Hexavalent chromium reduction by coffee, black tea, and green tea was investigated. When 2 grams of ground coffee, black tea, or green tea were introduced to 100 ml of 20 mg/L Cr(VI) solution, Cr(VI) reduction followed pseudo-second order reaction. The determined pseudo-second order rate constants (kobs) were 0.0040, 0.0435, and 0.1515 L/mg-min for coffee, black tea and green tea, respectively indicating that the green tea is the stronger reducing agent than coffee and black tea. According to the obtained pseudo second order kinetic equation, Cr(VI) in the contaminated water can be reduced to Cr(III) within 7 minutes when enough green tea is provided. When unground, untreated, dried tea leaves were applied, the Cr(VI) reduction rate was not as fast as ground products due to the slow dissolution rate of electron donors. Without any mechanical supports, however, all Cr(VI) were removed from the solution within 16 hours. It should be noted that critical factors to be considered to design Cr(VI) remediation process are the amount of dried tea leaves as well as the particle size of the tea leaves. Research also confirmed that fresh leaves were not as effective as dried tea leaves and dried stems for detoxification of Cr(VI) contaminated water. Adding dried tea leaves into Cr(VI) contaminated water could lower the toxicity by reducing Cr(VI) to Cr(III) which can be easily adopted and applied to small scale remediation process especially for person/town potentially exposed to Cr(VI) with very limited resources.

Development of a cost effective, environmentally friendly process for detoxifying hexavalent chromium contaminated water

248th National Meeting (2014)

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