Study On The Adsorption And Controlled Release Behavior Of Atrazine In Soil By Biochar

Biochar is a new type of environmental functional material produced by high temperature pyrolysis(<700?)of biomass such as wood,livestock manure and straw under anaerobic or anoxic conditions.Biochar can be widely used in carbon sequestration,crop yield increase,water purification,and heavy metal adsorption and soil improvement due to its large porosity,large specific surface area and many functional groups.In the field of soil improvement,biochar not only has the function of ensuring fertilizer and increasing efficiency,but also can stabilize the adsorption of pollutants in the soil,thus becoming one of the research hotspots in the field of agricultural environmental protection.Triazine herbicides are chemically stable with high water solubility,migration and difficult to degrade,and are long–term residual herbicides,which can cause great environmental risks to groundwater sources.After entering the food chain,such compounds will cause cancer and birth defects,and can also interfere with the normal function of hormones,which has been listed as a list of endocrine disruptors in many countries around the world.In this paper,biochar was prepared by using tea–stalk as raw material.The typical triazine herbicide atrazine was used as the research object.The effects of carbonization temperature and activation method on biocharperformancewereinvestigatedrespectively.Different temperatures and conditions of different biochar were discussed.The adsorption effect of the prepared biochar on atrazine in water and soil,and the long–term effects of biochar and activated biochar on atrazine were revealed by interception experiments,slow release experiments and pot experiments.(1)Preparation of biochar by using discarded tea–stalk,control of temperature to prepare biochar(BCs)intermediates,activation of BCs and KOH at 700?to obtain products,and analysis of the surface area and scanning electron microscopy of the products to understand their micro structure.(2)The adsorption characteristics of GBCs prepared by different carbonization temperatures were studied with 10 mg?L~–11 of atrazine.After activation of BCs prepared at different carbonization temperatures(300?,500?,700?),the equilibrium adsorption capacity can be increased by 50.4 times,538 times,and 661 times,respectively,before activation.At the same time,the half–life of biochar was also shortened after activation.The half–life of BC–300 was shortened by 30 times and the maximum shortening was achieved.Therefore,not only the equilibrium adsorption amount and the maximum adsorption amount are increased,but also the adsorption half life is shortened.(3)The adsorption law was discussed by the isothermal adsorption curve fitting.It is found that the fitting effect of BCs on Freundlich is better,so its adsorption behavior should work together in multiple conditions.GBCs showed a good fitting effect on Langmuir,which was a typical monolayer adsorption,and the maximum adsorption capacity was GBC–700>GBC–500>GBC–300.Comparing the changes in specific surface area,what is known that the increase in the activation contrast surface area was the main reason for the adsorption increase.(4)Through interception and controlled release experiments,the effects of BCs and GBCs on the migration performance of atrazine were systematically studied.The long-term continuous adsorption and sustained release behavior of BCs and GBCs in soil were simulated by pot experiment.The interception experiment found that after 10 times of herbicide leaching,the BCs and GBCs administration groups could better retain atrazine,and the retention effects were 80%and 90%respectively.After 20 times of leaching,the retention rate of GBC-500 and GBC-700application group can still maintain more than 90%.It can be seen that the activated biochar of high SSA has excellent retention and persistence for atrazine.The release test results show that atrazine can be released rapidly in the original soil.After 20 washes with deionized water,the cumulative release of atrazine is about 85%,so atrazine was highly mobile in the original soil.In comparison,when BCs and GBCs were applied to the soil,the release of atrazine was significantly reduced.The cumulative release of the BCs administration group after 20 deionized water rinses was about 25%to 37%.The cumulative release in the GBCs administration group was 11%(GBC–300).This shows that GBCs have a good adsorption and immobilization effect on atrazine in the soil.In addition,GBCs have a certain reversible adsorption and have a controlled release effect.In summary,the adsorption and controlled release of triazine herbicides in soils by tea–stalk biochar prepared under different conditions were systematically investigated which not only provided a rational method for the efficient removal of triazine herbicides in soil,but also can be used for groundwater safety in China.Governance and agricultural production provide relevant theoretical basis and technical support.