World Bank Category: Organizations, agencies, and programs Date: Established 1945 The World Bank has played an active role in the devel-opment, use, and conservation of natural resources
Trang 1Woody material is produced in many plants, but its
most useful manifestation is in the limbs and trunks of
trees There is a great diversity of tree species, and
most climatic zones have at least one that has adapted
to the prevailing conditions within that area Thus
wood is generally available in most inhabited regions
of the world Wood has played a dominant role as a
construction and engineering material in human
so-ciety, yet humankind has lived with this material for so
long that its significance is easily overlooked
Hardwoods and Softwoods
Trees are broadly classified into hardwoods and
soft-woods These terms can be misleading, since they are
not connected to the actual hardness of the wood
Hardwoods are broad-leaved deciduous trees
Soft-woods, on the other hand, have narrow, needlelike
leaves and are usually evergreen Oak, birch, and
bass-wood are common hardbass-wood species, whereas
long-leaf pine, spruce, and cypress are softwoods Some
hardwoods (oak) are actually hard Many others
(basswood) are actually softer than the average
soft-wood In fact, balsa is classified as a hardwood even
though it is one of the softest woods in the world
By far the majority of timber used in building
struc-tures comes from the softwood category Douglas fir,
southern pine, and redwood are some of the
impor-tant softwood species widely employed in structural
applications They are relatively strong and can be used in structural elements such as joists, beams, and columns By comparison, the stron-ger hardwood species, such as oak, are relatively heavy, hard to handle, and hard to nail As far as construc-tion is concerned, their utility is lim-ited; they are generally used only in flooring, cabinetry, and furniture
Supply and Disposal Wood is a renewable resource It does not exist in finite quantities; rather, it
is constantly produced in growing trees If forests are carefully man-aged, timber can be harvested on a sustained-yield basis year after year Wood is also a reusable resource The recycling of timber from old buildings is well documented The ease with which wood can be cut, joined, and worked into various shapes permits the extension of its functional life beyond that of many other construction materials
Wood is a biodegradable natural product: It can be reduced to its constituent carbohydrates and extract-ives through degradation After wood has reached the end of its useful service, it can be disposed of with lit-tle damage to the environment Unlike plastics or chemicals, timber has a very low pollution potential A study quantified the pollution potential of various construction materials, finding that steel is five times more polluting than timber, while aluminum and concrete blocks are respectively fourteen and twenty-four times more polluting From an environmental standpoint, timber is recognized as the most appro-priate construction and engineering material
Logging Tremendous quantities of timber are consumed each year throughout the world An average of about 3.5 billion cubic meters of timber is harvested annually The majority of hardwood harvest is used for fuel, while softwoods are primarily used in construction and manufacturing To produce the large quantities
of timber needed annually, logging operations have become highly organized and technologically ad-vanced When trees are removed in harvest, steps are taken to provide for forest renewal and to prevent
A pile of timber ready for processing (©Vadimb/Dreamstime.com)
Trang 2soil erosion Such steps include leaving some trees to
produce seeds, transplanting young trees, and other
methods of reseeding Sometimes a “prelogging”
op-eration is undertaken before the main harvest In this
phase, the small trees are removed for conversion into
poles, posts, and pulpwood During harvest, various
types of machinery are used to cut trees close to the
ground The limbs are then removed from the fallen
trees and the trunks are bucked into various lengths
and transported to sawmills for further processing
The remaining tree limbs are converted into chips for
sale to pulp and paper mills Frequently roads are
built to facilitate the transportation of trunks and the
deployment of heavy logging equipment At the
con-clusion of harvest, refuse should be disposed of so
that it will not interfere with the growth of new trees
Owing to careful management of forests and
im-proved efficiency of logging operations, the supply of
timber in the United States currently renews itself at a
higher rate than the removal level It must be pointed
out, however, that growth in world population will
in-evitably bring about an increase in timber
consump-tion The adequacy of timber supply will be a matter of
concern in the future
Physical Structure and Strength
As a material of botanical origin, wood is composed
