Biosorption of metal ions byAzotobacter vinelandii.

Azotobacter vinelandii was better than eitherDerxia gummosa orRhizobium trifolii for sorption of UO 2 (2+) . Its maximum binding capacity was 0.25 mmol UO 2 (2+) /g dry biomass with an affinity constant of 333 l/mmol at pH 4.1 according to the Langmuir model. In a semisynthetic medium,A. vinelandii showed the highest sorption capacity in the early stationary phase. The binding of UO 2 (2+) , Cu(2+), Ca(2+) and Zn(2+) was affected by the pH of the solution. With HCl as eluent, virtually all the sorbed UO 2 (2+) was released. The presence of Cu(2+), Cd(2+), Ca(2+), and Zn(2+) inhibited the UO 2 (2+) biosorption whereas Mg(2+) and K(+) had no effect.