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Protactinium or protoactinium (former name) is a chemical element with symbol Pa and atomic number 91. It is a dense, silvery-gray metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds where protactinium is usually present in the oxidation state +5, but can also assume +4 and even +2 or +3 states. The average concentrations of protactinium in the Earth’s crust is typically on the order of a few parts per trillion, but may reach up to a few parts per million in some uraninite ore deposits. Protactinium results from the radioactive decay of thorium 233. It was first identified in 1913 by Kasimir Fajans and Oswald Helmuth Göhring and named brevium because of the short half-life of the specific isotope studied, namely protactinium-234. A more stable isotope (231Pa) of protactinium was discovered in 1917/18 by Otto Hahn and Lise Meitner, and they chose the name proto-actinium, but then the IUPAC named it finally protactinium in 1949 and confirmed Hahn and Meitner as discoverers. Because of its scarcity, high radioactivity and high toxicity, there are currently no uses for protactinium outside of scientific research, and for this purpose, protactinium is mostly extracted from spent nuclear fuel.

Tantalum is a chemical element with symbol Ta and atomic number 73. Previously known as tantalium, its name comes from Tantalus, a villain from Greek mythology. Tantalum is a rare, hard, blue-gray, lustrous transition metal that is highly corrosion-resistant. It is part of the refractory metals group, which are widely used as minor components in alloys. The chemical inertness of tantalum makes it a valuable substance for laboratory equipment and a substitute for platinum. Tantalum, always together with the chemically similar niobium, occurs in the minerals tantalite, columbite and coltan (a mix of columbite and tantalite). Tantalum is dark (blue-gray), dense, ductile, very hard, easily fabricated, and highly conductive of heat and electricity. The metal is renowned for its resistance to corrosion by acids; in fact, at temperatures below 150 °C tantalum is almost completely immune to attack by the normally aggressive aqua regia. Its main use today is in tantalum capacitors in electronic equipment such as mobile phones, DVD players, video game systems and computers. It is also used as an additive in high strength alloys. Tantalum is generally insoluble in water, even in aqua regia. Tantalates, although a component of ores that contain tantalum, are not used for any commercial purpose.

Tellurium is a chemical element with symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur. It is occasionally found in native form as elemental crystals. Tellurium is far more common in the universe as a whole than on Earth. Its extreme rarity in the Earth’s crust, comparable to that of platinum, is due partly to its high atomic number, but also to its formation of a volatile hydride which caused it to be lost to space as a gas during the hot nebular formation of the planet. Tellurium was discovered in the Habsburg Empire, in 1782 by Franz-Joseph Müller von Reichenstein in a mineral containing tellurium and gold. Martin Heinrich Klaproth named the new element in 1798 after the Latin word for “earth”, tellus. Gold telluride minerals are the most notable natural gold compounds. However, they are not a commercially significant source of tellurium itself, which is normally extracted as a by-product of copper and lead production. Commercially, the primary use of tellurium is copper and steel alloys, where it improves machinability. Applications in CdTe solar panels and semiconductors also consume a considerable portion of tellurium production. Telluride and Tellurite can be removed from water by a variety of strong base anion resins.

Tin is a chemical element with the symbol Sn (for Latin: stannum) and atomic number 50, is a post-transition metal in group 14 of the periodic table. It is obtained chiefly from the mineral cassiterite, which contains tin dioxide, SnO2. Tin shows a chemical similarity to both of its neighbors in group 14, germanium and lead, and has two main oxidation states, +2 and the slightly more stable +4. Tin is the 49th most abundant element and has, with 10 stable isotopes, the largest number of stable isotopes in the periodic table, thanks to its magic number of protons. It has two main allotropes: at room temperature, the stable allotrope is β-tin, a silvery-white, malleable metal, but at low temperatures it transforms into the less dense grey α-tin, which has the diamond cubic structure. Metallic tin is not easily oxidized in air. The first alloy used on a large scale was bronze, made of tin and copper, from as early as 3000 BC. After 600 BC, pure metallic tin was produced. Pewter, which is an alloy of 85–90% tin with the remainder commonly consisting of copper, antimony, and lead, was used for flatware from the Bronze Age until the 20th century. Although once used in foil the high cost of Tin prohibited widespread use. Today, tin is used in lead/tin solders, as an additive to certain specialized alloys (such as bronze) and in a variety of niche applications such as catalysts. Anionic Tin can be removed by a variety of strong base anion resins. Tin compounds are rarely used in industry due to Tins scarcity. Tetravalent Tin can be removed by a variety of strong acid cation resins. Tin compounds are rarely used in industry due to Tins scarcity. Divalent tin can be removed by a variety of strong acid cation resins. Tim compounds are relatively rare because of Tins scarcity.

