Removal of hexavalent chromium from contaminated soil and water by Mg/Fe layered double hydroxide and its composite with biochar

Layered double hydroxides (Mg/Fe-LDH) and their composites along with date palm waste–derived biochar (Mg/Fe-LDH-BC) were synthesized, and their efficiency towards the removal of chromium (Cr(VI)) from contaminated soil and water was studied using of batch and column experiments. Kinetic, equilibrium, and pH sorption batch trials were performed in aqueous media, while column studies were conducted using a contaminated loamy sand soil. The Elovich kinetic model fitted best to the kinetic sorption data, followed by the power function and intraparticle diffusion, suggesting chemisorption mechanism for Cr(VI) removal. The Freundlich model was well fitted to the sorption data followed by Langmuir. The higher maximum sorption of Cr(VI) was exhibited by Mg/Fe-LDH (131.22 mg g−1) as compared to Mg/Fe-LDH-BC composite (45.05 mg g−1) at pH 2. Column transport experiment showed the sorption of Cr(VI) was increased by 4 to 5-folds in the existence of Mg/Fe-LDH and Mg/Fe-LDH-BC composite as compared to control. However, no significant changes in the sorption of Cr(VI) were observed with the increase in the application rate of the adsorbent materials from 1 to 2%. The Yoon-Nelson model was fitted best for the experimental data of Cr(VI) removal from soil columns with R2 values ranging between 0.75 and 0.98. These results suggested that Mg/Fe-LDH and Mg/Fe-LDH-BC can be employed as efficient immobilizing materials to remove Cr(VI) from contaminated soil and water.