is a chemical element
with the symbol Tl
and atomic number
81. This soft gray malleable poor metal
but discolors when exposed to air. Approximately 60-70% of thallium production is used in the electronics industry
, and the rest is used in the pharmaceutical industry
and in glass manufacturing
. It is also used in infrared detectors
Thallium is highly toxic
and is used in rat poisons
, and its use has been cut back or eliminated in many countries. It is used in murders
and has the nicknames "The Poisoner's Poison" and "Inheritance powder" (alongside arsenic
Thallium is very soft and malleable and can be cut with a knife. It has a metallic luster, but when exposed to air, it quickly tarnishes with a bluish-grey tinge that resembles lead. (It is preserved by keeping it under oil). A heavy layer of oxide builds up on thallium if left in air. In the presence of water, thallium hydroxide is formed.
Occurrence and production
Thallium occurs naturally in the minerals crookesite
, and pyrite
Thallium metal is obtained as a by-product in the production of sulfuric acid by roasting of pyrite, and also in the smelting of lead and zinc ores.
and tasteless thallium sulfate
was once widely used as rat poison
killer. Since 1975, this use in the United States
and many other countries is prohibited due to safety concerns. Other uses:
- thallium sulfide's electrical conductivity changes with exposure to infrared light therefore making this compound useful in photocells.
- Thallium(III) salts, as thallium trinitrate or triacetate, are useful reagents in organic synthesis performing different transformations in aromatics, ketones, olefins, among others.
- thallium bromide-iodide crystals have been used as infrared optical materials, because they are harder than other common infrared optics, and because they have transmission at significantly longer wavelengths. The trade name KRS-5 refers to this material.
- thallium oxide has been used to manufacture glasses that have a high index of refraction.
- used in semiconductor materials for selenium rectifiers,
- used as a dopant for sodium iodide crystals in gamma radiation detection equipment, such as scintillation counters,
- high-density liquid used for sink-float separation of minerals,
- used in the treatment of ringworm and other skin infections. However this use has been limited due to the narrow therapeutic index.
- radioactive thallium-201 (half-life of 73 hours) is used for diagnostic purposes in nuclear medicine, particularly in stress tests used for risk stratification in patients with coronary artery disease A(CAD). This isotope of thallium can be generated using a transportable generator which is similar to the technetium cow. The generator contains lead-201 (half life 9.33 hours) which decays by electron capture to the thallium-201. The lead-201 can be produced in a cyclotron by the bombardment of thallium with protons or deuterons by the (p,3n) and (d,4n) reactions.
- combined with sulfur or selenium and arsenic, thallium has been used in the production of high-density glasses that have low melting points in the range of 125 and 150 °C. These glasses have room temperature properties that are similar to ordinary glasses and are durable, insoluble in water and have unique refractive indices.
- an 8.5% thallium amalgam is used in thermometers and switches for use in low temperatures, because it freezes at -58 °C (pure mercury freezes at -38 °C).
- thallium is used in the electrodes in dissolved oxygen analyzers.
- thallium is a constituent of the alloy in the anode plates in magnesium seawater batteries.
In addition, research activity with thallium is ongoing to develop high-temperature superconducting materials for such applications as magnetic resonance imaging, storage of magnetic energy, magnetic propulsion, and electric power generation and transmission.
Thallium (Greek θαλλός
, meaning "a green shoot or twig") was discovered by Sir William Crookes
while he was making spectroscopic determinations for tellurium
on residues from a sulfuric acid
plant. The name comes from Thallium's bright green
spectral emission lines
. In 1862 Crookes and Claude-Auguste Lamy
isolated the metal independently of each other.
Although the metal is reasonably abundant in the Earth
's crust at a concentration estimated to be about 0.7 mg/kg, mostly in association with potassium
minerals in clays
, and granites
, it is not generally considered to be commercially recoverable from those forms. The major source of commercial thallium is the trace amounts found in copper
, and other sulfide ores
Thallium is found in the minerals crookesite TlCu7Se4, hutchinsonite TlPbAs5S9, and lorandite TlAsS2. It also occurs as trace in pyrite and extracted as a by-product of roasting this ore for sulfuric acid production. The metal can be obtained from the smelting of lead and zinc rich ores. Manganese nodules found on the ocean floor also contain thallium, but nodule extraction is prohibitively expensive and potentially environmentally destructive. In addition, several other thallium minerals, containing 16% to 60% thallium, occur in nature as sulfide or selenide complexes with antimony, arsenic, copper, lead, and silver, but are rare, and have no commercial importance as sources of this element. See also: Thallium minerals.
Thallium has 25 isotopes
which have atomic masses
that range from 184 to 210. 203
Tl and 205
Tl are the only stable isotopes, and 204
Tl is the most stable radioisotope
, with a half-life
of 3.78 years.
202Tl (half life 12.23 days) can be made in a cyclotron, while 204Tl (half life 3.78 years) is made by the neutron activation of stable thallium in a nuclear reactor.
Fluorides: TlF, TlF3
Chlorides: TlCl, TlCl2, TlCl3
Bromides: TlBr, Tl2Br4
Iodides: TlI, TlI3
Hydrides: none listed
Oxides: Tl2O, Tl2O3
Thallium and its compounds are very toxic, and should be handled with great care Contact with skin is dangerous, and adequate ventilation should be provided when melting this metal Thallium(I) compounds have a high aqueous solubility and are readily absorbed through the skin. Exposure to them should not exceed 0.1 mg per m² of skin in an 8-hour time-weighted average (40-hour work week). Thallium is a suspected human carcinogen.
