In this study, a heavy metal trapping gel with multiple ligand groups was prepared for the first time using response surface methodology. The gel was produced by condensing and grafting glutathione as a grafting monomer onto the main polyacrylamide chain, based on the Mannich reaction mechanism with formaldehyde. FTIR, SEM, TG-DSC, and zeta potentials were used to characterize the gel. The results demonstrated that the gel was morphologically folded and porous, with a net-like structure, which enhanced its net trapping and sweeping abilities, and that glutathione was used to provide sulfhydryl groups to boost the metal trapping ability of polyacrylamide. Coagulation experiments showed that the highest efficiency of the removal of Cd ions from water samples was achieved when the concentration of polyacrylamide–glutathione was 84.48 mgL⁻¹, the concentration of Cd was 10.0 mgL⁻¹, the initial turbidity was 10.40 NTU, and the initial pH was 9.0. Furthermore, the presence of two cations, Cu and Zn, had an inhibitory effect on the removal of Cd ions. In addition, analysis of the zeta potential revealed the flocculation of polyacrylamide–glutathione. The flocculation mechanism of glutathione is mainly chelation, adsorption bridging, and netting sweeping.

An efficient and controllable process for separating copper and cadmium was required to be developed due to the high cost of the long separation process of copper cadmium slag generated from the zinc smelting process. Therefore, a new process for the application and deep separation of copper and cadmium was developed by combining the Circulating Flow Electric (CFE) cadmium cement method and the 2-hydroxy-5-nonyl formaldehyde oxime (M5640) copper extract method. The process firstly removed copper ions utilizing M5640 and obtained a primary purification solution, followed by CFE method to extract cadmium in depth. The effects of extractant volume fraction, pH, Oil phase/Aqueous phase (O/A) ratio and reaction time on the removal of copper ions were investigated. The results showed that the removal of copper was above 97%, while the removal of zinc and cadmium was below 1.6%, respectively, proved that the selectivity of M5640 for copper was significantly higher than that for metals such as cadmium and zinc. The characterization results indicate that the oxygen on the hydroxyl group and the nitrogen on the oxime group co-ligated with the copper ions and subsequently formed chelated extracts. That was the mechanism of the copper ion purification by M5640. Furthermore, the extraction of high purity cadmium was carried out in the extraction residual liquid. A novel method of cadmium removal enhanced by coupling an electric field with a circulating flow field was developed and applied to the cement cadmium from sulfate solutions. The optimal process conditions of the method were explored, which were further fitted into statistical equations and optimized by response surface analysis. Since the fitted theoretical results were close to the experimental results, the optimization was considered as effective. The optimized experimental parameters were 6.23 mL/s of flow rate, 48.14 mA/cm² of current density, 2.25 of pH, and 0.93 of anode/cathode area ratio, respectively. Next, the extraction electrical efficiency, purity and its weight distribution in the cell of cadmium sponge under different flow fields were calculated and measured. The results were analyzed to prove the existence of an optimal interval for the distribution of cadmium under high-speed flow field.

In this work, a novel flow–electric field coupling configuration was designed and implemented for enhancing Zn-Cd cementation. A series of tests was conducted to explore the optimization of the Zn-Cd cementation process and its mechanism. Firstly, the various characteristics of the sponge cadmium at various locations in the device were compared, and it was concluded that the optimum purity of the sponge cadmium obtained from the anode was up to 94.1%. The generation and stripping of the cadmium sponge was revealed for the first time by cross-sectional electron microscopy. The four stages of the apparent reaction in the system were analyzed in relation to the pH, cadmium concentration and cadmium sponge flaking at each flow rate. It was proved that the separation of cadmium sponge mainly occurred in the third phase. Secondly, by comparing the morphology and specific surface area of the cadmium sponge at different flow rates, the optimum flow field velocity was identified as 30 mL/s. At this point, the specific surface area reached a maximum of 1.151 m²/g. Six flow field configurations were compared and preferred. The results demonstrated that the LCAH (Low-Cathode-Anode-High) modulation resulted in a sparser structure of the cadmium sponge, which was more easily exfoliated from the zinc anode surface by fluid impact. This was considered to be the most beneficial flow field configuration for improving the cadmium cementation rate and reducing the cost of the reaction. Moreover, the reaction steps of the system were analyzed. Its rate-limiting step was initially empirically identified as the diffusion step and proven by calculating the activation energy of 12.6 kJ/mol. It was confirmed that the diffusion process under different flow field configurations followed the first-order kinetic principle. In addition, the system’s reaction phases were compared. Calculations confirmed that the diffusion process under various flow field configurations followed first-order kinetics. The diffusion coefficient of LACH proved to be the highest in the comparative tests, and the evident experimental results supported this conclusion.