Natural Resources II Minerals

Lecture 07

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Unit Organization:

• Minerals
• Environmental Impact of Mineral Extraction
• Mineral Economics and Scarcity
• Response to Scarcity

Reading:

Textbook: Chapters 10

Ancillary Reading:

Minerals

One thing to keep in mind about minerals:  although there is a finite amount of any mineral resource on the Earth, how much of that is usable is technology-dependent and this makes it hard to determine mineral reserves

Minerals

Some minerals such as quartz, diamond, mica, marble, granite, zeolites, etc., are valuable as minerals and some are valuable for a specific component

• Metallic Minerals
  • Ferrous - iron and those metallic elements alloyed with iron: chromium, manganese, nickel, molybdenum)
  • Non-Ferrous - all the rest of the metallic elements (gold, mercury, lead) and the rare-earth elements (needed by the semiconductor industry
• Non-Metallic Minerals
  • Structural Materials such as sand, gravel, building stone, portland cement
  • Industrial Materials - phosphates (needed for fertilizers), various salts, sulfur, asbestos, abrasives and other non-metals needed for industrial processes
• Gemstones - some gemstones also have industrial applications, so there is some overlap here (diamonds, rubies)

Ores are mineral mixtures rich in a particular material of interest

• There is some overlap between mineral and energy resources
• Ore rich in uranium is both a mineral and energy resource
• Some solve this problem by considering uranium and fossil fuels as mineral resources

Demand and value of resources is set both by production costs, abundance of the material, and the need for the material

Mineral Deposits

• The distribution of elements is not uniform in or on the Earth
• Mineral deposits are those areas where geological processes have left concentrations of particular minerals
  • Ore deposits are those mineral deposits from which we have the technology to extract a valuable mineral resource
    • An example of what it means to be an ore deposit is iron, which is a very common component of the crust
      • Most is not available for extraction but iron ore deposits are enriched and close enough to the surface for them to be mined
    • Placer Deposits are where pieces of the ore occur among other unconsolidated rock debris (like river beds) and the pieces of ore must be separated from the dross
    • Lode Deposits are ores that are part of solid rock and the rock and the ore need to be crushed before separation
• Geologic processes can concentrate elements by factors of over 1000
  • Supergene Enrichment occurs when a valuable mineral dissolves into water over a large area or volume and then the water flows to another environment where the material precipitates out of solution to form an enriched zone
    • Silver mines were this way and the "veins" of silver were where the silver had precipitated
    • Copper deposits are formed by this method
  • The deposits from Supergene Enrichment were thought to be shallow but recent discoveries (in particular, gold discoveries) have found that some gold deposits extend much farther into the Earth than previously thought, increasing the gold reserves considerably
• Reserves are ore deposits that have been identified but the mineral has not yet been extracted

