Zinc
Zinc, the 30th element on the periodic table, is an abundant silvery-white metal that has numerous applications in the 21st century. This common metal, by today’s perspective, was not always so well known. The ancient Greeks are thought to have been aware of zinc, although they referred to it as pseudargyras or “fake silver”, but were unable to produce it [1]. The first recorded instance of the creation of something from zinc ore came from the ancient Romans in 200 BCE with the creation of brass, an alloy of zinc and copper. Following the fall of the Roman Empire, the methods of zinc production were lost to history. However, zinc makes a resurgence in 13th century India where it is said that metallurgists “rediscovered” that in order to produce zinc it must be vaporized and condensed. The first large scale zinc production took place in China in the 16th century [1]. Although nations in the East were readily producing zinc, the methods for zinc production did not each England until 1743. Zinc was finally identified as an element in 1746 by Andreas Marggrat [2].
Zinc is a mineral element that makes up roughly 65 grams per ton of the Earth’s crust. The lion’s share of the zinc that is used today is gathered through mining operations. These operations consist of 80% underground mines, 8% open pit mines, and 12% combination mines [1]. The zinc is mined from four different types of deposits: volcanic hosted massive sulfides, carbonate hosted, sediment hosted, and intrusion related [3]. All of these deposits contain zinc minerals in the form of sphalerite, or zinc blend crystal structure [3].
The zinc ore from these mines is essentially useless in the state it is found because the zinc concentration is only between 5-15%. In order for zinc to be produced economically by current methods the zinc must be concentrated to roughly 55% zinc. This process is done simply by crushing and grinding down the ore to achieve a separation from any other minerals [4].The zinc concentrate then goes through a process called “roasting and sintering”. This process removes the 25-30% sulfur that is present in the zinc concentrate. The concentrate is heated to over 900ºC at which point the zinc sulfide will become zinc oxide and the sulfur reacts with any oxygen present to create sulfur dioxide, which in turn becomes sulfuric acid [4]. The most common process for the production of zinc is the hydrometallurgic process. This process uses the byproduct sulfuric acid from roasting and sintering to “wash” the zinc oxide that is produced during the same process. The sulfuric acid dissolves zinc, causes iron to precipitate, and leaves any lead or silver undissolved [4]. This solution can be purified with the addition of zinc dust, while other elements are precipitated out through cementation, a process in which ions are reduced to zero valence at a solid metallic surface. The purified solution then undergoes an electrolysis process. The solution is electrolyzed between lead alloy anodes and aluminum cathodes [4]. An electrical current is circulated between the anode and cathode which causes the zinc in solution to deposit onto the aluminum cathodes in high purity. The zinc is then stripped off of the aluminum cathodes, dried, melted, and cast. Zinc that is created through this process is rated as either “high grade”, or 99.95% pure, or as “special high grade”, or 99.99% pure [4]. Ultimately 90% of the world’s zinc is produced using this method.
Zinc is a silvery-white metal with a blue tinge. It has an atomic number of 30, an atomic mass of 65.38 amu, and a density of 7.134 g/mL [5]. Solid zinc has a melting point of 419.527ºC and a boiling point of 907ºC. Zinc tarnishes when exposed to moist air [6]. Zinc metal can be dissolved by both strong acids and strong bases. Zinc tends to crystallize in the hexagonal close-packed structure [1]. Special high grade zinc (99.99% pure) is very ductile. Lower grades of zinc (99.8% pure), known as western grade, is very brittle at temperatures below 100ºC. However, when western grade zinc is heated above 100ºC it can be rolled into sheets that remain flexible [1].
Zinc, although not very useful by itself, is a very versatile element that is often combined with other materials. Of the roughly 12 million tons of zinc produced annually, half is used to galvanize steel or iron [7]. Galvanization is the process of coating iron and steel with zinc to protect the metal from corrosion. Galvanization is effective because as long as the zinc coating remains in contact with the steel or iron, the zinc is oxidized by the atmosphere and not the more valuable metal. Even as the zinc coating begins to break apart and become porous, as long as a thin layer of zinc exists on the top of the metal then it is protected. This essentially allows a piece of galvanized steel to be protected from environmental corrosion for up to 30 years, which ultimately can significantly reduce infrastructure maintenance costs. About 17% of the 12 million tons of zinc produced annually are used in the production of zinc base alloys, mainly to supply the die casting industry [7]. Die casting is a process for producing metal parts by forcing molten metal under high pressure into reusable steel molds [8]. Using zinc as the molten metal mentioned above, parts can be made with smooth or texture surfaces. The efficiency and economy of zinc die casting makes them among the world’s highest volume, mass produced items in the metalworking industry [8]. Another 17% of the world’s zinc supply goes to the production of brass and bronze, alloys of zinc. The remainder of the world’s zinc is used for zinc semi-manufactures applications and the production of zinc chemical compounds [7].
