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Book Review |
This is a welcome addition to the MAC series of Short Course Volumes, choosing as its theme the challenge presented to earth scientists by the weathering and draining of mine workings and waste piles. Chemical interaction of oxygen and water (ground and meteoric) with metalliferous wastes results in ‘acid mine drainage; or AMD, the movement of metal-contaminated acidic to neutral water into river systems and aquifers, often with serious to disastrous results. The book thus reflects the wider concern with the environmental and economic post-closure consequences of the exploitation of mineral resources, and the earth scientist’s central role in dealing with them. It reviews the current state of progress in understanding and controlling AMD from a variety of geo-scientific standpoints, spanning the range from pragmatic tests devised for regulatory and planning purposes to the evaluation of atom-scale reaction mechanisms through the evolving area of mineral surface chemistry. The result is a book of range and contrasts. The problems presented by AMD run from the atomic-scale to that of entire mine sites, and from the esoteric to the practical, placing mineralogy and chemistry alongside engineering and microbiology. Socio-environmental relevance is combined with scientific insight.
The Short Course is made up of twenty chapters each of which provides a summary and overview of one aspect of AMD and of mitigating its effects. It is understandably centred on sulphidic mines and waste piles, while also considering mineral processing, coal mines and power plants, drawing most of its examples from Canada, the USA and Australia. In each chapter there is emphasis on acquiring a broad understanding of the processes that are involved through their basis in chemical and mathematical terms and then by examining case studies where theory is applied to real circumstances. The text is dense and meticulous throughout, presented by an expert group of North American and Australian practitioners. The result, while not an easy read, is an impressive review of the state of the art.
The introductory chapter (W.A. Price) sets out the general nature of the problem of AMD generation and the evolving strategies used in its regulation and mitigation. Then follows a carefully structured review (R.R. Seal II and J.M. Hammarstrom) of ore-deposit classification in which systems based on geological context and mineral proportions have been translated into a practical classification in terms of geo-environmental models based on the drainage impact of mining activity. These introduce the themes of sulphide oxidation, acid generation, metal transportation, control and remediation processes that run throughout the book. Fluid migration and metal transport processes within waste piles are examined (L. Smith and R. Beckie) from a theoretical standpoint and also using data from lysimeter experiments. The complexity of modelling gas penetration into waste piles is examined in detail (A.I.M. Ritchie) in relation to controlling factors and migration processes. The combination of mathematical modelling with practical case studies that works well throughout this book is prominent in the chapter on hydrologic and geochemical processes within tailings impoundments (D.W. Blowes, C.J. Ptacek and J. Jurjovec), which sets out a concise explanation of sulphide oxidation chemistry and related phenomena.
Mineralogy is vital to understanding weathering processes in mine waste, needless to say, and is prominent is the next set of chapters. The first of these (J.H. Jambor) addresses two themes, one being the mineralogy of mine waste, its oxidative weathering and resulting mineral products, the other that of static tests used to predict AMD potential of sulphidic wastes and mine rock exposure, including the Sobek test (acid-base accounting or ABA) and related procedures. The next chapter (K.A. Lapakko) is a description of kinetic humidity-cell tests developed by the author and others to evaluate AMD potential of waste piles and predict drainage quality, comparing their performance with that of the better established static tests. The use of the Rietveld method of XRD quantification of the mineralogy of mine waste and its alteration products is described (M. Raudsepp and E. Pani). The application and potential of advanced surface analysis techniques such as synchrotron methods to determining atomic-scale reactions between minerals and fluids within sulphidic waste is discussed (C.G. Weisener).
Two chapters (the first by W.D. Gould and A. Kapoor, the second by D.K. Nordstrom) examine the growing evidence for the crucial roles that iron- and sulphur-oxidizing bacteria and other microbes play in AMD production, as well as those of sulphate-reducing microbes in mitigating AMD in passive (e.g. wetlands) and active (bioreactor) systems. Apart from their primary concern with AMD, these chapters vividly illustrate the remarkable abilities of microbes to inhabit environments of extreme acidity, alkalinity, heat and cold. Microbes accelerate reaction rates by several orders of magnitude and therefore play a central role in determining rates and longevity of acid production as well as metal solubility and speciation. AMD studies provide a setting in which their versatility can be evaluated in detail.
The emphasis moves to water chemistry, with a discussion (C.J. Ptacek and D.W. Blowes) of the application of geochemical modelling to pore-water evolution in waste piles and mine-workings settings, emphasizing modelling issues arising from heightened S and Fe concentrations and extremely low pH values. Then follows an examination by field-experiments using tracer injection to evaluate the impact of mine drainage on the chemistry of stream systems (B.A. Kimball, R.L. Runkel and K. Walton-Day), employing reactive solute-transport modelling to interpret downstream concentration profiles and to assess the likely outcomes of potential remediation strategies. Discussion of the principles of reactive-transport modelling of mineral weathering, contaminant release and attenuation (K.U. Mayer, D.W. Blowes and E.O. Frind) is illustrated by case studies of the Königstein uranium mine, Germany, and tailings impoundments at Nickel Rim, Ontario. In the next chapter, stable isotope fractionation is discussed (R.R. Seal II), emphasizing behaviour of 34S and 18O in sulphide oxidation and sulphate reduction, together with application of stable isotopes to geochemistry of cyanide, and discussing isotope patterns in mine-site case studies.
