Uses
Potassium cyanide (KCN) is a white crystalline substance with a slight odor of bitter
almonds. It is produced when hydrogen cyanide is absorbed in potassium hydroxide. It is
used to extract gold and silver from their ores, in electroplating computer boards, and as an
insecticide. Potassium cyanide is very toxic to the skin or when ingested or inhaled, and it is
used as a source of cyanide (CN) gas in gas chambers.
Description
Potassium cyanide, in addition to processes already described, can be prepared by the reaction of potassium carbonate with calcium hexacyanoferrate(II) or by thermal decomposition of K4Fe(CN)6 above 435°C. Rubidium and cesium cyanides can be prepared by the reaction of HCN with the metal hydroxides in alcohol or ether or with the corresponding metals in anhydrous ether or benzene. Hydrogen reduction of metal cyanates produces water and the corresponding cyanide, as does reduction with carbon monoxide.
Description
Potassium cyanide, KCN, is a cyanide salt that is found as a white, amorphous, deliquescent lump or crystalline mass with a faint odor of bitter almonds. It is soluble in water and has a specific gravity of 1.52. It is a poison that is absorbed through the skin. Target organs are the same as for sodium cyanide. Reaction with acids releases flammable and toxic hydrogen cyanide gas. The four-digit UN identification number is 1680. The NFPA 704 designation is health 3, flammability 0, and reactivity 0. The primary uses are in gold and silver ore extraction, insecticides, fumigants, and electroplating.
Chemical Properties
Potassium cyanide are white lumps, granular powder, or colorless solution. It may be shipped as capsules, tablets, or pellets. Toxic hydrogen cyanide gas released by potassium cyanide has a distinctive, weak bitter almond odor, but many people cannot detect it; the odor does not provide adequate warning of hazardous concentrations.
Chemical Properties
KCN is a white solid or colourless water solution with a faint bitter almond odour. As a solution, it is slightly soluble in ethanol. It is a poison that reacts with acid or acid fumes to emit deadly HCN. When heated to decomposition, it emits very toxic fumes. As a solid, KCN is incompatible with nitrogen trichloride, perchloryl fluoride, sodium nitrite, acids, alkaloids, chloral hydrate, and iodine. A synonym for KCN is potassium salt of hydrocyanic acid.
Uses
Extracting gold and silver from ores; electroplating baths; silver plating; case hardening steel by liquid nitriding; reagent in analytical chemistry.
Uses
Potassium cyanide is a white granular salt made by the absorption
of hydrogen cyanide in potassium hydroxide. It is soluble
in both water and alcohol and a lethal poison. If mixed with
acids it produces highly toxic hydrogen cyanide gas. This was
the preferred fixing chemical for collodion positives because
it contained no sulfides to darken the highlight silver. As a
fixing agent cyanide was particularly effective. After dissolving
the unexposed silver halides cyanide would also remove nonimage
fog producing very clean shadow areas. Prolonged
fixing would eventually remove image silver. Tincture of iodine
was added to dilute solutions of potassium cyanide and used
to remove unwanted non-image silver in photographic materials
and to remove silver stains.
Uses
Potassium cyanide is used for electrolytic refining of platinum; fine silver plating; as an electrolyte for the separation of gold, silver, and copper from platinum; and for metal coloring.
Production Methods
Potassium cyanide was made by the Beilby process before
the introduction of the neutralization or wet process. When
made by the neutralization or wet process, it contains 99%
KCN. Initially, potassium cyanide was used as a flux and later
for electroplating, which was the single largest use in the
1990s. The demand for potassium cyanide was met by the
ferrocyanide process until the latter part of the nineteenth
century when the extraordinary demands of the gold mining
industry for alkali cyanide resulted in the development of
direct synthesis processes. When cheaper sodium cyanide
became available, potassium cyanide was displaced in many
uses.
Definition
ChEBI: Potassium cyanide is a cyanide salt containing equal numbers of potassium cations and cyanide anions. It has a role as an EC 1.9.3.1 (cytochrome c oxidase) inhibitor, an EC 1.15.1.1 (superoxide dismutase) inhibitor and a neurotoxin. It is a cyanide salt, a one-carbon compound and a potassium salt.
