| The main forms of chromium are Cr???and Cr???.Among them,Cr???is highly toxic,difficult to be biodegraded,and prone to food chain enrichment.The improper treatment of chromium-containing wastewater will cause harm to human health and the ecological environment.The adsorption method is considered to be the first method for treating Cr???in wastewater due to its advantages such as simple operation,low cost and high efficiency.Biochar obtained from the pyrolysis of corn stalk is a very good adsorption material,which has the advantages of porous structure,abundant oxygen-containing functional groups,low cost and wide adaptability.However,the adsorption effect of biochar on Cr???in water is affected by factors such as its physical and chemical properties and surface characteristics.Therefore,the properties and surface structure of biochar can be improved by using modification technology to improve its adsorption effect on Cr???in water.In this paper,based on the review of the treatment status of chromium-containing wastewater,the properties of biochar,the modification technology,and the treatment of hexavalent chromium in wastewater,the following studies were mainly done:1.The biochar was modified with ferromanganse oxide to prepare the ferromanganse oxide-biochar composites?F1M3BC400?.The preparation conditions were optimized by single factor experiments as follows:the mass ratio of iron and manganese of the modifier was m?Fe?:m?Mn?=1:3,and the pyrolysis temperature was400?.2.Comparing the adsorption performance of unmodified biochar?BC400?and modified biochar?F1M3BC400?,when the initial concentration of Cr???was 800mg·L-1,initial p H=2,the adsorbent dosage was 2 g·L-1,and adsorption time was 24 h,T=30?,the maximum adsorption amount of Cr???increased from 59.23 mg·g-1 to118.03 mg·g-1.In addition,after six cycles of adsorption and desorption,the removal rate of Cr???by F1M3BC400 was lower than the original 91.79%,but still maintained a high level at 60.76%,indicating that F1M3BC400 could be desorbed by 0.5 mol·L-1Na OH solution for reuse after adsorption saturation.3.Specific surface area and pore diameter?BET?,scanning electron microscope?SEM?,infrared spectroscopy?FTIR?,X-ray photoelectron spectroscopy?XPS?and other characterization techniques were used to characterize the materials.The results show that after modification,the specific surface area of biochar increased from 4.87m2·g-1 to 15.23 m2·g-1,and the functional group-COOH and-OH were also strengthened;and Mn O2 particles were attached to the surface of F1M3BC400samples,which could provide more adsorption sites;the p Hpzc of F1M3BC400 was 8.3,so when the solution is acidic or weakly alkaline,it is beneficial for F1M3BC400 to adsorb Cr???.These show that ferromanganse oxide modification improves the adsorption performance of biochar.4.The optimal reaction conditions obtained by response surface methodology as follows:p H=1.66,initial Cr???concentration is 57.05 mg?L-1,and the asorbent dosage is 2.36 g?L-1.Under these conditions,the actual Cr???removal rate is 94.28%.5.The pseudo-second-order kinetic model can better describe the adsorption process of Cr???by F1M3BC400,indicating that the chemical adsorption process is the rate-limiting step of the whole adsorption reaction.The langmuir model fit the adsorption process of Cr???on F1M3BC400 well,indicating that the adsorption of Cr???by F1M3BC400 is monolayer adsorption.Thermodynamic studies show that the adsorption of Cr???by F1M3BC400 is a spontaneous endothermic reaction.6.According to the comprehensive research and analysis,the results show that F1M3BC400 removes Cr???in water mainly through electrostatic attraction,reduction,and the complexation reaction of Cr???with hydroxyl and carboxyl groups. |
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