Demand for Minerals

• Demand and value are linked but not directly, so that the value can be very great for minerals with small worldwide demand
  • The relationship is made complex by the many factors that determine supply of a mineral
    • Availability, political considerations, extraction costs, and market conditions (such as monopolies) are some of the factors and the importance of various factors varies among different minerals
• By bulk, construction materials and non-metals have the largest demand
  • Stone, sand, and gravel have the highest demand of all
  • A short construction primer
  • Much of modern construction involves Concrete
    • Pieces of a hard, durable mineral (stone, called the Aggregate) mixed with Cement and Water
      • The water plus cement forms a hydrated mineral so that the concrete forms a solid block
    • Cements are used to bind things together and those that harden (= set) in construction can be:
      • Hydraulic - those that incorporate water into the crystal matrix and are, as a consequence, less prone to water damage (Portland Cement)
      • Non-Hydraulic - those that do not incorporate water as part of the hardening process and thus prone to water damage (Gypsum - see below)
    • The cement (binding material) used for concrete is Portland Cement (Calcium Silicates - CaO•SiO₂ in a 3:2 ratio - named so because, when set, it is similar to Portland Stone that is quarried on the Isle of Portland in England) or, less commonly, fly ash or slag cement
      • Portland Cement is made by heating a mixture of Calcium Carbonate (CaCO₃ - limestone, usually formed by compaction of fossil animal and protistan shells - so it is most often biogenic) plus a Silicate (SiO₂ - usually as sand or clay) with small amounts of other ingredients
        • This happens in a rotary Cement Kiln (these are the largest industrial machines in the world) where the materials are moved slowly from the cool end to the hot end (up to 2700 degrees F.)
      • First, the CaCO₃ is decomposed into CaO (Calcium Oxide) and CO₂ and then the CaO and SiO₂ form a single mineral (this process was patented by Joseph Aspdin, and Englishman, in 1824)
      • When the product of the kiln is poured out, it solidifies into a mineral called Clinker, which is ground into a fine powder, bagged, and sold as portland cement
    • Concrete is formed when the water and the portland cement chemically bond to form a crystal mineral in which the harder pieces of aggregate are embedded
  • If steel is ignored, then clay, salt, phosphate rock, lime, gypsum, soda ash, and potash all have higher demand than metals
    • Lime refers to more than one mineral
      • Quicklime or Burnt Lime is Calcium oxide (CaO) - used mostly as a base ingredient for making other things (if heated to over 4000° F, it glow with an intense white light and was used to light stages before the introduction of the electric light, hence someone on stage is in the limelight)
      • Slaked Lime or Hydrated Lime is Calcium Hydroxide [Ca(OH)₂] - many uses - in sewage treatment and to produce drinking water, in foods, and in the production of sodium hydroxide, in mortar and plaster, etc.
    • Gypsum is an evaporate (formed by evaporation) composed of Hydrated Calcium Sulphate (CaSO₂·2H₂O) which forms sever soft crystal forms and is used as a fertilizer component, the main ingredient of plaster (burnt gypsum from a district of Paris, France became know as plaster of Paris) and one crystal form is alabaster, often carved into ornaments
    • Soda Ash is Sodium Carbonate, Na₂CO₃, which is used a water softener and plumbing descaler, as a dye fixative, as a food additive to control pH, and as a fine abrasive
    • Potash refers to several Potassium Salts (KCl, KOH, K₂CO₃,  KNO₃, and others) and is used as a component of fertilizers and in many industrial processes
      • Potash got its name from how it was first produced (by soaking wood ash and then letting the solution evaporate until a white ash formed in the pot containing the solution) but eventually natural deposits of these minerals were found and extracted
      • One of the reasons for making the potash from ash was that, if you mixed it with oil or fat and heated it, the fat would decompose into glycerol and fatty acid salts, which make a precipitate that can be pressed into cakes of Soap. 
• Ignoring fossil fuels, which are discussed elsewhere in this course, metals are the minerals with second greatest bulk demand
  • Can divide metals into high demand/low demand groups
    • High demand:  iron, aluminum, copper, manganese, zinc, chromium, lead, and nickel have the highest demand among metals
    • Low demand: tin, molybdenum, titanium, silver, mercury, platinum, and gold have significantly lower demand
• For all minerals, demand has been growing at exponential rates with some departures due to changes in technology and market forces
  • mineral demand increases for several reasons
    • Population increases
    • Technological changes that require more mineral input
      • Technology can also reduce demand for a particular mineral if another is substituted, but this is not common and may be impossible for some minerals
    • The benefits of current (and, most probably) future technology are not uniformly distributed worldwide nor within individual countries and, if average standards of living are to improve, then mineral consumption rates will continue to be high even with no increase in population.

Environmental Impact of Mineral Extraction

There are two sets of environmental costs due to mineral extraction

• One is the direct effect of the extraction process (plus transportation)
• The second is the effects that use of the minerals have on the environment (burning fossil fuels, heavy metal contamination of landfills from manufactured materials containing minerals, etc.)

We will address the first set of costs here and the second set when we discuss pollution and its costs

• However, do not think that the indirect costs are small
• Charcoal is still used in steel processing in Brazil and almost 200 square miles of forest are cleared each year just to supply a single iron ore smelter (Grande Carajas)

Cement

In 2010, 3.5 billion tons of Portland Cement were produced

• Worldwide, the only resource we use in large volumes is water

Production of Portland Cement today involves two polluting activities

• Consumption of lots of energy to heat the kilns
• The decomposition of the Calcium Carbonate (CaCO₃) into CaO and CO₂

Carbon dioxide production due to the production of Portland Cement is a large portion of total anthropogenic CO₂ production and so, is a driving force in global warming

• 3,300,000,000,000 - over three trillion pounds (1.5 gigatons) of CO₂ are produced each year by Portland cement production
  • 40% due to burning petroleum to heat the kilns
  • 50% due to Calcination of the limestone
  • 10% due to other sources (electricity consumption by the production plant, fuel use to transport the cement)

