Ammonium Nitrate

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Infobox on Ammonium Nitrate
Example of Ammonium Nitrate
Ammonium-Nitrate.jpg
Facts
Origin -
Stowage factor (in m3/t) 1 m3/t (bulk)
Humidity / moisture See text
Ventilation Ventilate well
Risk factors See text

Description

A white deliquescent crystalline solid. Most stable form is the non-anhydrate.

The chemical compound ammonium nitrate, the nitrate of ammonia with the chemical formula NH4NO3, is a white crystalline solid at room temperature and standard pressure. It is commonly used in agriculture as a high-nitrogen fertilizer, and it has also been used as an oxidizing agent in explosives, including improvised explosive devices. It is the main component of ANFO, a very popular explosive. It is used in instant cold packs, as hydrating the salt is an endothermic process.

Ammonium nitrate is an important fertilizer with the NPK designation 34-0-0 (34% nitrogen). It is less concentrated than urea (45-0-0) giving ammonium nitrate a slight transportation disadvantage. Ammonium nitrate's advantage over urea is that it is more stable and does not lose nitrogen to the atmosphere. During warm weather urea should only be applied before imminent rain in order to minimize nitrogen loss.

Health and safety data are shown on the material safety data sheets which are available from suppliers and can be found on the internet.

Heating or any ignition source may cause violent combustion or explosion. Ammonium nitrate reacts with combustible and reducing materials as it is a strong oxidant. Although it is mainly used for fertilizer it can be used for explosives. It was sometimes used to blast away earth to make farm ponds. Ammonium nitrates are also used to modify the detonation rate of other explosives. Example will be ammonia dynamites (Nitroglycerin).

Numerous safety guidelines are available for storing and handling ammonium nitrate. It should not be stored near combustible substances or certain fertilizers, especially urea.

Ammonium nitrate has a critical relative humidity of 59.4%, above which it will absorb moisture from the atmosphere.

The increased level of misuse by terrorists prompted the need to change how these substances should be dealt with. For example in Australia, the Dangerous Goods Regulations came into effect in August 2005 to enforce licensing in dealing with such substances. Licenses are granted only to applicants (industry) with appropriate security measures in place to prevent any misuse. Additional uses such as education and research purposes may also be considered but individual use will not. Employees of those with licenses to deal with the substance are still required to be supervised by authorized personnel and are required to pass a security and national police check before a license may be granted.

The processes involved in the production of ammonium nitrate in industry, although chemically simple, are technologically challenging. The acid-base reaction of ammonia with nitric acid gives a solution of ammonium nitrate.

For industrial production, this is done using anhydrous ammonia gas and concentrated nitric acid. This reaction is violent and very exothermic. After the solution is formed, typically at about 83% concentration, the excess water is evaporated to an ammonium nitrate (AN) content of 95% to 99.9% concentration (AN melt), depending on grade. The AN melt is then made into "prills" or small beads in a spray tower, or into granules by spraying and tumbling in a rotating drum. The prills or granules may be further dried, cooled, and then coated to prevent caking. These prills or granules are the typical AN products in commerce.

The Haber process combines nitrogen and hydrogen to produce ammonia, part of which can be oxidized to nitric acid and combined with the remaining ammonia to produce the nitrate. Another production method is used in the so-called Odda process.

Applications

Fertilizer, explosives, especially as prills/oil mixture, pyrotechnics, herbicides and insecticides, manufacture of nitrous oxide, absorbent for nitrogen oxides, ingredient of freezing mixtures, oxidizer in solid rocket propellants, nutrient for antibiotics and yeast, catalyst.

Shipment/Storage/Risk factors

Containerised shipments
Product is acceptable only in dry containers, NOT in operating or non operating reefers.

The reason for this is that Ammonium Nitrate is liable to evolve corrosive vapours, which could result in heavy damage to the reefers.

Fertilizer, oxidising agent, can give off toxic gases if heated. As an oxidising agent contact with combustible materials such as oil is dangerous. It is soluble in water and alcohol; decomposes above 135°C, giving off oxygen with increased risk of fire.

Aqueous solution, corrosive strong acid, reacting violently with bases.

Regardless the above, the following compounds are however NOT ACCEPTABLE: UN NO 0222: Ammonium Nitrate with more than 0.2% by mass of combustible substances, incl. any organic substance calculated etc. UN NO 2426: Ammonium Nitrate, liquid (hot concentrated solution)

Must be stowed ON DECK as per IMDG Code.

Please also ensure that all warehouses packing the Ammonium have the knowledge to stuff the container(s) according to the International Guideline for the Packing of Cargo (CTU PACKING GUIDE).

Ammonium nitrate decomposes into the gases nitrous oxide and water vapor when heated (non-explosive reaction); however, ammonium nitrate can be induced to decompose explosively by detonation. Large stockpiles of the material can be a major fire risk due to their supporting oxidation, and may also detonate, as happened in the Texas City disaster of 1947, which led to major changes in the regulations for storage and handling.

There are two major classes of incidents resulting in explosions:

  • In the first case, the explosion happens by the mechanism of shock-to-detonation transition. The initiation happens by an explosive charge going off in the mass, by the detonation of a shell thrown into the mass, or by detonation of an explosive mixture in contact with the mass. The examples are Kriewald, Morgan (present-day Sayreville, New Jersey), Oppau and Tessenderlo.
  • In the second case, the explosion results from a fire that spreads into the ammonium nitrate itself (Texas City, Brest, Oakdale), or from a mixture of ammonium nitrate with a combustible material during the fire (Repauno, Cherokee, Nadadores). The fire must be confined at least to a degree for successful transition from a fire to an explosion (a phenomenon known as "deflagration-to-detonation transition", or DDT). Pure, compact AN is stable and very difficult to ignite, and there are numerous cases when even impure AN did not explode in a fire.

Ammonium-nitrate-based explosives were used in the Oklahoma City bombing and in the 2011 Delhi bombing and the bombing in Oslo 2011.

Ammonium nitrate decomposes in temperatures normally well above 200°C. However the presence of impurities (organic and/or inorganic) will often reduce the temperature point when heat is being generated. Once the AN has started to decompose, then a runaway reaction will normally occur as the heat of decomposition is very large. AN evolves so much heat that this runaway reaction is normally impossible to stop. This is a well-known hazard with some types of N-P-K Fertilizers, and it is responsible for the loss of several cargo ships.

Under normal handling conditions, ammonium nitrate is not harmful. However, inhalation of high concentrations of ammonium nitrate dust can cause respiratory tract irritation. Symptoms may include: coughing, sore throat, shortness of breath, or even suffocation. When swallowed in high concentrations, ammonium nitrate may cause headache, dizziness, abdominal pain, vomiting, bloody diarrhea, weakness, a tingling sensation, heart and circulation irregularities, convulsions, collapse, and suffocation. Ammonium nitrate forms a mild acid when mixed with water. This acid can cause irritation to the eyes, nose, and skin.

The material must be kept as cool as possible and removed from confinement and flooded with water in the event of fire. It explodes more readily if contaminated with combustibles. It is a strong oxidizing agent. It may be made resistant to flame and detonation by proprietary process involving addition of 5% to 10% ammonium phosphate.

Bulk shipments
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.