Tellurium, from Copper Anode Slime to High Purity Product: A Review Paper
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ODUCTION
TELLURIUM, with the symbol of Te and the atomic number of 52, is a metalloid that belongs to the sixth group of the periodic table, known as the chalcogen group or oxygen family. Oxygen, sulfur, selenium, and polonium are the neighbor elements of tellurium located in the sixth group. Among elements of this group, tellurium, selenium, and sulfur share some similar chemical and electrochemical behaviors. The typical oxidation states of tellurium are 2, + 2, + 4, and + 6, with + 4 being the most frequent valances.[1,2] Some of the chemical and physical properties of elemental Te are listed in Table I. The main use of tellurium is in solar cells as the TeCd compound.[5] Besides the usage of tellurium in solar cells, there are some other applications for Te as refinery catalysts, accelerator agents in the synthesis of rubber, and an alloying element in the steelmaking process.[6,7] In steelmaking, Te is generally added as a free machining additive. Moreover, Te can act as a carbide stabilizer, with the addition of 0.04 wt pct. Te can improve the mechanical properties of the metal, such as the bending, turning, and cutting properties. There are other applications of Te in ALIREZA MAHMOUDI, SINA SHAKIBANIA, MOHAMMAD MOKMELI, and FERESHTEH RASHCHI are with the School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, 11155-4563, Tehran, Iran. Contact e-mail: [email protected] Manuscript submitted January 20, 2020; September 6, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
much lesser quantities, such as in biology, chalcogenide glass manufacturing, and complex formulations containing this metalloid.[3] Figure 1 shows the consumer market of tellurium.[7] Commercial-grade tellurium (99.95 pct) is traded for around $55 per kilogram (In 2019),[8] but in case of high-purity (6N) tellurium, its price can reach 100 times the price of commercial grade . Tellurium global refinery production (excluding the USA) is shown in Figure 2. Moreover, the price fluctuation is shown in Figure 2. It reached its peak in 2011 owing to the increasing demand for solar cell manufacturers. However, after that, due to the development of the new technologies and the decreased demand for tellurium in thermoelectric production, the price decreased gradually.[4,7] Tellurium is recognized as one of the critical elements[9–12] with an approximate production rate of 480 tons per year (2019), and about 90 pct of it comes from copper anode slime.[2,7] Major components of copper anode slime are copper, sulfur, silver, selenium, arsenic, lead, gold, nickel, antimony, and tellurium. Apart from copper anode slime, tellurium is also recovered in much lesser quantities from primary resources and other secondary resources, such as solar panel cell wastes. The tellurium concentration in the earth’s crust is reported to be around 1–5 ppb, which is considerably lower in comparison to its concentration in copper anode slime (generally 0.5 to 4 wt pct). In nature, tellurium is mainly found as tellurides of copper and gold. U
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