To ensure humanity's long-term existence in accordance with the planetary boundaries, recycling processes that operate with the lowest possible greenhouse gas emissions are essential. In the course of this work, selective chlorination reactions using solid metal chlorides for multimetal recovery from precipitation residues of the zinc and nickel industries were investigated. Jarosite and goethite, the two primary iron precipitates from hydrometallurgical zinc production, are generated on the scale of millions of tons annually and, due to a lack of processing options, immobilized and landfilled to the predominant extent. The novel process concept is based on a pyrometallurgical treatment of the mixtures at temperatures up to 1100 °C without the addition of carbon as a reducing agent. Chlorine compounds react with the contained valuable metals, whereby the formed valuable metal chlorides can be extracted due to low evaporation temperatures. With thermodynamic calculations and small-scale experiments, it was demonstrated that the three metal chlorides MgCl2∙6H2O, AlCl3∙6H2O, and FeCl3∙6H2O are suitable as effective chlorination agents. Verification was carried out in comprehensive experimental campaigns with industrial jarosite and goethite in untreated and thermally calcined forms. Especially the use of MgCl2∙6H2O and FeCl3∙6H2O lead to high extraction rates for the investigated valuable metals In, Ag, Zn, Pb, Cu, Sn, Au, and Bi. Furthermore, chlorine-containing industrial residues can provide the chlorine required for chlorination. In this context, the procurement, characterization, and experimental evaluation of the three residual materials iron pickling residue, magnesium salt slag, and aluminium salt slag was carried out. In addition to the elemental chlorine content, the concentration of chlorine affine elements such as Na and K was identified as decisive for the suitability of residual materials as chlorination agents. Further evaluations of the process concept were based on test campaigns with an untreated and calcined iron precipitation residue from the nickel industry, as well as experiments with Jarofix – a material which is generated in the course of the currently dominant treatment method for jarosite by means of immobilization. For the processing of the valuable metal chlorides, it is necessary to collect the resulting chloridic valuable metal fraction. For this purpose, a separator prototype was constructed, which condenses the vaporized metal chlorides abruptly in a cold inert gas stream directly after they exit the reaction crucible and enables filtering without adhering to cooler surfaces. This offers potential for exploring chlorination reactions in terms of the actual composition and structural properties of the formed condensates.
|Translated title of the contribution
|Chlorierung und Extraktion von Wertmetallen aus Eisenfällungsrückständen ohne Kohlenstoff als Reduktionsmittel
|Published - 2022
Bibliographical noteembargoed until 05-05-2027
- Precipitation residues
- multimetal recovery