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Paste Thickening of Fine Coal Refuse

The coal industry is being subjected to increasing public scrutiny with regards to its effect on the environment and impact on public health and safety. Recently, disposal and storage of fine coal waste slurry has drawn considerable public attention. This article discusses the emerging paste thickening technology as a possible solution to the fine coal waste slurry disposal problem. Paste-thickening studies were conducted on thickener underflow slurry from a central Appalachia preparation plant. Initial experiments were conducted with a laboratory scale T-Floc apparatus to optimize flocculant dosages to obtain maximum settling flux and underflow solids concentration. Results showed that the addition of anionic flocculant (400 g/t) to the slurry followed by cationic flocculant (100 g/t) provided the highest settling flux (3.85 tonnes/hr/m2) and solids concentration (35% by weight). Pilot-scale paste thickening tests were conducted using a Dorr-Oliver Eimco Deepcone™ thickener. The thickener concentrated the solids from 10% to 50% by weight using about 450 g/t of anionic and 150 g/t of cationic flocculants. The thickened paste had a yield stress of about 165 Pa that is sufficiently low to allow transport using a conventional positive displacement pump to a disposal area. The clarity of the overflow stream was similar to that currently obtained with a conventional thickener.