Articles tagged with: Tailings

Filtered Tailings Testing Checklist

I have always been a big proponent of filtered (or dry stack) tailings over conventional tailings disposal. Several years ago I had written a blog (Fluid Tailings – Time to Kick The Habit?)  that this is the tailings disposal approach the mining industry should be moving toward.
Recently I have been seeing more mining studies proposing to use the dry stack approach. In some cases, they no longer even do the typical tailings trade-off study that look at different options. The decision is made upfront that dry stack is the preferred route due to its environmental acceptability and positive perceptions.
Recently I came across a nice document prepared by BHP and Rio Tinto titled “Filtered Stacked Tailings – A Guide for Study Managers (March 2024)”. I will refer to this document as “The Guide”. You should definitely get a copy of this Guide if your project is considering a dry stack operation. An information link is included at the end of this post.

A Guide for Study Managers

The Guide covers several topics, including tailings characterization; site closure concepts; filtered tailings stack design; material transport, stacking systems; and tailings dewatering methods. The Guide covers all the basics very well. The one area that jumped out at me is the tailings characterization and testing aspect.
Many assume that dry stack is simply filter, haul, dump, then walkaway. Its all very easy! However, in reality, the entire dry stack approach is complex.
One needs to be able to consistently dewater tailings from different ore types, then transport it under different climatic conditions, and then place and compact the tailings efficiently.
One also needs to be able to deal with plant upsets, when the filtered tailings don’t meet the optimal product specifications. So its not really that simple.
One of the chapters in the Guide details the different test work that should be done to understand the dry stack approach.  The list of tests is a lot longer than I had envisioned.  I previously knew some of the types of lab testing required, however the Guide outlines a very comprehensive list.
The Guide also categorizes the tests according to study stage, be it concept study, order of magnitude study, or Pre-Feasibility level. Interestingly, the concept study can rely mainly on published information. However, the more advanced mining studies require the lab testing of actual tailings material.

Testing Checklist

To help organize the complexity of testing, I have listed their suggested tests as to whether the test is related to material characterization, process characterization, or filtered product characterization. Each aspect serves a different purpose in understanding the workings of the filtered tailings approach. The engineer will decide at which study stage they wish to do each of the tests, or which of the them they actually need to do.
To keep the blog post brief, I am not describing the details for each test. Most geotechnical or process engineers will already be familiar with them, or anyone can search the web to learn more.

MATERIAL CHARACTERIZATION TESTS

  • Chemical composition Testing: using atomic absorption or spectroscopy, identify the elements within the tailings stream to highlight contaminants and potential flocculation issues.
  • Conductivity Test: increase knowledge of the tailings stream.
  • Mineralogy Testing: identify mineral types and clay minerals (if any) that could impact on performance.
  • Particle Shape Analysis: are there fibrous minerals present, as well as settling and rheology effects.
  • Particle Size Distribution: are the tailings coarse, or mainly fine silt and clay sized particles that can impact on filtering and product performance.
  • pH Test: determine the acidity of the tailings steam, can relate to flocculant selection.
  • Tailings Slurry Density Test: assess the pumpability and amount of thickening and filtering that will be required.
  • Tailings Solid Mass Concentration and Moisture content: required for process mass balances.
  • Specific Gravity Testing: assess the SG of the tailing particles, i.e. light or heavy minerals.
  • Total Dissolved Solids Test: assess the fluid composition, are minerals dissolvable.
  • Zero Free Water Test: relates to the solids concentration at which the sample is fully saturated and may relate to transportability.

PROCESS CHARACTERIZATION TESTS

  • Total Suspended Solids: assess the quality of the return water from thickening or filtration.
  • Drained and Undrained Settling Test: to assess the thickening aspects and stack performance.
  • Setting Cylinder Tests: used to assess thickener settling performance.
  • Raked Setting Cylinder Tests: used to assess thickener settling performance.
  • Dynamic Continuous Settling Tests: used to assess thickening under continuous feed situation.
  • Minimum Moisture Content: assess the minimum moisture content achievable in filtration.
  • Vacuum/Pressure Filtration Test: often done by vendors, assess the filtering performance.
  • Compression Rheology: design consolidation / permeability data for filtering and disposal design.
  • Shear Rheology: provide information for pump and pipeline design.
  • Shear Yield Stress: provide processing insights for slurry dispersion and flocculation.

