Study on the mechanism of influence of Ca²⁺ on fine coal flotation pulp conditioning

In order to pinpoint the mechanism of the influence of Ca²⁺ ion concentration in the slurry on the flotation pulp conditioning, three samples with different metamorphic grades collected from Linhuan Coal Preparation Plant were taken as the research objects to explore the influence of ion concentration on wetting force and deadhesion force between coal and oil-water solution, coal-collector contact angle, and adsorption rate of collector as well as the radial distribution of moleculars in coal-n-dodecane, coal-water and n-dodecane-water systems. The study was made by using the self-developed coal-collector-water interaction force measuring system, collector-coal contact angle checkout system, and ultraviolet spectrophotometry, and through molecular kinetic simulation. The results showed that with the increase of ion concentration, the wetting and desorption forces between coal and oil-water solution decreased, and the wetting degree of coal samples with the same volume increased within the same time; at the same time, as the ion concentration increased, the interfacial tension between oil and water decreased, the indirect contact angle between oil dropleted and coal flakes decreased, and the spreading degree of oil droplets on the surface of coal flakes increased. In addition, high ion concentration could weaken the intermolecular forces between coal and n-dodecane, reducing the peak radial distribution of n-dodecane on the coal surface. However, the interaction force between coal and water molecules would first increase and then decrease with the increase of ion concentration, which will comprehensively affect the adsorption effect between middling coal and n-dodecane during slurry mixing.