Chromium(VI) removal from aqueous system using Helianthus annuus (sunflower) stem waste

The objective of this study was to investigate the Cr(VI) removal efficiency of sunflower waste from aqueous system under different process conditions. Two adsorbents were prepared by pre-treating the sunflower stem waste. One adsorbent was prepared by boiling it and second adsorbent was prepared by treating it with formaldehyde. Batch mode experiments were carried out as a function of solution pH, adsorbent dosage, Cr(VI) concentration and contact time. FT-IR spectra and SEMs of the adsorbents were recorded to explore the number and position of functional groups available for the binding of Cr(VI) ions and morphology of the studied adsorbents. The removal of chromium was dependent on the physico-chemical characteristics of the adsorbent, adsorbate concentration and other studied process parameters. Maximum metal removal was observed at pH 2.0. The efficiencies of boiled sunflower stem absorbent and formaldehyde-treated sunflower stem absorbent for the removal of Cr(VI) were 81.7 and 76.5%, respectively for dilute solutions at 4.0 g/L adsorbent dose. The applicability of Langmuir, Freundlich and Dubinin–Radushkevich isotherms was also tested. The results revealed that the hexavalent chromium is considerably adsorbed on sunflower stem and it could be an economical method for the removal of hexavalent chromium from aqueous systems.