SUMMARYBiosorption of heavy metals by various types of non-living (microbial) biomass appears as a very cost-effective new alternative for decontamination of metal bearing effluents. The understanding of metal biosorption mechanisms has progressed to the point where the process is being readied for scale up and field applications. Packed bed sorption columns is perhaps the most efficient equipment for this purpose. Process engineering aspects are examined for successful application of newly discovered biosorption materials which serve as natural and very efficient ion exchangers. Easy regeneration of biosorbents increases the process economy making it possible to reuse them in multiple sorption cycles. Optimization of the sorption/desorption cycles results in metal-free effluents and small volumes of highly concentrated metal desorbing solutions facilitating a conventional follow-up metal recovery.

Protonated or Ca-form Sargassum seaweed biomass bound up to 40 mg/g of Cr(III) by ion exchange at pH 4. An ion-exchange model assuming that the only species taken up by the biomass was Cr(OH)2+ successfully fitted the experimental biosorption data for Cr(III). The maximum uptake of Cr(VI) by protonated Sargassum biomass at pH 2 was explained by simultaneous anion exchange and Cr(VI) to Cr(III) reduction. At pH <2.0, the reduction of Cr(VI) to Cr(III) dominated the equilibrium behavior of the batch systems, which was explained by the dependence of the reduction potential of HCrO4 - ions on the pH. At pH >2.0, the removal of Cr(VI) was linked to the depletion of protons in equilibrium batch systems via an anion-exchange reaction. The optimum pH for Cr(VI) removal by sorption lies in the region where the two mechanisms overlap, which for Sargassum biomass is in the vicinity of pH 2. The existence of the optimum pH for the removal of Cr(VI) may be explained by taking into account (a) the desorption of Cr(III) from biomass at low pH and (b) the effect of pH on the reduction potential of Cr(VI) in aqueous solutions. Seventy percent of Cr(VI) bound to the seaweed at pH 2 can be desorbed with 0.2 M H2SO4 via reduction to Cr(III).

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AbstractÐThe biosorption of Cu, Zn, Cd and Fe from multicomponent mixtures was studied in a¯ow-through column packed with Sargassum algal biosorbent in the Ca-form. The eects of competitive ion exchange such as the elution order of toxic metals from the column, and the concentration overshoots in column euent were investigated both experimentally and by means of an ion exchange equilibrium column model (ECM

Abstraet--Biosorption of Cu 2 + by Sargassum fluitans seaweed biomass protonated by an acidic wash or loaded with Ca -'+ is based on ion exchange. The uptake of Cu 2+ is respectively accompanied by a release of either H + or Ca -'+ into the solution phase. The effects of Ca-, H-and H/Ca-cycles on the performance of a continuous-flow biosorption fixed-bed were established. The Ca-cycle applied to Sargassum biomass in a packed bed led to a high degree of a column utilization but did not allow an effective Cu recovery. The H-cycle permitted 100% Cu recovery but also shortened the sorption column service time. The combined Ca/H-cycle was shown to be inefficient due to the time consuming regeneration of biomass from the H-form to the Ca-form. Biomass pretreatment with 1% (w) solution of CaCI2 and with 0.1 M HCI resulted in the same Cu uptake of 75 mg/g. The Ca-pretreated biomass lost approximately 30% of its Cu capacity with subsequent acidic wash. The equilibrium aspects of Cu removal and recovery in a biosorption column were analyzed through the concept of ion-exchange isotherms. The dynamics of Cu sorption and of biomass regeneration in a fixed-bed column was predicted by numerically solving the equations of a proposed ion-exchange model.