Use of Carbonatites in the Production of Precipitated Calcium Carbonate: A Case Study from Eppawala, Sri Lanka

Abstract

The study investigates the possibility of using carbonatite in the production of precipitated calcium carbonate (PCC). We made use of fresh apatite-rich carbonatites found at the phosphate mining sites at Eppawala, Sri Lanka. Analyses of the fresh carbonatite were performed with the aid of optical microscopy, powder X-ray diffraction (XRD), atomic absorption spectrophotometry (AAS), UV/visible spectrophotometry (UVVS), and thermo gravimetric analysis (TGA). Quicklime obtained from calcinations of carbonatites was used in synthesizing PCC via a lime-soda process. The end product was analyzed with XRD, TGA, AAS, and UVVS. Results revealed that the most common CO3 2− phase available in fresh carbonatites is calcite (>65%). The Ca-rich CO3 2− phase can be distinguished easily from other available minerals because its mode of occurrence in carbonatite matrix is different to that of other minerals. The results of TGA show that the decomposition of CO3 2− phase initiates at about 340°C, which leads to lower energy consumption during calcinations. Post-magmatic hydrothermal process may have been the cause of the formation of thermally unstable CO3 2− phases. Hydration of quicklime from the carbonatite yields much higher Ca2+ in the solution than from marble under the same experimental conditions. The synthesized PCC particles are in the calcite polymorphic form. The purity of PCC varies from 96 to 98 wt%. The maximum precipitable CaCO3 from 1 g of quicklime is about 1.1 g. Hence, fresh carbonatites has great economic potential for the production of PCC.