Reduction And Adsorption Of Heavy Metal Ions From Aqueous Solution By Green Tea

Heavy metal contamination becomes a public nuisance to our environment, and also a threat to the potable water in our daily life due to the unqualified water dispenser. On the basis of green chemistry, this paper demonstrates how green tea can treat heavy metal contamination from aqueous solutions.This paper was focused on the reduction and adsorption of chromium from aqueous solution by green tea, the solutions were detected for Cr(VI) and total Cr by the diphenyl carbazide method at 540 nm using a UV-visible spectrophotometer. The optimum contact time to reach an equilibrium is approximately 2 hours; when the initial pH= 2, the maximum reduction and adsorption ability of green tea was found to be qr= 15.8 mg/g and qe= 30.4 mg/g respectively. Furthermore, the green tea has been divided into two experimental categories:tea water (TW), and treated tea leaves (TTL). The experimental data collected from contact time, initial pH, biomass dosage, temperature effects and XPS analysis showed that TW has a single ability to reduce Cr(VI) to less toxic Cr(III), and the converted Cr(III) could be bound with TTL in solutions.In this paper, the adsorption of Cd2+, Ni2+and Hg2+from aqueous solution was carried out by green tea. The concentrations of Ni2+were detected by Dimethylglyoxime spectrophotometric method at 530 nm; flame atomic absorption spectrometry was employed to detect the concentrations of Cd2+and Hg2+. Different from the reduction and absorption of chromium, the absorption of Cd2+, Ni2+and Hg2+by green tea was a faster process,15 minutes to reach equilibrium; as the pH and temperature increased, the amount of Cd2+, Ni2+ and Hg2+absorbed by green tea qe increased.