Environmental Impact of Abandoned Mine Waste:
A Review
ix
Evolution and Schizophrenia
Environmental Impact of Abandoned Mine Waste:
A Review
Claudio Bini
Author
Nova Science Publishers, Inc.
New York
ix
Evolution and Schizophrenia
Copyright © 2011 by Nova Science Publishers, Inc.
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ISBN 978-1-61324-837
Published by Nova Science Publishers, Inc. †New York
ix
Evolution and Schizophrenia
Contents
ix
Preface
ix
Acknowledgements
The Author is indebted with collegues and cooperators that provided data for this review, and helped in preparing the final draft of the paper. Particular thanks are due to Dr. Mohammad Whasha, who revised the English form; Dr. Diana Zilioli and Dr. Silvia Fontana assisted in the field survey and provided laboratory analyses.
Prof. Jaume Bech, Chair of Soil Science, University of Barcelona (Spain), is warmly acknowledged for critical review and suggestions that contributed to improve an early draft of the paper.
11
Introduction
Chapter 1
Introduction
Since the dawn of civilization and for long time, until the last decades of past century, mining activity, especially that concerning base (Cu, Fe, Pb, Zn) and precious metals (Au, Ag), as reported by George Bauer, (known as Agricola), in his book De re metallica (1556), represented a resource for human population, owing to its importance in many fields of interest: economic, cultural, technological (Figure 1).
By the second half of last century, however, mining activity, almost in European countries, declined until final closure, in the face of developing countries, owing to decreasing mineral resources, and to metal price drop. Since then, arose the problem of visible reminders and invisible inheritance of mine working (Davies, 1987), with reference to different aspects:
· Environmental: soil contamination by metals, soil and water acidification; damage to vegetation;
· Geomorphologic: landscape modification, geological hazard (erosion, flooding, landslides);
· Sanitary: risk for human health (inhalation, ingestion, contact);
· Casual/professional diseases: intoxication, lead poisoning, mercurialism.
Quite recently, however, abandoned mine sites have been discovered to constitute a chance, giving the opportunity to open Mine Parks and Museums; Archaeological Parks; protected natural areas, didactic-recreational itineraries, trekking areas, and other activities in open air. Yet, mine sites are actually natural scientific laboratories, where to explore natural processes involving rock-forming minerals, their transformation into soil-forming minerals, their interaction with organic matter, and fluxes from soil to plants. Furthermore, mine sites investigations have been addressed to soil remediation and environmental restoration, for example with application of phytoremediation technologies (Bini, 2009).
Figure 1. The front of the treatise De re metallica by G. Agricola (1556).
More recently, the European Mine Waste Directive (EC, 2006) has introduced new requirements for mine waste management, including that resulting from historical mining (Palumbo-Roe et al, 2009). The challenge in implementing the European Directive is to develop a pan-European risk-based inventory of abandoned mines, in order to select sites for remediation based on a common set of criteria. The characterisation of the mine waste and its transformations in the short and long term, forms the basis for a risk-based classification of abandoned mine sites (Servida et al., 2009).
In this paper, the effects of former mine activities, and the related environmental problems, with particular reference to Italy, are discussed, with the ultimate goal of investigating the fate of potentially toxic elements in the environment, and their impact on the conterminous land.
