Effect Of Woody Peat On The Cadmium Speciation And Bioavailability In Tobacco Soil

Soil cadmium pollution has become a serious problem in China,the point exceedance rate of cadmium is seven percent.Reducing the bioavailability by changing the chemical forms of cadmium has been considered as a promising alternative to the currently available remediation methods.Woody peat,which is rich in humic acid,has great potential in the remediation of heavy metal contaminated soil due to its hydroxyl and carboxyl groups,porous structure,and large specific surface area.In this paper,the adsorption performance of woody peat for cadmium,and the changes of cadmium speciation in the after-amended soil were studied.The effectiveness of woody peat remediation was confirmed by pot experiment of tobacco K326.The main contents are as follows.?1?The adsorption performance of woody peat for Cd???was explored.The effects of solution pH,dosage of woody peat,reaction temperature,initial concentration of Cd???and coexisting ions on the adsorption of Cd???were investigated.The results show that the adsorption amount of Cd???in aqueous solution increased with the increase of solution pH and temperature.The adsorption amount of 19.58 mg·g^-1 was obtained under the initial pH of 6 for 50 mg·L^-1 Cd???treated with 0.8 g L^-1 woody peat.99.94%of 25 m L 50 mg·L^-1Cd???were be removed by 0.20 g woody peat at pH 6.0,and the residual Cd???was below the emission limitation.The Cd???adsorption amount by woody peat decreased duo to the inhibiting effect of Cu²⁺,Zn²⁺,Ca²⁺,Mn²⁺,Mg²⁺and K⁺in the solution.The adsorption kinetics of Cd???by woody peat followed the pseudo-second-order kinetic model,and the adsorption isotherm data fitted well with the Langmuir equation.The Cd???adsorption by woody peat is a entropy increasing and endothermic process,and occurs spontaneously as the temperature is above 268 K.?2?The dynamic effect of woody peat on the soil cadmium speciation and pH were investgated by soil incubation experiments.The results showed that the soil pH increased in the first stage of incubation after the addition of 3%,5%and 10%of woody peat in the soil of 2.49 mg Cd???·kg^-1 soil,and the increased pH is positively correlated with the dosage of woody peat.No significant difference was found in the soil pH among the various woody peat treatments and the control 90 days latter?p>0.05?.The soil exchangeable cadmium fraction decreased with the incubation time,while the reducible,oxidizable and residual cadmium fraction of soil increased gradually during the incubation of 120 day.The cadmium content changed magnitude was positively correlated with the dosage of woody peat.After120 days of co-incubation with 3%,5%and 10%of woody peat,the soil exchangeable cadmium fraction was 0.47,0.33 and 0.15 times as much of the CK,while the soil reducible and oxidizable cadmium fraction increased by 75.82%,83.52%,98.90%and 36.73%,39.27%,45.45%,while the residual cadmium fraction increased by 8.33%,11.90%and22.62%,respectively.The cadmium activity index decreased from 1.41 to 0.38,0.25 and0.11 after the 120 days co-incubation of cadmium contaminated soil with 3%,5%and 10%of woody peat,respectively.?3?The effectiveness of woody peat remediation on cadmium contaminated soil was confirmed by pot experiments.1%,2%and 3%of woody peat were mixed well with two cadmium contaminated soil,which the soil cadmium content was 0.50 mg·kg^-1 and 1.47mg·kg^-1,then tobacco K326 were grew 15 days and collected 90 days latter.The effects of woody peat treatments on the cadmium content of various parts of tobacco were investgated.The result show that the pH of the woody peat treated soil was not significant different from the control,but the cadmium content,the transporting coefficient and the enrichment coefficient of cadmium decreased after the tobacco planting soil treated by 1%,2%and 3%of woody peat,and the decreased magnitude is positively correlated with the dosage of woody peat.The cadmium content of tobacco,growing in 0.50 mg Cd???·kg^-1 and 1.47 mg Cd???·kg^-1 soil,decreased by 28.80%to 63.15%and 17.04%to 43.29%,respectively.The tobacco cadmium enrichment coefficient decreased significantly after the soil treated by 1%?for 0.50 mg Cd???·kg^-11 of soil?or 2%of woody peat?for 1.47 mg Cd???·kg^-11 of soil?.