Green Synthesis of CHA Zeolite from Expanded Perlite Waste for Rapid and Selective Pb²⁺ and Cd²⁺ Removal

The increasing release of non-biodegradable heavy metals, particularly lead (Pb²⁺) and cadmium (Cd²⁺), poses severe risks to ecosystems and human health. Herein, we present a sustainable "treating-waste-with-waste" strategy that simultaneously addresses heavy-metal contamination in water and the accumulation of expanded perlite waste. Expanded perlite waste was directly converted into a high-purity, low-silica CHA zeolite via a simple, one-pot, template-free hydrothermal conversion. The resulting sodium-exchanged material (Na-CHA-p) demonstrated excellent Pb²⁺ and Cd²⁺ removal performance, featuring ultrafast adsorption kinetics (reaching equilibrium within 5 min for both ions), high adsorption capacities (555.6 mg·g^-1 for Pb²⁺ and 211.0 mg·g^-1 for Cd²⁺), and superior selectivity. This study demonstrates an efficient pathway for the high-value utilization of perlite waste and highlights the strong potential of waste-derived CHA zeolites as advanced adsorbents for heavy-metal wastewater remediation.