Abstract

BAZHKO, V.  and  YAHORAVA, V.. Evaluation of ozonation technology for gold recovery and cyanide management during processing of a double refractory gold ore. J. S. Afr. Inst. Min. Metall. [online]. 2017, vol.117, n.8, pp.749-756. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/2017/v117n8a4.

The depletion of conventional gold resources around the world has resulted in mining companies and research institutions exploring the recovery of gold from refractory and double refractory ores. However, conventional gold processing routes are not feasible for such deposits due to the low gold recoveries and higher reagent consumptions. A number of technologies have been developed to overcome refractoriness, one of which is ozonation. The unique chemical properties of ozone have been tested successfully on a laboratory scale for the pre-oxidation of refractory ores as well as for the detoxification of cyanide effluent streams. However, ozonation has never been implemented on a commercial scale due to the high capital and operating costs associated with ozone generation. Recent developments in ozone generation and contactor systems have revived interest in ozonation as a technology for the processing of refractory ores and the recycling and detoxification of cyanide streams. In order to demonstrate the viability of these new developments and to evaluate their impact on the entire cyanide management cycle, it is important to quantify the performance of ozonation technology on a double refractory ore. The effect of pH on sulphide, cyanide, and thiocyanate oxidation as well as the decomposition of the preg-robbing component was evaluated. Pre-oxidation of the material with ozone in an acidic medium (pH 1-2) resulted in the oxidation of sulphides and the liberation of gold. Partial destruction of the preg-robbing component was also observed. This resulted in increased gold recoveries during the subsequent cyanidation step. It was also established that ozone in an alkaline medium can oxidize more than 99% of CN^- and SCN^- within 30 minutes. Moreover, ozonation was found to be efficient for treatment of both filtrates and slurries. In an acidic medium (pH 2), 60% of the thiocyanate was converted to cyanide. This reaction can potentially be utilized for cyanide regeneration from thiocyanate formed during cyanidation of sulphide minerals. It is thus concluded that ozonation could be incorporated at different stages of gold processing in order to improve gold recovery, reduce operating costs by recycling cyanide, and minimize the environmental impact by efficient detoxification of the effluent streams.

Keywords : refractory gold; gold recovery; pre-oxidation; ozonation; cyanide detoxification.

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