Coal Preparation » Fine Coal
This project is aimed at the development of methods and equipment for the recovery of coal particles by flotation, focussing on sizes up to 1 mm, with possible extension to a top size of 2 mm.
The project is based on the idea that the best way to process a flotation feed containing a broad range of particle sizes, up to 2 mm top size for example, is to split the feed into size two fractions. The finer fraction goes to a flotation cell in the normal way, while the larger particles are suspended in clean washwater and distributed over the top of the froth in the flotation cell. A successful implementation requires the development of a simple and reliable way of distributing the coarse particles over the top of the froth.
The major benefit of the project is the ability to recover coarse coal particles of a minimum of 1 mm top size, by flotation, with the strong possibility based on results to date of being able to extend this top size to 2 mm. Gains to operating coal preparation plants will occur through:
- reduction in manning through a reduction in the complexity of circuits, by the elimination of spirals and other density-based separations for fine coal;
- increase in plant operating flexibility by extending the region of overlap between flotation and other separation methods such as cyclones and spirals;
- the recovery of coarse particles otherwise lost to tailings
- improvement of filtration and dewatering of coal flotation product, by extending the average particle size.
On a 0.3 tph closed-cycle pilot plant, it has been demonstrated that excellent yields for all size fractions up to 1.7 mm, with acceptably-low ash contents, can be obtained using the split-feed concept. The following table summarises the results for Run 7, for the entire feed size range 0 to 1.7 mm. The fraction in the range above 0.5 mm is 29.9 percent.
| Mass in range 0.5 - 1.7mm% | Feed ash% | Con ash% | Tails ash% | Mass yield% | Combustibles Yield% |
| 29.9 | 24.6 | 7.2 | 85.5 | 78 | 96 |
A new washwater distributor has been trialled for four months without any problems arising. Insufficient runs have been carried out for any firm recommendations to be made on any of the important variables, such as the size of split, the flotation conditions such as froth depth, air rate, solids loading on the froth.
Further work is needed in which the range of coals tested is extended, and different reagents tried, to examine the response of the larger particles. Scale-up, especially in relation to the distance of travel of the coarse particles to the overflow lip, is another important issue requiring further work. A larger scale pilot plant, suitable for transport to a mine site for in-plant testing, has been partially constructed. A further project has been approved, with funding from both ACARP and an ARC Industry Linkage Grant, to complete this investigation.