of hollow, elongated fibers These fibers are usually
arranged parallel with one another in the direction
of the length of the trunk They are cemented
to-gether by a substance known as lignin The fibers in softwoods are longer than those in hardwoods The length of the fibers, however, is not a criterion of the strength of the wood Owing to the parallel arrange-ment of their fibers, wood possesses different me-chanical properties in different directions and is said
to be anisotropic As an example, timber is five to ten times as strong in compression parallel to the grain as
it is perpendicular to the grain The varying strength
of timber in different directions must be taken into consideration in construction design By contrast, metals are isotropic, having the same characteristics
in any direction
The strength of timber is affected by its moisture content Wood in a living tree typically contains more moisture than the surrounding atmosphere When a piece of timber is cut from the log and exposed to air, its moisture content decreases to an equilibrium value determined by the temperature and relative humidity
of ambient air Should wood dry below a value called the “fiber saturation point,” it becomes stronger and stiffer That is why higher design stresses are allowed for timber which is used under relatively dry condi-tions, such as a girder in a building, than for timber used under relatively moist conditions, such as in a wa-terfront house or in a bridge
Wood has a high strength-to-weight ratio Com-pared with many other construction materials, wood, pound for pound, is stronger For instance, in bend-ing tests, Douglas fir has a strength-to-weight ratio
U.S Lumber Consumption
(billions of board feet)
Species group
End use
New nonresidential construction 5.8 5.1 4.4 4.3 3.9
Source: U.S Forest Service, U.S Timber Production, Trade, Consumption, and Price Statistics, 1965-1999 and U.S Department of
Commerce, Statistical Abstract of the United States, 2009, 2009.
Trang 3which is 2.6 times that of low-carbon steel Wood also
has very high internal friction within its fibrous
struc-ture and is therefore a good absorber of vibrations It
has much greater damping capacity than other
mate-rials, particularly the metals That explains why wood
is the preferred material for construction of houses in
earthquake-prone regions Finally, timber structures
can be designed to withstand impact forces that are
twice as large as those they can sustain under static
conditions Materials such as steel and concrete do
not permit such increase in the applied forces This
exceptional impact strength of wood is utilized in
tim-ber structures such as bridges and the landing decks
of aircraft carriers
Insulation and Fire Resistance
Because of its fibrous composition, wood has
excel-lent insulating properties At a low moisture content,
wood is classified as an electrical insulator This is what
makes wood such a common material for high-voltage
power-line poles and for tool handles Wood is also an
effective thermal insulator The thermal conductivity
of timber is only a fraction of that of metals and other
common construction materials For example, bricks
are about 6 times more conductive than timber, and
glass and steel are respectively 8 and 390 times more
conductive By utilization of stud walls or layers of
spongy materials, thermal insulation of timber
struc-tures can be further enhanced In addition, timber
structures may be designed to provide a degree of
acoustical insulation Sound is transmitted through
vibration of air particles Because of its high
vibration-damping capacity, wood is also a good acoustical
insu-lator
It is well known that wood is combustible On the
other hand, wood that is thick enough is also fire
resis-tant Because of the low thermal conductivity of wood,
the high temperatures of a fire cause a temperature
rise for only a short distance into the wood from the
surface exposed to the fire This is the reason larger
timber members may continue to support a structure
in a fire long after an insulated steel member has
collapsed because of elevated temperatures In fact,
buildings framed with large timber members have
been given the highest rating by fire underwriters
among all common buildings erected
Fabrication and Workability
Wood may be cut and worked into various shapes with
the aid of simple hand tools or with power-driven
ma-chinery It therefore lends itself not only to conver-sion in a factory but also to fabrication on site It is the latter fact that principally keeps conventional wood-frame construction fully competitive with any method
of prefabrication of houses yet employed
Timber can be joined with nails, screws, bolts, and connectors, all of which require the simplest kinds of tools and produce strong joints Timber may also be joined with adhesives, which can produce a continu-ous bond over the entire surface to which they are ap-plied and develop the full shear strength of the solid timber This use of adhesives provides a means of fab-ricating timber members of different shapes and al-most unlimited dimensions The prefabrication of large wood trusses, laminated beams and arches, and stress-skin panels has permitted wood to remain ex-tremely competitive as a building and engineering material
