Abstract: A low-grade copper oxide ore with highly alkaline was treated. According to the characteristics of the solution with the high content of calcium and magnesium， ammonia-ammonium sulfate leaching system was adopted to conduct leaching experiment for recovering copper from a low-grade oxidized copper ore. The thermodynamic model of Cu₂(OH)₂CO₃-(NH₄)₂SO₄-NH₃-H₂O was established in the leaching system of malachite (Cu₂(OH)₂CO₃) under the condition of double conservation of mass and charge. The fitting function of the Matlab software and the diff and solve functions were used to calculate the optimal ammonia concentration and total copper ion concentration of malachite under different ammonium sulfate concentrations， respectively. Parameters， such as ammonia concentration， ammonia-ammonium ratio and liquid-solid ratio were optimized. The results indicate that the appropriate conditions include an ammonia concentration of 1.2mol/L， an ammonia-ammonium ratio of 2∶1 and a liquid-solid ratio of 3∶1. Under these conditions， the copper leaching rate reaches ~70%. The calculated results are basically consistent with the experimental measurements.

Key words: ammonia leaching; ammonia ammonium ratio; thermodynamic;(NH₄)₂SO₄-NH₃-H₂O system; high-alkaline gangue low grade copper oxide