BAUXITE. P. Berthier (1821) discovered that a non-plas tic, clay-like substance from Les Baux, near Arles (France) was practically devoid of silica, either free or in combination. His analysis of it indicated 52.o% alumina, 27.6% ferric oxide, and 20.4% combined water. Berthier referred to it as "le mineral des Beaux." A. Dufrenoy (1847) coined the word Beauxite "nom donne a l'alumine hydrate de Beaux." H. St. Clair Deville (1861), the father of the aluminium industry, corrected the spelling to Bauxite to correspond with that of the type locality Les Baux. Since then material of similar composition to that of Les Baux has been called Bauxite in Europe and America.
F. R. Mallet (1881) compared the iron clays of Ulster (Irish bauxite) with Indian laterite, suggesting a similar origin for both Max Bauer (1899) produced chemical evidence showing that some Seychelles laterite was identical with bauxite in composi tion. H. and F. J. Warth (1903) conclusively proved that, chem ically, the aluminous laterite of India was bauxite. L. L. Fermor (1916) considered that bauxite is not a mineral and should be regarded as a variety of the rock laterite. F. W. Clarke (1920) expressed the opinion that bauxite shades into laterite and there is no dividing line between them. C. S. Fox (1923) stated that the word bauxite implies chemical purity, and that it refers to aluminium ore composed almost entirely of the hydrated oxides of aluminium and ferric iron with the former element present in a commercially extractable amount, whereas the word laterite carries a genetic significance. As all bauxites are not of lateritic origin, a distinction should be recognized in bauxites of various origin. The terms Laterite Type and Terra Rossa Type have been provisionally suggested (1927). The relationship between the terra rossa of the Mediterranean seaboard and the bauxites of southern Europe awaits proof. There are some bauxites which evidently do not fit into either of the above types.
The mode of occurrence of bauxite varies with the type to which it belongs; with the primary or detrital character of the deposit; and with the tectonic disturbances to which it has been subjected. In India bauxite is intimately, although irregularly, associated with the primary laterite which caps many of the ba saltic plateaux of the peninsula. No Indian plateau of this nature exceeds an elevation of 5,000f t. In Nyassaland bauxite has been located on the Lichenya plateau at an elevation of 6,000ft., where it overlies decomposed syenite. Bauxite on the Gold Coast is found in genetic association with horizontal beds of shale on Mt. Ejuanema, and with steeply inclined phyllites and mica schists with auriferous quartz reefs on Mt. Supirri. In British Guiana bauxite occurs as the residual weathering product of dolerite and epidiorite. This association is also true of the bauxite in Surinam and French Guiana. In Arkansas (U.S.A.) bauxite overlies kaolinized nepheline-syenite. An inter-trappean bed of bauxite occurs among Tertiary basaltic lavas both in Ireland (Ulster) and Germany (Hesse Nassau). The bauxites of Australia appear to be similar to those of India.
Common characteristics of bauxite are a pisolitic structure and a mottled appearance. This is particularly true of lateritic bauxite. The pisolites may be pea-size and cemented or potato size and loose. The colour of the mass often varies from cream and grey to pink and yellowish or dark red. In the terra rossa bauxite the texture is frequently granular and impervious, unless a pisolitic structure exists. The exposed surface of lateritic bauxite is rough, often scoriaceous, simulating vesicular lava. In cliff sections lateritic bauxite may have a vermicular structure with variegated colours.
A common property of vermicular lateritic bauxite, which is soft when freshly excavated, is its tendency to harden on ex posure. Another peculiarity of lateritic bauxite is the readiness with which its debris re-consolidates. Recognizable minerals are rarely seen in hand-specimens of bauxite. Gibbsite is commonly distinguished in thin slices under the microscope, especially in the matrix of pisolitic bauxite. The specific gravity is variable, from 2.45 to 3.25. The hardness also differs, some bauxites being soft and clay-like, others hard and tough. There is no reliable test for ascertaining the quality of bauxite short of a .chemical analysis.
Typical lateritic bauxites average the following composition: Silica 0.25 to io%, titania 1 to io%, alumina so to 65%, ferric oxide 0.2 5 to 15 % and combined water 20 to 33%. This is true of material from Arkansas, British Guiana, the Gold Coast and India. Terra rossa bauxites are slightly different. Silica 0.25 to 15 %, titania 1.25 to 4%, alumina 56 to 7 5 %, ferric oxide 0. 5 to 2 5 % and combined water from 8 to 15 % . Such is the material from France, the Adriatic seaboard and the Balkans.
