Recent Advances in Mitigation and Rehabilitation Technology in Major and Abandoned Mines in Sub-Saharan Africa T. C. Davies Department of Mining and Environmental Geology University of Venda Private Bag X 5050 Thohoyandou Limpopo Province Republic of South Africa theo. clavellpr 3@gmail. com
PROJECT DESCRIPTION IGCP/SIDA/UNESCO/UNIVEN/KNUST Project No. 606 researches on improvements in mitigation and rehabilitation strategies for environmental health impacts of major and abandoned mines in Sub. Saharan Africa, as well as assess the current status of research in pollution control technology. This year, we have put the focus on ‘small scale mining’ because of the tremendous contribution this kind of mining makes towards improving the lives and livelihoods of millions of Sub-Saharan Africans. A major scientific goal of the project is to identify ways by which process optimisation for profitability can be carried out sustainably, while at the same time ensuring minimum amount of negative environmental health consequences, and the general preservation of ecosystem integrity.
PROJECT SYNTHESIS * Impacts due to mining methods and mineral processing operations; * Dangers posed by abandoned mines; * What do we know about the relationship between mining, the fecundity of cultivable lands in the vicinity of mines, and environmental health? * Addressing the issues
Abandoned Mines § Abandoned mines in Sub-Saharan Africa are often dangerous and can contain deadly gases such as radon and methane. Standing water in mines from seepage or infiltration, poses a significant hazard as the water can conceal deep pits and trap gases below the water. Old mine workings and caves are sometimes hazardous, simply due to the lack of oxygen in the air.
Mining impacts The mining industry is undoubtedly of major importance to Sub-Saharan Africa’s economic well -being. However, mining methods and mineral processing operations are known to be associated with diverse and often profound chemical and physical impacts on miners and adjacent communities, as well as on other elements of the surrounding ecosystems. Mining in some quarters have accelerated soil erosion rates, which is a bane to agriculture; metals and toxins are often mobilised far beyond natural rates, and natural water resources are sometimes polluted beyond measure. Accidents - deaths? ? ?
WHAT DO WE KNOW SO FAR? We need to define clearly the boundaries of our present understanding of the relationship between environmental health and mining and mineral processing, investigate new discoveries in relations between them, and study much more deeply, geochemical interactions at tailings sites (e. g. , the dreaded acid mine drainage (AMD)), and wastewater courses and effects on agriculture.
SPECIFIC AIMS AND OBJECTIVES OF PROJECT 606 § Promoting and expediting the work of an § § ‘African Network of Earth Scientists’ researching the environmental health impacts of mining and ore processing activities, and seeking the best ways of addressing them; Compiling a complete inventory and database of abandoned and derelict mines in sub. Saharan Africa; Preparing a comprehensive documentation embodying research activities on the following 5 themes:
Theme 1 § Bridging knowledge gaps, and specifically assessing the rate of migration and distribution pathways of selected heavy metals known to be toxic, from tailings dams and mine spoils accumulated during several years of mining in Sub-Saharan Africa;
Theme 2 § Monitoring heavy metal concentrations in agricultural soils in the vicinity of major and abandoned mines in order to indicate the status of heavy metal contamination (PHEs), and assess environmental quality of these soils;
Theme 3 §Providing practical solutions to problems of metal contamination and the recommendations for improved land remediation strategies (rehabilitation technology);
Theme 4 §Assessing long-term impacts of mining on public health and the environment, and recommendation of strategies for protecting the health of our communities;
Theme 5 § Providing support to governments of Sub-Saharan African countries in developing their national strategic plans to combat the public health and environmental effects posed by abandoned mines (other organs of dissemination).
ADDRESSING THE ISSUES § Only then would we be able to properly address environmental health issues pertaining to the mining industry, point out the way forward in improvement of mitigation and rehabilitation strategies, and direct new research in the most fruitful directions.
PHYSICAL REHABILITATION Modern mine rehabilitation aims to minimise and mitigate the environmental effects of modern mining, which may in the case of open pit mining, involve movement of significant volumes of rock. Rehabilitation management is an ongoing process, often resulting in open pit mines being backfilled. 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 Killer § Uranium mining - extraction of U ore from the ground § Low concentrations, means U mining very volume-intensive § Undertaken as open-pit mining § Main use, as fuel for nuclear power plants § Uranium ore emits radon gas; odourless, colourless § Inadequate ventilation systems § Radon, a cancer-causing agent (small cell carcinoma) § Radioactive contamination of air, water and soil (radioactive dust/contaminated groundwater)
Uranium Producing Countries § Niger - Africa’s leading U producing nation (US invasion of Iraq) § Namibia - produces U at Rossing, where an igneous deposit is mined from one of the World’s largest open pit mines. § Gabon - Deposits reported to be exhausted. § South Africa - U from U deposits in PC quartzpebble 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 mining and milling § Serious health risks due to exposure to gamma radiation and the § § § inhalation of radon gas. This causes cancer. Radiation and radioactive radon gas can affect mineworkers as well as people living and working close to mining areas and roads that are used for transport of ores and yellow cake. Destruction of the environment. An open-pit mine can be hundreds of meters wide and deep. As the name suggests, large pits will be dug which can entail the destruction of local ecosystems. Pollution of the environment with radioactive materials. Radioactivity, either in solid, liquid or gaseous state, is transported by air, water and in soils and therefore negatively affects their quality. Water shortages. Uranium mining and milling needs the input of 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 already problematic.
