State Environmental Protection Key Laboratory of Wetland Ecology and Vegetation Restoration, School of Environment, Northeast Normal University, Changchun, Jilin, China.
Department of Civil and Environmental Engineering, University of Tennessee, Knoxville, Tennessee, USA.
Sci Rep. 2018 Sep 10;8(1):13558. doi: 10.1038/s41598-018-31967-5.
Red mud as a waste material is produced in large quantities by the aluminum industry. Heat activation has been used to enhance sorption capacity of red mud for its beneficial reuse as an effective sorbent. In this study, heat-activated red mud (HARM) was investigated for its Cd(II) sorption capacity under various process conditions (Cd concentration, pH and contact time) using response surface methodology (RSM). Analysis with RSM identified pH as the most important process parameter. The positive correlation between higher pH and greater Cd(II) sorption was likely due to: (i) decreased proton competition with Cd(II) for sorption sites at higher pH; (ii) enhanced sorption via ion exchange by monovalent Cd species from hydrolysis at higher pH; and (iii) improved thermodynamics of sorption at higher pH as protons are being released as products. Further analysis indicated the sorption process was thermodynamically favorable with a negative change in Gibbs free energy. Additionally, the sorption process exhibited a positive change in enthalpy, indicative of endothermic nature of sorption; this is consistent with sorption increase at higher temperature. These findings provide needed insight into the mechanisms underlying Cd(II) sorption by HARM for more effective applications of heat-activated red mud as sorbents for Cd(II) removal.
赤泥是铝工业产生的大量废弃物。热激活已被用于提高赤泥的吸附能力，以将其有益地再利用为有效的吸附剂。在这项研究中，使用响应面法（RSM）研究了赤泥在不同工艺条件（Cd 浓度、pH 和接触时间）下对 Cd(II)的吸附能力。RSM 分析确定 pH 是最重要的工艺参数。较高的 pH 值与更大的 Cd(II)吸附之间的正相关关系可能归因于：(i) 在较高 pH 值下，质子与 Cd(II)竞争吸附位点的能力降低；(ii) 通过水解产生的单价 Cd 物种的离子交换增强了吸附；(iii) 较高 pH 值下吸附的热力学更好，因为质子作为产物被释放。进一步的分析表明，吸附过程是热力学有利的，吉布斯自由能发生负变化。此外，吸附过程表现出焓的正变化，表明吸附是吸热的；这与在较高温度下吸附增加是一致的。这些发现为 HARM 吸附 Cd(II)的机制提供了必要的见解，以便更有效地将热激活赤泥用作 Cd(II)去除的吸附剂。
