Caco3 Polymorphs Production from Waste Materials: Phosphogypsum and Co2

The residue generated by the production of phosphoric acid is mainly CaSO4·2H2O, called phosphogypsum (PG), PG is often deposited in large rural areas or discharged into the sea forming a hazard to the environment and people living nearby. One way to recycle PG is to convert it to calcium hydroxide and sodium sulfate using NaOH solution and then the resulting suspension is bubbled with CO2 to obtain CaCO3. It has been reported in the literature that by lowering the pH during carbonation to a certain value, the process has been completed, reporting that the product obtained is CaCO3, and most researchers identify it as calcite, and that if the process continues at pH values lower than 7.0 the dissolution of CaCO3 is carried out. In this investigation, the results lead us to suppose that a specific pH value is not sufficient for such a statement, in addition to the fact that, together with calcite, and interesting amount of aragonite and vaterite is produced. An analysis of its chemical composition (XRF) was performed on the PG, and the solid materials produced during the process were characterized by thermogravimetric studies (DSC-TGA), the resulting by-products were characterized by scanning electron microscopy (SEM), quantitative analysis of their X-ray patterns and Fourier transform infrared spectroscopy (FTIR).