This review provides information about mine tailings. We list and provide links to leading publications and websites which offer more information on tailings. In doing so we can provide a quick review of the technology of tailings.
Tailings (also known as slickens) are the waste left over after removing the gangue from ore. Ore extracted from the earth's crust typically has two components: the ore mineral containing the desired metal, and waste material called gangue. Tailings and gangue are the uneconomic remainder from mining; as mining techniques and the price of minerals improve it is not unusual for tailings to be reprocessed using new methods or more thoroughly with old methods, perhaps to recover minerals other than those originally mined. In coal production and oil sands mining, the word 'tailings' refers specifically to fine waste suspended in water and the word 'gangue' is never used.
Tailings are produced when metallic ores are ground into a fine powder to free the metal-bearing mineral. Its maximum particle size of about 0.08 in (2 mm) is small enough to retain water and support plant growth. Fine dust is one potential hazard, especially if trapped in the lungs of miners. The greatest revegetation difficulties come from metals in lethal concentrations and deficiencies of critical nutrients, especially nitrogen and phosphorus. Some old tailings have remained barren for many years, with consequent high erosion rates. However, some metalophytes are able to survive on these wastes. Curiously, some plants have populations which can also survive on these tailings.
The U.S. EPA succinctly defines uranium mill tailings:
Uranium mill tailings are the radioactive sandlike materials that remain after uranium is extracted by milling ore mined from the earth. Tailings are placed in huge mounds called tailings piles which are located close to the mills where the ore is processed. The most important radioactive component of uranium mill tailings is radium, which decays to produce radon. Other potentially hazardous substances in the tailings are selenium, molybdenum, uranium, and thorium.
When certain authors were growing up in South Africa, these huge mounds were called "Slimes Dams". That became politically incorrect and we were later taught to call them tailings impoundments. Friends who emigrated to Australia now call them Tailings Storage Facilities.
THE CLASSIC TEXTS
Here is a brief survey of the classic texts on tailings. Get as many as you can and read them to expand on what you learn in this piece.
Steven Vicks' book from 1990 Planning, Design, and Analysis of Tailings Dams is still available from Amazon.com at the hefty price of $300. Maybe a colleague has a copy on their bookshelf if this is too pricy. While the book is dated, it remains the best there is.
Geoff Blight's more recent book Geotechnical Engineering for Mine Waste Storage Facilities is expensive, about $180, but also worth locating and reading. It focuses on South African practice, but is of such wide scope and brilliance that those of us practicing anywhere may benefit from his insights and clear explanations.
There are nearly thirty years of volumes from the conference series Tailings and Mine Waste on my shelf. The volumes are difficult to obtain, but again worth the effort, for they document the development of tailings practice in the past three decades. Luckily the proceedings of the 2011 conference are available free on-line at this link.
Paste and Thickened Tailings by Andy Fourie is a speciality volume for those faced with the design of a thickened tailings facility.
The most accessible adjuncts to this course are courses on Edumine. Here are some courses that deal with issue relevant to this topic.
Mine Closure: The Basics of Success is a course about the closure of mines. Because tailings facilities are a large part of a mine closure project, the course deals with many aspects of the closure of tailings facilities from planning, finance, regulatory compliance, and engineering.
Geotechnical Engineering for Mine GeoWaste Facilities. deals with the details of geotechnical engineering as applied to the design, construction, operation, and closure of mine tailings facilities and waste rock dumps. In this course you will find information on slope stability, settlement, consolidation, erosion, and seepage as these geotechnical processes affect tailings facilities.
Groundwater in Mining is an evitably in a tailings facility and is affected by the groundwater regime at the mine site. Hence in this course, I write about groundwater at mines and at the mine's tailings facility. Here you will find information about liners, seepage to groundwater, and potential impacts on groundwater from mine facilities.
Heap Leach Pads While a heap leach pad is not a tailings facility, there are indeed many similarities. In particular a pile of filter-pressed tailings is almost identical to a pile of material in a heap leach pad. In this course, I write of the siting of heap leach pads, their liners, construction, operation, and eventual closure.
