TRACE ELEMENTS SORPTION BY THE CHITOSAN-BASED MATERIALS
Authors: Pogorielov M. V., Gusak Ye. V., Babich I. M., Kalinkevich O. V., Kalinkevich A. N., Samokhvalov I. I., Danilchenko S. N., Skliar A. M.
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The most important function of enterosorbents is their ability to bind toxins both of exogenous and endogenous origin. Wide range of commercial sorbents applies in various intoxications, poisonings or infections, pathology of liver, pancreas or kidney with chronic renal failure. The toxic trace elements are determined among the most spread toxins. They get into the organism in different ways, including nutritional. Majority of the known sorbents exhibit high absorption properties for this type of toxicants, however development and research of new enterosorbents are relevant biomedical problem. Chitosan – a biologically active heteropolysaccharide consisting of N-glucosamine and N-aceto-glucosamine obtained by deacetylation of chitin, one of the most common natural polymers. Chitosan high sorption activity observed in several studies: so the active centers in sorption processes are amino groups, which form complexes with trace elements’ ions. Furthermore, a certain contribution is OH group (particularly the C3-position.) Adsorption – chelation (ion substitution) – is also discussed as possible mechanisms for the formation of complexes, wherein the interaction depends on the type of solution composition, pH, and the ion types. When cleaning the environment from pollutants, it is important to have not only an effective sorbent, but the sorbent in a convenient form. Powders are hard to remove; films and gels are not applicable for all cases. The most convenient form for sorption, are obviously porous beads or granules. In this regard, the aim of our research was to study the sorption activity of chitosan-apatite complex and lyophilized chitosan against toxic trace elements. Beads were obtained from a 2% solution of chitosan (200 kDa, 82 % deacetylation rates) by dropping the solution through a 2 mm diameter needle in a 5 % sodium hydroxide solution under continuous mixing. The beads were kept in the alkali solution overnight, permanently washed with water and freeze dried. Chitosan beads containing hydroxyapatite were prepared by adding a solution of chitosan in 1 M calcium chloride solution and 1 M solution of calcium dihydrogen phosphate (Ca/P ratio – 1.67). The beads were kept in a 5 % alkaline solution for 24 hours and then washed with water and freeze-dried. To determine sorption activity of samples, we placed 1 gram of each sample in a 100 ml solution (pH – 6.0) containing 5 mg per liter of a trace elements – Mn+2, Cr+3, Fe+2, Cd+2, and Cu+2. The solution was shaken by automatic shaker throughout the experiment at 30 oscillations per minute. We used activated carbon for comparison series. The solution was filtered in each series in 30, 60, 360 and 720 minutes and the content of trace elements was measure in a liquid phase by atomic absorption. It should be noted that for 12 h (720 min) the chitosan-apatite beads absorbed all trace elements almost completely (99–100 %), while the chitosan based absorbed cadmium and copper better exhibiting minimal affinity for iron, chromium and poorly absorbed manganese (Cd> Cu> Fe> Mn> Cr); activated carbon also absorbed cadmium and copper better, to a lesser sorbs iron, manganese and did not absorb chromium (Cu> Cd> Fe > Mn). When we used the chitosan-based beads as sorbents, it was difficult to consider the kinetics of absorption and the releasing of some elements in the solution after polymer restructuring. The chitosan apatite beads were
preferably hold in contact with a cleaning medium for 12 h; at the same time during the first 30 minutes that sorbent absorbed about 90 % of copper, manganese, iron, cadmium and 50 % of chromium. Beads of chitosan
during the first 30 min absorbed only 90 % of copper and more than 50 % of cadmium, manganese, and about 40 % of chromium.