Effect of Ca²⁺, Mg²⁺ and SO₄^2- ions on the zeta potential of calcite and dolomite particles aged with stearic acid

We report a detailed investigation of the effects of Ca²⁺, Mg²⁺ and SO₄^2- ions on the zeta potential of calcite and dolomite particles aged with stearic acid. Suspended in deionized water, the native and aged calcite particles have negative zeta potentials while the dolomite particles have positive zeta potentials. Our studies using optical and atomic force microscopy clearly show rhombohedral shapes on cleaved calcite chips when contacted by deionized water. On dolomite chips, however, no clear rhombohedral shapes are found. Increasingly higher concentration of divalent Ca²⁺ and Mg²⁺ ions increased the original positive zeta potential of the aged dolomite particles and altered the zeta potential of the aged calcite from negative to positive. The SO₄^2- ions caused the original negative zeta potential of the aged calcite to be more negative and altered the zeta potential of the aged dolomite from positive to negative. Zeta potential measurements showed the affinity of Ca²⁺, Mg²⁺ and SO₄^2- ions is affected by the presence of other potential determining ions. The presence of Mg²⁺ ions significantly affects the ability of SO₄^2- ions to modify the original surface charges of aged calcite and aged dolomite while the presence of Ca²⁺ ions has less significant effect on the negative surface charges developed by SO₄^2- ions.