Preparation Of Magnesium Phosphate Cement Mixed With Sludge And Study On Its Solidification Of Heavy Metals

With the development and economy of our society and the acceleration of urbanization,more and more sewage treatment plants has been built,leading to lots of sewage sludge in our society every year.Sewage sludge is a by-product of the sewage treatment process.The sludge must be treated before it is discharged,due to the complex components in the sludge which often contains pathogens,parasitic eggs,various heavy metals and other pollutants.The amount of by-product sludge will inevitably increase due to the increase of urban sewage treatment volume.Compared with the more mature system of garbage collection,classifica tion and disposal,our country's sludge disposal rate is low and the treatment method is simple.A lot of untreated sludge is randomly stacked and discarded,and the harmful heavy metals in the sludge are easy to enter the soil or groundwater,causing seri ous harm to the environment and further endangering the health of human beings.Therefore,the sludge residue needs to be disposed of.In this project,the magnesium phosphate cement material was prepared with sludge residue,the effect of sludge residue on the performance of magnesium phosphate cement and the mechanism of the heavy metal solidified in the magnesium phosphate cement were studied.Through the incorporation of different levels of sludge residues into magnesium phosphate cement,the effects of sludge residue on the performance of magnesium phosphate cement were studied,and the magnesium phosphate cement with good performance mixing with sludge were prepared.The effect of magnesium phosphate cement on the solidification of heavy metals in sludge was studied by analyzing the leaching toxicity of magnesium phosphate samples added with sludge.The effects of different heavy metals on the properties of magnesium phosphate cement and the existing forms of heavy metals in magnesium phosphate cement were studied by adding nitrate of six heavy metals,Pb,Zn,Cd,Cu,Cr and Ni,respectively.Magnesium phosphate cement material good performance was obtained with the incorporation of sludge residue.The compressive strength value of magnesium phosphate cement was 40.31 MPa when 5% sludge residue was mixed,which is higher than the sample with no sludge.However excessive sludge residue was will affect the process of hydration crystallization of magnesium phosphate cement,leading to the decrease of the compressive strength value.Solidified by magnesium phosphate cement,the leaching amount of heavy metals in sludge residue is reduced,much lower than the leaching standards of heavy metals in the wastes stipulated by the state.Magnesium phosphate cement has the effect of solidification on six kinds of heavy metal ions of Pb,Zn,Cd,Cu,Cr and Ni.Among them,the solidification effect of heavy metal lead was the best.When the content of lead nitrate was 5%,the leaching concentration of lead ion was very low,only 0.163 mg/L.The content of Pb in the hydration crystal is high and Pb3(PO4)2 is produced in the product,indicating that the Pb is solidificated in the crystal of the hydration product.In general,when the content of heavy metals is low,it has less impact on the cement hydration reaction and the leaching concentration of heavy metals is low.However,the hydration reaction process of magnesium phosphate cement is affected when more heavy metals mixed,leading to the weakening effect of the magnesium phosphate cement on the solidification of heavy metals and the increase of the leaching concentration.