Durability Wood is remarkably resistant to decay and is inert to the action of most chemicals It is widely used in facili-ties for bulk chemical storage; the timber may be in di-rect contact with the chemicals When wood is ex-posed to atmospheric conditions, it slowly erodes under the action of weather at a rate of about 0.64 cen-timeter per century There is no reason why, if prop-erly used, wood should not last for a long time Decay and insect damage are often significant problems, but these can be minimized by following sound methods
of design in construction and by using properly sea-soned timber In situations where biological wood-destroying agencies are difficult to control, the decay resistance of timber can be maintained by impregna-tion with suitable preservatives
Untold numbers of well-designed bridges and buildings made entirely or partly of wood have served satisfactorily for long periods with little maintenance Many that are more than a century old are still in ser-vice, whereas others, although in satisfactory condi-tion, have been altered or replaced to meet more stringent modern building codes If years of satisfac-tory service are a measure of durability, few construc-tion materials can rival timber
Significance of Wood Wood has remained a primary construction material for thousands of years essentially because no competi-tive material has all the advantages of wood No other natural substance can meet the ever-increasing
Trang 4mands of modern society for paper and other pulp
products It is also unlikely that a synthetic material
can be made that can compete economically with
wood as a source of pulp, particularly in the light of
the limited supply and high cost of petroleum On the
other hand, methods for converting wood into
vari-ous chemicals are continually in development There
is potential for using wood as a raw material to
pro-duce chemicals that are now obtained from
petro-leum
Future Prospects
Tremendous progress has been made in transforming
wood from a material of craftsmanship to one of
en-gineering Reliable structural grading, improved
fas-tenings, efficient fabrication, and glue-laminating have
all contributed to making wood a modern
construc-tion material Timber connectors and other
improve-ments in fastenings have permitted the use of small
timber members for larger spans It is expected that
even better methods of fastening will be developed so
that long, clear-span timber trusses will become
com-mon sights in new buildings
The increasing popularity of glue-laminating is of
particular significance A glue-laminated timber
mem-ber typically has greater strength than a solid sawed
member of the same size It may also have superior
surface properties such as higher fire resistance The
laminated arches used in churches and buildings are
common examples of this application Other
exam-ples include the exterior waterproof laminations in
such structures as bridges and ships
Fai Ma
Further Reading
Bowyer, Jim L., Rubin Shmulsky, and John G
Hay-green Forest Products and Wood Science: An
Introduc-tion 5th ed Drawings by Karen Lilley Ames, Iowa:
Blackwell, 2007
Breyer, Donald E., et al Design of Wood Structures 6th
ed New York: McGraw-Hill, 2007
Diamant, R M E Thermal and Acoustic Insulation
Bos-ton: Butterworths, 1986
Flynn, James H., Jr A Guide to More Useful Woods of the
World Madison, Wis.: Forest Products Society, 2007.
Green, Harvey Wood: Craft, Culture, History New York:
Viking, 2006
Hackett, Donald F., and Patrick E Spielman Modern
Wood Technology Milwaukee, Wis.: Bruce, 1968.
Hoadley, R Bruce Understanding Wood: A Craftsman’s
Guide to Wood Technology Newtown, Conn.: Taunton
Press, 2000
Panshin, A J., and Carl de Zeeuw Textbook of Wood
Technology: Structure, Identification, Properties, and Uses
of the Commercial Woods of the United States and Can-ada 4th ed New York: McGraw-Hill, 1980.
U.S Department of Agriculture, Forest Service,
For-est Products Laboratory The Encyclopedia of Wood.
New York: Skyhorse, 2007
Walker, John C F Primary Wood Processing: Principles
and Practice 2d ed Dordrecht, the Netherlands:
Springer, 2006
See also: Forest management; Forest Service, U.S.; Forests; Paper; Renewable and nonrenewable re-sources; Timber industry; Wood and charcoal as fuel resources
World Bank
Category: Organizations, agencies, and programs Date: Established 1945
The World Bank has played an active role in the devel-opment, use, and conservation of natural resources, such as forests and water, in developing countries By providing financial and technical assistance, it aims
to reduce global poverty by promoting better use of nat-ural resources It also helps developing countries adapt
to the threat of climate change.
