Handling of cyanide in mining

By Abigail Makumbe – Friday 29 May 2020

LOCAL – HARARE (Mining Index) – MINING chemicals are hazardous, especially if used in treatment of sands using sodium cyanide. They are however useful and necessary in mining operations.

Improper use of hazardous chemicals is very dangerous.

Chemicals can be corrosive and/or toxic, and misusing them can result in poisoning, burns, heavy metal poisoning, or other damage to the body or environment.

It is therefore needful to know the safe use requirements for the chemicals that you use in order to keep yourself and those around you safe. Material Safety Data Sheets (MSDS)) are very useful in helping guide users of chemicals in safe use, storage, disposal, handling spillage and accident response.

Illness or death among staff increases the costs for an organisation, so it is in the interests of miners to guard against hazardous chemical induced illnesses/deaths in their operations. Also, accidents in which chemicals are leaked into the environment can have considerable consequences for a company, fines from statutory bodies such as EMA and/or NSSA as well as loss of trust and morale of workers.

Chemicals used in mining and processing minerals contaminate the land, water, and air, causing health problems for workers and people living near mines. Toxic chemicals used in mining include:

• Sodium cyanide
• Acids e.g. sulphuric, nitric, hydrochloric, aqua regia
• Bases/alkalis e.g. caustic soda, hydrated lime, ammonia
• Ammonium nitrate and sodium nitrate
• Heavy metals such as mercury and lead (lead nitrate is used by some miners in cyanidation)

Risk assessment

Users of hazardous chemicals are encouraged to ask themselves these questions to help them constantly think safety on the job.

General rules for safe handling of hazardous chemicals

• Keep track of which chemicals are being used in the business: Keep a list of the substances, the amounts being used and the risks associated with them.
• This also applies to gathering information and distributing it to those who need it.
• Current material safety data sheets (MSDS) are mandatory.
• There may be a need for special instructions and training to ensure safe handling.
• Storing and using chemicals in a safe way is a further foundation for working with chemicals.
• Decide if a particular chemical is really needed. In many cases there can be another substance that is less hazardous to health and the environment, or perhaps a different method
• Surplus/expired chemicals and hazardous waste must be dealt with in accordance with the information in the safety data sheet and local bylaws.
• First Aid equipment must be available.
• Workplaces must be cleaned regularly. There must not be chemical spills on floors.

Cyanide

• Cyanide is used to separate gold from ore.
• Cyanide is toxic. It is deadly when swallowed as even a very small amount can kill a person. It therefore strictly regulated to protect people, animals, and the aquatic environment. In some countries it has been banned.
• Users have a responsibility to transport, use and dispose of cyanide in a way that safeguards life and natural resources
• It can also affect people through breathing in cyanide gases or through the skin. Effects may be long term so it is prudent to handle cyanide safely even if signs of harm are not evident.
• Cyanide is often spilled into waterways during gold mining processes like cyanidation, and/or when ponds filled with mine wastes burst and spill.
• Cyanide in water degenerates into less harmful substances when exposed to lots of sunlight and oxygen.
• Cyanide can kill livestock drinking water from mining operations, also fish and plants along rivers, and it makes water unsafe for drinking and bathing.
• Regulations limit the amount of cyanide which may be discharged into the environment, and discharge must be done after treatment to reduce the cyanide levels.
• In order to prevent fatalities, cyanide levels in tailings ponds can be reduced to safe levels by minimizing the amount of cyanide used, removing cyanide in waste streams and recycling it, and by using chemical (FERROUS SULPHATE, HYDROGEN PEROXIDE OR SODIUM HYPOCHLORITE) or biological reactions to convert the cyanide into less toxic chemicals.
• Deterrents like fencing, polyethylene balls, and netting are also used to keep people, animals and birds out of water bodies on mine sites.
• It is a statutory requirement to have a valid hazardous substances storage and use licence from EMA if using cyanide (Currently renewable annually. This is different from EIA)

Fires involving cyanide

• Cyanide is not combustible but upon contact with acids it will release highly flammable and toxic Hydrogen Cyanide gas (HCN)
• Sodium cyanide can also react with water to produce highly poisonous and flammable hydrogen cyanide gas and in that poses a very high risk of explosion & death if breathed
• Dry Chemical fire extinguishers ARE THE ONLY ONES TO BE USED to fight a fire involving cyanide.
• Do not use carbon dioxide extinguishers or foam extinguishers that may contain acidic compounds
• The Higher the pH of the Solution the Less HCN Produced.

