Adsorption behavior of chromium in an aqueous suspension of δ-alumina in absence and in presence of humic substances

Abstract

Abstract The radioisotope Cr-51 was exploited for studying the chromium adsorption behavior in aqueous media of alumina in aqueous media. Where, it represents 1.8% by weight and exists in earth’s crust in different forms. Factors affecting this adsorption behavior are pH, amount of alumina and humic acid presence. In case of pH adsorption curves, three different areas under peak can be described based on pH changes which lead to the formation of different species too. The first area is the maximum constant adsorption at pH, range 1–3, the second one is adsorption decreasing with increasing pH through pH range 4–7 and the third one is step-down adsorption at higher pH range. The increasing amount of alumina leads to increase in the percent adsorption, where 10 and 2 g/l alumina were found to have 100% while in case of 0.2 g/l it is 80%. The presence of humic acid decreases the adsorption of chromate with increasing pH to be 30% comparing to 80% in case of 0.2 g/l alumna at pH 2. This can be also indicated by adsorption capacity which is found to be 436.8 μg/g in case of 0.2 g alumina; and it decreases in presence of Humic Acid (HA) to 145.8 μg/g at same weight of alumina. Also, the equilibrium capacities are found as 54.6 μg/g for 2 g/l and 1.2 μg/g for 10 g/l. Triple layer model (TLM) was used for simulation of chromium adsorption behavior in presence of alumina with the applied conditions of study. The results showed high coincidence with the practically found data.