Municipal solid waste incineration fly ash (MSWI FA) and granulated lead smelting slag (GLSS) are toxic industrial wastes. In the present study, granulated lead smelting slag (GLSS) was pretreated as a geopolymer precursor through the high-energy ball milling activation process, which could be used as a geopolymeric solidification/stabilization (S/S) reagent for MSWI FA. The S/S process has been estimated through the physical properties and heavy metals leachability of the S/S matrices. The results show that the compressive strength of the geopolymer matrix reaches 15.32 MPa after curing for 28 days under the best parameters, and the physical properties meet the requirement of MU10 grade fly ash brick. In addition, the toxicity characteristic leaching procedure (TCLP) test results show that arsenic and heavy metals are immobilized effectively in the geopolymer matrix, and their concentrations in the leachate are far below the US EPA TCLP limits. The hydration products of the geopolymer binder are characterized by X-ray diffraction and Fourier transform infrared methods. The results show that the geopolymer gel and Friedel’s salt are the main hydration products. The S/S mechanism of the arsenic and heavy metals in the geopolymer matrix mainly involves physical encapsulation of the geopolymer gel, geopolymer adsorption and ion exchange of Friedel’s salt.

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.

Sulfide precipitation has been widely applied to remove arsenic from acidic wastewater containing As(III) and As(V), due to its simple process and high efficiency. However, the characteristics and composition of the precipitates are also of importance for its further treatment and disposal. To explore the characteristics of elemental S formed by reduction and the combined form of the generated S and As₂S₃, the characteristics of precipitates sulfurized from As(III) and As(V) and the effects of temperature, the S(-II) to As ratio (S/As), Cl⁻ concentration (c_Cl−), and the volume fraction of H₂SO₄ (φ_H2SO4(v)) on the sulfurization of As(III) and As(V) were investigated in detail. The results showed that the contents of As and S were 60.37% and 39.73% in precipitate-As(III), while they accounted for 47.46% and 52.64% in precipitate-As(V); both precipitate-As(III) and precipitate-As(V) were mainly composed of amorphous As₂S₃, while the latter contained elemental S. Temperature and S(-II)/As(III) slightly affected the sulfurization process of As(III), while for As(V), as the temperature increased, the content of As₂S₃ in precipitate-As(V) increased significantly. Additionally, with the S(-II)/As(V) increasing, the content of A₂S₃ increased continuously. This study provides a further clarification of the specific composition and structure of the complex precipitates of arsenic sulfide, which will benefit the efficient stabilization of the arsenic sulfide sludge.

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.