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Introduction: Colored Wastewater due to various environmental problems should be treated before discharge to the environment. Colors have many variety and different methods used for color wastewater treatment, the most widely methods that used is the absorption process by the low-cost adsorbent. To determine the isotherms and kinetics adsorption Process, absorption of methylene blue cationic dye as an indexed color were investigated by activated thermal power plant fly ash from of Zarand.

Methods: In this experimental study, raw fly ash during 5h, acid concentration 1.8M, acid to fly ash ratio 7 and temperature 29±2 ˚^C was activated by sulfuric acid. After determining the optimal values of parameters in the absorption process (pH, contact time, concentration of adsorbent) isotherms Freundlich and Langmuir Type 1, 2, 3, 4 and Kinetics of first and second types1, 2, 3 and 4 and the separation factor was determined.

Results: The activated fly ash removed 99.8% of methylene blue dye in concentration 50mg /L in optimal conditions (pH= 9, time: 30minutes, the  adsorbent dose 3g /L). Process comply from second kinetics with R = 1 and Langmuir isotherm type1 with R = 0.997.

Conclusion: Since the separation factor and the adsorption is in the range between 0 and 1, therefore the absorption process is optimal. In conclusion, active fly ash, acts as a strong adsorbent in methylene blue dye adsorption and Isotherms and kinetics study of absorption process of this practice is confirmed.