Study on solidification mechanism of magnesium phosphate cement on heavy metals Cu2+

Magnesium phosphate cement (MPC) can be used in the fields of solidification of heavy metal ions in hazardous waste. Scholars at home and abroad had done a lot of research on the solidifying efficiency, mechanical properties and solidifying mechanism of MPC solidifying copper ion. However, it is difficult to analyze and study the early hydration of MPC due to its rapid condensation. In view of the problems in current research, MPC suspension and paste were selected to systematically study the pH value, conductivity, ion concentration, hydration heat release, leaching toxicity, mechanical properties of MPC solidifying Cu2+. The product evolution process of MPC solidifying Cu2+ and the occurrence mode of Cu2+ in MPC were studied. The results showed that Cu2+ delayed the hydration reaction of MPC, the total amount of hydration heat in MPC suspension decreased and the total amount of hydration heat in MPC paste increased gradually in the later stage. The products of MPC suspension solidifying Cu2+ included Mg0.95Cu0.05O, Mg0.90Cu0.10O and Cu4(PO4)2O. The products of MPC paste solidifying Cu2+ included Mg0.95Cu0.05O and solid solution Mg0.45Cu0.55KPO4·6 H2O. The properties of the products were stable. The solidifying methods of MPC to Cu2+ included adsorption, physical coating, ion exchange, chemical bonding and many ways of synergy. The efficient solidification of Cu2+ by MPC conformed to the concept of environmental sustainable development.