Background The World Bank is also known as the International Bank for Reconstruction and Development It was created after the Bretton Woods Conference in 1944 Its original goal was to rebuild international eco-nomic systems after World War II Its focus shifted to helping developing countries with the stated goal of poverty reduction by offering financial, institutional, and technical support
Impact on Resource Use The World Bank suggests that poor countries have suffered from chronic poverty not because of a lack of natural resources but as a result of a “resource curse”— they lack the incentives to diversify their economies because of the abundance of natural resources Poor management, inadequate infrastructure, and a lack
Trang 5of know-how are also cited as causes of poverty
Cli-mate change has posed further threats to developing
countries, because poor people rely heavily on
natu-ral resources for their livelihoods More episodes of
flood and drought, owing to anthropologically
in-duced climatic variability, will severely affect their
sur-vival Because of this background, integrating natural
resources into sustainable development has become
the World Bank’s key strategy in rural development
and environmental conservation
To achieve sustainable natural resources
manage-ment, the World Bank focuses on four main areas:
forests, desertification, water, and biodiversity While
many programs take place at the community level, the
World Bank also promotes crosscutting and
cross-sectoral interventions at both national and
interna-tional levels through public-private partnerships and
civil society programs The World Bank also
intro-duces new technologies, such as biofuels, to help
de-veloping countries raise agricultural productivity and
capitalize on the rising commodity price levels
In the 1980’s, the World Bank adopted the
“Wash-ington Consensus” model of development to privatize
natural resources, such as water It argued that the state
was too weak and too inefficient to manage water
re-sources Based on the theory defining water as an
eco-nomic good and requiring users to pay for water, water
is supplied, delivered, and privatized through
market-based mechanisms and public-private partnerships
Such an approach to managing natural resources has
caused controversies, however Many poor people are
denied access to clean water because they cannot
af-ford it The policies of deregulation and liberalization
of markets are also blamed for neglecting issues such
as equity and long-term ecological sustainability
Since the 1990’s, the World Bank has promoted the
concept of “good governance.” It blames corruption
and weak institutional support for the
mismanage-ment of natural resources in developing countries
To combat corruption, it promotes transparency,
ac-countability, and public participation To strengthen
capacity building, it forms organizations, such as water
users, associations and village forestry committees,
to manage resources The World Bank is praised for
acknowledging the role of power in managing
natu-ral resources, but it is criticized for offering a
“one-size-fits-all” approach to institutional reforms and for
overemphasizing economic growth over long-term
re-source conservation
Sam Wong
Web Site World Bank http://www.worldbank.org/
See also: Biofuels; Capitalism and resource exploita-tion; Desertificaexploita-tion; Resource curse
World Commission on Environment and Development
Category: Organizations, agencies, and programs Date: Established 1983
The United Nations World Commission on Environ-ment and DevelopEnviron-ment, also known as the Brundtland Commission, issued a report in 1987 that popularized the concept of sustainable development: development that meets the needs of the present without depriving future generations of their ability to meet their own needs Several subsequent global initiatives sprang from the commission’s work.
