Study on dyes adsorption from aqueous solution using red mud activated by sulfuric acid

Abstract

The textile industry wastewater contains the majority of different dyes which are quite toxic and should be removed before disposal. They are often highly resistant for biodegradation and hence are difficult to be treated. The application of adsorbents of natural origin, especially indus-trial waste, is one of the most attractive solutions for wastewater treatments due to its high socio-economic advantages. In this study, the adsorption capacity of acid activiated red mud for some conventional dyes such as Reactive Red 195 and Direct Yellow 132 was investigated. In this acid activation process part of aluminum oxide, iron oxide on red mud will be dissolved into solution, thereby increasing the specific surface area of the remaining solid phase (from 55 m /g to 92 m2/g). The amount of red mud dissolved in the solution is about 30% weight. Solid residue is used in this adsorption study. The solution obtained after activation which includes iron sulfate salts, alumi-num sulfate used as a coagulant for wastewater treatment. The results showed that, for both dyes, pH 5 is most suitable for the adsorption processes. The adsorption kinetic was based on the pseudo second-order kinetic equation. The rate constants of the second-order model for adsorption of DY132, RR195 on RMA in a solution with a concentration of 100 mg·l-1, pH = 5 are 1.48 and 1.95·10-2 g/(mg·min), respectively, and the equilibrium adsorption capacities are 42.74 and 54.95 mg·g-1, respectively. The adsorption data were well matched to Langmuir isotherm model. The maximum adsorption capacities were found to be 48.54 and 84.31 (mg·g-1) for Reactive Red 195 and Direct Yellow 132, respectively.