Effect of succinic acid on the preparation of α-HH and its hydration properties.

• The differences of diffraction intensity of different crystal planes indicated the regulating action of succinic acid. • The connection between the hydration properties and crystal morphology characteristics of α-HH was established. • Preparation of α-HH from phosphogypsum is a way to realize effective utilization of phosphogypsum. Using phosphogypsum (PG), a solid waste from the phosphoric acid industry, to prepare α-hemihydrate gypsum (α-HH) with cementitious properties is an effective approach to realize the extensive utilization of PG. In this study, succinic acid (SA) was used as a crystal modifier to prepare α-HH at a reaction temperature of 130 °C and a stirring speed of 300 rpm. The phase composition and hydration properties of the prepared products and the mechanism of action of SA were investigated. Results indicated that SA had an excellent morphological control on α-HH crystals prepared under hydrothermal conditions. With an increase in the concentration of SA, α-HH crystal shape transformed from long needle-like to shortly columnar, which was caused by the physical adsorption of SA on the crystal surface changed the growth rate of crystals in different directions. The hα-HH crystals prepared at a concentration of 4 mM with SA are short columnar with an aspect ratio of 2.32 and a compressive strength of 24.7 MPa. Furthermore, the hydration processes were determined by the joint contribution of water requirement and SA concentration, and SA was used not only as a crystal modifier but also as a retarder in the hydration process of α-HH. [ABSTRACT FROM AUTHOR]