| Groundwater is an important freshwater resource for mankind,and its development and utilization have been increasing year by year in recent years.At present,about 61%of cities in the country use groundwater as a source of drinking water,and its water quality affects people’s health and safety.Studies have shown that the abuse of agricultural fertilizers,solid waste leaching and infiltration,and atmospheric deposition will all have a negative impact on groundwater quality.Among them,the pollution of farmland groundwater caused by the abuse of agricultural fertilizers is the main culprit of regional groundwater pollution.Groundwater pollution in farmland has a complex composition.Nitrate,as one of the most common pollutants,is widely detected in various polluted areas.Nitrate itself is not harmful,but the nitrite produced by its denitrification will cause serious harm to the human body.The development of practical and effective groundwater remediation technology brooks no delay.The iron-carbon micro-electrolysis technology has the advantages of wide application range,simple process,good comprehensive effect,etc.,and has broad application prospects in groundwater repair.The preparation innovation of iron-carbon materials is a hot topic in this field.In this paper,a new type of carbon-coated iron-carbon material was prepared by means of high-temperature carbonization reduction.The experiment discussed the influence of the sugar-iron mass ratio,carbonization reduction time,carbonization reduction temperature and pre-pyrolysis temperature on the removal effect of nitrate nitrogen of the prepared materials during the preparation process,so as to obtain the best of the new iron-carbon materials.Under the best preparation conditions,the SEM,XRD,FT-IR and nitrogen adsorption and desorption were used to characterize and analyze the apparent morphology,specific surface area,crystal structure and functional group composition of the iron-carbon material under the optimal preparation conditions.The basic performance of the material;the effect of the material dosage,initial solution concentration,initial p H and solution coexisting ions on the performance of the new iron-carbon material to remove nitrate nitrogen has been studied through static experiments,and the removal mechanism of the new material has been preliminarily discussed;The removal effect of the new iron-carbon material in the dynamic reaction was investigated.The main conclusions obtained are as follows:（1）The idea of preparing a new type of iron-carbon material by coating the reduced iron powder with agar and then carbonizing it at a high temperature is feasible.When the mass ratio of reduced iron powder to agar and starch is 1:3:1 and the mixed material is kept at a constant temperature of 800℃for 2h,the new iron-carbon material has the best removal effect on nitrate nitrogen..When the initial concentration of nitrate nitrogen is 30mg/L and the dosage is 20g/L,the removal rate of the new iron-carbon material for 48 hours without adjusting the p H is 85.6%,which is the removal rate of the reduced iron powder under the same experimental conditions.1.2 times,1.5 times of polysaccharide charcoal.（2）In the SEM image,it can be observed that the surface of the new iron-carbon material is wrapped with a sheet-like porous carbon shell,and the material has a large specific surface area;the nitrogen absorption and desorption test shows that the pore size of the new material is mainly distributed between 3.405～4.32nm.The material pores are mainly mesoporous,and the specific surface area of the new iron-carbon material is 208.281m2/g,which verifies the conclusion in the SEM;XRD test results show that the iron in the material mainly exists in the form of zero-valent iron,and the material is carbonized at high temperature After reduction,the conversion of iron oxide to zero-valent iron can be realized;FT-IR test shows that the surface functional groups of the new iron-carbon material are similar to that of polysaccharide carbon,but due to the inevitable oxidation of the material during storage,there are a small amount of Fe-O characteristic peaks in the test.（3）The effects of different experimental conditions on the removal of nitrate nitrogen by the new iron-carbon materials were investigated through static experiments.Studies have shown that the adsorption capacity of the new iron-carbon material is limited.With the increase of the initial nitrate nitrogen concentration,the unit adsorption capacity of the material for nitrate nitrogen continues to increase while the removal rate continues to decrease;the new iron-carbon material is under acidic conditions The removal of nitrate nitrogen can be achieved faster,and the removal effect is better.The material shows a better removal effect in a wider p H range.Under neutral conditions,the material also has a good removal effect on nitrate nitrogen.effect.Under the best experimental conditions determined by the static test,that is,the p H of the solution is 7 and the initial concentration of nitrate solution is 20 mg/L,1.5 g of the new iron-carbon material can remove 98.81%of nitrate after 48 hours of reaction.The presence of anions in the solution will seriously hinder the removal of nitrate nitrogen by the new iron-carbon materials,while Ca2+and Mg2+cations have little effect on the removal effect.（4）The experiment conducted data fitting analysis on the kinetic process of removing nitrate nitrogen from the new iron-carbon material.Among them,the quasi-second-order kinetic model has the highest value（0.956）.It shows that chemical adsorption plays a leading role in the process of material adsorption of nitrate nitrogen,that is,the new type of iron-carbon material mainly realizes the reduction and removal of nitrate nitrogen in water through electrochemical action;when the experiment is performed on the isotherm adsorption model fitting,it is found that the Langmuir equation is fitted The maximum unit adsorption capacity of is similar to the experimental value,and the degree of fit is also the largest,that is,the Langmuir isotherm adsorption model can better reflect the entire adsorption process of the new iron-carbon material for nitrate nitrogen.（5）The main product of new iron-carbon material reduction and removal of nitrate nitrogen is ammonia nitrogen.After 24 hours of reaction,the ammonia nitrogen content accounts for 68.7%of the initial nitrogen content;nitrite is an intermediate product in the reduction process,and its concentration first increases and then decreases.When the reduction and removal process of nitrate gradually stabilizes,The nitrite content in the solution also approached zero;the total nitrogen content in the solution dropped significantly after 24 hours,indicating that nitrogen was generated during the reduction process.（6）Column A with a new type of iron-carbon material as a filler shows a good removal effect in dynamic experiments.When the running time reaches 6120min,the material reaches complete failure,during which a total of 130.61mg of nitrate nitrogen is removed;when the dynamic test data is modeled,it is found that the Thomas dynamic model has a high correlation and the calculated equilibrium adsorption capacity It is the closest to the experimental value.Therefore,this model is more suitable for describing the dynamic adsorption process of nitrate nitrogen by new iron-carbon materials. |
