Since copper ions form a stable coordination compound in ammonia solution, Cu(NH 3 ) 2+ n , n = 1~4 , the solubility is large. An ammonium salt such as ammonium sulfate or ammonium hydrogencarbonate is added to the solution to buffer the pH of the solution and prevent the hydrolysis reaction of copper. As early as 1915 there have been mention of ammonia leaching of copper patents, industrial applications began in the 1920s.
Copper in basic carbonate minerals such as malachite and blue copper is easily dissolved in the ammonia solution by forming a complex:
CuC0 3 ·Cu ( OH ) 2 + 6NH 4 0H +( NH 4 )
It can be seen that sufficient ammonia concentration is ensured during the leaching to form a stable copper-ammonia complex. Although the temperature can increase the reaction rate, the partial pressure of ammonia is increased and the loss is increased. Therefore, it is preferred to select a moderate temperature. The chrysocolla can also be leached in an ammonia - ammonium salt solution. In the early days, these minerals were leached by lap filtration, and the recovery rate was about 80% .
The use of ammonia leaching to treat ore containing alkaline gangue reduces the acid consumed by acid leaching. However, if the mineral contains a mineral composed of an interlayer silicate such as montmorillonite, the sodium ion can exchange with copper ions to adsorb copper and cause loss.
Our Dongchuan Tangdan oxide copper deposit is a large, metal total reserves of 100 million t. Copper minerals are mainly malachite ( 55% ), porphyrite ( 20% ) and chrysocolla ( 11 %), chalcopyrite 5% and chalcopyrite 4% . Most of the copper minerals are embedded in the gangue with very fine particles, so the recovery rate of ore dressing is only about 70 %. The test shows that the ammonia leaching effect is good, the beneficiation of beneficiation and tailings, the total copper recovery rate can be close to 90% . The solution was leached with a solution of ammonia and ammonium carbonate at a concentration of 2 mol/L , and the effect of temperature on leaching was most significant.
references
   1. Chen Jiaxuan waits for the research and development of hydrometallurgy, Beijing: Metallurgical Industry Press, 1998 , 4~20
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