The HCl leaching process showed mixed results for the sulpidic materials. The process was highly effective in extracting Ni and Co from sulphide tailings yet the efficiency of the leaching was lower in Ni concentrates. The mineralogy of the laterites varied widely. A non-neglegible amount of Co is found to be contained in chromite, a poorly leachable mineral.
The bioleaching/oxidative leaching and precipitation processes were successfully designed and operated.
A mineral carbonation pre-treatment process was successfully developed for the Ni/Co-silicate tailings together with a subsequent CO2 sequestration investigation. As to leaching behaviour with HCl, carbonated materials from a hydrothermal treatment route yielded high Ni extraction efficiency and selectivity.
The use of biochar was investigated for nickel slag cleaning, and results revealed that biochar consistently outperformed coke in reducing residual concentrations of Ni and Co in the slag, achieving higher matte-to-slag distribution coefficients for both metals, and higher metal recoveries.
Flowsheets have been developed for 5 ENICON materials: limonitic laterite, saprolitic laterite, MHP, MSP and ferronickel (FeNi). The model that has been developed for leaching, solvent extraction, etc. has already shown to be predictive and valid against experimental results and were used to guide process design decisions.
As to the adaptation of the existing leaching/SX/EW route to the ENICON imtermediates (MHP/MSP), Mn removal plays a critical role and it became evident that Mn could be precipitated quantitatively, together with Fe. However, there was a considerable loss of Ni and Co, being co-precipitated with Mn and Fe. Washing of the precipitate did not sufficiently recover Ni and Co.
In terms of the mineral-matrix valorisation, a scientific breakthrough was achieved with the invention of akermanitic clinckers, which proved to provide CO2-lean construction materials with high compressive strength. This was the subject of 2 patent applications and 2 journal publications. Furthermore, alkali-activation of ENICON residues was successful. The leaching residues obtained from HCl leaching of laterites showed great potential to be used as supplementary cementitious material, due to their reactivity.
As to the LCA, the carbon-neutral smelting showed significant improvements in all but 3 studied impact categories. The higher infrastructure and land requirements associated with the use of H2 for reduction are the main drawbacks. Overall, the results support the viability of H2 as a more sustainable reductant, but its successful implementation will depend critically on upstream energy sourcing (i.e. the production of green H2) and resource efficiency. The environmental profile of the ENICON HCl-based process for the upgrading of ferronickel (FeNi) shows overall low environmental impacts. It combines efficient resource utilisation with reduced emissions and freshwater use, supporting the sustainability and scalability of battery-grade Ni-Co production. The environmental performance of alkali-activated mortar production showed many advantages over conventional Ordinary Portland Cement (OPC) production. The ENICON technology reduced the environmental impacts in all categories, but one (photochemical ozone creation potential).
As to the TEA for the processing of FeNi and limonitic laterites to produce battery-grade Ni and Co, it became evident that HPAL exhibits a higher profitability compared to the ENICON processes. The ENICON process for the limonitic laterite has the most chance of becoming profitable, through reduction of CAPEX costs.
