recent advances in mitigation and rehabilitation technology in major and abandoned mines in...
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Recent Advances in Mitigation and Rehabilitation Recent Advances in Mitigation and Rehabilitation Technology in Major and Abandoned Mines in Technology in Major and Abandoned Mines in
Sub-Saharan Africa Sub-Saharan Africa
T.C. Davies T.C. Davies
Department of Mining and Environmental GeologyDepartment of Mining and Environmental Geology
University of VendaUniversity of Venda
Private Bag X5050Private Bag X5050
ThohoyandouThohoyandou
Limpopo ProvinceLimpopo Province
Republic of South Africa Republic of South Africa
PROJECT DESCRIPTIONPROJECT DESCRIPTION
IGCP/SIDA/UNESCO/UNIVEN/KNUST Project No. 606 IGCP/SIDA/UNESCO/UNIVEN/KNUST Project No. 606 researches on improvements in mitigation and researches on improvements in mitigation and rehabilitation strategies for environmental health impacts rehabilitation strategies for environmental health impacts of major and abandoned mines in Sub-Saharan Africa, of major and abandoned mines in Sub-Saharan Africa, as well as assess the current status of research in as well as assess the current status of research in pollution control technology. This year, we have put the pollution control technology. This year, we have put the focus on ‘small scale mining’ because of the focus on ‘small scale mining’ because of the tremendous contribution this kind of mining makes tremendous contribution this kind of mining makes towards improving the lives and livelihoods of millions towards improving the lives and livelihoods of millions of Sub-Saharan Africans. A major scientific goal of the of Sub-Saharan Africans. A major scientific goal of the project is to identify ways by which process optimisation project is to identify ways by which process optimisation for profitability can be carried out sustainably, for profitability can be carried out sustainably, while at while at the same time ensuring minimum amount of the same time ensuring minimum amount of negative environmental health consequencesnegative environmental health consequences, and the , and the general preservation of ecosystem integrity. general preservation of ecosystem integrity.
PROJECT SYNTHESISPROJECT SYNTHESIS
* Impacts due to mining methods and mineral* Impacts due to mining methods and mineral processing operations;processing operations;
* Dangers posed by abandoned mines;* Dangers posed by abandoned mines;
* What do we know about the relationship* What do we know about the relationship between mining, the fecundity of cultivable between mining, the fecundity of cultivable
lands in the vicinity of mines, and lands in the vicinity of mines, and environmental health?environmental health?
* Addressing the issues * Addressing the issues
Abandoned MinesAbandoned Mines Abandoned mines in Sub-Saharan Africa Abandoned mines in Sub-Saharan Africa
are often dangerous and can contain are often dangerous and can contain deadly gases such as radon and deadly gases such as radon and methane. Standing water in mines from methane. Standing water in mines from seepage or infiltration, poses a significant seepage or infiltration, poses a significant hazard as the water can conceal deep hazard as the water can conceal deep pits and trap gases below the water. Old pits and trap gases below the water. Old mine workings and caves are sometimes mine workings and caves are sometimes hazardous, simply due to the lack of hazardous, simply due to the lack of oxygen in the air. oxygen in the air.
Mining impactsMining impacts The mining industry is undoubtedly of major The mining industry is undoubtedly of major
importance to Sub-Saharan Africa’s economic importance to Sub-Saharan Africa’s economic well-being. However, mining methods and mineral well-being. However, mining methods and mineral processing operations are known to be associated processing operations are known to be associated with diverse and often profound chemical and with diverse and often profound chemical and physical impacts on miners and adjacent physical impacts on miners and adjacent communities, as well as on other elements of the communities, as well as on other elements of the surrounding ecosystems. Mining in some surrounding ecosystems. Mining in some quarters have accelerated soil erosion rates, quarters have accelerated soil erosion rates, which is a bane to agriculture; metals and toxins which is a bane to agriculture; metals and toxins are often mobilised far beyond natural rates, and are often mobilised far beyond natural rates, and natural water resources are sometimes polluted natural water resources are sometimes polluted beyond measure. Accidents - deaths???beyond measure. Accidents - deaths???
WHAT DO WE KNOW SO WHAT DO WE KNOW SO FAR?FAR?
