Scattered elements

Catalog

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Thallium was independently discovered using flame spectroscopy in the 1860s by William Crookes and Claude-Auguste Lamy. Since thallium emits a special green light in a flame, Crookes suggested calling this new element "thallium", from the Greek "θαλλός" (thallus), meaning "green shoot". A few short years later, thallium was found in spring water, tobacco, sugar beets, and wine, indicating a wide distribution of this element in nature. In 1866, an independent mineral deposit of thallium, selenium, thallium, silver and copper was first discovered in the Skrikerum copper-silver polymetallic deposit in Sweden, which was named Cruxite in commemoration of the discovery and exploration of thallium by Sir William Crookes. .

Figure 1. Physical and chemical properties of thallium

Thallium (Tl) is located in the main group III of the sixth cycle of the periodic table of elements. In nature, there are 3 valence states (+3, +1, 0) (Fig. 1). Thallium is one of the most widely distributed trace elements on Earth, mainly found in silicate minerals and sulfides. Thallium has a soft texture, low melting point and tensile strength, high ductility, and its burning flame is pale green (Fig. 2).

Picture 2 A-thallium has a soft texture; B-thallium has a soft green burning flame

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Thallium itself is a highly toxic substance and one of the most toxic metal elements. The lethal dose for an adult is less than one gram. Thallium compounds are one of the major hazardous wastes listed on the WHO Key Restrictions List and are also on the list of priority pollutants in my country. Among these, the most toxic and hidden thallium salt is thallium sulfate.

Thallium sulfate is easily soluble in water, colorless and odorless, the onset of poisoning is slow, the initial symptoms of poisoning are hidden, like with influenza or bronchopneumonia, so it is not easy to detect, therefore thallium is more terrible than arsenic and mercury. The highly toxic substance is the "perfect poison" for some criminals or corrupt regimes who seek wealth, assassinate and eliminate dissidents. Mandela, the founding father of South Africa, was nearly poisoned by the former apartheid government with thallium sulfate during his imprisonment, and during the reign of Saddam Hussein in Iraq, many religious figures of various political views, civil rights activists and scientists were poisoned with thallium sulfate. Symptoms of deep thallium poisoning are mainly severe hair loss, damage to the nervous and digestive systems. The best treatment plan is to take Prussian blue, that is, iron ferrocyanide (Fe₄[Fe(CN)< sub >6</ sub>]₃), relevant departments should step up scientific publicity, let the masses better understand thallium poisoning and detoxification, and prevent similar incidents from happening again.

In the 1890s, the French dermatologist Sablan accidentally discovered that his patients lost a lot of hair after taking trace amounts of thallium salts, and then he began using this method to remove hair from patients with moss on the body. In the 1930s, hair removal creams containing 7 wt.% thallium acetate became popular in Europe and posed a great danger to ordinary families. Deaths from thallium acetate overdoses skyrocketed during this period, and the chemical was eventually phased out and banned in the 1950s.

Since the 1920s, people have been using thallium sulfate to make rat poison, which is effective in killing pests but inevitably leads to accidents, suicides, and murders. In the 1980s, large-scale mass poisoning occurred in French Guiana, and within three years, about 100 people died from chronic thallium poisoning. Rats infested the fields, and the sucrose produced was contaminated with thallium and leaked to the market, causing harm to the local population. In the 1970s, due to serious socialBecause of the environmental risks associated with the use of thallium, thallium-containing pesticides have been phased out, but thallium sulfate is still used as a pesticide and rodenticide in some underdeveloped areas.

After the 1980s, the use of thallium gradually moved into high-tech areas such as the electronics industry, optics and organic synthesis: thallium was used to make phosphors, batteries, lamps, semiconductors, electroplating and glass ceramics for electronics in the electronics industry AND in electronic devices such as varistors; thallium can be used in infrared optical fiber, optical glass, optical components and optical information materials in the optical field; thallium is mixed with various alloys, which can greatly improve the hardness, strength and corrosion resistance of the alloy.

