Coal Preparation » Fine Coal
The main goal of this project was to examine the effectiveness of using new generation reagents for maximising the recovery of product specification coal during coal flotation. Previous work had indicated that coarse-sized inertite, inertinite-rich and vitrinite-rich composite particles are poorly recovered in flotation columns such as Microcells and Jameson cells. Improved recovery of these components could boost the amount of saleable combustible material considerably. The use of targeted reagents for this purpose was seen as an attractive option as it required only minor modifications to the fines circuit.
The use of targeted reagents to improve the recovery of the difficult to float coal components was implemented in ACARP Project C16039. The flotation process analysis during the evaluation of the reagents as promoters was complemented by the use of the Coal Grain Analysis tool that enabled the flotation response of specific grain types, such as pure maceral components and composite grains to be determined. Remarkably high improvements in recovery were achieved by promoter reagents addition in laboratory and plant scale experiments. However, the flotation circuit of the plant where the tests were conducted was subsequently deemed to be operating at sub-optimal conditions at the time of testing. Hence there was uncertainty in the effectiveness and impact of the reagents determined from the data. This project is an extension of the previous ACARP Project C16039 with the aim of re-examining the effectiveness of this approach on plant scale against new benchmark operating regime.
The groups of reagents used were surfactants from the group of tri-block copolymers of polyethylene oxide (PEO) and polypropylene oxide (PPO) often denoted as PEO/PPO/PEO and commercially referred to as Pluronics. The reagents were added in small amounts as promoters to flotation feed slurry before the addition of a conventional collector. These reagents were found to significantly improve flotation recovery against the new benchmark operating conditions. Plant scale testing results showed significant improvements in recovery achieved for all components, especially for the coarse size fraction This improved recovery is accompanied by a small product quality (ash%) penalty.
The use of the Coal Grain Analysis tool allowed the selectivity of the reagents for specific coal grain types to be assessed. By this method it was determined that the recovery of each of the coal components is improved by the addition of the novel reagents, especially at the fine and coarse end of the size spectrum for the coal tested. The recoveries of the coarse composite grains were improved the most with the recoveries of vitrinite-rich, inertinite-rich and mineral-rich composite grains significantly improved. Although this has the potential to lead to elevated product ash value, the use of small amounts of Pluronics®L121 resulted in only marginally elevated product ash values.
A simple cost-benefit analysis showed that substantial additional resource recovery with an estimated value of about $8.8 M pa could be achieved from a flotation circuit treating 200 t/h feed that is otherwise lost to tailings.