The metal tin is one of the basic elements in chemistry and is listed on the Periodic Table as “Sn”. It has atomic number 50 and melts at 232 degrees Celsius (450 degrees Fahrenheit). Tin is the 49th most abundant element in the crust of the Earth. It is a malleable poor metal with a silver-like look and is not easily oxidized in air. Therefore, tin is used a lot to coat other metals to decrease corrosion.
Tin is obtained mainly from the mineral cassiterite, where it is stored as SnO2. The largest deposits of tin are currently found in China, Malaysia, Peru and Indonesia. It is estimated that at the current rate of consumption, the Earth will run out of mineable tin within 40 years.
The earliest use of tin is dated at around 3500 years BC. Metalworkers in what is now Turkey learned to add tin to relatively soft copper to form a much harder bronze. From this bronze, harder tools and better weaponry could be made. This ‘invention’ is the basis of our transition as a civilization from the copper age to the bronze age, which lasted for two millennia.
Because of the superiority of bronze tools, the search for other sources of tin was a priority for many civilizations. Large tin deposits were found in Cornwall, England, and were traded as far as the countries of the Mediterranean Sea. Indeed, to control the tin trade was one of the major causes of the invasion of England by the Romans. In chemistry, the symbol for tin, Sn, is an abbreviation of the Latin word for the metal, stannum.
Using tin as plating material dates to the era of the Roman Empire. The Romans coated their copper vessels with tin to keep them in bright-looking order. Tinplate, essentially iron coated with tin, was available in England in the 17th century and was used for metal containers. This ultimately led to a patented method of preserving food in tinplate cans by Pierre Durand in 1810. During the 19th century, tin cans slowly began replacing bottles for food packaging.
In the current age, most of the world’s tin is produced in Thailand, Indonesia, Australia, England, Bolivia and Nigeria. The United States does not have major tin deposits within its borders.
The Making of Tin
Extracting tin from tin ore is done differently according to the source of the ore deposit and its quality. Some deposits, like those in England, are located deep underground en require tunnels to reach. This ore contains around one percent of tin by weight.
Other tin deposits, like those in Indonesia, are located in gravel along streambeds and require dredges or pumps to reach. This ore contains as little as one-hundredths of a percent of tin by weight. Roughly 80% of the tin in the world is found in these low-grade deposits.
When the deposits of gravel are situated below the water level in the stream, they are brought to the surface by a floating dredge. This dredge operates in a man-made pond created along the bed of the stream. The gravel is passed through a series of shakers and revolving screens to separate the gravel from the tin ore. This is collected for further processing.
When the deposits of gravel are situated above the water level, they are fragmented by jets of water pumped by large water-cannons. The mud that breaks off the deposit is collected in a man-made pond. Subsequently, it is pumped in a sloped through with riffles (wooden slats), where the tin ore is collected for further processing.
The collected tin ore passed through a number of vibrating screens to separate the tin from coarser materials. Usually it then passes through a classifying tank filled with water. In this tank, the heavier ore sinks to the bottom while finer and lighter material floats on top. The lighter material is removed and the enriched tin ore is collected. As a next step it may pass through a floatation tank, where chemicals are added to make the individual tin particles float to the top of the surface, much like froth floatation with zinc, where it overflows to be collected.
The last step is drying the ore and pass it through a separator to magnetically remove any iron. The tin ore at the end of this step is around 75% tin by weight and consists mainly of cassiterite.
The concentrated tin is deposited in a furnace with carbon like coal or fuel oil and heated to 1400 degrees Celsius (2550 degrees Fahrenheit). At this temperature, the carbon reacts with the carbon dioxide in the furnace to form carbon monoxide. The carbon monoxide in turn reacts with the cassiterite and creates crude tin and carbon dioxide. The crude tin is collected for further refinement.
Because tin easily mixes with a lot of materials, it usually reacts with the residue in the furnace called slag. As a result of this reaction, the slag contains a reasonable amount of tin and is processed further before it is discarded. As in the first furnace, carbon is added to realize the eventual formation of crude tin and a residue that contains some tin. These processes are repeated until the tin concentrate in the slag is too low to justify reentrance in another furnace.
The crude tin from the furnaces is deposited in a furnace with a low temperature. Tin melts at a much lower temperature than most metals; thus by slightly raising the temperature in the furnace at each step it is possible to melt only the tin, leaving other metals, like iron and copper solid.
The melted tin in collected and placed in a poling kettle, where it is agitated with compressed air, steam or poles of green wood. The poling kettles is named after the use of these wooden poles which, being moist, generate steam along with agitation by stirring. Most of the impurities left in the tin rise to the surface as a scum and is removed. The refined tin is now 99,8% pure.
For some applications, an even higher purity is required. The tin may be processed further in by using electrolytic refinement. Electrical anodes are formed out of tin and placed in a tank with an electrically conducting solution and a cathode. By passed electricity through the tank, the tin is stripped from the anode and forms on the cathode, creating a very high grade tin ore.
The high purity tin is cast into small bars weighing about one kilogram while the lower grade tin is cast into ingots weighing between 11 and 45 kilogram.
Tin has been used as a solder in the form of an alloy with lead for a long time. Between 5% and 70% of the solder consists of tin. It is primarly used for joining pipes or electrical circuits. Since 2006, the amount of lead in these solders has decreased, because of regulations concerning hazardous materials. Decreasing the amount of lead has led to many problems, including the formation of tin whiskers, which causes electrical problems, and a higher melting point.
Tin is a material which bonds quite easily with other metals. Because of this quality, it is used to bond with iron to coat lead, zinc or steel. Tinplated containers are widely used to preserve food; this forms a large portion of the market for tin.
Tin can be used in combination with other metals to form a variety of practical alloys. It is commonly alloyed with copper and/or zinc. Bronze is mostly copper, but uses around one-tenth of tin. Pewter is an alloy consisting of 85% to 99% tin. Some coins have a small percentage of tin present.
The price of tin is influenced by a number of factors. Approximately 50% of tin worldwide is used in solder. The increasing environmental awareness is causing a resentment for the use of lead in solder and have resulted in a ban of this metal. Similar difficulties may arise for tin as it also has some negative qualities concerning the environment. The legal restrictions can therefore have a far-reaching effect on the demand for tin.
Similar to many other metal, tin demand will rise in accordance to economic stability or growth. As tin is a major component in construction work and luxurious electronics, economic downfall will cause a drop in the demand for these products and thus a declining demand for tin.
LME Tin Futures Contract
A Tin Futures Contract on the London Metal Exchange (LME) has the following specifications:
|Contract Size||5 tonnes|
|Price Quotation||US dollars per tonne|
|Contract Months||Monthly: 7 out to 15 months|
|Tick Size||$1.00 US dollars|