Nitric Acid

Infobox on Nitric Acid
Example of Nitric Acid
Facts
Origin	-
Stowage factor (in m3/t)	-
Humidity / moisture	-
Ventilation	-
Risk factors	See text

Nitric Acid

Description

Nitric acid (HNO3), also known as aqua fortis and spirit of niter, is a highly corrosive strong mineral acid. The pure compound is colourless, but older samples tend to acquire a yellow cast due to decomposition into oxides of nitrogen and water. Most commercially available nitric acid has a concentration of 68%. When the solution contains more than 86% HNO3, it is referred to as fuming nitric acid. Depending on the amount of nitrogen dioxide present, fuming nitric acid is further characterized as white fuming nitric acid or red fuming nitric acid, at concentrations above 95%.

Nitric acid is the primary reagent used for nitration - the addition of a nitro group, typically to an organic molecule. While some resulting nitro compounds are shock- and thermally-sensitive explosives, a few are stable enough to be used in munitions and demolition, while others are still more stable and used as pigments in inks and dyes. Nitric acid is also commonly used as a strong oxidizing agent.

Application

The main use of nitric acid is for the production of fertilizers. Nitric acid is neutralized with ammonia to give Ammonium Nitrate. This application consumes most of the quantities produced annually. The other main applications are for the production of explosives, nylon precursors, and specialty organic compounds.

Shipment / Storage / Risk factors

Pure nitric acid is a colourless liquid which fumes and is unstable. Commercial grades of nitric acid are approximately 68% and 94% concentrations. Because of its instability even dilute nitric acid gives off oxygen and is therefore a strong oxidizing agent.

Properties: transparent, colourless, or yellowish fuming, suffocating, hygroscopic, corrosive liquid. Will attack almost all metals. The yellow colour is due to release of nitrogen dioxide on exposure to light; strong oxidizing agent, miscible with water, decomposes in alcohol.

Nitric acid is generally transported in two concentrations, 65-75% and, to a limited extent, 95-98%. The 316L grades give the lowest corrosion rates at the likely carriage temperatures for the 65-75% concentration. For the 95-98% concentration, the corrosion rates of 316L and other principal grades are dependent on the precise concentration and temperature, even small temperature increases significantly increase the corrosion rate. However, in general, corrosion rates for these normal grades of stainless steel tend to be too high to be considered for use in chemical tankers. Special high silicon stainless steels with good resistance to 95-99% nitric are available and these should be considered where highly concentrated acid has to be transported regularly.

Nitric Acid must be shipped in accordance with the IMDG Code and internal ML rules. This commodity has only one UNNO but several different stowage restrictions based on the concentration of acid.

Dangerous fire risk in contact with organic materials. Highly toxic by inhalation, corrosive to skin and mucous membranes, strong oxidizing agent. TLV: 2 ppm in air.

Nitric acid is a strong acid and a powerful oxidizing agent. The major hazard posed by it is chemical burns as it carries out acid hydrolysis with proteins (amide) and fats (ester) which consequently decomposes living tissue (e.g. skin and flesh). Concentrated nitric acid stains human skin yellow due to its reaction with the keratin. These yellow stains turn orange when neutralized. Systemic effects are unlikely, however, and the substance is not considered a carcinogen or mutagen.

The standard first aid treatment for acid spills on the skin is, as for other corrosive agents, irrigation with large quantities of water. Washing is continued for at least ten to fifteen minutes to cool the tissue surrounding the acid burn and to prevent secondary damage. Contaminated clothing is removed immediately and the underlying skin washed thoroughly.

Being a strong oxidizing agent, reactions of nitric acid with compounds such as cyanides, carbides, metallic powders can be explosive and those with many organic compounds, such as turpentine, are violent and hypergolic (i.e. self-igniting). Hence, it should be stored away from bases and organics.

Note: For overseas carriage aspects of Chemicals, the readers are recommended to acquire or have access to a good chemical dictionary, and a copy of the International Maritime Dangerous Goods (IMDG) Code, issued by the International Maritime Organisation. Also consult the applicable MSDS sheet.