Assessment, Restoration and Reclamation of Mining Influenced Soils

Assessment, Restoration and Reclamation of Mining Influenced Soils covers processes operating in the environment as a result of mining activity, including the whole spectra of negative effects of anthropopressure and the environment, from changes in soil chemistry, changes in soil physical properties, geomechanical disturbances, and mine water discharges.

Mining activity and its waste are an environmental concern. Knowledge of the fate of potentially harmful elements and their effect on plants and the food chain, and ultimately on human health, is still being understood. Therefore, there is a need for better knowledge on the origin, distribution, and management of mine waste on a global level.

This book provides information on hazard assessment and remediation of the disturbed environment, including stabilization of contaminated soils and phytoremediation, and will help scientists and public authorities formulate answers to the daily challenges related to the restoration of contaminated land.

• Provides a thorough overview of the processes operating on mining-devastated areas, as well as origin, distribution, and deactivation of harmful elements
• Includes outcomes and recommendations of the Global Mining Initiative that are widely regarded as the code of conduct in the minerals industry
• Contains global case studies that elucidate various aspects of assessment and restoration of mine-contaminated land

• Language: English
• Publisher: Academic Press
• Release date: Sep 9, 2017
• ISBN: 9780128097298

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Bulgaria

Chapter 1

Classification and Environmental Impact of Mine Dumps

Mariya A. Pashkevich    Saint Petersburg Mining University, St. Petersburg, Russia

Abstract

Global industrial production uses and produces a vast amount of potentially hazardous substances and materials. Around 10 billion tons of oil equivalents are extracted, transported and stored for the purposes of energy production only; this mass is commeasurable to arsenals of nuclear weapons. The introduction of new technologies does not decrease the levels of technogenic environmental dangers. The natural constant yearning of society for the fullest satisfaction of material and cultural requirements causes increasing scales of production that are accompanied by waste accumulation and, consequently, heightened man-made ecological dangers.

Mining and processing industries are among the most intensive sources of environmental pollution, with wastes making up over 90% of extracted mineral raw materials. This leads to the formation of mine dumps that are technogenic geological structures made of rocks or sediments, which vary in composition (chemical, particle-size, bacteriological) and properties (physical and mechanical, capacity for filtration and absorption) from background rocks. The implemented technological processes primarily determine shapes and forms of mine dumps.

Development of a mine dump classification, encompassing their comprehensive characteristics, and assessment of the risk of the environmental impact of mine dumps are topical issues, because of the possibility of preventing or decreasing the adverse influence of such dumps. The classification and assessment can be performed by a targeted selection of type and design of landfills for planned enterprises, and by developing a set of measures to rehabilitate and reclaim affected territories, decreasing therewith expenses for construction and exploitation of mine dumps and environment protection measures.

The chapter suggests a complete classification of mine dumps based on their genesis; determines their multifactor environmental impact; and gives a methodological approach to ecological and economic risk assessment of the mine dumps affecting the environment.

Keywords

Mining sites; Tailings ponds; Environmental studies; Risk assessment; Soil pollution; Health impact of mine dumps

Acknowledgments

The analyses were performed using the equipment of the Common Use Centre of Saint Petersburg Mining University.

1.1 Notion, Origin, and Classification of Mine Dumps

1.1.1 General Concept

Mineral wealth makes up more than 70% of resources consumed in the global economy (by volume). Mining and processing plants are among the most nature-disturbing industries, causing irreversible damage to the natural ecosystem balance. These plants are the most intense sources of environmental pollution, having solid, liquid, and gaseous wastes (Fey and Desborough, 2004; Knissel, 1999; Lazăr et al., 2015; Sun et al., 2015). Approximately 70%–80% of general waste volume is produced by mining industrial sectors (Valente and Gomes, 2009; Zobrist et al., 2009). Humanity loses about 90%–95% of extracted mineral resources as wastes; the total amount of disturbed rock mass on the planet is over 100 billion tons (Horvath and Gruiz, 1996; Pashkevich and Petrova, 2015; Salomons, 1995). Formation of technogenic dumps is a result of this impact. The general scheme of dump formation by mining industries is shown in Fig. 1.1.

Fig. 1.1 General scheme of dump formation during mining.

