Study On Combined Remediation Of Heavy Metal-contaminated Soil By Saponin And Citric Acid

To repair the heavy metal polluted soils better is still a problem to besolved, and we need more environmental friendly,more economical andmoreconveniental way. In this paper, the cirtic acid or saponin singly andcitric acid-saponin combined was used to research the contaminated soils,and to study the effect of kinetics fitting curves of Pb, Zn, Cu.First, Taking soils contaminated by Zn, Pb and Cu as research objectsto study efficiency of saponin-citric acid combined remediation byoscillation extraction experiments, the result indicated that extractionefficiency of the heavy metals is better when citric acid at40mmol/L andsaponin at3%mass fraction.When the volume ratio of citric acid andsaponin is1:5(pH=5), the removal rates of Zn, Pb, Cu are93.5%,84.8%and33.6%, respectively. The extraction effect of heavy metals is Zn> Pb>Cu. The chemical forms of Zn, Pb and Cu in the soil awfully changed afterextraction by citric acid and saponin. Acid soluble form of Zn almost wasremoved, oxidation and residue forms reduced by more than90%. All formsof Pb reduced;Acid soluble state of Cu also reduced by80%, but residue,oxidation and residue forms did not change too much.Secondly, By leaching experiments, saponin-citric acid combinedremediation of contaminated soils by Zn, Pb, Cu was studied. The resultsindicated that the leaching efficiency of Zn and Cu is better when thevolume rate of40mmol/L citric acid solution and3%saponin solution is1:5, and the leaching efficiency of Zn and Pb is67.2%and68.8%,respectively. But to Cu, the volume ratio is1:1, and the the leachingefficiency is37.7%, less than the effect of single citric acid. The combinedeffect of citric acid and saponin is relation to their volume rate and the typeof heavy metal.The combined remediation can remove96%acid solubleform,38.9%oxidation form and51.5%residual form of Zn, whilereducible form increased significantly. Acid soluble, reducible, oxidationand residual forms of Pb are reduced by80%，81.4%,74.6%and52.9%，respectively. Acid soluble and reducible forms of Cu reduced by80%,oxidation and residue forms did not change too much.Finally, using citric acid at40mmol/L and saponin at3%mass fraction singly and combine,and the volume ratio of citric acid and saponin is1:5(pH=5) to fitting the desorption of Pb, Zn, Cu by Elovich equation, doubleconstant equation, pseudo-first order kinetic equation, The fitting from wellto bad is Elovich equation> double constant equation> pseudo-first orderkinetic equation.