Adsorption of Cd2+, Ni2+ and Zn2+ in aqueous solutions using anhydrite and red mud

ABSTRACT Various minerals and industrial waste have been studied for use as an adsorbent, in particular the anhydrite and the red mud. The red mud is an insoluble residue that is generated in large quantities during the processing of bauxite. The anhydrite is a calcium sulfate (CaSO4), crystallized as a rhombic way, and used as raw material in the industry. In this study, the Cd2+, Ni2+ and Zn2+adsorption capacity by anhydrite and by red mud was evaluated using adsorption isotherms obtained by the Langmuir and Freundlich models. The materials used showed adsorption ≥75±1% for all metals in aqueous solutions with a concentration of 0.5 mmol.25 mL-1. The Langmuir isotherm was more appropriate to describe the phenomenon of Cd2+, Ni2+ and Zn2+ removal, with highest adsorption capacity at 0.47 and 0.51 mmol.g-1 for Cd2+, 1.18 and 1.56 mmol.g-1 for Ni2+, and 0.84 and 1.47 mmol.g-1 for Zn2+, respectively. These values were higher than those ones obtained for other materials described in previous studies.

摘要 已有诸多研究探索以各类矿物与工业废弃物作为吸附剂的可行性，其中尤以硬石膏与赤泥为研究重点。赤泥是铝土矿加工过程中产生的大量不溶性残渣。硬石膏为硫酸钙（CaSO₄），呈斜方晶系结晶，是工业生产中的常用原料。本研究采用朗缪尔（Langmuir）与弗罗因德利希（Freundlich）模型拟合得到的吸附等温线，评估了硬石膏与赤泥对Cd²+、Ni²+及Zn²+的吸附性能。在所配置的浓度为0.5 mmol·25 mL⁻¹的水溶液中，两种材料对上述三种金属离子的吸附率均≥75±1%。朗缪尔吸附等温线更适用于描述Cd²+、Ni²+及Zn²+的去除过程，其最大吸附容量分别为：Cd²+达0.47与0.51 mmol·g⁻¹，Ni²+达1.18与1.56 mmol·g⁻¹，Zn²+达0.84与1.47 mmol·g⁻¹。上述吸附容量数值均高于既往研究中其他吸附材料的对应结果。