Using emulsified and pre-dispersed hydrocarbon oil in waste coal reprocessing: A case study

Waste coal is a major environmental hazard produced in the traditional coal preparation unit operations. In this paper, a case study is presented for further scavenging the combustible matter in waste coal using flotation with a self-designed collector (Ksw) consisted of kerosene (K), span (S) and water. The said collector took advantage of both the emulsification and pre-dispersion technique so that the waste coal processability could be improved to a greater extent. Our flotation tests have shown comparable combustible matter recovery when using Ksw and emulsified kerosene (Ks), and both collectors significantly outperformed that of K. At 4 kg/t collector dosage, combustible matter recovery was at 54.9%, 64.9% and 65.3% for K, Ks and Ksw respectively. However, Ksw represented an economically superior option due to its specific composition features. The zeta potential measurements and interaction energy calculations have suggested that although there existed an electrostatic repulsion between the selected oil droplets and coal particles, flotation of waste coal was still feasible because of the hydrophobic force dominating the interaction process. Further, it was found that the interaction energy calculation results could not sufficiently account for the superior flotation performance of using Ksw as collector. Dynamic light scattering (DLS) measurement has shown that the other key instruments at play were the diameter and number of the oil droplets. At 400 mg/L collector suspensions, emulsification reduced the effective diameters of K from 4.23 to 1.62 μm (Ks), and further decreasing to 1.12 μm (Ksw) when dispersion was imposed. The outcomes of this work have suggested Ksw as an economically and technically superior reagent over the conventional hydrocarbon oil collectors for waste coal reprocessing.