Negative impacts of U mining and milling (contd. ) § Waste rock. Waste-rock contains low grades of uranium which can be carried away by the wind. § Uranium mill tailings are normally dumped as a sludge in 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 other contaminants such as arsenic, as well as chemical reagents used during the milling process. Additionally, uranium mill tailings keep on emitting dangerous radon-222 gas for many years. The dangerous components of tailings are transported into the environment by wind, erosion or dam failures. This happened, for example, in 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. § 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 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 mining profits and revenue.
AMD Chemistry The following are the equations that show the generalised reaction pathway for pyrite to start to produce AMD: (1) 2 Fe. S 2 (s) + 7 O 2 (g) +2 H 2 O (l) → 2 Fe 2+ (aq) + 4 SO 42 - (aq) + 4 H+ (aq) (2) 4 Fe 2+ (aq) + O 2 (g) + 4 H+ (aq) → 4 Fe 3+(aq) + 2 H 2 O (l) (3) 4 Fe 3+ (aq) + 12 H 2 O (l) → 4 Fe(OH)3 (s) + 12 H+ (aq) (4) Fe. S 2 (s) + 14 Fe 3+ (aq) + 8 H 2 O (l) → 15 Fe 2+ (aq) + 2 SO 42 -(aq) + 16 H+(aq)
Pollutant Pathways We 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) AMD is highly acidic water, usually containing high concentrations of metals, sulphides, and salts as a consequence of mining activity. The potential volume of AMD for the Witwatersrand Goldfield alone amounts to an estimated 350 ML/day (1 ML = 1000 m 3). This represents 10% of the potable water supplied daily by Rand Water to municipal authorities for urban distribution in Gauteng province and surrounding areas, at a cost of R 3000/ML. In his Budget Speech to Parliament in Cape Town in February this year, Finance Minister Pravin Gordhan allocated R 3. 6 -billion for water infrastructure and services in 2011/12, "including funding for the acid water drainage threat associated with abandoned underground mines”. There is still a tremendous need for further technical research and innovation in the treatment of AMD, to enable cost-effective treatment of the range of AMD waters present in South Africa. Integrated solutions would be supported through improved links between universities, research organisations and the international research community.
EUTECTIC ICE CRYSTALLISATION 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
REVEGETATION Replanting 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 Venetia mine, South Africa
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. 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 1950 s; * 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 Africa sustainable management of the natural environment is key to the future prosperity of the ntries and communities in which we operate. By tackling environmental challenges in nership with government, NGOs and our communities we can help build sustainable ronments wherever we operate.
HYDROSEEDING Hydroseeding is the fastest, most cost effective and highest quality method of seeding vegetation, land rehabilitation and erosion control practices. Hydroseeding, also known as hydromulching, is the process of combining seed, fibre mulch, fertilizer tackifiers, bonding agents and optional soil amendments with water to mix in a Hydro. Seeder™ tank to form thick slurry. This slurry is applied with pressure via hose or tower onto the soil to create the ideal environment for seed germination and turf development. Vegetation establishes quickly providing uniform cover for erosion control.
The nickel hyperaccumulator Berkheya coddii native to South Africa (Source: Anderson and Meech, 2002)
CONCLUSION • Of all the advances that have been reported here today, I must say that serious challenges still remain, as rehabilitated land is not always returned to a land capability equivalent to its pre-mining state. This can only be achieved by careful management of soil resources, promotion of biodiversity and management of latent risks post-closure. § * According to Limpitlaw in South Africa (2005), to promote effective management of old mines, Government extension officers must become more involved with the stewardship of rehabilitated lands. This effort may be bolstered by creating a system of tradable pollution permits whereby active mines could offset their pollution loads by participating in the rehabilitation of abandoned mines, without assuming liability for those sites. § * Ultimately, an integrated approach to closure planning is required whereby joint action of stakeholders – mining companies, Governments and communities – assume responsibility for the long term sustainability of 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 Africa
ASSOCIATION OF APPLIED GEOCHEMISTS ABOUT THE ORGANIZATION Founded in 1970, the Association of Applied Geochemists is an international organisation specialising in the field of applied geochemistry whose purpose is to: * Advance the science of geochemistry as it relates to exploration and the environment * Facilitate the acquisition and distribution of scientific knowledge * Promote exchange of scientific information * Encourage research and development * Sponsor symposia, seminars and technical meetings * 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 606 UNIVEN PROJECT/SES/11/MEG/03 FUTURE PERSPECTIVES ? ?
Theme: “Together in Africa for a Leading Role in Geosciences” THANK YOU 58
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