Thallium

Thallium is a chemical element on the periodic table whose symbol is Tl and its atomic number is 81. This gray, soft and malleable p-block metal is similar to to tin, but discolors on exposure to air. It is very toxic and has been used as a rodenticide and insecticide, but its use has been reduced or eliminated in many countries due to its possible carcinogenic effects. It is also used in infrared detectors. Pure thallium is a bluish-white metal found in small amounts in the earth's crust. In the past, thallium was obtained as a byproduct of smelting other metals. Currently, most thallium is obtained as a by-product of refining heavy metal-rich sulfide ores. In its pure form, thallium is odorless and tasteless. It can also be found combined with other substances such as bromine, chlorine, fluorine and iodine. When combined, it turns to a white or yellow color.

Main features

This metal is very soft and malleable; it can be cut with a knife. On exposure to air it changes from a metallic sheen to rapidly clouding to a lead-like bluish-gray hue. It can be dispersed by the following dissemination methods:

• Internal air: The drill can be released into the inner air in the form of fine particles (aerosol).
• Water: The drill cannot be used to contaminate the water because it is not dissolved in the water.
• Food: Heat can be used to contaminate food.
• Outdoor air: The drill can be released into the outside air in the form of fine particles (aerosol).
• Agricultural: If the drill is released into the air in the form of fine particles (aerosol), it has the potential to contaminate agricultural products.

History

Thallium (Greek θαλλός, thallos, meaning "green shoot or branch") was discovered by means of flame spectroscopy in 1861. The name comes from the green glow in the lines of the element's emission spectrum.

After the publication of the improved method of flame spectroscopy by Robert Bunsen and Gustav Kirchhoff and the discovery of cesium and rubidium between 1859 and 1860, spectroscopic analysis became an approved method for determining the composition of minerals and substances. chemicals. William Crookes and Claude-Auguste Lamy began using this new method. It was used by William Crookes to make spectroscopic determinations of tellurium in selenium compounds. By 1862, Crookes was able to isolate small amounts of the element and determine the properties of some compounds. Claude-Auguste Lamy using a similar technique to Crookes's to determine the composition of a selenium-containing substance (which was deposited during the production of sulfuric acid from pyrite), concluded that a new element was in the presence from the green lines in the spectrum.

Visible aspect of Taliowith its characteristic green line.

Getting

Although thallium is not as rare as other elements (0.000085% abundance), it is found in association with potassium in clays, soils, and granites. These sources are not profitable for the industrial preparation of thallium.

Found in the minerals crookesite TlCu₇Se₄, hutchinsonite TlPbAs₅S₉, and lorandite TlAsS₂. It is found as a trace element in pyrite.

Obtaining thallium has a main difficulty: the small concentration in which it is found in minerals.

It is obtained mainly from the particles of molten lead and zinc fumes, and from the sludge obtained from the manufacture of sulfuric acid. The metal is obtained by electrolysis of an aqueous solution of its salts. It is also obtained by reduction with metallic sodium and by precipitation.

Applications

Historical usage

Thallium sulfate, which is odorless and tasteless, was used to kill rats and ants. Since 1972 its use was banned in the United States because of its toxicity. Other countries followed suit in subsequent years. Thallium salts have been used to treat dermatophytosis, other skin infections, and to reduce night sweats in tuberculosis patients. However, this use was very limited due to its narrow therapeutic index, and the development of more efficient drugs.

Optics

Crystals of bromide and thallium iodide are used in infrared crystals because they are harder and transmit longer wavelengths than other materials. These materials are known under the trade name KRS-5. Thallium oxide is used to make lenses due to its high refractive index.

Electronics

Heel bar showing corrosion.

The electrical conductivity of thallium sulfide changes on exposure to infrared light thereby making its compounds useful in photoresistors. Thallium selenide has been used as a bolometer for the detection of infrared light.

Medical Imaging

Thallium is used in scintigraphy to identify bone tumors and to monitor the effectiveness of anticancer therapies.

It is also useful in the detection of ischemic areas of the heart, since the thallium isotope 201 only binds to non-ischemic and non-infarcted tissue, thereby excluding tissue with some degree of damage from lack of oxygen supply, which can be seen graphically on a scintigraphy.

Toxicity

Thallium and its compounds are toxic to humans. Skin contact is hazardous and adequate ventilation should be provided during casting to prevent inhalation. Many thallium compounds are highly soluble in water and are absorbed. easily through the skin. Exposure should not exceed 0.1 mg per m² of skin over the average period of 8 hours per day (40 hours per week). Thallium is a suspected human carcinogen.

Part of the reason thallium is highly toxic is because in aqueous solution as a monovalent thallium ion (Tl⁺), it shows some similarities to alkali metal cations, especially with potassium. Therefore, it can enter the body through the potassium absorption pathway. Conversely, other aspects of thallium's chemistry differ significantly from that of the alkali metals, such as its high affinity for sulfide bonds. Because this substitution disrupts many cellular processes, thallium, for example, can "attack" proteins that contain bonds or disulfide bridges (those that contain cysteine and ferredoxin).

