Applications: Industrial Chemicals
Agrochemicals
Caustic potash is a major raw material in the preparation of certain herbicides and also of important pesticides (potassium salt of DMPA and DEPA).
Alumina
One of the major uses of caustic soda is the manufacture of aluminium oxide or alumina (Al2O3) from bauxite.
Bauxite is natural hydrated alumina containing impurities (iron and silica). The ore is added to a solution of caustic soda where sodium aluminate is formed. The solution is then filtered, washed, hydrolyzed and cooled to precipitate aluminium hydroxide. The latter substance is calcined by heating to form alumina. Alumina is reduced to metallic aluminium by electrolysis.
Batteries
Caustic potash is used as an electrolyte in primary and secondary (rechargeable) batteries. It is the required electrolyte in nickel/cadmium batteries whereas in alkaline batteries, caustic potash, caustic soda or lithium hydroxide may be used.
Mercuric oxide/zinc cells contain a 40% KOH solution saturated with zinc oxide.
The majority of rechargeable batteries (type nickel/cadmium) are found in portable equipment (mobile phones).
Concentrated sulphuric acid is used in lead-acid accumulators, among others in car batteries.
Biocides
Sodium hypochlorite can be used as a biocide to prevent the growth of micro-organisms in eg. pipe lines.
De-icers
As an alternative to ordinary salt (NaCl) several chemicals have been developed. The most effective in terms of limiting the corrosion are acetates. Calcium magnesium or potassium magnesium acetates are currently being used.
Potassium acetate solution is considered an environmentally safe anti-freeze for aircraft runways.
Caustic potash is used during these production processes.
Fertilisers
Caustic potash can be used in the preparation of high quality fertilisers for use in irrigation systems.
The essential property of such fertilisers is that they are completely soluble. The main sources for potassium in fertilisers for this application are potassium nitrate, potassium sulphate , mono-potassium phosphate.
Fire extinguishers
Potassium bicarbonate (as a dry powder) is a very effective extinguisher for fires involving gases, oils, greases and petrochemicals and is also effective against electrical fires.
Mixtures of potassium bicarbonate and sodium bicarbonate or potassium chloride can also be used. These mixtures are designed to ensure free flow and long-term stability.
Fire extinguishers
Potassium bicarbonate (as a dry powder) is a very effective extinguisher for fires involving gases, oils, greases and petrochemicals and is also effective against electrical fires.
Mixtures of potassium bicarbonate and sodium bicarbonate or potassium chloride can also be used. These mixtures are designed to ensure free flow and long-term stability.
Glass
The glass industry is the main outlet for potassium carbonate. The K2CO3 is used in high quality, high value glasses such as optical glasses and lead crystal.
It helps to control refractive index and scatter in lenses, prisms, etc. A high quality of potassium carbonate is needed with low concentrations of iron and cobalt in these particular applications.
Glass of cathode ray tubes (CRT glass) for television sets and computer screens has a big share in the consumption of potassium carbonate (because of the superior fluxing properties of potassium in the presence of barium and strontium oxides, used to screen out X-rays).
Metal Pickling
Pickling is the removal of oxides from the surface of metals by converting these to soluble compounds. The removal of oxides from the surface of metal strips or sheets is necessary if these products are to be processed further.
The majority of pickling processes involve the use of acids (sulphuric, hydrochloric,…) although other methods such as alkaline pickling are also used in special circumstances.
For ferrous metals other than stainless steel hydrochloric acid and sulphuric acid are widely used.
Hydrochloric acid offers some technical advantages over sulphuric acid (faster, cleaner, lower consumption).
Mining
Sodium sulphide and hydrosulphide are used as flotation reagent in copper, cobalt, molybden, tin and lead extractions.
Paper & Pulp
Caustic soda is widely used in the manufacture of wood pulp. The most commonly used process is the kraft or sulfate process, which consists of the following steps:
Incoming logs are slashed, debarked and reduced to the size of small chips.
Chips are charged to a digester where they are processed with steam and a white liquor containing sodium sulfide and caustic soda.
Pulp is separated from the cooking ("black") liquor.
Afterwards, the black liquor is regenerated to white liquor, which is recycled to the process. Caustic soda is further used to neutralize pulp containing bleaching agent (related to the production of paper with high whiteness).
Rayon fibres
This industry has historically been a relatively large user of caustic soda, in the process, cellulose is dissolved, repolymerized and then extruded into fiber form.
Wood pulp is also reacted with caustic soda to form sodium cellulose which is then further processed. Approximately 0.62 ton of caustic soda is required to make one ton of rayon.
Soaps and Detergents
Soaps are essentially the alkaline salts of fatty acids with small amounts of other ingredients (whitening agents,..) added.
Detergents are complex mixtures of many substances, all chosen to contribute a specific action to cleaning. Detergents contain surfactants, builders, corrosion inhibitors, anti-redeposition agents, fabric brighteners and other additives.
Caustic soda is directly used in the production process of both soap and detergents. In several cases caustic potash can also be used, e.g. household soap: stearic acid + NaOH -> sodium stearate + H2O.
Tanning
Sodium sulphide and sodium hydrosulphide are used in the leather industry as de-hairing agents.
Many other speciality chemicals are used at different stages in the processing of hides; (degreasing, neutralizing agents, tanning agents for softening and enhancing dyeing properties,..).
Textile and dyeing
Caustic potash and many other chemicals are used in textile treatment.
Treatments include sizing, scouring, bleaching, dyeing, printing, binding and finishing. As inorganic chemicals soda ash, caustic soda, sodium sulphate and hydrogen peroxide are used. Caustic potash is used where higher solubility is required.
