Biosorption of metals onto plant biomass: exchange adsorption or surface precipitation?

Heavy metal ions readily adsorb onto the nonliving biomass of many aquaphyt es. Further, in many cases the metal ions can be readily desorbed from the biomass by use of a suitable eluting agent, It has been shown in certain ca ses, at least, that the biomass can be subjected to a number of loading and elution cycles without the biomass losing its adsorption capacity. It has been widely reported that the adsorption is through a specific ion exchange mechanism and a number of researchers have shown experimental evidence sup porting such a mechanism. However, there is also evidence that the adsorpti on is through simple surface precipitation of metal hydroxide species, The present study examines some of the existing data on adsorption of metal ion s onto aquaphyte biomass and attempts to evaluate which mechanism is the mo re likely. (C) 2001 Elsevier Science B.V. All rights reserved.