镧改性生物炭对砷、镉的吸附特征研究

为研究改性生物炭对砷镉复合污染水体中镉和砷的吸附特征。本研究以牛粪、污泥、竹屑三种不同原料制备生物炭,利用镧(La)对生物炭进行改性,并采用元素分析、扫描电镜、傅里叶变换红外光谱和X射线光电子能谱等分析手段对改性前后的生物炭进行表征,结合等温吸附实验及吸附动力学实验,对比各生物炭对As (V)、Cd (II)的吸附性能并探讨其内在机理。结果表明,竹屑炭(BB)的芳香性大于牛粪炭(CB)和污泥炭(SB)。La改性使三种生物炭在热解过程中形成了酮类、酯类、羰基等含氧官能团,并在表面引入羟基。X射线光电子能谱结果显示La以氢氧化物的形式负载在生物炭表面。各生物炭对Cd (II)、As (V)的吸附符合准二级吸附动力学和Langmuir等温吸附方程。La改性生物炭对As (V)的最大拟合吸附量达到3.47～4.51 mg/g,显著高于未改性生物炭(1.82～2.50 mg/g)(p<0.05)。在As (V)、Cd (II)吸附过程中,La改性生物炭表面的La与As (V)发生络合反应,同时Cd (II)与镧基氢氧化物发生配体交换,生成Cd (OH)₂沉淀。本研究证明了La改性有效提高了生物炭对As (V)、Cd (II)同时吸附的能力。

Adsorption Characteristics of Arsenic and Cadmium by Lanthanum Modified Biochar

This paper aimed to investigate the co-adsorption characteristics of arsenic and cadmium in water by three lanthanum (La) modified biochars, which were prepared by cow dung, sludge and bamboo scraps, respectively. The raw and La-modified biochars were characterized by elemental analysis, scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, in combination with isothermal adsorption experiments and adsorption kinetics experiments to compare the performance of each biochar adsorption toward As(V) and Cd(II) and explore the mechanisms behind. The aromaticity of bamboo scraps biochar (BB) was greater than those of cow dung biochar (CB) and sludge biochar (SB). La-modification introduced hydroxyl groups and formed aromatic structures such as ketones, esters and carbonyl groups on the surface of biochar. The XPS spectra showed that lanthanum was loaded as hydroxide on the surface of the biochar. The adsorption of Cd(II) and As(V) by biochar was in accordance with the quasi-second-order adsorption kinetics and Langmuir isothermal adsorption equation. The maximum fitting adsorption capacity of La- modified biochar for As(V) was 3.47~4.51 mg/g, which was significantly higher than that of raw biochar (1.82~2.50 mg/g) (p<0.05). The main reason for the simultaneous removal of Cd(II) and As(V) by La-modified biochar was attributed to the complexation and co-precipitation function, As(V) complexes with La, while Cd(II) exchanged ligands with lanthanide hydroxide to produce Cd(OH)₂ precipitate. La modification effectively improves the ability of biochar to adsorb As(V) and Cd(II) simultaneously.