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Chapter 16 Geology and Nonrenewable Mineral Resources GEOLOGIC PROCESSES The earth is constantly changing as a result of processes taking place on and below its surface. The earth’s interior consists of: Core: innermost zone with solid inner core and molten outer core that is extremely hot. Mantle: solid rock with a rigid outer part (asthenosphere) that is melted pliable rock. Crust: Outermost zone which underlies the continents. Volcanoes Abyssal hills Oceanic crust (lithosphere) Abyssal Oceanic floor ridge Abyssal floor Trench Folded mountain belt Abyssal plain Craton Continental shelf Continental slope Continental rise Continental crust (lithosphere) Mantle (lithosphere) Fig. 15-2, p. 336 GEOLOGIC PROCESSES Huge volumes of heated and molten rock moving around the earth’s interior form massive solid plates that move extremely slowly across the earth’s surface. Tectonic plates: huge rigid plates that are moved with convection cells or currents by floating on magma or molten rock. The Earth’s Major Tectonic Plates Figure 15-4 The Earth’s Major Tectonic Plates The extremely slow movements of these plates cause them to grind into one another at convergent plate boundaries, move apart at divergent plate boundaries and slide past at transform plate boundaries. Figure 15-4 Fig. 15-4, p. 338 Trench Volcanic island arc Craton Transform fault Lithosphere Asthenosphere Divergent plate boundaries Lithosphere Rising magma Asthenosphere Convergent plate boundaries Lithosphere Asthenosphere Transform faults Fig. 15-4b, p. 338 GEOLOGIC PROCESSES The San Andreas Fault is an example of a transform fault. Figure 15-5 Wearing Down and Building Up the Earth’s Surface Weathering is an external process that wears the earth’s surface down. Figure 15-6 Parent material (rock) Biological weathering (tree roots and lichens) Chemical weathering (water, acids, and gases) Particles of parent material Physical weathering (wind, rain, thermal expansion and contraction, water freezing) Fig. 15-6, p. 340 What Are Resources? • An available supply that can be drawn upon as needed. – Hardin “Tragedy of the Commons” – Conservation – management/regulation of a resource so that it does not exceed the capacity to regenerate itself. • Natural Resources – Ecosystems (biotic and abiotic) – in terms of ecosystem or “natural” capital. Renewable vs. Nonrenewable • Renewable – Sun, plants, animals – Can be regenerated quickly • Nonrenewable – minerals, fossil fuels, and soil. – Formed slowly by geologic processes. – Cannot be regenerated quickly. MINERALS, ROCKS, AND THE ROCK CYCLE The earth’s crust consists of solid inorganic elements and compounds called minerals that can sometimes be used as resources. Mineral resource: is a concentration of naturally occurring material in or on the earth’s crust that can be extracted and processed into useful materials at an affordable cost. General Classification of Nonrenewable Mineral Resources The U.S. Geological Survey classifies mineral resources into four major categories: Identified: known location, quantity, and quality or existence known based on direct evidence and measurements. Undiscovered: potential supplies that are assumed to exist. Reserves: identified resources that can be extracted profitably. Other: undiscovered or identified resources not classified as reserves GEOLOGIC PROCESSES Deposits of nonrenewable mineral resources in the earth’s crust vary in their abundance and distribution. A very slow chemical cycle recycles three types of rock found in the earth’s crust: Sedimentary rock (sandstone, limestone). Metamorphic rock (slate, marble, quartzite). Igneous rock (granite, pumice, basalt). Erosion Transportation Weathering Deposition Igneous rock Granite, pumice, basalt Sedimentary rock Sandstone, limestone Heat, pressure Cooling Heat, pressure, stress Magma (molten rock) Melting Metamorphic rock Slate, marble, gneiss, quartzite Fig. 15-8, p. 343 ENVIRONMENTAL EFFECTS OF USING MINERAL RESOURCES The extraction, processing, and use of mineral resources has a large environmental impact. Figure 15-9 Surface mining Metal ore Separation of ore from gangue Smelting Recycling Melting metal Conversion to product Discarding of product (scattered in environment) Fig. 15-9, p. 344 Mining – Excavation of earth