About caustic soda flakes
CAUSTIC SODA
A major building block in many industrial processes – To be treated professionally Caustic soda – or sodium hydroxide – is the natural co-product of chlorine production; indeed, the laws of chemistry define that for every tonne of chlorine you produce, about 1100 kg of caustic soda is also produced, together with 28 kg of hydrogen. The caustic soda is widely used in industrial processes. However, because of its chemical and physical properties, it needs to be handled with proper care and professionalism.
WHAT IS CAUSTIC SODA?
Caustic soda is the common name of the compound sodium hydroxide. This is the natural co-product of the chlorine production by electrolysis of sodium chloride. Its chemical formula is NaOH. “Caustic” (as it is commonly called), is a white solid in its pure form. It is mostly traded as an aqueous solution, typically concentrated to 50%, but many other concentrations are commercially available depending on the applications of the compound. Caustic soda is also traded as concentrated solid pellets, flakes or bulk fused (about 98% concentration).
The solutions are also called “soda lye”; they are milky white to yellowish-brown coloured liquids.
PROPERTIES
The following properties of this substance are important:
The product is highly alkaline and strongly hydrophilic. This capacity makes caustic soda extremely corrosive to skin tissue and hazardous to all animal and plant life. All direct unprotected physical contact with the substance should be avoided.
The substance is moderately toxic; however, the major hazard is its corrosive effects.
Sodium hydroxide is not volatile.
It is not flammable.
MAJOR APPLICATIONS
Sodium hydroxide is a very widely used chemical in numerous applications:
It constitutes an essential reactant in the production of many useful organic chemicals (more than 30 % of caustic production goes into this application).
Inorganic chemicals like paints, glass and ceramics and uses in fuel cell production and cosmetics are also very important.
The paper, pulp and cellulose industries are major users of caustic soda.
Other areas where caustic is essential are: the food industry, water treatment (for the flocculation of heavy metals and acidity control), the soaps and detergents sectors, the textile sector (as a bleaching agent), mineral oils (preparation of greases and fuel additives) and the synthesis of the synthetic fibre rayon.
About four per cent of caustic production is used in the process of refining aluminium from its ore
bauxite.
The remainder of the caustic production (more than 17%) has miscellaneous applications, like the synthesis of pharmaceutical compounds, rubber recycling and the neutralisation of acids.
HUMAN EXPOSURE: ACUTE EFFECTS
The extremely corrosive character of caustic constitutes its main hazard when humans or animals are exposed to the concentrated substance.
Contact with the eye may cause irreversible severe damage if there is no immediate treatment. Inhalation is not likely, because the substance is not volatile. However, if mists of the concentrate are
inhaled, severe damage to mucous membranes and the lungs can be caused. Ingestion of the concentrate will cause major damage to the mucous membranes and all other tissues that come into contact with the product.
As stated before, caustic soda is extremely corrosive to the skin and can cause deep ulcerations and scarring. In this characteristic hides an extra risk: it generally does not cause pain until after major damage has been done. Contact with skin must lead to irrigating with plenty of water during at least tens of minutes after removing contaminated clothes.
Strong alkalis like caustic soda combined with human tissue form soluble compounds which may result in deep and painful destruction.
TO BE HANDLED CORRECTLY
In view of the chemical and physical characteristics of caustic soda, it is obvious that the substance should be handled correctly, using proper techniques, selected materials and protective equipment for the people possibly in contact with the product.
Typical protective equipment for workers will consist of special overalls, buttoned to the wrist and neck, full face shield, PVC elbow gloves, an apron and rubber boots. Special care must be given to eye protection: safety glasses are mandatory, especially if the face protection is not completely tight. Water supply should always be available near the point of use, including showers and water eye-bath.
Dilution of caustic shall always been done adding slowly the caustic to the water, with continuously stirring, and not water to the caustic. Metals need to be properly degreased before introduction of the caustic.
The material to use depends of the temperature and the concentration of the caustic. Carbon steel (below 50-55°C) and stainless steel are used safely for 50% caustic soda piping, valves, tanks and equipment; for temperature above 100°C, nickel alloys and even pure nickel have to be preferred. For cold diluted caustic plastic pipes and tanks can be used.
The storage tanks are always installed in containment bunds preventing emission to the environment; installations where spills are possible (loading station …) have a collection system to convey the leaked fluid, after dilution by washing, to a neutralisation unit.
Caustic soda solutions are usually transported in stainless steel road or rail tankers. In case of caustic soda leak during transportation, environmental protection measures include the containment of the leak with plastic sheets, sand bags, soil … After removal of the spilled liquid, contaminated areas can be washed with water or possibly neutralised with light acidic solution.
CHEMICAL REACTIVITY DATA
The dilution reaction with water produces a lot of heat that can lead to a boiling solution with alkaline droplets projection and reaction with concentrated acids is very violent. Caustic also reacts with aluminium, tin, copper, zinc (galvanised recipients) and their alloys with production of hydrogen and can thus form explosive gas mixtures. Sodium hydroxide also reacts violently with materials such as chlorinated compounds, oxidisers, organic molecules, and nitro compounds. The reaction with ammonium and amine compounds will release toxic substances.
KNOW THE HAZARD, MANAGE THE RISK
As it is the case with many chemicals, it is very important that caustic soda be handled
correctly, while understanding the hazard and with control of the risk.
This highly useful product can only play its full role as a key chemical in many industrial and
mining areas, if it is handled with the proper care and professionalism.