The next three chapters assess the performance of engineered strategies that seek to reduce AMD to meet regulatory water-quality requirements. The first (K. Walton-Day) looks over the wide range of passive and active mine-drainage treatments that exploit neutralization and addition of alkalinity, adsorption, ion exchange, oxidation, sulphate reduction, metal-organic complexation, plant uptake and microbial uptake to reduce acidity and metal concentrations in effluent. The next (D.W. Blowes, J.G. Bain, D.J. Smyth and C.J. Ptacek) focuses on use of permeable reactive materials as barriers within drainage pathways or mixed with tailings, discussing Canadian and US case studies at mines, processing sites and a coal power plant. Turning to a prevention rather than cure, the third chapter in this set (G. Ward Wilson) looks at the design parameters and performance of cover systems designed to limit water and air migration into tailings, considering in detail case studies from contrasting climatic regimes found at the Equity Silver Mine, British Columbia, and the Kidston Gold Mine, Queensland.
The final two chapters describe the design and implementation of waste treatment and mitigation strategies at Rum Jungle, northern Australia, and the Iron Mountain Mines, northern California. In both these case studies, the history of mining activity and post-closure AMD problems extends over many years. Rum Jungle ceased extracting uranium and other metals in 1971, and has a legacy of metal-enriched AMD affecting vegetation and aquatic life in the Finniss River downstream of the mine site (A.I.M. Ritchie and J.W. Bennett). Monitoring and testing of tailings dumps, open pits and downstream water quality set the scene for the Rum Jungle Rehabilitation Project, started in 1982, which included remodelling and covering of the tips as well as treatment of water in open pits. Key objectives of improving water quality and thereby lessening environmental impact have been met, but some aspects of AMD migration require further investigation and the weathering of the wastes will continue for many years to come. At Iron Mountain, the complex history of mining of gossan and massive sulphides lasted from 1879 to 1954 (C.N. Alpers, D.K. Nordstrom and J. Spitzley). The mining company was first sued for environmental damage as long ago as 1898–1904. Despite damming to control the release of acid mine waters, uncontrolled releases related to heavy rainfall caused fish losses until, following the Superfund Act in 1980, the site was listed as one of the most polluting mine sites in the USA. Since then successive Records of Decision have brought about establishment of an effective treatment and amelioration strategy. The story is complex and is given an admirably multi-faceted treatment. Richmond Mine is notable for the extreme levels of acidity of seeps sampled in the adit, having the highest concentrations ever recorded of As, Cd, Fe and SO4 in groundwater, as well as pH values reaching as low as –3.6. The basis for calibrating and measuring such extreme levels of acidity is discussed. The mines contain an extensive series of sulphate minerals whose solubility creates rapid metal release during high rainfall after a dry season. Oxidizing microbes live in temperatures up to 45°C and under pH values of 1.2 or less. Iron Mountain can be seen as a remarkable natural laboratory. Also remarkable is the sum of $1 billion that is estimated for past and future cleanup. Indeed, it is tempting to ask what the cost of post-closure AMD control and cleanup amounts to worldwide, and how it compares with the original profits of the mining activity that brought it about.
This is a book for scientists and students seeking to consolidate their understanding of an important area of applied environmental geochemistry and mineralogy. It is well written, authoritative and relevant. It is, moreover, to be welcomed as demonstrating the importance of earth science and mineralogy in solving problems of the real world rather than, or in addition to, being elegant science in their own right. The chapters draw the reader into their specialized areas and provide extensive bibliographies to enable them to pursue their interests further.
On the other hand, this is not a book for the beginner or general reader, in that it demands a good degree of prior specialized scientific knowledge to follow all the different aspects that are presented. Mineralogy, in the strict sense, is restricted to the small set of chapters describing weathering of sulphide and silicate grains in mine waste, quantitative mineralogical analysis, specifically by the Rietveld XRD technique, and application of mineral surface analysis methods to weathering processes. In a more diffuse manner, minerals are present throughout the text as the raw feedstock of AMD production, as agents of acid neutralization and as secondary minerals that both retard and promote toxic metal migration.
A few criticisms can be made. Firstly, the book has no index, a significant omission in a work so laden with factual content, and there is a small number of minor editorial errors. Both probably stem from a wish to publish while the course itself is fresh and relevant, and to sell it at a price that students will be willing to afford. There are also omissions from what could have been included, such as transportation of contaminants as airborne particulates and by other mechanisms, or the use of geophysical techniques to monitor and track migration of contaminated groundwater. However, these are dealt with elsewhere, and no short course can be expected to cover everything.
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