The Fundamental Theory Study On Treating Pyrite Slag With Low Concentration Lixiviant Heap Leaching Method In NH₄Cl-NH₃-H₂O System

The novel processing of treating pyrite slag with low concentration lixiviant heap leaching in NH4Cl-NH3-H2O system (MACA) was proposed, due to the shortage of iron ore resources whileas huge amounts of pyrite slag, rich in Fe, Au and Cu valuable metals, stockpiled because of low grade of Fe and many harm impurities. The valuable metals can be recycled, effectively in this processing while the leaching residue can be used as iron smelting raw materials through roasting-mineral processing.The theory study of low concentration lixiviant heap leaching pyrite slag in NH4Cl-NH3-H2O system was carried out firstly.Thermodynamics of Au-NH4Cl-NH3-H2O system was studied based on mass balance and electric neutrality theories by controlling the potential of solution. The concentration of various ions were calculated when the concentration of ammonia and ammonium chloride changed. The results shows that it is thermodynamically feasible to recycle gold from pyrite slag by low concentration lixiviant heap leaching method in NH4Cl-NH3-H2O system. Thermodynamics of Cu(Ⅱ) complexes equilibrium was studied in the same way in CuS-NH4Cl-NH3-H2O system. It shows that leaching CuS in NH4Cl-NH3-H2O system is thermodynamically feasible and foresee a new way to treat sulphide ores.The leaching kinetics of copper in NH4Cl-NH3-H2O system was carried out. The effects of ammonium total concentration, pyrite slag particle size, stirring speed, and reaction temperature on the leaching rate of copper were investigated respectively. The results of kinetic analysis indicated that copper leaching process in pyrite slag follows the reaction zone model of lump ore. The activation energy was calculated as about 14.3kJ/mol and the reaction is controlled by internal diffusion through the ash layer. The macro-kinetics equation obtained can be expressed as 1-2/3α-(1-α)2/3=4.34×10-5C0.39do-2exp(-14300/RT).The flask experiment and column leaching experiment were tested in order to study the heap leaching process. The effects of lixiviant concentration, pyrite slag particle size were studied. On the reasonable conditions, the gold leaching rate achieved 60 percent in flask experiment and the concentration of gold complexes ions reached 0.45mg/L in column leaching experiment which is the process basis for treating pyrite slag using low concentration lixiviant heap leaching method in NH4Cl-NH3-H2O system.