Sorptive removal of color from aqueous coffee and tea infusions

Aqueous coffee and tea infusions were decolorized by adsorption onto activated carbon. The color of the infusions has changed gradually from brown to colorless during the decolorization process. To understand the potentiality of activated carbon, experiments were conducted to determine equilibrium time, optimum dose of adsorbent, intraparticle diffusion, adsorption isotherm, optimum pH, and desorption of color from the coffee and tea infusions. The corresponding results show that around 80-82% of color removal was achieved with 100 mg/L of activated carbon within 2 h. The isothermal equilibrium sorption data fitted well into the Langmuir isotherm. Film diffusion seems to be the rate limiting step for coffee infusions but pore diffusion for tea infusions. The sorption process appears to follow anionic type as the extent of sorption is decreasing with increasing pH. Desorption studies revealed that the sorption interaction was more of chemical nature.