Department of Biological and Chemical Engineering, Guangxi University of Science and Technology, Liuzhou City, 545006, China.
Guangxi Key Laboratory of Green Processing of Sugar Resources, Liuzhou City, 545006, China.
Environ Sci Pollut Res Int. 2021 Jan;28(3):2728-2740. doi: 10.1007/s11356-020-10692-5. Epub 2020 Sep 5.
Targeting the removal of Pb in wastewater, sugarcane bagasse was treated with nitric acid and an alkaline solution to prepare adsorbents. On a typical adsorbent, the adsorption isotherms agreed well with the Langmuir expression, and the maximum adsorption capacity reached 200.3 mg/g. In the presence of 150 ppm Ca, a common cation in natural water, the Pb adsorption capacity slightly declined. In contrast, Mg obviously prohibited the adsorption for Pb. The spent adsorbent could be regenerated at least five times through elution with an EDTA solution. EDS and XPS results demonstrated that nitric acid functioned as an oxidant instead of nitrification agent in the treatment of bagasse. The adsorption process was consistent with quasi-second-order kinetics. Based on thermodynamic studies, the changes in enthalpy and Gibbs free energy were calculated to be - 33.3 and ca. - 18 kJ/mol, indicating that the adsorption process was exothermic and spontaneous. The equilibrium Pb adsorption amounts were proportional to the numbers of carboxylate groups on different adsorbents. The binding energies of Pd 4f and Pd 4f XPS spectra of Pb adsorbed were 0.6-0.7 eV lower than those of free Pb(NO), indicating the transfer of electrons during adsorption. The conversion of hydroxymethyl groups in sugarcane bagasse into carboxylate groups, as well as the chelation between Pb ions and carboxylate groups, was validated in this work, which is beneficial for the treatment of wastewater polluted by lead ions.
针对废水中 Pb 的去除，利用硝酸和碱性溶液对甘蔗渣进行处理，制备了吸附剂。在典型的吸附剂上，吸附等温线与朗缪尔表达式吻合较好，最大吸附容量达到 200.3 mg/g。在天然水中常见的阳离子 150 ppm Ca 的存在下，Pb 的吸附容量略有下降。相比之下，Mg 明显抑制了对 Pb 的吸附。通过 EDTA 溶液洗脱，可使废吸附剂至少再生 5 次。EDS 和 XPS 结果表明，在甘蔗渣处理中，硝酸的作用是氧化剂而不是硝化剂。吸附过程符合准二级动力学。基于热力学研究，计算了焓和吉布斯自由能的变化，分别为-33.3 和约-18 kJ/mol，表明吸附过程是放热和自发的。平衡 Pb 吸附量与不同吸附剂上羧酸盐基团的数量成正比。吸附后 Pb 的 Pd 4f 和 Pd 4f XPS 谱的结合能比游离 Pb(NO)低 0.6-0.7 eV，表明在吸附过程中发生了电子转移。本工作验证了甘蔗渣中的羟甲基基团转化为羧酸盐基团，以及 Pb 离子与羧酸盐基团之间的螯合作用，这有利于处理受 Pb 离子污染的废水。
