Adsorption characteristics of organic dyes on alumina powder from aqueous solutions

Adsorption of industrially important dyes (Acid Red 88, Acid Orange 8 and Bismark Brown R) on alumina from aqueous media has been investigated as a function of shaking time, amount of adsorbent, concentration of adsorbate and temperature. It is noted that the adsorption of Acid Red 88, Acid Orange 8 and Bismark Brown R on alumina decreases with an increase in temperature. The results obtained show that the adsorption isotherms at different temperatures are S-type and obey the Freundlich type of adsorption equation. Isosteric heats of adsorption (q_st) have also been calculated at different coverages from the adsorption isosters and have been interpreted. The q_st values for all the adsorption systems decrease with increasing surface coverage indicating that the alumina used possessed a heterogeneous surface with sites of different activities. The results also indicate that initial adsorption, whether by chemical or physical means, occurs first on the most active sites and then, as the concentration of adsorbate is increased, on sites of lesser activity.