Leaching of cuprite through NH4OH in basic systems

Cuprite is a difficult oxide to leach under acidic conditions (for the maximum extraction of 50%). In this research, the feasibility of leaching cuprite in an ammoniacal medium was studied. The working conditions addressed here were the liquid/solid ratio (120:1-400:1 mL/g), stirring speed (0-950 r/min), temperature (10-45 degrees C) and NH4OH concentration (0.05-0.15 mol/L). In addition, different ammoniacal reagents (NH4F and (NH4)(2) SO4) were analyzed. The experiments were performed in a 2 L reactor with a heating mantle and a condenser. The most important results were that the maximum leaching rate was obtained at pH 10.5, 0.10 mol/L NH4OH, 45 degrees C, 4 h, 850 r/min and a liquid/solid ratio of 400:1, reaching a copper extraction rate of 82%. This result was related to the non-precipitation of copper in solution by the formation of copper tetra-amine (Cu(NH3)(4)(2+)) . The liquid/solid ratio and stirring speed were essential for increasing the cuprite leaching. The maximum leaching rate was achieved at higher temperatures; however, significant copper leaching rate occurred at temperatures near the freezing point of water (17.9% over 4 h). Increasing NH4OH concentration and decreasing particle size increased the cuprite leaching rate. The two ammoniacal reagents (NH4F and (NH4)(2) SO4) had low extraction rate of copper compared with NH4OH. The kinetic model representing cuprite leaching was a chemical reaction on the surface. The order of the reaction with respect to the NH4OH concentration was 1.8, and it was inversely proportional to the radius of the ore particles. The calculated activation energy was 44.36 kJ/mol in the temperature range of 10-45 degrees C.