Biosorption of Metals: State of the Art, General Features, and Potential Applications for Environmental and Technological Processes

Abstract

The interactions among cells and metals are present since the life origin, and they occur successfully in the nature. These interactions are performed on cellular envelope (walls and membranes) and in cellular interior. They are based on the adsorption and absorption of metals by cells for the production of biomolecules and in vital metabolic processes (Palmieri, 2001). Some metals such as calcium, cobalt, copper, iron, magnesium, manganese, nickel, potassium, sodium, and zinc are required as essential nutrients to life existence. The principal functions of metals are: the catalysis of biochemical reactions, the stabilization of protein structures, and the maintenance of osmotic balance. The transition metals as iron, copper, and nickel are involved in redox processes. Other metals as manganese and zinc stabilize several enzymes and DNA strands by electrostatic interactions. Iron, manganese, nickel, and cobalt are components of complex molecules with a diversity of functions. Sodium and potassium are required for the regulation of intracellular osmotic pressure (Bruins et al., 2000). The interactions among metals and biomasses are performed through different mechanisms. For instance, on cellular envelope, the metal uptake occurs via adsorption, coordination, and precipitation due to the interaction among the surface chemical groups and metals in aqueous solution. Similar mechanisms are related in the exopolymeric substances (EPS). On the other hand, specific enzymes in some biomasses can change the oxidation state of the noxious metals followed by formation of volatile compounds, which removes the metal from aqueous solution. Finally, the life maintenance depends on the metal absorption by active transport according with the nutritional requirements of the biomass (Gadd, 2009; Palmieri, 2001; Sen & Sharadindra, 2009). The removal of metallic ions of an aqueous solution from cellular systems is carried out by passive and/or active forms (Aksu, 2001; Modak & Natarajan, 1995). As such live cells as dead cells do interact with metallic species. The bioaccumulation term describes an active process that requires the metabolic activity of the organisms to capture ionic species. In the active process the organisms usually tend to present tolerance and/or resistance to metals when they are in high concentrations and/or they are not part of the nutrition (GodlewskaZylkiewicz, 2006; Zouboulis et al., 2004).