Sodium Hydroxide (NaOH)

Sodium hydroxide is also known as sodium hydrate, caustic soda or lye. This is a white solid. It is available in flakes, pellets, granules and a 50% saturated solution. As it absorbs carbon dioxide from the air, it has to be stored in an airtight container. It can be dissolved in water accompanied by liberation of heat. It can also be dissolved in ethanol, methanol and potassium hydroxide.

Manufacturing of Sodium hydroxide
The following methods are used:

Membrane cell process
There exists a Nafion membrane to separate the cathode and anode reactions. Across this membrane, only sodium ions and a small quantity of water pass through it. A very standard quality of NaOH is produced. A very low consumption of electric energy is needed and the quantity of steam required for concentration of the caustic is very less.

Diaphragm cell process
A steel cathode is used. The reaction of caustic soda with chlorine is prevented using a porous diaphragm. This is often made of asbestos fibers. During this process, the anode area is separated from the cathode area using a permeable diaphragm. Brine is input into the anode compartment and this flows across the diaphragm into the cathode compartment. Caustic brine in a diluted condition leaves the cell. This has to be concentrated to 50% and the salt has to be removed. An evaporative process is used where there are three tons of steam per ton of caustic soda. This salt is separated from the caustic brine and is used to saturate dilute brine. The chlorine is purified by liquefaction and evaporation.

Mercury cell process
Sodium ions are reduced to sodium metal. This forms an amalgam with a mercury cathode. This then reacts with water to form NaOH. Although, mercury releases are harmful, modern plants are good in this respect.

Characteristics of Caustic soda

• The melting point is 318 degrees celsius
• The boiling point is 1390 degrees celsius
• The vapor pressure is 1 mm Hg at 739 degrees celsius
• The specific gravity is 2.12
• It is incompatible with a large variety of materials like many metals, cyanides, phenols, ammonium compounds, acids, nitro compounds and combustible organics
• It is very corrosive and leads to severe burns
• It causes serious permanent eye damage and is very harmful by ingestion
• It is harmful by skin contact or inhalation of dust

Symptoms of NaOH poisoning
Gastrointestinal symptoms include:

• severe abdominal pain
• vomiting blood
• diarrhea
• burns of the esophagus and stomach
• blood in the stool

Respiratory symptoms are:

• throat swelling
• breathing difficulty
• lung inflammation
• sneezing

Skin symptoms are:

• burns
• irritation
• necrosis in the skin or underlying tissues

Eyes, ears, nose and throat symptoms include:

• severe pain or burning in the nose, eyes, ears, lips and tongue
• loss of vision
• severe pain in the throat

Other symptoms are as follows:

• severe change in pH - very high or little acid in the blood that damages all the body organs
• Hypotension (low blood pressure) raises rapidly
• collapse

Effect of Sodium hydroxide upon the health

• This is very corrosive and can lead to severe burns in all tissues that are connected to it
• If solid or liquid sodium hydroxide are ingested, they may lead to spontaneous vomiting, chest and abdominal pain and difficulty while swallowing
• Inhaling low levels of sodium hydroxide as dusts, mists or aerosols can cause irritation of the nose, throat or respiratory airways
• Corrosive injury to the mouth, esophagus, throat and stomach is very fast and may cause hemorrhage, perforation or narrowing of the gastrointestinal tract
• Inhaling high levels can lead to swelling or spasms of the upper airway and this leads to obstruction and loss of measurable pulse, inflammation of the lungs and collection of fluid in the lungs
• Skin contact may lead to severe burns with deep ulcerations
• Eye contact may cause pain and irritation and in many cases, clouding of the eye and blindness