Characterizing the behaviour of platinum group minerals in a grinding circuit

•Method to determine gravity-recoverable platinum group minerals (GRPGM) introduced.•Cyclone partition curves show PGMs shifted to finer size than the total solids.•Cumulative rate of breakage identifies size reduction of PGMs relative to total solids.•Build up of PGMs in the circulating load and GRPGM ca. 80% offers opportunity for gravity recovery. This paper introduces a methodology to determine the gravity-recoverable platinum group minerals (GRPGMs) of a stream, and behaviour of platinum group minerals (PGMs) in a ball mill-cyclone circuit. The GRPGM is determined by a modification of the method developed for gravity-recoverable gold (GRG). Mineral behaviour in the circuit employs element and GRPGM cyclone partition curves and cumulative element selection functions. The methodology is illustrated on the grinding circuit at Vale’s Clarabelle mill (Sudbury, Canada). As an example, GRPGM for platinum (Pt) in the ball mill-cyclone circulating load was about 80%. The cumulative selection functions of Pt and palladium (Pd) were ca. 1.3 times higher than the solids for size fractions above 212 μm, which moderated their buildup in the closed circuit, but were ca. 60% that of the solids below 212 μm which contributed to buildup of these sizes. The partition curves showed more than 90% of the Pt and Pd above ca 50 μm reported to the cyclone underflow. The buildup of PGMs in the circulating load and the high GRPGM offers an opportunity for gravity recovery.