Encyclopedia of Global Resources part 133 pps

In the decades after the Rance tidal generating sta-tion began producing electrical energy, the device not only has been remarkably trouble-free but also has provided four indirect benef

tides flow in and out, so the turbines must be able to

function in either direction; second, most power is

generated during the two high and two low tides that

occur each day, but these variable times are usually

not synchronized with the peak demand times To

solve the first problem, the French engineers devised

turbines that can run in either direction to

accommo-date both incoming and outgoing tides The second

problem was solved by using the turbines as pumps,

making it possible to use surplus electricity to fill the

reservoir behind the dam to a greater depth than the

highest level of the tides Later, this extra water could

be released to turn the turbines at a time when power

is most needed, rather than when the ocean recedes

The operating policy of this plant was to optimize the

value of the power produced rather than maximizing

the amount The annual energy output from this

plant is 600 million kilowatt-hours, about 0.012

per-cent of France’s total energy consumption

In the decades after the Rance tidal generating

sta-tion began producing electrical energy, the device

not only has been remarkably trouble-free but also

has provided four indirect benefits: the development

of the large reversible turbines, the perfection of

cor-rosion control techniques, a roadway linking St Malo

and Dinard across the dam, and increased tourism

Although the major motivation to build the Rance

tidal power station was the fear of future power

short-ages, this plant has served as a prototype model for

tidal power plants as well as an invaluable source of

in-formation for future worldwide development

Other Tidal Power Plants

Modeled after France’s Rance tidal station and using

the French generators, the first Russian tidal power

station was installed in 1968, in the Kislaya Gulf, where

the tides can rise as high as 20 meters This facility was

abandoned in the mid-1990’s becasue of financial

dif-ficulties, but after a ten-year hiatus, it was modernized

and began producing 400 kilowatts of power

China has been developing and installing tidal

power stations for several decades As of 2009, eight

stations, with a total capacity of 6,120 kilowatts, have

been realized The largest single unit, an

experimen-tal station in Zhejiang Province, which became

opera-tional in 1980, is capable of producing 3,200 kilowatts

of power

An alternate means of using the tides to create

en-ergy at less cost and without the possible

environmen-tal impacts of barrage systems is to use underwater

generators rotated by the force of the water current as the tides come in and recede Operating on the same principle as wind turbines, these systems produce rel-atively constant and reliable energy without the argu-able visual pollution of wind turbines Several Euro-pean countries are presently focused on developing these current-driven devices because they do not re-quire the construction of large, costly dams and seem

to have minimal environmental impacts The requi-site hydrokinetic prototype devices in the 100-kilowatt range have been developed and are being tested and evaluated in European waters One-megawatt com-mercial units were expected to be available by the 2010’s

Because energy derived from a flowing fluid is di-rectly proportional to the cube of the flow velocity, a flow rate of at least 5 knots is essential for effective power production (doubling the flow velocity pro-duces eight times the power) For these systems the current velocity is more important than the tidal range; a high tidal range complicates these systems because the vertical location of the units would need

to be adjusted as the elevation of the sea level varies After three decades of research, Asia’s first tidal current power station, located in the Zhejiang Prov-ince of China, came online in January, 2006 This sys-tem uses tidal currents typically flowing between 6 and 13 feet per second to produce 40 kilowatts of power The world’s first substantial tidal current sys-tem, with a total 1.2 megawatts capacity, installed in Northern Ireland’s Strangford Lough, became opera-tional in July, 2008 These systems will serve as proto-types for future large-scale commercial applications and will validate this technology as environmentally benign and economically competitive

Proposed Tidal Power Plants Although about only twenty sites in the world have been identified as viable options for possible tidal power-generating stations of the Rance type, there are hundreds of sites where the water-current type of power stations would be feasible In the United States, tidal power units of both types are under serious con-sideration During the 1930’s, the Passamaquoddy Tidal Power Development Project received New Deal development funds for a tidal station based in Cobs-cook Bay, Maine, where the tides typically vary by 6 meters After several years of construction, the project was abandoned because of economic concerns, politi-cal complications, and potential problems

