: Uranium and thorium were found to be accumulated extracellularly on the surface of Aspergillus Ñavus. The rate and the extent of accumulation were subjected to variations in environmental parameters such as pH, temperature and the interference of certain anions and cations. The rates of uranium and thorium uptake by Aspergillus Ñavus were increased by chemical pretreatment of the cells. Accumulated uranium and thorium were removed chemically from Aspergillus Ñavus cells. The rate of uptake of uranium and thorium at 25¡C^3¡C was found to be extremely rapid at pH values of 4É5^0É2 and 2É5^0É2 respectively. Electron microscopic examinations showed that uranium and thorium were accumulated in a dense layer around the surface of Aspergillus Ñavus cells.
This paper discusses the possible application to use free and immobilized Cunninghamella elegans for the removal of cobalt from aqueous waste solutions. Results indicated that the maximum uptake occurred at; pH 4.0-5.5 ± 0.2, temperature range between 15 and 50°C and stirring rate 250 rpm. The uptake increased with the increase of metal ion concentration up to 40 ppm. Also, it was found that the best biomass weights used for biosorption were 0.25 and 0.5 g for both free and immobilized biomass. The reuse of control alginate beads, alive and dead immobilized Cunninghamella elegans beads was investigated for five cycles. Results showed that the percent uptake decreased slightly after the first cycle. While, in the case of alginate beads there was increase in the second cycle then returned to the same level of uptake. The uptake of cobalt in the presence of Cr(VI) and Cd(II) at different mixture concentrations 40, 50 and 60 ppm was investigated. The results showed that the uptake amount of Co(II) in the presence of other metal ions was lower than Co(II) alone except for Ca-alginate beads. SEM studies for control alginate beads, alive and dead immobilized Cunninghamella elegans beads were conducted to investigate the beads before and after the accumulation of cobalt ions.
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