Effects Of Four Soil Conditioners On Speciation And Biological Behaviors Of Cadmium And Lead

The aim of this research was to study and evaluate the remediation effects of four soil conditioners on cadmium and lead contaminated soils. Adsorption experiment, thermostatic incubation experiment and pot trial were conducted to investigate the effects of M soil conditioner which main ingredient is medical stone, T soil conditioner which main ingredient is montmorillonite, O soil conditioner which main ingredient is oyster shell and S soil conditioner which main ingredient is the silicate and calcium carbonate minerals (medical stone, montmorillonite, oyster shell, silicon and calcium minerals for short respectively) on the speciation and biological effect of cadmium and lead. The study indicated that oyster shell, silicon and calcium minerals had good adsorption on Cd, inhibited the test crops uptake on Cd, and have certain effects on soil improvement and Cd contaminated soil remediation. The main results in this study showed as follows:1. The adsorption experiment results indicated that oyster shell, silicon and calcium minerals had good adsorption on Cd, and medical stone, silicon and calcium minerals, oyster shell displayed better adsorption effects of Pb. The adsorption amount of each conditioner was obviously affected by the pH value in solution. The amount of each conditioner was decreased with increasing pH value, especially, when the pH value of Cd solution higher than8and the pH value of Pb solution higher than6, the sorption capacity decreased rapidly.2. The results in thermostatic incubation experiment were given as follows:(1) Speciation of Cd in the artificially Cd contaminated soil analyzed by the modified BCR sequential extraction procedure were acid extractable> reducible> residual> oxidizable. Medical stone, oyster shell, silicon and calcium minerals were applied. In the first35days, the concentration of acid-extractable Cd was decreased after application of silicon and calcium minerals, but on the65th day the concentration was increased. The concentration of acid extractable Cd had the trend of increase using medical stone and oyster shell. Main speciations of Cd analyzed by the modified Tessier sequential extraction procedure were exchangeable, organic bound and residual. With the application of3soil conditioners, the exchangeable was decreased of different level.(2) The speciation of Pb in the artificially Pb contaminated soil analyzed by the modified BCR sequential extraction procedure were reducible mostly, acid extractable secondly. After medical stone, oyster shell, silicon and calcium minerals were added, the concentration of acid extractable Pb was increased, but had not distinct change. Main speciations of Pb analyzed by the modified Tessier sequential extraction procedure were organic bound, carbonate bound, and residual. The speciation of Pb had no significant variation after addition of the3soil conditioners.(3) Speciation of Cd in the Cd contaminated soil analyzed by the modified BCR sequential extraction procedure were acid extractable> reducible> residual> oxidizable. Medical stone, montmorillonite, oyster shell, silicon and calcium minerals were applied. The concentration of acid extractable was decreased with the addition of medical stone, montmorillonite, silicon and calcium minerals, but had no regular change with addition of oyster shell. The speciation of Pb in the Pb contaminated soil were residual> oxidizable> reducible> acid extractable. After after20g medical stone applied in1kilogram soil, the concentration of residual Pb was decreased, while the concentration of residual Pb was increased with the application of silicon and calcium minerals, and the concentration of residual Pb had no regular change in the other treatments.(4) The concentration of Cd extracted by CaCl2was significantly decreased by10%-35%after addition of oyster shell, silicon and calcium minerals, medical stone had no obvious effect, but the concentration of Cd extracted by CaCl2was significantly increased by32%using montmorillonite. The concentration of Pb extracted by CaCl2had the trend of increase after montmorillonite added, but the other three conditioners had no evident effect and changed unregularly.3. The pot trial results were following:(1) Compared with the control, the shoot fresh weight of Brassica chinensis was increased by17.9%and18.0%respectively after addition of montmorillonite and oyster shell, but the weight was reduced by about17.0%with applied silicon and calcium minerals. Cd content in shoot was evidently increased by122.0%using montmorillonite, and after20g oyster shell, silicon and calcium minerals applied in1kilogram soil, Cd content in shoot was decreased by about26%. Cd content in root was decreased by about11.0%with the application of oyster shell. With silicon and calcium minerals applied at50g in1kilogram soil, Cd content in root was decreased by8.8%, while the Cd content was increased by21.5%after silicon and calcium minerals added at20g in1kilogram soil. Cd content in root was significantly increased by added montmorillonite and the maximal reduction was268.9%.(2) Added medical stone, montmorillonite, oyster shell, silicon and calcium minerals in10mg/kg Cd contaminated soil, the rate of emergence of Brassica chinensis was increased to88.5%,87.5%and87.0%respectively. The rate of emergence of Brassica chinensis was increased to84.7%,82.0%and76.7%after applied oyster shell, silicon and calcium minerals, medical stone in1000mg/kg Pb contaminated soil, and the addition of montmorillonite had no evident effect on the rate of emergence.4. The application of4soil conditioners had no significant effect to pH value in Cd and Pb contaminated neutral and alkaline soil. However in the contaminated acidic soil, the pH value was obviously improved from about3.3to more than7after added oyster shell, silicon and calcium minerals, and the pH value was increased from3.3to4.6by using medical stone. The application of montmorillonite had no significant influence on pH value.