| In recent years,many studies have used corn stalk biochar modification as an adsorbent to adsorb heavy metals in wastewater,but the broad-spectrum modified biochar materials that adsorb heavy metals are few and the effect is average.In this study,oxygen-limited pyrolysis biochar BCw,pyrolysis biochar BCN,and microwave pyrolysis biochar BCv were prepared by using different pyrolysis technologies.And modified and prepared the corresponding 3 kinds of recyclable chitosan modified biochar.Through composition,cost analysis and characterization,one is selected as the adsorption research object;through the adsorption experiment of modified microwave pyrolysis biochar to Pb2+ and As5+ separately polluted aqueous solution,the effect of modified biochar on Pb(The adsorption behavior of Pb2+ and As5+;by adsorbing Pb2+ and As5+ to contaminate the aqueous solution.Explore its potential to repair complex polluted water bodies;through magnetic detection and recovery experiments on the recyclable chitosan modified microwave pyrolysis biochar（HCBCv-Fe）,explore its recycling value.In this paper,firstly,the ground corn straw was pyrolyzed under different conditions,then modified with HNO3 acid to enlarge the capacity,and then loaded with Fe3O4 by coprecipitation method to magnetize the biochar;Finally,chitosan coated biochar was prepared;By means of elemental analysis,yield,cost analysis,SEM,EDS,FTIR,BET specific surface area and XPS,it was found that biochar with higher aromaticity and polarity could be prepared by microwave pyrolysis at 500℃ for 50 min;The yield of BCv was 39.16%,and the specific surface area was 104.647 m2/g,which was higher than that of BCN and BCW;HNO3 activation significantly increased the pore volume and specific surface area of biochar,and was beneficial to the subsequent Fe3O4 loading.The pore volume of hbcv increased by 0.2961 cm3/g;After magnetization treatment,there were two peaks of 710.9 eV and 724.5 eV corresponding to Fe2p3/2 and Fe2p 1/2;The loading of chitosan increased the specific surface area and amino functional group content of biochar;The hcbcv Fe biochar completely modified by microwave pyrolysis has superparamagnetism,and the pHpzc is 4.41.Pb2+and As5+ single pollution adsorption experiments show that the adsorption capacity of HCBCvFe on Pb2+ and As5+ can reach 112.2 mg/g and 34.53 mg/g respectively.When the pH of Pb2+ and As5+ single adsorption systems is controlled within the range of 5-6 and 4-5,it is beneficial to be adsorbed by microwave pyrolysis biochar materials.After 180 min and 200 min adsorption treatments,microwave pyrolysis biochar materials the adsorption of Pb2+and As5+ reaches equilibrium.As the concentration of Pb2+ and As5+ increases,microwave pyrolysis biochar adsorption showed that the adsorption capacity increased and the adsorption rate decreased.Acid radical anions would compete for adsorption sites and reduce the adsorption capacity of HCBCV-Fe to As5+.The fitting results of adsorption experiments show that the pseudo-second-order kinetic model and Langmuir model can better describe the adsorption behavior of HCBCv-Fe to Pb2+.Moreover,the pseudo-second-order kinetic model and Freundlich model can better describe the adsorption behavior of HCBCv-Fe to As5+.The research of Pb2+and As5+ composite polluted water shows that the adsorption of Pb2+is more dominant in the adsorption process of the two kinds of metal composite pollution,and there is a competitive relationship with the adsorption of As5+.HCBCV-Fe adsorbing As5+ first and then Pb2+ can promote the adsorption of Pb2+.The magnetic separation performance of HCBCv-Fe shows that under the condition of an external magnetic field,HCBCv-Fe can be separated from water within 3 min.Desorption regeneration studies show that,HCBCv-Fe five desorption regeneration rates are:94.91%,92.62%,90.78%,88.86%,85.11%.HCBCv-Fe adsorption capacity of Pb2+,As5+ respectively decreased by 32.51%and 21.64%,the adsorption capacity can still reach 62.183 mg/g and 13.067 mg/g. |
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