This study describes the effects of cell condition, pH, and temperature on lead, zinc, and copper sorption to Acidithiobacillus caldus strain BC13 with a Langmuir model. Copper exhibited the highest loading capacity, 4.76 +/- 0.28 mmol g(-1), to viable cells at pH 5.5. The highest k(L) (binding-site affinity) observed was 61.2 +/- 3.0 Lmmol(-1) to dehydrated cells at pH 4.0. The pHs that maximized loading capacities and binding-site affinities were generally between 4.0 and 5.5, where the sum of free-proton and complexed-metal concentrations was near a minimum. Of additional importance, lead, zinc, and copper sorbed to viable cells at pH values as low as 1.5. Previous studies with other acidithiobacilli did not measure viable-cell sorption below pH 4.0. In separate experiments. desorption studies showed that far less copper was recovered from viable cells than any other metal or cell condition, suggesting that uptake may play an important role in copper sorption by At. caldus strain BC13. To reflect an applied system, the sorption of metal mixtures was also studied. In these experiments, lead, zinc, and copper sorption from a tertiary mixture were 40.2 +/- 4.3%, 28.7 +/- 3.8%, and 91.3 +/- 3.0%, respectively, of that sorbed in single-metal systems. (c) 2010 Elsevier B.V. All rights reserved.