Biosorption of hexavalent and trivalent chromium by palm flower (Borassus aethiopum)

In this paper, results of Cr(VI) and Cr(III) sorption from aqueous phase by palm flower (Borassus aethiopum) is presented. Batch kinetic and equilibrium experiments were conducted to determine the adsorption kinetic rate constants and maximum adsorption capacities. Both Cr(III) and Cr(VI) adsorption followed a second-order kinetics. For Cr(III), maximum adsorption capacity was 6.24 mg/g by raw adsorbent and 1.41 mg/g by acid treated adsorbent. In case of Cr(VI), raw adsorbent exhibited a maximum adsorption capacity of 4.9 mg/g, whereas the maximum adsorption capacity for acid treated adsorbent was 7.13 mg/g. There was a significant difference in the concentrations of Cr(VI) and total chromium removed by palm flower. In case of Cr(VI) adsorption, first it was reduced to Cr(III) with the help of tannin and phenolic compounds and subsequently adsorbed by the biosorbent. Acid treatment significantly increased Cr(VI) adsorption capacity of the biosorbent whereas, alkali treatment reduced the adsorption capacities for Cr(VI). However, in case of Cr(III), acid treatment significantly reduced the adsorption capacity whereas the adsorption capacity of alkali treated biosorbent was slightly less than that of raw adsorbent. FT-IR spectrum showed the changes in functional groups during acid treatment and biosorption of Cr(VI) and Cr(III). Column studies were conducted for Cr(III) to obtain the design parameters require for scale-up.