Biosorption of Strontium from Aqueous Solutions

The migration of strontium to the geosphere is one of the major concerns in a proper handling of radionuclide waste solutions. The costly chemical reagents of toxic nature, generating secondary pollution with low efficiency for a minute concentration of metal ions, make their physicochemical separation rather limited in the application. Adsorption onto solid substances like activated carbon, kaolinite, montmorillonite, and colloidal silica is simpler in operation and the most robust; however, their ineptitude at high sodium concentration and very acidic pH are the principal disadvantages of it. The microbial techniques using various biomaterials have been identified as the potential alternative because of being effective to uptake lower content of radionuclides, inexpensive, free of secondary pollution, and exhibition of electronegative characteristics through the different organic functional group present therein. The passive removal of metals, termed biosorption, requires the selectivity and high metal uptake capacity of substrates for the applied remediation scenarios. A detailed description of cell wall constituents of fungi, bacteria, and algae is provided in order to explain the selective sorption and/or accumulation of strontium from the radiotoxic waste solutions. The influential role of cellular structure, cell wall, storage, and extracellular polysaccharides is evaluated for the strontium sequestration. Furthermore, the binding mechanisms are discussed, including the involvement of key functional groups and the exhibited ion-exchange process.