]⁺, [Co(NH₃)₅CO₃]⁺, [Ni(NH₃)_6-x(H₂O)_x]²⁺, and [Co(NH₃)₆]³⁺. From 4 M (NH₄)₂CO₃, distribution ratios were 5.0, 7.5, 18, and 75 for the respective complexes identified in the order above. This study points out some of the difficulties and opportunities in developing a viable ion exchange process for the recovery and separation of these metal ions.     

Leaching kinetics of ionic rare-earth in ammonia-nitrogen wastewater system added with impurity inhibitors

Ammonia-nitrogen wastewater is produced during the dressing and smelting process of rare-earth ores.Such wastewater includes a very high concentration of NH4＋, as well as other ions（e.g., NH4＋, RE3＋, Al3＋, Fe3＋, Ca2＋, Cl–, and Si O32–） with a p H of 5.4–5.6.Its direct discharge will pollute, yet it can be recycled and used as a leaching reagent for ionic rare-earth ores.In this study, leaching kinetics studies of both rare earth ions and impurity ion Al3＋ were conducted in the ammonia-nitrogen wastewater system with the aid of impurity inhibitors.Results showed that the leaching process of rare-earth followed the internal diffusion kinetic model.When the temperature was 298 K and the concentration of NH4＋ was 0.3 mol/L, the leaching reaction rate constant of ionic rare-earth was 1.72 and the apparent activation energy was 9.619 k J/mol.The leaching rate was higher than that of conventional leaching system with ammonium sulfate, which indicated that ammonia-nitrogen wastewater system and the addition of impurity inhibitors could promote ionic rare-earth leaching.The leaching kinetic process of impurity Al3＋ did not follow either internal diffusion kinetic model or chemical reaction control, but the hybrid control model which was affected by a number of process factors.Thus, during the industrial production the leaching of impurity ions could be reduced by increasing the concentration of impurity inhibitors, reducing the leaching temperature to a proper range, accelerating the seepage velocity of leaching solution, or increasing the leaching rate of rare earths.     

Simulation ofin situ uraninite leaching-part III: The effects of solution concentration

The effects of variations in the concentrations of leaching reagents have been simulated forin situ leaching of UO₂ by H₂O-(NH₄)₂CO₃-NH₄HCO₃. The model used in the simulations incorporates rate laws for the mineral reactions, equilibrium reactions among the solution species, and a mixing cell representation of solution flow. Of the component concentrations, the major factor affecting the rate of uraninite dissolution is the oxidant concentration. High peroxide concentrations lead to more rapid reaction with an early maximum in the U(VI) concentration. If lower oxidant concentrations are used, the reaction is under mixed kinetic and mass transfer control and the U(VI) concentration is lower but approximately constant for an extended period. Because they increase the concentration of the HCO _3/- anion, high ammonium carbonate and ammonium bicarbonate concentrations also result in some enhancement in the rate of U leaching; the reaction is known to be half-order in both HCO₃ ^- and H₂O₂. A 10:1 ratio of (NH₄)₂CO₃ to NH₄HCO₃ concentrations was found to result in a nearly constant pH during most of the leaching process. Calcite-containing gangue causes an immediate pH increase from about 8.9 to 9.4. The rate of the calcite reaction, calcite saturation index, and porosity are all independent of the lixiviant concentrations. Detailed calculations of solution speciation are necessary to predict the concentrations of individual species from those of components.     

