CAS Number 7757-82-6
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Linear Formula Na2SO4
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Molecular Weight 142.04
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EC Number 231-820-9
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MDL number MFCD00003504
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PubChem Substance ID 329752527
Sodium sulfate is the sodium salt of sulfuric acid. When anhydrous, it is a white
crystalline solid of formula Na2SO4 known as the mineral thenardite; the decahydrate Na2SO4·10H2O
is found naturally as the mineral mirabilite, and in processed form has been known
as Glauber's salt or, historically, sal mirabilis since the 17th century.
Detailed description
Another solid is the heptahydrate, which transforms to
mirabilite when cooled. With an annual production of 6 million tonnes,
it is a major commodity chemical product.
Sodium sulfate is mainly used for the manufacture of detergents and in the Kraft process of paper pulping. About two-thirds
of the world's production is from mirabilite, the natural mineral form of the
decahydrate, and the remainder from by-products of chemical processes such as hydrochloric acid production.
Applications
Commodity industries
With US pricing at $30 per tonne in 1970,6 up to $90
per tonne for salt cake quality and $130 for better grades, sodium sulfate is a
very cheap material. The largest use is as filler in powdered home
laundry detergents, consuming approx. 50% of world production. This use is
waning as domestic consumers are increasingly switching to compact or liquid
detergents that do not include sodium sulfate.[14]
Another formerly major use for sodium sulfate,
notably in the US and Canada, is in the Kraft process for the manufacture
of wood pulp. Organics present
in the "black liquor" from this process are burnt to produce heat,
needed to drive the reduction of sodium sulfate to sodium sulfide. However, this
process is being replaced by newer processes; use of sodium sulfate in the US
and Canadian pulp industry declined from 1.4 Mt/a in 1970 to only approx.
150,000 tonnes in 2006.[14]
The glass industry provides
another significant application for sodium sulfate, as second largest
application in Europe. Sodium sulfate is used as a fining agent, to help remove
small air bubbles from molten glass. It fluxes the glass, and prevents scum
formation of the glass melt during refining. The glass industry in Europe has
been consuming from 1970 to 2006 a stable 110,000 tonnes annually.[14]
Sodium sulfate is important in the manufacture of textiles, particularly in
Japan, where it is the largest application. Sodium sulfate helps in
"levelling", reducing negative charges on fibres so that dyes can
penetrate evenly. Unlike the alternative sodium chloride, it does not
corrode the stainless steel vessels used in
dyeing. This application in Japan and US consumed in 2006 approximately
100,000 tonnes.[14]
Thermal storage
The high heat storage capacity in the phase change
from solid to liquid, and the advantageous phase change temperature of 32 °C
(90 °F) makes this material especially appropriate for storing low grade solar
heat for later release in space heating applications. In some applications the
material is incorporated into thermal tiles that are placed in an attic space
while in other applications the salt is incorporated into cells surrounded by
solar–heated water. The phase change allows a substantial reduction in the mass
of the material required for effective heat storage (the heat of fusion of
sodium sulfate decahydrate is 82 kJ/mol or 252 kJ/kg[20]), with the further
advantage of a consistency of temperature as long as sufficient material in the
appropriate phase is available.
For cooling applications, a mixture with common sodium chloride salt (NaCl) lowers
the melting point to 18 °C (64 °F). The heat of fusion of NaCl·Na2SO4·10H2O,
is actually increased slightly to 286 kJ/kg.[21]
Small-scale applications
In the laboratory, anhydrous sodium sulfate is
widely used as an inert drying agent, for removing
traces of water from organic solutions.[22] It is more
efficient, but slower-acting, than the similar agent magnesium sulfate. It is only effective
below about 30 °C, but it can be used with a variety of materials since it
is chemically fairly inert. Sodium sulfate is added to the solution until the
crystals no longer clump together; the two video clips (see above) demonstrate
how the crystals clump when still wet, but some crystals flow freely once a
sample is dry.
Glauber's salt, the decahydrate, was historically
used as a laxative. It is effective
for the removal of certain drugs such as paracetamol(acetaminophen) from the body, for
example, after an overdose.[23][24]
In 1953, sodium sulfate was proposed for heat storage in passive solar heating systems. This takes
advantage of its unusual solubility properties, and the high heat of crystallisation (78.2 kJ/mol).[25]
Other uses for sodium sulfate include de-frosting
windows, in carpet fresheners, starch manufacture, and as
an additive to cattle feed.
At least one company, ThermalTake, makes a laptop
computer chill mat (iXoft Notebook Cooler) using sodium sulfate decahydrate
inside a quilted plastic pad. The material slowly turns to liquid and
recirculates, equalizing laptop temperature and acting as an insulation.
PRICE
$166.09/KG OR $75.49/KG
For more information:
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