ing the system into the existing regional

electric grid The concept for a tidal

power plant in this region was briefly

re-vived during the energy crises of the

1970’s, but although deemed

techno-logically feasible, it was again canceled

because of economic concerns

During the first decade of the

twenty-first century, two apprehensions

rekin-dled interest in this project One was

the rising cost of the fossil fuels, and

the second was increased anxiety about

fossil-fuel-induced global warming

Consequently, a study commenced on

the feasibility of constructing a huge

dam with three hundred

16-foot-diame-ter generators for a tidal power plant in

northern New England There is also

considerable interest in installing tidal

current devices in locations such as the

harbors of San Francisco and New York

City, where dams are unfeasible

Russia possesses a huge potential for

developing tidal energy, theoretically

enough to provide for the entire

coun-try’s electrical energy requirements

Two regions, Kola Bay and the Okhotsk

Sea coast, could provide 100 gigawatts

of power by Rance-type tidal stations

Several new tidal plants for industrial purposes are

planned to be constructed on the Okhotsk and Beloe

seas The Beloe Sea unit will be a 10-megawatt device,

with plans to eventually achieve 20,000 megawatts In

the Okhotsk Sea the tides can reach 17 meters,

allow-ing the proposed plant to output 20 gigawatts, with a

peak capacity of 90 gigawatts

Because of China’s increasing demands for energy,

as of 2009, several large-scale tidal generating stations

were under way, while still more were in the

plan-ning stages The proposed 300-megawatt generating

station at the mouth of the Yalu River will become

the world’s largest tidal plant by exceeding the

240-megawatt capacity of Rance Because the tidal-barrage

approach is not feasible in this region, an approach

termed “tidal lagoons” is being used The tidal

la-goons use a rubble mound impoundment structure

and hydroelectric generating equipment located at

least 1.6 kilometers from the shoreline, thus avoiding

the expense of a huge dam as well as possible

ecologi-cal disadvantages

Eight possible sites for tidal power stations have been identified in Great Britain; the most feasible and most studied site is the Severn estuary, where the tidal range can be as high as 14 meters Actualizing this proj-ect would require the construction of a 16-kilometer-long dam, forming a bridge between England and Wales and trapping 420 square kilometers of water, which would make this the United Kingdom’s great-est engineering project since the Channel Tunnel By incorporating 214 40-megawatt turbines, this power plant would produce an average power of 2 gigawatts, with a peak of 8.6 gigawatts, providing the energy equivalent of eight large coal-fired power plants and potentially reducing carbon dioxide emissions by 16 million metric tons annually

Several environmental organizations are vehe-mently opposed to this project, claiming the irrevers-ible effects would be devastating to migratory birds, which depend on the marshy mudflats; would acceler-ate coastal erosion in some areas; and would increase silting in other regions This huge dam might also

An underwater turbine used to generate tidal power in the United Kingdom (PA

Photos/Landov)