Although thallium is highly toxic, its radioactive isotope Tl is used in medicine to detect and diagnose diseases of the heart, liver, coronary arteries and other diseases, and also plays an indispensable role in radionuclide imaging of the heart (Fig. 3A); thallium-barium-calcium-copper-oxide high-temperature superconductors have broad application prospects in many high-tech fields, such as nuclear magnetic resonance imaging, the synthesis of permanent magnets in particle accelerators, the production of nuclear fusion reactors, and the production of superconducting optical fiber (Fig. 3B-E) ; thallium amalgam point can be used to make low-temperature thermometers used in polar alpine regions; The international project LORandite Experiment (LOREX) is dedicated to the use of gem-quality red thallium ore (lorandite) as a material for detecting solar neutrinos. experiments (Figure 3D); special optical fibers made from thallium bromide iodide are very suitable for long-distance, uninterrupted, multi-channel communications; special prisms with the addition of thallium iodide have excellent optical properties and are widely used in the manufacture of satellite optical systems, etc. (Fig. 3F). The broad application prospect of thallium has attracted people's attention, governments and scientists around the world have raised the guarantee of thallium supply to a strategic height, the "Rare Metals Protection Strategy" handbook, etc. China has a long history of research on thallium, which has traditionally been considered a "dispersed element", and in recent years is intensively studied as one of the key strategic metals.

Fig. 3. A-Tl is widely used in radionuclide cardiac imaging technology.

B-thallium is an important additive material for nuclear magnetic resonance (MNR) detection;

C-thallium copper oxide high-temperature superconductor is expected to be a key material for the Large Hadron Collider (LHC);

Class D red thallium ore is used as a naturally occurring material for detection in solar neutrino experiments;

In the future, high-temperature superconductors containing E-thallium are expected to be used in the production of key materials for nuclear fusion reactors;

Thallium iodide-added F-Optical lens system can be used for high resolution satellite imagery

In addition to applications in the field of materials science, thallium has begun to show signs of application in the field of rock geochemistry. The study of Himalayan leucogranites has shown that the enrichment in thallium is closely related to the high-separation crystallization of granites. The relationship between rubidium and thallium seems to indicate separative crystallization of minerals such as zircon, monazite and apatite and precipitation of hydrothermal fluid phases (Gao Lie et al., 2021). Foreign scientists used pyrite and iron-manganese oxides to study stable thallium isotopes. The evolution of the thallium isotope composition makes it possible to trace the redox conditions of deep-water basins in geological history (Nielsen et al., 2011).

Studies of thallium isotopes in volcanic rocks and eclogites allow us to trace the contribution of the final recycling of altered oceanic crust, pelagic sediments, and marine iron and manganese oxides to the evolution of mantle magma during the crustal-mantle evolution of subduction. zones also has the potential to be used to reveal the thermal structure of subduction zones (Wei et al., 2022).

In connection with the growing interest of researchers in recent years, the elements and isotopes of thallium will undoubtedly open up new prospects for geological research.

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As a rare element, the content of thallium in the earth's crust and rocks is very low and tends to dissipate, however, some special geological processes can also cause thallium enrichment. The spatial distribution of thallium minerals and mineralization is uneven, and they are concentrated in Central Europe, the Alpine-Zagros-Himalayan orogenic belt, the Pacific volcanic belt, the Russian Urals, Siberia, and the Sichuan-Yunnan-Guizhou region. my country on a global scale It occurs in igneous rocks, metamorphic rocks, sedimentary rocks and orebirths (Fig. 4).

Thallium halide and sulfate minerals have been found near numerous recent volcanic fumaroles in Kamchatka, Russia, Sicily, Italy, and the Chilean Andes (Fig. 5A–C). Sublimes deposited near some volcanic fumaroles are also enriched in thallium (Fig. 5d). Some modern submarine black pipes and sulfide or alunite silts near shallow marine hydrothermal vents are quite rich in thallium and may even form thallium minerals (Fig. 5E-G). The presence of talcusite and avicennite has been reported in world-famous alkaline complexes such as the Poudrett Pluton in Canada, the Ilimaussak Pluton in Greenland, and the Murunsky Pluton in Russia, as well as in their weathering zones (Fig. 5H). In a volcanic quarry in southern Poland, it was found that the content of thallium oxide in manganese oxides in the weathering zone can reach 20.82 wt.% (Fig. 5I).

The main source of industrial thallium is sulfur-zinc-lead deposits of polymetallic sulfide type. Thallium is mainly enriched in pyrite and sphalerite as an isomorphic substitution in base metal sulfide deposits, which is difficult to identify with the naked eye. Known sulfide deposits containing thallium include the Red Dog deposit in the United States and the Meggen deposit in Germany. The Xiangquan pyrite deposit in my country is a small pyrite deposit, but the thallium content of the pyrite of this deposit is so high that it can be developed as a large independent thallium deposit. The degree of thallium enrichment in different types of sulfide deposits is different, generally speaking SEDEX type deposits > VMS type deposits > MVT type deposits (Duan Hongyu and Wang Changming, 2022). It is worth noting that anomalous thallium enrichment sometimes occurs in MVT deposits, and MVT deposits in the Central European Alps and in the Sanjiang region in the southwest of my country have abnormal thallium enrichment. such as Changdong (Duan Hongyu and Wang Changming, 2022). It is interesting that these thallium-rich MBT deposits are located at both ends of the Alpine-Himalayan collisional orogenic belt, which makes us think about the anomalous enrichment of MBT deposits in the middle of the orogenic belt with thallium?

