Adsorption of hexavalent chromium using modified walnut shell from solution.

Modified walnut shell (MWS) was obtained using diethylenetriamine through a grafting reaction and its adsorption capacity toward Cr(VI) was enhanced. The adsorbent was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and elemental analysis and the results showed that the modification was effective. To optimize experimental conditions, the effect of temperature, solution pH, salinity, contact time, and Cr(VI) concentration on adsorption quantity were performed in batch mode. It showed that the adsorption ability for Cr(VI) onto MWH can reach 50.1 mg·g at 303 K with solution pH 3. Both the solution pH and salinity had a great impact on the adsorption capacity. The Langmuir model can predict the equilibrium process while the pseudo-second-order model can describe the kinetic process. The Yan model can be used to predict the column process. Additionally, there was also some regeneration ability for Cr-loaded MWH. Consequently, MWS is effective for removing Cr(VI) from solution.