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Overview
Disasters and Minewater: Good Practice and Prevention draws together all of the major minewater catastrophes that have occurred over the last half century. It examines incidents to find useful and positive information of great value that could prevent future disasters. Practical experience provides many lessons in respect of the causes of minewater incidents where lack of adhesion to good practice is principally to blame.
Disasters and Minewater: Good Practice and Prevention is of particular interest to students of mining, civil engineering and environmental engineering. It is an invaluable resource for mining engineers, geotechnical engineers, environmental engineers and disaster relief professionals and consultants. Disasters and Minewater is a valuable complement to Minewater Treatment: Technology, Application and Policy by M Brown, B Barley, and H Wood, ISBN: 9781843390046.
Author: Harvey Wood, Clean Rivers Trust, UK
Product Details
| ISBN-13: | 9781780400068 |
|---|---|
| Publisher: | IWA Publishing |
| Publication date: | 01/15/2012 |
| Series: | Integrated Environmental Technology Series |
| Pages: | 145 |
| Product dimensions: | 6.12(w) x 9.25(h) x 0.75(d) |
Read an Excerpt
CHAPTER 1
Disasters and Minewater
DEFINITIONS
The term disaster is an emotive word that is liable to stir up emotions of horror and revulsion. The use of it here is to convey it both in terms of damage or destruction of the human environment and the possible loss of life due to damage to the natural environment and its possible long-term detrimental effects.
Minewater in this context is any aqueous discharge emanating from a mine or any mineral retrieval or processing activity including liquid or semi-liquid storage impoundment; such as tailings dams.
Pollutions to water, however environmentally horrendous, such as took place in the Gulf of Mexico (2009), which are not brought about in the first instance by water, are outside the range of this work.
It should also be noted that listing the minewater incidents by region and nation is not a finger pointing exercise or in any way a suggestion that any country is more profligate or less caring for its workers, populous or environment. The identification of sites of disaster is not to be considered as placing blame; they are there for the purpose of demonstration that such events are universal issues.
1.2 OCCURRENCE
The occurrence of disasters brought about by minewater are many and various: the flooding of workings, inundation from flooded abandoned workings or from an aquifer deep below ground to the collapse or other failure of a tailings dam, its water sweeping away all surface obstacles from its path. Both underground and on the surface minewater has the ability to kill. At the surface it has the propensity to damage the surrounding land and in the worst cases make it unfit for human and agricultural uses for years into the future.
1.3 LOCATIONS
The location of such events does not rest with one country, continent or any other geographical region; it is a worldwide phenomenon that has taxed engineers' intellects since such activities began.
The focus of this work is international and covers the most mind numbing catastrophes imaginable. The best chronicled are mostly in countries that are used to reporting the facts and have not shirked responsibility in being candid. Others have occurred in countries which are more close-lipped who have agreed that an 'incident' has occurred and have left the world community speculating as to severity and reason. These occurrences have been difficult to investigate, and for reasons of honesty and due care the more vociferous or litigious sources of information have not been quoted. This is for the simple reason that there are many environmental organisations who see cover up or malpractice where mistake or error would be more likely. Such parts of the world are beginning to enter the new era of candour and openness and though slow to broadly publish disaster are active in finding reasons and learning from events but beyond the spotlight of the media.
Accidents in the United Kingdom, Italy, Spain, Hungary, Romania, China, Russia and the US are but a few of the countries that have been the scene for incidents that have grabbed the world' s headlines and at the same time the majority of these events have only lasted a few moments in the national and international collective memories. This is, though, not true of the local consequences (I hope the narrative allows this to be accepted).
Over the time scales covered by this publication many incidents that have taken place are lost to posterity. Before the main content of the work occurred, much had not been admitted to or those involved did not consider the events worthy of note above that of a hiccup in production or other activity, this particularly being the case with all events that occurred above ground. It is true that great efforts were mounted to save life below ground or to bring out the bodies of those fatally affected; nowhere more so than in the United Kingdom.
Conversely the mine owners have always taken an interest outside the norm of proprietors with regard to calamities underground. This is particularly true of those ill-liked entrepreneurs of the United Kingdom coal barons and their families.
1.4 CALAMITIES
The incidents that are discussed are varied and include: inundation of underground workings due to stopping failure; breaking though into old flooded workings and mining through the bed of the sea. All these have their place but are not relevant to the issues that compound the mass of this work, which instead considers surface water issues, either as rebound, slimes or slurry movement, dam accidents or the boring of exploratory holes to locate the hoped for source of profit.
These events are all to be anticipated, if not actually expected, in the wholly imperfect world of winning minerals. The global population require the products of the industry and all but a very few of the world's population use the bounty of the industry that the mining fraternity provides; from jewels on the fingers of the wealthy to our daily bread.
