A Byproduct Metal
by A. P. Thompson and H. R. Horner
though only recently publicized, is not
G ALLIUM,
a newly discovered element. The story of the
recognition of its existence and its actual identification and isolation is fascinating. In 1861, MendelE~eff presented his famous paper "The Relation of
the Properties to the Atomic Weights of the Elements" before the Russian Chemical Society. Subsequently, he predicted properties of a number of
undiscovered elements. Three he designated ekasilicon, ekaboron and ekaaluminum because of their
similarity to the elements indicated. These later became known as germanium, scandium, and gallium,
respectively, and were discovered during his lifetime. Lothar Meyer's work done contemporaneously
in Germany covered much the same ground, but
lacked the striking originality and boldness of concept and expression.
Gallium was the first of the three eka elements
to be identified and isolated. This was accomplished
in 1875 by the French chemist Lecoq de Boisbaudran who named the element in honor of his native
country. This was the culmination of a brilliant 15year study of spectra during the course of which he
developed his own law with regard to the periodicity of the lines of similar elements.
Boisbaudran in the early 1860's decided that there
was an element missing between aluminum and
indium. He predicted its major spectral lines and
undertook the search. In 1874, he began the investigation of some zinc blende from the Pyrenees and
according to his own words: "Between three and
four in the evening of August 27, 1875, I found indications of the probable existence of a new elementary body ... "." In November 1875 he isolated
more than a gram of the metal and within the next
2 or 3 years produced about 75 g.
Similarity between the properties, both chemical
and physical, predicted for ekaaluminum by Men-
delE~eff
and those actually found for gallium by
Boisbaudran is most striking; for example, a specific
gravity of 5.9 g per cc was predicted and 5.94 was
found.
As might be expected from its proximity to aluminum, gallium is widely distributed in the earth's
crust. It exists in roughly the same quantity as
lead, about 15 g per ton of earth! Lead, however, is
concentrated at favorable spots while gallium is almost universally disseminated but nowhere in significant commercial concentration. Insofar as the
authors are aware, there is no mineral that contains
gallium as a major constituent-the nearest exception being germanite, a complex zinc-copper-arsenic-germanium sulphide found in the copper ores
of Mansfeld, Germany, and in the Tsumeb copperlead mine, Southwest Africa. This mineral usually
contains from 0.1 to 0.8 pct gallium with one specimen reported to have contained as high as 1.85 pct.
To the extractive metallurgist, the question becomes one of determining where suitable natural or
artificial concentrations may be found. The periodic
table suggests that gallium might be expected in
ores or minerals containing zinc, aluminum, and
germanium. Boisbaudran's original work was done
on zinc ores and most gallium produced to date has
come from such materials.
Gallium is frequently associated with germanium
in the comparatively rare mineral germanite and in
coals. Unfortunately germanium is rare, and
materials containing it must be discounted as a
source of gallium. Further, almost any sample of
earth or clay, of which of course aluminum is a
major constituent, will show a gallium content on
A. P. THOMPSON is Director of Research, and H. R. HARNER is
Chief Chemist for The Eagle-Picher Research laboratories, Joplin,
Mo.
FEBRUARY 1951, JOURNAL OF METAl5-91
Fig. 1. Process used to recover gallium from lithopone
plant residues.
the spectrograph often in the order of 50 g per ton
or considerably over the average for the earth's
crust. It is also found in bauxite, the source of commercial aluminum and accumulates in the circulating liquors of the Bayer process from which it may
be recovered.
In Missouri-Kansas-Oklahoma zinc ore concentrates the metal averages about 0.005 pet or 45 g
per ton. It is present in the zinc sulphide mineral itself. Clean sphalerite crystals of four common types
were selected and the gallium content estimated
spectrographically. The results in pet gallium were:
"Black Jack", 0.005; "Rosin Jack", 0.02; "Ruby
Jack", 0.01; "Amber Jack", 0.001. The more highly
colored sphalerites tend to carry more of the metal.
The gangue also was tested spectrographically and
contained less than 0.0005 pet gallium, further proving the element to be in the zinc sulphide crystal.
Gallium is closely tied to the Tri-State lead and
zinc field of Southwest Missouri; Southeast Kansas,
and Northeast Oklahoma. During the early part of
the century, W. George Waring, studying the zinc ore
of the district, proved the presence of gallium and
other rare metals.
