The slow-cooling process : A mineralogical perspective

Amplats uses a matte slow-cooling process for the recovery of the platinum group metals. In this process, sulphide converter matte is cooled in 30 ton ingots for approximately four to five days. During slow cooling the platinum group elements (PGE) concentrate in a relatively small volume of magnetic Ni-Cu-Fe alloy. This alloy can be magnetically separated after milling, resulting in relatively fast recovery of the noble metals. To be able to optimize the process, an extensive investigation on the slow-cooling process was initiated in 1995. In this paper, a of the general features of a slow-cooled ingot will be presented. Information obtained is used to discuss a model for the slow-cooling process.