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Mineral Processing Lecture 2 – Mining 1st half:
Different stages of a mining project Different types of mining 2nd half: Copper mining Flow sheets
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Australian Minerals Industry
Mining Cycle Australian Minerals Industry The minerals and energy resources is a major contributor to the Australian economy iron, alumina, coal and copper are the biggest resources WA and QLD most resource-rich states Benefits of the resource sector: Exports Gross domestic product (GDP) Employment Government revenue Investment Regional and rural development Technology advances 30% of Australia's commodity exports Occupies 0.5% of Australia's land mass
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Mining Cycle Mining Cycle
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Exploration Exploration
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Exploration and Assessment
Geoscientists Geochemists assess rock and water samples Geophysicists determine size, quality and shape of deposit by drilling, satellite images and aerial surveys All factors are taken into to account when deciding whether a mineral deposit will be mined; mainly economic feasibility Core samples Determine the level of mineralisation Assess the value of soil; revegetation Exploration Mine site planning and construction Feasibility studies – structural geology Reserve and resource estimates Operation Open pit mining volumes Volumetric change calculations in leach pads and stockpiles Measuring and monitoring tailings
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Assessment based on ore type
Ore and ore bodies are classified by: Ore characteristics – chemical and mineralogical composition and physical attributes (texture, mineral associations, purity of minerals, hardness and porosity) Waste characteristics – chemical and mineralogical composition and physical attributes Ore body characteristics – physical morphology of the ore body including seam thickness, floor conditions, depth underground (if applicable), dip, faulting and dykes/intrusions Operations These characteristics are considered when selecting mining and processing equipment and processes.
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Assessment based on ore type
Ore body morphology The ore body influences the type of mining Vein-type: narrow and irregular Massive: irregular shape Tabular: flat or gently dipping Disseminated: fine grains in vast areas Determines the type of mine Operations The ore
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Process costs to be considered
Key drivers: Maximum return on process outputs Minimum operation costs Operations Maximising returns Minimising costs ↑ production rate ↓ labour costs ↑ process availability ↓ power costs ↑ process recovery ↓ use of consumable ↑ grade ↓ maintenance costs ↓ recovery of penalty metals
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Process costs to be considered
Revenge (R) Sum of all payments received for products and by-products Metal price paid for a product depends on its purity and form Undesirable elements can attract penalties Investment costs (I) Everything that must be bought and built to enable a plant to start Production costs (P) Sum of direct operating costs (DOC) and capital charges (CC) Annual Rate of Return (ROR) Ratio of annual profit (R – P) to investment costs (I) Not constant over the life of the project Can make process viable Environmental impact studies, site prep, buildings, processing plant, power lines, road, dams, Raw materials, energy, labour, testing, etc Process costs Interest payments, repayments, depreciation, etc
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Process costs to be considered
Investment cost Revenue Pre-commissioning, training, initial production Production cost Revenue exceeds production capital is required to cover costs of the plant and its construction Process costs Revenue is being generated PROFIT Investment paid off cumulative cash flow time = mean annual return
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Location, Utilities and Services
Ore body is geographically fixed Comminution is typically completed on site to reduce transportation costs Proximity to markets and ports Selling Purchasing of consumables If transport infrastructure is not available it will need to be built and is a capital investment Utilities: electricity Remote areas - typically the processing plant would have to generate its own power electric has the highest investment costs and potential – costs less to maintain per unit energy – potential supply issues oil and gas lowest investment costs – stored on site solid fuel is in-between – stored on site Utilities: water Collecting, sorting and distributing water in arid areas can be very expensive Maintenance of water quality Water treatment plant potentially required for recycling Process costs
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Regulations and Approvals
Environmental Protection Act covers all mining activities that disturb the natural land surface Local, State and Federal regulations must be abided by for the following: Land use Clean air Noise abatement Management of wastes Fauna and flora conservation Extensive and detailed plans need to be submitted on: Nature and impact of all stages of the mine cycle How these impacts will be managed Environmental Management Plan Environmental Impact Statement Plan of Operation Regulations Planning requirements
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Surface mining Design mining layout and blasts Probe drilling
Grade control drilling Operations Blasting Charging Production drilling Clearing the blast Marking the ore Clean-up Drop off Digging
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Surface mining Mountain top removal
Ore body located in the upper regions of the mountain Draglines push waste rock into the valleys below Operations
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Surface mining Strip mining ore body is near the surface
removes long strips of overlying soil and rock to expose ore – typically coal Operations
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Surface mining Open-pit mining
ore body is further below the surface and once the ore is extracted a crater-like hole remains utilizes blasting and mineral removing Operations
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Each step down is known as a bench
Surface mining Open pit mining Most economical for highly disseminated ores at shallow depths (up to about 50m) Involves excavation of overburden material in single and/or successive benches More cost effective than underground mining due to larger excavation equipment being used Lower grade ores can be mined However, there is a balance between how much waste rock and valuable mineral should be mined – strip ratio Operations Each step down is known as a bench
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Surface mining Strip ratio
Greatest amount of waste is generated for the 1st bench and decreases steadily with each successive bench within the deposit Waste (tonnes) Ore (tonnes) Strip ratio = Operations Example: What is the strip ratio if 10,001,999 tonnes of waste is produce for every 2,000,000 tonnes of ore? 10,101,999 2,000,000 Strip ratio = = 5.05 Why does it decrease with each successive bench? What is the greatest problem for high stripping ratios?
