Mechanisms of surface charge modification of carbonates in aqueous electrolyte solutions

Derkani, Maryam H. and Fletcher, Ashleigh J. and Fedorov, Maxim and Abdallah, Wael and Sauerer, Bastian and Anderson, James and Zhang, Zhenyu J. (2019) Mechanisms of surface charge modification of carbonates in aqueous electrolyte solutions. Colloids and Interfaces, 3 (4). 62. ISSN 2504-5377 (

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The influence of different types of salts (NaCl, CaCl2, MgCl2, NaHCO3, and Na2SO4) on the surface characteristics of unconditioned calcite and dolomite particles, and conditioned with stearic acid, were investigated. This study used zeta potential measurements to gain fundamental understanding of physico-chemical mechanisms involved in surface charge modication of carbonate minerals in the presence of diluted brines. By increasing the salt concentration of divalent cationic salt solution (CaCl2 and MgCl2), zeta potential of calcite particles is altered, resulting in charge reversal from negative to positive, while dolomite particles maintained positive zeta potential. This is due to the adsorption of potential determining cations (Ca2+ and Mg2+), and consequent changes in the structure of the diuse layer, predominantly driven by coulombic interactions. While chemical adsorption of potential determining anions (HCO3- and SO42-), maintained negative zeta potential of carbonate surfaces and increased its magnitude up to 10 mM, before decreasing at higher salt concentrations. Physisorption of stearic acid molecules on the calcite and dolomite surfaces changes the zeta potential to more negative values in all solutions. It is argued that divalent cations (Ca2+ and Mg2+) would result in positive and neutral complexes with stearic acid molecules, which may result in strongly bound stearic acid film, whereas ions resulting in negative mineral surface charges (SO42- and HCO3-) will result in loosely bound stearic acid film to the carbonate mineral surfaces. The suggested mechanism for surface charge modication of carbonates, in the presence of different ions, is changes in diffuse layer structure as a result of ion adsorption to the crystal lattice by having a positive contribution to the disjoining pressures when changing electrolyte concentration. This work extends the current knowledge base for dynamic water injection design by determining the effect of salt concentration on surface electrostatics.