Quantitative analysis of calcium carbonate polymorphs by infrared spectroscopy

The assessment of the polymorphic composition of calcium carbonate precipitates is important for understanding the mechanism of their formation at conditions of environmental or technological interest. A simple and accurate method is presented, based on infrared spectroscopy, for the quantitative analysis of calcium carbonate polymorphs. Standard curves have been constructed from the spectra of binary mixtures of pure components. For calcite–aragonite mixtures, the content in aragonite has been obtained from the ratio of the areas under the peaks at 1080 and 876 cm–1. For the aragonite–vaterite mixtures the aragonite content has been taken from the ratio of the areas under the peaks at 1785 and 873 cm–1. The vaterite content in vaterite–calcite mixtures has been obtained from the ratio of the areas under 745 and 876 cm–1. Test mixtures made of pure synthetic components gave results in excellent agreement with their true composition. The minimum content of the polymorph detected was 25 %. The standard curves obtained have been used to estimate the content of three calcium carbonate polymorphs, in precipitates formed by spontaneous precipitation in calcium carbonate supersaturated solutions.