Immobilization Of Thallium By Biochar Materials In Thallium Polluted Soils

In this study,straw biochar,iron-based biochar and manganese-based biochar with different concentrations(0,5,10,15,20g/kg)were used as passivating agents to remediate arable soils with Tl contamination.We explored the effects of types of biochar materials and added concentartions on the soil physical and chemical properties,Tl bioavailability,and Tl occurrence morphology under laboratory condition.The results demonstrated that iron-based biochar has a good passivation effect on Tl in contaminated farmland soil.Pot experiments were further conducted to investigate the regulatory effects of different amounts iron-based biochar to clarify the application effect of iron-based biochar in Tl contaminated soil.The main results are as follows:(1)All three types of biochar,including straw biochar,iron-based biochar,and manganese-based biochar,can increase the soil p H,content of nutrients(including organic matter,nitrogen,phosphorus,and potassium)in Tl-contaminated soil,which were directly proportional to the amount of biochar used.With the same amount of biochar,manganese-based biochar can significantly increase soil p H and the total nitrogen content,and iron-based biochar could increase the content of organic matter and the total potassium content in the soil.Notably,the three types of biochar have similar effect on the total phosphorus content in the soil,which slightly increase with biochar.(2)The chemical fraction analysis demonstrated that the application of all three biochar materials can effectively decrease the content of bioavailable Tl with the increase of the amount of biochar in Tl contaminated farmland soil.Importantly,iron-based biochar had the best effect on reducing soil available Tl content among the three biochar materials.Of notable,the bioavailable Tl was firstly decreased and then stabilized with time,the bioavailable Tl decreased rapidly at 30 days,and then stablized at 60 days.Therefore,it is reasonable suggested that crops should be planted after applying biochar for 30 days.In addition,we found that application of the three biochar materials could significantly change Tl fractions when cultured for60 days.The content of bioavailable Tl and oxidizable Tl was significantly decreased,whereas the content of residues fractions was significantly increased with the amount of biochar.The content of reduced Tl increased slightly due to the slight difference ofbiochar materials.The application of biochar material,especially iron-based biochar,can promote the bioavailable and oxidizable Tl turned into reducible and residue Tl fraction.Currently,we employed XPS analysis to further verified the morphological transformation of Tl.The results showed that the content of Tl(I)increased,while Tl(?)content decreased when conducting passivation treatment with iron-based biochar.Our results furtherly identified that the transformation of bioavailable Tl to residual state Tl was mainly due to lattice fixation.(3)Compared with the other two kinds of biochar,the iron-based biochar reduced the Tl content of bioavailability in Tl contaminated farmland soil most significantly.Therefore,iron-based biochar was selected for pot experiment,and the results showed that: The pot experiment showed that iron-based biochar can significantly reduce the contents of bioavailable Tl.Interestingly,the application of iron-based biochar could significantly decrease the content of Tl in the edible parts of cabbage and pakchoi on Tl-contaminated soil,with range of 26.07%-41.69% and24.2%-70.5%,respectively.Furthermore,we found that the application of iron-based biochar could increase the above ground biomass,vitamin C,soluble sugar and soluble protein,whereas decrease the nitrate content with the increase of iron-based carbon.Our results identified that the crop biomass,vitamin C,soluble sugar and soluble protein content in plants are the highest,and the Tl content and nitrate content in plants are the lowest with the application rate of 20 g/kg.To sum up,our study revealed that 20 g/kg iron-based biochar has the best effect on Tl passivation in contaminated soil,which can not only effectively reduce the content of bioavailable Tl in soil and crops,but also promote the growth of the crop and improve the quality of the crop.Therefore,iron-based biochar can be used as a good passivation remediation material for Tl contaminated soil,providing the research and theoretical basis for the follow-up research and practice.