Nitrates and Carbonates: Properties, Formation, and Environmental Impact

Posted on Apr 5, 2025 in Chemistry

Nitrates: Properties and Formation

Nitrates: Nitrates are salts derived from nitric acid. They are formed by the junction of the nitrate anion (NO3–) with a metal. They are less abundant than carbonates and are characterized by their high solubility and a structure similar to carbonates. Nitrates are an essential part of fertilizers. Plants convert them back into organic nitrogen compounds such as amino acids.

Inorganic nitrates are formed in nature by the decomposition of nitrogenous compounds such as proteins and urea.

Organic nitrates are nitric acid esters with alcohols.

Synthesis of Nitrates

Nitrates can be obtained by several methods:

  • By action of nitric acid on a metal.
  • By neutralization of a base with nitric acid.
  • By anion exchange.

Minerals Formed by Nitrates

  • Nitratine or sodium nitrate (NaNO3): Also known as Chilean nitrate or Caliche, a large reservoir exists in the Atacama Desert.
  • Nitrate or potassium nitrate (KNO3): An essential part of black powder.

Nitrates in Nature

As intermediate products, nitrates are present in the process of nitrification/denitrification used in wastewater treatment plants. This process exploits the fact that some organisms can reduce nitrate under anaerobic conditions directly to elemental nitrogen, eliminating nitrogen compounds from waters where eutrophication problems occur.

Nitrate Contamination

Nitrification produces a noticeable change in the oxidation of fixed nitrogen, passing from cationic form (NH4+) to anion (NO3–). In clay soils with a high negative charge, NH4+ is retained more easily, while NO3– is not retained and passes into groundwater. A negative side effect of nitrification is that nitrates are toxic to animals because they can cause the production of nitrosamines and other carcinogens. Nitrification inhibitors are sometimes used to reduce these effects in the soil.

Carbonates: Properties and Formation

Carbonates: Carbonates are formed by the carbonate anion (CO32-) combined with a metal. Generally, hardness ranges between 3 and 5, and they may be formed by very different mechanisms. Most carbonates, other than the alkali metal carbonates, are poorly soluble in water. This feature is important in geochemistry and is part of many minerals and rocks.

Organic carbonates: Organic carbonates are esters of carbonic acid, formed from (Cl2C=O) and the corresponding alcohol.

Carbonates in the Wild

They are found in some saline lagoons, for example, in Egypt, although most are derived from the lime in the Solvay process. They are an intermediate in the production of diverse products such as soap, sodium percarbonate used as a bleach, glass, and soda (NaOH).

Carbonate Pollution

Carbonate and bicarbonate ions, combined with magnesium, precipitate in the form of calcium carbonate (CaCO3) or magnesium carbonate (MgCO3) when the soil solution is concentrated under dry conditions. The concentration of Ca and Mg decreases in relation to sodium, and the sodium adsorption ratio (SAR) is higher. This causes alkalization and increased pH. A high pH level in water analysis indicates high values of carbonates and bicarbonates.

Carbonate Minerals

  • Aragonite (CaCO3): Transparent varieties and alabaster are used as gemstones.
  • Azurite (Cu3(CO3)2(OH)2): Highly prized as ornamental stone and for copper extraction.
  • Calcite (CaCO3): The purest crystals are used to manufacture lenses for microscopes, marble and ornamental stone, lithographic limestone in printing, and in general, for the construction, metallurgy, chemicals, fertilizers, and varnishes industries.
  • Cerussite (PbCO3): A mineral for the secondary extraction of lead and silver.
  • Malachite (Cu2CO3(OH)2): Used as ornamental stone and for copper extraction.
  • Siderite (FeCO3): Used in the extraction of iron.