The simultaneous adsorption behavior and competitive interactions between As(III), As(V), Sb(III) and Sb(V) by ferrihydrite were evaluated in multi-component (binary, ternary, quaternary) systems. In binary systems, Sb(III) had a stronger inhibitory influence on As(III) adsorption than Sb(V) did, and As(V) had a stronger inhibitory effect on Sb(V) adsorption than As(III) did. In ternary systems, NO3-, PO43- and SO42- did not compete with the adsorption of As(III) and Sb(III). NO3- and SO42- also had no distinct effect on the adsorption of As(V) and Sb(V), while PO43- competed with As(V) and Sb(V) for surface sites. In quaternary systems, the simultaneous adsorption behavior of the four redox species was pH dependent. Sb(III) always showed the strongest adsorption affinity regardless of pH. At pH 3.5 As(III) showed the lowest affinity could be due to the presence and negative effect of Sb(lll) and As(V). The Freundlich model provided a good fit for the simultaneous adsorption data under quaternary conditions. The study of competitive/simultaneous adsorption of the four possible redox species onto ferrihydrite contributed to a better understanding of their distribution, mobility and fate in the environment. (C) 2017 Elsevier B.V. All rights reserved.