Sodium sulfate (also known as sodium sulphate or sulfate of soda) is the
inorganic compound with formula Na
2SO
4 as well as several related
hydrates. All forms are white solids that are highly soluble in water. With an annual production of 6 million
tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
s, the decahydrate is a major
commodity
In economics, a commodity is an economic good, usually a resource, that has full or substantial fungibility: that is, the market treats instances of the good as equivalent or nearly so with no regard to who produced them.
The price of a co ...
chemical product. It is mainly used as a filler in the manufacture of powdered home laundry
detergents and in the
Kraft process of paper
pulping
Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibers from wood, fiber crops, waste paper, or rags. Mixed with water and other chemical or plant-based additives, pulp is the major raw mat ...
for making highly alkaline
sulfide
Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds la ...
s.
Forms
*Anhydrous sodium sulfate, known as the rare mineral
thenardite, used as a drying agent in
organic synthesis.
*Heptahydrate sodium sulfate, a very rare form.
*Decahydrate sodium sulfate, known as the mineral
mirabilite, widely used by
chemical industry
The chemical industry comprises the companies that produce industrial chemicals. Central to the modern world economy, it converts raw materials ( oil, natural gas, air, water, metals, and minerals) into more than 70,000 different products. ...
. It is also known as Glauber's salt.
History
The decahydrate of sodium sulfate is known as Glauber's salt after the
Dutch/
German
German(s) may refer to:
* Germany (of or related to)
**Germania (historical use)
* Germans, citizens of Germany, people of German ancestry, or native speakers of the German language
** For citizens of Germany, see also German nationality law
**Ge ...
chemist and
apothecary Johann Rudolf Glauber (1604–1670), who discovered it in Austrian spring water in 1625. He named it (miraculous salt), because of its medicinal properties: the crystals were used as a general-purpose
laxative, until more sophisticated alternatives came about in the 1900s.
In the 18th century, Glauber's salt began to be used as a raw material for the
industrial production of soda ash (
sodium carbonate), by reaction with potash (
potassium carbonate). Demand for soda ash increased, and the supply of sodium sulfate had to increase in line. Therefore, in the 19th century, the large-scale
Leblanc process, producing synthetic sodium sulfate as a key intermediate, became the principal method of soda-ash production.
Chemical properties
Sodium sulfate is a typical electrostatically bonded
ionic sulfate. The existence of free sulfate ions in solution is indicated by the easy formation of insoluble sulfates when these solutions are treated with
Ba2+ or
Pb2+ salts:
: Na
2SO
4 + BaCl
2 → 2 NaCl + BaSO
4
Sodium sulfate is unreactive toward most
oxidizing or reducing agents. At high temperatures, it can be converted to
sodium sulfide by
carbothermal reduction (aka thermo-chemical sulfate reduction (TSR), high temperature heating with charcoal, etc.):
: Na
2SO
4 + 2 C → Na
2S + 2 CO
2
This reaction was employed in the
Leblanc process, a defunct industrial route to
sodium carbonate.
Sodium sulfate reacts with sulfuric acid to give the
acid salt sodium bisulfate
Sodium bisulfate, also known as sodium hydrogen sulfate, is the sodium salt of the bisulfate anion, with the molecular formula NaHSO4. Sodium bisulfate is an acid salt formed by partial neutralization of sulfuric acid by an equivalent of sodium ...
:
: Na
2SO
4 + H
2SO
4 ⇌ 2 NaHSO
4
Sodium sulfate displays a moderate tendency to form
double salts. The only
alums formed with common trivalent metals are
NaAl(SO4)2 (unstable above 39 °C) and NaCr(SO
4)
2, in contrast to
potassium sulfate and
ammonium sulfate which form many stable alums.
Double salts with some other alkali metal sulfates are known, including Na
2SO
4·3K
2SO
4 which occurs naturally as the mineral
aphthitalite. Formation of
glaserite by reaction of sodium sulfate with
potassium chloride has been used as the basis of a method for producing
potassium sulfate, a
fertiliser.
Other double salts include 3Na
2SO
4·CaSO
4, 3Na
2SO
4·MgSO
4 (
vanthoffite) and NaF·Na
2SO
4.
Physical properties
Sodium sulfate has unusual solubility characteristics in water. Its solubility in water rises more than tenfold between 0 °C and 32.384 °C, where it reaches a maximum of 49.7 g/100 mL. At this point the solubility curve changes slope, and the solubility becomes almost independent of temperature. This temperature of 32.384 °C, corresponding to the release of crystal water and melting of the hydrated salt, serves as an accurate temperature reference for thermometer
calibration.
