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Comparative study of CTAB adsorption on bituminous coal and clay mineral

Adsorption of cetyltrimethylammonium bromide (CTAB) onto bituminous coal (BC) and a clay mineral, montmorillonite (MMT), was studied. Simultaneous measurements of the CTAB adsorption and zeta potential determination of the adsorption suspensions were carried out. The adsorption isotherms were found to be of the typical Langmuir type; values of the CTAB adsorption capacities were calculated (am = 0.65 mmol g−1 for coal and am = 3.24 mmol g−1 for MMT). The shape of the adsorption isotherms was correlated with zeta potential values at the adsorption equilibrium. The adsorption properties of both sorbents were studied by voltammetry on carbon paste electrodes (CPE) modified with coal-CTAB and MMT-CTAB system, respectively. Open circuit sorption with differential pulse voltammetry was performed in order to compare the sorption properties of the systems with the unmodified sorbents. The Cu2+ adsorption on BC and MMT decreased to approximately 50 % and 40 %, respectively. The surface adsorption mechanism of CTAB on coal based on hydrophilic interactions was proposed. In the case of montmorillonite, the CTAB intercalation is expected via ion exchange into the inter-layer space forming a double- or triple-layer arrangement.