Appreciable percentages of titania characterize Indian bauxites formed from the Deccan basaltic lavas. The oxides of manga nese, chromium, zirconium and vanadium have been noted in certain bauxites. Cobalt, nickel, tin, gold and diamonds have been found in others. The smaller percentage of combined water in the terra rossa bauxite is usually characteristic. Neither type of bauxite, when heated, gives up its combined water steadily— large emissions occur about 260°C. and 67o°C. with complete dehydration near 950°C. The silica in bauxite is usually combined with alumina and should not exceed io% in ore intended for aluminium reduction. In European practice this limit is about 3% and in America 5 to 6%. All the alumina in bauxite is not soluble in hydrochloric acid. Bauxite with over so% soluble alumina con stitutes fair aluminium ore. Material with more than 4% ferric oxide is not attractive to alum manufacturers.
The mode of formation of lateritic bauxite is the same as laterite (see LATERITE). The current opinion is that laterite represents the residual weathering product of rocks containing aluminium and iron silicates. W. A. K. Christie and C. S. Fox (1923) consider that Indian bauxites are indicative of the opera tion of capillary pressures, dialysis and electrolytic migration during laterite formation. To electrokinetic phenomena are largely ascribed the removal of the silica and the separation of the col loidal aluminium hydroxides from those of ferric iron in the de composed rock. Terra rossa bauxites are presumed to have the same genesis as terra rossa.
The world's annual production of bauxite exceeds one million tons. Over 6o% of this output is used for the extraction of aluminium. Another 15 % of the production is absorbed in the chemical industry, primarily for the preparation of aluminium hydroxide, but also for making sodium aluminate, aluminium chloride, aluminium sulphate and alum. The remainder of the bauxite output (about 15%) is used for the production of ab rasives (emery) and refractories; in the manufacture of alumina (fused) cements; and for kerosene purification. (C. S. F.) Bauxite in the United States.—The manufacture of bauxite elements is becoming an important industry. It was first located by Edward Nichols in 1883 in north-western Georgia. This ore of aluminium is claylike in appearance, some of it being soft and friable and some of it hard and brittle, ranging in colour from white and pink into brown and deep red.
Bauxite is generally formed through the weathering of certain igneous and sedimentary rocks, such as granite, syenite, basalt, limestone and clay. The term "bauxite" is applied to a mixture of hydrates of aluminium with impurities. The monohydrate of alu minium is called diaspore. The tri-hydrate is called gibbsite. Chemically pure diaspore and gibbsite are seldom found in nature and the term "bauxite" is applied to the impure varieties of these minerals, as well as to the mixtures of the two.
Generally speaking the bauxites of North and South America are tri-hydrates with varying amounts of silica, iron oxide and titanium oxide as the chief impurities; while the European ores, for the most part, are mixtures of mono-hydrates and tri-hydrates, also with silica, iron oxide and titanium oxide as the chief impuri ties. Typical American bauxite will analyze approximately 6o% aluminium oxide, called alumina, 5 % silica, 3% iron oxide, 3% titanium oxide and 29% chemically combined water. The free moisture in the ores as mined is generally driven off by heating in kilns before marketing.
Bauxite occurs in most countries of the world, with a tendency towards tropical or semi-tropical districts. The mines of southern France and those of southern United States have been longest in operation and have produced the largest amounts of bauxite, al though very extensive mining operations have been carried on in British and Dutch Guiana, in western Hungary and in Istria, Dalmatia and other Adriatic countries, where immense deposits of bauxite are found. Large deposits are known to exist also in central and western Africa, Australia, Rumania, India, Greece and Brazil, as well as in matey other countries. The known deposits are of sufficient magnitude to supply the world's requirements for a very long period of time. Moreover, new discoveries are being reported at frequent intervals.
Aluminium was a rare and expensive metal, obtained from cryo lite, untjl economical methods for its extraction from bauxite were discovered. In the year 1886 Charles M. Hall, of Oberlin, O., while a student at Oberlin college, discovered an electrolytic proc ess for extracting aluminium from alumina. Bauxite being the most readily available source of alumina, this material became recognized as the natural raw material for the metal aluminium. In the year 1889 patents were issued to Charles M. Hall covering his invention, and about this same time M. Paul Heroult of France invented a similar process, which has formed the basis of Euro pean development in aluminium manufacture.
Metallic aluminium is made from bauxite by first removing the impurities from the latter, thus producing alumina, which in turn is treated in an electrolytic bath which separates the metal from the oxygen. Four or five tons of bauxite are required to produce one ton of metallic aluminium.
The abrasive industry uses large quantities of bauxite, which in the process of manufacture is fused in specially designed electric furnaces. Considerable quantities of bauxite are also used for making quick-hardening cement, in the refractory industry, in manufacturing aluminium chloride used in petroleum refining, and for making aluminium sulphate, which is largely used in paper making and water purification. (W. C. N.)