Ammonia,oxidation leaching of chalcopyrite —reaction kinetics

The reaction for the ammonia, oxidation leaching of chalcopyrite, CuFeS₂ + 4NH₃ + 17/4 O₂ + 2 OH^- ⇌ Cu(NH₃)⁺² ₄2 + l/2Fe₂O₃ + 2 SO₄ + H₂O was studied using monosize particles in an intensely stirred reactor under moderate pressures to determine the important chemical factors which govern the kinetic response of the system. The reaction kinetics were studied at dilute solid phase concentration so that oxygen transport at the gas/liquid interface would not limit the rate. A catalytic electrochemical surface reaction was shown to control the reaction kinetics with the reaction rate determined by the following equation derived from electrochemical considerations: dα/dl=127 f/do (OH_- ^1/2 (k₁PO₁/1+k₂PO₁ (k₁+k₂(Cu⁺²)_o+k’₂α)(1-α)^2/3 (K P 1/2 Excellent agreement between theory and experiment was obtained both with regard to apparent reaction orders for oxygen, cupric, and hydroxyl, and with regard to geometric factors that influence the reaction rate. Further support for the reaction mechanism included an activation energy of approximately 10 kcal/mole obtained under a variety of experimental conditions and the fact that the initial reaction rate constant was several orders of magnitude less than predicted mass transfer coefficients. Formerly Metallurgy Graduate Student, University of Utah     

Sulphuric acid leaching of polymetallic nodules using paper as a reductant

Sulphuric acid leaching of manganese nodule for extraction of Cu, Ni, Co and Mn in presence of a novel cellulosic reductant, waste newspaper, has been reported. The various parameters chosen for the study were: time, temperature, H₂SO₄ concentration and amount of paper. To quantify the linear and interaction coefficients a 2³ full factorial design of experiments was followed. The regression equations were determined and the adequacy of these equations was tested by Fischer’s test. The linear coefficients for time, acid concentration and amount of paper were found to be significant for extraction of Cu, Ni, Co and Mn. While acid concentration and amount of paper showed positive interactions for Cu, Ni and Co extractions it had negative significance for Mn dissolution. Under the conditions for >97% extraction of metal values iron extraction was ∼40%. In order to reduce the iron contamination by discarding iron as jarosite effect of addition of ammonium sulphate during leaching was also studied. Iron extraction could be brought down to 14% from ∼40% with the addition of 30g/L (NH₄)₂SO₄ without affecting the recoveries of other metals.     

Fabrication of wide temperature lanthanum and cerium doped Cu/TNU-9 catalyst with excellent NH3-SCR performance and outstanding SO2+H2O tolerance

The effects of La on the catalytic performance,SO₂ and H2O resistance of Cu-Ce/TNU-9 catalyst were studied in the selective catalytic reduction of NO_x via ammonia(NH₃-SCR).The results show that the La doped Ce-Cu/TNU-9(CCL/T9) catalyst exhibits better SCR performance than Ce-Cu/TNU-9(CC/T9) and Cu/TNU-9(C/T9) in the wide temperature window(200-450 ℃) due to La benefiting from enhancing Cu⁺+Ce⁴⁺?Cu²⁺-+Ce³⁺ to facilitate ...     

高碱性氧化锌矿氨性浸出研究

以NH3—NH4C1体系浸出某高碱性氧化锌矿,考察了氨浓度、液固比、时间和温度等因素对锌浸出率的影响,并分析了相应的浸出过程,得到的最佳实验条件为:NH3:NH4Cl摩尔浓度比为1∶1、氨浓度5 mol/L、液固比为3∶1、浸出时间为2 h、浸出温度40℃,此时锌浸出率为89.3%。     

Ammonia,oxidation leaching of chalcopyrite —surface deposit effects

The reaction for the ammonia, oxidation leaching of chalcopyrite, CuFeS₂ + 4NH₃ + 17/4 O₂ + 2 OH_- = Cu(NH₃)₄ ⁺² + l/2Fe₂O₃ + 2 SO₄ + H₂O was studied using monosize particles in an intensely stirred reactor at moderate oxygen pressures. For dilute solids concentration, the rate is controlled by an electrochemical surface reaction. Under conditions of low stirring speeds and low oxygen pressure, the hematite reaction product passivates the surface and the reaction virtually stops. Even though stirring speed influences the rate of the electrochemical reaction, this effect is due to changes in the morphology of the hematite deposit which alters the surface reaction kinetics, rather than being indicative of mass transfer limitations. Formerly Metallurgy Graduate Student, University of Utah,     

Oxidative Pressure Leaching of Silver from Flotation Concentrates with Ammonium Thiocyanate Solution

