Tellurium

Discovery and History

Tellurium, was first discovered in the late 18th century. Its discovery is attributed to Franz-Joseph Müller von Reichenstein, a Hungarian mining engineer and mineralogist. In 1782, Müller von Reichenstein was exploring a gold mine in Zalatna, Transylvania (now in Romania), when he stumbled upon a new mineral. This mineral exhibited unusual properties, including a shiny metallic luster and a distinctive smell resembling that of decayed garlic. Müller von Reichenstein named the substance “tellurium,” derived from the Latin word “tellus,” meaning “earth.”

Following Müller von Reichenstein’s discovery, scientists and alchemists across Europe began studying tellurium. They were intrigued by its unique properties and sought to understand its nature and potential uses. Tellurium’s association with gold and other precious metals sparked speculation among alchemists, who hoped to find a way to transmute base metals into gold using tellurium-based compounds. However, these alchemical ambitions were never realized, and tellurium remained primarily a subject of scientific curiosity.

In the early 19th century, tellurium was classified as a new chemical element, distinct from sulfur and other related elements. Its atomic properties were elucidated through extensive chemical analyses and experiments. Tellurium’s classification as a metalloid, exhibiting properties of both metals and nonmetals, further enhanced its scientific interest.

During the industrial revolution, tellurium found several practical applications. Its semiconducting properties made it valuable in the production of electronic devices, such as thermoelectric generators and photovoltaic solar cells. Additionally, tellurium compounds were utilized in the manufacturing of certain types of glass, ceramics, and catalysts.

In the 20th and 21st centuries, research into tellurium expanded as scientists explored its potential applications in emerging technologies. Tellurium-based materials have become essential components in advanced electronics, including infrared detectors, optoelectronic devices, and semiconductor technologies.

Furthermore, tellurium’s role in renewable energy technologies has gained prominence, particularly in the development of high-efficiency solar cells. Tellurium-based thin-film solar panels offer a promising alternative to traditional silicon-based photovoltaic systems, contributing to the global efforts to mitigate climate change and transition towards sustainable energy sources.

Atomic Structure and Isotopes

Tellurium, symbolized by the atomic symbol Te and positioned as the 52nd element in the periodic table, is a fascinating metalloid with distinctive atomic structure and isotopic composition.

Atomic Structure of Tellurium

Tellurium’s atomic structure reflects its classification as a metalloid, characterized by its nucleus containing fifty-two protons, defining its atomic number, and a variable number of neutrons, contingent on the specific isotope. Surrounding the nucleus are fifty-two electrons, distributed across different energy levels or electron shells according to quantum mechanical principles.

The electron configuration of tellurium is [Kr] 4d^10 5s^2 5p^4, signifying the arrangement of electrons within its shells. Notably, tellurium possesses six valence electrons in its outermost shell, contributing to its chemical reactivity and bonding behavior. This configuration places tellurium in Group 16 of the periodic table, alongside other metalloids and nonmetals with similar electronic configurations.

Isotopes of Tellurium

Tellurium exhibits numerous isotopes, with varying numbers of neutrons in the nucleus. The most abundant naturally occurring isotope of tellurium is tellurium-130 (ⁱ¹³⁰Te), followed by tellurium-128 (ⁱ¹²⁸Te) and tellurium-126 (ⁱ¹²⁶Te). However, other isotopes of tellurium, including radioactive isotopes, have been synthesized in laboratories for scientific research and industrial applications.

• Tellurium-130 (ⁱ¹³⁰Te): Tellurium-130 is the most abundant stable isotope of tellurium, constituting approximately 34.08% of naturally occurring tellurium. It possesses fifty-two protons and seventy-eight neutrons in its nucleus.
• Tellurium-128 (ⁱ¹²⁸Te): Tellurium-128 is another stable isotope of tellurium, comprising fifty-two protons and seventy-six neutrons in its nucleus. It constitutes approximately 31.74% of naturally occurring tellurium.
• Tellurium-126 (ⁱ¹²⁶Te): Tellurium-126 is a stable isotope of tellurium, characterized by its nucleus containing fifty-two protons and seventy-four neutrons. It also constitutes a significant fraction of naturally occurring tellurium.

