Study On Adsorption Mechanism Of Iron-modified Biochar On Nitrogen And Phosphorus In Water And Soil Improvement Effect

In recent years,the application and discharge of excess nitrogen and phosphorus fertilizers in agricultural production in China have caused the accumulations of nitrate nitrogen and phosphorus accumulation in soil.Water eutrophication is easily caused by rainfall and irrigation,which leads to non-point source pollution.Therefore,the removal of nitrate nitrogen and phosphorus from water and the control of nitrogen and phosphorus leaching acctracted considerable attention.In this study,three types of oil product waste were used as raw materials to prepare biochar at a high temperature（600℃）under oxygen-deficient condition.Iron(Fe³⁺)was used to modify the biochar,in order to improve the adsorption potential of nitrate nitrogen and phosphorus.A series of characterization tests were carried out on the prepared materials to analyze the structural changes of biochar before and after modification.The adsorption and desorption mechanisms of nitrate nitrogen and phosphorus were studied via adsorption kinetics,adsorption thermodynamics and other adsorption experiments and influencing factors.The main conclusions are as follows:（1）Compared with the unmodified treatment,the adsorption capacity of nitrate nitrogen of the three biochar under the optimal modified condition was increased by 8.11～16.68 times,And the adsorption capacity of phosphoru of the three biochar was increased by 19.87～80.42times;（2）The surface structure of the three biochar modified was significantly changed.Compared with the unmodified biochar,the specific surface area and total pore volume of the modified biochar increased,the values of C/H and C/N increased,and the average pore size decreased.It was speculated that the rough particles with many micropores formed on the surface of the modified biochar provided more adsorption sites.The adsorption process may be mainly affected by the complexation and precipitation reaction of Fe³⁺and oxygen-containing functional groups.Compared with the unmodified biochar,the zero charge point of the three modified biochar increased,and the positive electricity was enhanced.（3）The pseudo-second-order kinetic equation could fit the adsorption kinetic process of nitrate nitrogen and phosphorus for modified biochar well（R²=0.962～R²=0.986）.Its adsorption behavior was more consistent with the Freundlich isothermal adsorption model（R²=0.987～R²=0.994）.The results show that the adsorption process of modified biochar for nitrate nitrogen and phosphorus is non-homogeneous chemisorption.Acid conditions（p H=3）are more conducive to the adsorption of nitrate nitrogen.Neutral conditions（p H=6～7）were more favorable for phosphorus adsorption.The removal rate of nitrate nitrogen and phosphorus increased with the increase of the amount of carbon,and the adsorption amount decreased with the increase of the amount of carbon.The maximum phosphorus desorption values of Fe HBC,FEDBC and Fe YBC were 1320.71 mg/kg～2329.12 mg/kg,which phosphorus desorption was 642.74 mg/kg～1650.78 mg/kg.It has a certain desorption regeneration potential;（4）With the increase of the amount of biochar,the leaching amount of nitrate nitrogen and phosphorus decreased gradually;Compared with C0 treatment,the cumulative leaching loss of nitrate nitrogen and phosphorus under FY3 treatment decreased by 90.31%and 65.45%.With the increase of culture time,the activities of urease,sucrase and catalase in soil increased gradually,while the activity of acid phosphatase increased first and then decreased.Overall,the application of biochar can significantly improve soil p H,delay the loss of nitrate nitrogen and phosphorus,significantly improve soil enzyme activity,enhance soil fertility level,and have a certain positive impact on soil improvement.Figure[42]table[15]reference[103]...