Application of Citrullus lanatus rind as biosorbent for removal of trivalent chromium from aqueous solution

Abstract Watermelon rind (WR) an agro waste was evaluated as an adsorbent for the removal of Cr^3+ ions from aqueous solution. Batch mode adsorption studies were performed by varying parameters such as pH, contact time, adsorbent dose and initial metal ion concentration. Maximum loading capacity of WR was found to be 172.6 mg g^-1 for Cr^3+ ions at pH 3. Kinetic studies show that removal of Cr^3+ ions is rapid and follows a pseudosecond order model. Equilibrium data fit better with the Langmuir isotherm than the Freundlich isotherm. Thermodynamic parameters such as ∆G°, ∆H° and ∆S° were derived for the current system. The negative values of ∆G°show that the nature of sorption process is spontaneous. FTIR studies reveal that hydroxyl and carboxyl groups were responsible for uptake of metal ions. Successive desorption of Cr^3+ ions reveals that WR can be an economical sorbent for the removal of heavy metals from aqueous solution. The results con- clude that watermelon rind an agro waste can effectively be used for the removal of chromium ions from aqueous solution.