Synthetic dyestuffs, a group of organic pollutants, are used extensively in textile, paper and printing industries and dyehouses. Due to their complicated structure, synthetic dyestuffs are more stable and show a high resistance in biodegradation [1]. There are different removal methods for the treatment of waste water from dyestuff such as adsorption [2] and advanced oxidation process (AOP) [3]. Among these methods, one of the novel, efficient and environmentally friendly approach to complete and rapid removal of dyestuffs is ultrasonic irradiation [4, 5]. In this study, manganese ferrite (MnFe2O4) as a magnetic powder was synthesized and used as an adsorbent in decolorization of reactive blue 250 (RB 250) from aqueous solution under sonication with ultrasonic bath and the results were compared with the stirrer method. Batch experiments were conducted to study the effect of the main parameters such as the amount of sorbent, concentration of sorbate, and stirring speed. Also, manganese ferrite powders synthesized with different types of precursors` anions, manganese (II) chloride and manganese (II) acetate, were used in the sorption process. According to the results, manganese ferrites obtained with manganese (II) acetate (acetate anion) show higher adsorption capacity than chloride anion. The optimum pH for the maximum adsorption efficiency was 1.8. The equilibrium between liquid and solid phase was described by Langmuir and Freundlich models. The time to reach equilibrium especially in the presence of ultrasound was very fast and removal efficiency was higher. It is suggested that the removal of RB 250 in the presence of ultrasound is a combination of degradation due to fenton like reaction in the presence of ultrasonic irradiation and sorption process. Furthermore, ultrasonic waves led to higher mass transfer on the surface of manganese ferrite and increased the available sorption sites by collapse of cavitation near the surface. Kinetics models were investigated and results in agreement with pseudo-second-order model.

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