FILTERED PRODUCT CHARACTERIZATION TESTS

  • Leaching Tests (long term): assess whether the tailings stack will continue to leach metals and contaminants over the long term.
  • Leaching Tests (short term): assess whether the tailings stack will rapidly leach metals and contaminants.
  • Acid Base Accounting Tests: will the stack be an ARD concern.
  • Net Acid Generation: relates to ARD and neutralizing potential.
  • Air Drying Tests: determine the rate of natural air drying and dry density.
  • Atterberg Limits Testing: determine the plastic limit, liquid limit with respect to moisture content and stackability.
  • Consolidation Tests (one-dimensional): to assess the consolidation and settlement of the stack over time.
  • Proctor Density Tests: assess the optimal compacted density and moisture content vs the moisture content delivered by filtration.
  • Critical Void Ratio Tests: assess compaction, consolidation, and liquefaction potential.
  • Shear Testing: determine the geotechnical strength of the filtered product for stack height design.
  • Permeability Testing: assess the internal drainage characteristics of the filtered product.
  • Soil-water characteristics Tests: assess the unsaturated behavior of the filtered product.
  • Flow Moisture Point Tests: assess how well the material can be transported and placed.
  • Conveyance Testing: assess how well the material can be conveyed (troughing, steepness).
  • Minimum Angle for Discharge: used in the design of hoppers and chutes.
  • Angle of Repose Tests: used in hopper design and dry stack design. Ground Bearing Pressure: used to assess the trafficability of the deposit.

Conclusion

A dry stack operation might be just as complex as conventional tailings disposal, although that might not be the perception. Certainly, the processing side of filtered tailings is more complex than conventional tailings. The transportation design may also be more complex, as is the tailings placement methodology. The main complexity missing from the dry stack is the need for a large sludge retaining dam, albeit that is a huge and important difference.
Some might view the suggested testing checklist as overkill and decide that not all test work is necessary. That is most likely true for some situations, especially for small mines not dealing with large quantities of tailings. However for a project with a high capital investment, one doesn’t want to see the entire mill off-line because the tailings disposal system isn’t functioning.
Major miners, such as BHP and Rio Tinto, typically spare no expense on material testing for metallurgical or geotechnical purposes. They have the funds available to test and engineer to a high level to adequately de-risk the project to meet their investment thresholds.
Junior miners often don’t have the time or funds to spend on such comprehensive testing programs. “Good enough” is often good enough.
One reason why junior miners sign 5-year JV deals with the Major is the amount of technical work required to properly evaluate a project.
The Major understands the amount of time needed for sample collection, testing, analysis of results, and follow up with more testing. It takes a fair bit of time to reach a comfort level for moving forward. Even then, there are no guarantees of success.
Each tailings disposal project is unique in size, location, type of mineralization, site layout, and throughput rate, so each company must decide what level of testing is “good enough” to address their risk tolerance.
For those that would like to get a copy of the the Guide, you can find more information at this LinkedIn link.   I thank BHP and Rio Tinto for putting their heads (and wallets) together to prepare (and share) this document.

 

Note: You can sign up for the KJK mailing list to get notified when new blogs are posted. Follow me on Twitter at @KJKLtd for updates and other mining posts. The entire blog post library can be found at https://kuchling.com/library/
Share

NPV and Sustainable Mining – Friends or Foes

I recently wrote a blog about the term “sustainable mining” and the different perspectives to it. Does sustainable mining mean having a long term sustainable mining industry or does it mean providing sustainable benefits to local communities? There are two ways you can look at it. If interested, the link to that blog is here.
It’s no surprise that the mining industry wants to promote more sustainable mining practices. It’s the right thing to do. However, in my experience, sometimes NPV analysis can be at conflict with sustainable mining practices. That opinion is from my engineering perspective.  Those working in the CSR field may have a different view on it.

Majors, mid-tiers, juniors see things differently

There are essentially three different types of mining companies; majors; mid-tiers, and junior miners. They have different financial constraints imposed upon them and these constraints will impact on their decision making.
In general to get financing and investor interest, development projects must demonstrate a high NPV, high IRR, and short payback period. This requirement tends to apply more to the small and mid tiered companies than to the major companies.  The majors normally have different access to financing.
A characteristic of NPV analysis and cashflow discounting is the penalizing of higher upfront costs whilst reducing the economic impacts of longer term deferred costs. This feature, combined with the need to manage NPV, will influence design decisions and operating philosophies.  Ultimately this will impact on the rate of adopting of sustainable mining practices.
Mining companies often have two masters they must try to satisfy. One master is the project investor(s) that wants their investment returns quickly and with limited risk. The second master is the local stakeholder that wants a safe project with long lasting benefits to the community.  NPV analysis often requires trading-off the needs of one master over that of the other. This trade-off is neither right nor wrong; it is simply a reality.
Major miners now seem to have a third master; i.e large pension funds. These funds are now demanding for more sustainable mining practices (mainly tailings related) and mining companies are trying to comply. Smaller mining companies thus far don’t have this third master to satisfy, although that may come soon. Hence smaller miners are apt to follow a somewhat different path with regards to sustainable mining implementation. NPV plays a significant role in their decision making.