Structure
Crystals of the decahydrate consist of
2)6">a(OH2)6sup>+ ions with
octahedral molecular geometry. These octahedra share edges such that 8 of the 10 water molecules are bound to sodium and 2 others are interstitial, being hydrogen-bonded to sulfate. These cations are linked to the sulfate anions by
hydrogen bonds. The Na–O distances are about 240
pm. Crystalline sodium sulfate decahydrate is also unusual among hydrated salts in having a measurable
residual entropy
Residual entropy is the difference in entropy between a non-equilibrium state and crystal state of a substance close to absolute zero. This term is used in condensed matter physics to describe the entropy at zero kelvin of a glass or plastic crys ...
(entropy at
absolute zero) of 6.32 J/(K·mol). This is ascribed to its ability to distribute water much more rapidly compared to most hydrates.
Production
The world production of sodium sulfate, almost exclusively in the form of the decahydrate, amounts to approximately 5.5 to 6 million tonnes annually (Mt/a). In 1985, production was 4.5 Mt/a, half from natural sources, and half from chemical production. After 2000, at a stable level until 2006, natural production had increased to 4 Mt/a, and chemical production decreased to 1.5 to 2 Mt/a, with a total of 5.5 to 6 Mt/a.
For all applications, naturally produced and chemically produced sodium sulfate are practically interchangeable.
Natural sources
Two thirds of the world's production of the decahydrate (Glauber's salt) is from the natural mineral form
mirabilite, for example as found in lake beds in southern
Saskatchewan
Saskatchewan ( ; ) is a Provinces and territories of Canada, province in Western Canada, western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on t ...
. In 1990,
Mexico
Mexico (Spanish language, Spanish: México), officially the United Mexican States, is a List of sovereign states, country in the southern portion of North America. It is borders of Mexico, bordered to the north by the United States; to the so ...
and
Spain
, image_flag = Bandera de España.svg
, image_coat = Escudo de España (mazonado).svg
, national_motto = '' Plus ultra'' (Latin)(English: "Further Beyond")
, national_anthem = (English: "Royal March")
, ...
were the world's main producers of natural sodium sulfate (each around 500,000
tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
s), with
Russia
Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-ei ...
,
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
and
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...
around 350,000 tonnes each.
Natural resources are estimated at over 1 billion tonnes.
Major producers of 200,000 to 1,500,000 tonnes/year in 2006 included
Searles Valley Minerals
Searles Valley Minerals Inc. is a raw materials mining and production company with corporate offices in Overland Park, Kansas. It is owned by the Indian company Nirma. It has major operations in the Searles Valley and in Trona, California where i ...
(California, US), Airborne Industrial Minerals (Saskatchewan, Canada),
Química del Rey (Coahuila, Mexico), Minera de Santa Marta and Criaderos Minerales Y Derivados, also known as
Grupo Crimidesa (Burgos, Spain), Minera de Santa Marta (Toledo, Spain), Sulquisa (Madrid, Spain), Chengdu Sanlian Tianquan Chemical (
Tianquan County
Tianquan County () is a county of Sichuan Province, China. It is under the administration of Ya'an City. In 1950, the county bore witness to the Battle of Tianquan, which resulted in the communists defeating the nationalists
Nationalism i ...
, Sichuan, China), Hongze Yinzhu Chemical Group (
Hongze District, Jiangsu, China), (Shanxi, China), Sichuan Province Chuanmei Mirabilite (,
Dongpo District,
Meishan, Sichuan, China), and Kuchuksulphat JSC (Altai Krai, Siberia, Russia).
Anhydrous sodium sulfate occurs in arid environments as the mineral
thenardite. It slowly turns to mirabilite in damp air. Sodium sulfate is also found as
glauberite, a calcium sodium sulfate mineral. Both minerals are less common than mirabilite.
Chemical industry
About one third of the world's sodium sulfate is produced as by-product of other processes in chemical industry. Most of this production is chemically inherent to the primary process, and only marginally economical. By effort of the industry, therefore, sodium sulfate production as by-product is declining.
The most important chemical sodium sulfate production is during
hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...
production, either from
sodium chloride (salt) and
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
, in the
Mannheim process, or from
sulfur dioxide
Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic a ...
in the
Hargreaves process.
The resulting sodium sulfate from these processes is known as ''salt cake''.
:Mannheim: 2 NaCl + H
2SO
4 → 2 HCl + Na
2SO
4
:Hargreaves: 4 NaCl + 2 SO
2 + O
2 + 2 H
2O → 4 HCl + 2 Na
2SO
4
The second major production of sodium sulfate are the processes where surplus
sodium hydroxide is
neutralised by sulfuric acid, as applied on a large scale in the production of
rayon. This method is also a regularly applied and convenient laboratory preparation.
: 2 NaOH(
aq) + H
2SO
4(aq) → Na
2SO
4(aq) + 2 H
2O(
l) ΔH = -112.5 kJ (highly exothermic)
In the laboratory it can also be synthesized from the reaction between
sodium bicarbonate and
magnesium sulfate.