1.1. Resource
Mineral exploitation, smelting and recovery of useful and/or precious metals in several countries of Europe dates back to VII century B.C. (Etruscan times) or even before (Thornton, 1996). After a large diffusion of Fe, Cu, Au, Ag, Sn, Pb mining during the Roman expansion in Europe and Britain, ore exploitation virtually ceased during the Middle Age (5th to 11th centuries), and became economically important again after the 15th century, when there was an increasing demand for silver for coinage, and lead for armaments. (Davies, 1987). Afterwards, alternate fortunes accompanied mine works, particularly during the Industrial Revolution and until the first decades of 20th century, when mining activity in the Old Continent ceased and most mines were abandoned, for both exhaustion of metal veins, price drop and major sensitivity of people to human and environmental health. Silver and mercury, for instance, have been used since early historic times, as reported by Bargagli (1995) and Forel et al. (2010). Silver exploitation in the Vosges Mountains is attested since the 10th century in the Val d’Argent (NE France), where up to 600 mines have been accounted for at least 3000 miners (Forel et al., 2010). Cinnabar exploitation in the Mediterranean basin (Spain, Italy, Croatia, Turkey, Tunisia) began in Etruscan times, was expanded by Romans and dominated the world mercury production for long time (Bargagli, 1995). Mercury production, as well as that of other metals such as copper, lead, silver, zinc, etc. depended on the market price, which reached 700US dollars/kg during early ‘70s (Gemici et al., 2009). The gradual decline in the demand, caused by the increasing environmental concerns of Hg, resulted in lowered price, drastic reduction in mining, and the final closing of many Hg mines until the early ‘80s.
Metals are indissolubly linked to the progress of mankind, having greatly contributed to the evolution of civilization, from the stone age (Neolithic period, 6.000 BC), through copper, bronze, iron and “gold age” (the California gold rush), to present time. Exploitation of metals such as Cu, Au and Ag, for example, is among the most long lasting mining operations, since their recovery started with the chalcolithic age (copper-bronze age), between 5500 and 3000 BC (Dill, 2009).
Combining archaeological and geological investigations, numerous studies have focused on ancient settlements, artifacts and archaeometallurgical slags found at different sites, shading some light on the techniques applied for the recovery of pure metals (Cu, Au, Ag, Pb, Sb, Sn and Fe) from the various raw materials (Francovich, 1985; Stiles et al., 1995; Mascaro et al., 1995; Heimann et al., 1998; Manasse et al., 2001; Manasse and Mellini, 2002; Costagliola et al., 2008; Dill, 2009).
Table 1. Mine production of heavy metals
Element / Mine production 1990antimony / 55
arsenic / 45
cadmium / 19
chromium / 6800
copper / 8110
lead / 3100
mercury / 6.8
nickel / 778
zinc / 6040
Data is in metric tonnes x103 / year.
Modified after McGrath, 1995.
Metals have been, and are still, mined in the majority of the countries of the world, and primary production of many metals continues to rise (Thornton, 1996). In 1950, the production of Pb was 1.7 million tonnes (Table 1), and that of Cu 2.8Mt, Cr 2.2Mt, Zn 1.9Mt, Ni 0.14Mt; in 1995, Pb production was up to 3.3 million tonnes; Cu 9.4Mt; Cr 12.8Mt; Zn 7.1Mt; Ni 0.9Mt (Thornton, 1996). The main reason for this interest towards metals is, obviously, related to their large utilization at worldwide level.
Nowadays, heavy metals are vital components of modern technology, being utilized in many industrial and agricultural activities (electronic, galvanic, metallurgy, varnish, tannery, wood preservation, fertilizers, pesticides, etc.) (Davies, 1987; Adriano, 2001). The metal over-utilization at worldwide level is responsible for serious threats to the environment, with potential risk for human health. Besides the occasional lead poisoning recorded during Roman domination ( Nriagu, 1983; Stiles et al., 1995), the first signals of threats appeared on agricultural land contaminated with heavy metals. In the middle of the 19th century, farmers living close to lead-silver mine areas in England complained that mine waste was deposited on fields by river floods, contaminating their land (Davies, 1980). It has been calculated that approximately 35% of the mineral waste discharged on the land was released to the environment. Overall, it can be estimated that for every ton of silver-free lead which was produced, as much as 2tons may have been lost to the environment (Davies, 1987). Similarly, Helios-Rybicka (1996) reported that approximately 700M tonnes for year of mineral commodities have been exploited in Poland, strongly influencing the hydrological system. Geomechanical processes (subsidence, slumps, landslides, erosion) led to the complete destruction of soils and irreversible changes of the landscape.
From that time, repeated threats to the environment have been recorded in current literature, (see f.i. Cappuyns et al., 2006; Palumbo-Roe et al., 2009), suggesting heavy metals to represent a concrete environmental concern.