vent salmon and other migratory fish from reaching

their spawning grounds

Plans are also in progress to construct a tidal power

station in Garolim Bay, on the western shore of South

Korea Although the tides average only 2.4 meters,

compensation would be achieved because water would

be trapped in a 85-square-kilometers area, four times

the area of the Rance estuary With a generating

ca-pacity of 520 megawatts, this would provide twice the

maximum power of the Rance power plant In 1981,

the project was assessed as economically feasible, but

the reduced cost of oil in the mid-1980’s caused the

project to be shelved When the cost of oil rose rapidly

in the early 2000’s, reassessment deemed the

proj-ect viable; the fundamental design was completed in

2007 Because Garolim Bay is an important spawning

ground for many species of fish, environmentalists

and local fishermen oppose this project Nonetheless,

the project continued to progress, as it was included

in the government’s 2008 renewable energy strategy

However, the Korean Federation for Environmental

Movement censured the project, asserting that the

spirit of renewable energy is violated by a power plant

that destroys valuable tidal flats and severely disrupts

the local ecology

Desirable and Undesirable Aspects of Tidal

Power Plants

Although tidal energy is a reliable and plentiful

alter-nate energy source, converting it into useful electrical

power is not always easy or desirable The positive

at-tributes of tidal energy are that it is renewable, it does

not consume nonrenewable resources, it produces no

noxious wastes, it does not contribute to global

warm-ing, and it does not create thermal pollution There is

no slag or fly ash to dispose of, there are no radioactive

waste products to be stored, and there is virtually no

aesthetic pollution Other advantages are the

longev-ity of the plants and their reliabillongev-ity Tidal plants have

a practical life of at least seventy-five years, compared

with thirty years for a fossil-fuel plant and twenty-five

years for a nuclear plant Tidal power stations are also

more reliable, because the tidal cycle is extremely

reg-ular Less reserve equipment is needed because there

are many small generating units rather than a few

large ones If one unit goes off line, the power

reduc-tion is small Finally, the water dammed during high

tides provides an almost ideal lake for water

recre-ation sports

On the negative side, tidal power can provide only

a fraction of the world’s energy needs Tidal dams, ex-cept in special cases, are quite expensive to construct, cannot work continuously, affect a large area, and may cause ecological disruptions to marine creatures and wildlife Furthermore, large tide differentials are essential for productivity Although there may be rela-tively few places where tidal dams may be economi-cally constructed, there are many more options for utilizing underwater current flow turbines Not only are they less expensive; the environmental impact is minimal

There is an urgent need for the development of al-ternate sources of energy, particularly sources that are nonpolluting Tidal power not only is a realistic and realizable concept but also could be a valuable com-plement to the world’s increasing use of alternate en-ergy sources, such as solar and wind As dwindling supplies of renewable resources continue to escalate

in cost, and as global warming from fossil fuels be-comes a more acute problem, the technological and economic barriers to increased utilization of tidal en-ergy are diminishing rapidly Tidal generating sta-tions stand posed to become a major contributor to the world’s future alternate-energy mix as humanity overcomes its addiction to fossil-fuel energy

George R Plitnik

Further Reading

Charlier, Roger Henri, and Charles W Finkl Ocean

Energy: Tide and Tidal Power London: Springer,

2008

Charlier, Roger Henri, and John R Justus “Is Tidal

Power Coming of Age?” In Ocean Energies:

Environ-mental, Economic, and Technological Aspects of Alterna-tive Power Sources New York: Elsevier, 1993.

Clancy, Edward P The Tides: Pulse of the Earth

Illus-trated by Warren H Maxfield Garden City, N.Y.: Doubleday, 1968

Clark, Robert H Elements of Tidal-Electric Engineering.

Hoboken, N.J.: Wiley-Interscience, 2007

Congressional Research Service Energy from the Ocean.

Honolulu, Hawaii: University Press of the Pacific, 2002

Goldin, Augusta Oceans of Energy: Reservoir of Power for

the Future New York: Harcourt Brace Jovanovich,

1980

Gray, T J., and O K Gashus, eds Tidal Power:

Proceed-ings of the International Conference on the Utilization of Tidal Power, 1970, Nova Scotia Technical College New

York: Plenum Press, 1972

Peppas, Lynne Ocean, Tidal, and Wave Energy: Power

from the Sea New York: Crabtree, 2008.

Thirring, Hans Energy for Man: From Windmills to

Nu-clear Power 1958 Reprint Bloomington: Indiana

University Press, 1976

Web Site

U.S Department of Energy

Renewable Energy: Ocean Tidal Power

http://www.energysavers.gov/renewable_energy/

ocean/index.cfm/mytopic=50008

See also: Hydroenergy; Ocean current energy; Ocean

thermal energy conversion; Ocean wave energy;

Oceans; Renewable and nonrenewable resources

Timber See Forests; Timber

industry; Wood and timber

Timber industry

Categories: Obtaining and using resources; plant

and animal resources

Increasing demand for timber and forest products has

resulted in loss of natural forest cover in many regions

of the world As global demand for wood has grown,

in-ternational agencies have found that reports of

unsus-tainable and illegal harvesting practices have also

risen in number.

Background

The timber industry is composed of a diverse group of

companies and organizations utilizing wood and fiber

harvested from forests in the production of solid wood

products (such as furniture and lumber),

reconsti-tuted wood products (such as particleboard), pulp and

paper, and chemicals In addition, many other

com-mercial products are derived from forest resources,

in-cluding types of medicine, food, specialty items such as

Christmas trees, and fuel A surprisingly high

percent-age of wood harvested is used solely for fuel, either as

firewood or as charcoal In 2005, the Food and

Agri-culture Organization of the United Nations (FAO)

es-timated that approximately one-half of all harvested

wood in the world is used for fuel and that the major-ity of energy needs in many developing countries is met by fuel wood, although this number declined slightly after the mid-1990’s While the amount of fuel wood harvested may have declined, global demand for timber overall continues to rise, with China emerg-ing as the world’s leademerg-ing consumer

