This study examined the lead biosorption capacities of two solid wastes from olive-oil production, two-phase olive mill solid (OMS) and olive stone (OS), using batch experiments at different temperatures. The aim was to determine the isotherms of these wastes and thus their applicability as alternative biosorbents for lead removal. In addition, the solids were characterised by Fourier Transform Infrared (FTIR) spectroscopy. The OS sorption isotherms were characterised as type I. However, a step characteristic of type IV isotherms was observed in the OMS lead ion sorption isotherms. Well-known non-linear isotherm models, such as Langmuir, Freundlich and Sips, were tested for fit to the OS experimental data, whereas a two-step Langmuir-type model and an adaptation of the Dubinin-Astakov model that can mathematically describe multistep-shaped isotherms were used for the OMS data. The maximum lead uptake was 6.57 mg/g for OS and 23.69 mg/g for OMS at 25 degrees C. The FTIR spectra before and after lead biosorption, confirmed that carboxyl groups were the main sorption sites for lead removal on the surface of both biosorbents. (c) 2010 Elsevier B.V. All rights reserved.