Spills involving cyanide

• AVOID over reaction
• Always wear proper PPE prior to clean up
• Shovel or sweep up dry spill
• Place into a drum, pail, spill container and cover
• Keep spill area dry, cover if needed and barricade off
• Report incident to Supervisor
• Decontaminate with hypochlorite or hydrogen peroxide
• Proper disposable must be in a high Ph area of plant
• For liquid spills elevate pH above 9, spray with sodium hypochlorite of hydrogen peroxide

Immediate signs and symptoms of exposure to cyanide

People exposed to a small amount of cyanide by breathing it, absorbing it through their skin, or eating foods that contain it may have some or all of the following signs and symptoms within minutes:

• Dizziness, Headache, Nausea and vomiting, Rapid breathing, Rapid heart rate, Restlessness, Weakness
• Exposure to a large amount of cyanide by any route may cause these other health effects as well:
• Convulsions, Loss of consciousness, Low blood pressure, Lung injury, Respiratory failure leading to death, Slow heart rate
• Long-term health effects of exposure to cyanide: Survivors of serious cyanide poisoning may develop heart, brain and nerve damage.
• However, cyanide does not cause cancer
• Cyanide poisoning is treated with specific antidotes (and if need be, supportive medical care in a hospital setting).
• Antidotes for cyanide poisoning are most useful if given as soon as possible after exposure. Sodium Thiosulphate based antidote may induce a running tummy. (it is a statutory requirement to have cyanide antidote on site if using cyanide)

Hazards of acids and bases

They are dangerous to human tissue. They may cause chemical burns, respiratory distress and fire hazards

Acids and bases – safe handling

• Follow Basic Safety Precautions
• Wear goggles and gloves.
• Obtain a Materials Safety Data Sheet for each acid.
• Dress appropriately for handling corrosive materials.
• Leave food and drink out of the lab or workspace.
• Locate the shower and eyewash before starting. However any available clean water can be used to wash off chemicals thoroughly, water can be stored in open drums for easy access in emergencies.
• Never try to neutralize acid on your skin with a base. This can cause more extreme damage.
• If acid comes in contact with the eyes, wash the eyes as quickly as possible, as acid can cause serious burns in 15 seconds. Facing downwards, hold the eyelids open, and wash the eyes in an eyewash for fifteen minutes. If there is no eye wash station, a plastic bottle with perforated lid can be used to flush eyes with lots of water. Face down to allow water to run off.
• Wash away acid that comes in contact with skin. Remove clothing, then shower/rinse skin for fifteen minutes.
• If acid is swallowed, drink water and consumable bases such as milk of magnesia. Do not try to dilute with strong bases. Do not induce vomiting.

Mixing acids with other chemicals

• Dilute the acid in proper glassware. Diluting acid releases a lot of heat. Plastic containers are subject to melting during dilution. Even glass containers may crack.
• Pour acid into base/water, always. In this instance, water is also considered a base. This allows the heat generated during dilution to be more effectively dispersed. Otherwise containers may crack/melt or boiling may occur.
• If you are unfamiliar with the procedure, test the reaction on a small scale first.
• Use precise amounts of acid. take just enough to do the task, leftovers cost money & require clean up or disposal. Returning chemicals to their original container may introduce contamination.
• Mix acid/base with instructed chemicals only. Be sure of the process you are doing, blind experiments can cause accidents (e.g., forming toxic gases, exploding, starting a fire etc).
• NEVER MIX ACIDS AND BLEACHING AGENTS.

Precautions

• Try not to get acid on yourself or someone else.
• Never add water or a base (caustic soda, hydrated lime, ammonia etc) to acid since this becomes a splash hazard. Instead, slowly add the appropriate amount of acid into the water or base with stirring (use glass rod for this) or swirling

Respiratory hazards

• Many acids and bases are highly toxic by inhalation.
• The fumes or airborne mist will irritate the mucous membranes of the nose, throat and lungs. Aqua Regia fumes are extremely irritating and damaging to the lining of the nose & breathing airways, work in a well-ventilated environment
• In severe cases, exposure may result in pulmonary edema, a life-threatening condition in which fluid in the lungs prevents oxygen from reaching the bloodstream.

Contact hazards

Concentrated acids and bases are corrosive and cause chemical burns if they come into contact with the skin, eyes or internal organs.

Fire hazards

• When acids or bases are mixed with other chemicals, combustion/fire can occur.
• In addition, acids can react with certain metals to release highly flammable hydrogen gas.
• Hydrogen gas is also released when some bases react with aluminium, magnesium, tin, and zinc metal.
• For this reason, never work with acids and bases while smoking or using other open flames, such as a Bunsen burner.

Protection

• Wear safety goggles or safety glasses that include side shields,
• Wear worksuit or coveralls, a plastic apron or rain suit may be needed safety shoes or rubber boots.
• Choose protective gloves that are resistant to the chemical you are handling. (rubber gloves are usually adequate).
• Depending on the amounts/concentration you work with, you may need to add a face shield or respiratory equipment.
• As much as possible, work in a place with free flow of air or outdoors

Handling acid or base incidents

• Corrosive/caustic chemicals, cause damage to human tissue such as skin, eyes, respiratory tract even stomach lining if ingested/swallowed
• Burns and splashes should be treated correctly, to stop further damage
• The chemical should be removed immediately to prevent any further contact.
• Brush away any excess in the case of dry chemicals (e.g. lime or caustic soda).
• Carefully remove contaminated clothing and/or any accessories.
• Flush the chemical from the affected skin with cool, running water for at least 20 minutes, to ensure removal of chemicals and to prevent further damage.
• If there is no running water use any clean water to thoroughly wash off the chemical
• Do not apply a household remedy to an acid/base burn, as these can sometimes cause further damage. Do not try to pop blisters or pull off dead skin.
• Putting a base on the acid burns is not recommended. The reaction will cause a lot of heat, so you may get heat burns and base burns on top of the acid burns. If injury is serious seek medical attention. ENDS// miningindex.co.zw

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