Use of Natural Zeolite and Its Mixtures to Refine High-Concentrated Heavy Metal-Contaminated Wastewater: an Investigation of Simultaneous Removal of Cd (II) and Pb (II) by Batch Adsorption Method.

This study investigated the simultaneous removal of Cd²⁺ and Pb²⁺ from wastewater using commercially available Japanese zeolite (JPZ) and its mixtures. A series of batch adsorption experiments were carried out to examine the simultaneous removal of Cd²⁺ and Pb²⁺ in binary and multi-metal solutions. Results revealed that JPZ (0.105–2.0 mm) exhibited a higher affinity for Pb²⁺ (>250 mg/g) over Cd²⁺ (<50 mg/g) in single metal solutions. However, in binary and multi-metal solutions, dominant adsorption of Pb²⁺ ions and hampering of Cd²⁺ ion adsorption were observed like in other types of low-cost adsorbents. Thus, steel slag (SS) grain, which is an industrial by-product and has a high affinity for Cd²⁺, was mixed with JPZ in different proportions to evaluate the potential use for simultaneous removal of Cd²⁺ and Pb²⁺. The JPZ+SS mixtures (JPZ+SS [4:1], JPZ+SS [1:1], and JPZ+SS [1:4]) were performed better than JPZ alone on simultaneous removal of Cd²⁺ and Pb²⁺. The JPZ+SS [1:1] mixture was identified as the most effective one for the simultaneous removal of Cd²⁺ and Pb²⁺ from binary and multi-metal solutions. The selectivity sequence in multi-metal solution was observed as Cd²⁺≈Pb²⁺≈Cu²⁺≈Zn²⁺≈Ni²⁺ and 100% removal of heavy metals were observed. The Cd²⁺ and Pb²⁺ removal by JPZ+SS mixtures mainly occurred due to the Ca²⁺ ion-exchange reaction along with the precipitation and surface complexation. Especially, the amount of SS grain in the mixtures played a vital role in the removal process of Cd²⁺ and Pb²⁺ from wastewater. [ABSTRACT FROM AUTHOR]