Cyanides

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 poisoning Poisoning 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 aid If 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: Send for medical assistance: call an ambulance immediately (dial 0, then 000). Call a person trained in First Aid. Notify the Safety Officer. Remove patient from contaminated area to fresh air if safe to do so, or use breathing apparatus if hydrogen cyanide or other volatile nitrile is present. If pulse is absent, start cardiac massage. NB. Do not use mouth-to-mouth or mouth-to-nose ventilation because of the danger of poisoning to the rescuer. If cyanide has been swallowed and the patient is STILL CONSCIOUS, make him/her vomit. Make the patient lie down and keep the patient warm. Do not in any circumstances walk him/her about. Remove all contaminated clothing, wash the affected areas with soap and copious amounts of water. When the ambulance arrives give 100% oxygen by mask if available; and Arrange for the urgent transfer of the patient to the Royal Melbourne Hospital for treatment with the hospital’s Cyanokit (cyanide antidote kit)   Cyanide handling It is the responsibility of all users of cyanide to: Complete a risk assessment of all facets of the process to be used including waste disposal. Where possible, alter the process to eliminate the need for cyanide or substitute cyanide with a less toxic substance. Ensure all safe practices involving cyanide are in accordance with statutory requirements, including appropriate codes of practice and standards. Ensure all emergency first aid equipment is in place, maintained, and that trained staff are available. Ensure ready access to emergency phone numbers. Ensure that all cyanide is stored under lock and key in the safe located in the Chemistry store. Ensure that all cyanide use details are recorded in a log book which notes the date, user, amount used, and current quantity on hand. Measures which must be taken to reduce the danger to health from the uses of cyanide include the following: all work involving gaseous cyanide must be conducted in a fume cupboard; enclosure or isolation of processes which might release cyanides; . provision of adequate local exhaust ventilation where hydrogen cyanide is likely to be released; provision of good general ventilation throughout areas where cyanides are used or stored; provision of adequate equipment and facilities for the safe handling, storage and transport of cyanide; provision and wearing of suitable personal protective equipment; attention to personal hygiene ensuring that all persons in an area where cyanide is used fully understand the hazards involved and receive annual instruction in signs and symptoms of cyanide poisoning. In addition to the usual rules for SAFE HANDLING OF ALL CHEMICALS, the following should be observed: Students should be familiar with the safe work procedure for cyanide and know the symptoms of cyanide poisoning before commencing any work. Working alone or outside working hours is NOT PERMITTED. At least one other person must be present in the same laboratory when any work involving cyanide is carried out. Other co-workers in the laboratory should be informed of the potential danger. All operations should be conducted in a fume hood that meets the performance standard of Aust Standard 2243.8 and on the minimum scale required. Eyes, mouth and nose must be protected from splashes by either a face shield or a fixed shield and hands by impervious gloves (eg PVC). Respiratory equipment, emergency showers and eye wash facilities should be located near the work area. Cyanide solutions must NEVER be pipetted by mouth: safety pipettes must always be used. All cyanide issued will be signed out by the laboratory supervisor and any residues or empty containers must be returned to him for proper disposal. CAUTION: Great care should be taken that cyanide salts do not come into contact with acid, which liberates highly toxic hydrogen cyanide gas. Solutions containing cyanide should never be washed down the sink. All solutions must be collected and destroyed as set out in the attached procedure.   Cyanide spills or leaks Do not enter the area unless wearing self-contained breathing apparatus and full protective clothing, including boots; Ventilate the area of the spill; Evacuate the area and move upwind to avoid inhalation of vapour and contact with skin and eyes; Notify the Safety Officer; Collect the spilled material in the most convenient and SAFE manner (ic cover with charcoal, collect into bucket with a lid); and Treat the spillage area with sodium hypochlorite solution to oxidise any uncollected traces of cyanide.   Cyanide disposal Waste Cyanide Destruction by Potassium Permanganate Potassium 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 toxicity Lethal 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 cyanide Trained 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 information Despite 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 Roques, H. "Chemical Water Treatment - Principles and Practice", VCH Publishers, 1996, Chapter 10, pp 423-477, and references cited therein. Department of Chemical Engineering Safe Work Procedure 6.1.1.3: Working with cyanide