کلیدواژهها
عنوان مقاله English
نویسندگان English
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
کلیدواژهها English
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