Formation of mine dumps leads to such negative consequences as changing the properties of rocks underlying dumps, modification of regional hydrological and hydrogeological regimes (Chalov et al., 2015; Pashkevich and Petrova, 2016; Romero et al., 2015; Schreck, 1998), and occurrence of geological processes and phenomena that can cause disastrous effects (Aragão and de Oliveira Filho, 2011; Chalov et al., 2014; Kabas et al., 2012; Lottermoser et al., 1999; Osborne, 1999; Pashkevich and Petrova, 2014a,b). Moreover, landscapes are transformed, agricultural areas are reduced, soil is polluted, erosion is intensified, and the state of the atmosphere is worsened (Alekseenko and Pashkevich, 2016; Bian et al., 2009; Kasimov et al., 2016; Pashkevich and Petrova, 2014a,b; Perelman, 1998).

Two groups of factors determine development of landscapes at the sites occupied by mine dumps:

I. Natural:

– physical and geographical conditions (climate, relief, hydrology);

– geological conditions (tectonics, mineralogical and chemical rock composition);

– hydrogeological conditions (filtration properties of rocks, the position of the regional confining layer relative to the local and regional bases of erosion);

– physicochemical conditions (chemical properties of water-bearing rocks and natural waters, redox and the acid-alkaline environment);

– physical conditions (temperature and pressure);

– biological conditions (the vital activity of plants and microorganisms).

II. Technogenic:

– mining (exploitation system, withdrawal of minerals from the landscape, lifting of deep rocks, which have composition and properties different from those of the near-surface rocks, to the Earth's surface, violation and replacement of a soil cover with artificial materials, groundwater extraction from the landscape for the purpose of dewatering, deterioration of protection conditions of groundwater);

– construction of enrichment plants and manufacturing facilities for mineral processing (sewage leakage, gas and dust emissions to the surface atmospheric layers, use of ground and surface water for the purpose of water supply);

– storage of mineral dressing and processing wastes (leakage of wastewater from storage, release of man-made deposits to the surface of landscapes with specific composition and properties, dispersion of dust blown from a storage surface);

– efficiency of dust and gas removal from atmospheric emissions and sewage treatment, dust control at the exposed surfaces of mine dumps, remediation activities.

The influence of technogenic factors on the formation and functioning of landscapes is ambiguous in time and space. Optimization of the interaction between mine dumps and the natural environment requires detailed classification and the improvement of methods for studying various landscape components formed on the site of mine dumps and also the improvement of the reliability of the forecast of their changes, especially at the stage of mining enterprise design.

It is proposed to divide mine dumps by genesis into three groups (Fig. 1.2): piled dumps, hydraulic-filled dumps, and technogenic sediments.

Fig. 1.2 Classification of mine dumps.

1.1.2 Piled Dumps

Piled dumps are formed from materials stacked during engineering works and can be either soils of natural origin with a broken genuine structure, or mineral wastes of industrial production, or solid domestic and industrial wastes (Table 1.1). Piled technogenic dumps can consist of rock materials (heaps, mounds, dams); civil engineering structures at hydraulic engineering, energy, or transport construction sites; exploitation of urban underground space; as well as dumps of household and industrial wastes.

Table 1.1

Classification of Piled Dumps

The characteristic features of piled dumps are: rock structure disturbance in the mound body, which causes reduced strength as compared to the natural bedding and increasing filtration properties of deposits; significant change in the strength of mound rocks over time; violation of the water balance in the area; and intrusion of deep rocks into the ground surface in the supergene zone, which has different acid-base and redox conditions, which can lead to leaching of harmful substances.

Mining wastes include hard rocks, gravels, clays, pebbles, sands, limestones, chalks, siftings of fine fractions, dump tailings of flotation concentration of ferrous and nonferrous metal ores, sulfur ores, apatite-nepheline concentrates, coal wastes, halite flotation wastes, screenings of phosphorite, phosphoric ore fines, etc.

Ferrous metallurgy wastes include stripping and overburden rocks, tails of dry and magnetic separation, tails of gravity concentration, slag, and sludge from the blast furnace and steelmaking, dust, gases and waste water (Beloglazov et al., 2014). For example, the modern smelting technology for 1 ton of pig iron creates on average 1.2 tons of tailings and 0.9 tons of ash.

Waste output per production unit in nonferrous metallurgy is incomparably higher than in the coal and iron ore industries (100–200 tons and in some cases up to 1000 tons per 1 ton of metal). Thus, smelting 1 ton of copper is accompanied by the formation of 4.2 tons of tailings and 30 tons of ash; obtaining of 1 ton of gold is accompanied by processing of 23 million tons of rock mass.