Historical Significance The development of the forest products industry par-allels the development of Western civilization From Robin Hood to Paul Bunyan, the utilization of forest products is ingrained in Western mythology and cul-ture Development of the first forest management techniques in the Middle Ages was motivated by secu-rity interests related to the continued availability of wood for shipbuilding Royal foresters planned for needs that might not arise for centuries Forest man-agers in Great Britain, for example, planted oak trees

in the sixteenth century to ensure that a supply of ships’ timbers would be available one hundred years

or more into the future

In the Americas, the westward movement of Euro-pean settlement was accompanied by, and in some cases motivated by, the development of the forest-products industry The first forest-products shipped back to Europe included forest products such as ships’ masts, ships’ timbers, potash, and tannin When explorers and settlers encountered the old-growth forests of North America, conservation principles that had been emerging in the Old World were ignored in the New World The forests of New England, the Deep South, and other sparsely populated areas seemed so inex-haustible that loggers clear-cut and then moved on with little thought that the resource might ever be ex-hausted

Eventually, first in Europe and then in North Amer-ica, the realization that natural forests could indeed

be depleted came to the forefront Government and industry realized that it was necessary to develop tech-niques for regenerating and managing forest ecosys-tems to ensure a continued supply of wood products

to meet human needs This process is still occurring

in many developing countries, as logging advances into areas that had experienced only limited harvest-ing for millennia Forests also continue to be lost to agriculture, and, indeed, according to FAO assess-ments, clearing land for agricultural development continues to be the leading reason for the loss of trop-ical rain forests in developing nations

Old-Growth Forests

All ecosystems develop within the context of natural

disturbance cycles Whether the natural agent is fire,

flooding, or windstorms, every hectare on the Earth is

subject to periodic disturbance even without the

in-fluence of human activity The disturbance intervals

may be very long in some systems; forests consisting of

late-successional species that have not been disturbed

for an extended interval are referred to in common

language as old-growth forests

The forest-products industry developed through

the utilization of these natural forests As these

re-sources became scarce, forest management techniques

were developed to ensure the restoration of forests

following utilization As old-growth forests containing

large trees were depleted, manufacturing technology

changed to use smaller material that could be

har-vested from second-growth forests This led to the

development of composite wood products such as

plywood, oriented strand board (often referred to

simply as OSB), medium density fiberboard (MDF),

particleboard, and laminated beams OSB, MDF,

and particleboard are often made from the materials,

such as sawdust and chips, left after logs are sawn

into lumber Prior to development of these products,

waste material in sawmills was generally disposed of

by burning

Sustained Yield Humans obtained goods and services from natural forests for millennia before increasing population, the development of agriculture, and improvements in technology allowing larger and faster harvests began

to lead to the depletion of natural forests Fear of the depletion of natural forests and an impending timber famine led to development of the sustained-yield con-cept, which holds that forests should be managed to produce wood products at a rate approximately equal

to the natural rate of biological growth The develop-ment of the sustained-yield concept was associated with the belief that properly managed forests could produce a continuous, never-ending flow of wood and fiber This concept is still evolving to include recogni-tion that the continued survival of all species and the maintenance of ecosystem structure and function, as well as the production of goods and services, are of vital interest to human society

In addition to managing natural forests to provide for sustained yield, researchers have developed hy-brids and fast-growing strains of desirable species, such as loblolly pine in the United States and eucalyp-tus in Australia, for use in plantations The 2002 FAO Global Forest Resources Assessment noted that be-tween 1990 and 2000, the number of hectares world-wide devoted to tree farming increased 428 percent,

U.S Timber-Based Industries, 2002

Paid Employees

Payroll (millions of dollars)

Shipment Value (billions of dollars)

Veneer, plywood, & engineered

Other converted paper

Source: U.S Census Bureau, 2002 Economic Census, Manufacturing, General Summary, 2005.

