Synthesis, characterisation and CO2 adsorption potential of NaA and NaX zeolites and hydrotalcite obtained from the same coal fly ash

Abstract

Hydrotalcites and zeolites are materials characterised by a high capacity for CO2 adsorption and can therefore be useful adsorbents for the capture of CO2 from flue gases. In this study, two types of zeolites (NaXFA and NaAFA) were successfully synthesised from South African coal combustion fly ash. Their CO2 adsorption properties, as well as those of a hydrotalcite (HTFA) synthesized from the same fly ash in our previous work, were investigated and compared. In addition, this paper reports the CO2 adsorption capacity of a novel hierarchical morphology NaX-type zeolite (NaXFA) made from fly ash. This material was characterized by plate-like structures arranged in ball-like clusters with crystal widths of between 63 nm and 99 nm. NaXFA was characterised by very high CO2 physisorption properties and was therefore the most suitable candidate for low temperature and pressure swing adsorption generally required in short-term CO2 adsorption applications. In contrast, both physisorption and chemisorption properties were observed for NaAFA and HTFA. However, HTFA was the most suitable material for chemisorption of CO2. The findings demonstrated the suitability of utilising HTFA for both short- and long-term capture of CO2.