Exploring calcite Coprecipitation: Synthesis, Crystal Growth, and pH effect

Abstract

In this study, the synthesis and crystal growth of calcite (CaCO3) was examined with a focus on the coprecipitation and hydrothermal methods; additionally, crystal nucleation and growth was monitored under acidic and alkaline conditions. In the experiments, different Ca2+ solutions (pH 1.4 and 8.1) were mixed with Na2CO3 (pH 11.6), and the rates for the addition of the reactants were adjusted. Using an acidic Ca2+ solution as the calcium source and the rapid addition of carbonate, larger crystals were precipitated and grown in a single-step coprecipitation process. The fast addition of carbonate in an initially alkaline calcium solution produced intermediate crystal sizes. However, the slow dropwise addition of carbonate led to smaller crystals due to localized supersaturation and rapid nucleation. Coprecipitation followed by hydrothermal treatment produced larger crystals with the best-defined morphology. Structural and compositional analyses were conducted using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed the formation of calcite with different crystal sizes and provided insight into the controlled synthesis of CaCO3 crystals; our study has relevance for various industrial applications and for the investigation of natural sources.