Recent technological advances might reduce the carbon footprint of Portland cement production

• Green Cement involves producing CaO in a different smelting process that decomposes the carbon dioxide into solid carbon and oxygen, which is released into the atmosphere rather than CO₂
  • The energy source for this smelting is electricity
  • As long as electricity is associated with CO₂ production, then green cement will still produce lots of CO₂ but, if the electricity comes from alternate sources (hydropower, solar, tidal, wind, etc.) then the cement becomes truly "green" (especially if the trucks are electric using green electricity)

Mining

• Excavation of ore from the Earth
  • Leaching soluble minerals from rock without removing the rock
  • Surface Mining - ore is uncovered by removing Overburden
    • Open pits, strip mines, and mountaintop removals are all forms of surface mines
    • Quarries are open-pit stone mines
  • Sub-surface mining involves digging shafts (vertical and horizontal) into the Earth to remove the ore
    • There are many types of sub-surface mines
    • the waste rock brought to the surface is Tailings
    • some of the rock is processed underground and the tailings are left behind as Backfill
• Processing of the ore to separate the valuable substance or substances from the waste, referred to as Gangue (pronounced "gang"), using mechanical means
• Extractive Mining refers to separation of the valuable portions of the ore from the rest using chemical means (gold mining)
• Some processes involve heat and chemical reactions (Smelting, used for iron, silver, copper and other metals)
• The electrolytic reduction of Aluminum from ore is also called smelting

These process mean that mining mostly pollutes through

• Consumption of lots of energy, most generated by fossil fuels
  • Steel production uses 5% of energy worldwide
• Exposure of rock surfaces that have not been in contact with water or the atmosphere
  • Thus oxides form and soluble minerals are leached from the newly exposed surfaces
  • These leachates are often pollutants in that are toxic for some or all living things

Smelting

• Smelting is a producer of pollution on land, in water, and in the air
  • Smelting aluminum consumes 1% of worldwide energy use with its associated environmental costs
• Smelting can release toxic gasses
  • 8% of all sulfur-containing gas emissions (that contribute to acid rain and climate change) come from smelting
  • Smelters often have dead zones (no plant or animal life) surrounding them
  • Almost all copper production leads to sulfur pollution (copper is most commonly found in sulfur-containing minerals)
• Uses many toxic materials in the processing (mercury, cyanide)
• Smelter wastes must be stored responsibly  or they will contribute to acid runoff

Acid Runoff

• Some of the tailings and overburden piled up near mines is made of rock that will leach acids
• In addition, many mines will flood (the water may be runoff that spills into the mine or may be groundwater that leaks into the mine) and the walls of shafts and backfill can contribute to acid runoff from mines
  • Sulphuric acid is the most common acid leached from mines and mine waste
  • Much of the acid is produced by bacteria that oxidize the materials for chemosynthesis
• Runoff acidity varies but can be very low
  • It must be mentioned that, if there is sufficient alkaline rock (like limestone) present, the pH of the runoff may be alkaline due to it's neutralizing power
• When,  downstream from the source of the runoff, the pH rises above 3, iron precipitates and colors the stream bed orange-yellow (the precipitate is called Yellow Boy)

Removal of Natural Rock

• Abandoned mines cover millions of acres of land in the US
  • Surface mines contribute the largest portion but subsurface mines often pollute land surrounding the entrances and have a larger footprint than expected
  • Abandoned mine area is over half of area taken by pavement of all kinds
• Overburden and Tailings amount to 25 billion tons per year
  • This "human-caused erosion" is more than twice the total annual sediment load of all of Earth's rivers
  • The surfaces affected by mining are prone to greater erosion than undisturbed surfaces
  • If not carefully controlled, the material can be deposited as silt over stream and lake beds, smothering benthic organisms
  • Piles of debris can be mobilized in heavy rains and cause damage to structures and people caught in the way of the flow

Heavy Metals

• Newly exposed rock may leach heavy metals into water
  • Most heavy metals are transition elements but the term refers to any metallic runoff that is toxic to living organisms
  • Mercury, lead and plutonium are all toxic in any concentration and have no positive uses in living systems
  • Many other heavy metals have some utility, sometimes to only a few species, but become toxic when their concentration is too great
• Runoff concentrations may increase as they are passed through a food web toward the larger consumers (this process is called Bioaccumulation)

