Spreading behavior of dodecane-oleic acid collector mixture in low-rank coal flotation

Abstract

Spreading of water-insoluble collectors on the mineral surface is important in flotation. In this study, the spreading behavior of dodecane (D), oleic acid (OA), and dodecane-oleic acid (D-OA) mixture in low-rank coal flotation was investigated. The viscosity and oil/water interfacial tension was measured to calculate the spreading coefficient and speed. The relaxation of coal-oil–water contact angle and the movement of three- phase contact line during the collector droplet spreading process were interpreted using the molecular kinetic (MK) model. It was found that the order of absolute values of spreading coefficient were D-OA < OA < D, and the spreading speeds were in the order of OA < D-OA < D. D-OA had the smallest coal-oil–water contact angle and the longest contact line length. The addition of OA can enhance the interaction between D and the low-rank coal surface, but at the same time reduce the spreading speed. This was mainly because OA not only increased the spreading force of the droplet but also increased the spreading resistance. MK model fitting results showed that the length of molecular displacement increased in the order of D < D-OA < OA, indicating that the hydrophobic sites were more dense than hydrophilic ones on the coal surface and D-OA interacted with both sites simultaneously. The molecular substitution frequency and the free energy of wetting activation had an opposite order. High molecular substitution frequency meant fast-spreading velocity, and thus the MK model fitting parameters were consistent with the contact angle relaxation results.