General Description
White amorphous lumps or a crystalline mass with a faint odor of bitter almonds. Density 1.52 g / cm3 Toxic by skin absorption through open wounds, by ingestion. Heating to decomposition produces toxic fumes. Used for gold and silver extraction, in chemical analysis, to make other chemicals, and as an insecticide.
Air & Water Reactions
Deliquescent. Soluble in water. Dissolution releases some poisonous hydrogen cyanide gas. The amount is not hazardous except in an enclosed space. If the water is acidic, dangerous amounts of hydrogen cyanide form at once.
Reactivity Profile
POTASSIUM CYANIDE is a basic salt and a reducing agent. Reacts with acids of all kinds to generate poisonous hydrogen cyanide gas. Can react violently with oxidizing agents: fusion with metal chlorates, perchlorates, nitrates, or nitrites can cause explosions [Bretherick 1979. p. 101]. A mixture with perchloryl fluoride may explode above 100°C. A mixture with nitrite salts may cause an explosion [Pieters 1957. p. 30]. Incompatible with iodine. Initiates the explosive decomposition of nitrogen trichloride.
Hazard
A poison as absorbed by skin.
Health Hazard
Ingestion of KCN or exposure to the salts or their aqueous solutions by eye or skin contact can be fatal; exposure to as little as 50 to 150 mg can cause immediate collapse and death. Poisoning can occur by inhalation of mists of cyanide solutions and by inhalation of HCN produced by the reaction of metal cyanides with acids and with water. Symptoms of nonlethal exposure to cyanide include weakness, headache, dizziness, rapid breathing, nausea, and vomiting. These compounds are not regarded as having good warning properties.
Effects of chronic exposure to sodium cyanide or potassium cyanide are nonspecific and rare.
Health Hazard
Potassium cyanide is a white solid or colorless water solution with a faint bitter almond
odor. As a solution, it is slightly soluble in ethanol. It is a poison that reacts with acid or
acid fumes to emit deadly hydrogen cyanide. When heated to decomposition, it emits very
toxic fumes. As a solid, potassium cyanide is incompatible with nitrogen trichloride, perchloryl fl uoride, sodium nitrite, acids, alkaloids, chloral hydrate, and iodine. A synonym
for potassium cyanide is potassium salt of hydrocyanic acid
Health Hazard
Potassium cyanide is a dangerous poison; toxicity comparable to that of sodium cyanide. Ingestion of 100–150 mg of this compound could be fatal to humans. Similar toxicity is observed when KCN is absorbed through skin or eyes. Intake of the quantity above can cause collapse and cessation of breathing.
At lower concentrations the acute toxic symptoms are nausea, vomiting, headache, confusion, and muscle weakness. KCN administered in test animals by the intramuscular, intravenous, intraperitoneal, ocular, and oral routes exhibited LD50 values within the range of 3–9 mg/kg; the acute toxic effects were ataxia, respiratory stimulation, paralysis, and seizure.
Smith and Heath (1979) observed the effect of temperature on KCN toxicity of freshwater fish. When the temperature of exposure was lowered from 15 (59) to 5°C (41°F) the toxicity of KCN to goldfish decreased by a factor of 5.
LD50 value, intraperitoneal (rats): 4 mg/kg
LD50 value, oral (rats): 10 mg/kg
LD50 value, oral (humans): 2.86 mg/kg
Potassium cyanide caused reproductive damage in test animals, producing harmful effects on fertility and embryo.
Health Hazard
POTASSIUM CYANIDE is classified as super toxic. Probable oral lethal dose in humans is less than 5 mg/kg or less than a taste (7 drops) for a 150 lb. person. It is an eye and skin irritant. Poisonous in very small quantities; a taste is lethal.
