Chile Saltpetre

Chile saltpetre, otherwise called sodium nitrate, is the chemical compound having the chemical formula NaNO3. To distinguish it from the ordinary saltpeter, potassium nitrate, this alkali metal nitrate salt is often called Chile saltpeter (because the large deposits were traditionally mined in Chile). The mineral form is also called nitrate, nitratine, or soda niter.

Sodium nitrate can be given as a white deliquescent solid, which is more soluble in water. It is a readily available nitrate anion (NO3−) source, which can be useful in many reactions, that are carried out on industrial scales for the production of pyrotechnics, smoke bombs, pottery and glass enamels, solid rocket propellant, and food preservatives (especially meats). It has been mined extensively for the above-listed purposes.

Occurrence

The largest accumulations of naturally occurring sodium nitrate are found in Peru and Chile, where the nitrate salts are bounded within mineral deposits, which are caliche ore. These Nitrates accumulate on land through sea-spray desiccation/oxidation and marine-fog precipitation followed by the gravitational settling of airborne KNO3, NaNO3, Na2SO4, NaCl, and I, in the hot-dry desert atmosphere. El extreme torrential/aridity rain cycles favour the accumulation of nitrates through both aridity and water remobilization or transportation or solution onto the basins and slopes; capillary solution movement forms the nitrate layers; pure nitrate produces rare veins.

The world supply of the compound was mined for more than a century, almost exclusively from the Atacama desert, which is located in northern Chile, until, at the 20th-century turn, German chemists named Carl Bosch and Fritz Haber developed a process for forming ammonia from the industrial scale atmosphere. Germany began converting the ammonia from this particular process into synthetic Chilean saltpeter with the onset of World War I, which was as practical as the natural compound in the formation of gunpowder and other munitions. By the 1940s, the need for sodium nitrate derived from natural sources led to a drastic decrease in this conversion process.

Chile still holds the largest reserves of caliche, with the active mines in such locations as Pedro de Valdivia, Pampa Blanca, and María Elena, and there it used to be referred to as white gold. Potassium nitrate, sodium nitrate, iodine, and sodium sulfate are all obtained by caliche processing. The previous Chilean saltpeter mining communities of Santa Laura, Humberstone were declared in Unesco World Heritage sites in 2005.

Synthesis

Industrially, the sodium nitrate can also be synthesized by neutralizing the nitric acid with sodium bicarbonate or sodium carbonate:

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or by neutralizing it with sodium hydroxide (but this reaction is very exothermic):

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or by mixing the stoichiometric amounts of sodium hydroxide and ammonium nitrate, sodium carbonate and sodium bicarbonate:

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Uses

Sodium nitrate is combined with sulfuric acid to form nitric acid, which is distilled off. At less pressure, the lower temperature required results in less decomposition. The theoretical 2 moles of nitric acid per 1 mole of sulfuric acid results in more high-end temperature, much decomposition, and a solid neutral sulfate, which is difficult to remove. It was a common practice to work with excess sulfuric acid to finish off the retort on a largely bisulfate substance, which is poured molten when this reaction was industrially important.

To create a hybrid aqua regia, which dissolves gold and other metals, hobbyist gold refiners also use sodium nitrate.

Whereas the less popular uses include the substitution of potassium nitrate typically used in black powder, as an oxidizer in fireworks, and as a component in instant cold packs.

Along with potassium nitrate and calcium nitrate, sodium nitrate is being used for heat storage and, more recently, heat transfer in solar power plants. In demonstration plants, such as the Archimedes project and Andasol Solar Power Station, a combination of sodium nitrate, calcium nitrate, and potassium nitrate is used as an energy storage material.

It can also be used in the waste water industry for facultative microorganism respiration. Nitrosomonas, a microorganism genus, absorbs nitrate rather than oxygen, causing it to expand quickly in the waste water to be processed.

Sometimes, sodium nitrate is also used by marine aquarists, who utilize the techniques of carbon-dosing. It is also used to increase the nitrate levels in the water and promote bacterial growth.

Food

Sodium nitrate is also a food additive and can be used in poultry and cured meats as a colour fixative and preservative; it is classified as E number E251 or INS number 251. It is approved for use in the US, EU, New Zealand, and Australia. There should be no confusion with Sodium nitrate to sodium nitrite, which is also used in a common food preservative and additive. For example, in deli meats.