Study On Hydrometallurgical Thermodynamics Of Metal (Cu, Ni, Au) In The System Of Me-NH₄Cl-NH₃-H₂O And Heap Leaching Process Of Their Low-Grade Ores

This work takes up with solving the quite austere problem of the depletion of rich nonferrous metal minerals, which can restrict social development as well as economic construction of China. In this paper, a brand new heap leaching system, METAL-NH₄Cl-NH₃-H₂O (for short, MACA), is brought forward for treating low-grade complicated minerals resources of nonferrous metal, which is relatively abundant in our country. Other than those traditional processes in this field such as acid leaching, ammonia leaching or bacteria leaching, this new hydrometallurgical process is provided with many merits such as good selecting properties, low solvability of impurities, not hardening of the heap surface, as well as environmental amity. What's more, the application scope of the process is also very broad. It can be applied not only to treat simple oxide ores for extracting metals such as Au, Ag, Cu, Zn, Ni et al., but also can be used in treating complicated mixed ores of oxide and sulfide minerals with high content of gangue.On the aspect of theoretics, the hydrometallurgy thermodynamics of copper, nickel and gold in the system of MACA is studied relatively thoroughly. The thermodynamics involves in this paper can be compartmentalized into two type. One is the model establishment and calculation of the dissolvability of the metal oxide in NH₄Cl-NH₃-H₂O system, such as Cu(II)-NH₄Cl-NH₃-H₂O and Ni(II)- NH₄Cl-NH₃-H₂O, and the other is the the model establishment and calculation of the oxidation and reduction potential of metal sulfide or metal in NH₄Cl-NH₃-H₂O system, the former as Cu₅FeS₄-NH₄Cl-NH₃H₂O and NiS-NH₄Cl-NH₃-H₂O, the latter as Au-NH₄Cl-NH₃-H₂O, Zn-NH₄Cl-NH₃-H₂O and Cu-NH₄Cl-NH₃-H₂O. The study results show that 1) the dissolvability of metal oxide increases as the concentration of NH₄Cl and NH₃·H₂O were increasing; 2) the oxidation potential of metal sulfide and metal decreases firstly sharply then slowly as the concentration of NH₄Cl and NH₃·H₂O were increasing. What's more, the results of thermodynamics study also showed that after de-oxygenized, zinc or copper powder can reduce aurous into gold powder from MACA system.