Synthesis of Sodalite from Sepiolite by Alkali Fusion Method and Its Application to Remove Fe3+, Cr3+, and Cd2+ from Aqueous Solutions

Abstract

The aim of this article is to study the sodalite synthesis from sepiolite through an alkali fusion method followed by hydrothermal process, and to investigate its application in heavy metal removal. The fused precursors were prepared through mixing sepiolite with sodium hydroxide (NaOH) and potassium hydroxide (KOH) activators, at 650°C. Hydrothermal reactions were performed at 100°C, 140°C, 180°C, and 220°C. Under the hydrothermal treatment at 140°C, pure sodalite 1 was formed from fused precursor of sepiolite-NaOH, for 48 h, while pure sodalite 2 was synthesized from fused mixture of sepiolite and KOH, at 180°C for 72 h. Pure sodalites and raw material were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR) analyses. The potential of two sodalites for removal of Fe3+, Cr3+, and Cd2+ cations from 0.001, 0.01, and 0.1 M aqueous solutions was evaluated through a series of batch experiments. The optimum adsorption of Fe3+ and Cr3+ was achieved from 0.001 to 0.01 M solutions. In contrast, Cd2+ was removed most efficiently from 0.1 M solution. In terms of contact time, the maximum adsorption amount from 0.001 M solutions was achieved between 1 and 2 h for pure sodalite 1 and between 30 min and 1 h for pure sodalite 2. The highest adsorption rate from 0.01 to 0.1 M solutions was observed between 30 min and 1 h, for both pure sodalite 1 and pure sodalite 2. Sepiolite was shown to be successfully used as raw material for formation of pure sodalite, and subsequently, pure sodalite has considerable capability to be used for environmental cleanups.