Mineral Economics and Scarcity

The costs of producing minerals are very variable and highly dependent on the type of mineral being extracted

• Material costs - the price paid for access to the ore deposits
  • For some minerals, the material is almost free (stone, sand and gravel are often in this category) but if the mineral is rare, then acquiring the rights to it may be costly
  • Finding uranium below you may increase the value of the mineral rights to your land but finding rock that's easy to crush into gravel under your property will not pay for your education, even though we need many times more gravel than uranium
• The second cost is the cost of extraction (and any post-extraction processing needed), which also varies greatly and is tied to the type of mineral and the geological formation
  • Entire mountains may be turned into deep pits during the extraction process
• The third cost is the cost of transportation
  • Transportation is usually most of the cost for bulk minerals like sand or gravel (so that almost all sand or gravel comes from local suppliers, as distant competitor's transportation costs make their prices non-competitive)
• The fourth cost is the cost of the environmental impact of the mineral, another highly variable cost and one that is often externalized so that it is paid by everyone, not just those who use the minerals

Factors affecting a mineral's price

Overall, prices for minerals have declined since 1950, although population has increased, consumption has increased, and environmental costs born by the producers have increased

• Reserves have increased for many minerals
  • New discoveries and better methods of extraction have both contributed
  • Environmental costs continue to be externalized
  • Government subsidies
    • Governments (including ours) sometimes give access to minerals on public land with no or low cost to the mining company
      • In the US and elsewhere, mining companies may benefit from tax law that exempts profit from taxation and exemptions from environmental laws concerning land reclamation and pollution emissions plus other subsidies such as loan guarantees (which lowers the cost of capital)
    • The World Bank has stated that government subsidies have significantly contributed to artificially low mineral prices worldwide
    • The reasons for the subsidies are varied and include
      • state security
      • maintenance of economic growth
      • promotion of economic development in "undeveloped" areas within the country
      • production of export commodities through which currency to pay international debts is acquired

Responses to Mineral Scarcity

Increased Reserves

• New discoveries of mineral resources continue to be made
• Recent pattern for new discoveries
  • Declining rate of discovery
  • Declining size of discovered reserve
  • Declining quality of discovered ores
• The lower quality of ores often means that both extraction and environmental costs increase (per unit of mineral delivered)

Increased Recycling

• Only fissionable elements are really lost and so, for many minerals, recycling can effectively add to the reserve
  • Recycling responds to the price of minerals, which we know are artificially low and so recycling has been suppressed indirectly
    • Recycling is very dependent on the type of mineral
    • Chemical changes to the mineral may make recycling too expensive
    • Soluble fractions are often lost to the ocean (where it is not economically worth recovering)
• Recycling will not be able to supply future demand caused by population growth or increases in standard of living
• Recycling may be very labor intensive if components of recycled goods are hard to separate
  • Thus, recycling companies use low-cost labor in developing countries to recycle products of developed countries
  • Environmental and worker safety regulations are often less rigorous in less-developed countries so that recycling can have costs that are exported from developed to less-developed countries

Increased Technology

• Technological improvements may lower the need for minerals per unit of goods produced with those mineral by
  • Substitution - using other materials to perform a scarce mineral's function
    • Non-copper wires (fiber optics for information transmission rather than copper wire)
    • Replacing tin cans (really steel cans with tin lining the inner surfaces) with aluminum cans or with steel cans with plastic linings
      • A note on tin cans - the tin or plastic coating is to prevent corrosion of the steel by the contents of the can but very acidic foods like tomatoes can, over time, corrode even tin and old cans of such products should be discarded.  Lastly, the plastic lining often contained Bisphenol A, which may be a hormone mimic and the FDA has warned about its use in products for children
  • Efficiency - better manufacturing techniques or new technology may decrease the mineral content of the finished goods

Increased Conservation and Durability

• It is obvious that, if we each use less of a mineral,  demand will be affected
• We can choose to possess less (a TV in every room?) but some see this as an unfair personal sacrifice if everyone does not agree to fewer TVs
• We can choose conserve through repair of goods, recycling of goods, and choice of goods that use less material (a civic or a SUV?)
• One way to use less that does not involve personal sacrifice is to use goods with greater durability
  • Reject goods with planned obsolescence
  • Reject goods which can't be repaired by design
  • Consider both durability and price when making consumer choices

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Last updated January 28, 2013