We need to We need to definedefine clearly the boundaries clearly the boundaries of our present understanding of the of our present understanding of the relationship between environmental health relationship between environmental health and mining and mineral processing, and mining and mineral processing, investigate new discoveries in relations investigate new discoveries in relations between them, and study much more between them, and study much more deeply, geochemical interactions at tailings deeply, geochemical interactions at tailings sites (e.g., the dreaded acid mine sites (e.g., the dreaded acid mine drainage (AMD)), and wastewater courses drainage (AMD)), and wastewater courses and effects on agriculture. and effects on agriculture.
SPECIFIC AIMS AND OBJECTIVES OF SPECIFIC AIMS AND OBJECTIVES OF PROJECT 606PROJECT 606
Promoting and expediting the work of an ‘African Promoting and expediting the work of an ‘African Network of Earth Scientists’ researching the Network of Earth Scientists’ researching the environmental health impacts of mining and ore environmental health impacts of mining and ore processing activities, and seeking the best ways processing activities, and seeking the best ways of addressing them;of addressing them;
Compiling a complete inventory and database of Compiling a complete inventory and database of abandoned and derelict mines in sub-Saharan abandoned and derelict mines in sub-Saharan Africa;Africa;
Preparing a comprehensive documentation Preparing a comprehensive documentation embodying research activities on the following embodying research activities on the following 5 5 themesthemes::
Theme 1Theme 1 Bridging knowledge gaps, and Bridging knowledge gaps, and
specifically assessing the rate of specifically assessing the rate of migration and distribution migration and distribution pathways of selected heavy pathways of selected heavy metals known to be toxic, from metals known to be toxic, from tailings dams and mine spoils tailings dams and mine spoils accumulated during several years accumulated during several years of mining in Sub-Saharan Africa; of mining in Sub-Saharan Africa;
Theme 2Theme 2
Monitoring heavy metal Monitoring heavy metal concentrations in agricultural soils concentrations in agricultural soils in the vicinity of major and in the vicinity of major and abandoned mines in order to abandoned mines in order to indicate the status of heavy metal indicate the status of heavy metal contamination (PHEs), and contamination (PHEs), and assess environmental quality of assess environmental quality of these soils; these soils;
Theme 3Theme 3
Providing practical solutions Providing practical solutions to problems of metal to problems of metal contamination and the contamination and the recommendations for recommendations for improved land remediation improved land remediation strategies (rehabilitation strategies (rehabilitation technology);technology);
Theme 4Theme 4
Assessing long-term impacts Assessing long-term impacts of mining on public health of mining on public health and the environment, and and the environment, and recommendation of strategies recommendation of strategies for protecting the health of for protecting the health of our communities; our communities;
Theme 5Theme 5Providing support to Providing support to
governments of Sub-Saharan governments of Sub-Saharan African countries in developing African countries in developing their national strategic plans to their national strategic plans to combat the public health and combat the public health and environmental effects posed by environmental effects posed by abandoned mines (other abandoned mines (other organs of dissemination).organs of dissemination).
ADDRESSING THE ISSUESADDRESSING THE ISSUES Only then would we be able to Only then would we be able to
properly address environmental properly address environmental health issues pertaining to the health issues pertaining to the mining industry, point out the way mining industry, point out the way forward in improvement of forward in improvement of mitigation and rehabilitation mitigation and rehabilitation strategies, and direct new research strategies, and direct new research in the most fruitful directions. in the most fruitful directions.
PHYSICAL REHABILITATIONPHYSICAL REHABILITATION
Modern mine rehabilitation aims to minimiseModern mine rehabilitation aims to minimise
and mitigate the environmental effects ofand mitigate the environmental effects of
modern mining, which may in the case of modern mining, which may in the case of
open pit mining, involve movement ofopen pit mining, involve movement of
significant volumes of rock. Rehabilitationsignificant volumes of rock. Rehabilitation
management is an ongoing process, oftenmanagement is an ongoing process, often
resulting in open pit mines being backfilled.resulting in open pit mines being backfilled.
Mining area must undergo rehabilitation.Mining area must undergo rehabilitation.
