Thomas, AD, Cowper Snr, NT & Whitton, S 2015, 'Recycling fine slurry – an alternative to paste for coarse rejects co-disposal in Queensland coal mines', in R Jewell & AB Fourie (eds), Proceedings of the 18th International Seminar on Paste and Thickened Tailings
, Australian Centre for Geomechanics, Perth, pp. 419-432.
Conventional co-disposal of coarse rejects (minus 50 mm) and fine thickener underflow tailings (minus
2 mm) is practised at a number of Queensland coal mines. The two streams are combined and pumped together to disposal. However, with the ratio of coarse rejects to tailings typically being about 70:30 on a dry mass basis, it is necessary to add large quantities of water to reduce the volume concentration of coarse rejects to an acceptable pumpable level. At the disposal site, the low concentration fines wash through the coarse rejects, forming a pond at the toe of the deposit. Water needs to be recovered from the pond and pumped back to the plant, and some water is lost through evaporation. The deposit also requires significant management with earthmoving equipment.
An alternative co-disposal system is described, in which no dilution water is required. By recycling some of the minus 2 mm thickener underflow in a recycle pipeline, the required reduction in volume concentration of rejects in the mixture is achieved without water dilution. With a thickener underflow concentration of 50% by weight (w/w), the total mixture concentration discharged to disposal is up to 75% w/w, and the discharged mixture is essentially homogeneous with minimal separation of fines. The emplacement can take the form of a cone-shaped deposit, thereby greatly reducing the earthworks required. The net effect is that total costs are about half of that required for the current co-disposal systems.
The 75% w/w concentration achieved by recycling fines is similar to the concentration likely to be delivered by proposed laminar flow paste pipeline systems, and is achieved with more reliable turbulent flow operation, avoiding the uncertainties associated with laminar flow.
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