Adsorption of Cr(VI) from aqueous and electroplating wastewater

The aim of this work was to investigate the use of activated rice husk carbon prepared by thermal activation and activated alumina in the removal of Cr(VI) from aqueous solution and electroplating wastewater through column studies. The optimum solution pH was found to be 2 for activated rice husk carbon and 4 for activated alumina in the batch process. This was further applied to the aqueous solution to optimise the column bed height, diameter and flow rate of solute. These optimised conditions were applied to the electroplating wastewater. It was observed that activated rice husk is an efficient adsorbent and comparable to commercially available activated alumina. The percent Cr(VI) removal from wastewater was 73.3% with activated rice husk and 75.3% with activated alumina after 1 h continuous flow at the rate of 5 ml min(-1) from 7.5 cm bed height of adsorbent in a column having diameter 2.5 cm. A long contact time of the samples with adsorbents resulted in desorption of Cr(VI) from the adsorbent surfaces. However, the adsorption rate increased with the more available adsorbent surface sites when column bed height and diameter were greater. There was a decrease in Cr(VI) removal compared to aqueous sample due to the presence of other metal ions in the wastewater sample.