The beneficiation and utilization of coal fines-A case of Hwange Colliery Company.

Abstract

Fine coal waste management has been a great challenge in the coal mining industry as little attention is given to its management and the fines are dumped as heaps on open sites. The characteristics of the coal fines at Hwange Colliery Company were analysed through particle size distribution and proximate and elemental analysis. Approximately 80% of the coal fines passed through the 2mm sieve. The coal fines had an average gross calorific value of 17.43 MJ\kg which has notable potential for energy extraction. Elemental analysis uncovered traces of heavy metals such as Fe, Co, Ni, and Cu, a potential environmental hazard. The potential environmental implications were assessed through water and soil quality analysis which revealed generally low turbidity levels in groundwater with readings ranging from 0.34 to 0.55 NTU. However, elevated sulfite concentrations averaging from 113.68mg/l and traces of nickel of up to 0.07mg/l, warrant continuous monitoring to ensure compliance with safety standards. Soil analysis indicated the presence of heavy metals near coal fines dump sites with lead levels reaching up to 52.32 mg/l, nickel at 36.17mg/l, and copper at 53.70mg/l which impact soil enzyme activity and agricultural productivity. A cleaner production assessment was done to determine the best coal fines utilization options. A feasibility analysis was done using a literature review and brickmaking, pelletization and briquetting were chosen to undergo cost-benefit analysis. Briquetting showed greater profitmaking potential with a payback period of 13 months, a net present value of $1 771 493.18 and an internal rate of return of 90%. Further analysis was done to assess the practicality of briquetting and the binder and binding ratio. The briquettes were produced at varying coal fines and binder ratios using molasses and kaolin clay as binders. Physical strength analysis results show that the briquettes that were produced using 20% molasses were stronger therefore the optimum. The high heating value for the optimum was 21.59MJ/kg which shows the binder did not reduce the energy potential of the coal fines. Thermogravimetric analysis showed that the addition of the binder had no significant effect on the combustion patterns of the briquettes. Therefore, briquetting was proposed to be the best beneficiation and value-addition technique for the coal fines that are being produced at Hwange Colliery Company.