改性粉煤灰对废水中镉的吸附作用

以工业固废粉煤灰(FA)为原料,将其与NaOH和Ca(OH)₂混合后,在250 ℃下焙烧1.5 h,制得改性粉煤灰(MFA).利用扫描电镜(SEM)、能量色散X射线光谱仪(EDS)、X-射线衍射仪(XRD)、全自动比表面积分析仪(BET)和傅里叶红外光谱仪(FTIR)等技术分析MFA的理化性质.BET分析表明,MFA的比表面积比FA增大了20.6倍.SEM分析表明,FA表面玻璃相溶解,表面粗糙,具有多孔结构.FTIR分析表明,-OH官能团在Cd²⁺的吸附过程中具有重要作用.静态吸附试验研究表明,当MFA的投加量为0.2 g、Cd²⁺初始浓度为100 mg·L^-1、溶液pH为7、25 ℃下吸附90 min时,Cd²⁺的去除率达到97.3%;共存阳离子(K⁺、Na⁺、Mg²⁺和Ca²⁺)均会抑制MFA对Cd²⁺的吸附,其中Ca²⁺的抑制作用最强.Langmuir等温吸附模型和准二级吸附动力学方程能较好地描述Cd²⁺在MFA上的吸附行为,且最大吸附量为55.77 mg·g^-1.热力学研究表明,MFA对Cd²⁺的吸附是一个自发的吸热过程.MFA吸附能力优于FA,在废水处理方面有一定的应用前景.

Adsorption of Cd2+ from wastewater by modified fly ash.

The modified fly ash (MFA) was prepared through roasting the mixture of fly ash and NaOH/Ca(OH)₂ at 250 ℃ for 1.5 h. The physicochemical properties of MFA were analyzed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), surface area analyze (BET), and Fourier transform infrared spectroscopy (FTIR) techniques. Results from BET analysis showed that the BET of MFA was enlarged by 20.6 times compared with FA. Results from SEM analysis showed that the glass phase was dissolved, with a rough surface and porous structure. Results from FTIR analysis demonstrated that -OH played an important role in Cd²⁺ adsorption. Results from the static adsorption experiment revealed that the removal efficiency of Cd²⁺ reached 97.3% when 0.2 g MFA was applied while the concentration of Cd²⁺ was 100 mg·L^-1, the solution pH was 7.0, the adsorption temperature was 25 ℃ and the adsorption time was 90 min. In addition, the coexisting cations (K⁺, Na⁺, Mg²⁺, and Ca²⁺) might inhibit Cd²⁺ adsorption. Among all the cations, Ca²⁺ showed a most significant inhibitory effect on the removal of Cd²⁺. Langmuir isotherm and the pseudo-second-order kinetic models could well describe the adsorption behavior of Cd²⁺ on MFA, with the maximum adsorption capacity of 55.77 mg·g^-1. Meanwhile, thermodynamic studies showed that Cd²⁺ adsorption onto MFA was spontaneous and endothermic process. MFA had better adsorption capacity than FA and had certain application pro-spects in wastewater treatment.