Grantville Gazette - Volume VIII, page 47
part #8 of Grantville Gazette Series
Bauxite takes its name from the town of Les Baux, in France, so that pinpoints one deposit, albeit one in enemy hands. There, it is found as a reddish rock. (EB11, "Les Baux")
The Irish deposit is at Irish Hill (near Larne), in county Antrim, Ireland. The Arkansas deposits are in Saline and Pulaski counties.
Several atlases likely to be in personal libraries, such as the Hammond Citation World Atlas and the Rand McNally Family World Atlas, show the location of major "Al" deposits.
{The up-timers, of course, are most interested in finding bauxite in Germany. There are several clues: (1) it is in basaltic rocks of the "Westerwald," and these rocks are tertiary basalts interbedded with pisolitic iron ore, like those of Antrim (EB11-B); (2) it is found in Hesse (EB11-A), and (3) it is deposited as a reddish clay, between layers of tertiary basalt, at Vogelsberg in Germany. (EB11, "Laterite")
The term "Westerwald" is pretty nondescript ("western forest"), but there is a forest so named at the modern border of Hesse and the Rhineland Palatinate. Vogelsberg is likewise shown by modern maps as a mountainous area in south central Hesse, west of Fulda.
Unfortunately, the German deposits are not significant enough to be shown in the Hammond atlas.
* * *
We know, within several miles, where to look, the next question is, would we know what are we looking for?
Both The Audubon Society Field Guide to North American Minerals, and the Eyewitness Handbooks: Rocks and Minerals provide photos and "tests" for bauxite. Bauxite isn't necessarily red; it can be white, yellow or brown. (EB11-B) Red is a sign of the presence of ferric iron oxide, although the ore's color "is no sure criterion of the iron content." (EA)
* * *
We want bauxites with a high alumina content. The 1911EB gives Grantville researchers the following composition data:
* Antrim (Irish) bauxites: 33-60% alumina, 2-30% ferric oxide, 7-24% silica, balance titanic acid and water. (Encyclopedia Americana says that the finest Antrim bauxite is "almost free from iron.")
* French bauxites: 58-70% alumina, 3-15% "foreign matter," 27% silica, iron oxide and water.
* American bauxites: 38-67% alumina, 1-23% ferric oxide, 1-32% silica. (EB11-Al, 768) (EA says that in America, ore is available with "as little as 1 percent iron oxide and 3 percent silica").
Would-be aluminum barons will no doubt show prospective investors the encyclopedia page which states "by far the greatest quantity of commercially exploited bauxite lies at or near the Erth's surface. Consequently, it is mined in open pits requiring only a minimum removal of layers of soil and rock covering the ore." (EB-IEP 389)
The modern EB says that "bauxite beds are blasted loose, dug up with power shovel or dragline, and the ore transported by truck or rail to a processing plant. . . . Refining plants are located near mine sites, if possible, since transportation is the major item in bauxite costs."
In the 1632 universe, we will still be able to use explosives to blast away overburden, if necessary. However, access to power shovels and dump trucks will initially be limited to mining sites within driving distance of Grantville. Hence, if we are mining it further away, we will be collecting the bauxite with pickaxe and shovel, carrying it out of the mine by wheelbarrow, hoist, or mine car, and shipping it to the processing plant by pack mule, wagon, barge or ship.
How much ore do we need? Assuming an alumina content of 50%, it takes two pounds of bauxite to make one pound of alumina, and two pounds of alumina to make one pound of elemental aluminum. (EA)
Bauxite Confidential
How easy is it to find and mine bauxite? Bauxite was discovered in 1821 by Pierre Berthier. Berthier was an amateur geologist, on holiday in Provence, and his attention was caught by a conspicuous band of red earth in the white face of a limestone ridge near Les Baux. (Raymond, 220-1)
In 1858, the prominent chemist Henri Deville, who had developed the first commercial process for making aluminum, was sent a sample of an "iron ore" which an engineer in Marseilles had been unable to smelt. Deville identified it as high-grade bauxite. The sample came from nearby Les Baux, and was found in a kilometers-long exposed seam—much like the one which Berthier had found previously. (Raymond, 224)
Germany. While Germany is not even listed in Brubaker's 1963 overview of bauxite countries, a German website says that in 1918, Germany was the "world's fourth largest bauxite producer." It adds, "The pit "Eiserne Hose" near the town of Lich has been in production until 1975. Miocene basalt is weathered to depths up to 100 m and overlain by bauxite." A photograph shows a roadside falloff on which a red soil is exposed. http://mindepos.bg.tu-berlin.de/mk/mkb1.htm
Rest of the world. About 80% of world bauxite production is from surface mines, usually exploiting "blanket deposits." (International Aluminum Institute, IAI) Blanket deposits may be exposed, or covered with some kind of overburden which must be removed by open-pit techniques.
According to IAI, "large blanket deposits are found in West Africa, Australia, South America and India. These deposits occur as flat layers lying near the surface and may extend over an area covering many kilometers. Thickness may vary from a meter or less to 40 meters in exceptional cases although 4-6 meters are average." That sounds promising.