The best executed of mining plans may be executed but the men or 'pixies' will creep in and re-order the operation. Land movement, earthquake, intense rain, draught or an un explained connectivity between an aquifer and the working face of a mine can all lead to disaster.
The other area of sadness, mining always carries this emotion at its core, is not covered in this work but it leads to continual losses of life: air problems. Fowl air or methane, one stops the breathing like a blanket and the other explodes, can both arise with little or no warning and are monitored for now in any enclosed space globally, but still there are lists of these tragedies annually from across the world.
It is notable that mining whatever substance will leave a fingerprint with which later generations will wish to prosecute those that have striven to improve the world and to provide both the pleasant and the necessary. Old workings will always have a negative aspect to them; not dissimilarly to the opinions of many who look down on those that win value from beneath the ground. The miner is synonymous with 'the hard man' as seen at the end of dictatorship in Romania or if a coal miner's grandson is prosecuted in Kent, UK.
1.5 THE MAIN ISSUES
The areas of mining that engender danger from water are many, and involve a range of engineering responses to deter disaster. Much that the engineer is required to undertake is not state of the art or ground breaking but everyday, and at times boring or tedious; two reasons already for accidents to occur.
Underground inrushes of water have been, from the fist mines in prehistory, the perennial fear of the miner. Drowning in a soup of dust laden water or slowly awaiting the end, as cut off from escape, the flood gradually rises about the person. Rock falls are the most common of catastrophic events that led to the development of mining methods which allowed for safer working even as far back as the stone age. The working of flints at Grimes Graves in Norfolk, United Kingdom was worked by a rudimentary method of pillar and stall, leaving virgin pillars of strata supporting the roof as the miner developed galleries to extract the flints that were the goal of the exercise. This method is still in use around the world today in many mines.
Rebound of groundwater from abandoned mines is a regular sight in areas of historic mining, particularly when dewatering has ceased across whole regions and mineral recovery has closed. Across Europe where the extraction of coal has been abandoned in favour of importation and increased reliance on nuclear electricity, the tell tale ochre staining of the streams and watercourses are common.
Similarly in metalliferous mineral mining areas the water courses show the same iron colouration, alongside a content of other metals such as arsenic, copper or aluminium. These may be as oxides or sulphidic and in some cases the water can be acidic with a pH of 2-5. The effect on the natural environment can be extremely damaging as it can be to human health, for those who come into contact with it. In gold and other precious metal mining areas the chemicals used to liberate the metal are allowed, sometimes wantonly but mostly by accident, to enter the natural environment. Cyanide is a common pollutant of water around sites of such extraction and ore dressing. In many mineral processes these wastes are held alongside washings wastes in dammed containment known as tailings ponds. These, if incorrectly engineered or maintained, are a considerable concern and are a regular source of flooding. Such events having taken place in Romania over the last decade and also in several other countries over the same time span.
The process treatment of bauxite is a special case: unlike other mined mineral refining operations (Hungary 2010) it produces a highly caustic, rather than acid or net alkaline, residue that can have a severe long-term effect on the natural environment. The wastes are known as red muds that are a continual burden, both for the refiners and the environment.
1.6 SUBSIDIARY ISSUES
Other areas of environmental dislocation have been caused by the exploration for, as well as exploitation of, minerals. Some instances considered to be notable include the mineral drilling test that unleashed an apparently limitless discharge of boiling muds that has not ceased for many years in the Far East. Of similar note is the trial project to burn coal in situ that caused untold litres of contaminated water to be vented in a rebound of groundwater that, combined with the super-heated coal below the aquifer, had been ejected from its subterranean confinement.
Mining disasters that impact on the environment are regular occurrences. Those that are not caused by water or involve it in their initial phase will receive and register the impact, notably the Gulf of Mexico oil production platform explosion and the resultant pollution from the failed seal on the production well. Other issues are also allied such as the major tanker groundings and sinkings that occur around the world.
Similarly acts of war and their resultant pollutions are, often after the event politically not noted as pollution incidents at all, as witnessed in Kuwait after the 1993 war. Then, oil production wells were set on fire, many of which burned for several weeks uncontrollably; the environmental effects on the waters of the Persian Gulf have not been reported widely.
Many minewater related environmental events occurred in countries such as the USSR and China before the modern approach to openness and perestroika came into being. Vast pollutions and large numbers of people are believed to have been affected, but it is only now that these events are starting to emerge from the fog of state embargos on information being known.
1.7 THE LAW AND REGULATION
Law and regulation nationally and internationally, with regard to cross border contamination events are no more than an apparent treaty but with little substance. The majority of national governments accept that mineral companies operate in a hugely competitive world market and costs have to be kept to a minimum. These governments are seldom advised by consultants. The consultants being more reliant on the mining companies for the majority of their day to day work. That is not to say that their advice is skewed away from the truth or that their advice is not excellent when governments commission their work. The problem lies in that few politicians are mining engineers or have the time or inclination to delve into the terminology any further than the glossary at the end of the report's text.
