Iodine is a kind of purple-black shiny flake crystal with atomic number of 53. The natural isotope is iodine-127 with 74 neutrons. Iodine has a high vapor pressure, which sublimates under slight heat. Pure iodine vapor is dark blue, and if it contains air, it is purplish red, and has a pungent odor. Iodine is easily soluble in many organic solvents, such as chloroform (CHCl3) and carbon tetrachloride (CCl4). The solution formed by iodine in ethanol and ether is brown. Iodine forms purple solution in solvents with low dielectric constant (such as carbon disulfide and carbon tetrachloride), in which iodine exists in molecular state. Although the solubility of iodine in water is very small, it is significantly increased in KI or other iodide solutions.
Preparation method of iodine:
Iodine can be separated from the solution by using its solubility in organic solvents.
Iodine can be extracted from mother liquor produced by algae, oil well brine and saltpeter. Acidify the aqueous solution containing 0.001%~0.01% iodide with sulfuric acid to pH 2.3~2.5, then oxidize the iodide to iodine with chlorine gas or sodium nitrite, use activated carbon to absorb iodine to saturation, and then dissolve the iodine with sodium hydroxide to generate sodium iodide and sodium iodate solution, and then inject chlorine gas to obtain iodine.
There are generally two methods to prepare iodine:
(1) I2 prepared by I:
I - has strong reducibility. Many oxidants, such as Cl2, Br2, MnO2, can oxidize iodine ions into iodine in acidic solution:
Cl2 + 2NaI → 2NaCl + I2
2NaI + 3H2SO4 + MnO2 → 2NaHSO4 + MnSO4 + I2 + 2H2O
The second equation is the main reaction of extracting iodine from algae ash, and the extracted iodine can be extracted and separated by organic solvent. In the above reactions, excessive oxidants should be avoided to prevent the simple iodine from being further oxidized into high-valent iodine compounds:
I2 + 5Cl2 + 6H2O → 2IO3-+ 10Cl- + 12H+
(2) Restore of IO3-:
The preparation of a large amount of iodine comes from the natural sodium iodate, and the reduction agent NaHSO3 is used to reduce the IO3- ion to simple iodine:
2IO3-+ 5HSO3-→ 3HSO4-+ 2SO42-+ H2O + I2
In fact, the above reaction is to first reduce iodate to iodide with an appropriate amount of NaHSO3:
IO3-+ 3HSO3-→ I- + 3SO42-+ 3H+
The obtained acidic iodide solution is reacted with an appropriate amount of iodate solution to release iodine:
IO3-+ 5I- + 6H+ → 3I2 + 3H2O
Iodine is a chemical element, the heaviest non-artificial and stable halogen, and it is a shiny purple black solid nonmetal under standard conditions.
Iodine is an essential micronutrient for living organisms, and plays an extremely important role in the growth of animals and plants. The iodide and iodate in seawater can enter the metabolism of most marine organisms. In advanced mammals, iodine is concentrated in the thyroid in the form of iodized amino acids, which is an essential component for the synthesis of thyroxine to regulate cell metabolism and the development and growth of neuromuscular tissue. Iodine deficiency can cause goiter, and is also the main factor causing mental retardation. Most of the iodine needed by human body comes from diet, such as seaweed, kelp, shellfish, eggs, cereals and green vegetables, among which kelp, seaweed and other foods are the most abundant in iodine. To prevent iodine deficiency, food iodine fortification measures can be taken, such as adding appropriate amount of potassium iodide and potassium iodate in salt to supplement iodine intake.
Almost half of the iodine is converted into organic iodine compounds, and iodide can be used in pigments, drugs, catalysts, colorants, cleaning and hygiene, animal food additives and other industries, such as preservatives (iodoform), disinfectants (iodine wine) and drugs (potassium iodide tablets, iodine glycerin, etc.). Radioisotope iodine-131 is used in radiotherapy and radiotracer technology. Iodine can also be used to make photographic films. In addition to being used as a photosensitizer for photographic films, silver iodide can also be used as a condensation nodule for artificial precipitation agents. It can be deployed in clouds by aircraft or rockets for artificial precipitation.
Stable iodine prevention refers to the emergency protective action of taking stable iodine (127I) compound to prevent or reduce the absorption of radioactive iodine by the thyroid when the nuclear or radiation emergency has or may lead to the release of radioactive iodine. Some countries will distribute iodine tablets (potassium iodide) to residents around the nuclear power plant and take them within four hours after the nuclear accident, giving priority to the position of iodine in the human body, so as to reduce the absorption of radioisotope iodine-131 by the thyroid and avoid inducing cancer.