小麦秸秆驱动菱铁矿热解制备磁性生物质碳及其吸附Cd^(2+)活性

Preparation of Magnetic Biomass Carbon by Thermal Decomposition of Siderite Driven by Wheat Straw and Its Adsorption on Cadmium

以小麦秸秆和菱铁矿为原料,在500℃下热处理改性,制备了一种C-Fe_3O_4复合材料.采用FTIR、XRD、SEM、BET、磁化率仪对C-Fe_3O_4复合材料(以下统称复合材料)进行表征.考察了接触时间、初始pH、初始Cd^(2+)浓度、离子强度对Cd^(2+)去除率的影响,结合吸附前后表征结果分析了复合材料对Cd^(2+)的吸附机制.结果表明:复合材料及单独煅烧制备的小麦秸秆炭的比表面积分别为23.38 m^2·g^(-1)和7.20 m^2·g^(-1),孔容积分别为1.04×10-1cm^3·g^(-1)和2.23×10-2cm^3·g^(-1),平均孔径分别为17.74 nm和12.38 nm;红外光谱显示复合材料和小麦秸秆炭表面富含羧基、羟基等具有金属离子吸附活性的官能团;磁化率测试结果显示复合材料的质量磁化率为42 900×10^(-8)m^3·kg^(-1).复合材料对Cd^(2+)的吸附动力学用准二级动力学模型拟合度最好;吸附等温线符合Freundlich模型;pH在3.0~6.0之间,吸附容量随pH增大而升高,pH在6.0~9.0之间,吸附容量趋于稳定;pH在4.0~9.0之间,解析量随pH增大而减少;离子强度从1 mmol·L^(-1)增至100 mmol·L^(-1),Cd^(2+)的吸附容量略有减少,解析率由0.51%提升至8.5%;说明复合材料主要通过表面络合作用及离子交换去除溶液中的Cd^(2+).此外,复合材料的磁化性能使其在固液分离方面比一般的吸附材料具有很大优势.

C-Fe_3O_4 composite material [magnetic biomass char（ MBC） ] was prepared by pyrolysis of a mixture of wheat straw and siderite at 500℃. The MBC was characterized by XRF,FTIR,XRD,SEM,XPS,and a magnetic susceptibility device. The effect of contact time,pH value,initial Cd^（2＋）concentration,and ionic strength on the adsorption capacity of the MBC to Cd^（2＋）was investigated.The results showed that the BET surface areas of the MBC and biomass char（ BC） were 23. 38 m^2·g^（-1）and 7. 20 m^2·g^（-1）,respectively,total pore volumes were 1. 04 × 10-1cm^3·g^（-1）and 2. 23 × 10-2cm^3·g^（-1）,and average pore diameters were 17. 74 nm and 12. 38 nm. The magnetic susceptibility of the MBC was 42 900 ×10^（-8）m^3·kg^（-1）. FTIR showed that phenolic hydroxyl and carboxyl functional groups bound metal ions on the surface of the MBC and BC. The kinetic data of the MBC were described well by the pseudosecond-order model. Isothermal adsorption of Cd^（2＋）by MBC and BC was fitted well by the Freundlich equation. The adsorption velocity increased with an increase of pH in the region 3-6 and then stabilized in the region 6-9. The adsorption capacity of Cd^（2＋）decreased slightly when ionic strength increased from 1 mmol·L^（-1）to 100 mmol·L^（-1）,whereas the desorption rate increased from 0. 51% to 8. 5%. The adsorption properties and characterization results illustrated that the removal mechanism of Cd^（2＋）likely was through adsorption and ion exchange on the surface of the MBC with a high amount of functional groups. In addition,magnetic adsorbents offered a significant advantage compared to other adsorbents in the aspect of separation from aqueous solution.