Articles tagged with: Tailings

51. Pre-Concentration – Savior or Not?

pre-concentration
Can pre-concentration become a savior for the mining industry by lowering metal production costs?
Pre-concentration is a way of reducing the quantity of ore requiring higher cost downstream processing, i.e. grinding in particular.  One can attain significant cost savings in energy consumption and operating expenses by using a low cost method to pre-concentrate minerals into a smaller volume. A previous blog “Remote Sensing of Ore Grades” discussed one new pre-concentration method currently under development.

Pre-concentration isn’t new

Pre-concentration has been around for many years.  However the techniques available are generally limited.  Hence many ore types are not amenable to it..unfortunately.
The main methods available are:
Ore sorting, which can be done using automated optical, electrical, or magnetic susceptibility sensors to separate ore particles from waste. The different sensors can rely on colour recognition, near infrared radiation, x-ray fluorescence, x-ray transmission, radiometric, or electromagnetic properties. The sensors can determine if a particle contains valuable mineral or waste, thereby sending a signal to activate air jets to deflect material into ore and waste bins.
Density separation, or specific gravity differences are another property that some pre-concentration methods can use. Gravity based systems such as dense media separation (DMS), jigs, or centrifugal concentrators are currently in commercial production.
Scrubbing, another very simple pre-concentration method is scrubbing, whereby simply separating fines or coatings may remove deleterious materials prior to final processing.

 BenefitsJig Plant 1

Pre-concentration provides several benefits:
  • If done underground or at satellite mine site, the ore hoisting or ore transport costs can be reduced.
  • If the pre-concentration rejects can be used as mine backfill, this can reduce backfilling costs.
  • Processing of higher grade pre-concentrated mill feed can reduce energy costs and ultimately reduce the cash cost of metal produced.
  • Grinding costs can be reduced if waste particles are harder than the ore particles and they can be scalped.
  • Minimizing waste through the process plant will reduce the quantity of fine tailings that must be disposed of.
  • Lowering operating costs may potentially allow lowering of the cutoff grade and increasing mineral reserves.
  • Higher head grades would increase metal production without needing an increase in plant throughput.

Limited ore types are suited for pre-concentration

Not all ore types are amenable to pre-concentration and therefore a rigorous testing program is required. In most cases a pre-con method is relatively obvious to metallurgical engineers but testing is still required to measure performance.
Testing is required to determine the waste rejection achieved without incurring significant ore loss. Generally one can produce a higher quality product if one is willing to reject more ore with the waste.  It becomes a trade-off of metal recovery versus processing cost savings.
Fine particles generated in the crushing stage might need to bypass the pre-con circuit. If this bypassed material is sent to downstream processing circuits, one may need to examine crushers that minimize fines to avoid excessive material bypassing the pre-con circuit.

Reject waste or reject ore?

One must decide if the pre-con system should reject waste particles from the material stream or reject ore particles from the stream.  The overall metal recovery and product quality may be impacted depending on which approach is used.

Conclusion

The bottom line is that the mining industry is continually looking for ways to improve costs and pre-concentration may be a great way to do this.   Every process plant design should take a look at it to see if is feasible for their ore type.
While the existing pre-concentration methods have their limitations, future technologies may bring in more ways to pre-concentrate.  This is probably an area where research dollars would be well spent.
Share

50. Landslide Blog – If You Like Failures

slope failure blog
For those of you with a geotechnical background or have a general interest in learning more about rock slides and slope failures, there is an interesting website and blog for you to follow.
The website is hosted by the American Geophysical Union the world’s largest organization of Earth and space scientists. The blogs on their site are written by AGU staff along with contributions from collaborators and guest bloggers.

Landslide Blog screenshot

The independent bloggers have editorial freedom in the topics they choose to cover and their opinions are those of their authors and do not necessarily represent the views of the American Geophysical Union. This provides for some leeway on the discussions and the perspectives the writers wish to take.

