Research On The Repair Of Uranium Pollution In Farmland System Of Uranium Tailings Reservoir By Straw Decomposition And Carbonization Of Luffa Vine And Straw

In this paper,a large number of samples were collected from paddy fields around a uranium tailings reservoir in southern China.The physicochemical properties of rhizosphere soil and non-rhizosphere soil and the chemical forms of uranium were simulated.The effects of straw flooding on the chemical ecological effects of uranium in paddy field system were studied.Besides,we explored the remediation efficiency of uranium contaminated soil under different conditions.A carbonized material of luffa vine straw was prepared to study its adsorption efficiency for uranium pollution.The main results are as follows:（1）The physicochemical properties of rhizosphere soil and non-rhizosphere soil contribute to rice straw flooding decomposition,but have different effects on uranium chemical ecology in paddy field system.Through analysis,it is known that the uranium in the local paddy soil is mainly in the residue state,and the weak acid extraction state is slightly higher than the reducible state and the oxidizable state.The release amount of uranium in the rhizosphere soil is lower than that in the non-rhizosphere soil,which is mainly due to the higher oxygen content in the water at the initial stage.As the reaction proceeds,oxygen is gradually consumed and the uranium attached to Fe-Mn oxide film is released into water with the decomposition of the film.Soil p H and Eh increased and decreased with the increase of flooding time,respectively.Thus,the formation of uranium precipitation and the gradual decrease of uranium content in water.Compared with rhizosphere soil,the proportion of weak acid extractable,reducible and oxidable forms of uranium in non-rhizosphere soil is relatively lower under the condition of straw waterlogging decomposition.At the beginning of the reaction,the content of organic matter（SOM）in the soil decreased slightly.When the reaction reached a certain extent,the active anaerobic microorganisms were dominant,so the SOM consumption rate accelerated,leading to the higher SOM content in the non-rhizosphere soil than the rhizosphere soil.（2）Under different decomposition time,temperature and water soil ratio of rice straw,the decomposition rate of straw,the transportation of uranium in straw,the p H of organic matter（SOM）and aqueous solution,the content of Fe and Mn,and the content of uranium in soil and water were mainly affected by the biochemical reaction of microorganisms in different stages.Decomposition time mainly affects the activities of aerobic and anaerobic microorganisms to change the Eh potential and p H of the environment.Temperature mainly affects the activity of microbial reaction enzymes,and then changes the transport of uranium in the system.The ratio of soil to water mainly changes the water requirement and p H of microbial reproduction,thus affecting the chemical form of uranium.Straw decomposition promoted the transport of iron,manganese and uranium in soil,and the adsorption and leaching promoted the remediation ability of soil.With the addition of straw,the uranium leached from soil is easily absorbed by straw,resulting in higher uranium content in straw.However,with the further decomposition of straw,uranium will also be released.Organic matter（SOM）is the bridge of uranium transport in the farmland system.Straw returning is conducive to the remediation of uranium contaminated soil.（3）Considering the remediation of uranium pollution by biochar materials,the phosphorylated biochar（LAC-PO₄）was prepared by phosphoric acid modification method using luffa vine and straw as raw material.The effects of p H,original uranyl ion content,time and temperature on the adsorption of uranium by phosphorylated biochar were studied by static experiments.The adsorbent was characterized by IR and SEM.The results showed that the p H of the solution had a significant effect on the adsorption performance,and the adsorption effect was the best when the p H was 5.0,the adsorption equilibrium time was240 min,and the maximum adsorption capacity was 197 mg/g.