MER Zeolite with Remarkable Pb2+ and Cd2+ Removal Capability Cost-Effectively Synthesized from Postprocessed Natural Stellerite

MER zeolite, a low-silica zeolite with an 8-membered ring aluminosilicate framework, has been recognized as a promising material in sorption, separation, and ion-exchange applications. Herein, we developed a cost-effective and rapid method to convert parent zeolite H-STI, which was derived from natural stellerite, into MER zeolite through interzeolite conversion with a crystallization time of 8 h. This MER zeolite exhibits high efficiency in removing Pb²⁺ and Cd²⁺ from simulated heavy metal wastewater over a pH range of 3–8. It also shows excellent selectivity in the presence of competitive cations, including Na⁺, K⁺, Ca²⁺, Mg²⁺, Zn²⁺, Cu²⁺, and Co²⁺. At 25 °C, with a MER-S dosage of 1/3000 g·mL^–1 for Pb²⁺ and 1/500 g·mL^–1 for Cd²⁺, the removal efficiencies were 99.7 and 99.9%, respectively. The distribution coefficients were 1097 L·g^–1 for Pb²⁺ and 550 L·g^–1 for Cd²⁺, and the sorption capacities reached 513 mg·g^–1 for Pb²⁺ and 171 mg·g^–1 for Cd²⁺, indicating that the product MER zeolite is one of the highest sorbents for Pb²⁺ and Cd²⁺ reported for zeolitic materials. The sorption for Pb²⁺ and Cd²⁺ both follows the chemisorption-dominated mechanism, driven by the ion-exchange process between the K⁺ in the channels MER-S and the Pb²⁺ or Cd²⁺ in solution. This work highlights the potential of rapidly synthesized MER zeolite for the effective removal of heavy metal cations, emphasizing its performance and practical applicability.