HYDRO 2014: Specifics of double refractory gold concentrates pressure oxidation in the presence of chlorides
A thermodynamic description of the equilibrium in liquid and gas phases under specific conditions of refractory gold pressure oxidation was generated using the HKF theory. The gold behavior was considered at 190–225°C in the presence of 1–100 mg/L of chloride ion, and under oxidation-reduction potential (ORP) of +700 to +1030 mV. The calculations show that the predominant form of gold(I) occurrence is [AuOH]⁰ compared to [AuCl₂]⁻. High ORP favors the formation of [AuCl₄]⁻ as a predominant form of gold(III). It is noted that this complex is responsible for the gold losses buildup during POX.
Laboratory test results for double refractory concentrate POX are shown. The combined negative effect of (i) organic carbon of the concentrate and (ii) dissolved chlorides in POX slurry on gold recovery is demonstrated. The effects of carbonate blending to the POX feed concentrate and incomplete oxidation of sulfides on POX performance were studied. The pilot tests results of continuous pressure oxidation are also shown and generally confirm the laboratory results and theoretic dependencies. A comparison of the experimental data with the results of thermodynamic calculations is made. As a result of current research, an effective process for POX treatment of carbonaceous sulfide concentrates in the presence of chlorides was developed.