Sorbent prepared from moss Rhytidiadelphus squarrosus has been used for obtaining quantitative data of the cobalt and strontium sorption from single and binary aqueous CoCl2 and SrCl2 solutions. It was shown that solution pH significantly influenced Co2+ and Sr2+ biosorption. The maximum uptake was reached at pH 5.0-6.0 and negligible biosorption was observed at pH 2.0. In both cases the Langmuir isotherm fits the experimental data better than the Freundlich isotherm. The maximum uptake capacity Q(max) at pH 6.0 calculated from Langmuir isotherm was 123 mu mol/g for Co2+ and 149 mu mol/g for Sr2+ ions. Results revealed that the presence of Co2+ ions caused more significant decrease of Sr2+ sorption in binary Co2+-Sr2+ mixtures than vice versa. Experimental biosorption data in binary system were well described by the extended Langmuir model and the values of affinity parameter b indicate higher affinity of moss biomass to Co2+ ions in comparison with those for Sr2+ ions. The scanning electron microscopy (SEM) connected with energy dispersive X-ray (EDX) analysis revealed the existence of Ca2+ <-> Co2+ and Ca2+ <-> Sr2+ ion exchange mechanism and confirms the key role of ion interactions in Co and Sr biosorption by moss R. squarrosus. (C) 2010 Elsevier B.V. All rights reserved.