Recent advances in effective collectors for enhancing the flotation of low rank/oxidized coals

Coal plays an important role in energy supply. However, low rank/oxidized coals are difficult to float with the common oily collectors, and hence effective collectors are urgently needed to be found or created. The difficult-to-float reason of low rank/oxidized coals primarily includes two aspects, i.e. abundant oxygen-containing groups on coal surface and porous surface of coal particle. The common oily collectors are difficult to adsorb on hydrophilic sites on low rank/oxidized coals surface and a porous structure of coal surface needs large consumption of collectors. This review is to highlight recent advances in the effective collectors for enhancing the flotation of low rank/oxidized coals, especially an overview of effective collectors proposed in the past decade. The effective collectors are achieved through the emulsion of common oily collectors, the mixture of several collectors/surfactants, the special collectors and bio-collectors. Throughout this review, the mechanism of the effective collectors enhancing the flotation of low rank/oxidized coals is discussed and the development directions of effective collectors in the future are also recommended. [Display omitted] •This review is to highlight recent advances in collectors for low rank coals.•As demand for energy supply increases, low rank/oxidized coals should be utilized.•Emulsion of oily collectors by surfactants benefits low rank coals.•Introducing oxygen-containing functional groups into oily collectors•Bio-collcetor may be a new way to solve low rank/oxidized coals flotation.