Peng Liu

Red mud is the residue produced from the alumina manufacturing process, which is one of the largest volume industrial solid wastes worldwide. The large-scale annual accumulation of the red mud not only occupies valuable land resources but also leads to soil alkalization, which also poses significant environmental risks. Therefore, it is crucial to explore feasible methods to effectively utilize red mud. This work outlines the preparation methods of the red mud-based adsorbents and their adsorption performance for pollutants is also investigated. It also provides a detailed overview of utilizing red mud-based adsorbents for pollutants treatment, including removal of heavy metal ions (Pb ²⁺ and Cd ²⁺ adsorption amount :730.16 and 215.37 mg/g), non-metal ions (phosphorus adsorption amount: 200 mg/g), and organic pollutants (methylene blue adsorption amount: 47.9 mg/g), as well as for gas adsorption such as CO ₂ and SO ₂ . Adsorption mechanisms of pollutants removal are comprehensively analyzed, and the regeneration process of the red mud-based adsorbents after use is also investigated. Furthermore, a preliminary economic analysis of the red mud-based adsorbents is conducted with the production cost of the $4.90 per kg. Finally, the future research directions for advancing red mud-based adsorbents development are proposed.

In this study, the recycled construction powder (RCP), a solid waste byproduct of the construction industry, is employed as a carrier to develop the RCP/C ₃ N ₅ /TiO ₂ heterojunction through the heterojunction construction strategy for photocatalytic degradation of sulfamethazine (SMZ). Formation of a Z-type heterojunction between C ₃ N ₅ and TiO ₂ on RCP/C ₃ N ₅ /TiO ₂ broadens the spectral absorption range and effectively enhances the separation of photogenerated electron-hole pairs, contributing to photocatalytic degradation of SMZ. Under the synergistic effect of the electric field in the Z-type heterojunction and the RCP induced dipole field, the efficient separation of photogenerated electrons and holes is realized, and the photocatalytic efficiency is improved. The generated active radicals, such as ·O ₂ ^⁻ and ·OH are generated, which degrade SMZ into small inorganic molecules. Under visible light irradiation, the RCP/C ₃ N ₅ /TiO ₂ heterojunction achieves efficient degradation of SMZ with a degradation removal of 97.40%. Impurity ions have a relatively minor impact on the degradation process of the SMZ. The photocatalytic degradation process of SMZ conforms to the Z-type charge transfer mechanism. Furthermore, the RCP/C ₃ N ₅ /TiO ₂ heterojunction exhibits excellent recyclability. This study realizes the resource utilization of solid waste, effectively reduces the cost of catalyst preparation, conforms to the concept of “treating waste with waste”, and provides an effective strategy for dealing with antibiotic pollution.

The acid mud produced in the nonferrous smelting process is a hazardous waste, which mainly consists of elements Hg, Se, and Pb. Valuable metal (Hg/Se/Pb) can be recovered from acid mud by heat treatment. For safe disposal of the toxic acid mud, a new resource utilization technology by microwave roasting is proposed in this paper. The reaction mechanisms were revealed through thermodynamics and thermogravimetric analysis, which showed that the main reaction was the oxidative pyrolysis of HgSe in the process of roasting. Moreover, the mercury removal effects of acid mud by microwave heating and conventional heating were studied, the recovery rate of mercury by microwave heating for 30 min at 400 °C was 99.5%: far higher than that of conventional heating for 30 min at 500 °C (44.3%). This was due to the high dielectric constant of HgSe, as microwaves can preferentially heat HgSe and reduce the adsorption energy of HgSe on the surface of PbSO₄ blocks, thus strengthening the pyrolysis process of HgSe and reducing energy consumption. The preferable prototyping technology for resource utilization of toxic acid mud should be microwave roasting. This study is of great significance for the realization of mercury pollution reduction and for green production of lead-zinc smelting.