Characterization of the high temperature caustic conditioning process for optimized gold recovery from double refractory ores

Abstract

Preg-robbing gold ores reduce the gold recovered with conventional aqueous cyanide processing by adsorption of the leached gold onto the ore which is then lost to the residue.

Many ore constituents adsorb gold in the form of aurodicyanide, with carbonaceous materials typically, and not unexpectedly, the most troublesome. This problem is addressed by adding the activated carbon used to recover the aurodicyanide earlier in the circuit to reduce the concentration of gold in solution available for adsorption on the preg-robbing carbon. Nonetheless, significant gold is still lost to preg-robbing carbon materials. Metso Outotec South Africa developed the HiTeCC (High-Temperature Caustic Conditioning) process through which some of the preg-robbed gold may be recovered. This process entails desorbing gold under high-temperature caustic conditions and then competitively adsorbing the gold onto fresh activated carbon. The success achieved to date with the HiTeCC process to recover gold suggests that preg-robbing is reversible under HiTeCC conditions.

Developmental work has shown that not all preg-robbing ores are equally amenable to the process and the respective roles played by the caustic addition, temperature, and the activity and quantity of activated carbon are, not well understood. The aim with the present investigation was to resolve these issues by applying existing models for the adsorption and desorption of aurodicyanide on activated carbon and preg-robbing materials to the HiTeCC process. A simulation program was developed to support the evaluation of the potential and application of the HiTeCC process to extract additional gold from double refractory ores. As a result of this, the use of experimentally determined preg-robber sorption isotherms to predict preg-robbing behaviour has been demonstrated. The behaviour of preg-robbing adsorption has further been defined by comparing preg-robbing isotherms at varying temperature and adsorbate compositions.