Nitric acid-anionic surfactant modified activated carbon to enhance cadmium(II) removal from wastewater: Preparation conditions and physicochemical properties

The authors used a nitric acid (HNO₃)-sodium dodecyl benzene sulfonate (SDBS) method to modify a lignite-based activated carbon. These modified carbons were appraised for their removal of Cd(II) from aqueous solutions. Response surface methodology was employed to optimize the preparation factors including nitric acid concentration C_N, temperature T and SDBS concentration C_S. Statistical analysis indicated that the interaction of C_N and C_S incurred the most effect on the maximum cadmium adsorption capacity (Q_m). The optimal Q_m appeared at C_N = 3.29 mol/L, T = 76 °C and C_S=30,700 mg/L. The optimal protocol achieved 44.21 mg/g Q_m for Cd(II) which was about 7 times larger than for this pristine lignite activated carbon (LAC) (6.78 mg/g). The physical-chemical properties of the modified activated carbons following each synthesis step were characterized relative to their surface area, oxygen functionality, and external surface charge. It was confirmed that the developed surface area, functional groups and negative charges were mainly responsible for the higher adsorption capacity for the LAC that have been more favorably tailored by this HNO₃-SDBS protocol.