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Near-zero-waste recycling of low-grade sulphidic mining waste for critical-metal, mineral and construction raw-material production in a circular economy

Periodic Reporting for period 2 - NEMO (Near-zero-waste recycling of low-grade sulphidic mining waste for critical-metal, mineral and construction raw-material production in a circular economy)

Reporting period: 2019-11-01 to 2021-04-30

With an estimated volume of 600 Mtonne/yr and a historic stockpile of 28,000 Mtonne, sulphidic mining waste from the production of Cu, Pb, Zn and Ni, represents the largest volume of extractive waste in Europe. When poorly managed, these “tailings” may cause major environmental problems such as acid mine drainage. In 2016 EIP Raw Materials launched a “call to arms” to transform the “extractive-waste problem” into a “resource-recovery opportunity”, as “tailings” still contain valuable & critical metals. Using a “4 PILOTS – 2 case-studies” concept, NEMO develops, demonstrates and exploits, therefore, new ways to valorise sulphidic mining waste. The 2 cases are the Sotkamo Ni-Co-Zn-Cu mine in Finland and the Luikonlahti processing facility in Finland; the 4 PILOTS are located at key points in the near-zero-waste flowsheet, encompassing the recovery of valuable & critical metals, the safe concentration of hazardous elements, the removal of sulphur as sulphate salts, while using the residual mineral fraction in cement, concrete and construction products. NEMO has established an interdisciplinary consortium, including 8 industrial partners (2 mining, 4 engineering, 1 machine manufacturing & 1 construction material company), 4 research institutes, 2 universities and 1 civil society organisation.
Two bioleaching options are benchmarked in Sotkamo: bioleaching heap with enhanced operating conditions and bioleaching pond. During the last period, the pilot plants were designed, constructed and tested. Promising results were obtained from the first step of the pond bioleaching pilot operation with metal extraction above 90%. The next phase will focus on the pilot demonstration completion of both bioleaching options. Data will be used to carry out economic and environmental assessments.
Several hydrometallurgical processing routes have been evaluated for sulphidic tailings with Co, Ni and Cu as the main target elements. These routes include tank bioleaching, acid pre-leaching combined with bioleaching under atmospheric conditions, as well as pressure leaching in alkaline and neutral media. Results have been promising which high metal recoveries and identification of significant by-product potentials for leaching residues. During the next phase of the project, the focus will shift towards precipitation processes and the production of battery-grade final products.
Additionally, pilot operations include improved sulphide precipitation of multi-metal leach solutions, separation and purification of rare earth elements (REE), additional metal recovery processes and pressure leaching of mixed sulphide concentrate. Highlighted results include selective sulphide precipitation in atmospheric environments and efficient re-leach of sulphide products in pressure environment. REE has been successfully recovered from mild solutions by producing a mixed REE concentrate; next, light and heavy REE will be separated to specific products.
Promising results were obtained with tailings from Boliden's Tara mine. The material can be used both as SCM (supplementary cementitious material) and as synthetic aggregate. Calcination is required to improve product quality. Granulation is possible with low cement addition. Tests on mortar prisms and concrete trials showed that appreciable amounts of the tailings could be used. In the next phase, these results will be tested on an industrial scale.
Guidelines on CODE compliant sampling are completed for the tailing storage sites recommending sampling methods, sample preparation and analysis. The initial set of documents for PILOTS 1, 2 and 3 have been compiled for the integrated engineering, and the initial models are also validated. Finally, three additional mining sites for the NEMO feasibility study are selected.
Stakeholder analysis has been complemented with information from the new mining partner. A systematic reporting tool to gather the data from the local meetings that the mining companies hold with their stakeholders has been developed. A high-level expert panel has been established and five meetings of the panel have been organised. A highly diverse audience has discussed the various aspects of recycling mining waste and the Social License to Operate (SLO) at each meeting, bringing their expert experiences to the discussion table. Reports from the meetings are available on the NEMO website. Although the Covid-19 situation resulted in the cancellation of many events, the team members managed to participate in several online events. Presentations were done on the technical aspects of NEMO and of the overall NEMO concept. The NEMO project video was launched in October 2020 and the second NEMO Newsletter was published in April 2021. The NEMO website is constantly updated with relevant news. Regarding exploitation activities, trends and business scenarios related to the NEMO exploitable results have been analysed, and exploitation strategy for the potential NEMO innovations has been defined.
Development and evaluation of novel and innovative unit processes and flowsheets for the hydrometallurgical valorisation of low-grade base metals from processing residues include for example 1) Low-duty bioreactor for cost-efficient hydrometallurgical processing, 2) Novel hydrometallurgical flowsheet for production of battery-grade metal concentrates, using hydroxide intermediates, 3) Process for Co and Ni extraction based on pressure leaching in alkaline and neutral media, 4) Integration of by-product valorisation (SCM, gypsum, DRI, etc.) in hydrometallurgical flowsheets. Project results will include techno-economic evaluation as well as life cycle assessment of different processing options, which will elucidate the most sustainable processing solution. Due to the environmental, social and economic benefits of reprocessing mine residues, project awareness and dissemination activities are expected to increase public acceptance to the NEMO technologies and revalorization of mining waste.
The versatile and high-end pilots established in the project can be used for various challenges, including beyond the project reach. The sulphide precipitation work has clarified the treatment of extremely polymetallic leachates into high-quality products and revealed operating parameters that have been not completely understood before. The REE processes signal that these elements can be recovered from mining waste side streams in the EU. Additional metals recovery processes are novel in terms that by changing chemicals and closing their loops, new products for the metal and agricultural sector can be produced.
With the final use of the residues as building material, the NEMO project "finds the meaning". We focus on high substitution rates in cement or concrete at industrially common product qualities. So far, substitution rates of 30% could be achieved at the same product quality. These values are covered by the EN standard and allow industrial application.
We will continue activities for monitoring the delivery of samples and the performance of the different pilots. These updates will be collected for the engineering activities. They will support the final validation of the models used as a base for NEMO’s ‘virtual plant’ that will be designed to simulate the whole zero-waste plant from a holistic point of view. Besides, the new additional mining sites will be studied to develop feasibility studies to implement NEMO technologies.