For millennia, microbes have been invisible little helpers in the area of mining. Since the discovery of their impact on processing ore in the middle of the last century, mining companies have been trying to capitalise on this fact. Most metals today are still extracted using conventional methods. But with primary resources growing scarcer, the age of Biomining (or Green Mining) lies just around the corner. The European Ecometals and Biomore projects are now trying to overcome some of the biggest hurdles.
What is biomining – a sustainable new method for one of our oldest professions, or just business as usual under a new name? The most common variation on the theme is currently a process known as bio- leaching. In general, the term refers to situations where the target metals in an ore are solubilised during bioprocessing. Up to 15% of the world’s copper is extracted in this way. In gold mining – the second most important biomining industry, with 5% of total output produced using biotech methods – experts speak of “biooxidation”. In this process, microorganisms are used to remove minerals that occlude target metals. After this biological pre-treatment, the gold is extracted chemically.
Mining can be a dirty business
New biomining ventures are growing more common, since compared to traditional pyrometallurgical methods, bioleaching consumes less energy and produces almost no pollutants (such as sulphur dioxide) or greenhouse gases (like carbon dioxide). One example is the Vuonos talc processing site in Eastern Finland. Last year, Dutch talc producer Mondo Minerals installed a technology that allows the extraction of nickel and cobalt from a by-product of talc production in Vuonos. The technology comes from South Africa’s state-owned Council for Mineral Technology (Mintek) and involves the production of bacterial inoculum. Mintek estimates that 10 cubic metres of this solution will be required when the plant runs at full throughput.
The Vuonos project will be closely watched as another biomining flagship project just drowned recently. In late May, the Finnish Government announced that the Talvivaara nickel mine will be closed down for good. In environmental terms, this surface mining operation turned into a nightmare. The mine in Sotkamo, which has been operational since 2008, employs a process known as “heap leaching” to extract nickel as well as zinc, copper and cobalt. In this process, piles of ore that have been blasted and ground are pushed into mounds up to 10 metres high. The heaps are aerated so that the microbes receive enough oxygen and carbon dioxide. In the past, heap leaching relied on naturally occuring microorganisms to take care of the job, but inoculation with the desired bacteria has now grown increasingly common. The most significant environmental issue is the accumulation of wastewater containing sulphuric acid, which has to undergo special treatment. And that’s where Talvivaara’s problems began, after it became public knowledge that several wastewater spills from the facility had acidified nearby lakes. Even worse, it was revealed that the mining company’s management was likely aware of the problems as early as 2009, but ignored them completely. The management was fined for aggravated environmental crimes last year. In addition to – or because of – those legal and environmental difficulties, mine operator, Talvivaara Sotkamo, filed for bankruptcy in autumn 2014 after reporting huge financial losses. The state took over shortly afterwards but could not turn the tide. The final shutdown will cost an estimated €300m, experts estimate.
One lesson learned from the Talvivaara fiasco is to try to reduce sulphuric acid through the development of new leaching methods. Françoise Bodénan, responsible for the Ecometals project at the French Bureau de Recherches Géologiques et Minières (BRGM), explains: “The main point is to work at nearly ambient temperatures with the help of bacteria avoiding massive consumption of chemicals.“ Helping to validate the idea of bioleaching unconventional resources to recover copper and other critical metals, “the projected Ecometals pilot operations will start in early 2017,” adds Bodénan.
The next level–Ecometals
The German-French Ecometals project is of strategic interest to both governments. The ten German partners are receiving €4.2m in support from the country’s Federal Ministry of Education and Research (BMBF), while their six French colleagues have been granted €1m from the Agence Nationale de la Recherche (ANR). Obligatory co-payments from industrial members of the consortium bring the total budget to €7.5m. Ecometals is mainly focused on research into copper and the associated metals that are found in black shale deposits rich in sulphides (copper schist) in Central Europe, especially Poland. On the continent, most accessible primary copper resources with a high or even moderate amount of these metals are exhausted. All that is left are low-grade ores, complex ores and played-out waste deposits. Sabine Kutschke, the German Ecometals project leader at the Helmholtz Institute Freiberg for Resource Technology (HIF), believes biomining provides the best options for exploiting these resources economically. “Because they have a quite different mineral matrix, new and efficient methods need to be developed,” she says. “And bioleaching is a reliable and promising option.”
There are 17 companies and research institutions from Germany, France and Poland in the Ecometals network. Currently most key metals have to be imported in all three countries, so ensuring a sustainable supply is a vital economic interest. One element that is in particularly high demand is the transition metal copper. With its excellent electrical and heat conductivity, copper is the material of choice in electrical cables, as well as for heat sinks in electrical devices that have to dissipate thermal energy. Demand for copper has grown dramatically in recent years. Global copper production more than doubled between 1980 and 2013, soaring from about 8 to over 18 million metric tons. Despite the fact that a significant fraction of consumed copper now comes from from recycling (US 33%, EU 45%), the high demand has encouraged theft – for example from power facilities at train and metro lines.
Since the search for surrogate solutions based on more abundant elements is still underway, more efficient copper recycling and mining technologies remain a key topic. Launched in January 2014, Ecometals will wrap up in mid-2017 if all goes according to plan. The consortium is focusing on three bottlenecks that are hindering the more efficient exploitation of low-grade ore deposits or metal waste.
1. About 5% of the world’s energy production is needed to break up mined ore bodies; the members want to improve thermal and chemical pretreatment.
2. The Ecometals partners aim to make bioleaching more eco-efficient, low-cost and low-energy. Chalcopyrite – the iron sulfide mineral where most of the unexploited copper is trapped – will play a key role in this regard. Ongoing work includes both optimising traditional acid-based leaching methods and advancing non-conventional methods in the neutral pH range.
3. The Franco-German team aims to develop a better extraction mechanism for the world’s most important copper ore. After optimising the processes at the lab scale, Ecometals will strive to establish one or more metal recovery processes at the pilot scale in early 2017.
Biomining is not only about getting metals out of rock. It also includes their recovery from process solutions, which is of particular importance when dealing with complex ores. The consortium is therefore also working on microbially mediated, selective metal precipitation (“biomineralisation”) and the development of biosorptive molecules (“bioabsorption”). On the one hand, the development of peptide-based bioabsorption methods is still in its early phase. On the other hand, work package leaders Geos Ingenieur GmbH from Germany, experts on the subject, are already seeking to implement the biomineralisation methods in a large-scale pilot plant that should become a central element in future research projects. The firm attracted attention two years ago when it produced the iron-oxyhydroxysulfate schwertmannite using iron-rich wastewater from a brown coal mine. After further processing, the mineral has now been successfully integrated into an anticorrosive coating product for railway carriages.
While Germany and Poland are interested in the bioprocessing of their copper schist black shale, copper-poor France could use the newly developed methods to begin the exploitation of its polymetallic deposits in the Massif Central. “The main objective of the French partners in Ecometals, however, is to work and develop a bioleaching process in stirred tank reactors. This process will allow us to address other types of ore worldwide,” says Bodénan. Continuous stirred tank reactors (CSTR) have been in development since the 1980s. They allow for greater control of processing parameters like pH, temperature, carbon dioxide or oxygen content than is possible with heap leaching. Most CSTRs work at temperatures of up to 50° C, but certain ores have been successfully processed wit