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Soybean stalk (SS), as a low-cost absorbent, has been used in this study to remove Remazol Black B (RBB) and Acid Orange 7 (AO7) dyes from aqueous solutions. The effects of operational parameters on the efficiency of dye removal, including solution pH, contact time, and initial dye concentration, have been investigated. All sets of experiments were carried out in batch mode. The results indicated that adsorption was strongly pH- and dye dose-dependent but slightly contact time-dependent. The equilibrium state for both dyes was reached after 60 min of the absorption experiment with more than 26% removal of dyes. The Freundlich and Langmuir adsorption models were used for the mathematical description of adsorption equilibrium and isotherm constants at 25°C. Both models were applicable for the description of dye adsorption isotherm in the concentration range studied. However, the Langmuir model showed higher correlation coefficient than Freundlich model. According to the Langmuir model, the highest adsorption capacity was found to be 17.5 and 9.9 mg/g for AO7 and RBB, respectively. Pseudo first and second-order models were used to determine the adsorption kinetics, and it was observed that pseudo second-order model was the best suited model for both dyes. The results revealed that SS could be employed as an effective and low-cost biosorbent for the removal of AO7 and RBB from contaminated effluents. POLYM. ENG. SCI., 54:239–245, 2014. © 2013 Society of Plastics Engineers