Physical properties and structural characteristics of alkali modified fly ash

Fly ash as residue from coal combustion has potential for environmental applications as an adsorbent for water pollution treatment. Adsorption performance of fly ash depends on fly ash origin and chemical treatment. Modification by the chemical treatment could increase the adsorption capacity. In this paper, fly ash was alkali modified with NaOH solution at various concentrations (2 N, 4 N, 6 N, 10 N) at a temperature of 60 °C. The physical properties and structural characteristics of unmodified fly ash and alkali modified fly ash were studied from Brunauer-Emmett-Teller (BET) surface area and pore size analysis, and also scanning electron microscope (SEM) analysis. The results showed that alkali modification could increase surface area, average pore radius, and total pore volume in fly ash. Unmodified fly ash and alkali modified fly ash could be classified as mesoporous materials and exhibited type IV nitrogen adsorption-desorption isotherms with H3 hysteresis loop according to the classification of the International Union of Pure and Applied Chemistry (IUPAC). SEM observations revealed that modified fly ash had rougher surface and more porous structure than that of unmodified fly ash. Alkali modification had changed the physical properties and structural characteristics of fly ash that supports its application as an adsorbent. (paper)