Research On The Factors Of Inflecting Strength And Chemical Speciation Of Pb²⁺ Immobilization By Geopolymer Based On Fly-ash

Geopolyer is a new type of environment-fridendly inorganic cementious material which is activated by alkali. The geopolyer possesses many merits such as excellent durability, faster growth rate in early stage, abundance in raw material, source saving, friendly to environment and so on. The investigation in gopolymer enriches the theory of inoranic cementious and the results are of value to engineering application of plastics. The affecting factors of fly ash-based geopolymer's strength and the speciation analysis on the heavy metal were investigated in this paper.Test investigation on the factors of the water/binder ratio, binder/sand ratio, curing regime, modulus and the percentage of sodium hydroxide in alkaline silicate of geopolymer based on fly ash were carried out in this paper. Also, the optional mixing proportion and curing regime were obtained. Finally, the causes and mechanism were analyzed. The results indicated that the ratio of water to binder and binder to sand were 0.4 and 1:3 respectively; the optional content range of sodium hydroxide in alkaline silicate activator was from 20% to 24%; the compressive strength reached to 48.4 MPa when the modulus was 1.4; the specimens were cured in room temperature for 24 hour was beneficial to the development of strength before the specimens were heated; in order to get the max compressive strength, the specimens should be heated 48 hour in the temperature of 65 degree because the increasing tendency of strength were slow after 48 hour.According to the compressive strength of solidified body used as the construction materials and the limits of Pb2+ leaching toxicity, the percentage of Pb2+ in fly ash-based geopolymer and cement solidification is 1.5%. Sequential extraction method was used to analyze the chemical state and migration of Pb2+ solidified by geopolymer based on fly ash and cement. The experiment showed that geopolymer based on fly-ash was equal to cement on solidification of Pb2+ in neutral environment although the chemical states of Pb2+ were different. In the acceleration test condition, the geopolymer based on fly ash was more efficient than cement in the case of Pb2+ solidification. When the condition of the test converted from natural to acidic, the type of Pb2+ migrated fromâ…¤toâ…£andâ…¢in cement while in the geopolymer based on fly-ash the type of Pb2+ converted toâ…¡. The solidification mechanism and migration rule of Pb2+ in cement and geopolymer were different.