Mercury—Spain’s “Liquid Silver” Bonanza
By “Awake!” correspondent in Spain
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-maʹdin (the mine) and az-zaʼūq (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-ʼutal, 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-ʹarīf, the teacher or skillful one.
The Spanish king Alfonso VII recaptured Almadén in the year 1151 C.E., 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.
A Visit to the Almadén Mine
Almadén is a town of some 11,000 inhabitants—a place of clean white rows of single- and two-story houses. As we make our way to the mine, we are impressed by the number of men on the streets, just standing around chatting with one another, or taking the occasional copita, or small glass of brandy or anisette. Why should these men be on the streets? Because the mercury miners can work underground only eight days a month, due to the toxic effects of the mercury vapors, coupled with the constant threat of contracting silicosis. The mercury vapors cause the disease called hydrargyrism or mercurialism, which affects the brain cells and causes a constant trembling of the extremities. Silicosis causes a hardening of the lungs and is marked by a shortness of breath. To avoid or minimize these effects the miners work one day and are free for the next two days (or three, if Sunday is included). A further safeguard is that after three months in the mine they work one month at the surface in the open air.
The town and the mine are built right on top of the almost vertical seam of cinnabar. The mine has three shafts, named “San Miguel,” “San Joaquín” and “San Teodoro.” We chose to be observers of operations at the San Joaquín shaft, which has a depth of 488 meters (1,600 feet).
The hardest and most dangerous work is the drilling out of the ore-bearing rock, but more interesting to us was the process that takes place above ground. The first stage is the arrival of the tubs or mine cars, loaded with cinnabar rock. These come up two at a time, each bearing about 15 hundredweight (760 kilograms) of rock.
From the pithead the rock is passed into two huge crushing machines that reduce it to gravel size. From there the crushed stone passes to a deposit and is drawn off by conveyor belt to feed the four ovens. These modern ovens are as high as a four-story building and are multideck or multihearth furnaces. Those in Almadén have eight decks. The crushed mineral starts its journey at the top deck and is kept in motion by rotating arms that work the mineral toward the openings, allowing it to pass into the deck below. A temperature of 800 degrees Celsius (1,500 degrees Fahrenheit) is needed to free the mercury vapor. The vapor passes through a system of water-cooled tubes where it condenses into liquid mercury.
However, much of the precious quicksilver is also trapped in the gray sludge that is the product of the baking and the condensing processes. This sludge is mixed with lime at hoeing tables out in the open air. There masked workers constantly hoe the mixture, causing a trickle of mercury to run out of the hoed mass every few seconds. The lime and the hoeing help the small droplets of mercury to coalesce and thus to form the snakelike flow that runs down into the small pozo, or well. From this section of the plant the mercury is taken to the almacén or warehouse, where it is stored in vats until it is measured into iron flasks. These flasks hold 34.5 kilograms, or 76 pounds, which is the standard weight for which prices are quoted on the London and New York markets.
While in the warehouse, we observe some of mercury’s interesting features. To illustrate a point, one of the employees climbs into the vat of mercury. Instead of sinking into the liquid, he remains completely on top of it! This looks very strange. But when we realize that mercury is 13.5 times as dense as water (about 1.2 times the weight of lead), we do not marvel that it supports the weight of a man almost as a solid object does. Furthermore, mercury is the only metal that is liquid at ordinary temperatures. It passes from the solid to the liquid state at −39 degrees Celsius (−38 degrees Fahrenheit) and boils at 357 degrees Celsius (674 degrees Fahrenheit). Another curious fact about mercury is that it is a liquid that a person can touch without getting wet. This is due to its great cohesiveness or high surface tension.
The next place that we visited was the analysis laboratory, where the laboratory chief explained to us the detailed control that is maintained daily to check the quality of the mercury, as well as the richness of the ore coming out of the mine. The laboratory makes a control analysis of all the materials that are used in the distillation process, and a similar analysis of all the resultant products, whether solid, liquid or gas. We were told that the mercury produced in Almadén has a purity rating of 99.997 percent, a purity surpassed only by the natural or native mercury that is occasionally found in pockets in the mine.
The Almadén mine produces from 7 percent to 11 percent mercury from its cinnabar ore, which proves it to be the richest cinnabar ore deposit in the world. Other very productive mines are located in Yugoslavia and Italy. But even after so many centuries, Almadén still holds first place. The shafts keep going deeper and deeper, and the cinnabar rock continues to appear. In fact, there is so much cinnabar in the region that the State has reserved the right to exploit all the ore within 25 kilometers (15 miles) of Almadén.
The next time that you look at the thermometer, or use a modern flash camera, or look into a mirror, you can think of the effort and ingenuity of the men who have, over the centuries, developed the mining and refining methods and the many uses of the versatile metal mercury.
[Picture on page 21]
View of the crushing and oven plant at the left, and the distillation tubes at the right