Mine tailings to treasure: providing society with sustainable resources
Sulfidic mining waste, residues from mining and processing sulfidic ores to produce copper (Cu), zinc (Zn), lead (Pb), nickel (Ni) and other critical metals, represents the largest extractive waste in Europe. Approximately 600 Mtonnes is produced a year and there is a historic stockpile of 28 000 Mtonnes deposited in either tailings storage facilities, dry stacked or back-filled in mines. When poorly managed, this waste can become an environmental hazard, causing problems such as acid-mine drainage, the outflow of acidic water from mine waste. At the same time, this waste represents a new stock of critical metals and minerals needed to move to a green circular society. Recently, the European Innovation Partnership on Raw Materials launched a ‘call to arms’ to transform the ‘extractive waste problem’ into a ‘resource recovery opportunity’. Responding to this call is the EU-funded NEMO project. “Using a ‘four pilots – three case studies’ concept, NEMO takes up the challenge to develop, demonstrate and exploit new ways to valorise sulfidic tailings,” outlines Mika Paajanen, project coordinator. The aim is to recycle up to 95 % of waste. Key to achieving this is increasing the technology readiness level of various innovative technologies within the near-zero waste treatment of sulfidic ores and sulfidic mining waste.
The NEMO concept
The project focuses on three cases: the Sotkamo Ni-Cu-Zn-REE/Sc (rare earth element scandium) mine in Finland, Luikonlahti processing facility in Finland and the Tara Zn-Pb mine in Ireland. Through four pilots, using NEMO technologies, the project aims to demonstrate cutting-edge bioleaching processes to recover additional metals from sulfiidic ores/residues and to boost the conversion of sulfides to sulfates – helping to eliminate the risk of acid-mine drainage. It also seeks to ‘clean’ the residual matrix allowing its use in cement and construction applications. “Results from the pilots to date include the development and evaluation of novel and innovative unit processes and flowsheets for the hydrometallurgical valorisation of low-grade base metals from processing residues. These include a low-duty bioreactor for cost-efficient hydrometallurgical processing and novel hydrometallurgical flowsheets for production of battery-grade metal concentrates,” confirms Paajanen. Additionally, two bioleaching options have been benchmarked: one in Sotkamo and one in BRGM France. In Sotkamo a bioleaching heap with enhanced operating conditions and in France a bioleaching pond. Metal extraction above 90 % was achieved in the first step of the pond bioleaching pilot. “NEMO has also developed processes and mixtures that can incorporate a high percentage of mine tailings and has demonstrated the potential use of mine tailings in concrete products. These developments were achieved by project partners Boliden, Thyssenkrupp, VITO and Resourcefull, specifically targeting the tailings from the Tara mine of Boliden,” emphasises Paajanen. A new understanding of the specific nature of the secondary raw materials at each studied mining site has also provided useful information on their suitability for various processing and valorisation methods and on their exploitation potential.
Looking onwards
“It is expected that NEMO’s technology will provide the EU with a range of benefits from new resources for the metal and agricultural sectors to a reduction in CO2 levels in the metal recovery process and the replacement of ordinary Portland cement,” concludes Paajanen. It will also be instrumental in eliminating acid-mine drainage and other environmental problems. The project will continue monitoring the delivery of samples and the performance of the different pilots. It aims to replicate its technologies and concepts in other mines within the EU and beyond.
Keywords
NEMO, copper, zinc, lead, nickel, sulfidic mining waste, valorise sulfidic tailings, green society, near-zero waste treatment