Impact of selenite, arsenate, and silicate oxyanions on the polymorphism and precipitation rate of calcium carbonate minerals in solutions with Mg2+ ions

Abstract

Abstract Selenic acid (Se(IV)), arsenic acid (As(V)), and silicic acid are widespread oxyanions in some Earth’s surface environments. To evaluate the effect of these oxyanions on the polymorphism and precipitation rate of calcium carbonate (CaCO3) minerals, precipitation experiments were performed in the systems containing these oxyanions by the batch method using 100 mL solution at 25 °C. Each solution contained 5.0 mmol/L Ca2+ and Mg2+, and 20.0 mmol/L HCO3− ions with 0.00, 0.01, 0.05, 0.1, 0.5, and 1.0 mmol/L of selenic, arsenic, or silicic acids. Additionally, adsorption experiments with the oxyanions on the surface of calcite and aragonite were conducted to evaluate the adsorption affinity for the surface of CaCO3 minerals. Results indicated that the oxyanions exhibited inhibition effect on the formation of aragonite resulting in the growth of calcite as a predominant polymorph with the decrease in the precipitation rate of CaCO3 minerals in the following order: selenic acid > arsenic acid > silicic acid. The adsorption experiments confirmed that the oxyanions showed higher adsorption affinity for the aragonite surface than the calcite surface in the following order: selenic acid > arsenic acid > silicic acid. This order of adsorption affinity is consistent with the effectiveness of oxyanions on the formation of CaCO3 minerals. Thus, the adsorption of oxyanions on the CaCO3 surface contributed to the inhibition of aragonite formation and to the decrease in overall precipitation rate of CaCO3 minerals depending on the degree of adsorption affinity of the oxyanions.