from 43.6 million to 187 million hectares Plantation

forests have the advantage of allowing for ease in

har-vesting and for providing for a predictable volume of

timber There are, however, a number of

disadvan-tages to the typical forest plantation, including loss of

diversity in the plantation (both floral and faunal)

and an increased risk of disease and insect

infesta-tions

Effects of Timber Harvesting

Harvesting forest products in such a way as to mimic

natural disturbance and to ensure the continued

func-tioning and survival of all ecosystem components is

possible However, many examples exist of harvesting

that have led to long-term disruption and alteration

of ecological processes Nutrient loss, erosion, and

loss of species following poorly designed or

improp-erly implemented harvesting operations can result in

the loss of biodiversity and a reduction in long-term

productive capacity

The removal of forest-canopy trees, whether

through harvesting or natural disturbance, leads to

increased soil temperature, increased decomposition,

increased leaching of nutrients and soil carbon, and,

if extreme, a reversion to an early-successional plant

community Removal of the canopy trees will usually

lead to increased erosion, which, if harvesting is not

properly implemented, can be severe and result in

degradation of water quality and aquatic habitat

In-creased runoff from lack of forest cover can also lead

to flooding downstream from cleared areas

Devastat-ing floods in Bangladesh, for example, may be

becom-ing more frequent and severe because of clear-cuttbecom-ing

of forests in the Himalayas in India

Practices meant to improve forest health and

en-courage sustainable harvesting have had unintended

consequences For example, twentieth century

pro-grams promoting fire protection resulted in the

inter-ruption of natural disturbance cycles in many

ecosys-tems In these cases, artificial disturbance through

harvesting may be the only way to ensure the

contin-ued presence of early-successional species in the

land-scape In many cases, these early-successional tree

species are fast growing, straight, and relatively easy

to artificially plant and regenerate These

early-successional forests are ideally suited for the

produc-tion of pulp and paper, fuel wood, and such products

as posts and poles The challenge to industrial and

public-land managers is to develop the appropriate

mix of all successional stages in the landscape in order

to ensure the continued survival of all species and the maintenance of ecosystem structure and function, while allowing for utilization to meet the needs of the globally expanding human population

As the global demand for timber continues to rise, illegal and unsustainable logging practices have also risen International agencies such as United States Agency for International Development and FAO have documented numerous cases of the illegal harvesting

of timber in national parks and preserves, particularly

in developing nations such as Gabon and Indonesia

David D Reed, updated by Nancy Farm Männikkö

Further Reading

Baldwin, Richard F Maximizing Forest Product Resources

for the Twenty-first Century: New Processes, Products, and Strategies for a Changing World San Francisco:

Miller Freeman Books, 2000

Bettinger, Peter, et al Forest Management and Planning.

New York: Academic Press, 2008

Bowyer, James L., Robin Shmulsky, and John G

Haygreen Forest Products and Wood Science: An

Intro-duction Drawings by Karen Lilley 5th ed Ames,

Iowa: Blackwell, 2007

Ellefson, Paul V., and Robert N Stone U.S

Wood-Based Industry: Industrial Organization and Perfor-mance New York: Praeger, 1984.

Evans, Julian, and John W Turnbull Plantation

For-estry in the Tropics: The Role, Silviculture, and Use of Planted Forests for Industrial, Social, Environmental, and Agroforestry Purposes New York: Oxford

Univer-sity Press, 2004

Gane, Michael Forest Strategy: Strategic Management and

Sustainable Development for the Forest Sector New York:

Springer, 2007

Klemperer, W David Forest Resource Economics and

Fi-nance New York: McGraw-Hill, 1996.

Peck, Tim The International Timber Trade Cambridge,

England: Woodhead, 2001

Richards, E G., ed Forestry and the Forest Industries, Past

and Future: Major Developments in the Forest and Forest Industry Sector Since 1947 in Europe, the U.S.S.R., and North America Boston: M Nijhoff for the United

Nations, 1987

Sills, Erin O., and Karen Lee Abt, eds Forests in a

Mar-ket Economy Boston: Kluwer Academic, 2003.

Smith, Wynet, et al Canada’s Forests at a Crossroads—

An Assessment in the Year 2000: A Global Forest Watch Canada Report Washington, D.C.: World Resources

Institute, 2000

United Nations Food and Agriculture Organization.

