Removal of hexavalent chromium ions from an aqueous solution by crude tamarind
(Tamarindus indica) fruit shell was examined in a rotating packed bed contactor by continuously
recirculating a given volume of solution through the bed. Reduction of Cr(VI) to Cr(III) within
the biosorbent appeared to be the removal mechanism. Depletion rate of Cr(VI) from, and
release of reduced Cr(III) ions into the aqueous phase, was influenced by mass transfer resistance
besides pH and packing depth. A mathematical model considering the reduction reaction to be
irreversible and incorporating intraparticle and external phase mass transfer resistances represented
the experimental data adequately. The study indicated that the limitations of fixed bed
contactor operating under terrestrial gravity in intensifying mass transfer rates for this system