Effects Of Heavy Metals To Hydration Process Of Magnesium Phosphate Cement And Their Existence Status Insolidify Forms

With the rapid development of mining, electroplating, metal lurgy and other industries, the economic has made great achievements. However, these industries also produce a large number of heavy meatal pollutions and cause hugh environmental pollution. As a new kind of binding material, the magnesium phosphate cement has a great potential in disposing the heavy meatal polloution. During the process of stabilization/solidification, the effect of the heavy meatal on the hydration of the magnesium phosphate cement (MPC) is very important, systematic research on this qustion can conribute a theory basis for the disposing of heavy metal pollution. In this paper, the effect of the Pb, Zn, Cu, Cr and Cd ion on the hydration process of the MPC was investigated by pH, heat of hydration, XRD, SEM and EDS. Morvever, the leaching toxicity of these meatal ion were tested by ICP..To MPC, the lead ion and cadmium ion has no significant effect on the setting time,the zinc ion can polong the setting time obviously, the effect of cupric ion and chromium ion is more complex. For cupric ion, when the content is low, it has no significtant effect on the setting time and in the condition of high content, the setting time of MPC prolonged. For chromium ion, when the content is low, it will decrease the setting time of the MPC and when the content is high, it can prolong the setting time.The result of the strength experiment showed that, the existed of the zinc ion has little effect on the strength of the sample for the MPC with lower M/P ratio,the lead ion,cadmium ion, cupric ion and chromium ion can increase the strength of the sample. For the MPC with higher M/P ratio, the existed of heavy metals will reduce the compressive strength of the sample.During the hydration reaction, the effect of the heavy meateals is different. It is observed that the change trendency and rate of the pH was not significant effect by lead ion and cadmium ion. The existed of the zinc ion and cupric ion have no effect on the change trendencv of the pH but they can delay the change rate of the pH. On the other hand, both the change rate and change trend of the pH was influenced by chromium ion. In addition, with the decreasing of the M/P ratio the effect of the heavy meatals was decreased.In hardened MPC, the phases of the heavy metals were different. For lead and chromium ion, the crystalline state can be observed. However, for zinc ion, cupric ion and cadmium ion, no obvious crystalline state can be found. the microstructure of the hydration product was influenced by the content of heavy metals. Furthermore, with the increasing of M/P ratio the influence of those heavy metals was enhanced.The leaching toxicity of all heavy metals was low. For the 1d sample, the highest leaching concentration of the lead ion, zinc ion, cupric ion, chromium ion and cadmium ion was 0.418mg/L,34ug/L 1.3mg/L,0.255mg/L and 0.427mg/L respectivly. In general, the mechanism of the solidification of heavy metal ions with magnesium phosphate cement included chemical reaction and physical encapsulationDuring the process of magnesium phosphate cement hydration reaction, the heavy metal ions can react with phosphate ion and other ions to form certain mineral or amorphous matter,these reactions reduced the leaching toxicity of the heavy metals. On the other hand, different binding capacity of the heavy metal ions and phosphate in the hydration process may lead to the difference of the leaching toxicity.