An investigation into the effects of UG2 Ore variability on froth flotation.
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Date
2013
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Abstract
South Africa is the world’s largest producer of platinum group elements (PGEs). Mining
takes place in the Bushveld Complex, and recent statistics, (Mudd, 2010), showed that the
UG2 reef is the main source of production, accounting for approximately 60% of world
mining production. However, recovery by flotation is complicated by variations in the
mineral composition, the need to grind fine and entrainment of chromite, which has an
adverse effect on the subsequent smelting of the concentrate. The recovery of PGEs is
variable, and it is influenced by PGE feed properties such as degree of liberation, mineral
type and grain size. Conventional rougher batch flotation tests on drill core samples do not
provide sufficient information for predicting plant performance.
The aim of this research was to develop a rigorous method for the testing of UG2 drill core
samples. A rougher-cleaner flotation test procedure was developed, and statistical tests were
applied to select an appropriate model, which included entrainment of hydrophilic minerals.
Fifty UG2 samples from across the Bushveld were milled at a fixed energy input, and the
new test procedure was applied to derive model parameters for all samples. There was a
significant variability in the PGE recovery, and typical feed characteristics such as PGE feed
grade and grind did not show a clear link to the PGE recovery. This was due to the complex
mineralogy of the PGE minerals and variations in ore hardness. Hence, a statistical modelling
algorithm was used to determine the factors affecting PGE recovery, and an empirical model
was developed, which relates the PGE recovery to feed properties. The model can be used to
estimate PGE recovery based on feed properties. Samples which had a high base metal
content (e.g. high nickel to iron ratio) had a high PGE recovery, and samples which were
altered (e.g. high Rb/Sr ratio and loss on ignition) had a low PGE recovery.
Depressant addition is used in PGE flotation to control the recovery of gangue, but it also
affects the flotation of composite PGE/gangue particles. Seven of the fifty UG2 samples were
selected for a more detailed investigation, using a more advanced batch flotation test and a
mineralogical liberation analysis. The advanced batch flotation test was a new development,
in which flotation model parameters were derived simultaneously for flotation after two
stages of grinding and a combined cleaning stage. The effect of a range of depressant
additions was also modelled. The floatable PGE fraction, determined from batch modelling,
was linked to the mineralogical liberation analysis of the feed. The model is the first of its
kind, and it makes it possible to predict the mineralogical characteristics of the feed from
flotation data.
A spread-sheet simulator was developed, to demonstrate how batch data (from the advanced
flotation test) could be used to predict plant performance. Scale-up parameters were derived
by using pilot-plant data for one of the ores. The spread-sheet was then used to optimise the
plant design and depressant addition for an ore, while constraining, the mass of concentrate
and the chromite content. The example showed that there was an optimum depressant
addition and rougher-cleaner volume capacity for an ore.
The gambit of this study was the linking of feed chemical assay and mineralogical properties
to PGE recovery. The application of mineralogical tests and modelling of data from the
advanced flotation test has demonstrated that the link is relatively complex.
Description
Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2013.
Keywords
Flotation., Ore-dressing., Mineral industries., Theses--Chemical engineering.