Background With human populations and activities exerting un-precedented pressures on the environment, the United Nations General Assembly passed a resolution
on December 19, 1983, establishing a special commis-sion to examine the concerns of global environment and development to the year 2000 and beyond This commission later took the name World Commission
on Environment and Development (WCED) The WCED was also referred to as the Brundtland Com-mission for its chair, Gro Harlem Brundtland, who was Norway’s prime minister and former minister of the environment Brundtland headed a commission
of twenty-one other members These commission-ers—government officials, environmental scientists, social scientists, and economists from developed and developing countries around the globe—served not
as representatives of their respective governments but
as individual, independent experts
The WCED held its first official meeting in Geneva, Switzerland, in October, 1984 At this meeting the commission chose key issues for analysis, including population, energy, industry, food security, human settlements, international economic relationships, en-vironmental management, and international cooper-ation
1360 • World Commission on Environment and Development Global Resources
Trang 6The WCED subsequently convened deliberative
meetings around the world to gain an intimate
under-standing of regional environment and development
concerns It also held open public hearings in
devel-oped and developing countries where governmental
representatives, researchers, experts, industrialists,
nongovernmental agency representatives, and
ordi-nary citizens could provide their insights and input
Impact on Resource Use
In the spring of 1987, the WCED published its final
re-port, Our Common Future, commonly known as the
Brundtland Report, which examined the political,
so-cietal, and economic changes necessary to achieve
sustainable development—that is, development that
addresses present needs without sacrificing future
generations’ abilities to address their own The report
stresses the necessity of recognizing and managing
the interrelation between environment and
develop-ment instead of prioritizing one over the other It calls
for intensified and cooperative efforts among all
na-tions to meet the needs of the poor, promote peace,
enhance security, conserve and share resources, and
assess environmental risk on a global basis Though
the WCED ceased its operations at the end of 1987,
the following year, the Centre for Our Common
Fu-ture was established in Geneva to promote the
mes-sages of the WCED’s final report and to encourage
di-alogue on sustainable development
Our Common Future and the work of the WCED laid
the groundwork for the 1992 United Nations
Confer-ence on Environment and Development, or Earth
Summit, in Rio de Janeiro, Brazil Sustainable
devel-opment was a key concept underlying the agreements
signed at the Earth Summit, including the Framework
Convention on Climate Change; the Convention on
Biological Diversity; the Rio Declaration on
Environ-ment and DevelopEnviron-ment; the StateEnviron-ment of Forest
Prin-ciples; the resolution on desertification that later led
to the United Nations Convention to Combat
Deserti-fication; and Agenda 21, a plan for achieving
sustain-able development worldwide
Karen N Kähler
Web Site
United Nations Documents
Report of the World Commission on Environment
and Development: Our Common Future
http://www.un-documents.net/wced-ocf.htm
See also: Agenda 21; Earth Summit; Sustainable de-velopment; United Nations climate change confer-ences; United Nations Convention to Combat Deser-tification; United Nations Framework Convention on Climate Change
World Conservation Union See
International Union for Conservation of Nature
World Resources Institute
Category: Organizations, agencies, and programs Date: Established 1982
The primary roles of the World Resources Institute are
to find practical ways to protect the Earth and to make people’s lives better in the present and the future It in-vestigates and analyzes global environmental and re-source issues and their relationship with population growth and developmental issues that include defores-tation, desertification, and global climate change.
Background The World Resources Institute (WRI) was established
on June 3, 1982, to address the need for research and practical solutions to help solve serious global envi-ronmental, resource, population, and development problems
The WRI held a global conference in 1984 at which seventy-five experts and leaders in science, industry, government, energy, agriculture, and environmental studies from twenty countries established a list of practical proposals to assess and address global envi-ronmental and development problems and issues In
1990, WRI conducted a feasibility study that laid the foundation for the creation of the Global Environ-ment Facility Two years later, the WRI launched the Global Biodiversity Strategy, which was instrumental
