The large number of stockpiles of phosphogypsum (PG), an abundant by-product during the process of producing phosphoric acid, is accompanied by many challenges owing to the toxicity of certain substances contained within PG. In this work, we investigate the transformation of PG into calcium carbonate (CaCO3) as an appropriate thermochemical energy storage (TCES) agent using the reversible reaction CaCO3 ↔ CaO+CO2. For the transformation of PG into CaCO3(1) and CaCO3(2), PG was reacted with Na2CO3 and K2CO3 in a proper aqueous medium, respectively. The composition and crystal structures of the resulting products have been confirmed by XRF and XRD to be highly pure (> 97%) with about 2% SiO2 in situ in CaCO3 obtained from PG. SEM-EDS analysis demonstrates that rhombohedra with homogeneous element distribution have been obtained successfully. STA tests in the temperature range from 550-800 °C within 10 decarbonation and carbonation cycles demonstrate the stability and reversibility of CO2 capture and release for both types of CaCO3 with CaCO3(1) having higher retention (>23% after 10 cycles) compared to CaCO3(2) (~19%). The above results confirm that CaCO3 obtained from PG, especially CaCO3(1), is a suitable choice for TCES.
Rmail et al. (Fri,) studied this question.
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