| Rice husk has been widely studied because of its high yield and utilization value in this era of rapid development of biomass research.Magnetic activated carbon can be recycled efficiently by the external magnetic field,which avoiding the secondary pollution caused by the loss of carbon.Now,most of the magnetic activated carbon is made by activated carbon,and the process is complex,its energy consumption is higher.Besides,original pores are easily blocked,and magnetic particles are easy to fall off.Therefore,it is of great significance to find a simple and efficient method to prepare activated carbon with high porosity and strong magnetic property.In this paper,a novel method of preparing magnetic activated carbon by one step has been put forward,in which magnetizing agent and activating agent are added to the rice husk,the processes of the activation and magnetization are carried out at the same time,and then magnetic activated carbon is obtained.The method proposed in this paper simplifies the process,reduces energy consumption,and magnetic agent inside generates magnetic particles,which are not easy to fall off,and do not affect the process of activation.The effect of pretreatments and activation parameters on the physical and chemical properties of magnetic activated carbon based on rice husk has been studied by controlling variable method,and the practical application of magnetic activated carbon has been investigated by adsorption experiment to Cr(VI).The results from researches of different pretreatments show that:The hemicellulose in rice husk is decomposed by hydrothermal method,and cellulose and lignin are released,thus the temperature and velocity of pyrolysis are increased.The cellulose and lignin are furtherly released after desilication,so rice husk is more easy to pyrolysis;the temperature of pyrolysis is reduced and the pyrolysis speed is improved by Na2CO3 remained after desilication.FeCl3·6H2O can promote the pyrolysis when the temperature is low,but inhibit after the temperature grows.And the carbon nanotubes are generated on the surface of carbon.FeCl3·6H2O is transferred to Fe3O4 in the activation reaction,which greatly enhanced the magnetism of activated carbon.The results from researches of activation parameters show that:The addition of ZnCl2 inhibits the generation of carbon nanotubes,but the new pores arc formed and enlarged inside the carbon.However,excessive ZnCl2 may cause the hole wall burnt or collapsed,resulting in a decrease of micropores,and the increase of mesoporous and large holes.With the increase of ZnCl2,the zinc iron complex formed,so the magnetic decreases.With the increase of activation time,pore structure slightly increases,Fe3O4 crystal zinc and iron complex form slowly.2 hours later,crystallization Fe3O4 has completed,but zinc iron complex continue to generate,so magnetic property of active carbon declines.With the raise of activation temperature,ZnCl2 is easier to volatile,which resulting in the decrease of specific surface area and pore volume.But the remaining activator reacts sharply,so the activated carbon obtained is dominated by mesoporous and large holes.Between 500 ℃～600 ℃,Fe2O3 transfers to Fe3O4 slowly,magnetic property enhances,but after 600℃,Fe3O4 is reduced to Fe3C,so activated carbon loses magnetic.The adsorption of magnetic activated carbon is a slow process,and the more developed the pore structure of magnetic activated carbon,the more time it takes to reach the saturation of adsorption.What influences the adsorption ability of magnetic activated carbon is the specific surface area and total pore volume of activated carbon.The best preparation technology of magnetic activated carbon which with not only adsorption capacity of Cr(Ⅵ)but also strong magnetic property is obtained in this paper:After hydrothermal pretreatment and desiliconization,rice husk is mixed with FeCl3·6H2O by 1:0.2,then steeped with ZnCl2 by 1:1,finally activates for 2 hours under 600℃,after washing and drying,magnetic activated carbon is obtained. |
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