Department of Social and Environmental Medicine, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
Department of Social and Environmental Medicine, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
J Environ Manage. 2020 Oct 15;272:111085. doi: 10.1016/j.jenvman.2020.111085. Epub 2020 Jul 24.
Powdered activated carbon blocks (PACBs) are waste products obtained from household drinking water purification systems. In this study, we demonstrate that they can be used as adsorbents for the cost-effective and environmentally benign removal of hexavalent chromium (Cr(VI)) from contaminated-water and rinse electroplating wastewater. To evaluate Cr(VI) sorption onto the PACB, studies on equilibrium, kinetics, and thermodynamics were performed using batch mode experiments. The experimental results indicated that Cr(VI) ions were efficiently adsorbed under acidic conditions (i.e., at initial pH below 3) and low initial Cr(VI) concentrations. The adsorptive behaviors of the PACB for Cr(VI) were well explained by the Langmuir isotherm, as well as pseudo-second-order kinetic models, suggesting that a Cr(VI) monolayer was adsorbed onto the PACB surface via chemisorption. The maximum adsorption capacity of Cr(VI) onto the PACB was determined to be 6.207 mg/g. The results of thermodynamic studies revealed that the adsorption process of Cr(VI) onto PACB was endothermic and non-spontaneous. Additionally, analysis of the PACB after Cr(VI) adsorption at an initial pH of 2 using scanning electron microscopy, energy dispersive spectrometry, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) revealed that the interaction between the surface oxygenic functional groups on the PACB and Cr(VI) was primarily responsible for Cr(VI) sorption via surface complexation and electrostatic interactions. Based on the result of XPS analysis, the presence of trivalent chromium on the PACB surfaces indicated that some synergistic redox reactions involving Cr(VI) could have occurred during the sorption process. Although a commercially available powdered activated carbon outperformed the PACB adsorbent with respect to Cr(VI) removal from wastewater, complete Cr(VI) adsorption could be achieved using relatively large quantities of the PACB. These findings indicate that the PACB adsorbent could be used as a cheap and efficient material for the removal of Cr(VI) from wastewater.
粉末状活性炭块（PACB）是家用饮用水净化系统产生的废物。在本研究中，我们证明它们可用作吸附剂，以从受污染的水中去除六价铬（Cr（VI）），并从冲洗电镀废水中去除六价铬（Cr（VI））。为了评估 PACB 对 Cr（VI）的吸附作用，通过批量实验进行了吸附平衡、动力学和热力学研究。实验结果表明，在酸性条件下（即在初始 pH 值低于 3 时）和低初始 Cr（VI）浓度下，Cr（VI）离子被有效吸附。PACB 对 Cr（VI）的吸附行为可以很好地用 Langmuir 等温线和准二级动力学模型来解释，这表明 Cr（VI）通过化学吸附单层吸附到 PACB 表面上。确定 PACB 对 Cr（VI）的最大吸附容量为 6.207mg/g。热力学研究结果表明，Cr（VI）在 PACB 上的吸附过程是吸热和非自发的。此外，在初始 pH 值为 2 时，使用扫描电子显微镜、能量色散光谱、傅里叶变换红外光谱、拉曼光谱和 X 射线光电子能谱（XPS）对 PACB 吸附 Cr（VI）后的分析表明，PACB 表面含氧官能团与 Cr（VI）之间的相互作用是通过表面络合和静电相互作用吸附 Cr（VI）的主要原因。基于 XPS 分析的结果，PACB 表面存在三价铬表明，在吸附过程中可能发生了一些涉及 Cr（VI）的协同氧化还原反应。尽管商业上可获得的粉末状活性炭在从废水中去除 Cr（VI）方面优于 PACB 吸附剂，但使用相对大量的 PACB 可实现完全去除 Cr（VI）。这些发现表明，PACB 吸附剂可用作从废水中去除 Cr（VI）的廉价且高效的材料。