The story of gallium in the Tri-State district began in 1915 with the early work of F. G. McCutcheon,
now rrianager of the Eagle-Picher Zinc Smelter at
Henryetta, Okla. At that time he was chief chemist
of the Bartlesville Zinc Co. of Bartlesville, Okla.,
producing high grade zinc by redistilling prime
western spelter made in large part from Tri-State
ore. The leady heels or residuum left in the retorts
was cast in slabs and stacked outdoors pending
shipment to a lead smelter. Following a rain, McCutcheon noticed beads or droplets of metal exuding
from the slabs." On analyses these beads proved to
92-JOURNAL OF METALS, FEBRUARY 1951
be an alloy of about 94 pct gallium and 6 pet indium.
The only explanation for the formation of the beads
of metal was that the heels were a complex mixture
of metals including sodium and calcium. The latter
are believed to have reacted with the rain-water to
release the beads of rare metal alloy. McCutcheon
subjected several slabs to steam and reproduced the
phenomena, collecting 300 g of alloy from one 700lb lot of heels so treated.
Working over a period of years, he developed recovery processes and produced the world's first
pound of gallium metal. He then located other TriState zinc residues containing gallium and continued
its recovery on a small scale as a hobby. By 19.44,
he had recovered some 6000 g of the metal.
The Eagle-Picher Research group at Joplin meanwhile had become interested in gallium recovery
from still a different Tri-State zinc ore residue. The
Eagle-Picher lithopone plant at Argo, Ill., was processing 10 tons per day of roasted zinc ore and producing about 1000 lb per day of iron mud leach
residue. McCutcheon pooled his knowledge with
that of the research dept. and a process shown in
Fig. 1 was developed for handling this material. It
consisted of a caustic leach that dissolved aluminum
and gallium compounds and some silica; precipitation as hydroxides; filtration and dehydration of the
cake; hydrochloric acid leach; precipitation as hydroxides; solution of cake in hydrochloric acid; ether
partition; electrolysis in caustic electrolyte; and
fractional recrystallization of the recovered metal.
The process is complicated, expensive, and to get
good recoveries of high purity metal, requires meticulous attention to detail. It must be remembered
that gallium is not a noble metal, but in the periodic
table is directly below aluminum, an element whose
metallurgy has proved most difficult. Since only
0.07 pet gallium is concentrated in the iron mud
leach residue, associated with about 10 pet aluminum
and 15 pet iron as well as variable amounts of a
great many other elements, the difficulty and expense of the separation can easily be realized.
Gallium is $2.50 to $7.50 per g depending on the
quantity purchased. A new recovery method must
be developed for each new gallium raw material.
Furthermore, use of strong hydrochloric acid is almost an essential step of any recovery process, introducing a severe materials-of-construction problem,
especially on a pilot plant scale.
The chemistry of gallium is comparable to that of
aluminum. Therefore, the complicated character of
the various chemical and metallurgical steps used in
the recovery of the element is not surprising. The
chemistry of gallium also bears a marked resemblance to that of the two succeeding elements, indium and thallium. The stability of the compounds
of these four elements decreases with increasing
atomic weight. As a corollary, the ease of reduction
to the metal increases with the atomic weight. All
are permanent in air at ordinary temperatures, but
when heated develop a protective oxide coating.
The normal hydroxides are amphoteric in the case of
the first three elements and basic only in the case
of thallium. Like aluminum, gallium forms alums.
The usual valence is three. With increasing atomic
weight, the tendency to form compounds of lower
valence becomes more marked, this property being
most noticeable in the case of thallium. Aluminum
normally shows no valence other than three while
gallium forms a number of divalent and even some
monovalent compounds.
ment, melting at 29.75"C (85.5"F) (about 70°C
higher than mercury) and boiling at 1983°C
(360l0F)."here
is some difference of opinion on
the boiling point, values up to 2100°C and higher
being reported. Visual proof of the low melting
point is shown in Fig. 2. The boiling points of
its congeners, aluminum and indium, are of the
same order while that of thallium is about 500°C
lower. The vapor pressure of gallium remains quite
low at comparatively high temperatures, being only
1 mm at 1315OC (2399°F).
Gallium is one of the few metallic elements that
expands on solidifying. The liquid density at 29.8"C
is 6.095 g per cc while the solid density at 20°C is
5.907 g per cc, roughly a 3 pct expansion on solidification-almost
as great as that of bismuth, 3.3 pct.
