What is one thing that we constantly hear about negatively yet we continue to do it (although we know it can be bad for us)? Is that thing smoking or is it fluid tailings storage? Can we break either of these habits?
Short term pain for long term gain.
Those of us in the mining industry constantly hear from stakeholders about the negative impacts of fluid tailings storage. By “fluid” I mean conventional tailings that can liquify and flow great distances. We know of numerous mines that have had failures, resulting in fatalities and catastrophic damage. Check out the horrific example video below. It appears some people were walking or driving mid-way up the dam face.
We also know of many mines that have used fluid tailings their entire operating lives without any incidents. Therefore some say it is fine to continue doing that.
The question for me has become whether the mining industry should kick the habit of fluid tailings storage even though not every dam has failed.
Quitting isn’t easy
Quitting smoking takes real effort, some pain, maybe a change in lifestyle, but most importantly an overall commitment to quit. It isn’t easy but pays off in the long run.
The same holds for fluid tailings storage.
Moving away from conventional tailings storage requires real effort, some pain, a change in operating style, and a commitment to quit. It won’t be easy but will pay off in the long run by avoiding major tailings incidents, less negative press, and fewer environmental permitting issues. No longer will consultants and regulators be disputing factors of safety of 1.2 versus 1.5, when they could be discussing factors of safety of 5 versus 10.
Quitting fluid tailings storage may bring relief to stakeholders, shareholders, regulators, and mine management. They’ll all sleep better at night knowing there isn’t a large mass of fluid being restrained simply by a dam at a factor of safety of 1.5. Engineers say they can design dams that will be stable for perpetuity. Even if one agrees with that statement, that is still no guarantee that failures won’t happen somewhere.
Conclusion
The bottom line is that no one wants to sit downwind of a smoker and no one wants to live downstream of a tailings dam. Perhaps it is time for the mining industry to kick the habit of fluid tailings storage, regardless of the cost and discomfort. Short term pain for long term gain.
In another blog post I have discussed how tailings storage always require a tradeoff between cost and risk. Normally lower cost options present high risks, and vice versa. How much risk is acceptable to a company or to the public? You can read that post at this link “Tailings Disposal Method Risk“.
For those wishing to pursue the dry stack approach, a series of laboratory tests are required to characterize the talings, the process, and the placement method. You can see a checklist of the test options at this blog post “Filtered Tailings Testing Checklist“.
The factors of safety on dams are really only factors of ignorance to protect against unknown issues. If the FOS was increased to say…2.0 then fluid filled dams would not be an issue.
I don’t know if even a FoS of 2 would cover off the possibilities. There is piping failure due to poor filter construction, higher than expected water levels & phreatic surfaces due to seasonal events, misidentified foundation conditions, etc.. Potentially a lot of things can theoretically can go wrong but most of them would disappear by using a dry stack. Its all the unknowns that are the problem. It will be interesting to see the cause of failure at Samarco in Brazil.
A talked with Jack Caldwell about dry stack. He was doing some work on a project in SA. They were having filtration problems that limited their output to (if I correctly recall) 4,000 tpd. Greens Creek is dry stack, but only 2,000 tpd. Trying to run a 50,000 tpd dry stack has never been done as far as I am aware. That is the biggest issue with dry stack. Second biggest is how to manage acid generation.
My gut feel says if the guys who can design a massive 40 ft 28 MW grinding mill were tasked with designing a large capacity filtering system, they could probably do it. However the impetus must be there for them to do this and it’s up to industry to ask for it. Likely the capex and opex wouldn’t be insignificant, but maybe that’s a new environmental cost the industry will need to start building into their economics in the coming years. Large capacity water treatment plants are now seen as a cost of doing business, something that really wasn’t the norm 20 years ago. Advanced tailings processing may be next.
Who says the engineers can design a 40 ft 28 mw grinding mill? The one at Mt Milligan was supposed to process 60,000 tonnes per day but it’s only averaging about 44,000.
My point is that there is already a lot of risk in building a mine, as is indicated by Mt Milligan. Adding more risk with untested technology is not going to encourage investors to fund new mines. Fluid filled dams have been around in various applications for centuries. The amount of geotech work done for a hydro dam is many times the amount done for a tailings dam. We need to ask why is that? When a P Eng puts his stamp on a design he has to be sure it will work. The designers of the Mt Polley dam should be hauled up in front of the discipline board to explain their design. Someone needs to be held accountable.
I was reading yesterday that BC’s Site C hydro dam will be earth filled. That tells me that BC is not concerned with fluid filled earth structures….
Be interesting to know what factor of safety they design to (versus a tails dam FoS) and what compaction specs they require for the entire dam (versus typical tails dam compaction requirements) to allow someone to make a good side by side comparison.
Yes, and also the geotechnical work done prior to construction.
I recall from a past job that downstream waste is normally compacted by driving on it with the trucks and placed in 5 meter lifts.. SG is normally assumed to be about 2.0. Core was also compacted by trucks, and sometimes by sheepsfoot. Normally laid down no more than 0.5 meters at a time. Also tested via densometer and with instrumentation and removed if it didn’t meet spec. Filter material normally produced onsite to a very tight spec. Lots of it thrown out if it doesn’t meet spec. An engineer or a tech onsite at all times during construction.