Physical and Chemical Properties

Tellurium, is a fascinating metalloid with distinctive physical and chemical properties. From its brittle crystalline structure to its semiconductor behavior and chemical reactivity, tellurium exhibits characteristics that make it essential in various industrial, scientific, and technological applications.

Physical Properties

• Appearance: Tellurium typically appears as a silvery-white, brittle solid with a metallic luster. In its pure form, it may exhibit a bluish tint.
• State: At room temperature, tellurium exists in the solid state. It has a crystalline structure and is relatively brittle, meaning it can be easily fractured or powdered.
• Melting Point: Tellurium has a relatively high melting point of 449.51 degrees Celsius (841.12 degrees Fahrenheit), indicating its stability at elevated temperatures.
• Boiling Point: The boiling point of tellurium is 988 degrees Celsius (1810.4 degrees Fahrenheit), indicating its high resistance to vaporization.
• Density: Tellurium has a density of approximately 6.24 grams per cubic centimeter (g/cm³), making it relatively dense compared to other metalloids and nonmetals.
• Electrical Conductivity: Tellurium exhibits semiconductor behavior, meaning its electrical conductivity increases with temperature. It has a relatively low electrical conductivity compared to metals but higher than typical insulators.
• Thermal Conductivity: Tellurium possesses relatively low thermal conductivity, making it a poor conductor of heat compared to metals.

Chemical Properties

• Reactivity: Tellurium exhibits variable reactivity depending on its chemical environment. It reacts slowly with oxygen in the air to form tellurium dioxide (TeO2) or tellurium trioxide (TeO3), depending on conditions.
• Halogen Reactivity: Tellurium reacts with halogens, such as chlorine (Cl) and bromine (Br), to form tellurium halides, such as tellurium tetrachloride (TeCl4) and tellurium tetrabromide (TeBr4).
• Acid Reactivity: Tellurium reacts with concentrated acids, such as hydrochloric acid (HCl) and nitric acid (HNO3), to form tellurium dioxide (TeO2) and tellurium dioxide (TeO3), respectively.
• Alloy Formation: Tellurium readily forms alloys with metals such as copper, lead, and silver, to enhance mechanical properties and create materials with specific characteristics. Tellurium-containing alloys are utilized in various applications, including bearings, electrical contacts, and photovoltaic cells.
• Solubility: Tellurium compounds exhibit variable solubility in different solvents. For example, tellurium dioxide (TeO2) is insoluble in water but soluble in concentrated acids, while tellurium tetrachloride (TeCl4) is soluble in organic solvents.
• Toxicity: Tellurium and its compounds are considered toxic and can pose health risks if ingested, inhaled, or absorbed through the skin. Exposure to high concentrations of tellurium can lead to symptoms such as nausea, vomiting, and neurological effects.

Occurrence and Production

Tellurium, is a rare metalloid with unique properties and diverse applications.

Occurrence of Tellurium

Tellurium is relatively rare in the Earth’s crust, occurring at low concentrations dispersed among various minerals and ores. It is primarily found in association with other elements, particularly in sulfide minerals and telluride minerals. Some of the most significant sources of tellurium include:

• Sulfide Minerals: Tellurium often occurs as a trace element in sulfide minerals, such as galena (lead sulfide), sphalerite (zinc sulfide), and chalcopyrite (copper iron sulfide). The presence of tellurium in sulfide ores contributes to its recovery during the processing of these minerals.
• Telluride Minerals: Tellurium also occurs in telluride minerals, where it forms chemical compounds with metals such as gold, silver, and copper. Examples of telluride minerals include calaverite (gold telluride), sylvanite (silver gold telluride), and hessite (silver telluride).
• Copper Refining: Tellurium is often recovered as a by-product of copper refining processes, particularly from copper anode slimes and electrolyte solutions. Copper refining facilities may extract tellurium through various methods, including precipitation, solvent extraction, and electrolysis.
• Coal and Oil: Small amounts of tellurium may also be present in coal deposits and petroleum reservoirs, where it accumulates as a trace element during organic matter decomposition. Tellurium is released into the environment through coal combustion and oil refining processes.

