Preparation Of Magnetic Biochar And Its Adsorption Properties For Pb²⁺

In our country,a large number of distiller’s grains wastes are produced every year,which contains a large amount of biomass resources.The unreasonable treatment of distiller’s grains will cause waste of resources,finding efficient resources treatment is an important topic.The widespread use of lead metal has led to the release of large amounts of Pb²⁺into nature,which in turn has caused serious environmental and human health problems throughout the world.Biochar is a carbon material rich in various functional groups obtained by thermal conversion of biomass under the condition of limited oxygen.Therefore,biochar materials have great potential in solving Pb²⁺pollution.This paper studied the preparation of lees biochar using lees as raw material,further activated lees biochar by K₂CO₃,loaded magnetic iron oxide by co-precipitation method,and used the prepared biochar material to remove Pb²⁺from wastewater.The prepared biochar and the process and mechanism of Pb²⁺adsorption by carbon materials were studied through various characterization test methods.Specific research conclusions are as follows:（1）Pyrolysis of distiller’s grains was performed in a sliding rail pyrolysis furnace at 400℃-800℃.With the increase of pyrolysis temperature,the yield of pyrolysis carbon decreases from 28%to 24%,the abundance of functional groups decreases,and the strength of oxygen-containing functional group increases significantly.The pore structure developed gradually,and the pore shape becomes regular round,but the pore wall is thicker.There are two kinds of pore structures,mesoporous and microporous,which are mainly mesoporous.Pb²⁺adsorption was carried out on the pyrolytic biochar at different temperatures.According to the adsorption capacity and characterization,the optimal pyrolysis temperature was 600℃.In the process of Pb²⁺adsorption by DC-600℃,the increase of p H significantly increased the adsorption capacity and removal rate.The increase of initial concentration made the adsorption capacity increase,while the removal rate decreased.The increase of temperature was conducive to the increase of adsorption capacity and removal rate,but the change trend was slow.The optimal adsorption conditions at DC-600℃were p H 5.5,initial concentration of Pb²⁺200 mg/L and reaction temperature 298K.At this time,the adsorption capacity was62.38 mg/g and the removal rate was 31.19%.（2）Pyrolysis was performed at 400℃to 800℃by adding activator K₂CO₃with mass ratio of 50%,100%and 200%to distiller’s grains.The addition of active agent and the increase of temperature will cause the yield to decrease.In the Pb²⁺adsorption experiment,the addition of activator significantly increased the adsorption capacity of Pb²⁺,and the adsorption capacity and removal rate of Pb²⁺first increased and then decreased with the addition of active agent.Through the analysis of the yield and adsorption capacity of Pb²⁺,the optimal pyrolysis temperature of 600℃and the optimal mass ratio of 100%were screened.With the addition of active agent,the abundance of functional groups increased,the proportion of oxygen-containing functional groups increased significantly,activated carbon produced a large number of micropores and mesoporous,showing a briquet-like,pore wall became thinner,a nanosheet structure,but when the value of active agent increased to 200%,the pore collapse,the number of pores decreased.The influence of p H,initial concentration and temperature on the adsorption of activated carbon is consistent with that of biochar.The optimal adsorption conditions of DC-K100%-600℃are p H 5.5,initial concentration of Pb²⁺600 mg/L and reaction temperature 298K.In this case,the adsorption capacity is 299.15 mg/g and the removal rate is 49.86%.（3）The mass ratio of activated carbon added to 25%,50%,100%of different mass ratio of iron,with the increase of the load of iron salt,the adsorption capacity appears to decrease first and then increase and then reduce the trend,the load of iron mass ratio of 50%,get the best adsorption effect.With the increase of Fe mass ratio,the peak strength of oxygen-containing functional groups increased,and a new characteristic Fe-O functional group appeared.The magnetic properties were successfully loaded on the activated carbon,and the magnetic properties were strong.After loading Fe₃O₄,some mesoporous pores were blocked,and the specific surface area decreased slightly,and the pore structure decreased.The effects of p H,initial concentration and temperature on the adsorption of magnetic carbon are consistent with that of activated carbon.The optimal adsorption conditions of DC-K100%-50%are p H 5.5,initial concentration of Pb²⁺600 mg/L and reaction temperature 298K.In this case,the adsorption capacity is 286.15mg/g and the removal rate is 47.69%.According to the response surface test results,the effect of p H is greater than that of initial concentration and temperature,and the response regression equation with better fitting effect is obtained.In the same molar concentration of polymetallic ion solution,DC-K100%-50%has better selectivity for Pb²⁺than Cu²⁺and Cd²⁺.In the study of recycling performance,the adsorption capacity of 600 mg/L solution is still better after four cycles,and the loss ratio of iron in the analytical solution is less than 3.5%.In the adsorption isothermal model,the experimental results are more consistent with the Langmuir model.In the kinetic study,the pseudo-second-order kinetic model fits well.The thermodynamic results show that the adsorption process is endothermic and the adsorption process is spontaneous.The adsorption mechanism of Pb²⁺in DC-K100%-50%is mainly chemical reaction,and pore adsorption also has a certain effect.