Effect Of Phosphorus On Properties And Heavy Metal Pollution Characteristics Of Ceramicite Fired With Sludge

Sewage sludge(SS),fly ash(CA)and coal gangue(CG)are typical solid wastes.Long-term storage or direct discharge will seriously harm the natural environment and biological health.Due to its high organic matter and heavy metal content and high calorific value,SS is an effective way to achieve resource utilization,reduction and harmlessness through high-temperature sintering.Based on the complementarity of chemical composition between SS and CA,CG,a lightweight aggregate(LWA)was manufactured from municipal sewage sludge(SS),coal gangue(CG),and coal ash(CA).Based on the study of the basic physical and chemical properties of the three raw materials,the mechanical properties and environmental safety characteristics of the LWA were evaluated by changing the additive content and the sintering temperature to determine the appropriate process conditions.Study on pyrolysis behavior and melt volatilization characteristics of raw materials by TG-DSC thermal analyser.SEM-EDS analysis of LWA microstructure by surface composition and XRD pattern for mineral phase identification.The distribution and migratory transformation characteristics of heavy metals in LWA were examined by BCR sequential extraction in combination with inductively coupled plasma optical emission spectrometry(ICP-OES)and the environmental safety performance of LWA was comprehensively evaluated by the OPTI index.The results show that the phosphorus in the sludge can promote the formation and fluidity of the molten liquid phase of the ceramsite lightweight aggregate during the sintering process,thereby promoting the stabilization of the aluminosilicate lattice to heavy metals during the sintering process,and the conversion of heavy metals in the ceramsite lightweight aggregate to the residue state,The addition of phosphorus can effectively reduce the leaching concentration of heavy metals.When the phosphorus content of the raw material is 21.57 mg/g,the sintering temperature is 1250?and it stays for 10 min,the stacking density of ceramsite lightweight aggregate was between 200 and 400 kg/m~3.The compressive strength reaches 9.45 Mpa;The water absorption rate was only 1.06%,and the mechanical performance was better than the standard stipulated by GB/T1743.1-2010.The leaching concentrations of Cu and Zn in ceramsite are lower than 0.75 mg/L and 0.79 mg/L,The residual content of Cu,Cr,Zn,Pb is98.78%,98.07%,98.95%,97.2%.The OPTI index of ceramsite is only 197,and the potential environmental risks are greatly reduced.