Landslide Blog

One specific area they cover well in their Landslide Blog are the various occurrences of rock falls and landslides from any location around the globe. They will present commentary, images, and even videos of slope movements as they happen.
Often they will provide some technical opinion on what possibly caused the failure event to occur. The Landslide Blog has a semi-regular email newsletter that will keep you updated on new stories as they happen.
The following links are a few examples of the type of discussions they have on their website.
Here is a description of a small water dam failure in Greece.
Here is some video of the Samarco tailings runout in Brazil.
From time to time the Landslide Blog will examine mine slopes, tailings dams, and waste dump failures, however much of their information relates to natural earth or rock slopes along roads or in towns.
Some of their videos are quite fascinating, illustrating the forces behind some of earth’s natural erosion processes. Check it out for yourself.
The bottom line on all of this is that the less the mining industry is mentioned in the Landslide Blog, the better it is.
Share

46. Tailings Disposal Method Risk

mine tailings
After the Mt Polley and Samarco tailings failures, there have been ongoing discussions about the benefits of filtered (dry stack) tailings as the only way to eliminate the risk of catastrophic failure. Mining companies would all like to see risk reductions at their projects.

Filtered tailings stack

However what mining companies don’t like to see are the capital and operating costs associated with dry stacking. The filtering cost and tailings transport cost are both higher than for conventional tailings disposal. Obviously this cost increase gets offset against improved environmental risk and simpler closure.

So what is a company to do?

In my experience when designing a new mining project, all companies at some point complete a trade-off study for different tailings disposal methods and disposal sites. Contrary to some environmental narratives, mining companies really do want to know about their different tailings options.  They would all adopt the dry stack approach if it was the most advantageous method.
The mining companies are fully aware of the benefits but the dilemma is the cost and being able to somehow justify the technology. Complicating their decision, companies also have other options for reducing their tailings risk.

The  final decision can get complex.

In a tailings risk analysis, people will use a risk-weighting approach to assign an expected economic impact to their tailings plans. For example, if the cost of a failure is $200 million and the risk is 0.1%, then the Expected Cost is $200,000. The problem with this is its based on a theoretical calculation on an assumed likelihood of failure.   In reality either the dam will fail or it won’t.  So failure remediation money will be spent ($200M) or it won’t be spent ($zero), it won’t be partially spent ($200k).
The accepted tailings risk therefore becomes a subjective factor.
While implementing a dry stack may reduce the risk of catastrophic failure to near zero, implementing a $100,000 per year monitoring program on a conventional tailings pond will reduce its risk.
Implementing a $500,000 per year monitoring program would reduce that risk even further.
Installing in a water treatment plant to enable periodic water releases may further lower the tailings risk.
The company can look at various mitigation options to keep lowering their risk, although none of the options would necessarily bring the risk down to zero. Ultimately the company could compare the various risk mitigation options against the dry stack costs in order to arrive at an optimal path forward.

What level of risk is acceptable?

So the question ultimately becomes how low does one need to reduce the tailings risk before it is acceptable to shareholders, regulators, and the public. I don’t think the answer is that one must lower the risk down to zero. There are not many things in today’s world that have zero risk. Driving a car, air travel, shipping oil by ocean tanker, having a gas furnace in your house..none of these have zero risk yet we accept them as part of living.
Environmental groups continually discuss ways of forcing regulators and mining companies to take action against the risk of tailings failure. This is commendable.
However they generally fail to provide any guidance on what level of risk would be acceptable to them or to the public. It seems to be difficult for these groups to define what an acceptable risk is. They offer no solutions, other than either zero risk or shut down all mining.

Conclusion

We know that mining is here to stay so we all should work together towards solutions.
The solutions need to be realistic in order to be taken seriously and to play a real role in redefining tailings disposal. Dry stack may not be the only solution and we should be looking for more ways to improve tailings disposal.
Since these other options don’t seem to be available yet, dry stack tends to offer the best solution in most circumstances.  I have written another blog on this topic “Fluid Tailings – Time to Kick The Habit?”
Share

36. Fluid Tailings – Time to Kick The Habit?

dry stack tailings
Smoking… we constantly hear about the negative effects of it.  We all know of people that have died due to lung cancer or other smoking related causes.  However we also know people that have smoked their entire lives yet lived into their eighties.  Yet there is still a push to get people to kick the smoking habit because statistically it is better for them.

Short term pain for long term gain.

Let’s compare all of that with the concept of fluid tailings storage.
Tailings. Those of us in the mining industry constantly hear about the negative impacts of tailings storage.  We know numerous mines have had failures resulting in fatalities and catastrophic damage. Check out the horrific example video below. It appears there are people 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.
The question for me has become whether the mining industry should kick the habit of fluid tailings storage even though no failures occurred in many circumstances?

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 tailings storage.
Moving away from fluid 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 1.3 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.  I tend to agree with that statement, however that is no guarantee for all tailings dams.

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.
I have written another blog on the issue of tailings management risk “Tailings Disposal Method Risk“.
Share