Red mud (RM), a hazardous solid waste generated in the alumina production process, of which the mineral composition is mainly hematite, is unable to be applied directly in the cement industry due to its high alkalinity. With the rise of geopolymers, RM-based grouting materials play an essential role in disaster prevention and underground engineering. To adequately reduce the land-based stockpiling of solid wastes, ultrafine calcium oxide, red mud, and slag were utilized as the main raw materials to prepare geopolymers, the C-R-S (calcium oxide–red mud–slag) grouting cementitious materials. The direct impact of red mud addition on the setting time, fluidity, water secretion, mechanical properties, and rheological properties of C-R-S were also investigated. In addition, a scanning electron microscope (SEM), X-ray diffraction (XRD), three-dimensional CT (3D-CT), Fourier transform infrared spectroscopy (FT-IR), and other characterization techniques were used to analyze the microstructure and polymerization mechanism. The related results reveal that the increase in red mud addition leads to an enhanced setting time, and the C-R-S-40 grouting cementitious material (40% red mud addition) exhibits the best fluidity of 27.5 cm, the lowest water secretion rate of 5.7%, and a high mechanical strength of 57.7 MPa. The C-R-S polymer grout conforms to the Herschel–Bulkley model, and the fitted value of R² is above 0.99. All analyses confirm that the preparation process of C-R-S grouting cementitious material not only substantially improves the utilization rate of red mud, but also provides a theoretical basis for the high-volume application of red mud in the field of grouting.

A novel composite cementitious material was constructed by synergistically utilizing multiple industrial solid wastes, including electrolytic manganese residue (EMR), red mud (RM), and ground granulated blast furnace slag (GGBS), with calcium hydroxide [Ca(OH)₂] as an alkaline activator. In addition, the mechanical properties of the composite cementitious materials were systematically analyzed under different raw material ratios, alkali activator dosages, and water-binder ratios. To further investigate the hydration products and mechanisms of the composite cementitious material, characterization methods, for instance, XRD, FT-IR, SEM-EDS, and TG-DTG, were employed to characterize the materials. To ensure that the composite cementitious material does not cause additional environmental pressure, it was analyzed for toxic leaching. The relevant experimental results indicate that the optimal ratio of the EMR–RM–GGBS–Ca(OH)₂ components of the composite cementitious material is EMR content of 20%, RM content of 15%, GGBS content of 52%, calcium hydroxide as alkali activator content of 13%, and water-binder ratio of 0.5. Under the optimal ratio, the composite cementitious material at 28 days exhibited a compressive strength of 27.9 MPa, as well as a flexural strength of 7.5 MPa. The hydration products in the as-synthesized composite cementitious material system primarily encompassed ettringite (AFt) and hydrated calcium silicate (C-S-H), and their tight bonding in the middle and later curing stages was the main source of engineering mechanical strength. The heavy metal concentrations in the 28-day leaching solution of the EMR–RM–GGBS–Ca(OH)₂ composite cementitious material fall within the limits prescribed by the drinking water hygiene standard (GB5749-2022), indicating that this composite material exhibits satisfactory safety performance. To sum up, it is elucidated that the novel process involved in this research provide useful references for the pollution-free treatment and resource utilization of solid wastes such as red mud and electrolytic manganese residue in the future.

This study achieved the preparation of budget-friendly stratified Ca-Al adsorbents using a simplified precipitation synthesis route with subsequent pyroprocessing, showing superior defluoridation capabilities in aqueous environments. The structural properties and defluoridation performance of the adsorbents were systematically investigated by optimizing critical synthesis parameters, including calcium-to-aluminum molar ratios, the solution pH during co-precipitation, and calcination temperature. Characterization results revealed that the optimal sample (prepared at a Ca/Al ratio of 2:3, initial pH of 10, and calcination temperature of 600 °C) exhibited a high specific surface area, ordered mesoporous structure, and abundant surface hydroxyl groups, facilitating efficient fluoride adsorption. Batch adsorption experiments demonstrated significant effects of adsorbent mass, solution pH, and initial fluoride concentration on removal efficiency. The isothermal adsorption characteristics conformed to the Langmuir model, complemented by pseudo-second-order kinetic compliance, which jointly confirmed chemisorption-dominated monolayer coverage. Notably, the maximum adsorption capacity reached 263.33 mg g⁻¹, surpassing most comparable adsorbents reported in the literature. The material maintained a superior fluoride removal performance across a wide pH range (4~12) and exhibited superior recyclability. Rapid adsorption kinetics were observed, with equilibrium achieved within 60 min. The material showed a good removal effect in actual fluoride-containing smelting wastewater, which further proved its application potential. In addition, the analysis of the adsorption mechanism showed that the removal of fluoride was mainly achieved through the coordination between fluoride and metal ions and the ion-exchange reaction with surface hydroxyl groups. These findings suggest that the adsorbent has significant prospects for practical water quality fluoride removal applications.

Ammonia zinc refining has the benefits of low energy consumption, high zinc recovery, and good environmental protection compared with traditional acid and alkaline zinc refining. However, in the production process of refining zinc with ammonia, the anode undergoes chlorine precipitation, and then the oxidation of the ammonia precipitation of some nitrogen occurs. Ammonia replenishment is a cumbersome process that results in large amounts of ammonia volatilization and environmental pollution. In ammonia zinc refining, it is important to ensure the concentration of ammonia and chlorine, as the graphite anodes used in conventional ammonia zinc refining do not retain chlorine and ammonia and dissolve slowly due to oxidation. Therefore, this paper proposes a new measure to conserve chlorine and ammonia to reduce anode chlorine generation by adding an anionic barrier layer and selecting manganese anode materials with selective oxygen precipitation. Under the conditions of 50 × 100 mm sized electrodes, a current density of 350 A/m², and a temperature of 60 °C, a graphite anode and manganese anode were used for electrowinning and for the collection of anode gas under different additive conditions. For the first time, we present a comparative analysis of gas composition, using gas chromatography to demonstrate the feasibility of the different measures used to preserve chlorine, ammonia, and oxygen for industrial applications, as well as the advantages of using these methods in reducing costs. And the experiments show that, by adding the anionic barrier layer, adding urea, and using manganese anode materials with selective oxygen precipitation, the nitrogen precipitation in the anode gas can be reduced to 40–50%, and oxygen precipitation reaches 48.76%.