FAO Yearbook of Forest Products, 2002-2006 Rome:

Author, 2008

_ State of the World’s Forests 2009: Adapting for the

Future—Society, Forests and Forestry Rome: Author,

2009

Web Sites

United Nations Food and Agriculture

Organization

State of the World’s Forests 2009

http://www.fao.org/docrep/011/i0350e/

i0350e00.htm

U.S Forest Service, U.S Department of

Agriculture

U.S Forest Products Annual Market Review and

Prospects, 2004-2008

http://www.fpl.fs.fed.us/documnts/fplrn/

fpl_rn305.pdf

See also: American Forest and Paper Association;

Forest management; Forestry; Forests; Land ethic;

National parks and nature reserves; Sustainable

de-velopment; United Nations Framework Convention

on Climate Change; Western Wood Products

Associa-tion; Wood and charcoal as fuel resources; Wood and

timber

Tin

Category: Mineral and other nonliving resources

Where Found

Although tin is widely distributed throughout the

Earth’s crust, the average concentration is very low,

less than 0.001 percent The primary ore mineral is

cassiterite (SnO2) which generally occurs in granitic

igneous rocks, associated hydrothermal veins near

ig-neous rocks, or the weathered and eroded debris of

granitic rocks The major producers of tin are China,

Indonesia, and Peru

Primary Uses

Traditionally, tin has been used in the production of tin

plate, used in making food containers Tin is also

al-loyed with lead to make solders; with copper to make

bronze; and with lead, brass, or copper to make pewter

Technical Definition Tin (chemical symbol Sn) is a silver-white metal that belongs to Group VIA of the periodic table Tin has an atomic number of 50 and an atomic weight of 118.65 Tin comes in two forms (allotropes): gray (alpha) tin and white (beta) tin Gray tin, a face-centered crystal-line structure with a density of 5.75 grams per cubic centimeter, changes into white tin at 13.2° Celsius White tin has a body-centered tetragonal structure with

a density of 7.28 grams per cubic centimeter The melt-ing point of tin is 231.97° Celsius, and the boilmelt-ing point

is 2,270° Celsius, giving this element one of the largest temperature ranges for a liquid metal Tin has ten sta-ble isotopes, the highest number of any element Description, Distribution, and Forms Tin is a widely distributed element in the Earth’s crust and can form both inorganic and organic com-pounds Tin generally forms two series of inorganic compounds Since tin has two valence states, II and IV, the inorganic compounds are built using these two states of tin Some of the more commercially impor-tant compounds of tin (II) include stannous chloride (SnCl2), stannous oxide (SnO), and stannous fluo-ride (SnF2) The most common tin (IV) compounds are stannic oxide (SnO2) and stannic chloride (SnCl4) Tin can also form compounds with carbon; more than five hundred organotin compounds are known Some of these compounds are nontoxic and are used extensively as stabilizers for polyvinyl chlo-ride Other organotin compounds are toxic and are used as biocides in fungicides and disinfectants Although tin is widely distributed throughout the crust of the Earth, it is concentrated in ore deposits in three main regions The primary tin regions are from the Korean Peninsula through China to Southeast Asia; Thailand to Indonesia; and Peru, Bolivia, and Brazil The tin deposits found in these regions are as-sociated with granitic igneous rocks, related hydro-thermal veins, or stream deposits (placers) that con-tain the eroded tin minerals More than 99 percent of the tin produced through history has been derived directly or indirectly from granitic rocks The tin-bearing granitic rocks were formed near convergent plate boundaries in or near subduction zones Some

of the granitic rocks produced in the subduction zones contain the tin ore mineral cassiterite; com-monly the associated hydrothermal veins also carry cassiterite These hydrothermal veins tend to be rich

in fluorine and boron and often contain minerals

such as tourmaline, apatite, fluorite, and topaz

Cassit-erite is also found associated with the minerals

ar-senopyrite, molybdenite, and wolframite Lode

de-posits of tin are found primarily in Bolivia and in

England The Bolivian lode tin ores also contain the

rare tin minerals stannite (CuFeSnS4) and cylindrite

(PbSn4FeSb2S14) These vein deposits are worked by

underground mining techniques used in mining many

other base metals

History

Early civilizations used tin as an alloy with copper to

make bronze The earliest bronzes appear to have

been an alloy of copper and arsenic, but the later dis-covery of tin/copper bronzes yielded a safer and better material The earliest tin bronze items were probably produced by the peoples of the Middle East

as long ago as 3500 b.c.e., and Egyptian bronze arti-facts date back to at least 3000 b.c.e Although these items contain about 10 percent tin, it is unlikely that these early people knew of tin as a distinct and sepa-rate metal No evidence of smelting of pure tin from ore or use of the metal by itself has been discovered Rather, tin ores may have been added to the copper ores when smelting the copper, and the resultant liq-uid contained both copper and tin

Data from the U.S Geological Survey, U.S Government Printing Office, 2009.

