Effect Of Desulfurized Gypsum Leaching On Chemical Species Of Heavy Metals In Reclaimed Tidal Flat Soil From The Pearl River Estuary

A soil column leaching experiment for eliminating heavy metals in reclaimed tidal flat soilwas conducted in laboratory. Desulfurized gypsum was used as amendment in leaching. Afterthat, the soil samples were analyzed for speciation of heavy metals Cd, Cr, Cu, Pb and Zn usingthe Tessier sequential extraction procedure. The study dealt with the effect of different leachingconditions on the chemical speciation of heavy metals, so as to provide the theory basis forimproving leaching scheme.The results of the study show that, after the desulfurized gypsum leaching, the contents ofexchangeable Cd, Cr, Cu, Pb and Zn were reduced1.01mg·kg^-1,1.73mg·kg^-1,0.97mg·kg^-1,12.30mg·kg^-1and68.75mg·kg^-1respectively. The contents of carbonate Cd, Cr, Pb and Zn werereduced0.51mg·kg^-1,0.69mg·kg^-1,1.53mg·kg^-1and29.25mg·kg^-1respectively. The contents ofFe-Mn oxides bound Cd, Cr, and Pb were reduced0.04mg·kg^-1,29.24mg·kg^-1and1.84mg·kg^-1respectively, while the contents of Fe-Mn oxides bound Cu and Zn increased by6.25mg·kg^-1and10.50mg·kg^-1respectively. The contents of Cr, Cu, Pb and Zn in organic fraction increasedby9.08mg·kg^-1,7.82mg·kg^-1,2.46mg·kg^-1and29.64mg·kg^-1, while the contents of Cd in thisfraction did not changed. In residual fraction, content of Cr was increased by15.68mg·kg^-1, Cuand Zn were reduced6.76mg·kg^-1and8.65mg·kg^-1respectively, the contents of Cd and Pb keptunchanged.By applying desulfurized gypsum in2-3times, the contents of Cd, Cr, Cu and Pb inexchangeable fraction and Cr, Pb and Zn in carbonate fraction were tended to decrease, as wellas Cd, Cu, Pb and Zn in Fe-Mn oxides bound fraction and Cr, Pb and Zn in organic fraction. Cr,Pb and Zn in carbonate fraction. The contents of Cd, Cr, Cu, Pb and Zn in other fractions werenot affected.By increasing freshwater amount each time, the contents of Cd, Cu and Pb in exchangeablefraction and Cr and Cu in carbonate fraction were tended to decrease, as well as Cd, Cu, Pb andCr in Fe-Mn oxides bound fraction and Cr and Pb in organic fraction. The contents of Cd, Cr, Cu,Pb and Zn in other fractions were not affected.By increasing leaching interval time, the contents of Cd, Cu and Pb in exchangeablefraction and Pb and Cu in Fe-Mn oxides bound fraction were tended to decrease, as well as Pb in organic fraction. The content of Fe-Mn oxides bound Cu was tended to decrease first then tendedto increase. The contents of Cd, Cr, Cu, Pb and Zn in other fractions were not affected.