Sunday, October 11, 2009

Mercury—Spain’s “Liquid Silver” Bonanza

HAVE you checked the temperature lately? If so, very possibly you consulted a mercury thermometer. Perhaps you wondered where the mercury came from. The source could well have been the Almadén mine in Spain, where the world’s richest mercury deposit is found. More than a quarter of the world’s mercury production comes from this seam.

“Quicksilver” in English, Quecksilber in German, vif argent in French, azogue in Spanish and hydrargyros in Greek—all are names for mercury—that elusive, slippery, silver-colored, “live” or “quick” liquid metal. In the modern world, mercury has more than 3,000 uses. How is it obtained?

Geologists say that eight elements form more than 98.5 percent of the earth’s crust, and that the remaining 95 or more, including mercury, constitute a mere 1.5 percent of the total. Consequently, mercury is not easy to find.

Mercury in Its Natural State

During the formation of the earth, mercury was one of the thermal liquids that pushed up to fill the cracks and fissures of certain parts of the earth’s crust. In some cases, it remained as pockets of liquid mercury, but in the majority of cases it combined with sulfur to form mercuric sulfide or cinnabar. The rock that contains this mineral has a reddish hue. On closer examination, it has a speckled appearance. Those red speckles contain the precious mercury, which is separated from the ore by the slow process of mining the rock, crushing it, roasting it and distilling and condensing the resultant vapor, then, by filtration or agitation, separating from the condensate the hydrargyrum (from the Greek word meaning “liquid silver”). Today we call it “mercury,” a name that was applied by the alchemists in the sixth century C.E.

When did man first discover mercury? One source says that mercury has been found in Egyptian tombs dated as early as 1500 B.C.E. We can find definite reference to the metal in the writings of Theophrastus (a disciple of Aristotle), who, about 300 B.C.E., described how “liquid silver” was prepared by a simple process of pounding cinnabar stone together with vinegar in a copper vessel. Actually, the pounding served to separate small quantities of free mercury, but did not liberate the mercury that was in compound form.

Pliny the Elder reported, about 50 C.E., that each year some 5,000 kilograms (11,000 pounds; 5 metric tons) of cinnabar were taken from Sisapo in Spain (possibly the area known today as Almadén) and were transported to Rome, where cinnabar was used as vermilion pigment. The mercury was used to recover the “noble” metal, gold, as well as being used with gold in a gilding process.

At the beginning of the eighth century C.E., the Arab invasion of the Iberian peninsula began. This Arab and Moslem occupation lasted for eight centuries. During this period, the Arabs encouraged the exploitation of the Almadén mercury mines. As a result, much of the present-day Spanish vocabulary that has to do with mercury mining springs from the Arabic. For example, even the full name of the town, Almadén del Azogue, is derived from the Arabic words al-ma′din (the mine) and az-za’ūq (the mercury), or The Mine of the Mercury. The Spanish word for the condensation chamber that is used to obtain the mercury is aludel, from the Arabic al-’utal, which refers to the receptacle that was used for condensing the mercury vapor into liquid. The old furnaces that were used in Almadén were called jabecas, derived from the Arabic sabīka, or ingot. Similarly, the men employed to construct the ovens were albañiles, from al-bannā, the bricklayer or builder, or were alarifes, from al-′arīf, the teacher or skillful one.

The Spanish king Alfonso VII recaptured Almadén in the year 1151 C.
and during the following centuries the Spanish crown ceded the mine for private exploitation. In the 20th century the direction of the mine was put in the hands of an administrative council that has progressively modernized the mine, a process that continues to this day.

Distillation Methods Through the Centuries

The primitive methods for obtaining mercury were far from efficient, as is shown by the fact that in the 17th century workmen were able to feed the new Bustamante furnaces with burned stone that had been thrown out after use in the Arab jabecas, or ovens, and were still able to get appreciable quantities of mercury. The first Bustamante furnace was installed in 1646. In two years, nine more of these were built, and eventually 16 were in operation. This boosted mercury production from 2,527 quintales, or hundredweight, in 1646 to an annual production of 7,000 hundredweight in 1776.

Uses of Mercury

As the centuries rolled by, the uses for mercury multiplied. In the 16th century, Paracelsus, a Swiss-born alchemist and physician, employed mercury in the treatment of syphilis. In 1558, Bartolomé de Medina improved the method for extracting silver by a process that involved the use of mercury. The weather barometer was invented in 1643 by the Italian physicist Torricelli, who used a column of mercury to determine the atmospheric pressure. The thermometer with which the doctor or nurse checks your temperature was invented in 1720 by the German scientist Gabriel Fahrenheit, who calibrated the tube containing the expanding column of mercury, making 180 divisions between the freezing and boiling points of water.

Another and less peaceful use for mercury was invented after E. C. Howard discovered mercuric fulminate, which was used until the 1960’s to detonate explosives. The list of uses has snowballed in our 20th century to include agricultural and industrial fungicides, electric switches and mercury batteries, to name only a few. Mercury in vapor form serves in ultraviolet lamps, and in mercury lamps that light the highways. In some cases, mercury vapor is used instead of steam for power generation. This versatile metal has also been used in dental fillings as an amalgam with a silver and tin alloy. It does not appear to be poisonous when so used.

Mercury—Friend or Foe?

This is a legitimate question, for in the last 20 years man has learned the hard way that mercury is a servant that has to be strictly controlled. In many countries, including Japan, Sweden, the United States and Canada, evidence has accumulated establishing the fact that mercury in certain forms is a poison that affects both human life and animal life.

Investigations have revealed abnormal amounts of mercuric compounds in certain fish and game birds. These excesses have been traced to industrial plants that have released mercury along with other waste products, and also to fungicides using methyl mercury. This compound, entering into the food chain, produces catastrophic effects.

Methyl mercury is especially dangerous to pregnant women, since it tends to accumulate in the fetus, causing brain damage to the unborn baby. In New Mexico, U.S.A., in 1969, a family was poisoned by eating pork from a hog that had been fed on grain treated with methyl mercury. Three children were severely crippled, and the fourth, poisoned while in the womb, was born blind and retarded. In the area of the Japanese city of Minamata, mercury poisoning reached epidemic proportions before the doctors finally tracked down the culprit—methyl mercury that had belched out of the effluent pipe of a nearby factory, contaminating the fish, which was a main local source of food. Jenie Hinaloc


Post a Comment