Sodium ethyl xanthate
Encyclopedia
Sodium ethyl xanthate is an organosulfur compound with the chemical formula CH3CH2OCS2Na. It is a pale yellow powder, which characteristically hydrolyzes to release malodorous products. Sodium ethyl xanthate is predominantly used in the mining industry as a flotation agent
.
. Sodium ethyl xanthate easily adsorbs on the surface of solid sulfides.
and with increasing temperature. Three pathways are proposed:
A. Dissociation into xanthic acid and then to carbon disulfide and alcohol.
B. Oxidation to dixanthogen.
C. Hydrolytic decomposition
Reactions A and B are minor and require acidic conditions. Reaction C proceeds in neutral or alkaline pH and is self-accelerating, as it is catalysed by the alcohol formed as a product. Its rate increases with concentration of the reagents and with temperature, from 1.1%/day at 20 °C to 4.6%/day at 40 °C for a 10% solution at pH=10. A decrease in pH from 10 to 6.5 increases the decomposition rate from 1.1%/day to 16%/day. Decomposition is also accelerated by the presence of metals, such as copper, iron, lead or zinc, which act as a catalyst.
Sodium ethyl xanthate can also be quantified using gravimetry
, by weighing the lead xanthate residue obtained after reacting SEX with 10% solution of lead nitrate. There are also several electrochemical
detection methods, which can be combined with some of the above chemical techniques.
for recovery of metals, such as copper, nickel, silver or gold, as well as solid metal sulfides or oxides from ore slurries
. This application has been introduced by Cornelius H. Keller in 1925. Other applications include defoliant
, herbicide
and an additive to rubber to protect it against oxygen and ozone.
The mechanism of flotation enhancement is as follows. The polar part of xanthate molecule attaches to the ore particles with the non-polar hydrocarbon part sticking out and forming a hydrophobic layer. Then the particles are brought to the water surface by air bubbles. Only a small amount of about 300 g/tonne of ore is required for efficient separation. The efficiency of the hydrophobic action increases, but the selectivity to ore type decreases with increasing length of the hydrocarbon chain in xanthates. The chain is shortest in sodium ethyl xanthate that makes is highly selective to copper, nickel, lead, gold and zinc ores. Aqueous solution (10%) with pH=7–11 are normally used in the process.
In 2000, Australia produced up to 10,000 tonne
s of sodium ethyl xanthate and imported about 6,000 tonnes, mostly from China. The material produced in Australia is the so-called 'liquid sodium ethyl xanthate' that refers to a 40% aqueous solution of the solid. It is obtained by reacting carbon disulfide with sodium hydroxide and ethanol in a closed process. Its density is 1.2 g/cm3 and the freezing point is −6 °C.
Other applications include defoliant
s and herbicide
s and as an additive to rubber to protect it against oxygen and ozone
.
.
Since 1993, sodium ethyl xanthate is classified as a Priority Existing Chemical in Australia, meaning that its manufacture, handling, storage, use or disposal may result in adverse health or environment effects. This decision was justified by the widespread use of the chemical in industry and its decomposition to the toxic and flammable carbon disulfide gas. From two examples of sodium ethyl xanthate spillage in Australia, one resulted in evacuation of 100 people and hospitalization of 6 workers who were exposed to the fumes. In another accident, residents of the spillage area complained of headache, dizziness and nausea. Consequently, during high-risk sodium ethyl xanthate handling operations, workers are required by the Australian regulations to be equipped with protective clothing, anti-static gloves, boots and full-face respirator
s or self-contained breathing apparatuses.
Froth flotation
Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in several processing industries...
.
Production
Xanthantes are prepared by the action of alcohols on carbon disulfide:- CH3CH2ONa + CS2 → CH3CH2OCS2Na
Properties
Sodium ethyl xanthate is a pale yellow powder. It is relatively stable at high pH and rapidly hydrolyses at pH <9 at 25 °C. It is the conjugate base of the unknown strong acid with pKa of 1.6 and pKb estimated as 12.4 for the conjugate baseConjugate acid
Within the Brønsted–Lowry acid-base theory , a conjugate acid is the acid member, HX, of a pair of two compounds that transform into each other by gain or loss of a proton. A conjugate acid can also be seen as the chemical substance that releases, or donates, a proton in the forward chemical...
