Soils and Minerals
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Transcript of Soils and Minerals
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SOILS AND MINERALS
Unit 5
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What is soil? Relatively thin surface layer of the Earth’s crust Consists of mineral and organic matter that has
been modified by natural actions of agents such as weather, wind, water, and organisms
VERY important many organisms live there and terrestrial plants could not survive without it
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How is soil formed? From parent material (usually rock) that is
slowly fragmented (broken down) into smaller and smaller particles
Weathering processes = biological, chemical, or physical processes that break down rocks can take a very long time, sometimes thousands of years
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What affects weathering processes? Organisms = Plant roots, insects,
bacteria, etc.Respiration produces CO2, which diffuses
into the soil and reacts with soil water to form carbonic acid (H2CO3)
Other acids form cracks in rock, which fill with water freezing and thawing
Climate = precipitation, temperature (freezing and thawing), wind currents, etc.
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Topography A region’s surface features mountains,
valleys, etc. Steeper slopes have little or no soil on
them, more runoff, and more erosion Moderate slopes and valleys tend to
have deep soils
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Typical Soil Composition 45% mineral particles – from weathered
rock 5% organic matter 25% water 25% air
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Terms to know… Humus = Partly decomposed organic
material in the soil; brown or black in color
Leaching = Movement of water and dissolved material downward through the soil
Illuviation = Deposition of a material into a lower soil layer from a higher layer as a result of leaching
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Terms to know… Sand = Large (0.05 – 2 mm in diameter) inorganic
particles in the soil; coarse enough to feel gritty Silt = Medium sized (0.002 – 0.05 mm in diameter)
inorganic particles in the soil; too small to feel gritty Clay = Small (<0.002 mm in diameter) inorganic
partilces in the soil; too small to settle out of suspension
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Terms to know… Soil water = water that fills
the pores (spaces) between soil particles; can originate as precipitation or groundwater
Soil air = air that fills the pores between soil particles; usually has the same gases as atmospheric air, but with more carbon dioxide and less oxygen
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Soil Horizons Distinctive horizontal layers
in soil Soil profile = a vertical
section from surface to parent material that shows the soil horizons
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Soil Horizons O horizon = uppermost
layer of soil, rich in organic material
A horizon = topsoil, dark and rich in organic material and humus, tends to be granular and nutrient poor due to leaching
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Soil Horizons E horizon = sometimes
occurs between A and B horizons, very heavily leached, not always present
B horizon = light colored subsoil, often a zone of illuviation where minerals and nutrients accumulate, usually rich in iron, aluminum, and clay
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Soil Horizons C horizon = weathered
pieces of rock, below most roots, usually saturated with groundwater
Bedrock = original parent material that the soil rests on
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Soil Properties Texture = determined
by proportions of sand, silt and clay
Loam = ideal agricultural soil, 40% sand, 40% silt, 20% clay
Soil triangle = tool used to classify soil
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Soil Properties Charge = some are positively charged
(K+) or negatively charged (NO-3)
Clay particles are usually negatively charged
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Soil Properties Soil acidity = measured on the pH scale (1-
14) 1-6.9 = Acid 7 = Neutral 7.1-14 = Base Close to 7 = weak Far from 7 = strong pH affects what minerals remain in the soil Optimum pH for plant growth = 6.0-7.0
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Major Soil Groups Spodosols = form in colder
climates with a lot of precipitation and good drainage (ex. Coniferous forest)O horizon = acidic litter (mostly
needles)E horizon = ash-grey, acidicB horizon = dark brown
Too acidic and nutrient-poor to be good for agriculture
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Major Soil Groups Alfisols = form in temperate
deciduous forestsA horizon = brown to grey-brownB horizon = contains most of the clay
and nutrients washed out of A and E horizons
If the deciduous forest is intact, soil fertility is maintained by continuous supply of plant litter
If soil is cleared for farmland, fertilizers must be used
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Major Soil Groups Mollisols = primarily found in
temperate, semiarid grasslands; very fertileA horizon = thick, dark brown to
black, rich in humusPrecipitation is not enough to
leach nutrients to lower layersMost of worlds grain crops are
grown on mollisols
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Major Soil Groups Aridisols = found in arid
regions; lack of precipitation and rich vegetation results in a lack of leaching and illuviation or distinct layers
Crops can be grown with irrigation
Rangeland for grazing animals
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Major Soil Groups Oxisols = primarily found in
tropical and subtropical areas with a lot of precipitation, low in nutrient mineralsO horizon = little organic material
because leaves and twigs are rapidly decomposed
A horizon = rich in humusB horizon = thick, highly leached,
acidic, nutrient-poor
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Major Soil Groups Pedalfers = found around here and in other temperate
regions that get significant rain; B horizons contain iron- and aluminum-rich materials red and orange
Pedocal = typical of dry climates like those found n the western United States; chemical weathering is slower. less clay; rich in calcium based minerals (calcite, limestone)
Laterite = form in hot, wet tropical areas; large amount of precipitation leaches out much of the silicate material making these soils orange and organically poor. One major reason for rainforest deforestation is the periodic need to replace the land exhausted by farming.
