Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

To address the projected requirements of future technology and ecology, and move towards a circular economy, a comprehensive consideration of the sources, processing methods, and life cycles of natural resources is needed. Certain important metal resources, such as chromium and vanadium, are currently available but unexploited in the slag by-products of steel production processes. This represents a significant potential source of these elements for European enterprise. To help meet the rising demand, the CHROMIC project seeks to develop a hydrometallurgical process for the recovery and purification of these valuable resources. By utilising an oxidative, high-alkaline leaching method, the process aims to avoid the destruction of the saleable slag matrix, as well as the presence of Si or Fe in the leachate solution. Various methods are being investigated for separation of the metal value from the resulting alkaline leach feeds, including solvent extraction (SX) which is the focus of this work.
In developing this SX process, the radiotracer technique has been employed, utilising chromium-51 and vanadium-48 radionuclides produced in-house at the HZDR cyclotron facility. The use of this technique, in combination with more conventional methods such as ICP-OES, allows for precise and powerful analysis of the process with minimal workup after experiments.
Aliquat 336, a quaternary ammonium based IL, is suitable for the separation of oxoanions from such alkaline solutions due to the presence of the organic cation species, independently of pH. This extractant is mostly used in its commercially available chloride form, although experiments involving alternative anions (e.g. OCl⁻, OH⁻, S₂O₈²⁻, CO₃²⁻) are also necessary to investigate the influence of competing anions (arising from the leaching conditions) on the SX process. Scrubbing and back extraction of the loaded IL phase has been demonstrated, using solutions of sodium chromate and sodium chloride. Experiments have now begun on the real leaching solutions of steel slags relevant to the CHROMIC project.