In the grand scheme of history zinc is of little strategic importance. In ancient Rome zinc was regularly smelted with copper to produce brass. Brass is a soft metal that was sometimes used for decretive purposes or for the manufacture of ceremonial weapons. Although it is now possible to make bronze using copper and zinc for decoration and architecture, during the Bronze Age the technology did not exist to make bronze in such a way. Bronze was regularly used in the production of weapons and armor. Without the ability to make a useful tool or weapon, zinc became relatively unimportant. In the present day the strategic importance of zinc can be argued. Zinc exists in such abundance that it cannot be considered a rare earth metal. This drastically decreases any benefit that may come with hoarding zinc. However, zinc is essential for the preservation of steel that is left exposed to the environment. Galvanization of metals through the addition of a coating of zinc is now considered an essential part of construction and it is responsible for the consumption for half of all zinc produced. However, there is little strategic value behind the galvanization of building materials.
Zinc is not a rare earth metal and can therefore be found in relative abundance in the Earth’s crust. This causes zinc to be an inexpensive metal, trading at .97USD/lb. or 2144 USD/ton as of January 22, 2015 [9]. This in no way compared to the current price of gold which is being traded at 1278.33 USD/oz. However, the price of zinc is not much different from other base metals such as aluminum, copper, and lead which are currently being traded at .83 USD/lb., 2.53 USD/lb., and .83 USD/lb., respectively [9].
Zinc metal is a relatively safe material according to its MSDS sheet. Zinc can be a skin and eye irritant and is hazardous if it is ingested or inhaled [10]. Zinc can be flammable and is known to ignite when it comes into contact with strong NaOH. It is recommended to wear a lab coat, gloves, and a dust respirator when handling zinc.
China currently produces the most zinc in the world with more than 5 million metric tons produced in 2013 [11]. The sheer amount of zinc that a single country can produce shows just how abundant it is. The effect of the commonality of zinc can be generalized by looking back throughout history. No single country, nation, or civilization has seemed to have benefited from zinc more than any other. Assuming an essentially even landscape for the distribution of benefits of zinc, it is not so much a stretch to assume that zinc has neither effected or been affected by culture. It is not a precious metal or even an uncommon metal and therefore no wars have been fought over it, like gold and silver, and it is not a very useful metal on its own. The effective mass production of zinc did not occur until the 16th century [1], which should be taken to imply that is was of little to no importance in the previous centuries for anything except acting as “fool’s silver”. The single greatest effect zinc has had on society is its use during the galvanization process. Society can have structures that last much longer before showing any real signs of environmental damage, mainly oxidation.
Ultimately zinc is an important metal in industry, but lacks the characteristics to become something that is coveted. Zinc’s relatively late resurgence of smelting methods coupled with its abundance in the Earth’s crust make it something that can be used productively by a civilization, but not something that has the power to change it.
References
[1]. “Zinc (Zn) | Chemical Element.” Encyclopedia Britannica Online. June 9, 2014. Accessed January 25, 2015. http://www.britannica.com/EBchecked/topic/657264/zinc-Zn.
[2]. “Zinc.” Royal Society of Chemistry. Accessed January 25, 2015. http://www.rsc.org/periodic-table/element/30/zinc.
[3]. “Zinc – Natural Occurrence.” International Zinc Association. Accessed January 25, 2015. http://www.zinc.org/basics/zinc_natural_occurrence
[4]. “Zinc Production – From Ore to Metal.” International Zinc Association. Accessed January 25, 2015. http://www.zinc.org/basics/zinc_production.
[5]. “Zinc Properties.” International Zinc Association. Accessed January 25, 2015. http://www.zinc.org/basics/zinc_properties.
[6]. “Zinc: Reactions of Elements.” WebElements Periodic Table»Zinc»reactions of Elements. Accessed January 25, 2015. http://www.webelements.com/zinc/chemistry.html.
[7]. “Zinc Uses.” International Zinc Association. Accessed January 25, 2015. http://www.zinc.org/basics/zinc_uses.
[8]. http://www.zinc.org/diecasting, accessed January 26, 2015.
[9]. “Zinc Prices and Zinc Price Charts.” InvestmentMine. Accessed January 25, 2015. http://www.infomine.com/investment/metal-prices.
[10]. “Zinc Metal MSDS.” Accessed January 25, 2015. http://www.sciencelab.com/msds.php?msdsId=9925476.
[11]. “Zinc.” USGS. January 1, 2014. Accessed January 25, 2015. http://minerals.usgs.gov/minerals/pubs/commodity/zinc/mcs-2014-zinc.pdf.