Production of Tellurium

The production of tellurium involves several steps, including extraction, purification, and refining processes. The primary methods employed for tellurium production include:

• Hydrometallurgical Extraction: Tellurium is often extracted from copper refining by-products, such as anode slimes and electrolyte solutions, using hydrometallurgical techniques. These methods involve leaching the raw materials with acid or alkaline solutions to dissolve the tellurium and other valuable metals.
• Precipitation and Crystallization: Once dissolved, tellurium is precipitated or crystallized from the leach solution through controlled chemical reactions or cooling processes. This step helps separate tellurium from other elements present in the solution and produces crude tellurium compounds.
• Electrolytic Refining: Crude tellurium obtained from precipitation or crystallization is further refined using electrolytic methods. Electrolysis allows for the purification of tellurium by selectively depositing it onto cathodes while separating impurities.
• Secondary Sources: In addition to primary production methods, tellurium may also be obtained from secondary sources, such as recycling processes and recovery from industrial waste streams. Recycling of end-of-life electronic devices, solar panels, and other tellurium-containing products can contribute to tellurium recovery and conservation efforts

Applications

Tellurium, is a remarkable metalloid with a wide range of applications across various industries. From semiconductor manufacturing to solar energy production and healthcare, tellurium’s unique properties make it indispensable in modern technologies.

• Semiconductor Industry: One of the primary applications of tellurium lies in the semiconductor industry, where it is utilized in the production of compound semiconductors. Tellurium compounds, such as cadmium telluride (CdTe) and bismuth telluride (Bi₂Te₃), exhibit favorable electrical and optical properties, making them ideal materials for photovoltaic cells, thermoelectric devices, and infrared detectors. Cadmium telluride thin-film solar cells, in particular, have gained widespread attention for their high efficiency and low manufacturing costs, contributing to the growth of renewable energy technologies.
• Thermoelectric Devices: Tellurium-based materials, notably bismuth telluride (Bi₂Te₃) and its alloys, are extensively used in thermoelectric applications. Thermoelectric materials have the unique ability to convert heat energy into electrical energy and vice versa through the Seebeck and Peltier effects. Bismuth telluride-based thermoelectric modules are employed in power generation, waste heat recovery, and temperature regulation systems, offering efficient and environmentally friendly solutions for energy conversion and management.
• Nuclear Medicine: Tellurium isotopes, such as tellurium-123 (¹²³Te) and tellurium-125 (¹²⁵Te), find applications in nuclear medicine for diagnostic imaging and cancer therapy. Tellurium-based radiopharmaceuticals are utilized in positron emission tomography (PET) scans and targeted radionuclide therapy (TRT) to detect and treat various medical conditions, including cancerous tumors and cardiovascular diseases. Tellurium isotopes emit gamma rays and positrons, allowing for precise imaging and localized treatment of pathological tissues.
• Metallurgy and Alloys: Tellurium is alloyed with metals such as copper, lead, and steel to improve mechanical properties and create materials with specific characteristics. Tellurium-containing alloys exhibit enhanced machinability, corrosion resistance, and electrical conductivity, making them suitable for various industrial applications. Tellurium-copper alloys are utilized in electrical contacts, switchgear components, and machining tools, while tellurium-lead alloys find applications in bearings, plumbing fixtures, and automotive components.
• Optoelectronics and Photonics: Tellurium-based materials play a crucial role in optoelectronic and photonic applications, where they are utilized for light detection, modulation, and emission. Tellurium compounds, such as tellurium dioxide (TeO2) and tellurium sulfide (TeS2), exhibit favorable optical properties, including high refractive index, transparency, and nonlinear optical effects. These materials are employed in optical fibers, lenses, switches, and laser systems for telecommunications, sensing, and information processing.
• Environmental and Catalytic Applications: Tellurium compounds, particularly tellurium dioxide (TeO2) and tellurium tetrachloride (TeCl4), find applications in environmental remediation, catalysis, and chemical synthesis. Tellurium-based catalysts are utilized in hydrogenation, oxidation, and hydrocarbon processing reactions, where they facilitate chemical transformations with high efficiency and selectivity. Additionally, tellurium compounds are employed in pollution control technologies, such as catalytic converters and sulfur removal systems, to mitigate environmental pollutants and enhance air quality.