in the development of the Convention on Biological Diversity
Impact on Resource Use The WRI established four main goals to concentrate its efforts on the development and use of global
Trang 7sources The first goal is to protect the global climate
system from further degradation from greenhouse
gases and other hazardous emissions The second
goal is to keep the public informed about any
deci-sions that affect natural resources and the
environ-ment The third goal is to use businesses and markets
to expand global economic opportunities, while
pro-tecting the environment The fourth goal is to reverse
the harm that has been done by deforestation,
deserti-fication, and global climate changes to ecosystems as
much as possible, so that needed goods and services
can be provided to people worldwide
The WRI is well known for its biennial publication of
the World Resources report, which provides an
authori-tative assessment of the world’s natural resource base
Produced jointly with the United Nations
Environ-ment Programme, the United Nations DevelopEnviron-ment
Program, and the World Bank, this report provides
the latest information on the status of economic,
pop-ulation, natural resource, and global environmental
conditions and trends for more than 150 countries In
2000, the WRI introduced its Global Forest Watch
program, an online Web site devoted to monitoring
forests worldwide One year later it launched
Earth-Trends, a Web site offering data and information
about the environmental, social, and economic trends
that help determine conditions in the world
Since 1985, the WRI has played a vital role in
pro-moting effective global response to climate change
It has worked on international agreements and United
States policies to protect climate systems
world-wide The WRI strongly advocates the reduction of
greenhouse-gas emissions and encourages the
devel-opment of clean energy alternatives that are
sup-ported by businesses, governments, and the general
public all over the world In 2001, the WRI and the
World Business Council for Sustainable Development
played an instrumental role in the development of a
global standard for measuring and reporting
emis-sions of greenhouse gases, known as the Greenhouse
Gas Protocol The WRI provides, and helps other
in-stitutions and governments provide, information and
practical proposals for policy and institutional change
that will help promote the wise, efficient use of global
resources with minimal harm to the environment and
in the best interests of people throughout the world
Alvin K Benson
Web Sites Global Forest Watch http://www.globalforestwatch.org/english/
index.htm World Resources Institute http://www.wri.org/
See also: Biodiversity; Ecology; United Nations Envi-ronment Programme; World Bank
World Wide Fund for Nature
Categories: Organizations, agencies, and programs; social, economic, and political issues; environment, conservation, and resource management
Date: Established September 11, 1961
One of the largest conservation organizations in the world, the World Wide Fund for Nature (formerly the World Wildlife Fund, and retaining that name in the United States) is dedicated to promoting the responsible use of natural resources Research campaigns and proj-ects focus on creating preserves, ensuring survival of all species, protecting against damage, and encourag-ing a balance between humans, wildlife, and the envi-ronment.
Background Established in 1961, the World Wide Fund for Nature (WWFN, formerly the World Wildlife Fund) was origi-nally the fund-raising arm of the International Union for Conservation of Nature (IUCN) The IUCN was founded in 1948 to conduct research and gather data identifying species in need of protection In 1961, headquarters moved from France to Switzerland, and the two organizations worked in tandem on cam-paigns A logo was created so the WWF would easily be identifiable “Chi-chi,” a popular giant panda housed
at the London Zoo, served as a model The group’s first projects included saving the Arabian oryx from extinction, creating a footpath through a reserved section of forest in Madagascar, and transporting eight endangered white rhinoceroses from South Af-rica to Zimbabwe for breeding
The first major campaign, Operation Tiger, fo-cused on saving both tigers and their habitats This
Trang 8cluded a ban on tiger hunting in India, tagging
and tracking remaining tigers to ensure their
population increased, and creating havens for
ti-gers in Indonesia, Thailand, India, and other
parts of Asia Smuggling and poaching of
endan-gered animals and plants was next on the list The
WWf’s efforts to arrest these activities resulted in
the Trade Records Analysis of Flora and Fauna in
Commerce (TRAFFIC) in 1976
By 1980, the goals of the organization had
broadened to address all aspects of nature and
world resources, including all species (whether
endangered or not), insects, flora, fauna, air, soil,
freshwater supplies, oceans, and coastlines This
new focus warranted a change in name from the
World Wildlife Fund to the World Wide Fund for