NPV…friend or foe

executive meetingThere are several scenarios where NPV analysis decision making may conflict with the objectives of sustainable mining. Here are a few examples.
1. Minimizing capital expenditures at the expense of operating costs. The likelihood of success in creating a long life sustainable mine will improve by having low metal cash costs. Naturally there will be a benefit in having low operating costs. However sometimes achieving low operating costs will require higher capital investments. For example, this could involve using large capacity material handling mining systems (IPCC) to lower unit costs.
NPV analysis will tend penalize these large investments by discounting the future operating cost savings. Being in the lowest cost quartile is good thing; being in the highest cost quartile isn’t.  Higher operating costs can hurt the long term sustainability of an operation, especially during downturns in commodity prices.
2. Tailings disposal method trade-offs are affected by NPV analysis. Currently there is an industry push towards safer and sustainable tailings storage methods, like paste or dry stack. However the upfront processing and materials handling capex can be significant. Hence less desirable conventional style tailings disposal may often be the winners in tailings trade-off studies due to NPV.
3. Closure considerations incorporated in the early mine design stage are affected by NPV analysis. A large cost component of mine closure is related to waste rock and tailings reclamation. However since final closure costs are  deferred, they might be given less consideration in the initial design. In many studies, high closure costs can be deemed insignificant in the project NPV due to discounting. Eventually these high costs will need to be incurred.  Unfortunately they might have been mitigated by wise decision making earlier in the project life.
4. Low grade ore stockpiling can help to increase early revenue and profit, thereby improving the project NPV and payback. Stockpiling of low grade and prioritization of high grade means that lower grade ore will be processed in the later stages of the project life.  Who hasn’t been happy to develop a mine schedule with the grade profile shown on the right?
If low grade years are coupled with a dip in metal price cycles, the mine could become economically unsustainable.  Shutting down a mine and putting it on “care and maintenance” is short term in intention but often long term in duration (over 30 years in some cases).
Mark Bristow of Barrick briefly discussed the issue of high grading in this interview.
5. Low strip ratios in the early stages of a project are often a feature of the ore body itself. However mine plans can also be designed to defer high strip ratios into the future via the use of proper pit phasing. This is another way to defer operating costs into the future. The NPV will see the benefit, long term sustainability may not.
6. Project life selection based on NPV analysis may not show significant economic difference between a 15 year project and one with a life of 25 years. Project decisions could then favor a short life project. This could relate to smaller pit pushbacks, smaller tailings ponds, smaller waste dumps, and easier permitting.  Possibly the local community would prefer a long life project that provides more sustainable jobs and business opportunities. NPV may see it differently.
7. Accelerated depreciation, tax and royalty holidays are types of economic factors that will improve NPV and early payback. They are one tool governments use to promote economic activity. These tax holidays will greatly enhance the NPV when combined with high grading and waste stripping deferral.
Unfortunately reality hits once the tax holiday is over and suddenly taxes or royalties become payable. At the same time head grades may be decreasing and strip ratios increasing. Future cashflows may carry an additional economic burden, which may conflict with the goal of a sustainable mine.

Conclusion

NPV is one of the standard metrics used to make project decisions. The deferral of upfront costs in lieu of future costs is favorable for cashflow and investor returns. Similarly, increasing early revenue at the expense of future revenue does the same.   Both approaches will help satisfy the financing concerns. However they may not be advantageous for creating long term sustainable projects.
Riskier projects will warrant higher discount rates.  This can magnify the importance of early cashflows even more and future cashflows become even less important.
It will be interesting to see how we (the mining industry) respond as industry leaders make greater commitments to sustainable mining. Both majors and juniors will equally need to work on keeping those commitments.  Will NPV analysis help or hurt?

 

Note: You can sign up for the KJK mailing list to get notified when new blogs are posted.  Follow us on Twitter at @KJKLtd for updates and insights.
Share

Sustainable Mining – What Is It Really?

