The adsorption and orientation of frother surfactants on heterogeneous wetting surfaces

Abstract

Despite the existence of heterogeneous wetting surfaces, studies on the adsorption of surfactants on such complex surfaces are limited. In this study, coal was chosen to prepare heterogeneous surfaces with both hydrophobic and hydrophilic constituents. To quantify the surface heterogeneity of coal, hydrophobic index (HI) was proposed and defined as the ratio of the atomic percentage of un-oxidised carbon to the atomic percentage of oxidised carbon. The adsorption of two frother surfactants, Methyl Isobutyl Carbinol (MIBC) and Dowfrother 250 (DF250) which are widely used in coal flotation, on the surfaces of coal with different HIs was studied. Adsorption isotherms and bubble attachment time measurements revealed that MIBC and DF250 could adsorb on the surfaces of coal, driven by hydrophobic interactions on hydrophobic sites and hydrophilic interactions on hydrophilic sites simultaneously with the former adsorption mechanism predominating. The former adsorption mechanism generated head-out adsorption of MIBC and DF250 without changing the surface hydrophobicity, but the latter adsorption mechanism gave rise to head-on adsorption of MIBC and DF250 resulting in an increase in hydrophobicity on the surface of coal with a low HI. Due to different structures, MIBC and DF250 exhibited different adsorption and orientation on the surfaces of coal.