MACROPOROUS CRYOGEL COMPOSITES FOR REMOVAL OF HEAVY METALS FROM AQUEOUS AND BIOLOGICAL MEDIA

Abstract

The deficiency of clean water is intensely associated with poor health, poverty and a general decline in living standards. Water is important not only for life but it is also the main resource for food and crops production and is used in most industrial processes. In spite of the natural source of water contamination, a continuous rise of heavy metals discharges to aquatic bodies caused by fast industrial development over the last century has been observed. Heavy metals such Cd2+ and Hg2+ are of the most toxic and, as all heavy metals, have a tendency to accumulate in the food chain potentially causing serious health disorders. Another source of water contamination is the nuclear power plants. Among the harmful radionuclides discharged are the radioisotopes of I-, Cs+ and Sr2+. To improve the availability of clean water, low-cost and effective treatment methods must be developed to remove toxic metal ions. Several water treatment technologies are available with adsorption/ion-exchange combined to chelation/complexation are the most effective. In this work, highly effective adsorbents based on polymeric cryogels were developed for the removal of Cd2+ Hg2+, Sr2+, Cs+ and silver-modified forms for targeted removal of I-. Two types of macroporous cryogels were synthesized by free-radical co-polymerization of acrylate-based precursors with allylamine under sub-zero temperature conditions. The adsorption/ion exchange capacity of cryogels is due to the presence of key monomers, methacrylic acid and 2-acrylamido-2-methyl-1-propansulfonic acid. The cryogels were comprehensively characterized and used for the removal of the above mentioned ions from model solutions. Kinetics and equilibrium studies were conducted, models were applied and in combination to post-sorption characterizations potential removal mechanisms were proposed. Finally, the cryogels were tested under environmentally relevant conditions (tap water, river water and sea water) and compared to commercial adsorbents (zeolite Y, ion exchange resin and activated carbon) for the removal of Hg2+ showing excellent behavior. After successful experiments on water, cryogels were used as enterosorbents in animal experiments by using rats. The rats were poisoned with LD50 dose of metals and were treated by cryogels. The results showed high survival rate and an overall decline of concentration of metals in animal tissues. The discoveries of this work demonstrate that cryogelic sorbents have possible implementation in water treatment and as poisoning antidotes.