Browsing by Subject "Calcite, zeta potential, surface charge, equilibration"

Surface charging behavior of commercial pure calcite and calcite samples from the Bukov underground research facility was studied by measuring the zeta potential of the samples after equilibration with CO2 gas and determining their cation exchange capacity. For zeta potential measurements, different calcite samples with grain sizes under 25 μm were submerged into five different electrolyte solutions: 0.01 M NaCl, 0.001 M CaCl2, 0.005 M NaCl + 0.0025 M MgCl2, 0.0025 M NaCl + 0.00375 M MgCl2, and a synthetic groundwater simulant (SGW2). A pH range of 6.5 – 11 was established and maintained across sample series for the duration of the experiments, and the samples were equilibrated with CO2 gas by regular bubbling of a 250 ppm CO2/N2 gas mixture into the solutions in 1-hour sessions. The length of the equilibration process varied from three days to one month, and after its conclusion the zeta potential of each sample was measured. The goal of the experiments was to evaluate the feasibility of equilibrating calcite samples with CO2 when studying their zeta potential. Additional goals included comparing different types of calcite in different solutions, as well as determining an optimal duration for equilibration. The results were compared with an earlier study where calcite zeta potential was determined under total CO2 exclusion. For the determination of cation exchange capacity, two cobalt hexamine trichloride solutions were used, one saturated with pure calcite and one saturated with Bukov calcite. Samples of both types of calcite were shaken for 1 hour in their respective solutions, and the ionic composition of the supernatant from each sample was determined using microwave plasma atomic emission spectrometry. Cation exchange capacity was calculated from the measurement results. According to the results obtained, long-term exposure and equilibration with CO2 may have a positive effect on the internal stability of calcite samples and lead to more reliable zeta potential measurements. Samples showed minimal fluctuation in the concentration of Ca in bulk solution after one week of equilibration, and no significant rise or decline in stability was noted to occur if equilibration was continued beyond one week. Compared to CO2 exclusion, equilibration produced more consistent trends in zeta potential values, though the results were heavily dependent on the electrolyte solution used in the experiment. Cation exchange capacity experiments also produced much larger values than the previous exclusion study despite using the same types of sample, hinting at a significant difference in the grain sizes used.