Part of the reason for thallium's high toxicity is that, when present in aqueous solution as the univalent thallium(I) ion (Tl+), it exhibits some similarities with essential alkali metal cations, particularly potassium (as the atomic radius is almost identical). It can thus enter the body via potassium uptake pathways. However, other aspects of thallium's chemistry are very different from that of the alkali metals (e.g., its high affinity for sulfur ligands due to the presence of empty d-orbitals), and so this substitution disrupts many cellular processes (for instance, thallium may attack sulfur-containing proteins such as cysteine residues and ferredoxins).
Thallium's toxicity has led to its use (now discontinued in many countries) as a rat and ant poison.
Among the distinctive effects of thallium poisoning are loss of hair (which led it to its initial use as a depilatory before its toxicity was properly appreciated) and damage to peripheral nerves (victims may experience a sensation of walking on hot coals). Thallium was once an effective murder weapon before its effects became understood, and an antidote (prussian blue) discovered.
Treatment and internal decontamination
One of the main methods of removing thallium (both radioactive and normal) from humans is to use Prussian blue, which is a solid ion exchange material which absorbs thallium and releases potassium. The prussian blue is fed by mouth to the person, and it passes through their digestive system and comes out in the stool.
Famous uses as a poison
- In 1953, Australian Caroline Grills was sentenced to life in prison after three family members and a close family friend died. Authorities found thallium in tea that she had given to two additional family members.
- In 1957, Nikolai Khokhlov, a former KGB assassin, was poisoned with thallium. Khokhlov fell ill with stomach cramps and nausea and within days his hair had fallen out and he was covered with marks on his skin. He fled the Soviet Union to Germany where doctors suspected thallium poisoning and tried every known antidote without success. Khokhlov was then taken to the US hospital and treated with hydrocortisone, steroids, and blood and plasma transfusions and he eventually recovered.
- In 1971, thallium was the main poison that Graham Frederick Young used to poison around 70 people in the English village of Bovingdon, Hertfordshire, of which 2 died.
- Zhu Ling (1973) the victim of an unsolved 1995 thallium poisoning case in Beijing, China. In 1994, Zhu Ling was a sophomore in Class Wuhua2 (Physical Chemistry) at Tsinghua University in Beijing. She began to show strange and debilitating symptoms at the end of 1994, when she reported experiencing acute stomach pain, along with extensive hair loss. Ultimately she was diagnosed on Usenet with poisoning by thallium. To this date speculation of the true poisoner is still discussed by many Chinese expatriates overseas
- In 1988, members of the Carr family from Alturas, Polk County, Florida fell ill from what appeared to be thallium poisoning. Peggy Carr, the mother, died slowly and painfully from the poison. Her son and stepson were critically ill but eventually recovered. The Carr's neighbor, George J. Trepal, a chemist and member of Mensa, was convicted of murdering Mrs. Carr and attempting to murder her family and sentenced to death. The thallium was slipped into bottles of Coca-Cola at the Carr's home and Trepal's.
- In June 2004, 25 Russian soldiers earned Honorable Mention Darwin Awards after becoming ill from thallium exposure when they found a can of mysterious white powder in a rubbish dump on their base at Khabarovsk in the Russian Far East. Oblivious to the danger of misusing an unidentified white powder from a military dump site, the conscripts added it to tobacco, and used it as a substitute for talcum powder on their feet.
- In 2005, a 17 year old girl in Numazu, Shizuoka, Japan, admitted to attempting to murder her mother by lacing her tea with thallium, causing a national scandal.
- In February 2007, two Americans, Marina and Yana Kovalevsky, a mother and daughter, visiting Russia were hospitalized due to thallium poisoning. Both had emigrated from the Soviet Union to the United States in 1989 and had made several trips to Russia since then.
- In February 2008, members of Iraqi air force club and some of their children were poisoned by cake laced with thallium. Two of the children died.
- Agatha Christie, who worked as a pharmacist, used thallium as the agent of murder in her detective fiction novel The Pale Horse — the first clue to the murder method coming from the hair loss of the victims. This novel is notable as being credited with having saved at least two lives after readers recognised the symptoms of thallium poisoning that Christie described.
- In Nigel Williams' 1990 novel The Wimbledon Poisoner, Henry Far uses thallium to baste a roast chicken in a failed attempt to murder his wife.
- Thallium figures prominently in the 1995 film The Young Poisoner's Handbook, a dark comedy loosely based on the life of Graham Frederick Young.
- "Concentrated thallium" is used as the poison of choice of the Wyoming Widow in the 2006 dark comedy Big Nothing
- In an episode of the TV show House, a doctor poisons a patient with Thallium to make it appear that she had polio.
- In Larry Niven's Known Space cycle of science fiction stories, Thallium is a soil component essential for the proper growth of Tree of life which, when ingested by hominid species, triggers the change from the Breeder lifestage to the Protector lifestage.
- In the "Page Turner" episode of CSI: NY, Thallium 201 is used to poison several individuals.