Use of metal cyanides
Information about working with cyanide, the treatment of cyanide poisoning and disposal of cyanide residues
Why is this important?It is important to know how to work with cyanide properly, to reduce the risk of injury to all persons handling, storing or dealing with cyanides in laboratories - this includes hydrogen cyanide and solid cyanides.If working with cyanide, you should also be able to anticipate and treat cases of cyanide poisoning. There is also a duty to protect the community and the environment when using and disposing of cyanide. What is cyanide?Cyanides are the salts of hydrocyanic acid and are among the most poisonous substances known. Sodium and potassium cyanides are solids, but are often used in solution with water.The most dangerous compounds are hydrogen cyanides (also known as hydrocyanic acid or prussic acid) and cyanogen, which are stored under pressure as liquids, but which are used as gases. Hydrocyanic acid gas is liberated from solid cyanides by the action of acids, water or even water vapour. The 'bitter almond' smell of hydrocyanic acid is a characteristic, but cannot be detected by some people. Cyanide poisoningPoisoning results mainly from breathing hydrogen cyanide gas or cyanide dust, but can also occur by absorption through the skin following contact with solutions of cyanide salts or even with hydrogen cyanide in the air. Cyanide dust can be absorbed through the skin if the dust is dissolved in sweat or other moisture.In cases of severe poisoning, loss of consciousness may be instantaneous, breathing may cease and convulsions may appear. Death is usually due to failure of breathing and may be extremely rapid. Symptoms of mild to moderate poisoning are mostly of a general nature. There may be headaches, dizziness, unsteadiness of pit, and a feeling of suffocation and nausea. As poisoning progresses there may be difficulty in breathing. Emergency procedures and first aidIf someone suffers from cyanide poisoning, it is most important that all first aid measures be carried out with the utmost speed. First aid procedures for cyanide poisoning are as follows:
Cyanide handlingIt is the responsibility of all users of cyanide to:
Cyanide spills or leaks
Cyanide disposalWaste Cyanide Destruction by Potassium PermanganatePotassium permanganate (KmnO4) is a well known oxidizing agent and has been reported to react with cyanide ions in alkaline or neutral media according to the following equation (see ref. 1):2 MnO4-(aq)+ 3 CN-(aq) + H2O = 2 MnO2(s)+ 3 CNO-(aq) + 2 OH-(aq) For each kilogram of cyanide to be oxidized requires 4.05 Kg of KMnO4. To enhance the cyanide oxidation rate, a catalytic amount of Cu(II) salt is found to be very effective. While using only KMnO4 as an oxidant cyanide levels did not drop much after 3-4 periods, but it came down to almost zero level after introduction of catalytic amount of CuSO4.5H2O salt. To destroy the waste cyanide in the lab use the amount of oxidants required according to the equations shown below: Amount of KmnO4(g) = V.[C). (4.05 x 10-3) (where [C] is the cyanide concentration of ppm and V is the volume in litres) Amount of Cu(SO4).5H20 = V.[C]. (2.5 x 10-4) For example, when we have treated 100 ppm 25L cyanide waste with 10g KMnO4 and 0.6g CuS04.5H20, a cyanide probe shows more than 99% cyanide being disappeared in less than two hours. To ensure complete oxidation of cyanide and metal cyanide complexes, it is better to keep permanganate treated waste cyanide standing overnight. It can then be disposed of as treated cyanide waste via the hazardous waste pickup. Potassium cyanide and similar salts readily dissolve in water to give the free cyanide ion, which can be easily complexed or oxidised. For small amount (< 1g), use dilute neutral ferrous sulphate solution in a basin to wash gloves and apparatus; flush to drain with ample water. Cyanide toxicityLethal doses of NaCN, KCN etc are around 0.2g for an adult, ie 5cc of I M solution of 0.4cc of saturated (KCN) solution at room temperature. Aqueous HCN is twice as toxic. Alarming symptoms occur at much lower levels.Gaseous HCN at 500 ppm is immediately fatal through respiratory failure. 100 ppm is dangerous to life in a few minutes. The smell of cyanideTrained observers can detect 2 ppm HCN in air. The sense of smell fatigues easily and fails at higher concentrations. Some 20% of adults have a hereditary inability to detect the characteristic odour. Clearly the odour is not a reliable warning signal. Any odour of HCN in an open laboratory is a danger warning and indicates poor chemical technique.Entry to the body(a) By inhalation of HCN, which is deliberately produced for a chemical purpose or unexpectedly released from solid or solution on contact with mineral acids or carbon dioxide. Chemical fires and uncontrolled reaction with nitrogenous material may evolve HCN, nitrites or cyanogen - all extremely toxic materials.(b) By ingestion (swallowing) deliberately or by accidental splashing of solid or solution onto the lips or mouth. (c) By absorption of solid, liquid, strong solution or gas through mucous membranes (eyes, nose, lips) or non-intact skin (also through intact skin on prolonged exposure).' General informationDespite the extreme toxicity and speed of action of cyanides, chemical work can be done in complete safety, provided the numerous ways toxic exposure can occur are appreciated and circumvented by RIGID ADHERENCE TO SAFETY RULES.Maximum permissible skin exposure levels for an eight-hour day, five-day working week: HCN - 10 ppm Cyanide salts - 5 mg/m3 References
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