. Sodium ethyl xanthate easily adsorbs on the surface of solid sulfides.
Decomposition in water
Sodium ethyl xanthate decomposes in water increases with decreasing pHPH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
and with increasing temperature. Three pathways are proposed:
A. Dissociation into xanthic acid and then to carbon disulfide and alcohol.
- C2H5OCS2Na + H2O → C2H5OCS2H + NaOH
- C2H5OCS2H → CS2 + C2H5OH
B. Oxidation to dixanthogen.
- 2 C2H5OCS2– + H2O + O2O → (C2H5OCS2)2 + 2 OH–
C. Hydrolytic decomposition
- 6 C2H5OCS2– + 3 H2O + O2O → 6 C2H5OH + CO32– + 3 CS2 + 2 CS32–
Reactions A and B are minor and require acidic conditions. Reaction C proceeds in neutral or alkaline pH and is self-accelerating, as it is catalysed by the alcohol formed as a product. Its rate increases with concentration of the reagents and with temperature, from 1.1%/day at 20 °C to 4.6%/day at 40 °C for a 10% solution at pH=10. A decrease in pH from 10 to 6.5 increases the decomposition rate from 1.1%/day to 16%/day. Decomposition is also accelerated by the presence of metals, such as copper, iron, lead or zinc, which act as a catalyst.
Detection
Sodium ethyl xanthate can be identified through optical absorption peaks in the infrared (1179, 1160, 1115, 1085 cm−1) and ultraviolet (300 nm) ranges. There are at least six chemical detection methods:- Iodometric method relies on oxidation to dixanthogen by iodine, with the product detected with a starch indicator. This method is however is not selective and suffers from interferences with other sulfur-containing chemicals.
- Xanthate can be reacted with a copper sulfate or copper tartrate resulting in a copper xanthate residue which is detected with iodine. This method has an advantage of being is insensitive to sulfite, thiosulfate and carbonate impurities.
- In the acid-base detection method, a dilute aqueous xanthate solution is reacted with a copious amount of 0.01 M hydrochloric acidHydrochloric acidHydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
yielding carbon disulfide and alcohol, which are evaluated. The excess acid and impurities are removed through filtering and titration. - In the argentometric method, sodium ethyl xanthate is reacted with silver nitrateSilver nitrateSilver nitrate is an inorganic compound with chemical formula . This compound is a versatile precursor to many other silver compounds, such as those used in photography. It is far less sensitive to light than the halides...
in a dilute solution. The resulted silver xanthate is detected with 10% aqueous solution of iron nitrate. The drawbacks of this method are high cost of silver and blackening of silver xanthate by silver nitrate that reduces the detection accuracy. - In the mercurimetric method, xanthate is dissolved in 40% aqueous solution of dimethylamine, followed by heating and titration with O-hydroxymercuribenzoate. The product is detected with thiofluorescein.
- Perchloric acid method involves dissolution of xanthate in water-free acetic acidAcetic acidAcetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
. The product is titrated with perchloric acidPerchloric acidPerchloric acid is the inorganic compound with the formula HClO4. Usually encountered as an aqueous solution, this colourless compound is a strong acid comparable in strength to sulfuric and nitric acids. It is a powerful oxidizer, but its aqueous solutions up to appr. 70% are remarkably inert,...
and detected with crystal violetCrystal violetCrystal violet or Gentian violet is a triarylmethane dye. The dye is used as a histological stain and in Gram’s method of classifying bacteria. Crystal violet has antibacterial, antifungal, and anthelmintic properties and was formerly important as a topical antiseptic...
.
Sodium ethyl xanthate can also be quantified using gravimetry
Gravimetric analysis
Gravimetric analysis describes a set of methods in analytical chemistry for the quantitative determination of an analyte based on the mass of a solid...