In British Guiana and Dutch Guiana (Suriname), we can find blanket deposits up to forty feet thick, and covered by up to sixty feet of overburden (typically sand and clay, not rock). The ore is 58-63% alumina, 2-5% silica, and 3-6% ferric oxide. The Gold Coast deposits are fairly similar: average thickness is 33 feet, maximum 60 feet; and as much as 64% alumina. (Bateman, 558-9)
Lancashire says that Jamaican bauxite is also near the surface (usually not more than 100 feet underground). Moreover, the overburden is soft, and thus easily removed. A map of bauxite mining areas shows that they cover about half of the central third of the island (the region earmarked by the Hammond Citation World Atlas as being of interest).
According to IAI, in southern Europe and Hungary, bauxite is most often found in pockets. These may need to be reached by tunneling.
Extracting Alumina
The alumina can be isolated from bauxite by the 1888 Bayer process. There is a general description of this process in both the Encyclopedia Americana and the modern Encyclopedia Britannica. The bauxite is washed with a hot sodium hydroxide solution, converting the aluminum oxide to a "green liquor" of saturated sodium aluminate. The bauxite impurities (silica, iron oxides, and titanium dioxide) are less soluble and to some degree are filtered out, using cloth filters, as a "red mud."
Crystal "seeds" are added to the liquor, and the solution is allowed to cool, so that an aluminum hydrate (hydroxide) precipitates out. The aluminum hydroxide is then heated (EA says to 1093.3 deg. C (2000 deg. F) to produce the purified aluminum oxide (alumina) in the form of a sugar-like powder. The 1911 EB provides some additional information, such as the specific gravity of the sodium hydroxide solution (from which a chemist can calculate its concentration).
The modern Encyclopedia Britannica says that alumina, after purification for smelting purposes, usually contains less than 0.1% of other oxides.
Alumina Confidential
Our heroes will be pleasantly surprised to discover that most bauxite will not require a great deal of processing. If there is a lot of clay mixed in, it can be removed by "washing, wet screening, cycloning or hand picking." (International Aluminum Institute) The ore should also be crushed so as to increase the surface area over which the dissolution can take place.
The necessary temperatures are dependent on the nature of the bauxite mineral. Gibbsite requires just 135-150 deg. C; Boehmite, 205-245; and diaspore, even higher temperatures. Sodium hydroxide concentrations may also need to be increased to complete extraction of the more stubborn minerals. (Lancaster)
The real bugbear is silica content. Lancaster says that ores with more than 7% silica cannot be economically processed, but of course that depends on the prices and availability of alumina and aluminum. Bateman says the allowable silica is only 4.5%. (554)
Essentially, the problem is that the same sodium hydroxide which dissolves the alumina (aluminum oxide) also dissolves the silica (silicon dioxide). The dissolved silica reacts with sodium aluminate to form sodium hydroaluminosilicate, which is essentially a waste product. "As a result, 0.666 kg NaOH and 0.85 kg Al2O3 per 1 kg of silica are lost irrevocably." (Rayzman) Silica content varies from one deposit to the next, and hence it would be prudent to assay it before beginning mining operations.
There is a trick for processing high-silica ores, and it is mentioned in the modern Encyclopedia Britannica. The infamous red mud is heated with limestone (calcium carbonate) and soda to regenerate sodium aluminate, and the solution is fed back into the Bayer process. The residue, rich in silicate, is called "brown mud."
Another possible problem impurity is ferric oxide. Bateman says that bauxite ore should have not more than 6.5%. (554)
The amount of "red mud" waste generated for each ton of alumina produced depends on the ore, being just 0.33 tons for Surinamese bauxite, one ton for the Jamaican, and two tons for the Arkansan. Efforts have been made to find uses for it, or alternatively to treat as a low grade iron, titanium or aluminum ore and extract metal from it. (Chandra, Waste Materials Used in Concrete Manufacturing, 292)
From Alumina to Metallic Aluminum: The Hall-Heroult Process
In nature, aluminum exists in an "oxidized" state (combined with other elements, especially oxygen). To obtain the metal, the aluminum must be "reduced," usually in an electrolytic cell.
The cell (pot) is the reverse of a battery; a battery uses a chemical reaction to create an electric current; an electrolytic cell uses a current to force a chemical reaction to occur.
Inside the cell is an electrolyte, a fluid medium in which ions and electrons can move. Like a battery, a cell has two poles. The cathode provides the electrons, and they leave the cell at the anode. Reduction occurs at the cathode and oxidation at the anode.
There is a decent description of the Hall-Heroult process in the Encyclopedia Americana. The electrolyte is a melted (982 deg. C) solution of alumina in cryolite; no water is involved. (Cryolite is needed because the melting point of pure alumina is 2050 deg. C.)
The cryolite is held in a carbon-lined cast-iron shell, whose bottom serves as the cathode. Carbon rods are suspended in the melt; they are the anode. Current is passed from the anode to the cathode, reducing the aluminum oxide to aluminum, and releasing oxygen (which attacks the carbon rods, producing carbon dioxide).
