Homogeneous precipitation of mixed anhydrous Ca-Mg and Ba-Sr carbonates by enzyme-catalyzed reaction

A modified homogeneous precipitation process involving catalytic decomposition of urea by the enzyme urease was used to precipitate mixed Ca-Mg and Ba-Sr carbonate particles in a reacting solution of their salts at room temperature. The structure and morphology of the obtained precipitates were investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). There are distinct differences in the formation and the nature of these solids. It was found that magnesium ions were only slightly incorporated into the calcite structure, making low-magnesium calcite, while the presence of barium and strontium ions in the reacting solution resulted in the formation of equimolar solid solutions of Ba-Sr carbonate. However, the presence of magnesium ions in the reacting solution at early stages of the precipitation process governs the formation of nonaggregated and nanosized calcite particles characterized by high specific surface area (SSA). Finally, this study has proven the recently renewed mechanism in which some of carbonate colloids could be formed through aggregation of preformed nanosized crystalline particles.