The problem of low-rank coal flotation continues to be a challenge due to the poor hydrophobicity and abundant oxygenated functional groups on particle surfaces. In this study, carrier flotation was used to improve the flotation performance of low-rank coal with polystyrene as a carrier material. Kerosene was used as a collector and played a role in the adhesion of fine low-rank coal to polystyrene due to its hydrophobic properties. The carrier feature of polystyrene was demonstrated by Turbiscan Lab Expert stability analysis and scanning electron microscopy analysis. The flotation experiments revealed that the optimum conditions were: collector dosage 5000 g/t, pulp concentration 40 g/L, and the ratio of low-rank coal to polystyrene 100:10. Under these conditions, the combustible recovery by carrier flotation was obtained as 70.59% when the ash content was 12.32%, which increased by 25.68 points compared with the combustible recovery of conventional flotation under almost the same ash content. The fine coal particles coated the coarse polystyrene particles through hydrophobic interactions between the polystyrene and hydrocarbon chains of the kerosene adsorbed on coal particles. The results suggested that the flotation performance of low-rank coal was significantly improved by carrier flotation with polystyrene, especially for fine particles.

Coal fly ash (CFA), hazardous to the environment and human health, has been considered to be a potential alternative source for rare earth elements (REEs) in recent years. However, information on how REEs distribute and occur in coal fly ash is still incomplete. In this work, particle size analysis, inductively coupled plasma–mass spectrometry, scanning electron microscopy, and electron probe microanalysis were applied to study the occurrence and distribution of REEs in a fly ash sample from the Qianxi coal-fired power plant in Guizhou province. The results show that the REEs content in the CFA was 630.51 ppm. Wet grinding-enhanced leaching experiments revealed that a part of the rare earth particles was encapsulated within the glass body. These rare earth particles could be liberated and released to a certain extent by wet grinding, which would increase the acid-leaching recovery of REEs from 23.49% to 41.68%. This study classifies the speciation of REEs in coal fly ash as (1) amorphous glassy particles with REE minerals or compounds encapsulated inside; (2) amorphous glassy particles with REEs distributed throughout; and (3) discrete REE minerals or compounds. The results of this study are a basis for developing an economically viable and environmentally sustainable technology for recovering REEs from CFA.

To solve the unwieldy problem of coal chemical wastewater reverse osmosis concentrate (ROC), a novel treatment method in which coking coal was used to adsorb the organic from ROC and the adsorption mechanism involved was investigated. The results showed that the organic components in the ROC of coal chemical industry can be effectively absorbed by the coking coal and the total organic carbon, UV₂₅₄ and chromaticity of treated ROC reduced by 70.18%, 70.15% and 59.55%, respectively, at the coking coal dosage of 80 g/L. The isothermal adsorption data were fitted to the Langmuir model well. The kinetics were expressed well by the quasi-second-order kinetic model. The intragranular diffusion model and the BET (Acronym for three scientists: Brunauer–Emmett–Teller) test showed that the adsorption occurred mainly on the surface of the coking coal and its macropores and mesopores. When the pollutants further diffused to the mesopores and micropores, the adsorption rate decreased. The result of X-ray photoelectron spectroscopy and fourier transform infrared spectroscopy spectra showed that the coking coal mainly adsorbed the nitrogen and oxygen species and the halogenated hydrocarbon organic compounds in the ROC. The chlorinated hydrocarbons and heterocyclic organics in ROC are adsorbed on the surface of coking coal.

How to improve coal flotation performance has been examined with a focus on the effect of particle size on flotation conditioning. A coking coal sample collected from the flotation feed of a coal preparation plant located in Lu’an, Shanxi province of China was investigated. The characters including mineral composition, size fraction, density fraction, and contact angle were analyzed. Classified and unclassified conditioning tests were carried out using different size fractions. The relationship between flotation indices (combustible recovery and flotation efficiency) and conditions (particle size, collector dosage, and conditioning stirring speed) was investigated. The results showed that the optimum conditions for different size fractions were different. The collector dosage and the conditioning stirring speed increased with the decrease of particle size. Meanwhile, the collision frequency between fine coal and diesel particles was much higher than the coarse particles, resulting most of the flotation agents adsorbed by fine particles, though the kinetic energy of coarse particles was higher. So a classified conditioning process was proposed. By conditioning optimizing, the flotation performance of classified conditioning was significantly improved compared with unclassified conditioning, especially for the +0.125 mm fractions.