Adsorption of Cr(III) and speciation of chromium in aqueous solution using Ambrosia beetle-generated acacia polycantha frass

Abstract

Acacia polycantha frass (APF) generated by boring activity of Ambrosia beetles was investigated using a batch technique for its potential to adsorb Cr(III) ions from aqueous solution. Studies were carried out to determine the effect of pH, adsorbent dose, and KBr concentration on the sorption behavior Cr(III) on the adsorbent. The adsorption process was found to be highly dependent on solution pH with maximum removal occurring at pH 11. Thermodynamic studies indicated that the sorption process was exothermic and spontaneous. Adsorption recoveries of up to 75 and 95% for a 5 mgL-1 solution were obtained for untreated and acid-treated APF respectively at room temperature. In all experiments the acid-treated adsorbent showed an apparently higher metal uptake than the untreated one. Reduction of Cr(VI) to Cr(III) in synthetic solution using hydroxylamine prior to adsorption preconcentration showed potential for studying chromium speciation.   Key words: Adsorption, entropy of activation, enthalpy of activation, chromium, speciation, acacia polycantha frass.