The safe treatment of heavy metals in wastewater is directly related to human health and social development. In this paper, a new type of recyclable adsorbent is synthesized through the oxidation of enhancer and modification with magnetic nanoparticles. The new adsorbent not only inherits the advantages of multiwall carbon nanotubes (6O-MWCNTs), but also exhibits a new magnetic property and further improved adsorption capacity, which is conducive to the magnetic separation and recovery of heavy metals. The adsorption results indicate that multiwall magnetic carbon nanotubes (6O-MWCNTs@Fe₃O₄) have a good performance for Pb(II) selective adsorption, with a maximum adsorption capacity of 215.05 mg/g, much higher than the existing adsorption capacity of the same type of adsorbents. Under the action of an external magnetic field, 6O-MWCNTs@Fe₃O₄ that adsorbed metal ions can quickly achieve good separation from the solution. The joint characterization results of FTIR and XPS show that under the action of both coordination and electrostatic attraction, the C=O bond in the –COOH group is induced to open by the metal ions and transforms into an ionic bond, and the metal ions are stably adsorbed on the surface of 6O-MWCNTs@Fe₃O₄. Pb(II) has a stronger attraction than Cu(II) and Cd(II) to the lone pair of electrons in oxygen atoms to form complexes, due to the covalent index of Pb (6.41) is more larger than that of Cu (2.98) and Cd (2.71).These data provide a new type of recyclable adsorbent for the efficient treatment of heavy metal ions in wastewater and enrich relevant theoretical knowledge.

Lead smelting slag (LSS) has been identified as general industrial solid waste, which is produced from the pyrometallurgical treatment of the Shuikoushan process for primary lead production in China. The LSS-based geopolymer was synthesized after high-energy ball milling. The effect of unconfined compressive strength (UCS) on the synthesis parameters of the geopolymer was optimized. Under the best parameters of the geopolymer (modulus of water glass was 1–1.5, dosage of water glass (W(SiO₂+Na₂O)) was 5% and water-to-binder ratio was 0.2), the UCS reached 76.09 MPa after curing for 28 days. The toxicity characteristic leaching procedure (TCLP) leaching concentration of Zn from LSS fell from 167.16 to 93.99 mg/L after alkali-activation, which was below the limit allowed. Meanwhile, C-S-H and the geopolymer of the hydration products were identified from the geopolymer. In addition, the behavior of iron was also discussed. Then, the hydration process characteristics of the LSS-based geopolymer were proposed. The obtained results showed that Ca²⁺ and Fe²⁺ occupied the site of the network as modifiers in the glass phase and then dissociated from the glass network after the water glass activation. At the same time, C-S-H, the geopolymer and Fe(OH)₂ gel were produced, and then the Fe(OH)₂ was easily oxidized to Fe(OH)₃ under the air curing conditions. Consequently, the conclusion was drawn that LSS was an implementable raw material for geopolymer production.

Corundum–mullite refractory material is an important material in rotary kiln incinerators due to its excellent properties, e.g., high temperature stability and chemical resistance, etc. However, in the process of use, the complexity of the sintering process will inevitably produce a large amount of spent corundum–mullite refractory material. Therefore, it is important to study the failure mechanism of corundum–mullite refractory material to prolong its service life. In this manuscript, the scrapping mechanism for the corundum–mullite refractory material was studied by XRD, XPS, SEM-EDS, FTIR, etc. The results indicate that chemical corrosion caused by impurity elements, such as Fe, Ca, Mg, Ti, etc., is one of the important scrapping mechanisms. The corundum structure remains stable throughout the service life, while mullite exhibits the opposite phenomenon. The Al-O-Si bonds in the mullite structure are depolymerized by impurity elements to release free tetrahedral structures, including the [AlO₄] tetrahedron and [SiO₄] tetrahedron. In the intervention of iron, the free tetrahedra, including [AlO₄], [FeO₄], and [SiO₄] can bond with each other by sharing bridging oxygen (BO), probably forming Fe-O(BO)-Si, Fe-O(BO)-Al, and Al-O(BO)-Si in an Al₂O₃-SiO₂-Fe₂O₃-Me_xO_y (Me = Ca, Mg, Ti, etc.)-based amorphous phase. These findings provide theoretical support for prolonging the service life of refractory materials in rotary kiln incinerators.