Colored wastewaters are the most obvious contamination due to the small of very small amount of artificial dyes. Activated carbon and sludge are conventional treatment technique for this contamination. This research proposed the alternative use of spent tea leaves of green tea (GT), decaffeinated green tea (DGT), peppermint (PM) and chamomile (CM). Batch equilibrium experiments were conducted at room temperature to determine the optimum conditions that maximize the removal of malachite green (MG) as a model dye. Results indicate that the adsorption is strongly driven by pH, reporting an optimum at 6. For all the adsorbents, less than 150mg of the tea leaves reached the maximum adsorption. The absence of salts and heavy metals also maximize the adsorption of MG. Time-dependent experiments showed that less than 1.5h are needed to reach the equilibrium. Mathematical models of Langmuir, Freundlich, Dubining-Radushkevich, and Temkin were used to fit the data. Modeling indicates an adsorption trend of PM〉DGT〉GT〉CM and a maximum adsorption capacity is reached with PM that is able to adsorb 69.7 mg of MG per gram of adsorbent. Desorption of MG from the adsorbents was also investigated, showing that 50% solutions of ethanol and acetone are good desorbing solutions for the recovery of the pollutant and recycling of the adsorbents. Finally, instrumental analysis such as thermo-gravimetric analysis, scanning electron microscopy and infrared spectroscopy were used to characterize the physical and chemical properties of the adsorbents, demonstrating their good potential as adsorbents for the removal of dyes from wastewaters. This study will promote further investigation on naturally-occurring biomaterials for their application on the decontamination of water resources.

Equilibrium studies on the adsorption and desorption of malachite green dye by spent tea leaves

256th National Meeting (2018)

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