Thermodynamics and technology of extracting gold from low-grade gold ore in system of NH4Cl-NH3-H2O
(School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China
Received 13 May 2005; accepted 29 August 2005)
Received 13 May 2005; accepted 29 August 2005)
Abstract: 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.
Key words: gold; gold extraction; NH4Cl-NH3-H2O; hydrometallurgy; thermodynamics; ammonium chloride