Effect of Zn2+ on the early hydration behavior of potassium phosphate based magnesium phosphate cement

Magnesium phosphate cements (MPC) have potential applications in the solidification/stabilization of heavy metals. In this paper, the effect of Zn ions on the early hydration behavior of magnesium phosphate cement was investigated. The results showed that the physico-chemical characteristics of the MPC were significantly influenced by Zn ions. The addition of Zn ions increased the final setting time of the MPC and decreased the compressive strength of the MPC. The effect of Zn ions on the hydration characteristics of the MPC was examined by pH, heat of hydration, XRD, SEM and EDS. It is observed that the zinc ions have no effect on the phases of the hydration products of the MPC, but the crystalline degree of the product is influenced by the zinc ions. Furthermore, in the early hydration reaction process of magnesium phosphate cement, addition of Zn ions slows down the increasing of the pH and delays the hydration exothermic peak of the MPC. Most zinc ions are exited in hydration products. The result of the TCLP of the zinc ions showed that the leaching toxicity of the zinc ions is lower than the standard requirement.