Separation and recovery of heavy metal ions and salt ions from wastewater by 3D graphene-based asymmetric electrodes via capacitive deionization

Abstract

Herein, a novel concept for the separation and recovery of heavy metal ions and salt ions from wastewater by 3D graphene-based asymmetric electrodes via capacitive deionization is presented for the first time. Instead of the traditional practice to adsorb heavy metals via the stirring method, we rationally design functional 3D graphene by grafting ethylenediamine triacetic acid (EDTA) and 3-aminopropyltriethoxysilane on the 3D graphene surface, and take advantage of capacitive deionization for wastewater treatment. In this process, Pb²⁺ is adsorbed by EDTA through chelation reaction and Na⁺ is adsorbed into the 3D graphene pores by electrosorption. Meanwhile, 3D graphene aminated with 3-aminopropyltriethoxysilane is used as an anode to minimize the co-ion effects and improve the removal efficiency. This research investigates the adsorption and desorption behaviors of Pb²⁺ and Na⁺ and the influence of operation conditions, such as pH, voltage, concentration and time on Pb²⁺ and Na⁺ removal. The removal efficiency is 99.9% at pH 6.0 for Pb²⁺ and 98.7% for Na⁺. It is worth noting that Pb²⁺ and Na⁺ can be separated and recovered in the desorption process in two steps due to the different adsorption mechanisms of Pb²⁺ and Na⁺. The desorption rates are ∼99.6% for Pb²⁺ and ∼97.2% for Na⁺, which remain at ∼94.3% and ∼88.2%, respectively, without further degradation after 8 cycles. Overall, CDI with 3D graphene-based asymmetric electrodes is a promising route for the separation and recovery of heavy metals and salt ions from wastewater.