Chemical Solidification Of Char-Lime On Lead And Cadmium In Soil

In this paper, the feasibility of solidification of Pb and Cd in soil by char-lime system which was made up of certain proportion of activated carbon and hydrated lime was studied. Tessier five-step sequential extraction method was used to explore the effects of hydrated lime/activated carbon ratio, the dosage of carbon lime, organic matter and pH of soil on the chemical speciation of lead and cadmium, The solidifying mechanism and its resistance to acidic impact was also observed.Rape was used as the indicator plant to determine the fractionation that most likely to be absorbed by plant. The results showed that the content of Pb and Cd in rape at different growth time increased with the content of Pb and Cd in soil, the correlation analysis between content of Pb and Cd in rape and the change of five species of Pb and Cd before and after planting rape showed that, the content of Pb and Cd in rape at different growth stages (35d and70d) had significant correlation with the change of exchangeble state of Pb and Cd in soil, the correlation coefficient respectively were:R (the Pb content of rape at35d-â–³Pbson)=0.9785; R (the Pb content of rape at70d-â–³Cdsoil)=0.9561; R (the Cd content of rape at35d-â–³Cdsoil)=0.9578; the R with (the Cd content of rape at70d-â–³Cdsoil)=0.9942, so we could examine the char-lime fixing efficiency at the basis of the reduced amount of exchangeable state of lead and cadmium.In solidification experiment, the exchangeable state of Pb and Cd were gradually reduced with the increase of the hydrated lime in char-lime. Exchangeable state of Cd gradually reduced with the increase of the dosage of char-lime, however the exchangeable state of Pb found to decrease first and then increase.The increase of soil organic matter content and pH value was in favor of increasing the solidifying efficiency of char-lime system on exchangeable state of Cd. But,for Pb, the increase of soil organic matter led to increase of exchangeable state of Pb, and soil pH had no influence on it. With the extension of the solidification time, the exchangeable state of Pb and Cd were gradually decreased. In order to investigate the tolerance of solidified Pb and Cd to acid soaking, the solidified Pb and Cd were soaked with acid solution according to national standard "Solid waste leaching toxicity method-Sulfate Nitrate method", the result showed that the leaching amount of Pb and Cd was lower than the limitation provided in national standard of "hazardous waste identification standard-leaching toxicity Identification".SEM/EDS, FTIR, BET surface area measurement, TGA testing results showed that the solidification mechanism of char-lime system on Pb and Cd in soil mainly was chemical precipitation and activated carbon adsorption as an auxiliary.