In many instances the mining regulation is stipulated during initial planning stages of an operation and the general site operation is seldom inspected when a site is operational. This is a sweeping generalisation; the construction and maintenance procedures of tailings dams are agreed internationally by the relevant professional engineering bodies that accredit the structural engineers. This acts as a self regulatory junta not unlike the doctors practising in the UK being overseen by the British Medical Council. If a design or management failure occurs those engineers may be required to cease operation in a country or continental region; though seldom globally. It is also to be considered that in many parts of the globe ad hoc mining operations are the norm for much of the mineral exploitation and these operations are totally unregulated at any stage of their operational existence.
CHAPTER 2
Minewater and Rebound
2.1 MINEWATER CHARACTERISATION
Contaminated minewater is produced where sulphidic minerals come into contact with water and air, thereby creating acidity and a developing, elevated sulphate and mineral content water. Such solutions are synonymous with the development of polluted minewater.
The natural breakdown of minerals, oxidation, is thus accelerated in a mined environment with the eased access for all the elements to come together more readily and rapidly.
The main contamination generating activity areas include:
• drainage from subsurface workings
• drainage from opencast mines
• mine waste tips
• tailings from mineral processing
• mineral storage
• mineral extraction processes from ores
The minewater is often acidic, though in certain circumstances there are mineral loadings (i.e.; bauxite or calcite) that may allow for neutral or net alkaline waters, still holding high metal concentrations.
The creation of contaminated minewaters can be considered a natural process that, through the actions of mining, has been speeded up. The process is a consequence of both the minerals and bacterial action that allows the transmogrification of sulphides to sulphates.
The terms acid mine drainage (AMD) and acid rock drainage (ARD) are commonly and universally used for these discharges though they are not necessarily acidic due to bicarbonates. The bicarbonate buffer that natural waters have, which acts as a natural mechanism, allows a natural regulation of pH. This though may be affected by high concentrations of metal ions that act as catalysts for bicarbonate destruction or neutralisation.
Fe3+, Mg2+ or Al3+ ions > hydrolysis > H+ ions
This bicarbonate controls the changes in pH. If its system is adversely affected its control of pH is lost allowing large variations in acidity. This can have widespread effects on the ecosystems that the waters enter. Another result of such action is that many photosynthetic organisms that abound in such waters in a slightly acidic regime are unable to survive below pH 4.2, due to that being when carbonate ions are converted to carbonic acid and are lost as a source of feed carbon for the organisms.
2.2 ENVIRONMENTAL IMPACTS OF MINEWATER
The impacts and consequences of minewater entering a natural environment are many and varied; no minewater discharge can be considered the same as any other. All discharges are unique and have a need to be considered on their own merits and considered as separate entities. The main problem elements are, though, possible to justify thus:
• acidity
• ferric precipitates
• other metals
• solids loading or turbidity
These generalisations and their consequences are outlined below, so as the consequential losses to the environment can be better understood.
2.2.1 Acidity
The acidity of the water may be, as already described, variable depending on the local geology as well as the water's general chemistry. The effects of variation of the pH have also been touched on: the more acidic, the lower the pH and generally the greater the environmental harm. This though needs the caveat that this could also be considered variation in the natural biological balance and a realignment of the balances that occur naturally. The action is accelerated in the outside environment as it is with the natural weathering of the strata in a mine system below ground.
Generally acidic minewater drainage can be the invisible source of the destruction of ecosystems that have developed in rivers and streams over millennia, resulting in the loss of vegetation, and vertebrate and invertebrate life forms. The loss of water-reliant mammals and birds is the next noticeable consequential change to the ecology of an affected watercourse. The Rio Tinto region of South Western Spain is a good example on a large scale of acidity and the repercussions of an extremely low pH environment. The extinction of the expected aquatic ecosystem though is at variance with the facts; the environment has in many areas developed its own, near unique, ecology over the last 5000 years of mining that has occurred in the area. These are either water and soil based life forms that are resilient to, or have developed tolerance to the negative elements around them or environmentally generated organisms that have abilities to sustain themselves on the negative elements available to them.
2.2.2 Ferric Precipitates
Ferric iron compounds, being the most common elements on the planet, have their place in this short lexicon of characteristic consequences. In air ferrous iron oxidises to ferric iron which via hydrolysis takes the form of ferrous hydroxides. This action is the cause of the characteristic red ochre staining of many streams and rivers. The hydroxide precipitation coats stream beds, suffocates the aquatic fauna and flora, coats fish gills and blocks the stream substrates denying silt living fauna light and causing them to die out.
(Continues…)
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