It is no surprise to anyone that permitting new open pit mines in today’s environment is getting more difficult and even impossible in some areas. Underground mines also have their challenges, permitting as well as requiring relatively high grades to be economic.
So where might our future metal supplies come from? What are the options?
Insitu leaching may be the answer
I recently came across an insitu leaching website, called BIOMore. This was an initiative sponsored by the EU that looked at insitu leaching technology for metal recovery. Environmental issues associated with mining in Europe, particularly open pit mining, raised concerns about how ore bodies in the EU might be developed in the future.
Insitu leaching technology was viewed as playing an important role. This is due to its minimal surface disturbance, ability to operate at great depth, and its potential in urban and developed locations. Sounds like a nice solution to have on hand.
The EU-funded BIOMOre research project was completed in 2018. It was designed to develop a new technological framework for the insitu recovering of metals from deep deposits. The process would rely on controlled stimulation of pre-existing fractures in combination with insitu bio-leaching. The study mainly focused on the application of existing technologies.
Fracing will be an issue
Insitu leaching essentially relies on exposing mineralized surfaces to leach solutions. This may require hydro-fracturing (fracing) to enhance insitu bio-leaching using bacteria and acid. Fracing is currently banned in some European countries so this is going to be a potential issue. From a leaching perspective, the trade-off would be between no fracing, reduced cost & lower metal recovery against higher cost & higher metal recovery with fracing.
If insitu leaching technology development is successful, it could help exploit European base metals from porphyry deposits (Cu, Au, Mo, Cu, REE, PGE, Re, Pb, Cu, Pt, Au) and other gold and uranium deposits. Insitu leaching would avoid building a mine, mine infrastructure, and it generates almost no tailings nor waste dumps. Leaching is expected to be cheaper than traditional mining and more acceptable to the public. Insitu leaching is being touted as “Green Mining”
What did they conclude
This study deliverables included comprehensive documentation, an economic evaluation, and risk analysis of a potential insitu bio-leaching operation. The basis was a theoretical deposit, looking at different well field set-ups.
The study concluded that accessing potential deposits at depths of around 1000 m is economically feasible only if curved wells are used. The most relevant operational parameters are sufficient permeability in the ore zone and an adequate contact surface between the ore and leaching solution. The depth of the deposit is indirectly relevant, but more importantly the well installation cost per volume of deposit is critical. Hence curved wells are optimal.
One interesting suggestion was combining an insitu leach operation with geothermal energy recovery. This might result in additional project revenue stream with only a marginal cost increase.
It was suggested that insitu leach operations might be attractive in former mining regions where high grade deposits have been mined out yet nearby low grade deposits are well defined. Social license for insitu leaching may also be more accepting in these areas.
If you are interested in learning more about insitu leaching technology and the chemistry aspect, the BIOMore study deliverables are available for downloading at this site.
In the past, mining engineers like myself were told to learn the basics of crushing, grinding, and flotation to become more well rounded. I may suggest that future mining engineers may need to learn the basics of directional drilling, hydro-fracing, and chemistry. Sounds like petroleum engineering.
Update: The University of Western Australia is also looking at electric fields to extract metals from hard rock ore, the sample principle as electro-plating. Check out more information at this link “No more digging – a new environmentally friendly way of mining“.
Some aspects are still uncertain