Mechanism of stearic acid adsorption to calcite

Abstract

This paper presents the interpretation of binding mechanism of stearic acid for calcite surface in two modification methods. In the "dry" method, a surface dissociation of stearic acid is assumed where H+ ion goes to a surface carbonate ion and stearic ion is chemisorbed on primary surface center of -Ca+ ion which is only available for chemisorption. The structure of adsorbed layer indicates chemisorption of stearate, but due to steric effects, and the oblique or gauche conformation of hydrocarbon chains. A part of surface -Ca+ centers can be blocked, which is explained by the result that physical adsorption dominates over 1.5%. In the "wet" method, by adding stearic acid, at concentration above the critical concentration of micelle formation in base solution, micelles are formed, and on the other side free stearic acid molecules or molecules from developed micelle dissociate. The resulting stearic ions can be chemisorbed on primary centers of -Ca+ ions or participate in ion exchange with OH- ions from secondary surface centers. With increasing adsorption density, the adsorbed ions and molecules, due to interactions of hydrocarbon chains, and thickness of double electrical layer, achieve a vertical orientation and keep the trans-conformation of hydrocarbon chains.