Thermodynamics and technology of extracting gold from low-grade gold ore in system of NH_4Cl-NH_3-H_2O

According to the principles of simultaneous chemical equilibrium and electronic charge neutrality, the thermodynamics of Au-NH4Cl-NH3-H2O system was studied by using the exponential computation method and through MATLAB programming, and the solid figure of potential-c(NH4Cl)-c(NH4OH) was drawn. The results show that when the sum concentration of Au+ and Au3+ is equal to 5×10-5 mol/L, φ(Au+/Au) is about -0.2 V; when the sum comes up to 0.5 mol/L, the value of φ(Au+/Au) increases to 0.2 V. In this case, φ(O2/OH - ) is as high as 0.7 V. This means that it is feasible to extract gold in this system. In addition, to predict the feasibility of reducing gold from the Au(I)-NH4Cl-NH3-H2O system with copper or zinc powder, the solid figures of potential-c(NH4Cl)-c(NH4OH) for both systems of Cu-NH4Cl-NH3-H2O and Zn-NH4Cl-NH3-H2O were also drawn. The results indicate that both copper and zinc powders can reduce Au+ into metal gold, and zinc powder can also reduce H2O into H2, while copper powder can not. The leaching results of a cuprous gold ore show that the extraction of gold can reach 80% in this system. The preliminary results of reduction with copper and zinc powders show that with deoxygenizing, the reduction effects are relatively good.

According to the principles of simultaneous chemical equilibrium and electronic charge neutrality, the thermodynamics of Au-NH4Cl-NH3-H2O system was studied by using the exponential computation method and through MATLAB programming, and the solid figure of potential-c（NH4Cl）-c（NH4OH） was drawn. The results show that when the sum concentration of Au^＋ and Au^3＋ is equal to 5× 10^-5 mol/L,ψ（Au^＋/Au） is about -0.2 V; when the sum comes up to 0.5 mol/L, the value of ψ（Au^＋/Au） increases to 0.2 V. In this case, ψ（O2/OH^-） is as high as 0.7 V. This means that it is feasible to extract gold in this system. In addition, to predict the feasibility of reducing gold from the Au（I）-NI-NH4Cl-NH3-H2O system with copper or zinc powder, the solid figures of potential-c（NH4Cl）-c（NH4OH） for both systems of Cu-NH4Cl-NH3-H2O and Zn-NH4Cl-NH3-H2O were also drawn. The results indicate that both copper and zinc powders can reduce Au^＋ into metal gold, and zinc powder can also reduce H2O into H2, while copper powder can not. The leaching results of a cuprous gold ore show that the extraction of gold can reach 80% in this system. The preliminary results of reduction with copper and zinc powders show that with deoxygenizing, the reduction effects are relatively good.