In order to prepare microwave-absorbing materials with low density and high wave absorption performance, CoFe₂O₄/SWCNTs composites with well-designed necklace-like structures were successfully prepared in this paper by a simple solvothermal method. CoFe₂O₄/SWCNTs composites with different cobalt salt contents were synthesized by adjusting the experimental parameters. The results of the relative complex permeability and relative permittivity of the samples, which were investigated by vector network analysis in the frequency range of 2 to 18 GHz, are collected to support the study of the microwave absorption characteristics of the samples. Different microsphere densities and different cobalt salt contents have obvious differences in the electromagnetic absorption properties of the composites. When the additions of FeCl₃·6H₂O, Co(Ac)₂·4H₂O, and NH₄Ac were 0.432, 0.200, and 0.400 g, respectively, the best reflection loss reached −42.07 dB, and the effective absorption frequency (RL < −10 dB) ranges from 3.2 to 18 GHz. Therefore, this is a preparation strategy of CoFe₂O₄/SWCNTs composites with necklace structure, which has the advantages of simple process, environmental friendliness, low cost, and high stability. The unique necklace-like structure design makes the carbon nanotubes partially exposed, which is more beneficial to achieve good impedance matching and giving the CoFe₂O₄/SWCNTs composite excellent electromagnetic loss capability.

A novel method of smelting of mixture of spent automotive catalyst (SAC) and spent fluid catalytic cracking catalyst (SFCC) to recover platinum and prepare glass slag was investigated. Compared to other metals collection processes for single hazardous waste solid, this method reduced the amount of fluxing materials addition and increased the processing types of hazardous solid waste simultaneously. The optimum SFCC addition, iron collector addition, Na₂B₂O₄•10H₂O addition, CaO/SiO₂ mass ratio, temperature, and holding time for platinum recovery were 20, 11, 16 wt%, 0.6, 1550–1600°C, and 60 min, respectively. In this proposed combined process, more than 98% of platinum is efficiently recovered from SAC. Meanwhile, the concentration of platinum in glass slag was less than 7 g/t. The leaching characteristics of heavy metals in slag confirmed the obtained glass slag is a non-hazardous slag due to the low leaching rate of heavy metal ions. This article proposed an effective and environmentally friendly method for the recovery of platinum from SAC via a combined smelting process. GRAPHICAL ABSTRACT