Fire Hazard
Contact with acid releases highly flammable hydrogen cyanide gas. Moisture may cause POTASSIUM CYANIDE to volatilize as hydrogen cyanide. When heated to decomposition, POTASSIUM CYANIDE emits very toxic fumes of cyanide and nitrogen oxides. Reacts with acids to produce hydrogen cyanide gas. Reacts with strong oxidizers such as nitrates and chlorates, nitrogen trichloride; perchloryl fluoride; sodium nitrate; acids; alkaloids; chloral hydrate; iodine. Avoid contact with acids.
Fire Hazard
Potassium cyanide is noncombustible solid. Reaction with acids liberates flammable HCN.
Flammability and Explosibility
Non flammable
Industrial uses
A white amorphous or crystalline solid of the composition KCN, potassium cyanide is employed for carbonizing steel for case hardening and for electroplating. For cyaniding steel the latter is immersed in a bath of molten cyanide and then quenched in water, or the cyanide is rubbed on the red-hot steel.
Commercial potassium cyanide is likely to contain a proportion of sodium cyanide. Potassium ferrocyanide, or yellow prussiate of potash, can also be used for case-hardening steel. It has the compositionK
4Fe(CN)
6and comes in yellow crystals or powder. The nitrogen as well as the carbon enters the steel to form the hard case. Potassium ferricyanide, or red prussiate of potash, is a bright-red granular powder of the composition K
3Fe(CN)
6, used in photographic reducing solutions, in etching solutions, in blueprint paper, and in silvering mirrors. Redsol crystals is the name of this chemical for use as a reducer and mild oxidizing agent, or toner, for photography.
Safety Profile
A deadly human poison
by ingestion. A experimental poison by
ocular, subcutaneous, intravenous,
intramuscular, and intraperitoneal routes.
Experimental teratogenic and reproductive
effects. Human systemic effects by
ingestion: convulsions, pulse rate increase.
Mutation data reported. Reacts with acids or
acid fumes to liberate deadly HCN. When
heated to decomposition it emits very toxic
fumes of K2O , CN-, and NOx. See also
CYANIDE.
Potential Exposure
Used in electroplating, steel hardening; extraction of precious metals form ores; as a fumigant; in insecticides; a reagent in analytical chemistry
Shipping
UN1680 Potassium cyanide, Hazard Class: 6.1; Labels: 6.1-Poisonous materials.
Purification Methods
A saturated solution in H2O-ethanol (1:3) at 60o is filtered and cooled to room temperature. Absolute EtOH is added, with stirring, until crystallisation ceases. The solution is again allowed to cool to room temperature (during 2-3hours), then the crystals are filtered off, washed with absolute EtOH, and dried, first at 70-80o for 2-3hours, then at 105o for 2hours [Brown et al. J Phys Chem 66 2426 1962]. It has also been purified by melting in a vacuum and by zone refining. HIGHLY POISONOUS.
Incompatibilities
A strong reducing agent; keep away from oxidizers. Potassium cyanide decomposes on contact with water, humidity, carbon dioxide, strong acids (such as hydrochloric, sulfuric, and nitric acids), and acid salts, producing highly toxic and highly flammable hydrogen cyanide gas. Potassium cyanide absorbs water from air (is hygroscopic or deliquescent); the aqueous solution is a strong base. Incompatible with organic anhydrides; isocyanates, alkylene oxides; epichlorohydrin, aldehydes, alcohols, glycols, phenols, cresols, caprolactum, strong oxidizers; nitrogen trichloride; sodium chlorate. Attacks aluminum, copper, zinc in the presence of moisture.
Waste Disposal
Consult with environmental regulatory agencies for guidance on acceptable disposal practices. Generators of waste containing this contaminant (≥100 kg/mo) must conform with EPA regulations governing storage, transportation, treatment, and waste disposal. In accordance with 40CFR165, follow recommendations for the disposal of pesticides and pesticide containers. Must be disposed properly by following package label directions or by contacting your local or federal environmental control agency, or by contacting your regional EPA office. Add strong alkaline hypochlorite and react for 24 hours. Then flush to sewer with large volumes of water.
