A novel process for comprehensive resource utilization of hazardous chromium sludge: Progressive recovery of Si, V, Fe and Cr

Chromium sludge is a hazardous solid waste which cannot be effectively treated but only piled up and abandoned, causing serious environment pollution and resource wasting. This work proposes an effective novel process to separately recover all resources in chromium sludge via a sustainable way. The obtained acid solving liquid from chromium sludge is desiliconized by cationic flocculant (PCAM) to induce coprecipitation of polysilicate gel and PCAM, which mixture is calcinated to generate the product of white carbon black in purity of 94.35% with a recovery of 92.58%. After desiliconization, V in the solving liquid is selectively extracted by microemulsion (ME), which is recovered as V₂O₅ in purity of 99.34% with a recovery of 95.53% by the subsequent procedure of stripping-precipitation-calcination. The Fe³⁺ in raffinate is reduced to Fe²⁺ cations by Na₂SO₃, and is then recovered by H₂C₂O₄ precipitation to generate the FeC₂O₄ product in purity of 99.12% with a recovery of 98.25%. Cr³⁺ cations in residual solution are recovered by alkaline precipitation and calcination to generate the Cr₂O₃ product in purity of 98.25% with a recovery of 92.68%. This work provides fresh penetrations into the synchronous detoxification, resource recovery and value-added utilization of hazardous industrial solid wastes.