Efficient removal and recovery of Cd²⁺ from aqueous solutions by capacitive deionization (CDI) method using biochars

Biochars are low-cost and sustainable materials for environmental technologies. In this work, we prepared three biochars using pomelo peel (P-BC), algae (A-BC), and corncob (C-BC) to recover Cd²⁺ from wastewater via capacitive deionisation (CDI). A-BC possesses the highest amount of mesopores and nitrogen functionality and attains the highest removal of Cd²⁺ via physical adsorption. For the electro-sorption capacity, C-BC and A-BC perform better capacitive removal of Cd²⁺ than P-BC due to the smaller charge-transfer and mass-transfer resistances. Also, this work investigated the impacts of surface morphology, cell voltage, NaCl, initial pH, and Cd²⁺ concentrations on Cd²⁺ capacitive removal and electrode regeneration performances. The results indicated that A-BC and C-BC may be prospective materials for Cd²⁺ removal from wastewater by CDI. However, the presence of competing cations at high concentrations may influence the removal of Cd²⁺ at a low level, requiring the modification of A-BC and C-BC in future work.