Nature in 1986 The WWF and the
black-and-white panda logo remain identifiers of the
organi-zation In the United States, which has specific
laws for fund-raising organizations, the WWF
re-mains known as World Wildlife Fund-U.S
Impact on Resource Use
As of 2009, the WWF network had funded eleven
thousand projects and programs in 130 countries
at a cost of nearly $1.17 billion Key projects have
included a moratorium on whale hunting,
stop-ping the ivory trade, saving rhinoceroses,
restor-ing orangutan habitats, and protectrestor-ing mountain
gorillas in Rwanda Recent projects include
estab-lishing marine preserves; creating national parks
in Colombia, Costa Rica, Nepal, and Bhutan;
pro-tecting the Amazon rain forest; establishing school
nature gardens in Zambia; and training local
peo-ple to be wildlife scouts to monitor species with
declin-ing numbers
In 1992, the WWF teamed with other organizations
to educate and alert politicians and businesspeople
about the environmental crisis during the Rio de
Janeiro Earth Summit The 1997 Living Planet
Cam-paign educated people about the world’s biodiversity
It included Global 200, a framework of 238 terrestrial,
marine, and freshwater ecoregions International
stan-dards for fisheries, established in 2000, help prevent
overharvesting of seafood During the 2009 global
climate summit in Copenhagen, Demark,
represen-tatives of WWF attended forums on food security,
water vulnerability, and the impact of climate change
on major companies, lending WWF’s insights on these
key issues
In recent decades, the focus has turned to sustain-able use of resources, reducing pollution, correcting wasteful consumption of resources, and restoring dam-aged habitats or resources For example, the WWF has worked with large corporations, such as Wal-Mart, on sustainable use of resources and agricultural issues
Lisa A Wroble
Web Site World Wide Fund for Nature http://www.worldwildlife.org/
See also: Conservation; Conservation biology; Earth Summit; Endangered species; Endangered Species Act; Global 200; International Union for Conserva-tion of Nature
Activists from the World Wide Fund for Nature (also known as the World Wildlife Fund) gather in front of the Angel of Independence monument
in Mexico City in 2006 (Henry Romero/Reuters/Landov)
Trang 9Zeolites
Category: Mineral and other nonliving resources
Where Found
Zeolites are found naturally wherever volcanic rock
and ash interact with alkaline groundwater They are
mined extensively in many parts of the world Zeolites
are also easily produced through artificial means;
often artificial zeolites are purer and therefore
prefer-able to the organic variety As of 2008, 175 cataloged
unique zeolite frameworks had been identified, 40 of
which are naturally occurring
Primary Uses
The primary use for zeolites is in laundry detergents
The mineral’s porous nature allows particles of dirt
and contaminants to be captured in the wash cycle
and then rinsed away in the rinse cycle Other
com-mon uses are as aquarium filters and cat litter Zeolites
are also used extensively within the medical
profes-sion as molecular sieves to filter and purify air to make
medical grade oxygen
Technical Definition
Zeolite is a crystalline mineral most commonly used
as an absorbent in commercial settings Zeolites are
microporous aluminosilicates with well-defined struc-tures that act as “molecular sieves,” capturing oxygen, minerals, and water and holding them within their many and variable-sized pores Zeolites generally con-tain silicon, aluminum, and oxygen in their frame and water or other molecules within their pores Their de-fining feature is a framework made up of four con-nected networks of atoms They are tetrahedrous in nature, with a silicon atom in the middle and oxygen atoms in the corners They can link together by their corners and form beautiful structures that contain cavities and channels in which other molecules can become trapped Because of this property, Zeolites are excellent means of filtering out impurities in many things
Description, Distribution, and Forms Zeolites are aluminosilicates They are more com-monly referred to as “molecular sieves” because of a particular ability within the substance to sort mole-cules by their sizes and shapes The size of a pore within the zeolite controls what molecules can flow into it These pores are generally noncylindrical in na-ture An “eight-ring” refers to a closed loop consisting
of eight silicon or aluminum atoms and eight oxygen atoms These atoms are tetrahedral in nature but not always symmetrical because of the bonding re-straints within the zeolite, which are often often based on the positioning of the oxygen atoms within the structure
Zeolite products are many and varied Found
in both natural and human-made forms, they are capable of absorbing and filtering out impurities
in water and other liquids They are resistant to heat and chemicals, which makes them excellent filtration devices in nuclear reactors and oil filtra-tion systems
