高锰酸钾改性生物炭对U(Ⅵ)的吸附特性

选用农林剩余物加工制得生物炭,用强氧化剂(KMnO_4、H_2O_2、HNO_3)对生物炭进行化学改性,选择最佳改性方法。通过吸附试验得出用0.01 mol/L KMnO_4改性的生物炭除铀效果最佳。采用KMnO_4改性的生物炭对废水中的铀进行吸附,考察吸附剂投加量、溶液pH值、吸附时间、溶液初始质量浓度等因素对U(Ⅵ)去除效果的影响。结果表明,当吸附剂投加量为0.3 g/L、U(Ⅵ)质量浓度为10mg/L、溶液pH=6、温度为25℃、吸附时间为120 min时,改性生物炭对U(Ⅵ)的去除效果最佳,吸附量达到32.57 mg/g,比未改性前提高了67.9%。对改性前后的生物炭进行了SEM、XRD、FTIR表征及表面含氧官能团测定、吸附动力学分析。结果表明,改性生物炭对U(Ⅵ)的吸附过程符合准二级动力学方程及Langmuir等温吸附模型(决定系数R20.99)。这表明对溶液中铀的去除可能是化学沉淀作用的结果,改性后含氧官能团增加,对溶液中铀的去除也可能存在官能团络合作用与表面吸附,使吸附剂化学吸附能力增强,除铀能力提高。

Adsorptive capability of U (Ⅵ) on the biochar modified by KMnO4

The purpose of this paper is to investigate the adsorptive feature of the biochar modified by KMnO4 to remove the U (Ⅵ) ions from the aqueous solution. The biochar we have adopted in this experiment can be gained by processing the residues of the agricultural activities with crops. In this paper,we have analyzed the biochar modified by the strong oxidizing agent (KMnO4,H2O2,HNO3),respectively,while investigating the optimum conditions to find the mechanism through batch experiments. The experimental results we have gained show that the effect on the modified biochar adsorbent can be optimized by using 0. 01 mol /L KMnO4 solution on the U (Ⅵ) removal. At the same time,we have also traced the effects of the dosage,the pH value of the initial solution,the adsorption time,the initial concentration of U (Ⅵ) and other factors. For example,if the original concentration of U (Ⅵ) is 10 mg /L with the absorbent dosage of 0. 3 g /L for the length of time in 120 min at the temperature of 25 ℃ at pH 6,it would be possible for the modified biochar to increase its maximum adsorptive power of U (Ⅵ) to 32. 57 mg /g with KMnO4 being used as its activator,which can increase the efficiency of about 67. 9％ as compared with the biochar not modified. What is more,the structure of biochars can be identified and determined by using the BET surface area,X-ray diffraction (XRD),Fourier transform infrared spectroscopy (FTIR),and the scanning electronic microscopy. At the same time,we have also analyzed the adsorptive mechanism by determining the oxygen functional groups on the biochar surface before and after the necessary modification. The results of the aforementioned experiment indicate that the removal process of U (Ⅵ) with the modified biochar can be well described by the pseudo-second-order model. It fits also the Langmuir isotherm equation with its correlation coefficient being over 0. 99. Theoretically speaking,the removal mechanism of U (Ⅵ) ions from the sewage aqueous solutions can be attributed to the chemical precipitation,through which the modified biochar particles on their surface can be adsorbed by the great amount of the functional groups. Furthermore,the kinetics analysis shows that it has been possible for the adsorption rate to be controlled mainly through chemical adsorption. It also tells us that the chemical adsorption capacity of the modified adsorbent can be enhanced by increasing the oxygen-containing functional groups, whereas the adsorption rate of the adsorbent can obviously be improved.