Leaching of calcium from phosphogypsum for carbon sequestration

Phosphogypsum (PG) is a waste by-product of the production of phosphoric acid from phosphate ores. Despite it being utilized already for building materials, most of the PG is left in stack and stored in large areas. Valorization of this industrial waste is being explored, including its use for carbon sequestration through indirect mineral carbonation. This process involves leaching a metal, usually Ca or Mg, from mineral wastes followed by the reaction of Caor Mg-rich leachate with CO2 to obtain stable and slightly soluble carbonates. PG samples were collected from a fertilizer production plant in the Philippines and was characterized through SEM-EDS, XRF, XRD, FTIR, and TGA. Philippine PG is mainly composed of Ca which may be leached out for use in mineral carbonation. Two leaching agents were investigated, namely NaCl and HCl. Using a response surface methodology, different factors such as leaching agent concentrations, contact time, temperature, and liquid-to-solid ratio were considered to optimize calcium extraction efficiency. Measuring the concentration of Ca in the leachate via atomic absorption spectroscopy (AAS), HCl is identified to have the highest extraction efficiency.