Monday, August 2, 2021

How is Gold Formed?: Origin and Process Explained

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Gold is one of the most precious metals in the world. This begs the question of how is gold formed? Since its inception, Humankind has been an inquisitive species, especially about the origin of everything. Hence, it is very understandable why one would be interested in gold origins, and we are here to answer that.  

Also Read: Platinum vs. White Gold – 3 Best Differences

Gold has been used for thousands of years in different regions for different purposes. The most popular uses have been ornaments and as currency in the form of gold coins. However, where does this yellow shiny metal come from? How is gold formed?

To understand how gold is formed, we must understand how all other elements are formed. And modern research has given us some insight as to how. To solve this mystery, we must look to the stars, literally.  

How is Gold Formed?: Origin and Process Explained

How is gold formed
How is gold formed

Most elements in existence were formed inside the cores of stars. Especially neutron stars. Let us take a look at them.

What is a Neutron Star?

How is Gold Formed?: Origin and Process Explained 1

Stars burn and emit a tremendous amount of energy. But where does this energy come from? The answer is nuclear fusion. After the Big Bang, light elements like hydrogen, helium, and lithium were formed. These stuck together to form heavenly bodies, and some of them became stars. Inside the star, light elements are forced together to form heavy elements. For example, hydrogen atoms fuse to form one helium atom. Helium atoms fuse to form lithium.

The star invests a bit of energy in forcing the atoms together but gets multitudes of it in return when they fuse. With lighter elements like hydrogen and helium, this is extremely easy. Hence, the star does not bother to fuse heavier elements above them. The energy that the star produces keeps it in a stable state.

When the stars are young and newly formed, they are full of these elements. However, these elements gradually run out. The process takes billions of years, yet, at one point, the star is almost out of the light elements. It is on the brink of death. At this stage, the star becomes unstable and can collapse on itself. That is, the gravitational pull of the core overwhelms the repulsive force of protons and electrons, crushing them together. The star keeps collapsing and becomes denser and denser. The star becomes so dense, and it is just a few stages away from a black hole. Its temperatures reach billions of degrees.

After a while, this causes protons and electrons in the core to get pushed together and form neutrons. Hence, the name neutron star. However, they do not only contain neutrons; they have many other elements in them too. Only supergiant stars (at least 10 to 15 times the Sun’s size) can form neutron stars.

In such a star, to get whatever energy it can, the star starts to fuse the heavier elements. However, this is not as efficient. The star gets less and less energy back the heavier elements it tries to fuse. Yet, the heavy elements are formed inside the star due to the process. However, this process stops at Iron as the star does not get any energy after fusing Iron. Most heavy elements are formed this way.

Credits to “Kurzgesagt – In a Nutshell” for this outstanding video.

How is Gold Formed From These Stars?

If the process stops at iron, how is gold formed? Well, heavenly bodies are not static. They are constantly moving and, in the process, collide with each other. Similarly, when two neutron stars collide, they explode in a spectacular explosion called a “kilonova”- the elder brother of a normal supernova. However, before exploding, the collision causes the formation of heavier elements and their variations. One of these is gold. This is the only way in which these elements can be formed.

When the stars finally explode, they shower their elements into the universe. These elements form planets, new stars, solar systems, asteroids, meteors, and other heavenly bodies. The explosion that created the earth itself is said to have created a volume of gold several times the mass of this planet. Some of this gold was here since the earth was spat out of this explosion, and more kept arriving in the form of meteors and asteroids that crashed on the earth’s surface from outer space. This is the origin of gold.

However, there is another step before gold, as you see it in day-to-day life, is made. We need to look into the purification part of the question “how is gold formed?”.

Despite gold being a noble metal, it does react or mix with other elements under certain conditions. For example, when the earth was a mass of molten metals resembling hot fluids, molten gold got mixed with other metals. Another is a chemical example where Gold very slowly reacts with Chlorine or other halogens at room temperature to form Gold chloride.

A special acid called Aqua Regia (a mixture of hydrochloric acid and nitric acid in a 3:1 ratio) is the only liquid that can literally dissolve gold. This makes gold impure. Hence, it has to be purified before it can be put to any use.

Gold is found within the earth’s crust and sometimes in flowing water bodies on the surface itself. The deepest gold mine in the world is in Africa and is 12,800 feet deep. At this depth, working without strong air-conditioning is practically impossible for humans. Gold is found mostly in its pure form mixed or embedded in some unwanted materials. These are also called gold nuggets. In some cases, however, gold compounds are found.

After being mined, gold ores are purified through various processes. We shall go over them one by one.

Cyanidation

Cyanidation refines more gold than any other process. In this method, metallic gold ore is made to react with oxygen to form oxidized gold. Then, this ore is dipped in an alkaline cyanide solution. The gold in the ore dissolves in this cyanide solution and is then filtered, and the solids are separated. The gold is later filtered from the solution—the process of cyanidation changes with the ore’s gold content.

If the gold content is more than 20 grams per ton of ore, a process called vat leaching is practiced. In this process, large containers are filled with ore and the cyanide solvent. The containers are equipped with agitators and drainage options. The agitators help dissolve the gold in the ore quicker.

However, if the amount of gold content in the ore is less than what is mentioned earlier, heap leaching is observed. In this process, the gold ore is arranged in heaps or large piles. The solvent is then sprinkled over it. The cyanide solution dissolves the gold on its way as it percolates through the pile. The gold solution is then collected at the bottom. This gold is only around 95% pure. A bar of this gold is often called the doré bar. A doré bar is later used in other refining methods.

However, two methods are most wildly used to refine gold, and they are Miller’s and Wohwill’s process. Their processes get gold to the maximum purity that can be obtained.

Miller’s Process

Francis Bowyer Miller invented this process of refining gold. Miller’s process is speedy and simple. Initially, gold ore is heated till all of it is melted. After that, chlorine gas is released into it. Chlorine reacts with all other metals and materials except gold at that temperature, and the compounds float to the surface of the molten gold. The impurities are then separated immediately.

Yet, Miller’s process only makes gold that is 98% to 99.95% pure. The next process gets even better.

Wohlwill’s Process

Wohlwill’s process includes the electrolysis of molten gold to derive its purest form. Firstly, an electrolyte of hydrochloric acid and gold chloride or chloroauric acid is produced and taken into a container. A gold bar of around 95% purity is then used as the anode, and the cathode is either 24k gold sheets or simply stainless steel.

The anode and cathode are then lowered into the electrolyte, and an electric current is passed through them. The anode starts to dissolve in the liquid, and the gold atoms are attracted towards the cathode. The gold keeps depositing at the cathode. After the anode has been completely melted, the cathode is taken out and molten or further processed as required. The gold from this process is used commercially and is 99.99% pure. This is the method to follow to get the purest gold possible.

For the normal man, there is another way of extracting gold without any fancy and huge equipment. How is gold formed at home? Firstly, nitric acid is added to the gold ore. Shortly after, muriatic acid and hydrochloric acid are added, and the mixture is agitated. Once the mixture settles, it is treated to neutralize all the acids. Then, the mixture is simply filtered, and the remaining muddy precipitate is gold. However, this gold needs to be thoroughly rinsed and treated with aqueous ammonia. White vapors will be formed due to the process. Rinse the gold once again, and it is ready to be used.

This truly answers how gold is formed. This is the journey gold takes before it appears in shops or on a person.

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