Efficient removal of phosphate impurities in waste phosphogypsum for the production of cement

Highlights: • H₂C₂O₄ was used for the purification of PG. • H₂C₂O₄ is effective in removing intercrystalline impurities in PG. • PG purified by 1% H₂C₂O₄ can be re-utilized in the cement industry. Phosphogypsum (PG) is an industry solid waste produced from phosphoric acid manufacture. To reduce environmental pollution of the PG, H₂C₂O₄ was employed to purify it, which then can be used for cement production. The optimal concentration of H₂C₂O₄ for PG purification was determined. In addition, differential thermal analysis (DTA), X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence (XRF) were used to determine the removal of phosphate impurity in PG. The effects of purified PG on cement hydration and the environmental implications were also investigated. The results demonstrate that H₂C₂O₄ can remove the intercrystalline phosphate impurities by destroying the part of the crystal structure of gypsum. With the best treatment concentration of 1% H₂C₂O₄, 77.7% of phosphate impurity (as P₂O₅) was removed from PG, which subsequently shortened the final setting time down to 220 min and successfully met the national standard (GB 175-1999). Portland cement prepared by the 1% H₂C₂O₄ treated PG possessed a comparable 3d compressive strength of 20.8 MPa and a 28d compressive strength of 44.6 MPa. It is concluded that PG purified by 1% H₂C₂O₄ treatment can be used for cement production. Meanwhile, this H₂C₂O₄ treatment can effectively reduce the environmental pollution from PG and offer a sustainable method for the utilization of PG.