Research On Preparation Of Porous Ceramic With Low Temperature Sintering Of MSWI Fly Ash

MSWI fly ash is one of the final residue after waste incineration, including ash, injection of adsorbent, the condensation product of flue gas and reaction products, which were collected by the flue gas purification system and heat recycling system(such as heater, waste heat boiler, etc). During the process of rubbish waste burning, low melting point materials would volatilize and captured by flue gas purification system after the condensation, and then turned into the waste incineration fly ash together with other materials. So the MSWI fly ash contained a large number of salinity, such as NaCl,KCl, etc. In addition, highly toxic dioxin-related compounds came into being during the burning process. MSWI fly ash had been identified as hazardous solid waste, which would bring serious environmental pollution if on effective treatment. At present, cement solidification and sanitary landfill were one of methods which were used for the treatment of the MSWI fly ash in our country. But the long-term stability of the cement solidified body may be poor, because of lots of chlorides in fly ash, Moreover, the dioxins in the fly ash could not be decomposed with the cement solidification method, which could bring a series of environmental pollution. According to above circumstance, preparation of porous ceramic with low temperature following the cement solidification and dry pressing molding were studied for the goal of MSWI fly ash harmless and resource recovery in this paper.The preparation of porous ceramics from MSWI fly ash was investigated in this paper. The sintering experiment of solidified body of cement and fly ash showed that the compressive strength of sintered body is extremely low when the sintering temperature was 900℃. When the sintering temperature rose to 1200℃, the compressive strength of sintered body was about 7.31 MPa. The flux of sodium tetraborate and kaolin as additive could lower sintering temperature and increase hardness of sinters. The best adding proportion fly ash/sodium tetraborate/kaolin which was got by orthogonal experiments was 4:2:3. XRD and SEM analysis results showed that the solidified body mainly came into being gehlenite and calcium silicate during sintering, sodium tetraborate had obvious effect on fusion; The result of leaching experiment showed that the heavy metal leaching of Ni、Cu、Pb、Zn、Cr and Cd concentration was lower than the national standard. Experiment of making foam concrete showed that the foaming effect is better while the adding amount of foam additives was 0.7%, and when the adding amount of bubble was 100%, the porosity was 85% and the volume density was 736 kg/m3; the sintering experiments showed that, the dry density of porous ceramic body decreased slowly at the beginning, then rapidly increased with the increasing of sintering temperature.The preparation method of the porous ceramics, which was made from MSWI fly ash/waste glass with CaCO3(foaming agent) and H3BO3(fluxing agent) was studied in this paper. The dry pressing molding experiments showed that the molding body possessed the highest compressive strength while the moisture content of fly ash was 12% and the addition ratio of starch was 6%. Sintering experiment results showed that with the increasing of boric acid, sintering temperature and glass powder content, the densification of sintered body could be higher. X-ray diffraction patterns of the porous ceramics showed that CaSiO3 was the major glass phase; the pore size of porous ceramics increased with adding the fluxing agent and foaming agent. leaching experimental results indicated that concentration of heavy metal leaching was below the state standard, and the leaching concentration of Pb, Ni and Cd were less than 0.5 mg/L in sintered body and the leaching concentrations of Cr and Cu were decreased from 18.3mg/L and 0.36mg/L to 4.3mg/L and 0.05mg/L with the sintering temperature raising to 1000℃, when the sintering temperature above 900℃, the pore diameter of porous ceramic gradually decreased with the increase of sintering temperature; The pore size of porous ceramics increased with the adding of flux and foaming agent.