Preparation Of Manganese Modified Biochar And Its Adsorption Of Heavy Metals In Water

Water is an important resource for human survival.With the rapid development of industry and agriculture,water pollution,especially heavy metal pollution in water,has become increasingly prominent.It is essential to find effective materials and methods for removing heavy metals from water.Biochar is a carbon-rich solid product formed by pyrolysis of biomass feedstock under lower temperature（300-700°C）and anaerobic conditions.It has abundant surface functional groups,unique interface structure and physicochemical properties.In this paper,raw biochar was prepared by the thermal cracking using cow dung and peanut shell as raw materials.The effects of different raw materials on the adsorption of Pb（II）,Cu（II）and Cd（II）onto the biochars from aqueous solution were studied.Take an example.Then,the peanutshell biochar was activated by KMnO₄,（NH₄）₂S₂O₈ and MnSO₄.The effects of activation modification on the structureof biocharthe peanutshell biochar and its adsorption behavior for Pb（II）,Cu（II）and Cd（II）fromaqueous solution were investigated.The main research contents and results are included as following:1.Preparation of cow dung biochar（CDC）and peanut biochar（PSC）and their adsorption properties for heavy metalsRaw biochar CDC and PSC were prepared under anaerobic conditions at 500°C with cow dung and peanut shell as biomass materials.The structure of two biochars and their adsorption behaviors for Pb（II）,Cu（II）and Cd（II）in water were studied.The results show that:（1）The adsorption processes of Pb（II）,Cu（II）and Cd（II）ions by CDC and PSC are consistent with the Langmuir model,indicating that the adsorption process is monolayer adsorption.Pb（II）has the highest saturated adsorption capacity on CDC and PSC,which is significantly higher than Cu（II）and Cd（II）.The adsorption effect of CDC samples on three metal ions is better than that of PSC.At a temperature of 30℃and a pH of 5.5,the saturated adsorption capacity of Pb（II）on CDC was 111.34 mg/g,Cu（II）was 21.67 mg/g,and Cd（II）was 28.11 mg/g.The saturated adsorption capacities of Pb（II）,Cu（II）and Cd（II）on PSC were 36.76 mg/g,12.16 mg/g and 15.27 mg/g,respectively.（2）The adsorption process of CDC to Pb（II）is an endothermic process.Increasing the temperature is beneficial to the adsorption reaction,and the degree of chaos in the adsorption process is reduced.The adsorption process of lead by PSC is also an endothermic process,and the chaos of the system increases during the adsorption process.（3）The adsorption process of CDC on three metal ions is consistent with the quasi-secondary kinetic model,and the adsorption of Pb（II）is the fastest,followed by Cu（II）and Cd（II）.The adsorption process of Pb（II）by PSC is more consistent with the quasi-first-order kinetic model,while Cu（II）and Cd（II）are more consistent with the quasi-secondary kinetic model.The time from the largest to the smallest is Cd（II）>Cu（II）>Pb（II）.（4）The pHpzc of PSC and CDC are9.8 and 10,respectively,and the surface of the material is positively charged.（5）Both CDC and PSC have no obvious pore structure,and the specific surface areas are 8.48and 3.35 m²/g,respectively,which are relatively small.The ash content of CDC was26.78%,which was significantly higher than that of PSC.CDC has a lower polarity than PSC and higher aromaticity than PSC,and has more aromatic functional groups on the surface.2.Preparation of peanut crust modified by potassium permanganate and its adsorption properties for heavy metalsPotassium permanganate modified peanut shell charcoal（Mn-PSC）was prepared by volumetric impregnation treatment with potassium permanganate solution.The modification of potassium permanganate to biochar structure and Pb（II）in aqueous solution was studied.The influence of Cu（II）and Cd（II）adsorption behavior.The results show:（1）The adsorption process of Pb（II）and Cd（II）by Mn-PSC can be described by Langmuir model.When the experimental temperature is 30°C and the pH is 5.5,the adsorption capacity of Pb（II）is 156.60 mg/g.It is about 4 times that of PSC;the adsorption capacity of Cd（II）is 44.05 mg/g,which is significantly higher than that of PSC 15.27 mg/g.The adsorption curve of Cu（II）on Mn-PSC accords with the Freundlich model,and the 1/n is 0.15×10^-1.The adsorption performance is very good.（2）The adsorption kinetic curves of Pb（II）,Cu（II）and Cd（II）on Mn-PSC are consistent with the quasi-first-order kinetic model and the quasi-second-order kinetic model.It shows that the adsorption process of Mn-PSC on three kinds of metal ions has both physical adsorption and chemical adsorption.The adsorption can reach equilibrium in a short time,and the adsorption effect is much better than the original Peanut shell biochar.（3）The pHpzc of Mn-PSC is 9.7,and the surface is positively charged.As the ionic strength increases,the equilibrium adsorption amount decreases.（4）The ash content of Mn-PSC becomes large,and the oxygen-containing functional group increases.（5）The Mn element is uniformly distributed on the surface of the Mn-PSC in an amorphous form.3.Effect of modification methods on adsorption properties of peanut shell charcoalTwo kinds of manganese-modified biochar SM-PSC and SN-PSC were prepared by treating the PSC with potassium permanganate,manganese sulfate,ammonium persulfate and manganese sulfate after equal volume impregnation.The effects of manganese modification on the biochar structure and adsorption behavior of Pb（II）,Cu（II）and Cd（II）in aqueous solution were studied.The results show:（1）When the solid-liquid ratio is 1 g/L,the removal rate of SN-PSC is close to 100%,which is more suitable for practical applications.（2）The isothermal adsorption data of SN-PSC and Pb（II）,Cu（II）and Cd（II）ions were consistent with the Langmuir model.The saturated adsorption capacities were 866.56 mg/g,23.36 mg/g and 35.94 mg/g,respectively.The adsorption process of Pb（II）and Cd（II）by SM-PSC is more consistent with the Langmuir model.The saturated adsorption capacity is 230.43mg/g and 40.06 mg/g,respectively.The isotherm of SM（II）by SM-PSC is more in line with Freundlich.model.The adsorption effect of SN-PSC on Pb（II）is better than that of SM-PSC,while for Cu（II）and Cd（II）,the adsorption effect of SM-PSC is better.（3）The adsorption kinetic curves of Pb（II）,Cu（II）and Cd（II）on SN-PSC and SM-PSC are more consistent with the quasi-secondary kinetic model,and the adsorption process is mainly dominated by chemical adsorption.SN-PSC and SM-PSC significantly shortened the time for triple metal ions to reach equilibrium,especially Pb（II）reached adsorption equilibrium in 2 min.（4）The pHpzc of SM-PSC is 6.6,indicating that the SM-PSC surface is positively charged.The pHpzc of SN-PSC was 2.0,indicating that the SN-PSC surface was negatively charged.With the increase of ionic strength,the equilibrium adsorption amount of Pb（II）decreased by SN-PSC and SM-PSC.（5）The specific surface area of SM-PSC increased to 29.77m²/g,indicating that the sample modified by manganese sulfate and potassium permanganate became loose..The ash content of SN-PSC and SM-PSC increased,which were 16.48%and 19.37%,respectively,and the oxygen-containing functional groups of SN-PSC increased.The polarity of SN-PSC increases and the aromaticity decreases,while the aromaticity of SM-PSC increases and the polarity decreases.