Only within the past decade has the potential of metal biosorption by biomass materials been well established. For economic reasons, of particular interest are abundant biomass types generated as a waste byproduct of large-scale industrial fermentations or certain metal-binding algae found in large quantities in the sea. These biomass types serve as a basis for newly developed metal biosorption processes foreseen particularly as a very competitive means for the detoxification of metal-bearing industrial effluents. The assessment of the metal-binding capacity of some new biosorbents is discussed. Lead and cadmium, for instance, have been effectively removed from very dilute solutions by the dried biomass of some ubiquitous species of brown marine algae such as Ascophyllum and Sargassum, which accumulate more than 30% of biomass dry weight in the metal. Mycelia of the industrial steroid-transforming fungi Rhizopus and Absidia are excellent biosorbents for lead, cadmium, copper, zinc, and uranium and also bind other heavy metals up to 25% of the biomass dry weight. Biosorption isotherm curves, derived from equilibrium batch sorption experiments, are used in the evaluation of metal uptake by different biosorbents. Further studies are focusing on the assessment of biosorbent performance in dynamic continuous-flow sorption systems. In the course of this work, new methodologies are being developed that are aimed at mathematical modeling of biosorption systems and their effective optimization. Elucidation of mechanisms active in metal biosorption is essential for successful exploitation of the phenomenon and for regeneration of biosorbent materials in multiple reuse cycles. The complex nature of biosorbent materials makes this task particularly challenging. Discussion focuses on the composition of marine algae polysaccharide structures, which seem instrumental in metal uptake and binding. The state of the art in the field of biosorption is reviewed in this article, with many references to recent reviews and key individual contributions.

Biosorption of Heavy Metals

Particles of two different sizes (0·105–0·295 mm and 0·84–1.00 mm diameter) of two marine algae, Sargassum fluitans and Ascophyllum nodosum, were crosslinked with formaldehyde (FA), glutaraldehyde (GA) or embedded in polyethylene imine (PEI), followed by glutaraldehyde crosslinking. They were used for equilibrium sorption uptake studies with cadmium, copper, nickel, lead and zinc. The metal uptake by larger particles (0·84–1·00 mm) was higher than that by smaller particles (0·105–0·295 mm). The order of adsorption for S. fluitans biomass particles was Pb > Cd > Cu > Ni > Zn, for A. nodosum copper and cadmium change places. Uptakes of metals range from qmax = 378 mg Pb g−1 for S. fluitans (FA, big particles), to qmax = 89 mg Zn g−1 for S. fluitans (FA, small particles) as the best sorption performance for each metal. Generally, S. fluitans is a better sorbent material for a given metal, size and modification, although there were several exceptions in which metal sorption by A. nodosum was higher. The metal uptake for different chemical modifications showed the order GA > FA > PEI. A comparison of different sorption models revealed that the Langmuir sorption model fitted the experimental data best.

Biosorption of heavy metals (Cd, Cu, Ni, Pb, Zn) by chemically-reinforced biomass of marine algae

Native fungal biomass of fungiAbsidia orchidis, Penicillium chrysogenum, Rhizopus arrhizus, Rhizopus nigricans, and modified spruce sawdust (Picea engelmanii) sequestered metals in the following decreasing preference pb>Cd>Ni. The highest metal uptake was qmax = 351 mg Pb/gA. orchidis biomass. P.chrysogenum biomass could accumulate cadmium best at 56 mg Cd/g. The sorption of nickel was the weakest always at < 5 mg Ni/g. The spruce sawdust was modified by crosslinking, oxidation to acidic oxoforms, and by substitution. The highest metal uptake was observed in phosphorylated sawdust reaching qmax = 224 mg Pb/g, 56 mg Cd/g, and 26 mg Ni/g. The latter value is comparable to the value of nickel sorption by wet commercial resin Duolite GT-73. Some improvement in metal uptake was also observed after reinforcement of fungal biomass.

Accumulation of cadmium, lead, and nickel by fungal and wood biosorbents

Solution extraction of transition and post-transition heavy and precious metals by chelate and macrocyclic ligands

Acid/base and Cu(II) binding properties of natural organic matter extracted from wheat bran: modeling by the surface complexation model.

Iminodiacetic acid-cellulose sorbent, a chelating sorbent based on sawdust, was synthesized in a two steps reaction sequence. The pH dependence of me metal ion extraction for Cr(III), Cu(II), Pb(II) and Ni(II) was studied. The sorptive capacity and kinetic characteristic of the sorbent were found to be excellent in metal ion removal. The application of the sorbent for recycling and preconcentration of metal ions were investigated.

K. W. Cheng

Papers

Synthesis and characterization of iminodiacetic acid-cellulose sorbent and its analytical and environmental applications in metal ion extraction