A New Strategy for the High-Value Utilization of Cobalt Slag: A Solid-State Reaction for the Preparation of Microwave-Absorbing Composite Materials with Excellent Properties

Abundant valuable metals such as manganese and cobalt are present in cobalt-rich slags from the hydrometallurgical zinc industry. However, due to the high cost of traditional hydrometallurgical separation methods, these metals cannot be effectively recovered. In this paper, a novel recycling strategy based on mineral phase recovery was proposed, utilizing cobalt-rich slags as raw materials to fabricate microwave-absorbing composite materials. A feasible solid-phase thermochemical method has been developed to recover the mineral phase from cobalt-rich slags, with calcination temperature 800 °C and duration 90 min, yielding MnCo₂O₄ spinel. The results demonstrated that under the conditions of a ball-to-material ratio of 20:1 and ball milling time of 4 h, the MnCo₂O₄ powder and graphene materials, after being ball-milled and compounded, exhibited appropriate electromagnetic parameters and impedance matching. At 5.2 GHz, the minimum reflection loss of the composite material reached -40 dB. This study provides a new approach for the value-added utilization of valuable metal resources in cobalt-rich slags.