We hear a lot about the need for the mining industry to adopt sustainable mining practices. Is everyone certain what that actually means? Ask a group of people for their opinions on this and you’ll probably get a range of answers.   It appears to me that there are two general perspectives on the issue.
Perspective 1 tends to be more general in nature. It’s about how the mining industry as a whole must become sustainable to remain viable. In other words, can the mining industry continue to meet the current commodity demands and the needs of future generations?
Perspective 2 tends to be a bit more stakeholder focused. It relates to whether a mining project will provide long-term sustainable benefits to local stakeholders. Will the mining project be here and gone leaving little behind, or will it make a real (positive) difference? In other words, “what’s in it for us”?
There are still some other perspectives on what is sustainable mining. For example there are some suggestions that sustainable mining should have a wider scope. It should consider the entire life cycle of a commodity, including manufacturing and recycling. That’s a very broad vision for the industry to try to satisfy.

How might mining be sustainable?

The solutions proposed to foster sustainable mining depend on which perspective is considered.
With respect to the first perspective, the solutions are board brush. They generally revolve around using best practices in socially and environmentally sound ways. A sustainable mining framework is typically focused on reducing the environmental impacts of mining.
Strategies include measuring, monitoring, and continually improving environmental metrics. These metrics can include  minimizing land disturbance, pollution reduction, automation, electrification, renewable energy usage, as well as proper closure and reclamation of mined lands.
Unfortunately if the public hates the concept of mining, the drive towards sustainability will struggle. Trying to fight this, the industry is currently promoting itself by highlighting the ongoing need for its products. Unfortunately some have interpreted this to mean “We make a mess because everyone wants the output from that mess”. I’m not sure how effective and convincing that approach will be in the long run.

Focusing on localized benefits

If one views sustainable mining from the second perspective, i.e. “What’s in it for us”, then one will propose different solutions. Maximizing benefits for the local community requires specific and direct actions. Generalizations won’t work.  Stakeholder communities likely don’t care about the sustainability of the mining industry as a whole.
They want to know what this project can do for them. Will the local community thrive with development or will they be harmed? Are the economic benefits be short lived or generational in duration? Can the project lead to socio-economic growth opportunities that extend beyond the project lifetime? Will the economic benefits be realized locally or will the benefits be distributed regionally?
One suggestion made to me is that all mining operations be required to have long operating lives. This will develop more regional infrastructure and create longer business relationships. A mine life of ten years or less may be insufficient to teach local entrepreneurship.  It maybe too short to ensure the long term continuation of economic impacts. Mine life requirement is an interesting thought but likely difficult to enforce.
Nevertheless the industry needs to convince local communities about the benefits they will see from a well executed mining project. Ideally the fear of a mining project would be replaced by a desire for a mining project. Preferably your stakeholders should become your biggest promoters. Working to make individual mining projects less scary may eventually help sustain the entire industry.

What can the industry do?

We have all heard about the actions the industry is considering when working with local communities. Some of these actions might include:
  • Being transparent and cooperative through the entire development process.
  • Using best practices and not necessarily doing things the “cheapest” way.
  • Focusing on long life projects.
  • Helping communities with more local infrastructure improvements.
  • Promoting business entrepreneurship that will extend beyond the mine life.
  • Transferring of post-closure assets to local communities.
There are teams of smart people representing mining companies  working with the local communities. These sustainability teams will ultimately be the key players in making or breaking the sustainability of mining industry.  They will build and maintain the perception of the industry.
While geologists or engineers can develop new technology and operating practices, it will be the sustainability teams that will need to sell the concepts and build the community bridges.
The sustainability effort extends well beyond just developing new technical solutions. It also involves politics, socio-economics, personal relationships, global influences, hidden agendas. It can be a minefield to navigate.

Conclusion

As a first step, the mining industry needs to focus more on local stakeholders and communities. Remove the fear of a mining project and replace it with a desire for a mining project. Mining companies must avoid doing things in the least expensive ways. They must do things in ways that inspire confidence in the company and in the project.
The ultimate goal of sustainable mining will require changing the public’s attitude about mining. Perhaps this starts with the local grass roots communities rather than with global initiatives. As a speaker said at the recent Progressive Mine Forum in Toronto, the mining industry has lost trust with everyone. It is now up to the mining companies, ALL OF THEM, to re-establish it. Unfortunately just one bad apple can undo the positive work done by others.  The industry is not a monolith, so all you can do is at least make sure your own company inspires confidence in the way you are doing things.
As an aside, I have recently seen suggestions that discounted cashflow analysis (i.e. NPV analysis) and sustainable mining practices may be contradictory. There may be some truth to those comments, but I will leave that discussion for a future blog.  You can read that blog at this link.
Note: You can sign up for the KJK mailing list to get notified when new blogs are posted.
Share

Mineral Processing – Can We Keep It Dry?

