Effects Of Different Amendments On Thallium Fractionation In Highly Contaminated Soils

Based on the validation of the optimized IRMM sequential extraction procedure of thallium?Tl?in soils,the distribution of Tl fractions in the highly Tl-contaminated soil of Lanmuchang in Guizhou Province was investigated on this method.The effects of two amendments on Tl fractionation and physicochemical properties of the contaminated soil were studied.The results are as follows:?1?The Tl contents in the studied soils vary from 50.4 to 301 mg/kg,reflecting the high Tl contamination of the studied soils.The acid exchangeable and oxidizable Tl in five soils are almost within 10%.The reducible and residual Tl account for 27.0–58.4%and 31.6–62.5%,respectively.It should be noticed that the labile Tl?consist of acid exchangeable,reducible and oxidizable Tl?ranges from 21.4 to 205 mg/kg with high mobility and bioavailability.Therefore,the immobilization/stabilization of labile Tl should be given priority in the treatment of Tl-contaminated soil.?2?Mineral amendments increase soil pH by 0.44–1.55 units.The increase of dosage resulted in the larger pH value of soils.The correlation between soil pH and Tl fractions after treatment indicates that the soil pH changes after the treatment may be responsible for transformation of Tl fractions.Mineral amendments can significantly reduce the labile Tl contents in soils,transforming the acid exchangeable Tl to reducible and then to residual Tl.At60 days,21.7–54.1%of labile Tl are converted to residual Tl.The changes of mineral composition of the soil have been found.The disappearance of kaolinite creates conditions and opportunities for Tl?III?to enter the new silicate lattice.XPS results showed that the treatment reduced Tl?I?and increased Tl?III?content on soil surface.Considering Tl fractionation and XRD results,Tl?III?in reducible fraction can enter into Al₂O₃,Fe₂O₃ and SiO₂ due to isomorphism during the soil mineral reaction,thus entering the newly formed silicate structure.In addition,due to the similar ionic radius with K⁺,acid exchangeable Tl?I?may enter the interlayer structure or lattice of silicate minerals,such as clay minerals by replacing K⁺.?3?Silicon fertilizer can increase soil pH by 0.75–1.51 units.The increase of dosage of the amendment resulted in more elevated soil pH.There was also a correlation between soil pH and Tl fractions after adding silicon fertilizer,indicating that the changes of soil pH indeed affect the transformation of Tl fractionation.Silicon fertilizer can reduce the labile Tl contents in soils,and the overall trend of Tl fractionation transformation was similar as that of mineral amendments.At 30 days,15.7–34.4%of labile Tl in five soils was converted to residual Tl.The similar phenomenon can be seen during the treatment indicated that the change of mineral composition?such as the disappear of the kalinite?may account for the transformation of Tl fractions,resembling the mineral amendment.XPS results showed that silicon fertilizer can also decrease Tl?I?and increase Tl?III?contents.?4?The results show that mineral amendments and silicon fertilizers have an important effect on the Tl fractionation transformation in soil,resulting in a significant decrease in acid exchangeable Tl,which is converted into reducible fraction,and then into residual fraction.Apparently,the labile Tl decreases while the residual Tl increases.In comparison,the effect of mineral amendments on Tl immobilization is better than that of silicon fertilizer.