3,000

100,000

2,000

38,000

100 2,000 100 3,500 4,000

Metric Tons of Tin Content

175,000 150,000

125,000 100,000

75,000 50,000

25,000 Vietnam

Portugal

Peru Malaysia

Indonesia

Congo, Democratic

Republic of the

Russia

Thailand

Other countries

2,000

150,000

China

Brazil Bolivia

Australia

16,000 12,000

Tin: World Mine Production, 2007

The Romans learned how to “roast” the tin from

ore deposits, and they used tin as a coating on iron

ob-jects Because tin is easy to apply to other metals, and

because it does not corrode under normal

condi-tions, this use of tin has continued to the present

Food canning was developed in 1812, and much of

the tin mined today is used to coat steel food

contain-ers Tin was also used to produce pewter as far back as

1500 b.c.e., and this alloy was used extensively by the

Romans In the early 1800’s, tin was first mixed with

copper and antimony to make a babbitt metal that

re-duced friction of bearings in machinery This alloy,

created by Isaac Babbitt, was an important

contribu-tion to the Industrial Revolucontribu-tion

Obtaining Tin

Deposits of cassiterite are concentrated in the upper

levels of the granitic intrusions and associated

hydro-thermal veins, and they are commonly exposed to

weathering and erosional forces As a result, most of

the currently operating mines are working tin

depos-its less than 300 million years old The older deposdepos-its

have generally been eroded away The older tin ores

that have escaped erosion are found primarily in the

central parts of continental masses The oldest known

tin ores are found in South Africa and are more than

2.5 billion years old

Because cassiterite is both heavy (with a specific

gravity of 6.8 to 7.1) and hard (with a Mohs scale

hard-ness of 6 to 7), it is commonly found as a placer

mineral in streams and rivers that drain tin-bearing

igneous regions As the rocks of the tin region are

weathered and eroded, the softer minerals are broken

down into small clasts, and the lighter materials are

carried downstream to the oceans The heavy

miner-als such as cassiterite and wolframite (a

tungsten-bearing mineral) are left behind in the alluvial

de-posits Most of the Southeast Asian deposits of tin are

alluvial accumulations that formed in ancient rivers

that are now exposed on dry land

A small percentage of tin has been produced from

base-metal sulfide deposits These deposits

occasion-ally contain cassiterite concentrated in

volcanic-sedimentary deposits that were formed in or near

high-temperature submarine vents The major

depos-its of this type are found in Canada and Portugal The

Neves Corvo, Portugal, deposit is a massive sulfide ore

containing copper, zinc, lead, silver, and tin

Although many of the tin deposits first exploited

were located in Europe, the majority of the tin mined

now comes from Asia and South America World pro-duction of tin is approximately 280,000 metric tons The largest producer is China, which mines about 40 percent of the world total Second in mine produc-tion is Indonesia (30 percent of the world total), fol-lowed by Peru (16 percent), Bolivia (6 percent), and Brazil (4 percent) Additional countries—including Australia, Malaysia, Vietnam, and Russia—also mine tin The last operational tin mine in the United States closed in 1990 World tin reserves have been esti-mated at about 6 million metric tons, most of which is

