Influence of the modification method on the surface adsorption of stearic acid by natural calcite

Abstract

In order to obtain hydrophobic materials, the surface of natural limestone with the high content of calcite was treated with different amounts (0.5, 1, 1.5, 2, 3 and 4 %) of stearic acid. Two methods were used for the modification: the solution and the dry coating methods. Using the solution method, it was suggested that at lower initial concentrations of stearic acid, the surfactant monomers initially sorbed forming a monolayer on the calcite surface, which then in the presence of excess surfactant develops into a bilayer configuration. When the dry coating method was applied, some form of bilayer existed on the calcite surface, even when the amount of stearic acid was low. The effect of surface modification by both methods was evaluated by the floating test, which represents the ratio of the floating product to the overall weight of the sample after mixing in water and stirring vigorously. This ratio is called the active ratio. Measurement of the active ratio showed that at the lowest surface coverage of calcite with stearic acid, the active ratio for the solution method was 65.5 % and 55.5 % for dry coating. Using the solution method, an active ratio over 99.9 % was achieved with 1.5 % stearic acid, while by dry coating, the same active ratio was obtained with 3 % stearic acid.