Evaluating floatability of platinum group minerals in Platreef ore

Automated mineralogical analysis of platinum group minerals (PGM), using the Mineral Liberation Analyzer (MLA), provides information used to understand flotation efficiency, primarily from a PGM liberation and association standpoint. To date, however, there is no consistent understanding regarding PGM speciation and its impact on floatability. Previous studies of PGM from UG2 ores concluded that a larger dataset is needed from which the various aspects for floatability can be modelled. Distribution and mode of occurrence of telluride, arsenide, sulfurarsenide and alloy species need to be integrated to fully understand the impact of PGM speciation on flotation, and for this, ores other than PGE-sulfide-rich UG2 must be assessed.

The Mineralogy Division developed a flotation predictor (Bushell, 2012) which predicts flotation performance using mineralogical information such as PGM grain size and liberation distribution as inputs to calculate PGM floatability. A shortcoming of the predictor is that the PGM are treated as one mineral group, i.e., no distinction is made on the flotation response of individual PGM species. Increasingly, however, it has become relevant to understand individual species in terms of their floatability, as this would make the predictor more accurate in its assessment of PGM recovery, as well as upgrading of PGM and their effect on grade.

In a recent study by Carelse et al. (2020), the flotation response was evaluated for individual liberated PGM species, by performing laboratory scale flotation rougher rate tests on feed samples, with different head grades, from two Platreef ores- a pyroxenite and a feldspathic pyroxenite. All rougher rate test products (5 rougher concentrates, RC1-5, and 1 rougher tails, RT) and the feeds were subjected to analysis using autoSEM to assess if PGM species show different flotation behavior by virtue of the concentrate streams and tails they report to. Grain size for the different liberated PGM species, as well as modal proportions of gangue minerals, were also taken into account.  

To discern how PGM species respond to flotation, only liberated PGM were considered for the two ores. From the liberated PGM, conclusions can be drawn on the floatability of the various PGM species for a given flotation regime since liberated PGM species can be directly linked to flotation response. In total 1529 liberated grains were studied from the two ores and their flotation products.

To determine which species upgrades in each of the concentrates, upgrade ratios were used (Figure 1). The upgrade ratio represents the number % of each PGM species in each product relative to the number % of each PGM species in the feed. Number % was used to eliminate the bias caused by large grains to the volume%. The most dominant liberated PGM species were used. Trends are relatively similar for all species except in RC3 for PdBiTe, RC4 for PtAs and PtS, and RC2 for PtBiTe. PdBiTe shows highest upgrade ratios for both ores into the first concentrates (RC1). PtBiTe shows the highest upgrade ratios for both ores into later concentrates (RC4) although significant upgrading occurs in RC2 for the pyroxenite ore as well. PtAs shows the highest upgrade ratios for both ores into the RT. PtS shows upgrading into later concentrates (RC4 and RC5) for the feldspathic pyroxenite ore although significant upgrading also occurs in RC2.

The preliminary findings suggest that properties of the species may play a role in floatability. Upgrade ratios of species such as PdBiTe and PtBiTe show maximum upgrading in the same given concentrate for both ores. PtAs also maximally upgraded into RC5, for both ores, when considering the concentrates only. The study has shown that focusing on liberated species only, can give valuable information on how different species float in an ‘optimised’ laboratory environment.

References

Bushell, C. (2012). The PGM flotation predictor: Predicting PGM ore flotation performance using results from automated mineralogy systems. Minerals Engineering, 36-38, 75-80.

Carelse, C., Chetty, D and Manuel, M. (2020). A preliminary evaluation of  liberated Platinum Group Minerals in Platreef Ore with respect to their floatability, IMPC Conference Proceedings, 2020.