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Major Soil Groups
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Who lives in the soil? Millions of microorganisms
(bacteria, fungi, algae, microscopic worms, protozoa, etc.) can occupy 1teaspoon of fertile agricultural soil
Bigger organisms live there too plant roots, insects, earthworms, moles, snakes, groundhogs, etc.
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Why are soil organisms important? They provide various ecosystem
services such as: Decaying and cycling organic materialPreventing erosionBreaking down toxic materialsCleansing waterAffecting the atmosphereCastings = bits of soil that have passed
through the gut of an earthworm, moving nutrients from deeper layers to the surface
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Why are soil organisms important? Ants make tunnels and chambers that
aerate the soil They also bring food from the surface
down into the soil some of it decomposes and adds nutrients to the soil
Also bury seeds in soil grow into plants
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Why are soil organisms important? Plants are affected by the properties of soil, and the soil is
affected by the plants that grow in it Mycorrhizae = associations between plants and fungi that
enable the plants to absorb enough nutrients and minerals Mycelium = tiny thread-like extensions of fungi that go
deeper into the soil than the roots of a plant, allowing the plant more access to nutrients and minerals and the fungi access to the food produced by photosynthesis
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Nutrient Cycling Nutrients (like nitrogen and phosphorus)
cycle between soil and organisms Decomposition = bacteria and fungi Reabsorption = mainly plants Leaching Runoff Dust storms http://www.youtube.com/watch?v=gnp4Y
wjz-po
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Soil Problems Human activities Erosion Mineral depletion
Sustainable soil use = using soil resources wisely without a reduction in the amount or fertility of the soil so that it is productive for future generations
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Erosion The wearing away or removal of soil from the land Caused by water, wind, ice, etc. A natural process that can be accelerated by human
activity About 4.6 billion tons of soil are eroded from US
croplans and rangelands each year
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Major Types of Erosion Surface erosion = rain, wind, frost, etc.
detach soil particles from the surface that are washed or blown away
Fluvial erosion = water gouges shallow channels or deep gullies in soil
Mass-movement erosion = gravity combines with heavy rain or earthquakes; whole slopes can slump, slip or slide
Stream bank erosion = not dramatic, can occur in regions where there is frequent flooding
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Surface erosion Sheet erosion = rain falls on
bare or sparsely covered soil and moves loose material (silt, clay, humus) downhill soil loses fertility
Wind erosion = soil on surface is blown away, can form dunes, more severe if vegetation has been grazed or disturbed
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Fluvial erosion Rill erosion = water runoff from shallow
slopes and gathers is small V-shaped channels or rills
Gully erosion = occurs on loose subsoils, they are deep and generate a lot of sediment, which is usually deposited into rivers
Tunnel gullying = water enters on a slope through cracks in the soil after a dry period, forming a tunnel that collapses on itself, forming a gully
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Mass-movement erosion Slips = common where rock is
mudstone or siltstone, topsoil and subsoil becomes saturated and slides downhill
Earth flows = saturated soils move downhill, but vegetable mats are left behind
Scree erosion = occurs in steep mountainous areas, soil erodes in fan shapes
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The American Dust Bowl The semi-arid prairie soil of the
American mid-west were cleared for crops and overgrazed by animals
The disturbance of the native vegetation left the soil vulnerable to erosion the fertile topsoil was removed by wind and water
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The American Dust Bowl Dust could be seen as far as the east
coast and the Atlantic Ocean
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Nutrient Mineral Depletion In a natural ecosystem, essential
nutrient minerals cycle between soil and organisms (especially plants)
Nutrients and minerals usually return to soil through decomposition
