Uranium and thorium uptake on hydrophilic plants
The hydrophilic plants were used with the purpose of purifying the radioactive waters containing UO22+ and Th4+ ions. The efficiency of using these plants, rendering by the degree of uptake (bioaccumulation and biosorption) of these plants in the absence
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"Al.I. Cuza" University, Faculty ofChemistry, 11-Carol I, 6600- Iasi, Romania
Abstract. The hydrophilic plants were used with the purpose of purifying the ra-
dioactive waters containing
uol+ and Th4+ ions. The efficiency of using these
plants, rendering by the degree of uptake (bioaccumulation and biosorption) of these plants in the absence of ionic competition was studied in the case of radioactive effluents simulated by U0 2(N0 3) 2 and Th(N0 3) 4 solutions. Under identical experimental conditions, the degree of decontamination of radioactively wastewater decreases according to the following series: Riccia jluitans > Lemna minor > Pistia stratiotes > Elodea canadensis. The influence of certain environmental fac-
tors (like temperature, pH, anion nature, etc.) was studied in order to optimize the process. A thin layer radiochromatography study Ieads to the conclusion that the biochemical fractions in which U022+ and Th4+ place themselves are ofa polysaccharide and lipoid fractions.
lntroduction Biosorption is the property of certain dead organic masses to bind and concentrate various heavy metals, including radionuclides from highly diluted solutions; biomasses having this property, since they act like chemical substances, are ionic exchangers of biological origin. The cellular membrane of certain types of microorganisms, algae, fungus or even plants having separate organs is - mainly responsible for this phenomenon. Some new studies show that the biosorption process is a very complex one, metallic species being deposited in the solid biosorbent through a multitude of subprocess, among which the most significant ones are sorption, ionic exchange, complexation, etc (Volesky 1994). Biosorption also appears as part of the whole of process of retaining heavy metals and radionuclides on the surface ofliving cells and on the extracellular polymers (Nakajima et al. 1986; Francis et al. 1991). B. J. Merkel et al. (eds.), Uranium in the Aquatic Environment © Springer-Verlag Berlin Heidelberg 2002
480
Alexandru Cecal et al.
The contrary of biosorption is the active, metabo1ic bioaccumu1ation on 1iving cells during which the physico-chemica1 process mentioned above are supp1emented by the bio1ogica1 process of transport through membrane. This process depends on the degree of toxicity of the chemica1 species, on the radioactivity of the isotope accumu1ated, etc. (Pribil and Marvan 1976). For the purpose of purifying waters containing a-active radiocations there were used bacteria (Francis et al. 1990; Bouby et al. 1996; Wade Jr. and DiCristina 2000), fungus (Cebotina and Liubimova 1981; Tsezos et al. 1997), algae (Havlie and Robertson 1973; Horikoshi et al. 1979) or even superior plants (Duff et al. 1997). A study on the use of Lemna minor in retaining of 137Cs+ out of natural waters (Bergamini et al. 1979) lead to the idea of using this plant in purifying waters containing U0 22+ and Th4+ ions (Cecal et al. 1999, 2000).
Materials and methods The starting a-active solutions contain U02(CH3C00) 2 0.1 M (pH = 2.5),
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