Removal of dyes from aqueous solutions by adsortion on mixtures of fly ash in batch and column techniques

Adsorption and removal of commercial dyes were studied in aqueous suspensions of fly ash mixtures
with a sandy clay loam soil of low organic matter content. The commercial dyes, acid orange 7, acid yellow
23, disperse blue 79, basic yellow 28 and direct yellow 28 represent the widely used nitroazo structures.
Batch and column experiments were carried out at equilibrium conditions for concentrations of
dyes between 5 and 60 mg l-1. The logarithmic form of Freundlich equation gave a high linearity and
the k constants are increasing with the increase of fly ash content in adsorbent mixtures and the affinity
between the adsorbent surface and adsorbed solute. The mean removed amounts of dyes by adsorption
batch experiments in soil mixture with 20% fly ash content were up to 53.0% for acid yellow 7,
44.9% for acid yellow 23, 99.2% for direct yellow 28, 96.8% for basic yellow 28 and 88.5% for disperse
blue 79. The removal of dyes from column experiments decrease with the increase of the solution concentration
form 10 to 50 mg l-1 at 20 °C, showing the process to be highly dependent on the concentration
of the solution. The mean removed amounts of dyes by adsorption on columns of soil mixture
with 20% fly ash content and for initial concentration of dye solutions 50 mg l-1 were up to 33.8% for
acid yellow 7, 59.4% for acid yellow 23, 84.2% for direct yellow 28, 98.2% for basic yellow 28 and 60.3%
for disperse blue 79.