Smelting

Smelting is a way to get useful metals from rocks called ores. We heat the ore and use a special chemical to take the metal out. This helps us get important metals like iron, copper, silver, tin, lead, and zinc. We use these metals in many things around us.

To smelt, we use heat and a carbon source, like charcoal or coke. This helps remove other materials. The ore is heated until the metal stays behind while other parts turn into gases or a waste material called slag.

Smelting often happens in big factories called blast furnaces, especially for making pig iron that is turned into steel. There are also special plants for getting aluminium through a process called electrolysis. Smelters can work for different customers or be part of a single mining operation, usually close to the mine.

Process

Smelting is more than just melting metal from its ore. Most ores are made of the metal mixed with other elements like oxygen, sulfur, or carbon. To get the pure metal, we need to cause a chemical reaction that removes these extra elements.

One common step is called roasting. Roasting is used for ores that contain sulfur or carbon. Roasting burns away the unwanted parts, turning them into gases. This leaves behind an oxide, which is easier to work with.

The final step is reduction. In this step, the metal oxide is turned into pure metal. This happens at high temperatures using a reducing agent, often carbon monoxide. The reducing agent takes away the oxygen from the metal oxide, leaving the pure metal behind. Sometimes extra materials called fluxes are added to help remove impurities.

History

Of the seven metals known in antiquity, only gold is found in its pure form. The others – copper, lead, silver, tin, iron, and mercury – are usually found in minerals. These minerals are mixed with other materials like silica and alumina. Heating these minerals turns them into oxides, which can then be melted to get the metal. Carbon monoxide helps remove other elements.

Humans learned to melt metals more than 8000 years ago in the Old World. Using metals like copper and bronze changed society greatly, leading scholars to divide ancient history into the Stone Age, Bronze Age, and Iron Age.

In the Americas, civilizations in the central Andes could melt copper and silver long before Europeans arrived.

Copper and bronze

Copper was the first metal to be melted. The earliest evidence of copper melting comes from between 5500 BC and 5000 BC in Pločnik and Belovode, Serbia. Copper-tin bronzes, which are harder and last longer, were made around 3500 BC.

Tin and lead

Early lead pieces were found in Çatalhöyük in Anatolia (Turkey), dated to about 6500 BC, but they were minerals, not pure lead. Lead was easy to shape and was used for water pipes and storage in Ancient Greece and Ancient Rome. Tin was less common.

Early iron smelting

The oldest evidence of iron making comes from around 2200–2000 BC in Kaman-Kalehöyük. In Ancient Egypt, iron working appeared between the Third Intermediate Period and 23rd Dynasty.

Later iron smelting

From the medieval period, a new method using a blast furnace was developed. This made pig iron, which needed more steps to become usable. These older methods are no longer used today. Now, steel is made using a Bessemer converter or other modern processes.

Environmental and occupational health impacts

Smelting can hurt the environment by making wastewater and slag and putting dangerous metals like copper, silver, iron, cobalt, and selenium into the air. Smelters also release sulfur dioxide, which helps create acid rain. Acid rain can make soil and water too sour for plants and animals to live well.

People who work in smelters can sometimes get sick because of the bad air and water. Rules in places like the United States try to help by setting standards for clean air and clean water.