| Heavy metal waste is a type of long-term effects of environmental pollutants. Most of heavy metal wastes need to be solidified or stabilized except for part of them that could be reclaimed and reutilized. Ordinary stabilization technology, such as cement stabilization, can not solidified heavy metal wastes effectively, and also has problem about long-term stability . Geopolymer is a kind of new material with network structure of aluminosilicate, it is synthesized by materials rich in SiO2 and Al2O3 activated with alkali solution, and it can immobilize toxic ions effectively.Metakaolin-based geopolymer was first synthesized in this study. A optimal oxide proportion of geopolymer was confirmed as n(SiO2)/n(Al2O3)=3.8, n(Na2O)/n(SiO2)=0.30 after experiment. It was studied fly ash and slag was added individually to synthesize geopolymer. It is found that 30% of fly ash or slag leads to optimal result, compressive strength to most geopolymer are over 40 MPa. It was concluded that geopolymer based on MK+slag possess best properties according to compressive strength, even reaches to 86MPa, while compressive strength to geopolymer based on MK+fly ash grows up apparently late. Solidifying compound including Pb2+, Cu2+, Zn2+, Cd2+ were studied based on the condition above. Most geopolymer show high performance on solidifying heavy metal according to leachate concentration. However, there are different limit of addition for different heavy metal, that is if the concentration is over limit the properties of geopolymer will gets worse quickly. It was demonstrated that solidifying Pb2+ is better than solidifying Cd2+ on condition that both Pb2+ and Cd2+ are added. Leaching experiment showed there is nearly no impact on geopolymer after leached with pH value of simulated acidic rain was 3.0 or higher. The reaction product were investigated by scanning electron microscopy(SEM). The results showed it has larger specific surface area and stronger compare to portland cement. |
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