Trivalent chromium and iron are the products of the traditional reduction of hexavalent chromium by ferrous salts in industrial wastewater. Although there have been a few studies of Cr(III) adsorption, none have considered the effect of Fe(III) on Cr(III) adsorption in a binary system representing expected products of hexavalent chromium in industrial wastewater. The biosorption of Cr(III) and Fe(III) ions onto pretreated ground orange peel in single and binary systems was studied in batch experiments using a variety of techniques. The kinetic results showed a rapid rate of biosorption of Cr(III) and Fe(III) in single and binary systems and mutual interference effects in the competitive binary Cr(III)–Fe(III) system. Second order kinetic models showed the best fit for all systems. The behavior of competitive Cr(III)–Fe(III) biosorption were successfully described by the multicomponent Langmuir model, obtaining maximum capacities for Cr(III) and Fe(III) of 9.43 and 18.19 mg/g respectively. SEM/EDS results confirmed that the metals adsorb on the surface and FTIR identified the hydroxyl groups on the carboxylic acids as the active binding sites.