Optical analysis of particle size and chromite liberation from pulp samples of a UG2 ore regrinding circuit

Since the early seventies high chromite and low base metal sulphide (BMS) contents of the UG2 reef
imposes technological challenges to mineral processors and extractive metallurgists. Forty years later,
particle size distribution and size by size mineralogy are considered as key factors to the continuous
improvement of the UG-2 ore metallurgy. With the successful development of ultra fine grinding technologies,
a compromise has to be found between fine grinding to achieve platinum group minerals liberation
and to avoid the overgrinding of gangue minerals, especially chromite gangue which is detrimental in
smelting process. Indeed, fine chromite grains, despite of being naturally hydrophobic mineral, can be
recovered in flotation concentrate by entrainment. In addition, overgrinding also increase liberation of
naturally floatable gangue (talc) which contaminate the concentrate and need to be controlled during flotation.
In this paper, innovative techniques of single particle image analysis from both dry and wet samples
have been tentatively used to assess the chromite particle size distribution and the chromite grade of
samples taken from a secondary milling circuit. Preliminary results demonstrate excellent potential for
online particle imaging making use of both the particle geometry (size, shape) and the optical properties
(translucency).