Formation of piled dumps leads to such negative consequences as reduction of land area suitable in most cases for agricultural use, changing natural landscapes, development of erosion processes, soil contamination and decreasing productivity of adjacent lands, changing properties of rocks laying under dumps, modification of regional hydrological and hydrogeological regimes, deterioration of atmospheric air and sanitary living conditions of people in the surrounding areas.

1.1.3 Hydraulic-Filled Dumps

Hydraulic-filled dumps are based on aggradational materials that arise in the course of engineering activities, during waste stocking in special constructions using hydraulic methods. The main types of hydraulic-filled dumps are:

– hydraulic fills formed during storage of overburden rocks by hydraulic methods;

– tailings serving for aggradation of wastes of solid mineral processing;

– ash disposal sites accumulating ashes and slags of the thermal power industry;

– sludge collectors and household waste storage designed for long-term accumulation of a variety of industrial and domestic residuals.

Hydraulic-filled dumps pose serious environmental risks, due to the possible pollution of air, ground and surface water, and soil cover in vast areas. In the traditional aggradation technology, thick (50–100 m) strata of finely dispersed materials are formed in the inner zones of tailings and hydraulic fills. These sediments remain for decades in an uncompacted state that determines their low load-bearing capacity and eliminates any possibility of using these hydraulic fill areas.

The largest scale hydraulic-filled dumps are formed by the ferrous and nonferrous metallurgy industries, where more than 800 million m³ of various tailings and sludges are stored each year.

Characteristics of a number of these tailings, as well as chemical and mineral composition of the impounded wastes, are presented in Tables 1.2 and 1.3. These data show that the relative content of mineral phases in ore tailings varies widely, with a considerable diversity of mineral composition itself. A wide range of mineral compositions of tailings leads to a significant difference in element concentrations and to multicomponent chemical compounds (Gal'perin et al., 2006; Gumenik et al., 1988; Verzohin and Matveeva, 1994).

Table 1.2

Characteristics of Tailings of Ferrous Metallurgy Enterprises

Table 1.3

Mineral Composition of Tailings Produced by Nonferrous and Ferrous Metal Concentrating Factories

The chemical and mineral composition of tails is determined by the mineral structure of processed ores and enrichment technology. Particle-size distribution of various types of tails ranges widely for different types of minerals and has significant fluctuations in different mining periods (Table 1.4). It depends on methods and stages of ore preparation, on major enrichment technologies and hardness of the minerals that make up an ore.

Table 1.4

Particle-Size Distribution of Tailings of Nonferrous and Ferrous Ore Concentrating Factories

The chemical and mineral composition of hydraulic fills, as well as storage conditions and technology, determine the classification of hydraulic fills by toxicity degree. Aggradational wastes of nonferrous metallurgy are the most toxic, classified according to levels of salinity and sulfidity (Table 1.5).

Table 1.5

Classification of Tailings of Nonferrous Ore Mining and Processing Enterprises by Their Toxicity

Due to the increased environmental hazard of hydraulic-fill exploitation, separation according to responsibility class is performed, depending on the storage volume of tailings, engineering geological characteristics of the stored materials and soil foundation, the design of waste storage, the topographical position of a dump in relation to other industrial and civil objects. The adopted responsibility classifications for tailings and sludge storage tanks are shown in Table 1.6 (Gal'perin et al., 2006).

Table 1.6

Discrimination of Tailings and Sludge Storage Tanks Into Liability Classes

Land topography is one of the determining factors of hydraulic-filled dump design. It is divided into the following types: ravine, plain, gully and plain; floodplain; hill.

1.1.4 Technogenic Sediments

Technogenic sediments arise from activities of industrial and agricultural enterprises, transport, and household facilities, having a low thickness and considerable length (area). According to the origin, technogenic sediments can be classified as (Fig. 1.2):

– atmospheric fallouts, resulting from airborne particulates and aerosols precipitating on the Earth’s surface and originating from organized and unorganized emissions of various industries;

– bottom sediments in watercourses and reservoirs, resulting from suspended mechanical and colloidal impurities and originating from discharges of industrial, municipal, and agricultural enterprises into water bodies;

– artificial soils resulting from reclamation of lands disturbed by mining, construction, and other works, as well as areas of agricultural development.

