Mining is big business, but also one of the world’s biggest polluters. A 2019 report estimated that the world’s 3,500 large-scale mining operations produce over 100 billion tonnes of solid waste per year. The ratio of useful materials to waste minerals is staggering; waste mass can be several times that of base metals, and can be millions of times that of rare elements such as gold.

This waste is of particular concern due to its often toxic content, with poisonous materials such as mercury a frequent by-product of mining operations. Recent accidents, such as the collapse of a tailings dam at Vale’s Brazilian operations near the town of Brumadinho, have also shone a spotlight on existing waste storage and treatment facilities, with growing concern that simply collecting vast reserves of solid and liquid waste is both unprofitable and highly dangerous. As demand for minerals, particularly rare earths and other uncommon commodities, grows, this problem is set to only increase.

A promising counter to this growing problem is that of waste recovery. Rather than cutting down on waste itself, companies are investing in new industrial processes to extract and re-use some of the useful materials that are often dumped among tonnes of less useful mining waste. With platinum group metals (PGMs), base metals, and even rare commodities such as gold among these unintended by-products of mining, there are a number of initiatives across the mining industry to improve the reclamation of resources, and push the sector towards a truly circular economy.

Mineworx moves to pilot plant

Canada-based Mineworx has been involved in the mining industry for some time, having entered into the sector in 1975 with the acquisition of the Cehegín iron ore project in Spain, which produced four million tonnes of ore in its first fourteen years of operation. Since then, the company has moved into the development of more advanced technologies, aiming to increase the environmental viability of both its operations in particular and mining in general. The business reached a major milestone in April when it announced an agreement with Tennessee’s Davis Recycling Inc. to construct a pilot plant; the operation will see  platinum group metals (PGMs) recycled from used catalytic converters.

The project will see the miner enter into a PGM recovery business that it values at around $30bn annually, and the move is a critical step in demonstrating the efficacy of the technology, which builds on the work of another partner, EnviroLeach. This third company has developed a water-based process to extract PGMs from catalytic converters, with up to 90% of the precious metals being recovered. The process removes the need for harmful substances, such as cyanide, to be used in the extraction process, which have been an industry standard but pose significant risks to human health and environmental safety.

This collaborative approach could help share information that could be beneficial across the mining industry, a sector which could see an increased demand for innovative waste treatment in the future. EnviroLeach notes that global electronic waste is predicted to increase to 78 million tonnes by 2026 as electronic devices become more widespread, and demand for gadgets increases.

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Comstock targets mercury removal

Another mining company targeting a particular mineral is Comstock Mining, a Nevada-based miner that aims to improve the recovery and removal of mercury from mine tailings. The poisonous metal has long been a source of public health concerns in both artisanal mining and large-scale operations. A 2018 report found that over 1,000 tonnes of mercury was produced in the artisanal gold mining sector, due to the metal’s use in separating gold from non-precious ores. Notably, the waste that flooded the town of Brumadinho in the infamous Vale tailings dam collapse was found to contain dangerous quantities of mercury, arsenic, and manganese.

Considering these dangers, and the widespread nature of mercury in the mining industry, Comstock’s work could prove beneficial for miners across the sector. The miner owns the Comstock Lode, a gold and silver deposit that was first mined in the mid-19th century and saw almost $4m in investment from the company in 2018. The company plans to use this deposit to test a pilot mercury clean-up operation, backed by technology firms Mercury Cleanup and Oro Industries.

The joint venture will see the construction of a two ton per hour pilot plant to treat the 15 million pounds of poisonous mercury that have been produced over the course of the Comstock Lode’s mining life, and a successful operation could demonstrate a way forward for a mining industry that still struggles with mercury production.

VTT’s collaborative project

Many of these mine waste projects are collaborative in nature, and this is especially true for VTT’s MetGrow+ project, a collaboration with 19 companies, research organisations, and universities from nine European companies. The project was a four-year, $8.7m initiative to find ways to improve recovery of a number of waste minerals, such as cobalt, nickel and zinc, and improve Europe’s self-sufficiency with regard to metal production.

The project focused more on supply chain optimisation than technological innovation, and VTT reports that miners could see waste mineral recovery increased by up to 20% by following the initiative’s recommendations.

A key challenge for the project was developing a robust framework that could be applied to the mining industries of several European countries, each with a different balance of mineral exports and imports. The researchers overcame this by developing the “MetGrow Calculator”, an online tool that works out the optimal waste recovery process for a mine or region based on characteristic input by the user. VTT claims this system can take into account factors such as local access to mineral reserves, and will recommend an appropriate waste management system.

In addition to supply chain optimisation, the researchers completed work into the best uses for residual material from which metals have already been recovered. VTT noted that many recovered materials can be repurposed for use in building by being reworked into concrete, highlighting the project’s broad scope and attempts to improve efficiency across the breadth of the mining and construction industries.

Scandium International seeks industry support

A project at an earlier stage of development, and one seeking, rather than benefitting from, industry support, is Scandium International’s ion exchange project. The initiative will use ion exchange technology, a process usually used in the purification of drinking water, where ions are moved between two electrolytes to separate a compound into its component parts.

Scandium International expects to extract cobalt, nickel, and copper from mining waste. The miner also noted that the technology could be used to extract other minerals, such as rare earth elements, but that this would depend on the financial viability of the process itself.

This need to demonstrate technological and economic viability is a key challenge for Scandium International, and it has put out a call for copper miners and processors to sign up for involvement in the project. The miner seeks a partner with a functional copper plant, which can be used to demonstrate the efficacy of the technology on a demonstration scale, before being scaled up to larger productions, or expanded to include other resources.

Scandium International is particularly reliant on this external support considering its own limited mining resources. The company has just completed a feasibility study on its Nyngan scandium mine in New South Wales, Australia, and is a firm with big ideas and significant belief in new technologies, but perhaps lacks the material facilities to put many of these ideas into practice.

Mint Innovation’s “bio-refineries”

Moving from theory to practice is a similar challenge faced by Mint Innovation, a New Zealand technology start-up that uses microorganisms to recover metal from waste streams. The technology is unlike anything else in the mining sector, with the company envisioning a “bio-refinery” to recover gold from waste in a two-stage process. First, a traditional leaching process removes base metals such as iron and copper from electronic waste, before a patented acidic compound is applied to the waste, strong enough to dissolve gold that is then absorbed by microbes in the compound.

While gold is Mint’s first objective, the technology has uses across the mining industry, with the microbes able to absorb palladium, platinum, and rhodium with minimal chemical alterations. The start-up is also bullish about the scalability of its solution, relying on a business model where local recyclers help collect electronic waste and aid in distributing the recycled materials, potentially enabling the company to build its bio-refineries in any city with significant electronic waste with minimal up-front costs.

While the technology needs further development, namely in finding a way to recycle the chemicals used in the gold-absorbing compound, and the start-up is still in search of a financial backer to help realise its lofty ambitions, Mint’s work is an example of innovative and technologically-driven solutions to a sector that is still struggling to clean up its waste management.