Facile preparation of high-strength α-CaSO 4 ·0.5H 2 O regulated by maleic acid from phosphogypsum: experimental and molecular dynamics simulation studies

Crystal modifier is a significant factor in preparation of α-hemihydrate gypsum (α-HH) from phosphogypsum (PG). The influence of maleic acid, reaction temperature, time, and solid–liquid ratio on the preparation of high-strength α-HH from PG was systematically studied herein. The optimum condition for α-HH prepared by hydrothermal autoclave method was pH of 4, temperature of 140 °C for 2.0 h with solid–liquid ratio of 4:5. Crystal modifier of maleic acid can effectively regulated the crystal morphology of α-HH. SEM–EDS and FTIR analysis suggested that maleic acid could preferentially absorbed on the top face of α-HH crystals that decreased the growth rate of α-HH along the c-axis, resulting in the morphology of α-HH crystals transformed to hexagonal prisms, and the regulatory mechanism was estimated by molecular dynamics (MD). When maleic acid (0.1%) was added, the obtained α-HH showed aspect ratio of 1.2, and the flexural and compressive strength of the hardened α-HH could reach to 14.79 and 46.24 MPa, respectively. All of these results will help to design long-term effectiveness of phosphogypsum recycling strategies.