for the purpose of extracting ore or minerals • Metallic Minerals – mined for metals (Zn) which can be extracted through smelting. • Nonmetallic Minerals – mined to be used in their natural state (salt, gems). • Mineral Deposit – area in which a particular mineral is concentrated • Ore - rock or mineral from which a valuable substance can be extracted for a profit Natural Capital Degradation Extracting, Processing, and Using Nonrenewable Mineral and Energy Resources Steps Environmental effects Mining Disturbed land; mining accidents; health hazards, mine waste dumping, oil spills and blowouts; noise; ugliness; heat Exploration, extraction Processing Use Solid wastes; radioactive material; air, water, and soil pollution; noise; safety and health hazards; ugliness; heat Transportation or transmission to individual user, eventual use, and discarding Noise; ugliness; thermal water pollution; pollution of air, water, and soil; solid and radioactive wastes; safety and health hazards; heat Transportation, purification, manufacturing Fig. 15-10, p. 344 Types of Metals • Abundant Metals: concentration >0.1% in the earth’s crust – Iron, Aluminum, Silicon, Magnesium, Titatnium, Manganese • Scarce Metals: <0.01% in the crust – – – – Ferro-alloys: Nickel, Chromium Base Metals: Copper, Lead, Zinc Precious or Noble Metals: Gold, Silver, Platinum Special Metals: Gallium, Arsenic, Germanium, Rare earths, Berrylium, Scandium etc.. Highly Uneven Distribution S Africa Chile 50% Gold 75% Chromium 90% Platinum Group 50% Molybdenum 15% Lead 30% Copper Cuba 40% Nickel Guinea and Australia 25% each of Aluminum Zaire 50% cobalt USA Mineral Supply and Demand • World Scenario: – Assumptions: • Present demand = present production • Future projection is based on constant 1995 figures • Unrestricted distribution – Iron, Aluminum, Chromium, Cobalt and Platinum will last centuries – Copper, Lead, Zinc, Gold and Silver will last several decades only – Ditto for phosphates and sulfur • Alleviating Factors: – More exploration – Better technology – Reclassification of sub-economic resources to reserve Reduce Consumption? – New technology adds to the existing needs e.g., cellular phones, computers, microwave oven – In the US, population grew by 65% and consumption grew by 130% between 19501990 – Great demand for resources in the developing countries where there is a genuine need and where the great majority lives • If demand cannot be reduced, supplies must be increased or extended Conservation - Recycling – In USA 60% of lead, 40% of copper, 1/3rd of nickel and almost ¼ of Al, Cr, Co and Zn is recycled – Recycled Al requires 20 times less energy than new Al – Difficult to do with finished products like cars or fridges – Special problem with alloys – Road salt, fertilizers, lead in gasoline gets too disperse – Reduces waste disposal problem Metals are emitted in air during… Mining, smelting, refining, Manufacturing and Recycling Air emissions are mostly particulates Particulates fall out by gravity or wash out by rain Soil Vegetation Water Impact of Mining Activities Mining Hazards • Most hazardous activity in the US: Activity Mining Deaths per 100,000 workers (1989) 43 Agriculture 40 Construction 32 Life Cycle of a Metal Resource Surface mining Metal ore Separation of ore from gangue Smelting Melting metal Conversion to product Recycling Smelting – heating to release metals but creating air polluting byproducts Chemical removal processes such as using cyanide to remove gold can create Toxic holding ponds Discarding of product Surface Mines • Open pit mines – Where large 3D ore body lies close to the surface – Leaves a large exposed hole on the surface – Exposed rocks prone to weathering and polluting • Strip mines – Mostly for coal where minerals occur in layers paralleling the surface – Waste rocks dumped back as spoil banks – Newer regulations require reclamation involving grading, restoring, and replanting – Can cause changes in topography and drainage Extracting Mineral Deposits • Surface mining - shallow deposits in US extracts 90% of non-fuel minerals and rocks and 60% of the coal. – Overburden – soil and rock overlying deposit. – Spoils – discarded overburden Open-pit Mining Area Strip Mining Mountaintop Removal Figure Extracting Mineral Deposits • Subsurface (Shaft) mining - deposits that are