Biosorption

Biosorption is defined as a physio-chemical interaction which occur between metal(loid)s and extra-cellular compounds such as polysaccharides, proteins and lipids with amino, carboxyl, phosphate and sulphate groups (Volesky 2003; Febrianto et al. 2009) . It is an alternative process for removing arsenic and trace metals from contaminated solutions and a mechanism of metal(loid) immobilization by biomass. (Veglio and Beolchini 1997; Kratochvil and Volesky 1998). Biosorption is defined also as the passive binding of trace elements on a biosorbent (biomass) containing chemically active sites or functional groups (e.g. Volesky 2003) . Numerous biological materials have been tested for the removal of toxic arsenic ions from aqueous solution over the last two decades. Arsenic biosorbents were taken from inactive, dead biological biomass, such as algae (Hansen et al. 2006; Vilar et al. 2006) . vascular plants (e.g. Mohanty et al. 2006; Pandey et al. 2009), fungi (Dambies et al. 2002; Say et al. 2003; Loukidou et al. 2003; Mohan et al. 2007; Cernansky et al. 2007) . and bacterial materials (e.g. Kuyucak and Volesky 1988). A plant-based biosorbent mainly consists of cellulose and lignins. Primary plant cell walls consist of micelles of cellulose, hemicellulose (including pectins) and glucoproteins. The negatively charged, carboxylic groups act as cation exchangers and anion repellers (Ross and Kaye 1994). An essential step for industrial improvement of biosorption is biomass immobilization which provides biosor-bent particles with the adequate size, density and mechanical strength required by continuous systems (Volesky 2003).

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