Thorium

Thorium is a chemical element with the symbol Th and atomic number 90. It is a weakly radioactive, light silver metal that turns olive grey when exposed to air. Thorium is soft, can be shaped easily, and has a high melting point.

All known forms of thorium are unstable. The most common form, ²³²Th, has a half-life of 14.0 billion years, which is about the age of the universe. It slowly changes through a series of steps called the thorium series, ending as a stable form of lead. On Earth, thorium and uranium are the only elements without stable forms that still exist naturally in large amounts. Thorium is found to be more common in the Earth's crust than uranium, mainly coming from sands called monazite while extracting rare-earth elements.

Thorium was discovered in 1828 by the Swedish chemist Jöns Jacob Berzelius. He found it in a new mineral from Norway and named it after Thor, the Norse god of thunder and war. Though it had many uses in the past, such as in welding, optics, and lighting, these uses have mostly disappeared because of concerns about its radioactivity. Today, thorium is still used in some special applications, like strengthening magnesium and in certain types of nuclear reactors. Scientists also study thorium to learn about the ancient oceans.

Bulk properties

Thorium is a soft, shiny, and radioactive metal that can be bent or shaped easily. It is found in the periodic table between actinium and protactinium, and below cerium. Pure thorium can be stretched and shaped into different forms.

Thorium is not very dense and is harder than some other similar metals. It has a high melting point, much hotter than many other metals, and it can stay strong even when heated. The way thorium behaves can change a little depending on tiny amounts of other materials mixed in, but it usually stays fairly consistent in its properties.

Isotopes

Main article: Isotopes of thorium

There are seven natural isotopes of thorium, but none are stable. ²³²Th is the main isotope found in nature, with a very long life—about 14 billion years. This makes it one of the longest-lasting radioactive elements found in large amounts on Earth.

Thorium can lose atoms through a process called alpha decay, starting a chain that ends with a stable form of lead. This decay chain creates traces of other elements like lead, bismuth, and radon. Some of these decay products have uses in medicine, such as treating certain diseases. Scientists also study thorium isotopes for possible use in very accurate clocks and to learn about the age of old materials like coral and cave formations.

Chemistry

Thorium is a reactive metal. It can catch fire if it is broken into very small pieces and exposed to air. In larger pieces, it changes slowly when left in air, turning gray and then black on the surface over time.

Thorium does not dissolve easily in water but will dissolve in certain acids. It forms compounds with many other elements, such as oxygen, sulfur, and halogens like chlorine and fluorine. These compounds have different properties and uses. Some are very heat-resistant and have been studied for use in nuclear energy.

Occurrence

Main article: Occurrence of thorium

Thorium is a rare element in the universe. It forms during huge explosions in stars called supernovae and collisions of neutron stars. These events scatter thorium across space.

On Earth, thorium is more common. It is found in small amounts in many rocks and minerals. One important source is a mineral called monazite, which contains about 2.5% thorium. Monazite is found in places like India, South Africa, Brazil, Australia, and Malaysia. Another mineral called thorite also contains thorium and was the first place thorium was discovered. Thorium stays in place in the environment because it does not dissolve easily in water.

History

In 1815, a scientist named Jöns Jacob Berzelius studied a special rock from Sweden. He thought he found a new element and named it "thorium" after Thor, the Norse god of thunder, but later learned he was wrong.

In 1828, a priest and rock expert named Morten Thrane Esmark found a black rock in Norway. He gave it to his father, who then passed it to Berzelius. Berzelius confirmed it was a new element and named the rock thorite.

Berzelius studied the new element and found it was very reactive. In 1914, two Dutch scientists finally separated the metal itself.

In 1898, scientists discovered thorium was radioactive—the same year radioactivity was first found in another element, uranium. Later studies showed thorium changes slowly into other elements over time.

Thorium was first used in 1885 in gas lamps, which gave off bright light when heated. It was also used in many other things, like special glasses and ceramics.

Today, thorium is being studied for use in nuclear power because it could provide a lot of energy and create less waste than other nuclear fuels. Some countries, like India and China, are working hard to use thorium in power plants in the future.

Production

See also: List of countries by thorium resources

Because there isn't much need for thorium, it isn't profitable to mine it by itself. Instead, it is usually taken from materials used to get rare earth elements, which are often made as a by-product from mining other minerals. Right now, most thorium comes from a material called monazite, but there are other sources that could be used if needed. We don't know much about where thorium can be found because there hasn't been much reason to look for it.

Making thorium involves gathering thorium-containing minerals, taking the thorium out of those minerals, cleaning it, and sometimes turning it into useful compounds like thorium dioxide.

There are two main types of minerals that contain thorium. The first type is found in certain rocks and are usually small in size. The second type is found where rivers meet the sea in mountainous areas. These deposits have thorium mixed with other heavy minerals. The way thorium is gathered depends on which type of deposit it comes from.

For the first type, the rocks are broken into small pieces and processed to separate the thorium. For the second type, which is often found in sand along coasts, special methods using magnets are used to purify it. In the past, thorium was made using a method with strong acids, but today a different method using sodium hydroxide is used because it gives a cleaner result, even though it costs more.

Concentration

Purification

To use thorium in nuclear technology, it needs to be very pure. This is done using special liquid solutions that can separate thorium from other elements.

Modern applications

Uses of thorium that do not involve its radioactivity have become less common since the 1950s because of worries about its radioactivity and the materials it changes into over time.

Most uses of thorium involve a compound called thorium dioxide, also known in some industries as "thoria". This compound can stay solid at very high temperatures—around 3300 °C (6000 °F)—which is higher than most other known materials. Because of this, it helps keep flames solid and very bright, which is why thorium was used in old gas lamp mantles. When thorium is heated, it gives off light that we can see, making the flame very bright. Though thorium is still used in some mantles, it has been replaced by another material called yttrium since the late 1990s.

Thorium dioxide has been used to make strong wires for electronic tubes and X-ray machines. It also helps make special glass for cameras and scientific tools by changing how light passes through it. However, because thorium is radioactive, other materials that are not radioactive are now used instead.

Potential use for nuclear energy

Thorium can be used to create nuclear power. When certain atoms in thorium absorb particles called neutrons, they change into another type of atom that can be used as fuel in a nuclear reactor. This process is similar to how we use uranium today.

Using thorium has some benefits. There is more thorium available than uranium, and it could provide energy for a very long time. Thorium can also help make reactors safer and work better. However, there are challenges too. Some by-products from using thorium are very hard to handle because they give off strong radiation. Also, using thorium needs more advanced technology than the methods we use today. Scientists are still studying and working on these issues.

Hazards and health effects

Natural thorium decays very slowly, and the radiation it gives off cannot pass through our skin. Handling small amounts of thorium, like in gas lamps, is generally safe. However, breathing in thorium dust can increase the risk of certain health issues.

Thorium can build up inside the body over many years, and some of its breakdown products are more dangerous. When thorium is heated, it can release these products into the air, which people can breathe in. Workers who handle thorium need to take special care to stay safe.