Red mud (RM) is a waste residue of alumina refinery, which consists of fine particles of silica, aluminium, iron, calcium and titanium oxides and hydroxides. Fly ash (FA) is the main combustion solid residues produced during the combustion of pulverized coal in thermoelectric power stations.
This study explores the feasibility of developing effective adsorbents from the industrial waste red mud and fly ash for phosphate removal. The experimental work emphasised on the evaluation of phosphate adsorption characteristics of these solid waste material. The effects of different activation methods, the adsorption isotherm, and kinetics were examined in batch experiments. It was found that all activated RM show different levels of ability to remove phosphate. In particular, the RM 2MHCl showed the greatest adsorption capacity among all the RM samples, which is approximately 0.57mg P per gram adsorbent. However, all the fly ash samples exhibited extremely low phosphate adsorption capacity, and any chemical or physical treatments did not show significant enhancement.
The Langmuir and Freundlich isotherm were used to analyse the adsorption data, the result indicated that the Freundlich isotherm provides a better fitting than the Langmuir isotherm. The kinetics of adsorption of phosphate onto red mud was studied on the basis of the pseudo-first order and pseudo-second order rate mechanism and it was found that the experimental data follow the pseudo-second order rate expression.