Various pre-treatment, metal extraction, metal recovery and residue valorisation methods were developed with promising results. First, selected materials were sampled and characterised. Pre-treatment studies of some of the materials provided promising results (roasting for jarosite and landfilled Zn-rich sludge; magnetic and density separation for ASR). For some materials, physical pre-treatment did not provide any added value. Such materials have to be processed without pre-treatment, i.e. be application of downstream processing methods.
The objective of high leaching yields (>90 %) was achieved for laterites (Ni, Co, Mg: atmospheric acid leaching; Ni: solvometallurgy), jarosite (Zn, Pb, Ag: roasting and two-stage leaching; Ge: autotrophic bioleaching; Zn: DES), Cr-rich sludge (Cr and Ni: heterotrophic bioleaching) and landfilled Zn-rich sludges (Zn: heap leaching, DES and solvometallurgy). Plasma-pyro technology performed well with all studied materials. To develop economically and environmentally viable processes, selectivity and flexibility were studied reaching the METGROW+ beyond the state-of-the-art for majority of the sample materials.
Results from physico-chemical metal recovery experiments showed that the proposed processes were valid for the clean-up of the pregnant leach solution (PLS) and for the recovery of metals. The target selectivity of >85% combined with a recovery yield of >90% was achieved for Ni and Co in Greek laterites PLS, for Zn in Zn-rich sludge PLS and for Zn and Pb in jarosite PLS. Combinations of different metal recovery methods showed promising results.
The reactivity of leach residues for the residue valorisation showed clear potential for the use of certain residues as supplementary cementitious materials (SCM) and the production of alkali activated inorganic polymers (AAIP), which may be used as binders in the construction sector or construction materials with various beneficial properties. In some cases, the reactivity increased by mixing two different residues.
Validations were completed for Greek laterites using acid leaching and chemical precipitation or heap leaching, for Polish laterites using acid leaching and solvent extraction, for Cr-rich sludges using heap leaching, and for goethite and fayalitic slag using plasma-pyro technology. Zn-rich sludges were validated through modelling. All validations showed technically promising results.
Various assessments (e.g. LCA, TEA, sensitivity, risks) were done for complete process flow sheets for all material streams with most promising technologies. Processes Building Information Modelling (BIM) and digital twin methodology were used as METGROW+ visualization tools for atmospheric leaching of Polish saprolitic laterite and for plasma-pyro treatment of Zn-rich sludge. The approach included the physical layout over the terrain and the process equipment layout including mechanical, electrical and piping connections.
The main outcome of the project, the free public version of the METGROW+ toolbox (
https://app.metgrowplus.eu(opens in new window)) was developed. The toolbox aids in process selection decision making.
