Phosphogypsum is an industrial byproduct that is limited in its high-value application due to the presence of dyeing impurities (such as organic matter and carbon black). The flotation method has been verified to be effective in separating these dyeing impurities from gypsum. In this study, microemulsion was used as the collector method of dyeing impurities for their separation from gypsum. The results of flotation tests showed that the microemulsion collector exhibited excellent collection capability and selectivity under natural pH conditions (pH = 1.5). With a microemulsion collector consumption of 400 g/t, purified gypsum of 65.1% whiteness, 95.74% yield, and 97.01% recovery was obtained. The purified gypsum of 65.1% whiteness, 95.74% yield, 97.01 recovery obtained by a used microemulsion collector amount of 400 g/t was better than using the same dosage of kerosene collector. The dispersion behavior of the microemulsion collector was studied by low-temperature transmission electron microscopy. The microemulsion collector demonstrated superior dispersibility, as it forms nano-oil droplets with an average size of 176.83 nm in the pulp, resolving issues associated with poor dispersibility observed in traditional kerosene collectors. Additionally, the nano-oil droplets effectively adsorbed onto the surface of dyeing impurities through hydrogen bonding, enhancing their hydrophobicity. Therefore, the microemulsion collector holds great potential for application in flotation whitening processes involving phosphogypsum.

Fine gangue contamination limits the flotation upgrading of coking coal middlings, yet the relative roles of water entrainment and slime coating remain unclear for different gangue minerals. This study investigated the contamination behaviors of quartz, kaolinite, and calcite through flotation tests, bubble-particle attachment measurements, zeta potential analysis, DLVO calculations, SEM-EDS observations, foam drainage and settling tests. Results showed that the addition of gangue minerals reduced combustible recovery, and the combustible recovery decreased from 91.68% for low-ash coal to 86.87%, 84.77%, and 82.55% for the coal–quartz, coal–kaolinite, and coal–calcite systems, respectively. Quartz exhibited limited coal–gangue association and a stronger tendency toward water entrainment, whereas calcite showed more pronounced surface attachment, consistent with slime-coating contamination. Kaolinite displayed intermediate behavior, with particle association that could not be fully explained by classical DLVO calculations. These findings demonstrated that gangue contamination depended on the combined effects of interfacial interactions, particle association, and water-mediated transport. The integrated approach provides a basis for identifying mineral-specific contamination tendencies and developing targeted strategies to improve flotation selectivity.