Stabilization of Amorphous Calcium Carbonate in Inorganic Silica-Rich Environments

Abstract

Temporal stability of amorphous calcium carbonate (ACC) has been affected in a deliberate manner in purely abiotic systems. The authors monitored the progress of calcium carbonate pptn. at high pH from solns. contg. different amts. of sodium silicate. Growing ACC particles provoked spontaneous polymn. of silica in their vicinity, which was probably caused by a local decrease of pH nearby the surface. This led to deposition of hydrated amorphous silica layers on the ACC grains, which arrested growth and altered the size of the particles. Depending on the silica concn., these skins had different thicknesses and exhibited distinct degrees of porosity, impeding to varying extents the dissoln. of ACC and energetically favored transformation to calcite. Under the given conditions, crystn. of calcium carbonate was slowed down over tunable periods or completely prevented on time scales of years, even when ACC coexisted side by side with calcite in soln.