Influence of Neutralization on Hydration of Hemihydrate Phosphogypsum Plaster

Abstract

Effect of lime on hydration of hemihydrate phosphogypsum (HPG) plaster were investigated aiming at neutralizing HPG since it was obtained by calcining phosphgypsum without any purification. Results showed that neutralization would lead to retardation and strength degradation, particularly with small amounts of lime (0.1%-0.4%). As a result, the role of lime in HPG plaster can be described as 1) reacting with impurities in HPG and the reactant would affect the dissolution of HPG, gypsum nucleation and growth; 2) increasing ion concentration and supersaturation by excessive lime which can promote the hydration again. The gypsum crystal changed from needle-like to tiny crystal with little interlocking and then long prismatic crystal with comparable strength due to the mechanism of lime. Therefore, sufficient lime is needed for neutralization which is economic and beneficial for the application of HPG.