A combined geochemical and biosorption tool for mine water clean-up and valorisation

Cobalt (Co), nickel (Ni) and copper (Cu) are critical minerals vital for the clean energy transition. The International Energy Agency predicts that there will be a 16% shortfall in supply of Co and a 31% shortfall in supply of Cu by 2035. Mining operates with high production losses and generates severe toxic discharges. Working and legacy mine discharge is a global challenge for the mining industry to address. These effluents often contain high levels of heavy metals and low pH, which leads to severe damage to entire ecosystems if not treated. Treatment methods used include chemical additions (e.g., paste thickeners, lime, or coagulants), which often create a sludge that is difficult to discard or valorise. This outlines the acute need for new technology to remediate mining effluent and reduce reliance on primary mineral sources. This proposal will combine a calcium silicate (CS) ‘sponge’ with naturally occurring microalgae to develop a hybrid tool to remove dissolved metal ions, initially Co, Ni and Cu, from mine waters and reclaim the metal from the CS and biomass. CS can sequester 400g Co or Ni per kg of CS. This is at least 10 times more than other materials that adsorb Co, including activated carbon and is 100 times more concentrated than virgin cobalt ore. In addition, sequestration takes place at ambient temperature and under mild conditions. It is low cost, easily up-scaled and is a completely new approach to cleaning up mine effluent and tailing ponds (current and legacy). Our initial results show that Co or Ni metal can be directly recovered post-sequestration by heating to 700 oC, providing a new route to valorising waste and reducing reliance on primary mineral sources. To extend the range of metal ions removable and enhance metal recovery, we propose to combine CS with a biosorption approach. The partnering research team in Canada are pioneering using microalgae that is naturally adapted to mining sites (Sudbury, Ontario) to develop a passive approach to water remediation. This is also a low cost approach, which will help manage mines and protect water supplies. CS sequesters metal by coupled dissolution-precipitation reaction while microalgae sequesters by biosorption. These very different mechanisms affect the range of metals sequestered (microalgae expected to be more versatile); the metal loading (CS expected to be much higher) and the metal recovery (biomass combusts at a lower temperature). The aim is to develop a combined tool/ filtration unit that uses the advantages of both approaches – the long-term passive metal uptake by naturally adapted microalgae and the active, high metal loading capability of CS. In addition, microalgae can generate organic matter with useful properties for soil and ecosystem regeneration. Co, Ni and Cu are found within tailings ponds at Canadian mining, mineral processing, and smelting sites, including those of the industrial partner, Glencore. Once developed, we will trial the CS-microalgae tool at tailing ponds in Canada operated by the industrial partner. Combined the CS and microalgae tool will be optimised for metal removal, recovery and surrounding ecosystem remediation, creating a low cost and practical solution.