Harvesting crops stops this cycle soil is depleted of nutrients
Especially severe in rainforests
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Soil Problems in the USA Rates of erosion measured every 5
years Good news: erosion is declining (since
1982) Bad news: erosion is still happening at
significant levels approximately 25% of agricultural lands in US are losing topsoil faster than it is being replaced
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World Soil Problems 75 billion tons of topsoil lost each year,
especially in Asia, Africa, and Central and South America
Caused by the amount of agriculture needed to feed densely populated areas over-exploitation of soil
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Solving Soil Problems… Conservation tillage = residues from previous
crops are left in the soil, covering it and keeping it in place
No-tillage = soil is undisturbed over the winter During planting, a narrow furrow is cut for
seeds Traditionally, soil would be cut and turned in the
spring, weeds would be removed, and seeds would be covered
Plant cover removed = more risk for erosion http://www.dailymotion.com/video/x6ie2l_benefits-of-conservation-tillage_tech
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Solving Soil Problems… Crop rotation = planting a series of
different crops in the same field over a period of years
Same crop over and over = more pests accumulate, same nutrients get depleted
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Solving Soil Problems… Contour plowing = plowing in
curved lines that conform to shape of land instead of straight lines
Strip cropping = alternating strips of different crops on natural contours
Terracing = making level areas on steep slopes for crops
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Solving Soil Problems… Organic fertilizers = animal manure,
crop residue, bone meal, compost, etc. Slow acting, long lasting
Instead of… Commercial inorganic fertilizers =
manufactured from chemical compounds, exact chemical composition is known, but they are only available for a short time before they wash away
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Solving Soil Problems… Shelter-belts = rows of trees between
fields that lessen the impact of wind
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Soil Conservation Act of 1935 Authorized formation of Soil
Conservation Service Works with US citizens to conserve
natural resources on private lands Farmers tend to use less soil when
prices are lower, but more when prices are high
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Food Security Act (Farm Bill) of 1985 Provisions for two main soil
conservation programs:Conservation compliance programConservation Reserve Program
Farmers with highly erodible land must develop a 5-year conservation plan, or lose federal subsidies
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Conservation Reserve Program (CRP) Voluntary program that pays farmers
$50 per acre per year to stop producing crops on erodible farmland
Planting native grasses and “retiring” the land for 10 years
Very beneficial and effective
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Grasslands Reserve Program (2002) Pays farmers to protect up to 2 million
acres of virgin and improved pastureland for at least 10 years
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General Mining Law of 1872 Passed to encourage settlement in the western
states Allows companies or individuals (of any origin)
to stake mining claims on federal land, purchase the land for $2.50-$5 per acre, extract all valuable minerals from the land, and keep all the profits
In 1995, ASARCO obtained land with $2.9 billion worth of copper and silver for $1,745
Congress has since put a hold on all such sales (1996)
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Minerals Elements or compounds of elements
that occur naturally in the Earth’s crust We use minerals for many things…
Steel, aluminum, copper, sulfur, sodium chloride, crushed limestone, silver, gold, etc.
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Minerals Sulfides = mineral compounds combined with
sulfur Oxides = mineral compounds combined with
oxygen Rocks = naturally formed aggregates, or
mixtures, of minerals with varied chemical compositions
Ore = rock that contains a large enough concentration of a particular mineral that can be profitably mined and extractedHigh-grade ores and low-grade ores
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Minerals Metals = minerals such as
iron, aluminum, copper, etc. They are malleable, lustrous, and good conductors of heat and electricity.
