| China is not rich in copper. Based on the present available copper resources and its exploitation speed, China will be in serious short of copper by 2020. With the depletion of the-easy-to-process copper sulphide, attention has been directed to various copper oxides, which constitutes a very important part of china's copper resource and exists atop of most copper sulphide deposits.Xisa oxidized copper ore in Yunnan is a refractory oxidized copper ore due to its adverse characteristics, such as high calcium and magnesium contents, high oxidation, complex intergrowthing, limonite which tends to slime. Based on the analysis and careful comparison of the ore sample to other well-known copper ores, and the successful experience of ammonia leaching at Tangdan oxidized copper ore, an ultimately process named as " ammonia leaching—solvent extraction-electro winning" at normal temperature and pressure was proposed and tested, providing a bridge between research and future design. The test works included flotation, ammonia leaching and solvent extraction, and the main conclusions are:(1) Xisa copper ore is a refractory oxidized copper ore. The copper content is 1.65%, but 99% is in oxidized state. Copper sulfide is extremely low, which makes the ore to be a highly oxidized copper ore. Copper in integrated sulphide-oxide state is as high as 28.48%. Gangue minerals are mainly calcite and weathered limonite which tends to slime and contaminate bubble and mineral surfaces.(2) Flotation is not an achievable method for Xisa oxidized copper ore.The limonite, containing high clay minerals, caused the flotation impossible, even if various measures were taken to eliminate this interference and to enhance sulfide flotation performance. Both the copper recovery and grade were unacceptable low if only flotation was used.(3) Two-stage ammonia leaching is necessary to Xisa oxidized copper ore. At room temperature and atmospheric pressure, only the free copper oxide and limited integrated sulphide-oxide copper could be leached by a single leaching process. Basically, copper sulfide could not be leached under normal conditions. By optimization of the leaching conditions,6.54% extra copper could be leached out in the second leaching stage, increasing the total copper recovery from 52.04% to 58.58%.(4) Based on the characteristics of organic phase and recycled electrolyte, a two-stage extraction and one-stage back-extraction process was obtained using McCabe-Thiele isotherm method. The copper concentrations in various extraction and back-extraction processes were calculated, and a proper processing flow sheet was determined.(5) the loss of ammonia by volatilization during leaching and filtering operation was small, which was economically beneficial to the recycle of leaching solution and the reduction of ammonia makeup; washing operation before back-extraction guaranteed that only ammonia be washed out, but not copper, which facilitated the discharging of excess water as effluent and alleviated the expansion of water volume in the extractive system.The study has the following innovative points:(1) A two-stage ammonia leaching was proposed, which increased the leaching rate of the free copper oxide.(2) The ammonia contents in various products in the leaching, solvent extraction and washing stages were measured, presenting a clear picture about the volatilization loss of ammonia and water expansion. This ensured a precise control of water volume at various stages.(3) McCabe-Thiele isotherm method was applied to the calculation of extraction and back-extraction processes of copper from ammonia solution. According to this method, the real concentration of copper in each extraction stage could be accurately predicted, and the essential data needed to design the stage number of extraction and back-extraction could also be provided. |
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