Surface Water Management at Mines Control the surface water upgradient, coming from, and downgradient of the tailings facility and you will have a successful project. Hence in this course, I write of the fundamental principles of surface water management at mines and the application of these principles to tailings facilities.
Mine Water and Chemical Water Balance AnalysisAn overall perspective of the water and chemical mass balance of a mine is an essential part of prudent mine planning and management. Obviously the tailings facility is a major part of the water and chemical mass balance of a mine. Hence in this course, I set out the methods and procedures you may apply to compile a mass balance for your mine and specifically your tailings facility.
TAILINGS.INFO & TAILPRO
There is only one website devoted exclusively to the technical aspects of tailings: Tailings.info
. They describe themselves thus: It is run by Jonathan Engels, now in Perth,and is a complete database for tailings with information on disposal, storage and safety. Another useful tool from the same organisation is Tailpro
Here is an e-mail from Mr Engels, where he gives an overview of what Tailpro tries to achieve.
"Thank you for your past interest in TailPro, the online resource designed to assist tailings related engineers. I am pleased to announce that I have now been granted permission to distribute free public access". The login details are as follows:
The International Council on Mining & Metallurgy and the International Commission on Large Dams jointly developed this site: ICMM Library. To find the full list of publications on tailings, type tailings into the search box, or use this resource to look for other areas of interest. The site is really a list of books and papers on tailings.
Somewhat outdated and focused on uranium mill tailings is the site run by the World Information Service on Energy. See also the U.S. Department of Energy on Uranium Mill Tailings.
The Uranium Mill Tailings Remediation Control Act (UMTRCA) of 1978 (Public Law 95-604) must stand as the pinnacle of legal demand imposed on those who work in tailings. A good description of the resulting program and its success is to be found on the Energy Information Administration site at this link
. While the objective of UMTRCA is closure of uranium mill tailings sites, I suggest that until the spirit and intent of UMTRCA is an every-day part of the design, construction, operation, and closure of all tailings impoundments, mining will not truly be able to claim to be an industry that puts into practice the principles of sustainability.
A detailed and fascinating comparison by the U.S. Environmental Protection Agency of the Nevada regulations governing tailings impoundments versus the regulations governing uranium mill tailings is to be found at this link.
Uranium Mill Tailings are also dealt with internationally under the Internation Atomic Energy Agency (IAEA). This IAEA Report deals with the long-term management of Uranium Mill Tailings across a range of jurisdictions.
On our bookshelf we are lucky to have the these publications related to tailings. These include:
- Tailings Management :Problems and Solutions in the Mining Industry by G.M. Ritcey (1989)
- Geotechnical Engineering For Mine Waste Storage Facilities :by Geoff Blight (2010)
- Management, Stabilisation and Environmental Impact of Uranium Mill Tailings:Proceedings of the Nuclear Energy Agency (NEA) Seminar (1978).
- Tailings Disposal Today :Proceedings of the International Tailings Symposium (1972)
- Canadian Uranium :Mill Waste Deposal Technology, prepared by Steffen Robertson & Kirsten (B.C.) Inc (1987)
In addition this Tailings Specific repository we are also in possession of the entire proceedings of the Tailings & Mine Waste Conference from 1978, to 2011 when it was held here in Vancouver. Note that all the publications for this conference are available on the infomine website
One unique aspect of this years conference was the inclusion of facilitated discussions, which have not been attempted on such a scale before. They were led by SRK Corporate Consultant, Daryl Hockley who managed to coordinate and bring together the minds of almost 400 people and direct them to answer the question "How can we Most Improve the Management of Tailings & Waste Rock"?
Infomine also provides links to the continuous conferences from the Tailings & Mine Waste 2011 conference. The purposes of these are to bring to light the state of the art in the industry and highlight the current and future issues that will have to be faced
The European Commission (2003) has a document which describes the "best available techniques for management of tailings and waste rock in mining activities
". I have downloaded it and read it, and urge you to do so if you are interested in the theory and practice of tailings impoundments and waste rock dumps and what is happening in this field in Europe.
