| Excessive application of nitrogen fertilizer in agricultural production leads to massive accumulation of nitrate nitrogen in the soil,which will be lost with irrigation or rainfall,and further threatening the quality and safety of the water body and stimulating agricultural non-point source pollution.Therefore,leaching resistance control of soil nitrate nitrogen?NO3?-N?and nitrogen removal from water have become the focus of many scholars.Biochar,as a porous carbon-rich material derived from biomass pyrolysis,has a regulatory effect on soil nitrogen conversion and nutrient transport,which makes its potential for slowing control of nitrate nitrogen leaching in soil to be noticed.However,this potential is often constrained by the amorphous nature of biochar surface.To improve its performance,the surface of biochar needs to be modified.In this study,peanut shells were used as raw materials to prepare biochar by anaerobic pyrolysis at 600?,and metal-gel composite modification was performed on it,through batch adsorption and control experiments.Combined with electron microscope scanning?SEM?,Fourier transform infrared spectroscopy?FTIR?,X-ray diffraction analysis?XRD?and other technologies,explore the effect of composite modified biochar on the adsorption of NO3?-N in water and the conversion of soil nitrogen.Therefore,it can provided a theoretical basis for the preparation and application of new environmentally friendly materials.Main results for this study are as follows:?1?Iron,manganese,magnesium ion modified make the specific surface area and pore volume of biochar increased 6.70-12.20 times and 2.30-5.00 times than unmodified biochar,respectively,and EC increased 0.50-3.10 times.Among them,iron ion modification reduced the pH of biochar by 0.76 units,and magnesium ion modification increased it by 2.36 units.The modification of iron,manganese and magnesium significantly enhances the adsorption capacity of biochar to NO3?-N.In the condition of pH=7,when the initial concentration of NO3?-N solution is 100 mg·L-1,the maximum adsorption capacity reaches 4.40,3.90,3.70 mg·g-1,increase 26.90%-48.60%than unmodified.The best mass ratios of iron,manganese,magnesium ions and biochar are 0.8,0.2,and 0.2,respectively.The modification effects represent as follows:iron ion>manganese ion>magnesium ion.?2?The adsorption dynamics can be better fitted by the Langmuir equation,adsorption dynamics accord with pseudo-first-order kinetic equation.The adsorption process is single layer adsorption,controlled by particle diffusion.Acidic conditions?pH<4?are favorable for the adsorption of NO3?-N by iron,manganese and magnesium ion modified biochar.In the presence of SO42-and Cl-in the solution,competitive adsorption sites were generated with NO3?,inhibiting the adsorption effect,of which the inhibition of Cl-is greater.The metal ions or oxides loaded on the surface of the modified biochar can adsorb NO3--N through electrostatic exchange and coordination exchange,tube energy groups such as hydroxyl groups,carbonyl groups and aromatic hydrocarbons were distributed on the surface,which may adsorb NO3--N through the nitro alkylation and nitration.?3?The composite modified biochar was prepared from iron ion modified biochar as the skeleton.Compared with single polyacrylamide gel modified biochar?PBC?,iron ion-gel compound modified biochar?PFBC?in the potassium nitrate solution was increased by 2.93 g·g-1 and 4.33g·g-1 respectively,and the adsorption capacity of NO3--N increased by 1.13 times than FBC.Polyacrylamide gel can effectively fill the pores of ferric ion biochar,and it is evenly distributed on the surface,which increases the number of hydrophilic groups such as-OH,-NH2,-C=O and-COO,at the same time increase-CH3,-CH2,C?H,C=C and other hydrophobic groups,the water absorption and water retention of the composite modified biochar are enhanced,the water absorption rate of PFBC is increased by 7.37%compared to PBC,and the salt tolerance is increased by 11.13%compared to PBC.Compared with BC and FBC,the removal rate of nitrate nitrogen in water by PBC and PFBC increased by 61.29%and 54.34%,respectively.?4?Addition of composite modified biochar?PFBC?has no significant effect on soil pH,but significantly increases soil EC value,inhibits the soil NO3--N leaching.The soil NO3--N leaching loss of PFBC decreased by 64.22%,relative to control treatment?CK?,and the soil leaching loss decreased by45.00%,58.04%,respectively,relative to FBC and unmodified biochar?BC?.The addition of PFBC can increase the soil microbial biomass carbon and microbial biomass nitrogen by 1.16 times and 3.26 times,respectively,and significantly enhanced soil respiration?P<0.05?.The CO2 emission intensity increased by 1.31%.Promote the process of soil ammonia oxidation,increase the soil nitrogen nitrification rate,NH4+-N oxidation rate increases by 0.88 times,NO3--N accumulation rate increases by 5.66 times.Adding compound modified biochar cannot change the soil microbial community structure,but changed the abundance of microbial groups,significantly reduce the soil microbial diversity index?Chao1,Observed species,PD whole tree,Shannon?,and significantly improve the soil absolute abundance of OTU315,OTU2267,OTU2262. |
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