Adsorption of Cr(VI) from synthetic solutions and electroplating wastewaters on amorphous aluminium oxide

The adsorption behaviour of amorphous aluminium oxide was studied with respect to Cr(VI) in order to consider its application to purify electroplating wastewaters. A batch method was employed using Cr(VI) concentrations ranged from 10 to 200 mg/l. The Langmuir model was found to describe the adsorption process well, offering a maximum adsorption capacity of 78.1 mg/g. The effect of ionic strength (0-0.1 M KNO3), pH (3-9) and competitive solutes (molar ratio [Cr(VI)]/[SO42−] = 1 and 100) on the retention process was evaluated. Cr(VI) adsorption on amorphous aluminium oxide appeared to be dependent on ionic strength with a more pronounced effect in acid conditions. Conversely, adsorption was not affected by pH in acid medium, but decreased when pH sifted to alkaline values. The presence of SO42− greatly reduced Cr(VI) removal across the entire pH range when both solutes were present in similar concentrations. Amorphous aluminium oxide also showed a high adsorption capacity when used in the purification of Cr(VI) electroplating wastewaters. The adsorbent doses required to attain more than 90% of Cr(VI) removal varied between 1 and 5 g/l depending on Cr(VI) concentration in wastewaters.