Study on mechanism of non-ionic compound collector for enhancing flotation of long flame coal

Compound collectors containing non-ionic surfactants have proven to be effective in low rank coal slime flotation but flotation performance often differs distinctly due to the presence of different non-ionic surfactants. In this paper,batch flotation tests were conducted using long-flame coal slime with the presence of kerosene composited with ODEA,OP-4,and Span80,respectively. Reagent dispersion tests,contact angle tests,X-ray photoelectron spectroscopy analysis and molecular dynamics simulation were used to interpret the mechanism underpinning the surfactant effect. Results show that all the compound collectors showed better collectivity and selectivity than kerosene,and improved the overall flotation performance. Kerosene+OP-4 and kerosene+ODEA had similar effects on flotation,while Kerosene+Span80 outperformed the other two compound collectors and kerosene. The mechanism analysis shows that all the nonionic surfactants improved the hydrophobicity of long flame coal particles,but the degree of hydrophobicity enhancement varied with surfactant type,mainly determined by the ability of the surfactant to cover the hydrophilic sites of the coal particle as well as to emulsify and disperse hydrocarbon oil. Due to hydrogen bonding,polar groups of Span80 molecules could effectively cover the hydrophilic sites of coal surface with its hydrophobic end pointing to the water phase,which greatly increased the surface hydrophobicity of coal particles. In comparison,ODEA molecules was not so good as Span80 but outperformed OP-4. Meanwhile,in the presence of the nonionic surfactants,the size of kerosene droplets decreased,and the measured chord length mainly fell between 50 and 150 μm. Compared to kerosene+OP-4 and kerosene+ODEA,the number of droplets was much greater in the system with kerosene+Span80,which favored the flotation by increasing the contact time and contact area with the coal. Interestingly,a greater capacity of OP-4 for emulsion and dispersion of hydrocarbon oils compensates for the poorer coverage of hydrophilic sites on the coal surface to some extent,which resulted in similar flotation test results using kerosene+OP-4 and kerosene+ODEA as observed.