Synthesis of high-purity Na-A and Na-X zeolite from coal fly ash

Abstract

Coal fly ash (CFA) was used as a raw material for the synthesis of zeolite molecular sieve. The synthesis began with the pretreatment of CFA to remove impurities (e.g., Fe₂O₃, CaO, etc.) under various acid types (HCl, H₂SO₄, and HNO₃) and acid/CFA ratios (5–25 mL_acid/g_CFA). High product purity (up to 97%) was achieved with HCl (20%wt), and acid/CFA ratio of 20 mL_HCl/g_CFA. The treated CFA was then converted to zeolite by the fusion reaction under various Si/Al molar ratios (0.54–1.84). Zeolite type A was synthesized when the Si/Al molar ratios were lower than 1, whereas sodium aluminum silicate hydrate was formed when the Si/Al molar ratio were higher than 1. The highest water adsorption performance of the zeolite product, i.e., the outlet ethanol concentration of 99.9%wt and the specific adsorption capacity of 2.31 × 10⁻² g_water/g_zeolite, was observed with the Si/Al molar ratio of 0.82. The zeolite was tested for its water adsorption capacity repeatedly 10 times without deactivation.

Implications: 

This work evaluated the technical feasibility in the conversion of CFA to zeolite, which would help reduce the quantity of waste needed to be landfilled. This adds value to the unwanted material by converting it into something that can be further used. The synthesized products were shown to be quite stable as water adsorbent for the dehydration of ethanol solution.

Additional information

Notes on contributors

Panu Panitchakarn

Panu Panitchakarn is a postgraduate student and Prasert Pavasant is a lecturer in the Department of Chemical Engineering Faculty of Engineering at Chulalongkorn University in Bangkok, Thailand.

Navadol Laosiripojana

Navadol Laosiripojana is a lecturer at the Joint Graduate School of Environment, CHE Center for Energy Technology and Environment, King Mongkut’s of Technology Thonburi, Thailand.

Nawin Viriya-umpikul

Nawin Viriya-umpikul is researcher at National Nanothecnology Center, National Science and Technology Department Agency, Thailand.

Prasert Pavasant

Panu Panitchakarn is a postgraduate student and Prasert Pavasant is a lecturer in the Department of Chemical Engineering Faculty of Engineering at Chulalongkorn University in Bangkok, Thailand.