Chromium biosorption from aqueous environments by mucilaginous seeds of Cydonia oblonga: Thermodynamic, equilibrium and kinetic studies

Hexavalent chromium Cr(VI) is one of the most toxic heavy metals in aqueous solutions, hence it is highly imperative to treat the wastewater containing Cr(VI) before its discharge. At present work, the rate of biosorption was studied under a variety of conditions, including initial Cr(VI) concentration (5-50 mg/L), amount of biosorbent (0.5-3 g/100 mL), pH (1-8), temperature (298-318 K) and contact time (30-120 min). Biosorption of Cr(VI) is in all cases pH-dependent showing a maximum at equilibrium pH values between 2 and 3. The biosorption data fitted well with Langmuir and Freundlich isotherms. The biosorption capacity calculated from the Langmuir isotherm was q = 33.58 mg Cr(VI)/g of dry seeds (at 303 K). Biosorption kinetics data well fitted using pseudo-second-order. Thermodynamic studies confirmed that biosorption of Cr(VI) ions by mucilaginous seeds of Cydonia oblonga was spontaneous and endothermic nature.