Procedure to use phosphogypsum industrial waste for mineral CO2 sequestration

Highlights: ► Phosphogypsum wastes are proposed to reduce CO2 greenhouse gas emissions. ► Phosphogypsum dissolution with NaOH results in Ca(OH)2 precipitation and Na2SO4. ► Aqueous carbonation of Ca(OH)2 with CO2 results in the CaCO3 precipitation. ► Metals contained in the phosphogypsum are transferred to the final calcite. ► Applications of CaCO3 and Na2SiO4 by-products are proposed to improve viability. - Abstract: Industrial wet phosphoric acid production in Huelva (SW Spain) has led to the controversial stockpiling of waste phosphogypsum by-products, resulting in the release of significant quantities of toxic impurities in salt marshes in the Tinto river estuary. In the framework of the fight against global climate change and the effort to reduce carbon dioxide emissions, a simple and efficient procedure for CO2 mineral sequestration is presented in this work, using phosphogypsum waste as a calcium source. Our results demonstrate the high efficiency of portlandite precipitation by phosphogypsum dissolution using an alkaline soda solution. Carbonation experiments performed at ambient pressure and temperature resulted in total conversion of the portlandite into carbonate. The fate of trace elements present in the phosphogypsum waste was also investigated, and trace impurities were found to be completely transferred to the final calcite. We believe that the procedure proposed here should be considered not only as a solution for reducing old stockpiles of phosphogypsum wastes, but also for future phosphoric acid and other gypsum-producing industrial processes, resulting in more sustainable production.