Synthesis of Cancrinite Zeolite From Toraja Natural Bentonite for Heavy Metal Removal From Wastewater

Abstract

This study explores the production of cancrinite (CAN) zeolite from bentonite found in Toraja (a place in South Sulawesi Province, Indonesia) and its effectiveness in removing Pb2+ and Fe3+ ions from wastewater. The synthesis was carried out using a hydrothermal method with varying NaOH concentrations, where a single phase of zeolite was formed at 5 M, as confirmed through XRD analysis. FTIR results showed the characteristics of CAN zeolite with typical absorption peaks at 676, 622, and 565 cm-1, as well as the presence of carbonate groups (CO₃2-) at 1300-1400 cm-1. SEM analysis revealed thin columnar needle-like crystals characteristic of CAN zeolite. Nitrogen adsorption-desorption tests revealed that CAN zeolite is mesoporous with an average pore size of 5.38 nm and a specific surface area of 51.97 m²/g. The optimal conditions for Pb2+ adsorption were achieved with a contact time of 180 minutes and a pH of 5, while for Fe3+, the optimal conditions were a contact time of 30 min and a pH of 3. The adsorption isotherm was evaluated using Langmuir, Freundlich, and Sips models, with the best described by the Sips model in non-linear fitting. The maximum adsorption capacities for Pb2+ and Fe3+ ions were 194.95 mg/g and 196.63 mg/g, respectively. The adsorption kinetics for both ions followed a pseudo-second-order kinetic model. This study reports about natural Toraja bentonite, a rarely explored precursor for CAN zeolite synthesis. It also assesses the zeolite's adsorption capacity for two metal ions of different valences, highlighting its potential in wastewater treatment.

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