Andres, and two co-authors, reported in 2003 that they have reviewed published work on the sorption of rare earth elements by microbial biomass. First, the biosorption capacities and the various experimental conditions performed in batch-reactor experiments are compared. Secondly, sorption modelling generally used in biosorption studies are described. Thirdly, the microbial cell wall characteristics of the metallic ion binding sites are considered. From these observations it seems that the important functional groups for metallic ion fixation are the carboxyl and the phosphate moieties. Moreover, the competing effect of ions like aluminum, iron, glutamate, sulfate, etc. is described. Finally, some adsorption results of the rare earth elements in dynamic reactors are presented.
Further, in the last 15 years, numerous studies have shown that micro-organisms (bacteria, yeast, fungi) may interact with ions such as heavy metals or radionuclides. Many types of phenomena can take place, such as biosorption, bioaccumulation, resistance/ detoxification mechanisms, and direct or indirect utilization in the microbial metabolism. It has been shown that lanthanum, europium and terbium. were accumulated during growth, in the space between the inner and outer membrane of the cell envelope (periplasmic space) oi Escherichia coli.
On the other hand, they may influence the environment by producing mineral acids. chelating agents such as siderophores, or by-products of the metabolism (organic adds etc.). For example, the interactions between a mycobacterial siderophore (mycobactin) and europium ions have been shown by a spectrophotometric approach. Moreover, some siderophores such as ferrioxamine B could deplete europium fixation by goethite or boehmite. Biosorption encompasses the uptake of metals by the whole biomass (living or dead) through physicochemical mechanisms such as adsorption in exchange or surface precipitation. The processes take place on the cell wall with rapid kinetics.
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