Sorption of Uranium by Cladosporium Sphaerospermum Isolated From Soil

A kind of fungus, which was identified by molecular biology technology as cladosporium sphaerospermum, was isolated from the soil in a potential site for disposal of low radioactive waste.The sorption behavior of uranium by this living fungus was investigated. When the initial concentration of uranyl ion is 10 mg/L, the sorption efficiency for uranium is 94.1%. Sorption equilibrium time is about 24 h.The experimental data can be described with the pseudo-second order equation with much high regression coefficient.The uranium adsorbability is closely in connection with its pH value of which the best range is from 5 to 9. When pH ≤2, the thalli scarcely adsorb uranium. The relationship between sorption capacities and concentration of uranium in aqueous solutions can be described by the Langmuir adsorption equation. The accumulating adsorbing capacities finally reach to about 6.6 mg/g. Except Ca²⁺, coexistent ions such as Na⁺, K⁺, HCO₃^-, CO₃^2- and SO₄^2-_scarcely inhibite the sorption of uranium on the fungus. Three desorption agents was investigated. Citric acid is found to be the best desorbent with a desorption rate of up to 67%, followed by HNO₃ about 60%, and lastly EDTA about 40%. Additionally, the bacteria were observed by infrared spectroscopy. The results show that uranium is absorbed in the form of UO₂²⁺.