SOME CONVENTIONAL APPROACHES
Waste dumps are contoured to flatten them out, to further stabilize them against erosion. If the ore contains sulphides, it is usually covered with a layer of clay to prevent access of rain and oxygen from the air, which can oxidise the sulphides to produce sulphuric acid (acid mine drainage (AMD)). Landfills are covered with topsoil, and indigenous vegetation common to the applicable area is planted to help consolidate the material. Dumps are usually fenced off to prevent livestock denuding them of vegetation. The open pit is then surrounded with a fence, to prevent access, and it generally eventually fills up with groundwater. Tailings dams are left to evaporate, then covered with waste rock, clay if need be, and soil, which is planted to stabilize it.
Uranium ore. Image: United States Geological Survey and the Mineral Information Institute
Radon Gas - The Silent KillerRadon Gas - The Silent Killer
Uranium mining - extraction of U ore from the groundUranium mining - extraction of U ore from the ground
Low concentrations, means U mining very volume-intensiveLow concentrations, means U mining very volume-intensive
Undertaken as open-pit miningUndertaken as open-pit mining
Main use, as fuel for nuclear power plantsMain use, as fuel for nuclear power plants
Uranium ore emits radon gas; odourless, colourlessUranium ore emits radon gas; odourless, colourless
Inadequate ventilation systemsInadequate ventilation systems
Radon, a cancer-causing agent (small cell carcinoma)Radon, a cancer-causing agent (small cell carcinoma)
Radioactive contamination of air, water and soil (radioactive dust/contaminated Radioactive contamination of air, water and soil (radioactive dust/contaminated groundwater)groundwater)
Uranium Producing CountriesUranium Producing Countries
Niger - Africa’s leading U producing nation (US Niger - Africa’s leading U producing nation (US invasion of Iraq)invasion of Iraq)
Namibia - produces U at Rossing, where an Namibia - produces U at Rossing, where an igneous deposit is mined from one of the World’s igneous deposit is mined from one of the World’s largest open pit mines. largest open pit mines.
Gabon - Deposits reported to be exhausted.Gabon - Deposits reported to be exhausted.
South Africa - U from U deposits in PC quartz-South Africa - U from U deposits in PC quartz-pebble conglomerates of the Wits Basin. pebble conglomerates of the Wits Basin.
Uranium Resources of South Africa
First Uranium said it restarted its ‘Mine Waste Solutions’ facility in South Africa on Tuesday 02 August, after nuclear regulators suspended operations recently due to concerns about pipeline maintenance at the gold and uranium tailings reprocessing plant. The company said ‘last week’ that the suspension involved a pipeline used to pump tailings material, which has been reprocessed to extract gold and uranium, into a new tailings storage facility.
Potential negative impacts of uranium Potential negative impacts of uranium mining and millingmining and milling
Serious health risks due to exposure to gamma radiation and the Serious health risks due to exposure to gamma radiation and the inhalation of radon gas. This causes cancer. Radiation and inhalation of radon gas. This causes cancer. Radiation and radioactive radon gas can affect mineworkers as well as people radioactive radon gas can affect mineworkers as well as people living and working close to mining areas and roads that are used for living and working close to mining areas and roads that are used for transport of ores and yellow cake. transport of ores and yellow cake.
Destruction of the environment. An open-pit mine can be hundreds Destruction of the environment. An open-pit mine can be hundreds of meters wide and deep. As the name suggests, large pits will be of meters wide and deep. As the name suggests, large pits will be dug which can entail the destruction of local ecosystems. dug which can entail the destruction of local ecosystems.
Pollution of the environment with radioactive materials. Pollution of the environment with radioactive materials. Radioactivity, either in solid, liquid or gaseous state, is transported Radioactivity, either in solid, liquid or gaseous state, is transported by air, water and in soils and therefore negatively affects their by air, water and in soils and therefore negatively affects their quality. quality.
Water shortages. Uranium mining and milling needs the input of Water shortages. Uranium mining and milling needs the input of large quantities of fresh water. This can lead to water shortages in large quantities of fresh water. This can lead to water shortages in other sectors of society as in many places in Africa water supply is other sectors of society as in many places in Africa water supply is already problematic. already problematic.