Due to its great toxicity it was used in many countries as rodenticide and to control ants, but its use is currently restricted in some of these nations. It is considered a probable carcinogen.

Among its most notable effects of thallium poisoning are alopecia (which led to its initial use as a depilator, before its toxicity was known) and peripheral nerve damage. Thallium was a toxic agent used effectively to cause deaths by poisoning before its toxic potential was known and the discovery of Prussian blue as an antidote.

These are some effects related to the dose of ingestion.

Symptoms

Course of time

The adverse health effects of thallium are dose-dependent and occur in three stages. The gastrointestinal phase may occur immediately with large swallows or may be delayed 24-48 hours with smaller swallows. This is followed by a neurological phase 2 to 5 days or more after ingestion, although it can occur as early as 12 hours after massive ingestion. In case of acute toxicity, alopecia may occur 2-3 weeks after exposure. Death can occur in severe cases 5-7 days after exposure due to paralysis and respiratory failure.

Eye exposure

Acute ocular exposure is unlikely to produce local or systemic effects other than mild local irritation.

Exposure by ingestion

Transient nausea and vomiting (emesis) are noted first, followed by painful sensations in the arms/hands and legs/feet within 1 to 5 days (sometimes longer).

Other effects include: visual effects; rapid heart rate and high blood pressure; abnormal heart rhythms; respiratory insufficiency; unusual, painful, or burning sensations; muscle aches and weakness; headache; seizures, delirium, and coma; loss of appetite; excessive salivation; inflammation of the mouth, lips and gums; possible green discoloration of urine soon after exposure; Kidney damage; breakdown of red blood cells; severe acne; and dry, crusty desquamation of the skin.

As more serious effects we have possible damage to the nerves that control the muscles of the head and neck and the respiratory muscles.

Risks

Air and Water Reactions

Flammable in dust or dust form. Insoluble in water.

Fire hazard

Not combustible, the substance itself does not burn, but may decompose on heating to produce toxic and/or corrosive fumes. Containers may explode when heated. Runoff can contaminate waterways.

Danger to health

Highly toxic, can be fatal if inhaled, swallowed, or absorbed through the skin. Avoid any contact with the skin. Effects of contact or inhalation may be delayed. Fire may produce irritating, corrosive and/or toxic gases. Runoff from fire control or dilution water can be corrosive and/or toxic and cause contamination.

Radioactivity profile

Thallium is a reducing agent. It reacts so vigorously with fluorine that the metal becomes incandescent.

Answers

Isolation and evacuation

As an immediate precautionary measure, the area of the spill or leak should be isolated in all directions at least 50 meters (150 feet) for liquids and at least 25 meters (75 feet) for solids.

For a spill, we must increase, downwind, as necessary, the isolation distance shown above. And for a fire, if a tank, rail car or tank truck is involved, a radius of 800 meters (1/2 mile) must be isolated in all directions.

Firefighting

• Small Fire: Use a dry chemical, CO2 or sprayed water.

• Large fire: Polished water, nebulized or normal foam is used. The containers of the fire area should be moved in case there is no risk, to make a fire control water dam for subsequent disposal and not to spread the material. Try to use sprayed or nebulized water, and do not use straight jets.

• Fires involving tanks or vehicle/wheel loads: Combat fire from the maximum distance or use unmanned hose supports or control nozzles. Do not enter water in containers. Cool the containers with plenty of water until long after the fire is turned off. Remove immediately if the sound is lifted by the ventilation safety devices or the decoloration of the tank. Always stay away from the tanks wrapped in fire. For massive fires, use unmanned hose supports or monitoring nozzles; if this is impossible, remove from the area and let the fire burn.

Answer without fire

Do not touch damaged containers or spilled material unless wearing appropriate protective clothing. If possible to do so without risk, stop the leak and prevent entry into waterways, sewers, basements, or confined areas. Cover with plastic sheeting to prevent spreading and absorb or cover with dry earth, sand or other non-combustible material and transfer to containers. Water must not be introduced into the containers

Protective clothing

Use positive pressure self-contained breathing apparatus (SCBA) and chemical protective clothing specifically recommended by the manufacturer. May provide little or no thermal protection. Structural firefighters' protective clothing provides only limited protection in fire situations which is not effective in spill situations where direct contact with the substance is possible.

First Aid

Make sure medical personnel are aware of the materials involved and take precautions to protect themselves. Move victim to fresh air, call 911 and administer artificial respiration if victim is not breathing. Do not use the mouth-to-mouth method if the victim ingested or inhaled the substance. Artificial respiration should be administered with the aid of a pocket mask fitted with a one-way valve or other suitable respiratory medical device. Administer oxygen if you have difficulty breathing. Then isolate and remove contaminated clothing and shoes. In case of contact with the substance, immediately flush skin or eyes with running water for at least 20 minutes. In case of light skin contact, avoid spreading material on healthy skin. Keep victim calm and warm. The effects of exposure (inhalation, ingestion or skin contact) to the substance may be delayed.