It’s common to see mining conferences present their moderated panels discussing “disruption” and Mining 2.0.   The mining industry is always looking for new technologies to improve the way it operates. Disruptive technologies however require making big changes, not tweaks.  True disruption is more than just automating haulage equipment or having new ways to visualize ore bodies in 3D.
Insitu leaching is a game changing technology that will eventually make a big difference.  Read a previous blog at “Is Insitu Leaching the “Green Mining” Future”.  Development of this technology will negate the need to physically mine, process, and dispose of rock.  Now that’s disruptive.
However, if we must continue to mine and process rock, then what else might be a disruptive technology ?

Is dry processing a green technique

Process water supply, water storage and treatment, and safe disposal of fine solids (i.e. tailings) are major concerns at most mining projects.
Recently I read an article titled “Water in Mining: Every Drop Counts”.
That discussion revolved around water use efficiency, minimizing water losses, and closed loop processing.   However another area for consideration is whether a future technology solution might be dry processing.

Dry processing is already being used

By dry processing, I am not referring to pre-concentration ore sorting or concentrate cleanup (X-ray sorting). I’m referring to metal recovery at the mineral liberation particle size.
In Brazil Vale has stated that it will spend large sums of money over the next few years to further study dry iron ore processing. By not using water in the process, no tailings are generated and there is no need for tailings dams.
Currently about 60% of Vale’s production is dry (this was a surprise to me) and their goal is to reach 70% in the next five years.   It would be nice to eventually get to 100% dry processing at all iron ore operations.   The link to the article is here “Vale exploring dry stacking/magnetic separation to eradicate tailings dams”.

Is dry grinding possible

Wet grinding is currently the most common method for particle size reduction and mineral liberation.  However research is being done on the future application of dry grinding.
The current studies indicate that dry grinding consumes higher energy and produces wider particle size distributions than with wet grinding. However it can also significantly decrease the rate of media consumption and liner wear.
Surface roughness, particle agglomeration, and surface oxidation are higher in dry grinding than wet grinding, which can affect flotation performance.
Better understanding and further research is required on the dry grind-float process. However any breakthroughs in this technology could advance the low water consumption agenda.
You can learn more about dry grinding at this link “A comparative study on the effects of dry and wet grinding on mineral flotation separation–a review”.

Electrostatic separation

Electrostatic separation is a dry processing technique in which a mixture of minerals may be separated according to their electrical conductivity. The potash industry has studied this technology for decades.
Potash minerals, which are not naturally conductive, are conditioned to induce the minerals to carry electrostatic charges of different magnitude and different polarity.
In Germany, researchers have developed a process for dry beneficiation of complex potash ores. Particle size, conditioning agents and relative humidity are used to separate ore.
This process consumes less energy than conventional wet separation, avoiding the need to dry out the beneficiated potash and the associated tailings disposal issue.
Further research is on-going.

 

Eddy current separators

The recovery of non-ferrous metals is the economic basis of every metal recycling system. There is worldwide use of eddy separators.
The non-ferrous metal separators are used when processing shredded scrap, demolition waste, municipal solid waste, packaging waste, ashes from waste incineration, aluminium salt slags, e-waste, and wood chips.
The non-ferrous metal separator facilitates the recovery of non-ferrous metals such as aluminium, copper, zinc or brass.
This technology might warrant further research in conjunction with dry grinding research to see if an entirely dry process plant is possible for base metals or precious metals.  Learn more at the Steinert website.

Conclusion

Given the contentious nature of water supply and slurried solids at many mining operations, industry research into dry processing might be money well spent.
Real disruptive technologies require making large step changes in the industry. In my opinion, insitu leaching and dry processing are two technologies that we will see more of over the next 20 years.
Ultimately the industry may be forced to move towards them due to environmental constraints.  Therefore let’s get ahead of the curve and continue researching them.

