Research On The Solidification And Stabilization Of Heavy Mental By Magnesium Slag And Geopolymer Based On Fly-Ash

Heavy metal waste is a type of long-term effects of the environmental pollutants. In addition to the recyclable parts, most of heavy mental wastes need to be solidified/stabilized in order to achieve the purpose of harmless. Owing to the advantages of easy implementation, low cost etc., solidification/stabilization treatment has become an important means of disposing hazardous wastes containing heavy metals. In this paper, according to the characteristics of the magnesium slag and fly ash, different processing methods were chosen to deal with the industrial wastes to reach the goal of solidifying/stabilizing heavy metals by utilizing magnesium slag and geopolymer based on fly-ash. The solidification/stabilization effect was evaluated through the leaching toxicity experiments. The composition and structure of the samples were characterized by XRD and FTIR. The morphology of the samples were observed by SEM/EDX. The main conclusions are as follows:(1)When the content of Pb in the slag materials doping with 60% magnesium slag reached 2.8% which exceeded the slag solidification of Pb, a thermal treatment at 1150 ℃,6 hours could make Pb stability exist in the slag material so that Pb couldn’t be leached. When the Cd content didn’t exceed 1.25%, Cu content didn’t exceed 3.45%, Pb content didn’t exceed 1.97%, heavy mental Cd、Cu and Pb could stability exist in the slag materials doping with 60% magnesium slag without a thermal treatment. The concentration of heavy metals in leaching solution had significantly reduced through a sintering process while different volume fraction of hydrochloric acid and sulfuric acid were used as the leaching agent.(2)When the slag materials doping with different contents of magnesium slag were prepared, the solidification/stabilization effects of Cd and Pb became better with the increase of content of magnesium slag. Meanwhile the concentration of Cu and Zn in the leaching liquid met the standard of GB5085.3-2007. The slag materials doping with different contents of magnesium slag were prepared. The concentration of Zn in the leaching liquid had suffered different degrees of reduction along with the increase of Cd content in the slag materials when the content of magnesium slag was constant, which illustrated that Cd could promote the solidification/stabilization of Zn to some certain extent.(3)The BCR experiment showed that the speciation distribution of Pb in waste acid residue was oxidizable > reducible > residual > acid extractable, the speciation distribution of Cd in waste acid residue was acid extractable > oxidizable > reducible > residual. Doping magnesium slag could promote a non-steady state of heavy metals Pb, Cd, Cu and Zn in the slag transform into a stable state, which may achieve the purpose of solidifying/stabilizing heavy metals Pb, Cd, Cu and Zn.(4)The geopolymer based on fly-ash was prepared using the selected optimal conditions which was stirring 15 min, curing at 80 ℃,adding 19% alkali activator.(5)The compressive strength of the geopolymer based on fly-ash with Pb and Cd were higher than without Pb and Cd at 3d and 7d by curing at 80 ℃ from 3h to 48 h.Through the leaching toxicity experiments, it could be found that the geopolymer based on fly-ash curing at 80 ℃ could effectively solidify/stabilize 1.5% Pb and 1.5% Cd. However when the content of Pb and Cd reached 3% separately, geopolymer based on fly-ash could solidify/stabilize Pb but couldn’t completely solidify/stabilize Cd.