Magnesian calcite synthesis from calcium bicarbonate solution containing magnesium ions in the presence of fluoride and phosphate ions.

Abstract

Magnesian calcites were precipitated from 10 mM Ca(HCO3)2 (Ca 2+, 400 mg/1) solutions contain ing 35 or 53.5 mM Mg ions (Mg2+, 850 or 1300 mg/1) in the presence of fluoride and phosphate ions in various concentrations. Magnesian calcite formation from aqueous solution was favored by the presence of fluoride ions (0.5 to 2.5 mM) or phosphate ions (0.025 to 0.5 mM) in a parent solution. Aragonite and/or monohydrocalcite are formed below or above the critical concentrations of these ions. The presence of phosphate or fluoride ions in a solution inhibits adsorption of Mg2+ ions on calcite surface, which may cause the magnesian calcite formation.

A novel phosphorylated glycoprotein in the shell matrix of the oyster Crassostrea nippona

“…This notion is supported by the fact that phosphate content in the foliated layer far exceeds that in the aragonitic shell layers [20]. One study identified phosphate as favorably controlling calcite formation when added to the calcium carbonate solution in trace amounts [39]. The precise effect of phosphate in polymorphism control awaits future study.…”