改性蓖麻秸秆对镉的吸附特征研究

Study on the adsorption characteristics of modified castor straw towards cadmium

以蓖麻秸秆为研究对象,通过红外光谱、扫描电镜和比表面分析仪对改性前后蓖麻秸秆粉末的结构进行了表征,采用正交设计法研究了NaOH浓度、时间和温度对改性后蓖麻秸秆粉末对Cd^(2+)吸附的影响,并分析了改性前后蓖麻秸秆粉末对Cd^(2+)的吸附热力学和动力学特征。结果表明:NaOH改性使蓖麻秸秆中较多的羟基暴露出来,使得蓖麻秸秆的表面结构疏松、比表面积增加、有效吸附位点增加,提高了改性蓖麻秸的吸附能力;10%NaOH在150℃、反应8 h后制得的改性蓖麻秸秆粉末对Cd^(2+)的吸附率最大,达71.24%,是改性前的1.79倍,吸附率提高了78.50%;改性蓖麻秸秆粉末对Cd^(2+)的吸附是单层吸附,既有物理吸附也有化学吸附,改性后蓖麻秸秆粉末对Cd^(2+)的最大吸附容量是138.81 mg/g,是改性前的2.21倍,其吸附过程更适合用伪二级动力学模型描述。

To study the adsorption performance of the castor straw modified by sodium hydroxide to Cd^(2+),the structure of the castor straw powder before and after modification were characterized by infrared spectroscopy,scanning electron microscopy and specific surface area meter,and the effects of concentration of sodium hydroxide,modification time and temperature on the adsorption of Cd2 +by the modified castor straw powder were studied by orthogonal design. The results showed that after modification of sodium hydroxide,more hydroxyl groups exposed in the castor straw,the surface structure of the castor straw loosen,the specific surface area and the effective adsorption sites increased,and the adsorption capacity of the modified castor straw improved. The modified castor straw powder prepared by 10% NaOH at 150℃ for 8 h had the highest adsorption efficiency of Cd^(2+)up to 71. 24%,which was 1. 79 times of that of the unmodified powder,and the adsorption efficiency increased by 78. 50%. The adsorption of modified castor straw powder to Cd^(2+)was monolayer adsorption,including both physical adsorption and chemical adsorption. The maximum adsorption capacity of the modified castor straw powder on Cd^(2+)was 138. 81 mg/g,which was 2. 21 times higher than that before modification. The pseudo second order kinetic model is more suitable to describe the adsorption process.