, by weighing the lead xanthate residue obtained after reacting SEX with 10% solution of lead nitrate. There are also several electrochemical
Electrochemistry
Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor and an ionic conductor , and which involve electron transfer between the electrode and the electrolyte or species in solution.If a chemical reaction is...
detection methods, which can be combined with some of the above chemical techniques.
Applications
Sodium ethyl xanthate is predominantly used in the mining industry as flotation agentFroth flotation
Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in several processing industries...
for recovery of metals, such as copper, nickel, silver or gold, as well as solid metal sulfides or oxides from ore slurries
Slurry
A slurry is, in general, a thick suspension of solids in a liquid.-Examples of slurries:Examples of slurries include:* Lahars* A mixture of water and cement to form concrete* A mixture of water, gelling agent, and oxidizers used as an explosive...
. This application has been introduced by Cornelius H. Keller in 1925. Other applications include defoliant
Defoliant
A defoliant is any chemical sprayed or dusted on plants to cause its leaves to fall off. A classic example of a highly toxic defoliant is Agent Orange, which the United States armed forces used abundantly to defoliate regions of Vietnam during the Vietnam War from 1961 to 1970.Defoliants differ...
, herbicide
Herbicide
Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
and an additive to rubber to protect it against oxygen and ozone.
The mechanism of flotation enhancement is as follows. The polar part of xanthate molecule attaches to the ore particles with the non-polar hydrocarbon part sticking out and forming a hydrophobic layer. Then the particles are brought to the water surface by air bubbles. Only a small amount of about 300 g/tonne of ore is required for efficient separation. The efficiency of the hydrophobic action increases, but the selectivity to ore type decreases with increasing length of the hydrocarbon chain in xanthates. The chain is shortest in sodium ethyl xanthate that makes is highly selective to copper, nickel, lead, gold and zinc ores. Aqueous solution (10%) with pH=7–11 are normally used in the process.
In 2000, Australia produced up to 10,000 tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
s of sodium ethyl xanthate and imported about 6,000 tonnes, mostly from China. The material produced in Australia is the so-called 'liquid sodium ethyl xanthate' that refers to a 40% aqueous solution of the solid. It is obtained by reacting carbon disulfide with sodium hydroxide and ethanol in a closed process. Its density is 1.2 g/cm3 and the freezing point is −6 °C.
Other applications include defoliant
Defoliant
A defoliant is any chemical sprayed or dusted on plants to cause its leaves to fall off. A classic example of a highly toxic defoliant is Agent Orange, which the United States armed forces used abundantly to defoliate regions of Vietnam during the Vietnam War from 1961 to 1970.Defoliants differ...
s and herbicide
Herbicide
Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
s and as an additive to rubber to protect it against oxygen and ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
.
Safety
Sodium ethyl xanthate has moderate oral and dermal toxicity in animals and is irritating to eyes and skin. It is especially toxic to aquatic life and therefore its disposal is strictly controlled. Median lethal dose for (male albino mice, oral, 10% solution at pH~11) is 730 mg/kg of body weight, with most deaths occurring in the first day. The most affected organs were the central nervous system, liver and spleenSpleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...
.
Since 1993, sodium ethyl xanthate is classified as a Priority Existing Chemical in Australia, meaning that its manufacture, handling, storage, use or disposal may result in adverse health or environment effects. This decision was justified by the widespread use of the chemical in industry and its decomposition to the toxic and flammable carbon disulfide gas. From two examples of sodium ethyl xanthate spillage in Australia, one resulted in evacuation of 100 people and hospitalization of 6 workers who were exposed to the fumes. In another accident, residents of the spillage area complained of headache, dizziness and nausea. Consequently, during high-risk sodium ethyl xanthate handling operations, workers are required by the Australian regulations to be equipped with protective clothing, anti-static gloves, boots and full-face respirator
Respirator
A respirator is a device designed to protect the wearer from inhaling harmful dusts, fumes, vapors, or gases. Respirators come in a wide range of types and sizes used by the military, private industry, and the public...
s or self-contained breathing apparatuses.