Flocculation studies on high-ash coal slurry for improved clarification of water

The present paper is a part of the study done on settling of coal fines by flocculation to enhance the clarification efficiency, such that the process water could be recycled in coal washing circuits. In this study, flocculation performance results of the tests carried out using two polymer flocculants, namely Nalco-83370(+) and Magna-1011, varied at different pulp densities, flocculent dosages and pH conditions (at natural, acidic and alkaline) are compared. Further, using the settling test data, the settling rate and the critical settling time (CST) have been estimated graphically besides the per cent turbidity removal, for each of the tests. For the best test conditions, the kinetics of settling and the floc characterization studies were carried out. The maximum settling rate with minimum turbidity values could be possible at 2% solids concentration (w/w) of coal slurry with 8 gpt of flocculent dosage when tests were conducted using a Jar apparatus. Using Nalco-83370(+) flocculent, a maximum settling rate of 0.3222 cm/s with a turbidity reduction ratio of 99.02% (having residual turbidity 41.7 NTU) could be achieved, while the Magna-1011 flocculent gave a maximum settling rate of 0.4667 cm/s with 98.54% reduction in turbidity ratio (with 61.9 NTU) at a natural pH of 7.2. Hence, it is concluded in the paper that the best results were obtained with Magna-1011 in terms of settling rate and with Nalco-83370(+) in terms of turbidity removal when analysed within the range of parameters studied.