Selenium

Selenium
W. Oelen · CC BY-SA 3.0 · source
Name	Selenium
Atomic number	34
Category	Nonmetal, metalloid
Appearance	Gray metallic luster; red allotrope
Discovered	1817
Discovered by	Jöns Jakob Berzelius
Phase	Solid
Density	4.8 g/cm³ (gray)
Melting point	221 °C
Boiling point	685 °C

Selenium Selenium is a chemical element with diverse allotropes and semiconductor behavior, used across electronics industry, glassmaking industry, photovoltaic industry, and biomedical research. It exhibits multiple oxidation states and unique photoconductive properties exploited by photocell manufacturers, solar energy companies, and rectifier developers. Selenium’s role in biology links it to studies at institutions such as National Institutes of Health, World Health Organization, and research groups in Harvard University and Oxford University.

Introduction

Selenium exists in several allotropes including gray, red, and amorphous forms and shows metalloid characteristics, which attracted attention from Siemens-era technologists and modern semiconductor firms. Its photoconductivity made it central to early television and xerography development, and its trace nutrient status placed it in debates at Food and Agriculture Organization and Centers for Disease Control and Prevention. Applications span chemical industry processes, glassworks operations, and renewable energy manufacturing.

History and Discovery

Selenium was identified in 1817 by Jöns Jakob Berzelius during investigations of impurities in sulfuric acid production linked to Fahlun (Falun) mining residues; contemporaries included Antoine Lavoisier-era chemists and later commentators such as John Dalton. Its name derives from parallels drawn with the element discovered earlier by Carl Wilhelm Scheele—oxygen and sulfur debates of the period influenced Berzelius’s nomenclature choices, and his work circulated among Royal Swedish Academy of Sciences correspondents. Industrial adoption accelerated in the late 19th and early 20th centuries as inventors like Chester Carlson and firms such as Eastman Kodak exploited photoconductive properties; wartime demand from World War II production and postwar electronics booms further expanded commercial use.

Chemical Properties and Occurrence

Selenium sits in period 4 of the periodic table and shares chemical affinities with sulfur and tellurium, displaying oxidation states commonly −2, +4, and +6. It forms compounds such as selenides, selenates, and organoselenium species studied by researchers at Max Planck Society and universities like Caltech. Naturally, selenium is found in sulfide ores associated with minerals mined in regions like Kopeisk and deposits near Southeastern United States, often co-occurring with metals processed by companies such as Freeport-McMoRan and Rio Tinto. Geological cycles involve selenium mobilization in oxidizing environments, relevant to environmental studies at United States Geological Survey and European Environment Agency.

Biological Role and Toxicity

Selenium is an essential micronutrient incorporated as selenocysteine into enzymes such as glutathione peroxidases and thioredoxin reductases, researched at institutions including Massachusetts Institute of Technology and Johns Hopkins University. Its dietary significance prompted public health actions by World Health Organization and Food and Agriculture Organization regarding fortification and deficiency disorders observed in regions like Keshan province and investigations by teams from Peking University. Excess exposure causes selenosis with characteristic symptoms documented in occupational studies at National Institute for Occupational Safety and Health and in environmental incidents affecting communities near Cerro de Pasco and former mining sites investigated by Environmental Protection Agency. Epidemiological links between selenium status and conditions studied by American Cancer Society and National Cancer Institute are complex and subject to ongoing clinical trials at major medical centers such as Mayo Clinic.

Production and Industrial Applications

Commercial selenium is recovered as a byproduct of copper refining by firms like Glencore and BHP and refined using processes developed in collaboration with metallurgical researchers at Imperial College London. Major uses include decolorizing glass at traditional Murano glassworks and modern glass manufacturers like Corning Incorporated, and enabling photoreceptors for photocopying and light meters used by corporations such as Xerox. Selenium compounds serve in agrochemical formulations and as additives in steel and battery components produced by companies such as ArcelorMittal and Panasonic. Photovoltaic and thin-film solar research at National Renewable Energy Laboratory explores selenium-containing absorber layers in tandem-cell architectures investigated by Tesla-funded and academic consortia.

Analytical Methods and Measurement

Analytical determination of trace selenium employs techniques developed in laboratories at Brookhaven National Laboratory and Argonne National Laboratory, including hydride generation atomic absorption spectroscopy and inductively coupled plasma mass spectrometry (ICP-MS) used by environmental agencies like Environment Canada and Australian Radiation Protection and Nuclear Safety Agency. Speciation analysis distinguishing selenite, selenate, and organoselenium forms relies on hyphenated methods combining high-performance liquid chromatography with ICP-MS, standardized in studies from ISO committees and validated by interlaboratory trials coordinated by International Atomic Energy Agency. Biomonitoring protocols for selenium in blood, urine, and hair samples follow guidelines from Centers for Disease Control and Prevention and are employed in clinical research at Karolinska Institutet and population studies by European Food Safety Authority.

Category:Chemical elements