Use Of The ESIX For The Separation Of Pb, Cd Ions From Aqueous Solution

Heavy metal pollution is becoming an increasing importance because of its serious threat to environment and human health. Most of the conventional methods are inefficient in heavy metal recovery, only transferring the contaminants from one phase to another one. As clean and safe technology, electrochemical treatment has received considerable attention in recent years. Electrochemically Switched Ion Exchange (ESIX) is a novel ion separation technology which combines electrochemistry with ion-exchange via reversible electrochemical modulation of the matrix charge density. Ion loading and unloading can be easily controlled by changing the redox states of ESIX films formed on conductive substrates to separate ions from mixed solutions and regenerate the matrix. Because the main driving force is the electrode potential in the ESIX process, the secondary waste created by chemical regeneration and associated rinse water of conventional ion exchange technology is eliminated. So this technology has gradually become a hot issue in the fields of wastewater treatment and water purification due to its environment friendliness. In this paper, NiHCF films and PANI-SnP composite films were synthesized as ESIX film electrodes. On the basis of their properties study, Electro-remove and recover heavy metal ions Pb²⁺ and Cd²⁺ in aqueous solutions by ESIX technology, which is a beneficial trial in wastewater treatment.The removal of heavy metals from aqueous solutions is of great importance. Electroactive nickel hexacyanoferrate (NiHCF) thin films were synthesized by cathodic deposition and investigated as electrochemically switched ion exchange (ESIX) materials for the separation of Pb²⁺ from aqueous solutions. In 0.1 mol/L Pb(NO₃)₂ solution, cyclic voltammetry (CV) combined with electrochemical quartz crystal microbalance (EQCM) technique was used to investigate the electroactive, reversibility of the film electrodes and the mechanism of ion exchange. The electrochemical behavior of NiHCF film electrodes was also compared with that in Co(NO₃)₂ and Ni(NO₃)₂ solutions. The ion selectivity of the film was investigated in 0.1 mol/L mixture solution containing [Pb(NO3)²⁺Co(NO₃)₂] and [Pb(NO3)²⁺Ni(NO₃)₂], respectively. The elementary composition of NiHCF films in reduced and oxidized form were also characterized by energy dispersive X-ray spectroscopy (EDS). Experimental results show that the electroactive NiHCF films have reversible electrochemical behavior in aqueous solutions containing Pb²⁺, Co²⁺ and Ni²⁺, respectively. NiHCF film electrodes display a high Pb²⁺ selectivity in both Pb²⁺/Co²⁺ and Pb²⁺/Ni²⁺ binary mixtures and the Pb²⁺ can be separated effectively from aqueous solutions by ESIX processes.Electroactive PANI-SnP composite thin films were synthesized by drop-coating method and investigated as electrochemically switched ion exchange (ESIX) materials for the separation of Cd²⁺ from aqueous solutions. The components and morphology of the composite film were characterized by fourier transform infrared spectrometer (FTIR) and scanning electron microscope (SEM). In 0.1 mol/L Ni(NO₃)₂ and Cd(NO₃)₂ solution, cyclic voltammetry (CV) was used to reversibly intercalate and deintercalate heavy metal ions from the matrix and to investigate the electrochemical behavior of PANI film, SnP film and PANI-SnP composite film. CV and electrochemical quartz crystal microbalance (EQCM) were used to investigate the loading mechanism of PANI-SnP composite film. The elementary composition of PANI-SnP composite films in reduced and oxidized form were also characterized by energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Experimental results show that the electroactive PANI-SnP composite films have reversible electrochemical behavior in aqueous solutions containing Cd²⁺ and Ni²⁺, respectively. PANI-SnP composite film electrodes display a high Cd²⁺ selectivity in Cd²⁺/Ni²⁺ binary mixtures and the Cd²⁺ can be separated effectively from aqueous solutions by ESIX processes.