Coal Preparation » Fine Coal
In the Australian coal industry, flotation is used in the final stage of coal preparation, to recover fine particles with a typical top size of 0.25 mm. Particles of screen sizes between 2 mm and 0.25 mm are usually treated using gravity separators such as spirals, teeter-bed separators, or reflux classifiers. It would be advantageous to be able to treat particles in the size range 0 to 2 mm in a single operation, doing away with the spirals and teeter beds etc. In an earlier project, C25021 Coarse particle flotation for the plant of the future, a new flotation cell known as the NovaCell was used to treat a NSW coal of top size 2 mm. The NovaCell uses a gentle fluidized bed zone to capture the coarser particles and a high-shear zone to collect the very fine particles.
In this project, the upper size limit was raised to 4 mm. Experiments were conducted on a sample of unprocessed Queensland run-of-mine coal (ROM) whose top size was 75 mm. The ROM material was screened to remove a sample for flotation, with a top size of 4 mm, and 16% ash. This fraction was tested batchwise in a laboratory NovaCell, with conventional reagents. The size-by-size performance was analysed, for 12 size fractions, for the feed, the two product streams and the residues. Overall, the yield was 70%, with a product ash of 7% and combustibles recovery of 77%. This report describes the test procedure and the results.
The implications for circuit design in coal preparation plants were examined and suggestions are made relating to the introduction of NovaCells into the fine particle circuit in existing plants. Where the feed to the fines section already passes through a 2 mm screen, the undersize can go straight to NovaCell flotation, replacing the suite of existing separation devices, giving a high yield and low ash product.