Potential of tea factory waste for chromium(VI) removal from aqueous solutions: Thermodynamic and kinetic studies

The objective of this study is to assess the uptake of hexavalent chromium Cr(VI) from aqueous solutions onto tea factory waste (TFW). The study also investigates the effects of process parameters such as pH, initial concentration of Cr(VI) ion, temperature, agitating rate and adsorbent mass. The nature of the possible adsorbent and metal ion interactions was examined by the FTIR technique. Zeta potential values of the TFW were defined at different values of pH according to deionized water. The maximum adsorption is noted at pH 2.0. The adsorption data follow the Langmuir model better than the Freundlich model and the adsorption equilibrium was described well by the Langmuir isotherm model with maximum adsorption capacity of 54.65 mg g−1 of Cr(VI) ions on TFW at 60 °C. Adsorption capacity increased from 30.00 to 39.62 mg g−1 with an increase in temperature from 25 to 60 °C at 400 mg L−1 of initial Cr(VI) ion concentration. The adsorption of Cr(VI) ions increased with increasing temperature indicating endothermic nature of the adsorption process. Using the first-order kinetic constants, the activation energy of adsorption (Ea) was determined as 18.57 kJ mol−1 according to the Arrhenius equation. The present investigation aimed the heavy metal adsorption from synthetic wastewaters with another pollutant matter. This study indicated that the TFW can be used as an effective and environmentally friendly biosorbent for the treatment of Cr(VI) containing aqueous solutions. Various thermodynamic parameters, such as ΔG°, ΔH° and ΔS° have been calculated. The thermodynamics of Cr(VI) ion onto TFW system indicates spontaneous and endothermic nature of the process.