Study On Preparation,Characterization And Adsorption Properties Of Galla Residue Biochar

Biochar prepared by pyrolysis of waste biomass under anaerobic conditions is a carbon-rich,stable,aromatized porous material.Since biochar contains various oxygen-containing functional groups,ash content,elemental composition and the like,it has been widely concerned that it has been used in the adsorption of organic pollutants,soil improvement,and promotion of crop growth.In this paper,galla residue was used as raw material to prepare biochar by oxygen-limited pyrolysis at different pyrolysis temperatures from 200°C to 600°C.The physicochemical properties of biochar from galla residue at different pyrolysis temperatures were determined.A series of characterization methods were used to analyze the biochar from galla residue.The content of gallic acid and ellagic acid in residue biochar was further determined.At the same time,aiming at the pollution of water caused by the large amount of lead and phenol waste water discharged every year,the adsorption effects of lead and phenol on the biochar of drug residue were studied in solution system,and the relationship between the structure of biochar of galla residue and its adsorption performance was analyzed,and the adsorption properties of lead and phenol were discussed by a series of influencing factors.The adsorption kinetics model and adsorption isotherm were used to fit the experimental data and preliminarily explore the adsorption mechanism.The results provide theoretical basis and data support for the application of galla residue biochar in water environment.The main results are as follows:（1）With the increase of pyrolysis temperature,the pyrolysis degree of galla residue biochars increased,the yield and volatile matter decreased,the content of carbon increased,the content of hydrogen,oxygen decreased,the content of p H,ash and fixed carbon increased,the number of surface functional groups decreased,and aromatic compounds were formed gradually（2）The content of gallic acid and ellagic acid in biochar of residue biochar at different pyrolysis temperatures was determined.The content of gallic acid and ellagic acid in residue biochar were higher at 200°C and was 39.50 mg/g and 24.53mg/g,respectively.The content of ellagic acid was 7.01,1.02,1.05 mg/g and no gallic acid between 300°C and 500°C.At 600°C,the content of gallic acid and ellagic acid were none.（3）The effects of p H value,contact time and initial concentration of solution on the adsorption of lead by biochar were investigated.The adsorption kinetics model and adsorption isotherm model were studied.The results showed that the equilibrium adsorption time of lead by residue biochar at different pyrolysis temperatures was 24 hours,and the maximum adsorption capacity of residue biochar for Pb²⁺was 200℃>300℃>400℃>500℃>600℃.The adsorption process accords with the quasi-second-order kinetic equation,and R²of the quasi-second-order kinetic equation is 1.0000,0.9998,0.9992,0.9990 and 0.9983,respectively from200℃to 600℃.The adsorption isotherm of biochar on Pb²⁺is more in line with Langmuir isotherm adsorption model,indicating that the mechanism of biochar adsorbing lead is chemical adsorption.The R_Lvalues of biochar adsorbing Pb²⁺in Langmuir model are all between 0 and 1,and the adsorption performance of biochar on Pb²⁺is better.（4）The effects of contact time,initial concentration and temperature on the adsorption of phenol by biochar were studied.The results showed that the higher the temperature was,the better the adsorption of biochar from residue was.The adsorption of phenol by biochar tended to balance in 10 h.In the same adsorption time,the adsorption capacity of four kinds of biochars for phenol was 400°C>500°C>600°C>300°C.The four kinds of biochars basically conform to Langmuir and Freundlich models.