Negative impacts of U mining and milling Negative impacts of U mining and milling (contd.)(contd.)
Waste rock. Waste-rock contains low grades of uranium which can be carried away Waste rock. Waste-rock contains low grades of uranium which can be carried away by the wind. by the wind.
Uranium mill tailings. Uranium mill tailings are normally dumped as a sludge in Uranium mill tailings. Uranium mill tailings are normally dumped as a sludge in special ponds or piles, where they are abandoned. The tailings still contain 85% of special ponds or piles, where they are abandoned. The tailings still contain 85% of the initial radioactivity of the original ore. Also, the sludge contains heavy metals and the initial radioactivity of the original ore. Also, the sludge contains heavy metals and other contaminants such as arsenic, as well as chemical reagents used during the other contaminants such as arsenic, as well as chemical reagents used during the milling process. Additionally, uranium mill tailings keep on emitting dangerous radon-milling process. Additionally, uranium mill tailings keep on emitting dangerous radon-222 gas for many years. The dangerous components of tailings are transported into 222 gas for many years. The dangerous components of tailings are transported into the environment by wind, erosion or dam failures. the environment by wind, erosion or dam failures. This happened, for example, in This happened, for example, in Zambia in 2006 where failure of a tailings slurry pipeline of a copper mine caused Zambia in 2006 where failure of a tailings slurry pipeline of a copper mine caused the contamination of a river that served as an important drinking water supply. the contamination of a river that served as an important drinking water supply.
Social impacts. Uranium mining can cause conflict. In Niger, an Areva base was Social impacts. Uranium mining can cause conflict. In Niger, an Areva base was attacked by dissatisfied Tuareg rebels. At the same time, Areva was accused by the attacked by dissatisfied Tuareg rebels. At the same time, Areva was accused by the Nigerian government of supporting Tuareg militia groups to deter competitors. Social Nigerian government of supporting Tuareg militia groups to deter competitors. Social conflict due to uranium mining can also be caused by the unequal distribution of conflict due to uranium mining can also be caused by the unequal distribution of mining profits and revenue. mining profits and revenue.
AMD ChemistryAMD Chemistry
The following are the equations that show the generalisedThe following are the equations that show the generalisedreaction pathway for pyrite to start to produce AMD:reaction pathway for pyrite to start to produce AMD: (1) 2FeS(1) 2FeS22 (s) + 7O (s) + 7O22 (g) +2H (g) +2H22O (l) →2FeO (l) →2Fe2+ 2+ (aq) + 4 SO(aq) + 4 SO44
2- 2- (aq) +(aq) +4H4H++ (aq) (aq)
(2) 4Fe(2) 4Fe2+ 2+ (aq) + O(aq) + O2 2 (g) + 4H(g) + 4H++ (aq) →4 Fe (aq) →4 Fe3+(3+(aq) + 2Haq) + 2H22O (l)O (l)
(3) 4Fe(3) 4Fe3+ 3+ (aq) + 12H(aq) + 12H22O (l) → 4Fe(OH)O (l) → 4Fe(OH)33 (s) + 12 H (s) + 12 H++ (aq) (aq)
(4) FeS(4) FeS22 (s) + 14 Fe (s) + 14 Fe3+ 3+ (aq) + 8H(aq) + 8H22O (l) → 15FeO (l) → 15Fe2+ 2+ (aq) + 2SO(aq) + 2SO442-2-(aq) (aq)
+ 16H+ 16H++(aq)(aq)
Pollutant PathwaysWe have identified SIX main pathways by which pollutants derived from natural processes of mineralization, or from mining and ore processing operations, can enter the human body:
* Through consumption of food crops having anomalous concentrations of elements derived from agricultural soils developed over mineralized bedrock;
* Consumption of food crops from soils contaminated by leachates, effluents and emissions from nearby mining sites, e.g., as in AMD;
* Consumption of water contaminated by AMD or by some other forms of mining waste;
* Inhalation of particulate matter / dust in the mining environment or from other industrial
sites;
* Direct dermal contact with ores and associated materials.
* Intake of contaminants through geophagic practices.
