Coal Preparation

Improved Flotation Recovery and Reduced Cost via Adjusting Frother Chemistry and Froth Behaviour

Coal Preparation » Fine Coal

Published: July 16Project Number: C23035

Get ReportAuthor: Liguang Wang, Hangil Park and Junyu Wang | The University of Queensland

This report provides detailed information on a cyclic frother with high flash point and its coal flotation performance, two frother concentration measuring techniques, and a froth diagnostic tool.

Coal flotation tests at laboratory scale using mechanically agitated cell and Jameson cell have been carried out to compare the performance of a cyclic frother, 4-methyl cyclohexane methanol (MCHM) with the industry standard frother MIBC. Pure MCHM, crude MCHM, and a MCHM-rich frother were tested. The flotation feed samples were collected from a coal preparation plant in central Queensland. It was found that the cyclic alcohol frother can match the coal flotation performance benchmark set by MIBC, at reduced cost and with less safety concern. MCHM is more surface active than MIBC and in the presence of 0.03 M NaCl, at a given concentration, MCHM gave better gas dispersion and more stable froth and foam than MIBC. Increasing salt concentration from 0.03 M to 0.5 M would increase the stability of coal-laden froth and particle-free foam and improve gas dispersion, obviating the necessity for adding frothers.

Two new methods to determine the concentration of frother in flotation cells and plant water circuits were developed and evaluated. One is based on the correlation between frother concentration and the lifetime and rupture thickness of a single horizontal foam film formed from the frother solution. This method was, however, limited to frother solutions at high salt concentrations (e.g. 0.5 M NaCl). The other frother analysis method was developed with using a formulated liquid. This method is fast, robust, and is immune to the variations in diesel, flocculant, and salt concentrations. Within the limited period of time, we managed to test only one type of liquid formulation, and the measuring accuracy of frother concentration was 0.9 ppm or better, depending on the concentration range of interest. Further work with other liquid formulations should improve the measuring accuracy so it has great potential for online frother analysis in coal preparation plants. This technique has attracted commercial interests from a few manufacturers and The University of Queensland has filed a patent application on it.

Two froth diagnostic tools have been developed and tested. One tool based on the air-recovery concept was brought to a site in Central Queensland. There was a stronger correlation between one of the outputs (that is, froth overflowing velocity x froth height over the lip / aeration rate) and flotation performance than between froth overflowing velocity and flotation performance. It is recommended that further on-site work over a longer period of time be carried out to corroborate this finding.


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