关键词: 磷石膏, 原位淋溶, 无害化处理, 水泥缓凝剂, 抗压强度, 凝结时间

Abstract:

Phosphogypsum，as a by-product of the wet-process phosphoric acid industry，is limited in its application as a cement retarder due to the presence of soluble phosphorus and fluorine impurities.To address this issue，a modification method for stockpiled phosphogypsum based on an in-situ leaching process was proposed.Ca（OH）₂ and CaCO₃ solutions were used to carry out harmless treatment of phosphogypsum，and the modified phosphogypsum was then used to prepare cement.The physical properties of the hydrated cement samples were measured to systematically evaluate the impact of the modified phosphogypsum on cement performance.The experimental results showed that the soluble phosphorus and fluorine contents in phosphogypsum treated with Ca（OH）₂ were reduced to 0.03% and 0.08% respectively，meeting the first-grade index standards of "Phosphogypsum"（GB/T 23456—2018） and making it suitable for use in gypsum building materials.When it was used as a retarder and added to P·O42.5 cement，the standard consistency water requirement of the cement was reduced to 26.4%，the initial and final setting time were shortened to 314 min and 365 min respectively，and the 28 d compressive strength reached 50.2 MPa，meeting the requirements of "General Portland Cement"（GB 175—2023）.The compounding experiments showed that when the dosage of modified phosphogypsum was 5%，the comprehensive performance of the cement could meet the standard requirements，and the substitution rate of natural gypsum could be increased to 83%.This study verified the feasibility of the in-situ leaching process in the harmless treatment and resource utilization of phosphogypsum，providing technical support for alleviating the pressure of phosphogypsum stockpiling and promoting green production in the cement industry.

Key words: phosphogypsum, in-situ leaching, harmless treatment, cement retarder, compressive strength, setting time