Go to the Infomine library for a copy of Morgenstern's 1997 paper Oil Sand Geotechnique. In clear prose, it will tell you all you need to know about the geotechnical issues involved in oil sands mining, from open pit slope stability, through tailings disposal, to in-situ bitumen recovery.
Software to model the tailings dam is available from http://www.riftxone.com/
. They are in Australia.
Canada: There are many resources available on the web regarding the different approaches to tailings. The best we've come across is The Mining Association of Canada (MAC) which has three significant documents relating best template for a Management Guide, a Maintainance & Surveillance Manual, and an Audit & Assessment Guide. This is the Canadian volume entitled Developing an Operation, Surveillance, and Maintenance Manual for Tailings and Waste Management Facilities. A copy may be downloaded free from the web; it is one of the best bargains of the computer age.
United States: The U.S. EPA is responsible has many publications on tailings, the The Design and Evaluation of Tailings Dams was produced in 1994 but is still a comprehenive and relevant report.
Australia: The government has produced a national Management Guide to aid in sustainable mining development.
Europe: As referenced to in the publications section, the European Commission has produced a document on management techniques for tailings and mining waste. Tailpro also has Tailings Management Facilities which acts as a guide in the tailings management facilities with a view to "give an overview of the situation in some of the European countries and in the world".
TAILINGS DAM SAFETY
One useful link regarding Tailings Dam Safety is provided by the Dam Safety Committee whose goal is for all tailings dam owners in New South Wales to "apply appropriate dam safety management practices to their dams using a risk management approach in line with a whole of Government approach to safety".
A more holistic look at the Tailings Dam Guidelines is undertaken in this (as yet unreleased) publication.
"We count grass…and a whole lot more." Thus begins the website of Synergy Resource Solutions
a group who hail from Bozeman, Montana. We find this approach practical and reliable. It may be expensive for the large areas of a mine tailings impoundment. Surely there is a better way. Canada Center for Remote Sensing
tells of the use of their imaging spectrometer data analysis system to monitor revegetation of the Copper Cliff, Sudbury, mine tailings impoundment. Maybe this works…they conclude only "Results….indicate that these techniques can be employed …to monitor the rehabilitation efforts." Sadly, for a site paid for by the Canadian taxpayer, all you get are the abstracts of some of the papers leading to this profound conclusion.
Codisposal is undertaken to reduce the volume of waste disposal facilities: get some of the fine-grained tailings to fill the voids of the coarse-grained rock is the general idea. Concrete is a good example of the ideal codisposal mix. This give rise to three lovely new words, that describe the basic methods:
- Co-mingling-mix the two after deposition: this is being done to fill an open pit at the Kidston mine in Australia.
- Co-placement-mix the two just before placement: this is being done at the Argyle Mine in Australia.
- Co-disposal, or mixing before transport to the disposal site.
Codisposal is not easy: it is expensive, involves considerable moving of equipment and discharge lines, bow-waves develop, there is high pipe-wear, and limited encapsulation of the tailings. There are advantages however: pumping is less costly than trucking, the end result is a stable landform, and water return is high. For a superb set of photographs and more facts and details see the new presentation in the Infomine library by Mike Gowan of Golder Associates.
IN-LAKE TAILINGS DISPOSAL
In terms of dealings with a single topic, no book does it better for in-lake tailings disposal than Mine Pit Lakes
. It deals with every aspect water quality in pit lakes, its critical parameters, and how to predict its effects into the future.
SUBMARINE TAILINGS DISPOSAL
Similar to In-lake disposal of tailings is the practice of submarine tailings disposal (STD). This form of tailings disposal is generally viewed as a potentially harmful. The issues involved with STD are best highlighted by Philip Shearman in his article on the topic. Derek Ellis also covers the topic extensively in his publication Underwater Tailings Placement At Island Copper Mine.
