Experimental Study On The Immobilization Of Arsenic In Polluted Soil By Activated Carbon Supported Nano-titanium Dioxide

Based on the serious non-point source pollution of cultivated soil in China,exogenous stabilizing agents play an irreplaceable role in the field of soil arsenic remediation.The addition of stabilizing agent makes arsenic immobilized or formed some new arsenic compounds in soils,which greatly reduces the mobility and bioavailability of arsenic in soil.Then,the absorption of arsenic by plants could be inhibited.In recent years,nano-TiO₂ and its modified composites have been widely used in the field of water arsenic removal because of their special physical and chemical properties,such as strong theoretical adsorption,large surface area,good photocatalytic properties and high arsenic affinity.To spread nano-TiO₂ in the remediation of arsenic contaminated soils,nano-TiO₂ must be modified to reduce the possible toxicity of nano-TiO_2.Therefore,it is of great theoretical and practical significance to study nano-TiO₂ composite modified materials as an stabilizing agent for arsenic pollution in soils.In this study,sol-gel synthesis was employed to prepare for activated carbon-supporting nano-TiO₂?ACT?and modified by iron?ACTI?.Use the TEM,XRD,SEM and other technologies to characterization the new meterial.The red soil,black soil,purple soil and yellow soil were as the test soil.The Toxicity Characteristic Leaching Procedure?TCLP?,Simple Bioavailability Extraction Test?SBET?and Cai-sequential extraction method were employed to investigated the dosage of material and incubation time how to affected asrenic bioavalibility and arsenic forms.And the result was compared with nano-titanium dioxide?particle diameter 15nm/100nm?,calcium carbonate,ferric oxide?Fe₂O₃?,activated carbon,zeolite,montmorillonite.The main results were summarized as follows:?1?The characterization results of ACTI and ACT showed that:the BET specific surface area is large and the volume of particles is small;XRD,SEM and TEM characterizations indicate that materials had a rough surface,good dispersion,narrow pore size distribution and successfully loaded nano-TiO₂and Fe₂O₃.The Infrared Spectrometry characterization results showed that the hydroxyl and Ti-O bonds both present in two material,and Fe-O bonds appear in the ACTI.?2?There was an influence on soil when adding activated carbon-supporting nano-TiO₂ and its Fe-modified materials in soil.The pH and the content of ammonium nitrogen increased in red soil,purple soil and yellow soil,while content of nitrate nitrogen decreased;the pH and the content of nitrate nitrogen of black soil decreased,the content of ammonium nitrogen increased.After adding the material,the pH of red soil and purple soil is neutral,yellow soil is alkaline,and the black soil is acidic.?3?Activated carbon loaded nano-titanium dioxide and its modified materials can reduce the TCLP leaching toxicity in soil effectively.The optimum amount was 0.05 g when treated with ACTI and ACT for 14 days?water/soil=2:1?.In this case,the TCLP leaching toxicity were cut down92.03%⁹6.02%and 89.85%⁹3.99%,respectively.When the ratio of water to soil was 2:1 and the addition amount was 0.05 g,ACTI and ACT could reached equilibrium on the seventh day in the tested soil.ACTI and ACT showed the largest decrease of arsenic TCLP leaching toxicity in yellow soil,but the stabilization effect of it in the purple soil were significantly higher than control material.ACTI and ACT treatment soil TCLP leaching toxicity decreased range of yellow soil>purple soil>red soil>black soil.The leaching toxicity of acidic soil and neutral soil was greater than that of calcareous soil when ACT and ACTI were used to treat with different pH values of soil.?4?ACT and ACTI can effectively reduce the bioavailability in the tested soil.When the water to soil ratio is 2:1 and treated for 14 days:the optimal addition amounts of ACT and ACTI in purple soil were 0.15 g and 0.10 g,and in this situation the bioavailability of soil is reduced 90.73%and 93.36%;the optimal addition of ACT and ACTI in yellow soil were 0.15 g,and in this situation the bioavailability of soil is reduced 70.71%and 73.49%.ACTI and ACT could decrease bioavailability of soil in the order of black soil>purple soil>yellow soil>red soil.The stabilization effects of ACTI and ACT in the tested soil were better than the control materials,and the fixing effect in purple soil was significantly different from other materials.When ACT and ACTI were used to treat different pH soils,the biogenicity of acidic soils showed the largest decrease.?5?The sequential extraction results of soil arsenic showed that:ACTI and ACT have higher stabilizing efficiency in the mobile fraction than mobilization fraction,and the residual content for soil after treatment is relatively high and can be increased more than 10 times.ACTI and ACT increased the residual state in the test soil,which decrease as the following:black soil>purple soil>yellow soil>red soil.The residual arsenic in acid soil increases greatly when pH of soil is different.The activated carbon-supporting nano-TiO₂?ACT?and its iron-modified material?ACTI?were highly effective in recovery of arsenic-contaminated soils,and the arsenic fixation effect is better in several types of soils.From the perspective of arsenic TCLP leaching toxicity,SBET bioavailability,and arsenic morphology transformation,the effect of ACTI on soil arsenic fixation was better than that of ACT.