: 2 NaHCO
3 + MgSO
4 → Na
2SO
4 + Mg(OH)
2 + 2 CO
2
However, as commercial sources are readily available, laboratory synthesis is not practised often.
Formerly, sodium sulfate was also a by-product of the manufacture of
sodium dichromate
Sodium dichromate is the inorganic compound with the formula Na2 Cr2 O7. However, the salt is usually handled as its dihydrate Na2Cr2O7·2 H2O. Virtually all chromium ore is processed via conversion to sodium dichromate and virtually all compound ...
, where sulfuric acid is added to sodium chromate solution forming sodium dichromate, or subsequently chromic acid. Alternatively, sodium sulfate is or was formed in the production of
lithium carbonate,
chelating agent
Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These ligands a ...
s,
resorcinol
Resorcinol (or resorcin) is an organic compound with the formula C6H4(OH)2. It is one of three isomeric benzenediols, the 1,3-isomer (or '' meta''-isomer). Resorcinol crystallizes from benzene as colorless needles that are readily soluble in ...
,
ascorbic acid
Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) ...
,
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
pigments,
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available ni ...
, and
phenol
Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it r ...
.
Bulk sodium sulfate is usually purified via the decahydrate form, since the anhydrous form tends to attract
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
compounds and
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
s. The anhydrous form is easily produced from the hydrated form by gentle warming.
Major sodium sulfate by-product producers of 50–80 Mt/a in 2006 include Elementis Chromium (chromium industry, Castle Hayne, NC, US), Lenzing AG (200 Mt/a, rayon industry, Lenzing, Austria), Addiseo (formerly Rhodia, methionine industry, Les Roches-Roussillon, France), Elementis (chromium industry, Stockton-on-Tees, UK), Shikoku Chemicals (Tokushima, Japan) and Visko-R (rayon industry, Russia).
Applications
Commodity industries
With US pricing at $30 per tonne in 1970, up to $90 per tonne for salt cake quality, and $130 for better grades, sodium sulphate is a very cheap material. The largest use is as
filler in powdered home laundry detergents, consuming approximately 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.
Another formerly major use for sodium sulfate, notably in the US and Canada, is in the
Kraft process for the manufacture of
wood pulp
Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibers from wood, fiber crops, waste paper, or rags. Mixed with water and other chemical or plant-based additives, pulp is the major raw ...
. 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, due to advances in the thermal efficiency of the Kraft recovery process in the early 1960s, more efficient sulfur recovery was achieved and the need for sodium sulfate makeup was drastically reduced. Hence, the use of sodium sulfate in the US and Canadian pulp industry declined from 1,400,000 tonnes per year in 1970 to only approx. 150,000 tonnes in 2006.
The
glass
Glass is a non- crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenchin ...
industry provides another significant application for sodium sulfate, as second largest application in Europe. Sodium sulfate is used as a
fining agent
Finings are substances that are usually added at or near the completion of the processing of brewing wine, beer, and various nonalcoholic juice beverages. They are used to remove organic compounds, either to improve clarity or adjust flavor or a ...
, 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.
Sodium sulfate is important in the manufacture of
textiles, particularly in Japan, where it is the largest application. Sodium sulfate is added to increase the
ionic strength of the solution and so helps in "levelling", reducing negative electrical charges on textile fibres so that dyes can penetrate evenly (see the theory of the
diffuse double layer (DDL) elaborated by
Gouy and Chapman). Unlike the alternative
sodium chloride, it does not corrode the
stainless steel
Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's r ...
vessels used in dyeing. This application in Japan and US consumed in 2006 approximately 100,000 tonnes.
Food industry
Sodium sulfate is used as a diluent for food colours.
[ It is known as ]E number
E numbers ("E" stands for "Europe") are codes for substances used as food additives, including those found naturally in many foods such as vitamin C, for use within the European Union (EU) and European Free Trade Association (EFTA). Commonly ...
additive E514.
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), 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.
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. 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, is 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.
In 1953, sodium sulfate was proposed for heat
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...
storage in passive solar heating systems. This takes advantage of its unusual solubility properties, and the high heat of crystallisation (78.2 kJ/mol).
Other uses for sodium sulfate include de-frosting windows, starch
Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human die ...
manufacture, as an additive in carpet fresheners, 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.
Safety
Although sodium sulfate is generally regarded as non-toxic, it should be handled with care. The dust can cause temporary asthma or eye irritation; this risk can be prevented by using eye protection and a paper mask. Transport is not limited, and no Risk Phrase or Safety Phrase applies.
References
External links
*Calculators
surface tensions
an
densities, molarities and molalities
of aqueous sodium sulfate
{{Authority control
Sulfates
Sodium compounds
Desiccants
Alchemical substances
Articles containing video clips
Photographic chemicals
E-number additives