engleski

Homogeneous precipitation by enzyme-catalyzed reactions. 3. Mixed Ca-Mg and Ba-Sr carbonates

A modified homogeneous precipitation process involving catalytic decomposition of urea by 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 obtained precipitates were investigated using scanning electron microscope (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 in calcite structure, making low-magnesium calcite, while the presence of barium and strontium ions in reacting solution resulted in the formation of equimolar solid solution of Sr-Ba carbonate. However, the presence of magnesium ions in reacting solution at early stages of precipitation process governs the formation of non-aggregated and nanosize calcite particles characterized by high specific surface area (SSA). Finally, this study has proven the recently proposed mechanism in which some of carbonate colloids could be formed through aggregation of preformed nanosized crystalline particles.

enzyme; precipitation; urease; mixed anhydrous carbonates; nanoparticles

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