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Most of dyes used in production processes caused serious environmental pollution when discharged to the water resources. Azo dyes are the most used synthetic compounds in the industries such as textile, food, leather and cosmetic. Due to their toxicity and hard degradation, these kinds of compounds are classi fied as environmental hazardous materials that have to be treated before discharging to the environment. Direct blue 71 (DB 71) is one of azo dyes that is resistant to aerobic degradation and under anaerobic condition is reduced to potential carcinogenic aromatics. Different kinds of physical, chemical and biological methods such as adsorption, ultra filtration, reverse osmosis, coagulation and electro coagulation are widely used for efficient dye removal but they just transport contaminants from water to sludge and generate secondary wastes which need more treatment. Adsorption with many advantages is a proper method that is applied to treat dye compounds. In recent years, use of low cost materials as adsorbent for dye removal has been highlighted. Since natural absorbents are inexpensive and may be achieved without any cost and they are usually in abundance in nature, absorption of solute ions by these materials are a proper method to eliminate color from polluted waters and industrial wastewaters. In this study, removal of azo dye Direct Blue 71 was evaluated with two new natural adsorbents of walnut and peanuts shells. These adsorbents are produced from agricultural wastes. The effect of pH, contact time and adsorbent dosage on the removal efficiency has been studied. According to the results, maximum removal of dyes by the two natural absorbents (0.75 gr/L walnut shell in 50 mg/L initial dye concentration with pH of 9 in 45 minutes and 1 gr/L peanut shell in 50 mg/L initial dye concentration with pH of 9 in 60 minutes) was 55 and 60 percent, respectively. Comparison of prepared adsorbent in the laboratory and commercial ones in optimum condition have similar dye removal efficiency that means suitable and cheap adsorbent could be prepared in the laboratory. Removal efficiency of DB71 was also obtained 85 and 83 by the two walnut and peanut shells adsorbent powder, respectively. The results have also shown that amongst four isotherms of Langmuir, Freundlich, Temkin and Dubinin-radushkevich, Freundlich isotherm has the highest correlation coefficient which implying heterogeneous surface of adsorbent for both sorbents. It has also shown that the maximum surface adsorbent capacity for the monolayer of activated carbon of the walnut and peanut shells were 26 and 28 mg/gr, respectively. From the n values 3.58 and 3.72 of the Freundlich isotherm for both adsorbent of walnut and peanut shells, it could be concluded that physical adsorption process has been happened. The data could also indicate that pseudosecond- order was the best adsorption kinetics model for the two adsorbents

Keywords: pH, pH, dye concentration, adsorbent dosage, activation

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