Calcium Carbonate: Polymorph Stabilization in the Presence of Inhibitors
Calcium carbonate is a common scale component in water-intensive processes primarily because of the inverse solubility of this salt [1-3]. The relatively high calcium and carbonate concentration levels in natural waters result from the composition of geological formations with the aquifer . The calcium carbonate scaling problem depends not only on the solution composition (pH, calcium, and carbonate concentrations), but also on the crystal morphology of the precipitated phase. The polymorphism of the calcium carbonate system is responsible for the formation of particles of various shapes and sizes [4-6]. Some crystal shapes will pack together and form tenaciously adhering scale deposits, whereas others can be readily swept away in the stream of salt solution in contact with the surface . Depending on the experimental conditions and/or on the presence of foreign compounds or metal ions in the aqueous medium in which scale deposits are formed, three calcium carbonate polymorphs may be formed: calcite, aragonite, and vaterite . The formation of amorphous calcium carbonate has been reported [9,10] in addition to the two hydrate forms of calcium carbonate: monohydrate or monohydrocalcite and hexahydrate or ikaite [11,12].