in Southeast Asia and South America World con-sumption is about 350,000 metric tons annually Pure tin can also be obtained by recycling tin-plate scrap and tin-plated steel cans Other secondary tin can be extracted from other scrap materials and from solutions commonly involved in the manufacturing of electronic equipment Total production of secondary tin from recycling averages about 15,000 metric tons per year, and the United States is the largest producer The vein deposits of South America, England, and Australia are mined by the same techniques used in hard-rock base-metal mining throughout the world Alluvial sands are generally mined by surface mining methods The sands can be cleared of any barren overburden and then excavated by directing high-pressure water jets that disaggregate the sands These sands are then washed over a series of baffled sluices that will retain the heavy minerals such as cassiterite The cassiterite and other heavy minerals are periodi-cally removed from behind the baffles This ore is then sent to smelters for refining Some alluvial cassit-erite has been washed out to the oceans, and in some Southeast Asian areas the shallow ocean floor is dredged to recover the ore Stream tin accounts for about 80 percent of the tin recovered each year Although cassiterite is almost 79 percent tin, the tin ores and concentrates vary in the amounts of im-purities they contain Generally the ores are first roasted to drive off any sulfur in the associated miner-als, and then the tin minerals are heated in the pres-ence of carbon (coke) to reduce the cassiterite to liq-uid tin with the release of oxygen, which reacts with the carbon to form carbon dioxide Commonly, lime-stone is used as a flux to reduce the temperature of the reaction to approximately 1,400° Celsius The liquid tin is extracted and the floating slag removed and re-processed The smelted tin is then refined either elec-trolytically or by fire Elecelec-trolytically refined tin can reach a purity as great as 99.999 percent

Uses of Tin

Tin and its alloys have many important commercial

and industrial uses In the past, primary use was in the

production of tin plate, which is used in the

produc-tion of food containers Tin plate is made by coating

steel with a thin (1 micrometer thick) layer of tin

Un-til the middle of the twentieth century, tin plate was

manufactured by immersing the steel in a hot bath of

molten tin, but most tin plate is now made by

electro-lytically plating the tin onto the steel The tin plate is

used primarily to make cans for food and beverages

However, aluminum has become the metal of choice

in the production of food cans

Tin alloys are also used in coating steel and other

metals Zinc, nickel, copper, and lead are each alloyed

with tin to produce coatings with specific properties

Terneplate is a tin/lead coating for steel that is

com-monly used to retard corrosion Many gasoline tanks

are also made of terneplate

Because of its low melting temperature and its

abil-ity to alloy with many metals at different

concentra-tions, tin has long been a major component of solders

used to join metal parts The most common solder is

an alloy of tin and lead Tin and lead can be alloyed at

all possible relative concentrations, but most

com-monly the tin in solder ranges from 30 percent to 70

percent Tin/lead solders soften over a range of

tem-peratures, and this allows for use in a variety of

differ-ent soldering techniques Because of the toxic effects

of lead, much research has been concentrated on

pro-ducing lead-free solders Tin/silver solders and tin/

zinc solders that melt at low temperatures have been

developed In addition, silver and indium are usable

alloy metals for lead-free solders

Babbitt metals are important tin, antimony, and

copper alloys that are commonly manufactured into

bearings that run against steel shafts This white metal

alloy is soft enough to allow for irregularity in the steel

shafts Babbitt metal can also embed any loose metal

particles that arise from the running of the machine,

which helps to reduce scratching or scoring of the

other machine parts, thus prolonging the life of the

machines Babbitt’s discovery of these alloys was an

important ingredient in the Industrial Revolution

Al-though Babbitt and others experimented with various

concentrations of tin, antimony, and copper, the best

white metals contain about 7 percent antimony and 3

percent copper These tin alloys do not bear heavy

loads well, however, and are replaced by a

tin/alumi-num alloy when necessary This alloy, composed of

about 80 percent aluminum, is used in diesel engines and some automobiles Heavy-duty bearings are com-posed of leaded bronzes

Two traditional uses of tin are in the production of bronze and pewter Tin bronzes today are composed

of tin and copper or tin, copper, and lead The bronze used in the making of bells and musical instruments contains up to 20 percent tin to give it the correct tonal qualities The pewter of ancient Roman times was an alloy of tin and lead, but the recognition of the toxic nature of lead has caused a shift in the composi-tion of modern pewter Most pewter today is an alloy containing mostly tin, with only minor amounts of copper and antimony The copper and antimony give strength to the weak tin and allow it to be used in plate ware as well as in jewelry

Tin is utilized in many other ways It is used in small amounts to soften some metal alloys, making the met-als easier to machine It is met-also alloyed with aluminum and titanium for use in the aerospace industry Silver and tin are alloyed to make one of the most commonly used dental fillings

Tin has also replaced the lead and tin/lead cap-sules that surround corks on wine bottles Research

Cans &

containers 26%

Electrical 24%

Construction 11%

Transportation 11%

Other 28%

Commodity Summaries, 2009

Data from the U.S Geological Survey,

U.S Government Printing Office, 2009.

U.S End Uses of Tin