too deep for surface mining – Disturbs less – produces less waste – but also less effective – dangerous. Underground Mines • Generally less disruptive than surface mines • Tunnels closely follow the ore body • Some waste rock on the surface • Shallow abandoned mines can cause collapse Sources of Metal Pollution • Mining – Air – Water – Land • Fossil Fuel Combustion – Air – Water – Land Harmful Environmental Effects of Mining • Acid Mine Drainage (AMD) • Heavy Metal Contamination • Processing chemical pollution • Erosion and Sedimentation 99 tons of waste for every ton of Copper Acid Mine Drainage (AMD) – Sulfur in ores react with water and oxygen to form sulfuric acid which leaks out from the mine • Bacteria in acid water hastens the process – Acid is carried off the mine site by rainwater or surface drainage and deposited into nearby streams, rivers, lakes and groundwater. AMD severely degrades water quality, and can kill aquatic life and make water virtually unusable. Acid Mine Drainage Heavy Metal Contamination & Leaching • Heavy metal pollution is caused when such metals as arsenic, cobalt, copper, cadmium, lead, silver and zinc contained in excavated rock or exposed in an underground mine come in contact with water. – Metals are leached out and carried downstream as water washes over the rock surface. – leaching is particularly accelerated in the low pH conditions such as are created by Acid Mine Drainage. 3. Processing Chemicals Pollution – occurs when chemical agents (such as cyanide or sulphuric acid used by mining companies to separate the target mineral from the ore) spill, leak, or leach from the mine site into nearby water bodies. • These chemicals can be highly toxic to humans and wildlife. 4. Erosion and Sedimentation – erosion of the exposed earth may carry substantial amounts of sediment into streams, rivers and lakes. – Excessive sediment can clog riverbeds and smother watershed vegetation, wildlife habitat and aquatic organisms. Mineral Processing • Crushing of ores produces tailings (waste) • Traces of pollutants like mercury, arsenic, cadmium and uranium may leach out of tailings and contaminate groundwater and landfills • Processing chemicals (e.g., Cyanide) are major hazards • Smelting releases toxic elements, SO2 etc and causes acid rain which can destroy vegetation Four PBT Metals • • • • • PBT: Persistent, Bio-accumulative, Toxic Lead Mercury Cadmium Arsenic Lead; Adverse Effects • Affects Nervous system of human fetus and small children • Most of the lead is stored in bones and along with Calcium, is released in mother’s milk • Affects IQ, causes delinquency, kidney cancer • In adults: affects nervous system and kidney, anemia, infertility Sources of Lead • Similar to other metals: mining, smelting, coal burning power plants, incinerators • Lead paints , lead contaminated soil, plumbing – affects children in poorer households – Made worse by poor diet low in Ca and Fe • For people living in Lead free environment: – Food is the major source Sources of Lead • Gasoline – Lead level in exhausts fell 90% after banning of lead in gasoline – the substitute, Benzene, is carcinogen – Lead in the blood of Children fell to 4 -6 microgram/lt (threshold: 10 micrograms/lt) – Major problem now in China • The following are banned: – Lead in gasoline, in paint, in printing ink, in solders in plumbing and cans, in sealing wine bottles, in toys – Imported products can still have lead – Car batteries still contain lead Mercury • Much of the mercury in the environment originates as mercury vapor from coal burning power plants and incinerators (2-3000 tons) and from natural sources (2700 to 6000 tons) • Elemental Mercury not as injurious as methylmercury • Most of the mercury ends up in the ocean where bacteria in the bottom sediments convert elemental mercury to methylmercury • Methylmercury biomagnifies up the food chain – Some game fish has Hg conc. 200,000 X that of surrounding water – Can cause problems to humans eating these fish, particularly among children, old people and pregnant women Adverse effects of Mercury • 95% of the exposure comes from eating contaminated fish. • Toxic to nervous system • Minamata Tragedy: – Chisso Corp discharged mercury in Minamata bay from 1930 – Biomagnification in Fish upto 40 ppm (0.5 ppm safe limit) – 200,000 people