The largest technogenic sediments in the Russian Federation are formed in the areas of fuel-energy enterprises, ferrous and nonferrous metallurgy, and the petroleum and petrochemical industries. Distribution of technogenic products on the soil surface depends on both the impact of meteorological, topographic and geochemical factors and on characteristics of emission sources.

Technogenic sediments are, as a rule, located in zones of man-made impact by cities, industrial agglomerations, and highways. Coming into the atmosphere from torches of enterprises, exhaust pipes of vehicles, dusting surfaces of waste repositories and then settling on the soil surface in the form of aerosols, dust or dissolved compounds, and polluting elements, in conjunction with atmospheric precipitation and temporary surface water flows, these sediments create unfavorable conditions for the natural processes of soil formation and contaminate soil. The most dangerous are technogenic deposits containing heavy metals, especially compounds of mercury, arsenic, lead, cadmium, nickel, copper, and zinc.

Table 1.7 shows Russian cities and industrial agglomerations with a maximum total index of soil pollution by heavy metals. The most toxic technogenic deposits are observed in the areas of metallurgical enterprises, where more than 150 thousand tons of copper, 122 tons of zinc, 90 tons of lead, 12 tons of nickel, 1500 tons of molybdenum, 800 tons of cobalt, and 31 tons of mercury falls onto the soil surface per year (Bekker and Agaev, 2015). As a result of activities of the energy sector companies, the soil surface receives monthly 1600 tons of mercury, 3600 tons of lead, 7000 tons of zinc, etc. With vehicle exhaust gases, 260 tons of lead get on the Earth's surface per year. This explains the high total index of soil pollution in large industrial centers such as Moscow, Saint Petersburg, and Yekaterinburg (Table 1.7).

Table 1.7

Pollution of Surface Sediments in Some Cities and Industrial Agglomerations by Heavy Metals

a Soil pollution index for the 5-km zone around the city.

In the areas of technogenic deposits, inhibition and even complete disappearance of vegetation, as well as a sharp increase in the activity of soil erosion processes, are observed. Contaminated soil loses its structure, which leads to reduction of its porosity, permeability and a sharp deterioration of the water-air regime.

Technogenic deposits in the form of bottom sediments are formed in areas of discharging sewage containing mechanical and colloidal impurities, and sparingly soluble compounds precipitating from water at changing Eh-pH conditions. The greatest damage to water bodies and watercourses is caused by the wastewaters of woodworking, pulp and paper, chemical and petrochemical industries, fuel and energy, agriculture, and public utility sewage. Impurities entering water bodies are divided into mineral, organic, and biological types.

Mineral pollutants are sands, clays, fly ashes, slags, emulsions and solutions of salts, acids, alkalis, oils, radioactive, and other inorganic compounds.

Organic contaminants are various substances of plant and animal origin, and numerous wastes like resins, phenols, colorants, alcohols, aldehydes, etc.

Biological contaminants are pathogenic bacteria and viruses tending to enter water bodies and watercourses with municipal sewage waters.

Discharge of polluted wastewater in Russia amounted to 15.2 km³ in 2013. A significant amount of sewage is discharged without any treatment: 3.5 km³ or 20% of the total volume of polluted wastewater. More than 60% of wastewater discharged without any treatment is formed on the territories of seven Federation subjects: Saint Petersburg, Primorsky Krai, Kemerovo, Irkutsk, Chelyabinsk, Sverdlovsk, and Krasnodar Regions. Reasons for discharge of wastewater into water bodies without treatment are violations of operational procedures of treatment facilities due to their physical and technological obsolescence; lack of treatment facilities; and emergencies. In the Russian Federation, the main contributions to contamination of natural waters is made by enterprises involving mineral complexes, and chemical and petrochemical, woodworking, and pulp and paper industries.

A significant number of contaminants settling on the bottoms of ponds and streams are dumped with municipal and surface drains of cities and industrial agglomerations. The characteristic components of the surface run-off of cities and industrial agglomerations are suspended solids, with content ranging from 130 to 11,300 mg/L. Rainfall and street washwaters form the surface runoff. Its composition depends on a number of meteorological parameters (the intensity and amount of rainfall, the duration of the preceding dry weather period), intensity of industrial development, and the intensity of vehicular traffic.

Technogenic deposits in the form of artificial soils are widespread in the areas of land disturbance from mining and construction and on the territories of agricultural development of nonchernozem soils with low humus and mineral content.

