Synthesis and characterization of zeolites prepared from industrial fly ash

Abstract

In this paper, we present the possibility of using fly ash to produce synthetic zeolites. The synthesis class F fly ash from the Stalowa Wola SA heat and power plant was subjected to 24 h hydrothermal reaction with sodium hydroxide. Depending on the reaction conditions, three types of synthetic zeolites were formed: Na-X (20 g fly ash, 0.5 dm3 of 3 mol·dm-3 NaOH, 75 °C), Na-P1 (20 g fly ash, 0.5 dm 3 of 3 mol·dm-3 NaOH, 95°C), and sodalite (20 g fly ash, 0.8 dm3 of 5 mol·dm-3 NaOH+0.4 dm 3 of 3 mol·dm-3 NaCl, 95 °C). As synthesized materials were characterized to obtain mineral composition (X-ray diffractometry, Scanning electron microscopy-energy dispersive spectrometry), adsorption properties (Brunauer-Emmett-Teller surface area, N2 isotherm adsorption/desorption), and ion exchange capacity. The most effective reaction for zeolite preparation was when sodalite was formed and the quantitative content of zeolite from X-ray diffractometry was 90 wt%, compared with 70 wt% for the Na-X and 75 wt% for the Na-P1. Residues from each synthesis reaction were the following: mullite, quartz, and the remains of amorphous aluminosilicate glass. The best zeolitic material as characterized by highest specific surface area was Na-X at almost 166 m2·g -1, while for the Na-P1 and sodalite it was 71 and 33 m 2·g-1, respectively. The ion exchange capacity decreased in the following order: Na-X at 1.8 meq·g-1, Na-P1 at 0.72 meq·g-1, and sodalite at 0.56 meq·g -1. The resulting zeolites are competitive for commercially available materials and are used as ion exchangers in industrial wastewater and soil decontamination. © 2014 The Author(s).