1.2. Problem
Rocks and ore deposits are composed of a pool of chemical constituents. The major elements (Si, Al, Ca, Mg, etc.) are invariably accompanied by minor (Fe, Mn, Ti, P, etc.) or trace amounts of other metals. Among these, heavy metals can be defined (Adriano, 2001) as those having a metallic density >5 gcm-3 (e.g. Cu, Co, Ni, Pb, Zn, etc.). Other important constituents, particularly utilized in modern industrial activities, are antimony, arsenic, bismuth, cadmium, chromium, germanium, selenium, tallium, etc. In addition, many metals are essential for life functions. Chief concern focuses on Cu and Zn, which are essential micronutrients but may be harmful when present in large concentrations, and on Cd, Hg and Pb, which have no known beneficial metabolic role but are known toxins (Kabata-Pendias and Pendias, 2001; Ghorbel et al., 2010). The important point is that many of these metals are also potential contaminants to the environment, and constitute a potential risk to vegetation and human health, when their concentrations are above a certain threshold (Davies, 1987; Kabata-Pendias, 2004). Yet, these metals are ordinarily present in rocks, sediments and soils, but locally may become concentrated in rocks as ore bodies and generally dispersed in the environment through pollution as a consequence of mining the ores. (Davies, 1987; Alloway, 1995).
Mining is only one of the pathways by which metals enter the environment. Mining itself affects relatively small areas, and this could not pose problems. The environmental problem arises when ores are mined, milled and smelted, and a certain amount of metals is released in the surrounding areas and to waterways. Depending on the nature of the waste rock and tailings deposits, a wide dispersion of the metals both in solution and in particulate form is possible (Sivri et al., 2010). Erosion of waste rock deposits or the direct discharge of tailings in rivers results in the introduction of metals in particulate form into aquatic ecosystems (Helios-Rybicka, 1996; Cidu et al., 2009). Smelting of ore deposits results in the release of metals to the atmosphere (Mihalik et al., 2011); when metals have been released through the atmosphere, they end up as diffuse pollutants in soils and sediments. (Nriagu, 1990; Salomons, 1995).
Figure 2. Geological and hydrological hazard determined by mine dumps in the Metalliferous Hills district (Southern Tuscany, Italy). (Photo Bini).
A second environmental (geomorphologic) concern is connected to mining operations. Excavation of ore bodies brings out important landscape modifications; earth movements, dam building and impoundment construction, may create severe geological hazard (Figure 2). Erosion processes may concur to convey waste in rivers nearby; landslides may be activated in loose material dumps, with relevant risk for population living in the conterminous land; surface hydrology and hydrological processes may be strongly modified, and constitute a further concern.
Mining areas are frequently constituted of highly tectonized and fractured rocks and detrital fragments (Tanelli, 1985), easy erodible by runoff and percolating water. The causes of accelerated surface erosion are related to both geological (tectonic structure, lithology), morphologic and climatic conditions (steep slopes, rainy events distribution, temperature gradients); vegetation cover may have great influence on attenuating, or enhancing, erosion phenomena, when land cover is scarce or lacking, as it happens frequently with metal-contaminated sites. A correlation between tectonic structure, minerogenesis and surface processes has been recorded (Lattanzi et al., 1994; Benvenuti et al, 1999; Mascaro et al., 2000) at nearly every mine site.
Access to exploitation areas is allowed through earth movements such as opening new tracks and new excavations, and this may enhance earth surface processes, landslide formation, hydrological regime alteration, contaminant dispersion (Helios-Rybicka, 1996). The hydraulic characteristics of mineral bodies (e.g. coarse grain size, permeability, hydraulic conductivity), in turn, are responsible for water percolation and circulation in the subsoil, where contaminants are convoyed to groundwater (Cidu et al., 2009). Moreover, apart from geomechanical processes (subsidence, slumps, landslides, erosion) which may lead to the complete destruction of soils and irreversible changes in the landscape, the drainage of open pits influences hydrological systems (Helios-Rybicka, 1996).