A Brief Overview of Tin and its Mining Process
The metal tin with a silver tinge has the symbol Sn, which is a short form of the Latin word Stannum. Tin has the atomic number 50 with a melting point of 232°C. Tin is not among the most abundant element in the Earth’s crust and is not easily corroded in air. Consequently, tin is used frequently as a coating over other metals to reduce corrosion. Tin is found mostly in the mineral cassiterite, where it is deposited as an oxide and the largest tin deposits are in China, Peru, Indonesia, and Malaysia.
History of Tin
The earliest use of tin goes back to thousands of years and metalworkers discovered that by adding tin to the comparatively soft copper, a much harder alloy called bronze is formed. From bronze, harder tools and superior weaponry could be built. This ‘discovery is the foundation of our evolution as a civilization from the copper age to the bronze age, which continued for close to two millennia. Due to bronze tools’ supremacy, the quest for other tin sources was the main concern for various civilizations.
The Making of Tin
Obtaining tin from its ore is carried out based on the ore deposit’s source and its quality. Some deposits are found way deep under the ground and require elaborate passageways to get there, especially in many European nations. This ore comprises about 1% of tin by weight.
Tin deposits in places such as Indonesia, are often found along creek beds and require pumps or dredges to get to it. This ore often comprises just about one-hundredths of a percent of tin by weight. Almost 80% of the tin found worldwide is accumulated in these low-quality deposits.
When gravel deposits are located under the water in a stream, a floating dredge is needed to lift them to the surface. This dredge works in an artificial pond built along the stream bed. The gravel is passed through a series of spinning screens and shakers to keep the tin ore separate from the gravel. The ore is accumulated for further processing.
When gravel deposits are above the water surface, they are separated by water jets pumped by cannons. The sludge that splits off the deposit is accumulated in an artificial pond. Later, it is pumped in with riffles, where the ore is amassed for further processing.
The accumulated tin ore is dispatched through several vibrating screens to keep the tin away from rough materials. Normally, it is then transmitted through a sorting tank filled with water. In this tank, the denser ore drops to the floor while the lighter material floats on the surface. The lighter material is thrown away, and the tin ore is gathered. In the next step, the ore is passed through a floatation tank, where chemicals are added so the metal particles float on the surface.
Finally, the ore has to be dried by passing it through a separator to get rid of any iron through magnets. The tin ore at the end of this procedure is about 75% tin by weight and contains mainly cassiterite.
During the smelting procedure, the concentrated tin is placed in a furnace with coal and carbon and heated to 1400°C. At this high temperature, the carbon reacts with carbon dioxide to form carbon monoxide. The carbon monoxide then reacts with the cassiterite and forms carbon dioxide and unrefined tin. The unrefined tin is accumulated for more refinement.
As tin easily blends with many substances, it normally reacts with the deposit called slag. Due to this reaction, the slag which has a fair quantity of tin is processed further before being removed. Carbon is added to extract the final formation of unrefined tin and scum that contains some tin. These procedures are carried out repeatedly until the tin in the slag is too low to warrant re-entrance in another furnace.
The unrefined tin extracted from the furnaces is dumped once again in another furnace at a low temperature. Tin has a low melting point than most metals, so by marginally increasing the temperature in the furnace at each step, only the tin can be forced to melt, leaving other metals such as copper and iron to remain in solid form.
The melted tin is accumulated and kept in a poling kettle, where compressed air is pushed through steam or poles of green wood. Most of the contaminations sticking to the tin come to the surface as a residue and is taken off. The refined tin is now close to 99.9% pure. Mostly refines tin specs are available in Sn 99.9% min & Pb 300ppm max, Sn 99.9% min & Pb 100ppm max and Sn99.9% min & Pb 50ppm max and Sn 99.99% min and Pb 24% max
For certain applications, tin with higher purity is needed. So, it is processed further through electrolytic refinement that creates an extremely high-quality tin ore.
The high purity tin is molded into small bars weighing about a kilogram while the low-grade tin is molded into ingots weighing between 11kg and 45kg.