creates a solution with a lower freezing
point than water by itself. The brine
forms below the surface of the ice and
snow  and prevents the water from
freezing into ice and bonding with the
road surface.  Therefore, salt causes
snow  and ice to melt.   Salt is an
inexpensive, widely available, and
effective ice control agent.  It does,
however, become less effective as the
temperature decreases below about -9.4f
C to -6.70 C (150 F to 20f F). At lower
temperatures, more salt would have to be
applied  to  maintain  higher  brine
concentrations to provide the same degree
of melting. Most winter snowstorms and
ice storms occur between -3.9f C to 00 C
(250 F and 320 F), a range in which salt
is most effective.
In highway deicing, salt has been
associated with corrosion to motor
vehicles, bridge decks, unprotected steel
structures, and reinforcement bar and
wire used in road construction. Surface
runoff, vehicle spraying, and windblown
actions also affect roadside vegetation,
soil, and local surface and ground water
supplies. Although there is evidence of
environmental loading of salt during peak
usage, the spring rains and thaws usually
dilute the concentrations of sodium in the
area.
Salt is also added to stabilize the soil
and to provide firmness to the foundation
on which highways are built. The salt
acts to minimize the effects of shifting
caused by changes in humidity and traffic
load in the subsurface.
Distributors.-A tremendous amount
of salt is marketed through various
distributors, some of which specialize in
certain markets such as agricultural and
water-treatment services. In addition to
these two categories, distributor sales
include grocery wholesalers and/or
retailers, institutional wholesalers, U.S.
Government    resalers,  and  other
wholesalers and retailers.
Other.-The other uses of salt include
categories not discussed above.


Geology-Resources
The definitions of reserves and reserve
base are published in the U.S. Geological
Survey Circular 831, 'Principles of a
Resource/Reserve  Classification  for
Minerals."
The oceans are the world's largest
resource of salt. Seawater contains 3.5%
dissolved solids by weight with sodium
chloride representing the major
component, approximately 2.5% by
weight. The world's oceans contain
about 42 x 101' tons (46 x 1015 short tons)
of sodium chloride, which is equivalent to
530 million cubic kilometers (4.5 million
cubic miles) in volume or a cube
measuring 795 kilometers (165 miles) on
edge.
Domestic salt resources are found
mainly in four large depositional basins,
covering an area totaling about 0.2
million square hectacres (0.5 million
square miles) in 18 States. These basins
are (1) the gulf coast, which covers part
of   Alabama,  Arkansas,   Florida,
Louisiana, Mississippi, and  eastern
Texas; (2) the Permian, which is in part
of Colorado, Kansas, New Mexico,
Oklahoma, and western Texas; (3) the
Salina, covering part of Michigan, New
York, Ohio, Pennsylvania, and West
Virginia; and (4) the Williston,
encompassing part of Montana, North and
South Dakota, and Wyoming. The gulf
coast and Permian basins extend into
Mexico; the Salina and Williston both
extend into Canada. The identified salt
resources of the United States are
estimated at 55 x 1012 tons (61 x 1012
short tons) and are being depleted at the
rate of about 35 million tons (39 million
short tons) annually. At the present level
of production, the United States has
enough salt to mine for more than 1.6
million years.  Solar evaporation of
coastal seawater would extend this rate
virtually forever.
Salt can be geologically classified by
its occurrence as evaporite deposits and in
solutions.
Evaporite Deposits.-Bedded, diapiric
flow, and playa salts are the major types
of dry salt deposits. Bedded salt deposits


were formed by the accumulation of
precipitated salts on the seafloor of
ancient landlocked marine bodies of
water.    Extensive  and  widespread
evaporation was essential to form these
massive rock salt deposits, some of which
measure up to 914 meters (3,000 feet) in
thickness.
Salt domes form when vertical or
lateral pressures are applied to stratified
salt deposits in which low-density salt
will flow plastically through the
surrounding rocks of higher density. The
salt domes of Romania, the Federal
Republic of Germany, and the gulf coast
of the United States are examples of
diapiric salt flows. The appearance is
usually cylindrical with circular or
elliptical diameters.  A  cap rock of
anhydrite is common with overlying
layers of gypsum and calcite. Oil, gas,
and sulfur are associated with many
domes and    represent large mineral
resources. There are 329 proven salt
domes in the gulf coastal province and
offshore regions of the United States.
Louisiana has 183 domes onshore and
offshore; Texas, 83; Mississippi, 61; and
Alabama, 2.
Playas are flat, vegetation-free floors
of an undrained desert basin that may
occasionally be covered by water.
Postevaporation minerals such as sodium
carbonate, sodium sulfate, sodium
chloride, borates, nitrates, phosphates,
and potash result from the leaching of the
rocks surrounding the basin by water
flowing into the playa. Searles Lake in
California is a classic example of a salt-
bearing playa lake.
Salt in Solution.-Ocean, lake, and
ground water are the primary aqueous
mediums in which salt is dissolved.
Seawater contains many dissolved
minerals, the major one being sodium
chloride.   Other dissolved minerals
include various calcium, magnesium,
potassium and sulfate compounds.
Water tends to accumulate on land in
topographic depressions created by
tectonic uplifts or subsidences of the
Earth's upper crust. As mineralized
solutions from upland sources drain into
these  basins,   solar   evaporation


SALT-1993












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