Enhancement of floatability of low-rank coal using oxidized paraffin soap

The processing of low-rank coal is becoming more urgent with depletion of high-rank coal and severe environmental pollution in China. The flotation of low-rank coal suffers poor efficiency with hydrocarbon oils unless it is at a high dose. A representative non-polar oil, diesel oil (DO), was used as a collector to float a long-frame coal. The feasibility of oxidized paraffin soap (OPS) was explored to improve flotation performance. Experimental measurements (polarized optical microscopy, zeta potential, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, contact-angle analysis) were used to explore the influence of OPS in low-rank-coal flotation. Poor flotation performances of coal samples were received using OPS or DO as collectors at an economical dose. The flotation efficiency of coal samples was improved considerably upon addition of OPS plus DO. OPS reduced the surface tension of aqueous solutions and promoted dispersion of DO in suspensions. Addition of OPS plus DO reduced the absolute value of the zeta potential on coal particles. Moreover, OPS improved DO adsorption on low-rank coal particles, and the hydrophobicity of low-rank coal was improved visibly. OPS reduced the contact angles of coal-bubble and coal-DO in aqueous solution, which enhanced the adhesion probability of particles to bubbles. This study suggests that OPS is an effective surfactant for improving the floatability of low-rank coal.