Ultrafine coal flotation and dewatering: Selecting the surfactants of proper hydrophilic–lipophilic balance (HLB)

Fine and ultrafine coal (−200 µm) enrichment and its further dewatering processes are more difficult than that of coarser sizes. Utilization of this size fraction, however, is inevitable owing to economic and environmental enforcements. Chemical reagents are widely used in fine coal dewatering to achieve lower cake moistures. Surfactants of the same structures are also used effectively in coal flotation within preparation and coal washing processes. These surfactants contain hydrophilic and lipophilic groups, the ratio of which is known as hydrophilic–lipophilic balance (HLB). Flotation separation efficiency and dewatering performance of hard bituminous coal slimes as well as water recovery characteristics and related entrainment degree during the flotation were investigated using eight various nonionic surfactants of different HLB values. The main motivation of the study is to suggest proper reagent properties by which highest efficiency in both flotation and dewatering can be achieved. This can result in significant economic advantages for industrial processes and also reduce the environmental disadvantages of using chemicals. The flotation separation efficiency of the most lipophilic surfactants (lower HLB) and conventional oily collectors were found to be the highest, while the surfactants with moderate HLB (~10) showed the best filtration performance.