Treatment of acid mine drainage (AMD) Treatment of acid mine drainage (AMD)
Eutectic Freeze Crystallization (EFC) provides an alternative method for the treatment of hypersaline aqueous waste streams emanating from mining and other industrial operations. The process is capable of producing potable water, as well as pure salt(s), by operating at the eutectic point with lower energy consumption than evaporative crystallization.
EUTECTIC ICE CRYSTALLISATION
REVEGETATIONReplanting and re-building the soil of mined-out land.
• Establishing long-term plant communities requires forethought as to appropriate species for the climate, size of stock required, and impact of replanted vegetation on local fauna;
• The motivations behind revegetation are diverse, but it is usually erosion prevention that is the primary reason;
• Revegetation helps prevent soil erosion, enhances the ability of the soil to absorb more water in significant rain events, and in conjunction reduces turbidity dramatically in adjoining bodies of water;
* Revegetation also aids protection of engineered grades and other earthworks;
• Revegetation is often used to join up patches of natural habitat that have been lost, and can be a very important tool in places where much of the natural vegetation has been cleared.
Environmental monitors inspect revegetated growth on a rehabilitated site near Environmental monitors inspect revegetated growth on a rehabilitated site near Venetia mine, South AfricaVenetia mine, South Africa
Anglo Coal South Africa has an active land rehabilitation programme. Ecologist Johan van der Walt inspects a Anglo Coal South Africa has an active land rehabilitation programme. Ecologist Johan van der Walt inspects a rehabilitated pit area at Kriel colliery where grass species have started to diversify.rehabilitated pit area at Kriel colliery where grass species have started to diversify.
An environmentalist is studying natural biodiversity and indexing species for their importance in reforestation.
COMBATING SOIL EROSION FROM MINING
Soil erosion is perhaps the world’s most chronic environmental problem
that is literally costing the Earth. The soil it carries off now totals 20
billion tons a year and this loss is not only severely degrading the
environment, it is eroding the economic viability of countries. Despite
enormous effort, standard soil conservation methods have been largely
unsuccessful. However, a remarkable tropical grass may hold the key to
a cheap, practical solution for controlling soil erosion on a huge scale in
tropical and semi-arid regions. It also has many attributes that make it
useful to farmers. Vetiver (Vetiveria zizanoides) is a densely tufted,
perennial clump grass with stiff leaf bases which overlap.
HOW EFFECTIVE IS VETIVER IN CONTROLLING SOIL EROSION?
* This deeply rooted, persistent grass has restrained erodable soils for decades in India, the Caribbean and in Fiji, where its use was discovered by John Greenfield in the late 1950s;
* The key is to plant the grass as a hedge along the contour, preferably set out with the aid of a simple “A” frame, with a space of 10 cms between the grass slips;
* Vetiver grows to a height of around one metre but should be cut back to a planting height of 150 mm;
* The thatch can then be placed behind the newly planted slips to provide an instant filter to control run-off.
An African Baobab tree typical of those found in the area around Venetia Mine in South AfricaAn African Baobab tree typical of those found in the area around Venetia Mine in South Africa
The sustainable management of the natural environment is key to the future prosperity of the countries and communities in which we operate. By tackling environmental challenges in partnership with government, NGOs and our communities we can help build sustainable environments wherever we operate.
HYDROSEEDINGHYDROSEEDINGHydroseedingHydroseeding is the fastest, most cost effective is the fastest, most cost effective
and highest quality method of seeding vegetation, and highest quality method of seeding vegetation,
land rehabilitationland rehabilitation and erosion control practices. and erosion control practices.
Hydroseeding, also known as Hydroseeding, also known as hydromulchinghydromulching, is the, is the
process of combining seed, fibre mulch, fertilizer process of combining seed, fibre mulch, fertilizer
tackifiers, bonding agents and optional soil tackifiers, bonding agents and optional soil
amendments with water to mix in a amendments with water to mix in a HydroSeederHydroSeeder™™
tank to form thick slurry. This slurry is applied with tank to form thick slurry. This slurry is applied with
pressure via hose or tower onto the soil to create the pressure via hose or tower onto the soil to create the
ideal environment for seed germination and turf ideal environment for seed germination and turf
development. Vegetation establishes quickly providingdevelopment. Vegetation establishes quickly providing
uniform cover for uniform cover for erosion controlerosion control..