To restore the productivity of disturbed lands and areas affected by wind and water erosion, mixes of clays, loams, sandy loams, peats, sapropels with mineral and organic additives are created. These mixes are applied to the leveled surface of disturbed lands, forming a layer of artificial soils. The resulting soils differ in structure, texture, grain size and chemical composition from the natural ones. Nevertheless, agricultural development of these lands leads, in some cases, to the complete restoration of land productivity.

There are cases of adverse results of artificial soil formation. Thus, for the reclamation of land disturbed by open mining operations, and for increasing productivity of arable land affected by erosion, JSC Phosphates (Moscow region) applied mixes based on glauconite sandy loams, which had in their composition a number of chemical nutrients favorable for a fertile layer formation, such as K, P, and Corg. For this reason, artificial soils made of glauconite sandy loams were placed on the surface of over 300 ha, but this resulted in nearly 100% decrease of agricultural land productivity during a 5-year period. Falling land productivity was associated with a sharp increase in acidity (the pH value dropped to 2.5) caused by oxidation of pyrite contained in the glauconite sandy loams (up to 2.5%).

1.2 Peculiarities of Environmental Impact of Mine Dumps

1.2.1 Determination of the Nature of Environmental Pollution

Mine dumps are among the major sources of pollution and disturbance of various environmental components in the areas where enterprises for extraction and processing of mineral raw materials are located; this produces a need to examine these negative effects. Investigations involve the following tasks:

• determination of the nature of a danger and the nature of technogenic environmental pollution;

• study of migration pathways of contaminants;

• definition of objects of environmental protection.

The main difficulty in conducting studies and impact assessments of mine dumps is the lack of common criteria for risks to objects of environmental protection (people, natural landscapes, and their components), as well as the lack of time frames within which these criteria are evaluated.

The European Environment Agency described the state of research being conducted in the areas of waste storage facilities as follows:

• a hazard of mine dumps impacting the environment is determined qualitatively, in the complete absence of quantitative estimates;

• a method of determining the danger scale is based on selective sampling, which does not exclude the possibility of incomplete coverage of the studied object (this applies to waste disposal sites, polluted media, and methods of distribution). This is particularly important in determining the type and amount of harmful substances in wastes;

• an information on the scale of danger is limited due to: the partial data on the composition and amount of harmful substances and their derivatives; the lack of necessary parameters for determining the composition of these substances; the lack of sufficient information on the properties and distribution of materials and their derivatives in protected environments; the lack of knowledge about the relationship between the physical and chemical properties of substances and their effects; the lack of uniform and generally accepted criteria for assessing their impact.

In this context, it is proposed to carry out the assessment of the negative environmental impact of mine dumps based on the following provisions:

• The various compounds contained in waste, dust, and other substances have neither the same kind of impact on people and the landscape nor the same degree of harmfulness. Each country has a national inventory of pollutants ranked according to the degree of danger.

• Waste repositories, dumps, and contaminated sites represent a high and prolonged risk of groundwater contamination. A real risk of contamination depends on the distance between the store and the water intake, volume of water intake, and hydrogeological conditions.

• Mine dumps pose a contamination risk for surface waters that are used for drinking, domestic use, and irrigation.

• Mine dumps represent a risk of air pollution from dust and gaseous products of waste biodegradation. Negative impacts of mine dumps can manifest in release of allergens that cause human reactions.

• Apart from the danger of toxic air pollution, a number of mine dumps are explosive and flammable.

• Mine dumps may pose a risk of direct contact between man and landfilled wastes:

– in a case of skin exposure to harmful substances;

– by inhalation of toxic substances emitted from the storage surface (Fig. 1.3);

Fig. 1.3 Environmental impacts caused by mine dumps.

• Mine dumps may pose a risk of contamination of the surface soil layer, cultivated plants, human and animal intoxication after low-quality reclamation.

• Mine dumps disturb the surface stability and lead to adverse landscape transformation.

1.2.2 Characteristics of Risks Caused by Stored Wastes

The nature of the dangers of mine dumps—in particular, the spectrum of polluting components—is determined by their industrial origin. Studies of the chemical composition of wastes produced by enterprises for extraction and processing of various minerals have allowed classification of these objects and identification of a list of potentially dangerous pollutants (Table 1.8).

Table 1.8

Possible Pollutants Released From Dumps of Mining and Processing Industries