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Surface mining Alters the landscape – reducing the value of the natural environment Reclamation isn’t equal to original use: Eliminates existing vegetation Destroys the genetic soil profile Displaces or destroys wildlife and habitat Alters current land uses (e.g. farming) Changes the topography of the area mined Operations Environmental impacts: Water Land Wildlife Victor Mine – Canada
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Underground mining Underground mining
Ore body is too deep to be economically or technically viable for open-pit mining – more selective More complicated than open-pit as ventilation, blasting underground and stabilisation are much more complicated and risky Dependent on the geometry, ground support, shaft location and logistics Operations Stopes – large openings of ore connected to tunnels Drifts – horizontal passages Ore passes – vertical chutes Ramps – spiral or inclined drifts Levels – horizontal workings with a shaft station Waste rock is placed back in stopes to provide support for overlying rock.; prevent cave-ins
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Underground mining Underground mining Benefits include:
More selective than open-pit Higher grade ores are extracted due to greater heat and pressures the further down the deposit is located Lower quantities of waste rock is generated as it is used to re-fill stopes to stabilise the mine Disadvantages: Costly Additional health and safety requirements, e.g. ventilation, mine collapse Land subsidence Flooding → ground water contamination Operations
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Overview of a mineral processing circuit
Waste rock Mine Waste rock pile CLOSED CIRCUIT ROM Crushing Wastewater Oversize Screening FRONT END OPERATION Water Undersize Recycled water Grinding Oversize Classification Undersize Tailings management facility Water and Reagents Separation Tailings Wastewater Dewatering BACK END OPERATION Concentrate Waste water
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Comminution Comminution - reduction of particle size to liberate the valuable mineral 1. Blasting 2. Crushing Operations Basic crushing and grinding circuit 3. Grinding Ball mill
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Screens – coarse particles
Sieving – Coarse particles A screening machine consist of a drive that induces a vibration in a mesh with known apertures that allows particles to pass through Ideal screening has a monolayer of a mixture of particle sizes on the screen surface so that every particle has the chance to pass or be retained Operations
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Classification – fine particles
Cyclone – Fine particles Separates particles in a liquid suspension based on the ratio of their centripetal force to fluid resistance ratio is high for dense and coarse particles ratio is low for light and fine particles Operations
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Mineral separation processes
Beneficiation (enrichment) – separation of valuable mineral from gangue material to produce a concentrate Flotation Gravity separation Magnetic separation Electrostatic separation Specific gravity Operations Surface chemistry Magnetic
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Dewatering processes Dewatering – separation of solid and liquid to remove and recover water. Necessary because: Downstream process streams require drier products Tailings management and discharge water quality Reduce water consumption and discharge amounts Essential in dry environments Operations Thickeners are large diameter cones which accelerate settling of solids. Classified into 4 groups: Screens Gravity separation or sedimentation Filtration Thermal drying The type of method used depends on the particle size and slurry %.
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Dewatering processes Above the line: Liquid handling characteristics
Below the line: Solids handling characteristics Thickeners Operations Sedimentation classifiers Vacuum filters Vibrating screens Moisture content % Solid bowl centrifuge Vib. screen Basket centrifuge Thermal drying Particle size (mm)
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Metal separation processes
Extractive metallurgy – separation of valuable metals from mineral concentrates: Hydrometallurgy Electrometallurgy Pyrometallurgy Electrometallurgy Operations Hydrometallurgy Pyrometallurgy
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Mining Wastes Mining Wastes Waste rock:
Unprocessed waste typically created during comminution. Contains non-valuable material and is used in the construction of tailings dams. Reclamation Tailings dams Processed waste generated during beneficiation. Fines of non-valuable material associated with chemical mixtures used to concentrate the valuable mineral.
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Circuit flowsheet Copper mining
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Remove equipment and structures Stabilise waste piles
Mine Closure There are 3 objectives: Remove equipment and structures Stabilise waste piles Control the spread of pollutants Each mine site is unique and demands a unique closure plan and approach. Closure Number of reasons for closure: Economic Social/community pressures Geologic Technical Closure of downstream industries Regulatory Policy changes Flooding of the mine
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Interim mine closure (design and operate for closure)
Types of closure: Interim mine closure (design and operate for closure) Rehabilitate on the go Seldom used as decreases profits → most defer costs of closure to the end Temporary mine closure Strike Economic crashes Metal price or ore grade fluctuations Premature mine closure (unplanned and permanent) Regulatory breaches or change in government Extreme damages – collapse, flood, fire Closure at the end of mine life Closure May reopen if metal prices increase or exploration leads to new deposits.
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Constructive interaction with the community
Mine Closure Closure plan: Orderly reduction of staff to meet the reducing and changing needs for mining, processing, monitoring and construction of closure works Constructive interaction with the community Calm and professional interaction with the regulators who have approved original plans Adequate money available to close the mine Closure
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Reclamation and Rehabilitation
Land rehabilitation is the process of returning land to some degree of its former state. Aims to minimise and mitigate the environmental effects and is performed during or at the end of the mine cycle. Waste dumps: are contoured to suit natural land features to reduce erosion Sulphide wastes: are usually covered with a layer of clay to prevent access atmospheric conditions that result in oxidation - minimise sulphuric acid production. Landfills: are covered with topsoil and vegetation. Open pits: eventually fills up with groundwater and may require treatment if it turns acidic. Tailing dams: are left to evaporate and then covered with waste rock, clay, soil and vegetation. Reclamation
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