Two comprehensive books on the topic of paste tailings from the Australian Centre for Geomechanics
1) Paste and Thickened Tailings - A Guide (Second Edition)
2) Paste 2006
OIL SANDS TAILINGS
Alberta's Oil Sands are one of the Province's principal economic drivers but the vast quantities of tailings produced every day pose a huge threat to its continued use. There are many detailed publications regarding the oil sands, many of which are included in the preceedings for the 2011 Tailings & Mine Waste conference,but for an introduction to the issues involved this government publication is adequate.
The Oil Sands mines are some of the largest mines in the world (Suncor processes approximately 500,000 tonnes of oil sands ore every day), and consequently they produce huge amounts of tailings. This video by Suncor gives a very good explanation of the issues with Mature Fine Tailings (MFT).
The research that Suncor is doing with MFT is also being carried out by the other major oil sands producers. This new emphasis on research into MFT flocculation in the Albertan Oil Sands has made it a leader in flocculated tailings technology. Huge time and expense has been spent in bringing this technology from laboratory scale experiments, to full production in the field. The main driver behind the knowledge base expansion of this emerging technology is Directive 74.
Directive 74 was issued in February 2009 by the Energy Resources Conservation Board (ERCB) . As regards its purpose, it states:
This directive sets out new requirements for the regulation of tailings operations associated with mineable oil sands. It is the first component of a larger initiative to regulate tailings management. The directive specifies performance criteria for the reduction of fluid tailings and the formation of trafficable deposits. These criteria are required to ensure that the Energy Resources Conservation Board (ERCB/Board) can hold mineable oil sands operators accountable for tailings management. Operators may use a suite of technologies to meet the requirements of this directive
The main points of interest in this piece include
- The performance criteria of these trafficable deposits
- The use of a suite of technologies to meet these requirements
The definition of a trafficable deposit is also defined in the Directive. It is:
A deposit typically created through a process involving self-weight consolidation, drying, enhanced drainage, and/or capping with minimum undrained shear strength of 5 kPa one year after deposition. The trafficable surface layer must have a minimum undrained shear strength of 10 kPa five years after active deposition.
At present, all the major operators are flocculating tailings (using a host of technologies) to try and achieve these goals.
The efficacy of flocculation is highly dependent on the density of the fine tailings. Densification of the MFT is achieved by allowing the fines time to settle to pond bed and undergo self-weight consolidation. The Fine Tailings are then left for three years at which point they become Mature Fine Tailings (MFT). Flocculation acts to join the colloidal particles through long chain polymers into flocs which will then settle. This is carried out just before deposition into a drying cell. This settling and movement of the flocs down the beach expels water from their structure and increases the solids content of the flocculated MFT.
MFT is flocculated in order to reduce the resultant water content and increase the strength. However, the flocculation process requires the input of water in the form of dilution water and polymer water to bring about flocculation. The efficacy of flocculation is measured by subtracting the water added from the water released. This then divided by the water in the MFT which returns either a positive or negative percentage. A positive percentage implies that the process was well flocculated and that more water was removed from the MFT than was added. A negative result implies the opposite.
DRY TAILINGS BEACHES
Prediction of the Beach Profile of High Density Thickened Tailings From Rheological and Small Scale Trial Deposition Data
is the title of the PowerPoint presentation. The corresponding technical paper
has the same title. Either way they are a powerful set: substantive information on a critical topic. The author of both is Gordon McPhail who did his PhD on the prediction of the beach profile for conventional hydraulically deposited tailings. Now he turns his mind to the beach profile for high density thickened tailings.
The many potential advantages of thickened tailings, including reduced water loss, makes it a popular consideration for many mines. The problem however is to predict the beach profile, the slope of the tailings on discharge, and hence to be able to predict what the geometry of the tailings deposit will be.
In this paper, Gordon sets out the physical principles, the governing mathematics, and the results of flume tests to demonstrate that his approach works. If you are about to design a facility for thickened tailings, you need this paper.
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