 

Note: You can sign up for the KJK mailing list to get notified when new blogs are posted.
For those interested in reading other mining blogs, check out the Feedspot website at the link below.  They have over 50 blog sites you check out.  https://blog.feedspot.com/mining_blogs/
Share

Global Risks – Our Fears Are Evolving

Recently I wrote a blog about how the adoption of new technology in the mining industry will increase the risk of cyber crime. However this is just one of many risks the industry faces today.  This raises the question as to what are the main risks impacting all global businesses.  Luckily for us, the World Economic Forum undertakes an annual survey on exactly this subject.
Each year business leaders are queried about what they view as their major risks. The survey results are summarized in the Global Risk Report.
The 2019 report can be downloaded at this link. http://www3.weforum.org/docs/WEF_Global_Risks_Report_2019.pdf.
The study rates risks according to the categories “likelihood” and “impact”. A risk could have a high likelihood of occurring but have a low economic impact. One might not lose sleep over these ones.
Another interesting feature in the report is seeing how the top risks change from year to year.  Some risks from 10 years ago are no longer viewed as key risks today.

2019 risk situation

In 2019 environmental related risks dominate the survey results. They account for 4 of the top 5 risks by “impact” and 3 of the top 5 by “likelihood”. Technology related concerns about data fraud and cyber-attacks were also viewed as highly likely (#4 and #5). See the image below for the top 5 risks in each category.
Although the Global Risk survey wasn’t specifically directed at the mining industry, all of the identified risks do pertain to mining.

 

10 year risk trend

It is also interesting to look at the detailed 10 year  table in the report to see how the risk perceptions have changed over the last decade.
None of the top five “Impact” risks from ten years ago are still in the top five now and only two from 2014 still exist. In the “likelihood” category, a similar situation exists.
It will be interesting to compare the 2024 list with 2019 list to see how risks will continue to evolve.

How about the mining industry

EY Global Mining & Metals also undertake a risk survey, focused on mining only. You can read their article at this link “The Top Risks Facing Mining and Metals”.  Their top 10 risks are listed below, many are different than those from the World Economic Forum ranks. You must read the EY article to fully understand the details around their risk items.
  1. License to operate (difficulty to acquire)
  2. Digital effectiveness (lack thereof)
  3. Maximizing portfolio returns (can this be done)
  4. Cyber security (increasing risk of attack)
  5. Rising costs (can costs be controlled)
  6. Energy mix (acceptable power sources)
  7. Future of workforce (lack of interest in the sector)
  8. Disruption (falling behind competitors)
  9. Fraud (increasing sophistication)
  10. New world commodities (versus reduced demand for some commodities)

Conclusion

My bottom line is that the Global Risk Report is something that we should all read. Download it and then compare with what your company sees as its greatest risks. The only way to mitigate your risks is to know what they are.  The only way to work with others is to know what their issues are.
Note: If you would like to get notified when new blogs are posted, then sign up on the KJK mailing list on the website.  Otherwise I post notices on LinkedIn, so follow me at: https://www.linkedin.com/in/kenkuchling/.
Share

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.   Blue Sky Uranium is a recent project that I was involved in where a simple scrubbing step resulted in 4-5 times increase in grade and volume reduction.

 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.
Note: If you would like to get notified when new blogs are posted, then sign up on the KJK mailing list on the website.  Otherwise I post notices on LinkedIn, so follow me at: https://www.linkedin.com/in/kenkuchling/.
Share

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.
Note: You can sign up for the KJK mailing list to get notified when new blogs are posted.
Share

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.

What should a mining company do?

In my experience, when designing a new mining project, all companies will 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 what are their tailings disposal options.  They would likely all adopt the dry stack approach if it was the most advantageous and least cost 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 ways for reducing tailings risk.

The tailings decision gets 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 to a degree.
Implementing a more expensive $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.  At that point the costs for dry stack may be competative.

What level of risk is acceptable?

So the question ultimately becomes how low does one need to bring 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 life.
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 is difficult for these groups to actually define what an acceptable risk level is. They offer no solutions, other than its 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 where I suggest the industry just bite the bullett and go to dry stack in all new projects.  The trend appears to be going that way but no where near 100% acceptance.   You can read that post at this link  “Fluid Tailings – Time to Kick The Habit?”

 

Note: If you would like to get notified when new blogs are posted, then sign up on the KJK mailing list on the website.  Otherwise I post notices on LinkedIn, so follow me at: https://www.linkedin.com/in/kenkuchling/.
Share

Fluid Tailings – Time to Kick The Habit?

dry stack tailings
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“.

 

Note: If you would like to get notified when new blogs are posted, then sign up on the KJK mailing list on the website.  Otherwise I post notices on LinkedIn, so follow me at: https://www.linkedin.com/in/kenkuchling/.
Share