Recycling metals using bacteria: bioleaching
Bioleaching: let's see how it works
Biolixiviation: recovery of ores and wastes
Copper, nickel, zinc, cobalt or gold... we consume more and more metals. To keep this up, we need to devise production methods that fit into a circular economy by recovering resources and waste. With this in mind, the Geological and Mining Research Bureau is looking at ways to put waste to effective use.
In a circular economy, you extract a ton of ore somewhere to make something of it. It takes energy to extract it, treatment has to be optimized.
To do this, scientists turned towards a natural phenomenon: bioleaching. Let me explain. Extracting metals from the ground produces a lot of waste: mineral matter that contains a small amount of metal. Bacteria develop in this waste, polluting the soil.
These bacteria develop naturally in contact with the air, in the presence of such ore and waste. The environmental impact of this is very high, with acidification caused by the action of the bacteria, triggering leeching of the metals within the waste.
The bacteria release small quantities of metal from the rock, which are then recoverable. The ability of bacteria to produce energy by dissolving metals is called bioleaching. Researchers have developed an industrial process to optimize this phenomenon and produce metals. First, the ore must be ground down to facilitate the bacterial action. It is then mixed in a bioreactor with a nutrient solution.
It's a simple product, similar to a fertilizer. It contains nitrogen, phosphate, potassium and magnesium. It is shaken, to put the bacteria in contact with their environment: the nutrient solution and the solids. It is then left for a while. We can then recover a solution that contains metals.
By treating this waste, we can recover several types of metals.
At this stage, gold, cobalt and copper are three metals that can be recovered by bioleaching. Work is also being done on the recovery of nickel. Zinc, too, can be recovered.
The method makes it possible to recover waste metals and the sulfuric acid produced by the bacteria responsible for pollution.
The advantage of bioleaching is that in reducing the environmental impact, we also find an effective use for the contents of the waste, thus killing two birds with one stone.
Bioleaching isn't just research, it is already being applied, as in Uganda, where tons of waste from a copper mine have for years contaminated the soil and nearby lake.
The initial pile of accumulated mining waste in Uganda was one million tons. That one million tons contained 1% cobalt. Overall, between 10,000 and 15,000 tons of cobalt is estimated to have been produced in this period.
Today, bioleaching produces 5% of the gold and 20-25% of the world's copper. The BRGM is looking to improve this technique and apply it to other types of waste.
We are trying to find new targets for this process, new applications. We're working on the waste from coal mines, which have a great impact on the environment. For some time, we have been looking at electronic waste: computers and end-of-life phones. We want to adapt bacteria to collect the metals contained in this electronic waste.
All this research will allow us to recycle our waste and be part of tomorrow's circular economy.