Effect of maleic acid and pH on the preparation of α-calcium sulfate hemihydrate from phosphogypsum in Mg(NO3)2 solution

Phosphogypsum (PG) is a by-product of the wet-process phosphoric acid process, which causes serious environmental issues. In this work, PG was taken as raw material to prepare α-calcium sulfate hemihydrate (α-CSH) at atmospheric pressure using Mg(NO3)2 solution, an environmentally friendly chlorine-free salt solution. The crystallization water content and mechanical strength α-CSH were detected, meanwhile relationships between structure, morphology properties discussed deeply by DSC, XRD, SEM, FTIR XPS characterization techniques. results showed that with increase maleic (MA) concentration slurry pH, dehydration rate reduced, causing changing crystal from elongated prism short column. MA adsorbed on surface complexation carboxyl (COO) Ca atom, adjusting growth crystal. Well crystallized can be successfully prepared hydrothermal method in 25 wt% reaction time 6.0 h 95 °C, average aspect ratio 1.24. corresponding sample paste has 3d bending/compressive 8.9/36.8 MPa, displaying better than commercial product. This solution provides alternative technology for preparing controllable properties.