Lignocellulosic residues are interesting materials for the production of heavy metal adsorbents for aquatic systems. Whole fibers taken from coconut (Cocos nucifera) husks were functionalized with the thiophosphoryl (P=S) group by means of the direct reaction with Cl(3)PS, (CH(3)O)(2)ClP=S or (CH(3)CH(2)O)(2)ClP=S in order to obtain an adsorptive system for 'soft' metal ions, particularly Cd(2+). These functionalized fibers (FFs) were characterized by means of elemental analysis, infrared spectroscopy, thermal analysis and acid-base titration. Adsorption isotherms for Cd(2+) fitted the Langmuir model, with binding capacities of 0.2-5 m mol g(-1) of FF at 25 degrees C.

One of the problems that affect the environment is the chemical pollution of the nature of the water, mainly by the presence of toxic metals, among them the chromium, copper, nickel, zinc, among others. Numerous studies report the application of biosorption with the use of Eichhornia crassipes for the treatment of effluents from diverse origins, with very satisfactory results. However, several factors influence biosorption, such as pH, temperature, and contact time, and, therefore, cannot be neglected. Submerged macrophytes have important prospective to bioconcentrate heavy metals due to their larger surface area compared to non-submerged plants. On the other hand, the magnetite nanoparticles also present good results for the treatment of aqueous solutions contaminated by chromium and by other metal ions. The adsorption capacity of the Fe3O4 nanoparticles is high for various metal cations. Besides, these nanoparticles, which constitute polymer nanocomposites, are of particular interest because they combine excellent magnetic properties, greater stability of magnetic nanoparticles, and have higher biocompatibility, allowing more excellent suitability with biological materials involved in the removal of metallic cations. Therefore, the treatments described in this study are of great relevance as excellent alternatives in the treatment of several types of effluents.

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