Ball milling modified phosphogypsum as active admixture: Milling kinetics and activation mechanism

Abstract

Mechanical ball milling significantly enhances the recovery rate and utilization efficiency of phosphogypsum (PPG). This study investigates the mechanical activation of PPG. Mechanical ball milling was conducted at a speed of 300 r/s for periods ranging from 30 to 120 min. The particle composition and structure of activated PPG were analyzed using laser particle size testing. The grinding kinetics mechanism was analyzed based on classification theory, and its chemical activity was characterized through activity index testing. Results indicate that after 30 min of grinding, the median particle size of PPG powder increases to 83.42 μm. The specific surface area reaches 5.2729 m²/g, and the morphology shows agglomeration, forming spherical structures of varying sizes. When grinding exceeds 60 min, the median particle size of PPG decreases to 32.45–37.88 μm. The spherical structures shatter and become irregular fragments. The Swebrec function and RRB are suited for describing the grinding kinetics of PPG in the initial (less than 60 min) and the later (more than 60 min) stage of grinding, respectively, and the fractal characteristic curve of PPG powder adheres to a linear fitting law. As curing time increases, the activity index of PPG cement mortar test blocks rises by 30.7–56.5 %. After 28 days of curing, the highest activity index value exceeds 75 %, meeting the requirements for S75 grade slag grinding particles according to the Chinese national standard GB/T 18046–2017.