PGM converter matte mineral characteristics and effects on downstream processing

The investigations revealed that the minerals and associated boundaries showed relatively different indentation hardness. The indentation-induced breakage of nickel sulfide, copper sulfide and NiCu-alloy structures appeared preferential and related to the iron end point. The softest mineral was found to be copper sulfide, which exhibited the average indentation hardness of 1975 and 2978 MPa within the low and high iron matte respectively. The increasingly harder minerals were nickel sulfide and NiCu-alloy in both low and high iron mattes with mean values around 5000 MPa. The laboratory batch grinding of the converter mattes at specific energy inputs resulted in product size distributions correlated to the underlying mineralogy. Although the trends for the breakage rates was found to be similar for both mattes, the matte with Fe content of 5.17% exhibited higher breakage rates in the specific energy ranges from 5 kWh/t to 25 kWh/t. This indicated that the matte with 5.17% Fe produces finer product than that of the 0.15% Fe matte at the same energy level. Moreover, a higher degree of overall liberation was achieved for copper sulfide and NiCu-alloy present within the high iron matte particles compared to particles within the low iron matte. 40% of particles within the high iron matte are completely liberated at 5 kWh/t specific energy, in contrast to about 20% within the low iron matte. However, Ni extraction achieved during leaching of minerals within the high iron matte was lower as opposed to minerals of the low iron matte. This was attributed to favorable Ni mineralization and chemistry of the low Fe matte which appears to be the most important driver for the downstream processing.