Iodine

Iodine is a non-metallic chemical element belonging to Group 17 of the periodic table, known as the halogens. It has the symbol I and atomic number 53. Recognised for its distinctive violet vapour and metallic lustre, iodine plays an indispensable role in biological, industrial, and commercial contexts. Its diverse applications range from essential medical uses to vital industrial processes and economic importance in global trade.

Physical and Chemical Properties

Iodine is a shiny, grey-black solid at room temperature, subliming easily into a violet-coloured vapour when heated. It is moderately soluble in water but dissolves readily in organic solvents such as alcohol and carbon tetrachloride. Chemically, iodine is less reactive than other halogens like chlorine and bromine, yet it forms numerous compounds, including iodides, iodates, and organoiodine compounds. Its relatively mild reactivity allows it to be safely employed in various industrial and biological contexts.

Natural Occurrence and Extraction

Iodine is not found in its elemental form in nature but occurs mainly as soluble iodide ions in seawater and certain mineral deposits. Large quantities are also concentrated in seaweeds and marine organisms. Commercially, iodine is extracted from natural brines and nitrate deposits, especially in countries such as Chile, Japan, and the United States. The principal industrial extraction method involves oxidation of iodide ions using chlorine gas, followed by sublimation and purification of the elemental iodine.

Biological Importance and Everyday Uses

Iodine is an essential trace element for human health. It is a critical component of the thyroid hormones thyroxine (T₄) and triiodothyronine (T₃), which regulate metabolism, growth, and development. Iodine deficiency leads to disorders such as goitre, hypothyroidism, and intellectual impairment, particularly in children.
To prevent such deficiencies, iodised salt has become a major public health measure across the world. By fortifying table salt with potassium iodide or iodate, populations are provided with a consistent and affordable source of dietary iodine.
In daily life, iodine solutions such as tincture of iodine and povidone-iodine are widely used as antiseptics for disinfecting wounds and surgical areas. These preparations kill bacteria, fungi, and viruses by disrupting cellular proteins. Additionally, iodine compounds are used in water purification tablets, making it invaluable for travellers, military use, and emergency relief efforts.

Industrial Applications

Iodine’s chemical versatility makes it a key element in several industries:

• Pharmaceutical Industry: Iodine is used in the manufacture of radiocontrast agents for medical imaging, particularly in X-rays and CT scans, due to its high atomic number and ability to absorb radiation. Compounds such as iohexol and iodixanol are crucial diagnostic tools.
• Photography: Silver iodide was historically used in photographic film emulsions because of its light-sensitive properties. Though largely replaced by digital methods, the compound remains significant in certain specialised imaging processes.
• Catalysis and Organic Synthesis: Iodine serves as a catalyst or reagent in numerous chemical reactions, including alkylation, halogenation, and oxidation processes. It is employed in the production of acetic acid and polymers.
• Dye and Pigment Manufacture: Iodine compounds are involved in producing dyes and inks, particularly those requiring high stability and vivid colours.
• Feed Additives: Iodine supplements are added to animal feed to ensure healthy thyroid function in livestock, improving growth and milk production.
• Electronics and Materials Science: Iodine is used in the production of polarising films for LCD screens and in the growth of single crystals of semiconductors such as silicon.

Environmental and Agricultural Applications

Iodine also plays a role in air purification systems and biocidal applications. Certain iodine compounds are effective in controlling microbial growth in industrial water systems and swimming pools. In agriculture, iodine-based disinfectants are used to sterilise equipment, animal housing, and dairy machinery. Additionally, iodine vapour has been used in insect control and seed disinfection, improving crop health and yield.

Economic Importance and Global Production

The global iodine market is valued for its stable demand across health, industry, and technology sectors. Chile remains the world’s largest producer, accounting for over half of global output, followed by Japan and the United States. The industry benefits from iodine’s limited availability and wide applicability, which maintain relatively high market prices.
Iodine’s economic impact extends beyond production; it contributes to pharmaceutical exports, diagnostic medicine, and agricultural productivity. Furthermore, its role in public health—especially through iodised salt—provides long-term economic benefits by preventing iodine deficiency disorders that can reduce national productivity and increase healthcare costs.

Safety, Storage, and Environmental Concerns

Although iodine is indispensable, it must be handled carefully. Exposure to high concentrations of iodine vapour can irritate the eyes, skin, and respiratory tract. Ingesting excessive iodine may cause thyroid dysfunction or poisoning. Industrial handling therefore requires protective equipment and proper ventilation.
Environmentally, iodine compounds are generally stable and not highly toxic, but improper disposal of iodine-containing waste can lead to contamination. Sustainable extraction and recycling practices are increasingly encouraged to limit ecological impacts.

Modern Developments and Future Prospects

Recent innovations in iodine chemistry have expanded its utility in emerging fields such as nanotechnology, energy storage, and environmental sensing. Iodine-based electrolytes are being developed for iodine-sulphur batteries and solar cells, offering environmentally friendly alternatives to conventional materials. In medical research, iodine nanoparticles are under investigation for targeted drug delivery and cancer imaging.
The future of iodine lies in balancing its traditional applications with novel technologies that exploit its unique chemical and physical properties. As global emphasis shifts toward sustainability and advanced healthcare, iodine remains a vital element bridging medicine, industry, and economic growth.
Iodine thus occupies a distinctive place in both everyday life and modern industry. From maintaining human health to supporting high-technology applications, its significance continues to expand, reflecting the element’s enduring scientific and economic value.