The nickel hyperaccumulator Berkheya coddii native to South Africa (Source: Anderson and Meech, 2002)
CONCLUSIONCONCLUSION
• Of all the advances that have been reported here today, I must say that Of all the advances that have been reported here today, I must say that serious challenges still remain, as rehabilitated land is not always serious challenges still remain, as rehabilitated land is not always returned to a land capability equivalent to its pre-mining state. This can returned to a land capability equivalent to its pre-mining state. This can only be achieved by careful management of soil resources, promotion of only be achieved by careful management of soil resources, promotion of biodiversity and management of latent risks post-closure.biodiversity and management of latent risks post-closure.
* According to Limpitlaw in South Africa (2005), to promote effective * According to Limpitlaw in South Africa (2005), to promote effective management of old mines, Government extension officers must become management of old mines, Government extension officers must become more involved with the stewardship of rehabilitated lands. This effort may more involved with the stewardship of rehabilitated lands. This effort may be bolstered by creating a system of tradable pollution permits whereby be bolstered by creating a system of tradable pollution permits whereby active mines could offset their pollution loads by participating in the active mines could offset their pollution loads by participating in the rehabilitation of abandoned mines, without assuming liability for those rehabilitation of abandoned mines, without assuming liability for those sites. sites.
* Ultimately, an integrated approach to closure planning is required whereby * Ultimately, an integrated approach to closure planning is required whereby joint action of stakeholders – mining companies, Governments and joint action of stakeholders – mining companies, Governments and communities – assume responsibility for the long term sustainability of communities – assume responsibility for the long term sustainability of closed mines.closed mines.
Goals of the GEM Working Group on “DUSTS”
The aim is to improve responses to emissions of dust and other particulates.
The objectives are to: a) review, collate and disseminate material on the existing understanding of the nature, behaviour and impacts of dust and particulates in the Earth system and to stimulate new investigations into associated under- researched areas; b) review existing legislation, regulation and management responses and to set out good practices in forms that can be readily appreciated and followed by administrators, land managers and the public; and c) to develop and disseminate innovative approaches to dealing with dust issues. The Group will organise conference sessions and aims to produce a book on emissions of dust from geological sources by 2013-2014.
GRN Cells in AfricaGRN Cells in Africa
ASSOCIATION OF APPLIED ASSOCIATION OF APPLIED GEOCHEMISTSGEOCHEMISTS
ABOUT THE ORGANIZATIONABOUT THE ORGANIZATION
Founded in 1970, the Association of Applied Founded in 1970, the Association of Applied Geochemists is an international organisation Geochemists is an international organisation specialising in the field of applied specialising in the field of applied geochemistry whose purpose is to: geochemistry whose purpose is to: * Advance the science of geochemistry as it * Advance the science of geochemistry as it relates to exploration and the environment relates to exploration and the environment * Facilitate the acquisition and distribution * Facilitate the acquisition and distribution of scientific knowledge of scientific knowledge* Promote exchange of scientific information * Promote exchange of scientific information * Encourage research and development * Encourage research and development * Sponsor symposia, seminars and technical * Sponsor symposia, seminars and technical meetings meetings * Support students in applied geochemistry * Support students in applied geochemistry
To achieve these goals, the Association of Applied Geochemists:
published the Journal of Geochemical Exploration from 1972 until 2000, and currently publishes GEOCHEMISTRY: Exploration, Environment, Analysis starting in 2001
publishes quarterly a newsletter, EXPLORE publishes in a digital format a bibliography of geochemically oriented
papers, now available to AAG Members on the ASSOCIATION OF APPLIED GEOCHEMISTS web page
holds biennial International Geochemical Exploration Symposia with associated field trips
holds regional meetings of specialised interest and co-sponsors meetings with other scientific societies
organises workshops and short courses supports a student paper prize supports a distinguished lecture series
IGCP/SIDA/UNESCO PROJECT 606UNIVEN PROJECT/SES/11/MEG/03 FUTURE PERSPECTIVES ????
Theme:“Together in Africa for a Leading
Role in Geosciences”
THANK YOUTHANK YOU
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