Nonmetallic minerals = minerals such as sand, stone, salt, phosphates, etc. that lack such qualities
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Mineral Distribution and Formation Some abundant minerals: Iron and
aluminum Some rare minerals: copper, chromium,
molybdenum, etc. Abundance ≠ easy to mine Minerals are distributed unevenly rich
deposits or almost none
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How do deposits form? Magmatic concentration = cooling magma
solidifies and separates into layers, heavier minerals on the bottom (iron, magnesium, etc.), lighter minerals on top (silicon)
Hydrothermal processes = groundwater that has been heated in the earth seeps into cracks and fissures and carries minerals, which settle out and form deposits
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How do deposits form? Sedimentation = weathered rock
particles are carried by wind and/or water and settle out, forming deposits
Evaporation = water containing minerals evaporates away, but leaves the minerals behind salt deposits
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Discovering mineral deposits Aerial or satellite photography Measuring Earth’s magnetic field and gravity Looking for typical areas in the Earth’s crust
for a particular mineral Ocean floor mapping
Once a possible location is determined, geologists drill or tunnel for mineral samples to identify
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Extracting Minerals - Mining Surface mining = minerals are
extracted near the surface Subsurface mining = minerals are too
deep and need to be extracted with alternate methods
Overburden = soil, rock, vegetation, etc. that must be removed to access the mineral
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Surface Mining Open-pit surface mining = giant hole is
dug quarry Strip mining = trench is dug to extract
minerals, then a new trench is dug and overburden is dumped into old one, creating a spoil bank
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Subsurface mining Shaft mine = direct vertical
shaft to a vein of ore Slope mine = slanting
passage that makes it possible to haul the broken ore out of the mine in cars
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Processing Minerals Smelting = melting ore at high
temperatures to help separate impurities, can be done in a blast furnace
http://www.youtube.com/watch?v=Ea_7Rnd8BTM
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Words to Know… Coke = modified coal used as an
industrial fuel Slag = less dense than iron ore, floats
on the top, formed when limestone reacts with impurities in the ore
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Mining and the Environment Disturbance to land prone to erosion Air pollution Water pollution
Developed nations tend to have laws and mechanisms to minimize environmental damage; developing nations either don’t have them or are still developing them
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Mining and Water Digging too deep = hitting the water table
Open-pits must now be pumped dryGroundwater, springs, etc. start to run dry
Disturbed soil can runoff into water = increased turbidity, might contain dangerous chemicals or heavy metals
Thermal pollution = increasing the temperature of water so that native organisms can no longer survive
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Cost-Benefit Analysis of Mine Development Environmental economists suggest that
cost-benefit analyses should be performed before developing a mine
Benefits of mine vs. benefits of keeping land intact for wildlife, habitat, watershed protection, and recreation purposes (all in $ amounts)
Should consider long term
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Refining Minerals Removing waste products (tailings)
from ore, usually left behind on ground or in water near a processing plant
Smelting plants can emit large amounts of air pollution
Heavy metals (such as lead, cadmium, arsenic, and zinc) can pollute atmosphere, water, and land
Takes huge amounts of energy
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Waste Production for Selected MineralsMineral Amount of Mined
Ore (Million Tons)Percentage of Ore That Becomes Waste During Refining
Iron 25,503 60
Copper 11,026 99
Gold 7,235 99.99
Zinc 1,267 99.95
Lead 1,077 97.5
Aluminum 856 70
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Restoration of Mining Lands When a mine is no longer profitable to
operate, the land can be reclaimed, or restored to a seminatural conditionPrevents further degradation and erosionEliminates or neutralizes local sources of
pollutantsMakes land productive for purposes other
than miningMakes land visually attractive
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Restoration of Mining Lands Derelict lands = lands that have been
degraded by mining Some restoration techniques:
Filling in and grading the land to its natural contours
Planting vegetation to hold soil in placePlants might have to be able to survive
heavy metals or without topsoil
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Surface Mining Control and Reclamation Act of 1977 Reclamation of areas that are surface
mined for coal is required No requirement for non-coal mines
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Creative Approaches Wetlands = trap sediments and
pollutants that enter them from upstream areas, improving the quality of water downstream
Cow manure = dumping cow manure on mining sites can cause the pH to increase as bacteria consume the manure; toxic materials precipitate out
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Creative Approaches Phytoremediation = using specific
plants to absorb and accumulate toxic materials, ex. Streptanthus polygaloides (twist flower) absorbs nickel and other toxic materials
