ALKALI MODIFICATION OF FLY ASH FOR ADSORPTION OF SELECTED DYES

Abstract

Fly ash (FA) is an industrial waste material generated during coal combustion in thermal power plants. In order to reuse this kind of industrial waste, and at the same time to reduce its quantity, fly ash was used as a cheap material for the preparation of efficient adsorbents for the removal of selected dyes from water. For that purpose, different modification methods were used to obtain alkali-activated fly ash samples. The success of the modification process and characterization of the unmodified and modified materials was monitored by Fourier transform infrared spectroscopy, and scanning electron microscopy/energy dispersive spectroscopy. The adsorption properties of examined samples were studied through the adsorption of methylene blue, crystal violet, alizarin red, and methyl orange. All samples showed the highest adsorption efficiency for crystal violet removal, while the sample modified with a combination of NaOH, Na2SiO3, and diatomaceous earth (FA/geopolymer) was the most efficient adsorbent for all selected dyes. Therefore, the influence of initial pH value and contact time on adsorption was examined for the adsorption of crystal violet onto FA/geopolymer. It was found that alkaline modification improves the adsorption characteristics of fly ash making it a promising candidate to solve the problem of colored wastewater.