Raw materials are crucial to the economy and well-being in Europe. Reliable, economical and environmentally sound access to raw materials has therefore been a growing concern in recent years – but for many raw materials, Europe is dependent on imports from other continents.
Raw materials of high economic importance as well as a high risk of supply are placed on the list of “critical” raw materials by the European Commission, which is revised regularly. One way of reducing raw material criticality is through recycling in Europe. Many changes have been made already to transfer the European economy from a linear to a more circular one, needing less mining and imports of raw materials. BIOMIMIC wants to contribute to these efforts by developing recycling processes for diluted and complex waste solutions that currently cannot be treated in an economic and ecological way.
During the extraction of metals in mining or recycling, waste solutions are often created that still contain considerable amounts of the originally targeted metals mixed with other substances. On the one hand, these metal concentrations are too high for easy and safe disposal. On the other hand, concentrations are usually too low for metal recovery in an economic and ecological way using current technologies. The BIOMIMIC project aims to develop low-cost, efficient biotechnological processes for metal recovery from these complex and diluted waste solutions. Besides environmental and financial benefits, realization of such processes would also contribute to Europe’s supply of raw materials. Especially noteworthy are raw materials that are currently considered “critical” by the European Union due to their high economic importance and risk of supply.
Three waste solutions
Three waste solutions were exemplarily chosen within BIOMIMIC to demonstrate the development of such a biotechnological processes:
- A leachate from bauxite residue created during alumina production
- Drainage waters from shut-down mine shafts
- A leachate from fly ash generated during incineration of municipal solid waste. These three example solutions are broadly important, as explained below.
Global production of alumina has almost tripled in the last 30 years and reached 132 million tonnes (Mt) in 2017. Nowadays, more than 60 % of global supply of alumina is produced in China, which only entered the market in the early 2000s. Europe’s contribution on the other hand has been quite stable over several decades with around 6 Mt per year.
Currently, alumina is produced in six European countries: Spain (1.6 Mt in 2016), Ireland (1.3 Mt), Germany (1.0 Mt), Greece (670 kt), France (500 kt) and Romania (470 kt). Alumina is produced from the natural ore bauxite. During the process, an alkaline residue is generated as a side product. This residue is currently useless and needs to be deposited in controlled landfills. Rainfall, water sprinkling during dry weather (to avoid dust) and water contained in the residue itself generate a leachate with considerable metal concentrations.
Work done within the BIOMIMIC project leads to an estimate of 5.9 million m3 of bauxite residue leachate being produced yearly in the EU. This leachate contains mostly aluminium (1790 t) but also molybdenum (14 t) and nickel (1 t) as well as the “critical” raw materials gallium (12 t) and vanadium (37 t). BIOMIMIC targets the recovery of vanadium from this waste solution with a biosorption process that could potentially supply Europe with 17 t of vanadium per year (approx. 0.15% of European demand).
Closed mines leaks drainage water with high amount of metals
Even after mining operations are shut down and shafts are closed, mines generate drainage waters that often contain high amounts of metals. These drainage waters come both from rain and from ground water.
In the traditional mining area around Freiberg (Germany), mining operations for metals like silver, zinc and lead started in the Middle Ages and lasted until 1968. Today, monitoring of rivers in the region receiving such drainage waters shows metal concentrations exceeding thresholds from the European Water Framework Directive even 50 years after mine closure. Within BIOMIMIC, metal concentrations in three drainage adits near Freiberg have been analysed and a bioreduction process for the recovery of metals from these drainage waters has been developed. Per year, 85 t of zinc, 800 kg of copper, 630 kg of nickel and cadmium each and 400 kg of lead could be extracted through this BIOMIMIC process in Freiberg.
Compared to the European demand for these metals, the amounts do not have a significant impact on security of supply. Seen from an environmental point of view, however, they provide major reductions in terms of metal loads introduced into receiving rivers. Furthermore, the processes can be transferred to other mining areas in Europe, which would increase the recovered amounts of metal and the avoided environmental impact.
Large amounts of ash with broad variety of metals
Municipal solid waste generation has been decreasing in the EU in recent years and further efforts are undertaken to continue this trend. From a maximum of 261 Mt in 2007, values went down to 249 Mt in 2017. The amounts of municipal solid waste that is incinerated per year, on the other hand, has been increasing consistently since 2000 and reached 68 Mt in 2017. Since the European Union aims for no more than 10 % of municipal solid waste going to landfill per year, this development is expected to continue during the next decade.
By the incineration of waste, large amounts of ash are generated that contain a broad variety of metals. While recycling processes for recycling of ash from bottom ash are widely used, fly ash has so far only been deposited. Only in Switzerland, the FLUWA/FLUREC process for the recovery of zinc, cadmium, lead and copper is currently established. BIOMIMIC estimated that the amount of fly ash generated through municipal solid waste incineration was around 1.4 Mt in 2017. The largest amounts are produced in Germany (320 thousand tonnes, kt), France (250 kt), the United Kingdom (220 kt) and Italy (120 kt). More than 20 different metals (including “critical” raw materials like cobalt, antimony or tantalum) are contained in this fly ash. Targeting the recovery of these metals, two bioreduction processes are being developed in the BIOMIMIC project, which could provide up to 57,000 t of aluminium, 669 t of zinc, 136 t of lead, 88 t of copper, 55 t of cadmium, 46 t of manganese, 12 t of cobalt and 5 t of nickel. For the “critical” raw material cobalt, this translates into 0.65% of European demand.