Titanium is a chemical element with symbol Ti and atomic number 22. It is a lustrous transition metal with a silver color, low density and high strength. It is highly resistant to corrosion in sea water, aqua regia, and chlorine. Titanium was discovered in Cornwall, Great Britain, by William Gregor in 1791 and named by Martin Heinrich Klaproth for the Titans of Greek mythology. The element occurs within a number of mineral deposits, principally rutile and ilmenite, which are widely distributed in the Earth’s crust and lithosphere, and it is found in almost all living things, rocks, water bodies, and soils. The metal is extracted from its principal mineral ores by the Kroll and Hunter processes. The most common compound, titanium dioxide, is a popular photocatalyst and is used in the manufacture of white pigments (“Titanium White”). Other compounds include titanium tetrachloride (TiCl4), a component of smoke screens and catalysts; and titanium trichloride (TiCl3), which is used as a catalyst in the production of polypropylene. Titanium dioxide is an insoluble compound used in paint pigments and in water treatment in granular form as an adsorbent for arsenic. Titanium chloride is a highly reactive liquid used as an intermediate in the production of titanium metal.

Tungsten, also known as wolfram, is a chemical element with symbol W and atomic number 74. The word tungsten comes from the Swedish language tung sten, which directly translates to heavy stone. Its name in Swedish is volfram, however, in order to distinguish it from scheelite, which is alternatively named tungsten in Swedish. A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth almost exclusively in chemical compounds. It was identified as a new element in 1781, and first isolated as a metal in 1783. Its important ores include wolframite and scheelite. The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all the elements. Its high density is 19.3 times that of water, comparable to that of uranium and gold, and much higher (about 1.7 times) than that of lead. Polycrystalline tungsten is an intrinsically brittle and hard material, making it difficult to work. However, pure single-crystalline tungsten is more ductile, and can be cut with a hard-steel hacksaw. Tungsten has many niche uses including filaments for incandescent light bulbs, X-ray tubes, and various electrodes. In water tungsten generally forms the divalent tungstate oxo anion. Tungstate is a minor contaminant of molybdate and is removed in the same ways. Tungsten carbide is one of the hardest substances known and is used to harden saw blades and as an abrasive for various sanding and grinding applications.

Vanadium is a chemical element with symbol V and atomic number 23. It is a hard, silvery grey, ductile, and malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an oxide layer (passivation) stabilizes the free metal somewhat against further oxidation. Andrés Manuel del Río discovered compounds of vanadium in 1801 in Mexico by analyzing a new lead-bearing mineral he called “brown lead”, and presumed its qualities were due to the presence of a new element, which he named erythronium (derived from Greek for “red”) since, upon heating, most of the salts turned red. Four years later, however, he was (erroneously) convinced by other scientists that erythronium was identical to chromium. Chlorides of vanadium were generated in 1830 by Nils Gabriel Sefström who thereby proved that a new element was involved, which he named “vanadium” after the Scandinavian goddess of beauty and fertility, Vanadís (Freyja). Both names were attributed to the wide range of colors found in vanadium compounds. Del Rio’s lead mineral was later renamed vanadinite for its vanadium content. In 1867 Henry Enfield Roscoe obtained the pure element. Vanadium is in important additive to high strength steel. It is also used as a catalyst in the production of sulfuric acid. Vanadium in water is almost always present as an oxo anion. Vanadium (vanadate) is present at low concentrations in many groundwaters that also contain arsenic. Vanadate loads almost quantitatively onto arsenic selective medias and also onto the chromate selective weakly basic anion resin SIR-700.

Xenon is a chemical element with symbol Xe and atomic number 54. It is a colorless, dense, odorless noble gas found in the Earth’s atmosphere in trace amounts. Although generally unreactive, xenon can undergo a few chemical reactions such as the formation of xenon hexafluoroplatinate, the first noble gas compound to be synthesized. Naturally occurring xenon consists of eight stable isotopes. More than 40 unstable xenon isotopes undergo radioactive decay, and the isotope ratios of xenon are an important tool for studying the early history of the Solar System. Xenon is used in flash lamps and arc lamps, and as a general anesthetic. The first excimer laser design used a xenon dimer molecule (Xe2) as the lasing medium, and the earliest laser designs used xenon flash lamps as pumps. Xenon is used to search for hypothetical weakly interacting massive particles and as the propellant for ion thrusters in spacecraft. Its relative scarcity has limited wide spread use Xenon is an inert gas and does not (easily) form compounds, nor does it ionize in water.