were poisoned – Chronic nervous system damage, miscarriages, deformed fetus – Settled in 1996 after 30 years of litigation Reducing Risk from Mercury • Regulations: EPA has set standards for drinking water, air-emissions and is tackling the biggest source: coal burning power plants • Reduce workplace exposure • Reduce or eliminate mercury containing products: – – – – In rechargeable batteries and button cells Remove batteries from municipal solid waste Green Lights program: Hg free fluorescent light Phase out mercury from hospital and lab products Cadmium • • • • • Discovered in 1817, heavily mined since mid-40s Bioaccumulates in kidney – increases with age Itai-itai disease among older women in Japan Cancer, birth defects in rats Sources: – – – – Mining and smelting of Zn, Pb, Cu Coal burning Phosphatic fertilizers, sewage sludge Nicad batteries: a major source in Municipal Solid Waste Cadmium… • 90% of the exposure (of non-smokers) is through food – Fish, scallops and oysters – Liver and kidneys of larger animals : beef, venison – Readily taken up by plants – concentrated in Tobaccos. 90% of inhaled Cd is absorbed by the body • Control: EPA regulations • Power plants still not controlled • Nicad batteries still a major problem Arsenic • • • • Metal smelting of Copper and Lead Used to be common weed killer Emitted by volcanoes Naturally present in soil – Major environmental problem in Bangladesh • Level in seafoods higher than in land-grown food. • Much of the Arsenic in Food is not bioavailable • CCA (Chromated Copper Arsenate) used to treat wood including playground equipments – can contaminate soil SUPPLIES OF MINERAL RESOURCES Depletion curves for a renewable resource using three sets of assumptions. Dashed vertical lines represent times when 80% depletion occurs. Figure 15-16 Production A Mine, use, throw away; no new discoveries; rising prices Recycle; increase reserves by improved mining technology, higher prices, and new discoveries B Recycle, reuse, reduce consumption; increase reserves by improved mining technology, higher prices, and new discoveries C Present Depletion Depletion Depletion time A time B time C Time Fig. 15-16, p. 348 SUPPLIES OF MINERAL RESOURCES New technologies can increase the mining of low-grade ores at affordable prices, but harmful environmental effects can limit this approach. Most minerals in seawater and on the deep ocean floor cost too much to extract, and there are squabbles over who owns them. Getting More Minerals from the Ocean Hydrothermal deposits form when mineral-rich superheated water shoots out of vents in solidified magma on the ocean floor. Figure 15-17 Black smoker White smoker Sulfide deposits Magma White crab White clam Tube worms Fig. 15-17, p. 350 USING MINERAL RESOURCES MORE SUSTAINABLY Scientists and engineers are developing new types of materials as substitutes for many metals. Recycling valuable and scarce metals saves money and has a lower environmental impact then mining and extracting them from their ores. Solutions Sustainable Use of Nonrenewable Minerals • Do not waste mineral resources. • Recycle and reuse 60–80% of mineral resources. • Include the harmful environmental costs of mining and processing minerals in the prices of items (full-cost pricing). • Reduce subsidies for mining mineral resources. • Increase subsidies for recycling, reuse, and finding less environmentally harmful substitutes. • Redesign manufacturing processes to use less mineral resources and to produce less pollution and waste. • Have the mineral-based wastes of one manufacturing process become the raw materials for other processes. • Sell services instead of things. • Slow population growth. Fig. 15-18, p. 351 Case Study: The Ecoindustrial Revolution Growing signs point to an ecoindustrial revolution taking place over the next 50 years. The goal is to redesign industrial manufacturing processes to mimic how nature deals with wastes. Industries can interact in complex resource exchange webs in which wastes from manufacturer become raw materials for another. Sludge Pharmaceutical plant Sludge Greenhouses Waste heat Fish farming Waste heat Oil refinery Surplus sulfur Local farmers Surplus Electric power natural gas plant Waste calcium sulfate Cement manufacturer Sulfuric acid producer Wallboard factory Area homes Fig. 15-19, p. 352