Spent grain is a solid waste from the brewery process which is used as feed for ruminants or as organic fertiliser. Due to the large scale generation of spent grain, new technological and industrial applications are being developed. In this work, spent grain was modified by chemical treatments for use in the biosorption of hexavalent chromium. For spent grain treated with acid, alkali, petroleum ether and hydrogen peroxide, the amount of hexavalent chromium removed was respectively 97, 21, 0.9 and 0.5%. The kinetic data of spent grain biosorbent treated with acid, untreated and treated with alkali were applied to pseudo‐first order, pseudo‐second order and intraparticle diffusion models. The pseudo‐second order model showed the best fit to the kinetic data, indicating chemisorption in the biosorption processes. The effects of pH and biosorbent concentration were analysed for spent grain treated with acid. The optimum values for pH and concentration of the biosorbent were pH 2 and 2 g/L.