Research On Solidification/Stabilization Of MSWI Fly Ash In Alkaline Slag

MSWI fly ash is defined as hazardous waste in many countries around the world due to organic and toxic materials and the high leaching ratio of heavy metals. The main disposal for MSWI fly ash is solidification/stabilization. At present time the solidification/stabilization ways include silicate cement solidification, melting solidification, plastic material solidification, and chemical medicament solidification. Due to the high properties and big use of waste residue, this paper made a great deal of research on solidification/stabilization of MSWI fly ash by using alkaline slag cement.The fly ash was from Yancheng. The chemical composition, mineral composition, heavy metal and micro-structure of fly ash were tested. And the alkaline slag cement was used for the solidification/stabilization of raw fly ash, water washing fly ash and thermal treatment fly ash, and the TCLP test was taken.The results showed that: the compressive strength fell quickly with the increase of the content of fly ash when the fly ash was solidified in alkaline slag cement, and the phenomenon of swelling could be seen. With the water washing process, the mass loss of fly ash was 2.7%, it indicated that there were some soluble salts in fly ash. The water washing pretreatment had little influence on the effect of compressive strength of the solidification blocks, with the mass addition of 10% of fly ash, the water washing process even had no improvement on the strength of test blocks, and when the mass of fly ash increased, the effect of solidification improved. Then the fly ash was heated at 700℃, 800℃, 900℃and 1000℃respectively for 3h, with the same content of heating fly ash, the compressive strength of solidification blocks improved greatly compared to the blocks with raw fly ash, especially the group of 900℃. When the content of heating fly ash was 30%, compared with the same content of raw fly ash, the compressive strength of 28d increased from 12.4Mpa to 46.0Mpa, and no swelling was found. It indicated that the thermal pretreatment maybe an effective way for the utilization of fly ash as the alkaline cementitious material admixture.The heavy metals contained in fly ash falls into five formations. The Fe-Mn oxide state is greatest in Pb, Cu, Zn and Cd, and residual state in Cr is the most. The TCLP test was performed on the solidification blocks maintained for 28d, and the extraction toxicity was kept within identification standards for extraction toxicity.