Biosorption of zinc ions from aqueous solutions onto natural dye waste of Hibiscus rosa sinensis: Thermodynamic and kinetic studies

The objective of the study is to assess the uptake of zinc ions from aqueous solutions onto natural dye waste (aqueous color extracted) of Hibiscus rosa sinensis flower. The study investigates the effects of process parameters such as pH, temperature, agitating rate, adsorbent mass, and particle size. The extent of adsorption increased with an increase of pH. Furthermore the adsorption of zinc increases with increasing adsorbent doses and decreased with the adsorbent particle size. The adsorption data follows both Langmuir and Freundlich adsorption models, however the Langmuir model is better suited than the Freundlich model and the adsorption maxima at equilibrium to be 94.339 mg/g of zinc ions on Hibiscus Dye Waste (HDW) sorbent at 20 degrees C. The adsorption of zinc 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 86.357 kJ/mol according to the Arrhenius equation. This study indicated that the HDW can be used as an effective and environmentally safe Biosorbent for the treatment of zinc containing aqueous solutions. (C) 2011 American Institute of Chemical Engineers Environ Prog, 2012