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. (C) 2017 Elsevier B.V. All rights reserved.