In some low-temperature hydrothermal deposits of gold, arsenic, antimony, mercury and thallium, thallium is not only enriched in pyrite and other sulfides, but also can form various exquisite independent minerals. The Payu realgar deposit at Jepaiyu, Changde, Hunan is rich in sulfur salts and sulfide minerals of thallium, arsenic, antimony, and mercury, and is also a source of shimenite, a new mineral of thallium (Fig. 6A-C). In recent years, some scientists have discovered gem-quality red thallium ore in disseminated gold deposits at the far end of Jhul.intana, Huangshi, Hubei (Fig. 6D). In the hydrothermally altered veins of the Xiangquan thallium deposit, people discovered the presence of arsenic-sulfide and thallium-lead ore (Fig. 6E).

Even in the 1970s, under the leadership of Academician Tu Guanchi, Chinese geologists and geochemists conducted systematic studies of new minerals and geochemical properties of thallium and obtained a number of step-by-step results. Since 1988, when An Shuren and Chen Dayan discovered thallium ore and red thallium ore in the Lhamuchang gold-mercury thallium deposit, Chinese scientists have discovered 12 kinds of thallium minerals in China, including many new thallium minerals such as thallium alum, etc. (Fig. 6F). Independent thallium deposits have been discovered in my country, including the Lampuchang thallium deposit in Xingzhen, Guizhou, the Longtan thallium deposit in Nanhua, Yunnan (Zhang Zhong et al., 1999), and the Maanshan Xiangquan thallium deposit in Anhui (Fan Yu et al. . , 2007). As for the search for new deposits of thallium, Chinese scientists have also made a great contribution by proposing anomalous searches for the elements of thallium, mercury, arsenic, antimony, gold, lead and zinc, control of ore in the phase transition zone of sedimentary rocks, as well as migration and enrichment of organic complexes. et al. provide theoretical guidance for the next step in the search for thallium deposits (Tu Guangchi et al., 2004).

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The process of regional industrialization will inadvertently release thallium into the environment, posing a huge threat to human health. Some sulfuric acid plants use thallium-containing pyrite as the main industrial raw material. Dust generated from the roasting slag generated during the pyrite smelting process and tail gases generated during the sulfuric acid production process release large amounts of thallium into the environment. environment, causing thallium to the soil and crops near the plant. The content is seriously exceeded. In addition, the waste slag from the sulfuric acid plant is often reused as filler in the cement plant and enters the cement production process. The dust emitted from the plant enters the atmosphere, posing a great threat to the densely populated areas around the plant. The mining, processing and smelting of some thallium-containing sulfide ores, as well as the production process of thallium-containing coal-fired power plants, will also release large amounts of thallium into the environment, and the resulting problem of thallium pollution is becoming increasingly important. (Chen Yongheng et al., 2011). Chen Yongheng and other scientists, based on many years of experience in studying and researching thallium pollution in pyrite mines and non-ferrous metal mines, suggested that in the process of using thalliumContaining minerals, we should attach great importance to the impact and consequences of thallium pollution, take the necessary measures to prevent pollution, and actively conduct research on management technology (Chen Yongheng et al., 2002).

Given the current situation of potential thallium air pollution and thallium water pollution that our country is facing, Chinese scientists are working hard to find solutions, constantly improving the thallium extraction rate and thallium removal technology, and reducing the adverse effects. Consequences of thallium pollution. For example, Ma Qiang et al. (2020) developed an activated carbon-supported manganese oxide catalyst that uses catalytic oxidation to oxidize reduced thallium ions to an oxidized state, thereby effectively reducing the emission of thallium pollutants to the atmosphere (Fig. 7). Liu Huang et al. (2015) summarized recent advances in thallium-containing wastewater treatment technology and proposed to use the adsorption between microorganisms and heavy metal ions and the redox effect of microorganisms to treat highly concentrated thallium-containing wastewater. wastewater, thereby reducing the concentration of thallium in water below the regulatory limit (0.1 μg / l) to ensure the safety of drinking water for the inhabitants of our country. It is believed that in the near future, with the constant improvement of the technology to combat heavy metal pollution and the increase in the efficiency of processing and utilization of metallic thallium, thallium will certainly turn from a "poison" that threatens human health and development into a "child". which contributes to social, economic and technological development.