Coal Preparation » Fine Coal
ACARP Project C16044 investigated the use of eucalyptus oils as both frother and collector in coal flotation. The application of eucalyptus oils as reagents in froth flotation dates back to the beginning of the process itself. It was realised early on that natural oils are complex mixtures of many different organic constituents. Essential oils of eucalypts are composed predominantly of terpenes, compounds which contain a sequence of two or more isoprene units (C5H8) joined either head-to-head or head-to-tail. Monoterpenes (C10) and sesquiterpenes (C15) are the major classes of terpenes found in eucalyptus oils each of which can be divided into a number of sub-classes, varying across and within different species of the eucalypts.
Ten eucalyptus oil samples were analysed using gas chromatography and mass spectrometry techniques. The results showed they contain a wide range of closely related functional groups which might affect flotation. For each oil, surface activity was evaluated in a two-phase system using a froth column and a bubble sizer to estimate the dynamic foam stability index (DFI) and the critical coalescence concentration (CCC). On the basis of these parameters, it was shown that E. Citriodora oil was a promising frother.
Sequential laboratory flotation experiments were carried out using the tree-test on a Bowen Basin coal sample obtained from Peak Downs Mine. The Whiten equation was fitted to the experimental data to model the flotation response, allowing the frothing properties of the oils to be compared with MIBC. The flotation response curves were analysed using a new statistical methodology with the results confirming the characterisation work showing that E. Citriodora oil has good frothing properties, comparable with the industry standard frother MIBC.
Timed laboratory batch flotation tests carried out to evaluate collecting effect showed that eucalyptus oils generally give a higher ultimate recovery, but lower rate constants compared to the industry-standard collector, diesel. Eucalyptol and !-pinene were shown to be the most effective eucalyptus oil collectors.
The interaction between maceral species and the flotation reagents was evaluated using coal grain analysis (CGA). Flotation models are presented for different flotation products based on the microscopic characterisation of individual coal grains. The maceral and mineral abundance data demonstrate that MIBC floats vitrinite better than E. Citriodora oil, while their inertinite recovery is comparable. Eucalyptus oil collectors, compared to diesel, have better vitrinite recovery and higher inertinite loss to tailings.
The substantial experimental work described in this report was carried out by Mr Paul Botman as part of his MPhil research at the JKMRC, supervised by Dr Peter Holtham.