Study On The Adsorption Of Methylene Blue By Sludge-lavender Biochar And Green Synthetic Materials

In recent years,with the rapid development of China’s dye industry and industrialization,a large amount of sludge has been generated in the natural environment and a large part of the dyes are directly or indirectly released into the environment during production and use.Most of the dyes are unstable and difficult to degrade naturally when discharged into water.There are many ways to remove dyes from wastewater,and adsorption method is widely used because of its advantages of simplicity,efficiency and cheapness.Sludge contains a variety of complex components and has a wide yield.Resource management is the general trend of environmental protection.Lavender contains a variety of organic groups such as hydroxyl and amino groups,and is an excellent adsorbent.There are few studies on the removal of methylene blue（MB）by using lavender as adsorption material.In this paper,biochar was prepared by mixing sludge from sewage treatment plant and lavender,and biochar-loaded nano-zero-valent iron（LA-n ZVI/BC）was synthesized from lavender extract as biochar material.The adsorption properties of mixed biochar and green synthetic biochar for MB in aqueous solution were studied by adsorption method.The main conclusions are as follows:（1）Through scanning electron microscopy（SEM）,it can be observed that the dry sludge has a massive structure,and its surface is smooth and smooth.After high temperature pyrolysis,the lumpy structure on the surface of biochar is reduced,and the pores are scattered and rough,with agglomeration phenomenon.The porosity is larger than that of dry sludge,and the specific surface area increases significantly,which is consistent with the test results of specific surface area and pore size analyzer（BET）.By Fourier transform infrared spectroscopy（FTIR）,it was found that sludge biochar（SL）was rich in oxygen-containing functional groups and aromatic structures,which provided favorable conditions for adsorption of MB.（2）The sludge and lavender were pyrolyzed in accordance with the same quality.The sludge and lavender were mixed in accordance with the mass ratio of 3:2 and 1:1 and then the biochar was prepared by pyrolysis.The pyrolysis temperature was 500℃and the pyrolysis time was 180 min.Under these conditions,four biochar ratios were obtained by pyrolysis:sludge biochar（SL）,lavender biochar（LA）,sludge/lavender mixed mass ratio3:2 biochar（SL-LA 40%）,sludge/lavender mixed mass ratio 1:1 biochar（SL-LA 50%）.Through the adsorption experiment,the best conditions for MB adsorption were obtained:The initial p H of the solution is 8,the dosage is 0.05 g,the adsorption equilibrium time is360 min,and the initial concentration is 50 mg/L.Under these conditions,the experimental results show that the adsorption capacity of MB from large to small is LA>SL-LA 50%>SL-LA 40%>SL.In the range of MB initial concentration is 20-500 mg/L,The adsorption capacity of MB increases with the increase of initial concentration.The maximum adsorption capacity of LA and SL is 144.50 mg/g at 30℃,and 114.29 mg/g at 30℃.Quasi-second-order kinetics and Langmuir adsorption isotherm model can describe the adsorption process well.The adsorption rate constants of SL,SL-LA 40%,SL-LA 50%and LA were 0.00471,0.00694,0.00723 and 0.00365 g·（mg·min）^-1when the dosage of SL,SL-LA 40%,SL-LA 50%and LA was 0.05 g,the initial p H of solution was 8 and the initial concentration of MB aqueous solution was 50 mg/L,respectively.（3）The kinetic model and isotherm model showed that the adsorption of MB by biochar with four proportions was mainly monomolecular adsorption,and the adsorption process was endothermic.The increase of temperature was conducive to the adsorption,and chemical adsorption was the main.（4）Among the four ratios,SL has the lowest adsorption performance for MB,so green synthesis of sludge biochar loaded with nanometer zero-valent iron can improve its adsorption performance.The concentration of lavender extract,solid-liquid ratio and Fe SO₄·7H₂O were selected as the influencing factors,and the adsorption capacity of MB was taken as the experimental index.Through orthogonal experiment,the solid-liquid ratio（A）>the concentration of lavender extract（B）>the concentration of Fe SO₄·7H₂O（C）was obtained.The best condition is A₃B₁C₁.The solid-liquid ratio was 1:200 g/m L,the concentration of lavender extract was 100 g/L,and the concentration of Fe SO₄·7H₂O was0.1 mol/L.The adsorption properties and mechanism of MB in aqueous solution were studied by green synthesis.The results showed that compared with SL,the adsorption capacity of LA-n ZVI/BC for MB was significantly improved.Under neutral or weak alkaline conditions,adding 0.05 g of green synthetic materials,and vibrating at 30℃for360min,the initial concentration of MB in the range of 20～500 mg/L,the greater the initial concentration of MB,the greater the adsorption capacity,LA-n ZVI/BC adsorption capacity is 205.34 mg/g.Langmuir isotherm model can describe the adsorption process well.The adsorption mechanism is related to electrostatic interaction,hydrogen bond,coordination complexation,π-π,ion exchange and so on.（5）The green synthetic materials were characterized by SEM,FTIR and XPS（X-ray p Hotoelectron spectroscopy）.The results showed that:The lavender extract can reduce the bivalent iron ions to nano-zero-valent iron particles,form sp Herical particles on the surface of biochar,and form LA-n ZVI/BC materials uniformly.The organic compounds in the lavender extract,such as brass,polysaccharides,polyp Henols,etc,attach to the surface of LA-n ZVI/BC.Improve the material stability and MB adsorption.