Kibali Gold Mine sulphide concentrate treatment – understanding the preoxidation of sulphide concentrates

ABSTRACT Kibali Gold Mine (KGM) processing plant treats both free milling and partially refractory ores. The flotation concentrate, is subjected to ultrafine grinding in 8 parallel FLS VXP 2500 ultrafine grinding (UFG) mills and undergoes a two stage preoxidation process at controlled pH of 10.2, prior to cyanidation. The primary objective of preoxidation is to reduce the reactivity of sulphide surfaces and thus reduce cyanide and oxygen demand downstream. Complex interactions amongst operational parameters of feed density, pH and dissolved oxygen concentration, complicates the circuit. This work demonstrates the impact of these interactions on gold dissolution and cyanide consumption. Aggressive preoxidation conditions have shown that the sulphide oxidation reactions not only increase temperatures but also generate cyanicides consistent with observed high cyanide consumption and poor dissolved oxygen concentration. From the extensive analysis of plant data and laboratory testwork, the plant has established and defined a niche operating domain for optimal preoxidation processes. This has been shown by the resultant drop in the sulphide concentrate residues from above 5 g/t at commissioning to below 3 g/t, currently achieved.