Fixed bed studies for the sorption of chromium(VI) onto tea factory waste

The adsorption of Cr(VI) ions from aqueous solutions onto waste of tea factory in fixed beds was investigated. Experiments were carried out as a function of liquid flow rate, initial feed of Cr(VI) concentration, particle size, feed solution pH and bed depth. The bed capacities were found to increase with decreasing flow rate and particle size. The maximum bed capacities for the tested flow rates were found to be 55.65, 40.41 and 33.71 mg g(-1) at 5, 10 and 20 ml min(-1), respectively. When the initial Cr(VI) concentration is increased from 50 to 200 mg l(-1), the corresponding adsorption bed capacity appears to increase from 27.67 to 43.67 mg g(-1). The longest breakthrough time and maximum of Cr(VI) adsorption is obtained at the lowest examined pH value. Decrease in the particle size from 1.00-3.00 to 0.15-0.25 mm resulted in significant increase in the treated volume, breakthrough time and bed capacity. Breakthrough volume varies with bed depth and the treated volume considerably increases from about 4200 to 11800 ml as the bed depth increases from 5 to 30 cm. Thomas model for tea factory waste on Cr(VI) adsorption was used to predict the breakthrough curves under varying experimental conditions. This study indicated that the tea factory waste can be used as an effective and environmentally friendly adsorbent for the treatment of Cr(VI) ions in aqueous solutions. (c) 2006 Elsevier Ltd. All rights reserved.