Piloting the MesoTHERM Flow Sheet to Demonstrate the Feasibility of a Biooxidation Circuit for Treatment of a Complex Copper-Gold Concentrate

Abstract

A continuous pilot plant campaign has been conducted over the 2021–2022 period to demonstrate the technical feasibility of Metso Outotec’s novel BIOX^® MesoTHERM process for treating high-grade copper-gold concentrates. The concentrate hosted refractory gold, as well as primary and secondary copper sulphide minerals. The pilot plant program was structured such that each hydrometallurgical unit operation in the envisioned full-scale plant flow sheet could be validated. Demonstration of the key features of the MesoTHERM technology which involved the series operation of the mesophile and thermophile biooxidation circuits in continuous mode spanned over a period of several months. The circuit configuration and performance proved that near-complete oxidation of all sulphide minerals was attainable, realizing not only high levels of copper solubilization but also liberating gold for recovery in a downstream cyanidation process. Another key component of the program involved a continuous copper solvent extraction – electrowinning pilot campaign to produce raffinate for recycling to the biooxidation circuits, i.e., to prove fresh acid requirements can be offset. Copper cathodes were also produced during the trial. Ancillary neutralization circuits, as well as solid-liquid separation stages, were investigated in continuous mode to further validate the processing circuits’ feasibility. From the pilot program, sufficient design data may be abstracted to support the engineering of a full-scale plant and allow process performance guarantees to be offered.