Mineralization of calcium carbonate by controlled release of carbonate in aqueous solution

The generation of carbon dioxide from organic precursors in aqueous media in presence of calcium chloride and under conditions where calcium carbonate is formed was investigated. Photochemical decomposition of pyravic acid, 2-nitro-phenylacetic acid and 4-benzoylphenyl acetic acid gave ill-defined morphologies of calcium carbonate contaminated by organic by-products. Alkaline hydrolysis of dimethyl- and diethyl-carbonate yielded amorphous calcium carbonate in form nanospheres of narrow distribution of radii if the precipitation occurred under quiescent conditions. Addition of a polymer surfactant gave spherical particles as well, however consisting of vaterite. The formation of spherical particles of amorphous calcium carbonate is rationalized in terms of a liquid-liquid phase separation followed by rapid gelation of the droplet phase of high concentration of calcium carbonate. A lower critical solution temperature is postulated and its value was estimated as 10 degrees C. (c) 2005 Elsevier B.V All rights reserved.