The Hall-Heroult process was developed in 1886, and by 1892, it was routinely producing aluminum which was over 99% pure. (Wallace, 9) If you need material of, say, 99.9% purity, you will need to further refine it.
The principal inputs are: alumina (aluminum oxide), cryolite, electricity, and carbon (for the rods). We have already discussed alumina. What about cryolite?
Cryolite
The 1911EB says that, except for "mechanical losses," the initial charge of cryolite would last indefinitely. That makes sense, because cryolite acts a flux, reducing the melting point of the alumina, not a reactant. So, the amount of cryolite you need should be dictated just by how much alumina you want to process at one time.
In practice, as the encyclopedia implies, some cryolite is lost. However, there are some tricks (which Grantville must re-invent) for regenerating it once smelting is underway.
Natural Cryolite. Cryolite ("frost stone") is a mineral, sodium aluminum fluoride (Na3AlF6, so NaF:AlF3 is 3:1). 1911EB reveals that cryolite can be found "almost exclusively at Ivigtut (sometimes written Evigtok) on the Arksut Fjord in SW. Greenland." The article on "Greenland" notes that the mines are in the district of Frederickshaab, and provides a lovely map showing the location of Ivigtut, "Arsuk" Fjord, and a prominent landmark, Cape Desolation.
This information will be meaningful to down-time mariners, at least the whalers who frequented Greenlandic waters. Both the Cape, and a fjord of the correct shape, are shown on a map made by William Barents and published in 1598. (Braat)
Once our shivering crew of geologists is disembarked at Ivigtut, they know that they want to look for a "granitic vein running through gneiss," and that the cryolite is "accompanied by quartz, siderite, galena, blende, [and] chalcopyrite."
Once they locate the correct formation, they can look for the actual mineral. 1911EB sets forth its color, crystal form, cleavage, hardness, specific gravity and "flame test" result. Most distinctively, it is "nearly transparent on immersion in water."
A picture would still be nice, and there we are in luck. There is one in Hochleitner, Minerals: Identifying, Classifying, and Collecting Them (1992), which also mentions that it is found in pegmatites (probably more accurate than "granitic veins"), in association with siderite, fluorite, topaz and quartz. There are more photos in The Audubon Society Field Guide to North American Minerals, and Eyewitness Handbooks: Rocks and Minerals.
Whittaker states that cryolite "was traded as early as the beginning of the 18th Century amongst the native people of the western coast of Greenland." It is possible that the mineral was already known in 1632 to the Inuit Eskimos, in which they can be paid to guide an expedition to the source.
Still, it doesn't take much imagination to appreciate that mining cryolite in Greenland will be arduous and perhaps dangerous. According to 1911 EB, Deville toyed with the idea of using cryolite as an aluminum ore, but, "finding the yield of metal to be low, receiving a report of the difficulties experienced in mining the ore, and fearing to cripple his new industry by basing it upon the employment of a mineral of such uncertain supply," decided to produce aluminum instead by chemical reduction of aluminum chloride (see below).
Anyone seeking to raise money for a cryolite expedition will have to explain away Deville's mid-nineteenth century objections. One possible excuse would be that Deville was influenced by the French supply of bauxite, which might not be made available to other powers.
Synthetic cryolite. The uptimers know that cryolite can be synthesized (EA), and they at least know its chemical formula (Na3A1F6).
There are several chemists in Grantville and each will have a personal library of chemistry texts. It is within the realm of possibility that even a general chemistry book will explain how cryolite is made. For example, my own library includes a 1993 introductory college chemistry text which suggests adding sodium hydroxide and hydrogen fluoride to aluminum hydroxide (from the Bayer process). The reaction is 3NOH + Al(OH)3 + 6HF -> Na3AlF6 + 6H2O. (Ebling, 880)
But I think that a good chemist could probably work it out without this help.
Cryolite Confidential
More on Natural Cryolite. There are contradictory accounts about early mining at Ivittuut. What I think is most accurate is that there were two separate operations there. Julius Thomsen and George Horwitz obtained a license to mine cryolite in 1854, but didn't commence large-scale mining until 1859. In the meantime, in 1854-55, two other entrepreneurs extracted forty tons of silver-bearing galena (itself lead sulphide). (Greenland BMP) They decided, after six months, that the formation wasn't rich enough to warrant further work. (Whittaker)
About 3.7 million tons of cryolite ore, with an average cryolite content of 58%, were mined in the period 1854-1987. The mine closed because it had become uneconomic to compete with synthetic cryolite (see below).
Cryolite was initially wanted for use in a new process for production of soda (sodium carbonate), which Thomsen had patented in 1853. Thomsen decomposed cryolite with calcium hydroxide into calcium fluoride and sodium aluminate. He filtered off the former, and added carbon dioxide to get aluminum hydroxide and sodium carbonate. (Hornburg 31)
The Thomsen synthesis was used until the 1890s, when it was superseded by the 1864 Solvay ammonia-soda process. (Hornburg) The handwriting had been on the wall for several years, of course, and Thomsen's company, Oresund Chemiske Fabriker, had been trying to develop other markets: soap factories, manufacture of enamel, insecticide ("cryocide"), abrasives. (Hornburg; Grossman)
