Mineral Facts and Problems: 1960 Edition Page: 20
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MINERAL FACTS AND PROBLEMS, ANNIVERSARY EDITION
mud, which contains the complex sodium alu-
minum silicate compound, is sintered with
limestone and soda ash, then leached with
water to recover alumina and soda. The brown
mud residue has a composition, on a dry basis,
somewhat similar to that of Portland cement.
The additional cost required in capital in-
vestment, raw materials, and processing by the
combination method is partly offset by higher
recoveries of alumina and soda and partly by
lower mining costs. A major advantage of
the combination process is the decreased need
for selective mining, as high-silica bauxite,
previously regarded as unsuitable for alumina
production, can be used. The upper limit of
silica for use in this process is now about 15
percent; however, in practice, bauxite contain-
ing as high as 25 percent silica is mined and
blended with low-silica ore in proportions that
will give a feed material of approximately 12
to 13 percent silica. The combination process
is used in the two plants in Arkansas and in
plants in the U.S.S.R. and China (21).
In 1952 the American Bayer process was
modified to treat the high-iron, low-silica
bauxite of Jamaica. The major modifications
resulted from difficulties in filtration of the red
mud slurry and from the small amount of
boehmite in the ore (19).
In the U.S.S.R., alumina is extracted from
nephelite flotation concentrate containing about
30 percent alumina, obtained as a byproduct
of apatite from deposits in the Kola Peninsula
(21). The process used is a variation of
the lime-soda sinter method, but no soda is
added as it is already present in the feed.
In Norway alumina is extracted commer-
cially from high-iron bauxites by the Pedersen
smelting process. In this process, bauxite,
limestone, coke, and iron ore are smelted in an
electric furnace to produce pig iron and a
calcium aluminate slag containing 30 to 50
percent alumina. The slag is leached with
sodium carbonate solution, and the alumina
trihydrate is precipitated by carbon dioxide.
During World War II the process was also
used at a Swedish plant to treat andalusite.
During World War II the U.S. Government
erected four demonstration plants to test the
following alkaline and acid processes:
1. Laramie, Wyo.-Anorthosite calcined with lime-
stone and soda ash; sinter leached with soda solution
to extract sodium aluminate; alumina trihydrate pre-
cipitated by carbon dioxide and calcined to alumina
2. Harleyville, S.C.-Clay sintered with limestone;
sinter leached with sodium carbonate solution to form
sodium aluminate; alumina trihydrate precipitated by
carbon dioxide and calcined to alumina.
3. Salt Lake City, Utah.-Alunite roasted, then
leached with sulfuric acid solution; alumina and po-
tassium sulfate recovered from the alum.
4. Salem, Oreg.-Calcined clay leached with am-
monium bisulfate to form an alum; converted to alu-
minum hydroxide and calcined to alumina.
After the war the plants were shut down
before the processes had been adequately
tested. In 1952 to 1954 the plant at Laramie
was reactivated by the Bureau of Mines and
successfully operated at an output of 30 tons
of alumina a day. The cost of producing
alumina from anorthosite or other aluminum
silicates, at the rate of 1,000 tons a day, was
estimated to be one-fourth to one-half again
as much as the cost of producing alumina from
By 1956 all the Government-erected plants
had been sold to industry to be used for other
More than 90 percent of the alumina pro-
duction is consumed by the aluminum indus-
try. Alumina also is used for abrasive, refrac-
tory, or chemical applications in which a high
degree of purity is desirable. Its minor uses
include production of the nose cones of mis-
siles, artificial sapphires, and thread guides for
Over 90 percent of the bauxite consumed in
the United States is used by 6 alumina plants
and the remainder by about 150 abrasive,
chemical, refractory, and other plants. Fused
bauxite is used in bonded or coated abrasives
or as abrasive grain. Since 1949 the refractory
industry has used increasing quantities of
bauxite as a substitute for diaspore clays. Alu-
minum sulfate and other aluminous chemicals
are produced from bauxite for treating water
and sewage, dyeing, tanning leather, and siz-
ing paper. Bauxite is also used in the produc-
tion of high-alumina cement, in low-density
insulating materials, as an adsorbent or cat-
alyst by the oil industry, and as a flux in
making steel and ferroalloys.
Most bauxites contain small quantities of
gallium and vanadium, which dissolve in the
Bayer process liquors. Gallium is recovered in
the United States by one company, and vana-
dium is recovered in a French operation. In
Norway iron is produced as a byproduct of
the Pedersen process. In the U.S.S.R. potash,
soda, and cement are produced as byproducts
in recovering alumina from nepheline syenite.
RESERVES (3, 7, 13, 21)
The earth's crust averages 15 percent alu-
mina, but the commercial ore (bauxite) usu-
ally contains more than three times this pro-
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United States. Bureau of Mines. Mineral Facts and Problems: 1960 Edition, report, 1960; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc38790/m1/28/: accessed July 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.