Theoretical And Technological Study On Treating Low Grade Copper Oxide Ore In The System Of MACA

There is a large amount of low grade refractory copper oxide ore, of which the gangue is alkaline, exiting in our country. And Tang Dan copper ore is the most big and the typically one. It is very difficult to treat this kind of resoure with acidic lixiviants. In order to extract the copper from this kind of copper oxide ore, many hydrometallurgical processes or leaching-flotation combined processes with the ammonical solution as lixiviant are developed by the researchers. Though these research, it is became feasible to extract copper from the copper oxide ore of which the copper sulfides content is relatively high or the copper oxides content is relatively high but the bonded copper oxides is relatively low. However, because that the leaching rate is too low and the effect of flotation is also not very good, it is still very difficult to use the copper oxide ore of which the oxided rate is more than 90% and bonded rate is more than 30%. In this research, an attempt was made to solve this problem. The NH4Cl-NH3-H2O was used as the lixiviant in this research. The mechanical activating method and NH4HF2 activating method were proposed to strengthen the leaching process after the leaching thermodynamic and dynamic characteristic of the copper oxide ore in the NH4Cl-NH3-H2O solution is systemicly researched. LIX84-1 was used to extract copper from Cu-NH4Cl-NH3-H2O solution. The balance of extraction, ammonia co-extracting and stripping with H2SO4 was determined. The exploration test of directly electrowinning copper from Cu-NH3-Ethylenediamine-NH4Cl-H2O was also conducted in this research.Thermodynamic models were constructed based on both mass and charge balance. And the models were solved with exponential computation method. The dissolving characteristic, the stable area and condition converting to another phase of each phase were determined. The forecast by thermodynamic model was validated to be reliable by the X-ray diffraction patterns of the final solid, the equilibrium concentration of the copper and the equilibrium pH of each solid phases.It was found that the leaching speed and the final leaching rate of the sample was increasd by decreasing the particle size of the sample, increasing the ammonia and ammonium chloride concentration, rising the leaching temperature and liquid to solid rate. The leaching process could be described with the shrinking core model and diffusion through the'ash layer' was the controlling step. The activation energy was calculated to be 23.279kJ/mol. A semi-empirical equation as following was also fitted to describle the leaching process:The process minerolagical performance of the samples before and after leaching was investigated. The reason why the leaching rate of the sample was so difficult to be improved could be ascribed to the bad leaching characteristic of the enwrapped bonded copper oxide.The apparent activation energy of the samples activated for 15min and 30min was depressed from the unactivated 24.13kJ/mol to 15.40kJ/mol and 14.76kJ/mol, respectively. The leaching process was controlled by the diffusion step through the'ash layer'. The improving of the leaching effect was the co-contribution of increase of both surface area and imperfection content. The phase analysis of the samples shows the bonded copper oxide was greatly released after the mechanical activating. When leaching the sample under the optimal condition, the leaching rate was 6.35% higher than the agitation leaching test. It is means that the milling-leaching prosess have some activation effort but the effort is very limited.Thermodynamic calculation shown that the gangue components of Fe2O3, Al2O3, SiO2 encompassing the bonded copper oxdies could be dissolved partly in the NH3-NH4Cl-NH4HF2-H2O solution. The copper leaching rate was attained 89.85% and the NH4HF2 consumption was about 32.7-42.5kg per ton ore after leaching the sample under the optimal condition. The concentration of Fe, Al and Si in the leached out solution was evidently increased. When the concention of NH4HF2 in solution is 0 mol·L-1,0.1mol·L-1,0.3mol·L-1 and 0.5mol·L-1, the activation energy of leaching process was analysized to be 24.13kJ/mol,21.44 kJ/mol,32.68 kJ/mol and 33.51 kJ/mol, respectively.When using LIX84-1 to extract copper from the leached-out solution after leaching the ore with the solution containing NH4Cl 3mol/L, NH3 2.5mol/L, the extracting-washing-stipping condition was selected according to the equillibrium curves to be:extracting steps 2, extracting A/O 1:1; washing steps 1, washing A/O 5:1; stripping steps 2, stripping A/O 1:2. The whole extracting effect was more than 97% and the stripping solution could be used to electrowinning copper.The exploration tests of directly eletrowinning copper from Cu-NH3-Ethylenediamine-NH4Cl-H2O solution shown that the electricity efficiency and cell voltage was complicatedly inflounced by each operation parameter. It was very difficult to eletrowinning well plated copper when the concentration of copper was lower than 5g·L-1 unless the electricity density was low to 50～100A·m-2. Most of the electricity efficiency was lower than 80% due to the inflounce of Cu(Ⅰ). All these limit the usage of this technology in the industry.Though all of these theoretical and technological study, the reason why leaching rate of the copper oxide ore of which the oxided rate was more than 90% and bonded rate was more than 30% was so difficult to be improved was checked. Some processes are also proposed to solve that problem, which providing a direction for the future work.