History Zeolite was given its name by Swedish mineralo-gist Axel Fredrik Cronstedt Cronstedt heated a material then referred to as stilbite and observed that a small piece of the substance produced a large amount of steam Cronstedt, pulling from
Zeolites are known for their high absorbency (USGS)
Trang 10the Greek words zeo, which means “boil,” and lithos,
which means “stone,” named the material zeolite
Obtaining Zeolites
Zeolites are formed when volcanic rock and layers of
ash are subjected to groundwater containing alkaline
These types of zeolites are seldom pure, often
con-taining contaminates from other minerals and
sub-stances Open-pit zeolite mines can be found in
Ar-kansas, Idaho, and New Mexico Topsoil is removed
from the site, making access to the zeolite possible
The zeolite can be blasted free, cut free with ripper
blades, or scraped from the ground with a bulldozer
or top loader Once removed from the ground, the
zeolite is crushed, dried, and milled Once processed,
the substance is ready to use
Uses of Zeolites
Zeolites can be found in many places Their
adaptabil-ity as a natural and human-made filter makes them
useful in both household and industrial settings
Oxygen concentrators containing zeolite are
com-monly used to produce medical-grade oxygen The
zeolite is able to filter impurities out of the air
Zeo-lites are also commonly used in water filtration
sys-tems for the same reason; they capture impurities in
the water when water is filtered through them
Zeolites are resistant to radiation, making them
quite useful in nuclear reactions They capture debris
and waste products inside nuclear reactors These
waste products can be removed easily and disposed
of without inhibiting the reactor’s capabilities Once
filled with fission by-products, the zeolite can be
hard-pressed This seals in the fission waste, making the
by-product more easily disposable than the by-by-products
of more conventional radioactive waste disposal
methods
In agriculture, a naturally occurring zeolite called
clinoptilolite is used in the treatment of soil The
absor-bent nature of this particular zeolite allows for vital
minerals to be time-released into the soil Potassium
and nitrogen, in particular, are substances that can be
released in this manner Also, because zeolites are
ab-sorbent, water can be introduced into arid soil In
re-gions where water is overly abundant in the soil,
intro-ducing zeolites can help prevent root rot and improve
harvests Zeolites introduced into waterlogged soil can
capture and retain up to 55 percent of their weight
Zeolites are also commonly used in the heating and
refrigerating industry Zeolite’s ability to absorb heat
makes it useful in the capture and collection of heat and moisture that would escape otherwise The intro-duction of zeolite into such environments improves the efficiency of both tasks
This ability of zeolites to capture impurities in water and other liquids is not overlooked in the pet supply industry Zeolite is an ingredient in many aquarium filters It captures and filters ammonia and other nitrogenous compounds in aquariums, keeping the water from becoming toxic to fish and other aquatic creatures
Another common use for zeolites is in cat litter The nonclumping variety of cat litter is commonly made of zeolite or diatomite This porous litter cap-tures liquid, and is easily removed from the litter box Zeolites introduced into the food supply of animals can improve the animal’s ability to process the food and help to improve the animal’s bone density Addi-tionally, zeolites can reduce the airborne ammonia in holding pens by up to 80 percent
Zeolite is also used in the petrochemical industry, filtering out impurities in crude oil and other petro-leum products Zeolite is hydrogenized and turned into powerful acid via ion exchange Once zeolite is acidified, processes such as isomerization (a process that converts one compound into another with the same number of atoms, only rearranged), alkylation (which transfers the alkyle group of one atom to an-other), and catalytic cracking can be carried out Cat-alytic cracking is a process that requires a furnace and
a reactor Crude oil is heated in the furnace, then sent
to the reactor, where it is introduced to the acidic zeo-lite It is run through the zeolite three times; each time it is filtered through a cooler version of the acidi-fied zeolite The next step is the separation of hydro-gen from the crude oil It is sent to a fractionator (yet another separation process that divides components
of a compound by their physical qualities) in the final step and becomes the end product
Roger Dale Trexler
Further Reading Auerbach, Scott M., Kathleen A Carrado, and Prabir
K Dutta Handbook of Zeolite Science and Technology.
Boca Raton, Fla.: CRC Press, 2003
Peiper, Howard Zeolite: Nature’s Heavy Metal Detoxifier.
Sheffield, Mass.: Safe Goods, 2006
Xu, Ruren, et al Chemistry of Zeolites and Related Porous
Materials: Synthesis and Structure New York:
Wiley-Interscience, 2007