The thermodynamics and technologies of the selective pressure leaching of silver from flotation concentrates were investigated in an ammonium thiocyanate medium. Thermodynamic analyses, which include silver solubility in NH₄SCN solution and Eh-pH diagrams of the Me-MeS-NH₄SCN-H₂O system at 25 °C, were discussed. The effects of several factors, such as temperature, leaching time, oxidant, pH value, flotation concentrates concentration, surfactant concentration, and so on, on the extraction percentages of silver and zinc were investigated. The following optimal leaching conditions were obtained: NH₄SCN concentration 1.5 M, lignin concentration 0.5 g/L, Fe³⁺ concentration 2 g/L, flotation concentrates addition 200 g/L, and oxygen pressure 1.2 MPa at 130 °C for 3 hours. Under these optimum conditions, the average extraction percentage of silver exceeded 94 pct, whereas the average extraction percentage of zinc was less than 3 pct. Only 7 pct of ammonium thiocyanate was consumed after 4 cycles, which indicated that ammonium thiocyanate hardly was oxidized under these oxidative pressure leaching conditions.     

Insight into leaching of rare earth and aluminum from ion adsorption type rare earth ore: Adsorption and desorption

Clay minerals are inferred to be the primary host materials for ion-exchangeable rare earth in ion adsorption type rare earth ore(IAREO).During the rare earth leaching process,the adsorption and desorption reactions of the cations controlling the leaching process continue to occur at the clay minerals-leaching agent solution interface.In order to understand the leaching mechanism and behavior of rare earth and co-leached aluminum,adsorption,competitive adsorption,and desorption experiments were ...     

Kinetics of Dissolution of Tenorite in Ammonium Media

In this work, the dissolution kinetics of tenorite (CuO) in a NH₄OH-H₂O system was studied. The studied temperature range was 5–55°C, ammonium hydroxide concentration between 0.1 and 0.75 M, and a particle size range of 5–24 µm. The stirring speed, pH of the ammonia solution, and various agents were also studied. The results indicated that the leaching of tenorite occurred quickly with a particle size of 5 µm in a 0.45 M solution of NH₄OH for a pH value equal to 10.5. Dissolution of CuO also increases as temperature and the concentration of NH₄OH increase. For concentrations less than 0.10 M, there is almost no leaching tenorite. By decreasing the particle size, the dissolution of CuO increase. Results show the stirring speed had no significant effect on the leaching rate of tenorite for values above 250 rpm. Leaching kinetics was analyzed using the model of the surface chemical reaction. The reaction rate was of the order of 2.2 with respect to the concentration of ammonium hydroxide and inversely proportional to the initial particle size. Activation energy of 59 kJ/mol was estimated for the temperature range of 5–55°C.     

Improving the Estimation Accuracy of Copper Oxide Leaching in an Ammonia–Ammonium System Using RSM and GA-BPNN

In this study, a response surface methodology (RSM) model was used to analyze and optimize the factors affecting copper leaching efficiency in a copper oxide ammonia-ammonium (AA) system based on the parameters of AA concentration (ammonium hydroxide and ammonium bicarbonate matched with 1: 1), leaching time, grinding fineness, liquid-solid ratio, and temperature. The RSM analysis showed that five individual variables had a significant influence and that the interaction between AA concentration and leaching time had the most significant influence on leaching efficiency. In order to improve the estimation accuracy of the copper leaching efficiency, a model consisting of a genetic algorithm and a back propagation neural network (GA-BPNN) was used to optimize the operation index. A back propagation feed forward neural network with 3 layers (5–10–1) was applied to predict copper leaching efficiency. The genetic algorithm was applied to analyze the optimal leaching conditions. The results revealed that the GA-BPNN model outperformed the RSM model for predicting and optimizing copper oxide AA leaching. The optimization results of the GA-BPNN resulted in an R² of 0.99827 and the highest predicted copper leaching efficiency of 79.49% was obtained under the conditions of an AA concentration of 4.78 mol/L, a leaching time of 157 min, a grinding fineness of 86.86% (–74 μm content account), a liquid-solid ratio of 2.87: 1, and a temperature of 313.17 K. A prediction and optimization method combining RSM and GA-BPNN, as used in this paper, can be further employed as a reliable and accurate method for ore leaching.