Zeolite synthesis from aluminum saline slag waste

Abstract

This work describes the synthetic procedures developed to obtain zeolite X (NaX), zeolite A (LTA) and sodalite (SOD) using aluminum saline slag waste (AlSSW) as aluminum source in a two-step hydrothermal method involving alkaline extraction of Al, with separation of the residual waste, and hydrothermal treatment at low temperatures and long reaction times. Use of the mother liquor obtained after filtration and separation of the zeolite is also analyzed in the alkaline extraction of Al. The synthetic parameters that determine the type of zeolite, purity, crystallinity, specific surface area, pore size and pore volume include the Si/Al molar ratio, pH, nucleation temperature and time, and crystallization temperature and time. These critical parameters were studied and determined to synthesize NaX, LTA and SOD as individual phases. The materials obtained were characterized by X-ray diffraction, scanning electron microscopy and N2 adsorption/desorption measurements at −196 °C. The characteristics of the best zeolites obtained are similar to those of IZA references and the specific surface areas are in the range of commercial ones: NaX ranges from 450 to 500 m2/g and LTA from 250 to 300 m2/g. The results show that it is possible to synthesize zeolites from AlSSW, thus allowing these materials to be applied as promising adsorbents and catalysts.