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Mining and the Economy The economies of industrialized countries
require the extraction and processing of large amounts of minerals to make products
More industrialization = more minerals used Developed countries = lots of restrictions,
may have exhausted their own supplies Developing countries = economies extremely
dependent on selling minerals to developed countries, little to no restrictions
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Consumption of Select Minerals
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Distribution vs. Consumption
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Distribution vs. Consumption Certain minerals are necessary for many
products that are vital to the economic success of a nation, but are only present in limited amounts
International trade is necessary to acquire the mineral
Some countries stockpile certain minerals (ex. Titanium, tin, manganese, chromium, platinum, and cobalt) to reduce their dependence on other countries
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Will We Run Out of Important Minerals? Mineral reserves = mineral deposits that
have been identified and are currently profitable to extract
Mineral resources = deposits of low-grade ores; potential sources of minerals, but currently unprofitable supply and demand
Total resources (world reserve base) = combination of a mineral’s reserves and resources
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Will We Run Out of ImportantMinerals? Reserves and resources fluctuate with
economic, technological, and political changes
Technological advances can decrease the cost of extracting ores resources can be reclassified as reserves
Political turmoil can make it so that a mineral reserve cannot be mined reclassified as resource
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Will We Run Out of Important Minerals?
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Increasing Our Mineral Supplies Locating and mining new deposits
may be blocked by heavy vegetation, shifting ice, too deep in the earth, etc.
New technology may allow us more access
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Minerals in Antarctica No substantial deposits, only small amounts Antarctic Treaty = international agreement
(1961) that limits activity in Antarctica to peaceful uses such as scientific studies
Environmental Protection Protocol to the Antarctic Treaty (Madrid Protocol) = (1990) No mineral exploration or development for minimum of 50 years, preserves Antarctica as a marine ecosystem
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Minerals from the Ocean Minerals could possibly be extracted
from seawater or where they have accumulated in loose sediments
Total amount of minerals available = high
Concentration of seawater = low
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Minerals from the Ocean Manganese nodules = small rocks the
size of potatoes that contain manganese and other minerals on the ocean floor
~1.5 million tons available, but dredging them from the sea floor would hurt sea life in the area
International waters = Who has the right to these minerals?
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U.N. Convention on the Law of the Sea (UNCLOS) Formed in 1982, became effective in
1994 Allows for deep seabed mining beyond
national jurisdictions US has refused to ratify it
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Biomining Using microorganisms to extract
minerals from low-grade ores Very effective for copper mining Thiobacillus ferroxidans can be mixed
with sulfuric acid to leach copper into an acidic solution
Gold and phosphates can also be extracted in similar manners
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Mineral Substitutes Find an inexpensive or abundant material to
replace an expensive or scarce one Plastic, glass, and aluminum have been used as
substitutes for tin Plastic has partially replaced lead and steel in
cables Glass fibers have replaced copper wiring in
telephone cables Some minerals have no known substitutes. For
example, platinum cannot be replaced as a catalyst for many reactions.
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Mineral Conservation Reuse = the same product is used over
and over again, such as washing and refilling a glass bottle
Recycling = products are collected, remelted, reprocessed, etc. into new products, such as melting down metal cans and making new ones
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Changing Our Mineral Requirements Stop the “throwaway” mentality repair
or repurpose Waste from one industrial process can
be used as raw materials in another economic and environmental benefits
Sustainable manufacturing = reducing waste by more efficient manufacturing processes or converting the waste into useful products
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Dematerialization Decreasing weight
and/or mass of materials needed in a product
Can have negative effects flimsier products can break more easily and be cheaper to replace than to repair
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In Conclusion… Soil and minerals are both important
limited resources Both can be permanently damaged or
used up Both can be protected AND enjoyed by
sustainable use and development
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Vids http://www.pbs.org/wgbh/nova/education
/earth/rare-earth-elements.html Rare earth minerals
http://www.youtube.com/watch?v=Ego6LI-IjbY Soil Stories – The Whole Story
http://www.youtube.com/watch?v=pVoXW4YrqTs Surviving the dust bowl
http://www.teara.govt.nz/en/soil-erosion-and-conservation/3 Types of erosion