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Tantalum: A Metal That Kills Primates
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Background:
Tantalum is metallic chemical element. It has atomic number 73, a high density ( 7.4 g/cm3), and a high melting point (2996 oC.) Tantalum generally acts a nonreactive or inert metal. It is a relatively rare and expensive element ($50-300 per pound) and as a result it is used only where its special properties can justify the expense. The element was discovered in 1844. It is normally found in ores that contain considerably more Niobium and the two elements have relatively similar properties and applications. Tantalum deposits are fairly limited and mining occurs only in a few locations. The major producing areas are Thailand, China, Australia, Central Africa ( the Democratic Republic of the Congo, Rwanda.).
Applications
For a few years, Tantalum was used for filaments in light bulbs. It was quickly replaced with the cheaper element Tungsten. In both cases the metals were used because they can withstand the 2000-3000o C temperatures associated with incandescent filaments. In projector lamps or lamps subject to vibration, Tantalum remained the metal of choice through the 1950's.
Tantalum has been used for surgical implants because it does not corrode inside the body and it seldom sets off biological rejection. Examples include metal plates for skull injuries and screws and plates for repairing broken bones or joint replacements. Again, other elements such as Titanium or surgical stainless steel are more commonly used now. Tantalum is also used in chemical processing plants as a liner for reaction vessel. This can prevent corrosion and lead to long lifetime for the equipment. (To keep costs down, one seldom makes the apparatus out of solid Tantalum.)
Electrolytic Capacitors
One important application for Tantalum emerged around 1985-1990. Electrical capacitors made from Tantalum had several important advantages over those made from more traditional materials such as Aluminum. Tantalum capacitors could be made much smaller than other types, and modern electronics places a strong priority on "small." Tantalum capacitors also perform better at the high frequencies that are used in computers, cell phones and video games.
The limited supply of Tantalum capacitors has, at several times, been the limiting factor in the manufacture of electronic devices. It was the major reason for the delayed introduction of the Sony Playstation -II devices in 2000. One important consequence has been a high demand for the element and exceedingly high prices for the ores in 1999-2000.
Mining of Tantalum
Tantalum is an element with high atomic mass and its ores generally have very high density. This means that it is relatively simple to separate metal bearing ore from other rock and soil occurring in a mining location. Large commercial operations have machinery that does this efficiently with large volumes of raw ore.
However, Tantalum mining is one of the few cases where one or two person mining operations can be effective. This is very similar to the Gold Rush prospector who needed little more than a shovel and a metal pan to find and isolate gold dust. The tantalum miner can go to a region where the ore is known to be present, dig a hole, and wash the dirt in a large plastic bucket. All the dense ore remains in the bottom of the bucket. A better scheme is to make a wooden trough and run a stream of water over the dirt.
The discovery of Tantalum ores in the Congo in the 1990's has been a story with very mixed outcomes. Hundreds of individual miners were recruited to dig for the ore called coltan. This is a local name for an ore rich in Niobium (formerly called Columbium) and Tantalum; the name is a shortened form of Columbite + Tantalite. In one sense this is an economic bonanza. A sucessful miner might collect a kg of ore in a day and receive $20-40 for it. This is hundreds of times times what he could make farming or working in an industrial job. With extremely high unemployment this is a great opportunity (much as Gold was for the 49'ers.) It is also an important export product for one of the poorest regions of Africa.
Environmental problems
Much recent mining has occurred illegally in the Okapi Faunal Reserve and in the Kahuzi-Biego National Reserve ( Park) in DR Congo, near the Rawanda border. The government of DR Congo is virtually nonexistent due to civil war and has no power or interest in limiting this activity. In fact, rival armies, including forces from Rawanda, finance their activities by extorting a portion of each miner's yield. Mining of this sort leaves the area covered with large holes (perhaps the size of cars.) As one would imagine, there is no incentive to back fill the holes after mining. The washing of ore can lead to erosion and silting up local rivers.
A much more immediate problem occurs from the presence of about 4000 miners and camp followers in this region far from conventional food sources. A lucrative business of killing wild animals for meat has thrived. In this case, threatened colonies of lowland gorillas have been relatively easy prey and are a prized source of meat. Some sources estimate 50% reduction in gorrilla population. Elaphants and monkeys have also been killed as "bush meat.". This is a region where reliable data is unavailable and it is unknown how much damage the animal population in the area has suffered.
A serious international effort has been made to get manufacturers to limit their purchase of Tantalum to sources that pledge not to buy material from such rogue mining operations. This is, as one might expect, relatively successful as long as a ready source of the material is available at an acceptable price. The recent opening of large mines in Australia and decreased demand for electronics has greatly relieved the economic pressure.
Sources:
Basic data on the element:
CRC Handbook of Chemistry and Physics, page 431 (41 st edition, 1960 edition)
Noyes, Textbook of Chemistry (Henry Holt and Company, Publishers)
(1912 edition with an interesting historical perspective)
information on mining and cost
http://minerals.usgs.gov/minerals/pubs/commodity/niobium/231798.pdf
http://www.miningweekly.co.za
An interesting personal memoir with insight into Tantalum vs. Tungsten (see below)
Oliver Sacks, Uncle Tungsten (Memoirs of a Chemical Boyhood) (Knoff, published 2001)
Description of African Mining and Ecology
New York Times, April xxx, 2001 (Sunday Magazine section)
http://www.npr.org/programs/re/archives/010502.coltan.html
http://wcs.org/news/4735#story1
http://www.chapmanspira.com/htms/Zaire/Zaire2.htm
Oliver Sacks is an interesting character and a gifted writer. He is a neurologist by training. Part of his professional life was portrayed in the movie "Awakenings" where he was played by Robin Williams. The movie was based on his book of the same name. He is famous in some circles for the book "The Man Who Mistook his Wife for a Hat." (I really recommend that book; it is a serious look at neurological disorders and the basic issues of reason and perception.) Other books include "The Island of the Color Blind" and the best book I've ever found on the subject of Migraines.
The sad saga of the government of the Congo is perhaps best illistrated by the evolution of a new word: "kleptocracy" government by theft.