Effect of Cd~(2+) on early hydration process of magnesium phosphate cement and its leaching toxicity properties

摘要

Cadmium pollution is a type of heavy-metal pollution that is harmful to human health and the environment. Magnesium phosphate cement (MPC) is a fast-setting material with rapid strength development that can solidify and stabilize pollutants quickly. Hence, it has excellent potential for the stabilization/solidification of cadmium pollutants and the rapid reduction of the environmental toxicity of cadmium ions. However, there has been insufficient research into the influence of Cd2+ on the early hydration process of MPC. This paper studies the effect of cadmium ions on the setting time, compressive strength, pH change tendency, and heat of hydration at the onset of hydration on the performance of MPCs with different magnesia to phosphate ratios and cadmium ion content. The results demonstrate that the strength of MPC was reduced and the setting time delayed with higher additions of Cd2+. However, the addition had minimal effect on the tendency of pH change in the MPC system. The addition of Cd2+ slowed the hydration rate of MPC; the total heat release was also reduced. When the M/P ratio of MPC was 4:1, the compressive strength of the sample decreased from 32.32 MPa to 9.05 MPa; the final solidification time of the sample increased from 686 s to 838 s by adding 4% cadmium nitrate. The hydrated products were analyzed by XRD, SEM, and EDS. It was determined that the addition of cadmium ions did not produce new apparent crystalline phases. The quantity of cadmium ion leached was below the standard requirement, which is the most critical factor for the solidification of cadmium ions. The results indicate that MPC is beneficial in the stable solidification of cadmium ions. (C) 2019 Elsevier Ltd. All rights reserved.