This property provided an interesting problem in the
packaging of the metal for sale. If packaged directly in a glass container as the liquid metal, expansion on solidification breaks the container. On
warming a little, the gallium melts, and flowing like
mercury, is often lost or contaminated. One supplier
packages the liquid metal in rubber bulbs. EaglePicher supplies the metal as clean crystals dipped
from the melt while cooling-, packed in sealed Pliofilm bags. Should the metal accidentally become
warm and melt it cannot escape. On resolidifying,
the elastic Pliofilm prevents rupture and loss.
Gallium crystallizes in the orthorhombic system,
and beautiful specimens are produced. The exact
shape of the crystals varies from thin square plates
to thick and massive spear points. A typical example is shown in Fig. 3.
As might be expected from its position in the
periodic table, gallium is a chemically active metal.
The literature contains an imposing list of alloys
and solid solutions with other metals.
Since certain suggested uses for gallium are based
upon its long liquid range and low vapor pressure
at elevated temperatures, the matter of reactivity
and of a suitable container is important. The Atomic
Energy Commission, which is much interested in the
possible use of liquid metals as heat-transfer media,
recently has released information on this subject.
The section on gallium discusses its properties in
this connection quite thoroughly. The introductory
paragraphs dealing with materials to handle liquid
gallium are most interesting: "
"Gallium is more aggressive in its attack on
most solid metals at a given temperature than any
other molten metal that has been tested. It can be
contained successfully a t high temperatures only
in some of the refractory oxides, quartz, graphite,
and such metals as wolfram, and tantalum.
"The mechanism of attack on solid metals by
gallium differs widely from one metal to the next,
Fig. 2. Molten gallium can be handled with impunity as the melting
point is below body temperature.
and from one temperature to the next. With tantalum at 600°C (1112°F) for example, the attack
occurs chiefly through solution, although at 800°C
(1472°F) there is perceptible evidence of diffusion into the solid metal to form a compound.
Molybdenum reacts with gallium at these temperatures to form more than one reaction product,
one of which is a solid solution. Wolfram, however, is not attacked by gallium at temperatures
up to 800°C (147Z°F), although it might be expected to behave like molybdenum since compounds of molybdenum and wolfram are isomorphous.
"Although gallium does not readily attack most
ceramics, it tends to wet magnesia under certain
conditions, but does not wet beryllia or alumina.
An anodized coating on aluminum, however,
offers no barrier to penetration by gallium even
at moderate temperatures."
Important physical properties of gallium are
summarized in Table I.
A wide variety of uses has been suggested for
gallium, ranging from low melting-point alloys to
the treatment of bone cancer.'' The first use proposed
was as fill material in high temperature thermometers. Practical difficulties arose such as the
Fig. 3. A crystal over 3 in. long formed by seeding super-cooled gallium with solid gallium.
FEBRUARY
1951, J O U R N A L O F METALS-93
Table I-Physical Constants of Gallium
Atomic No.
Atomic Weight
Isotope Abundance
::1
69.72
61.2
Mass No. 09. l-'el
:18.8
Mass No. 71. Pl'l
Crystal Structurl'
Density -- 20"C (5)
29.65"C (s'
29.SOC 11,
, G per
Orthorhombic
5.907
5.9037
0.0948
('I
, G per ('('
. G PCI'
ec
Specific Volume at Melting Point. ISolzdi
I Liquirtl
Melting Point
Boiling Point
Latent Heat of Fusion ._- G-cal per g
Btu per Ib
0.1694
0.1641
[85.5"F) 29.75"C
[3601 "F) 1983"C
19.16
:14.5
Latent Heat of Vaporization, G-cal per g
Heat of Combustion (2 Ga + 3 0 = Ga,.o,) , Kcal
Vapor Pressure - 1315"C (2399"F), Mm of Hg
1726"C (3139"F), Mm of Hg
1983'C 1.3601 "F), Mm of Hg
Specific Heat -
solid ,16' to 24.2"C, Cal per g
liquid, 21" to 130"C, Cal per g
Linear Thermal Coefficient of Expansion -0" to 30"C, Cm per em
Volume Resistivity at 20"C, Microhm-em
Volume Conductivity at 20"C, (Copper-100 Pet!, Pet
Volume Resistivity of Liquid at 46.1 "C, Microhm-em
Magnetic Susceptibility at 18"C, Cgs units
Reflectivity - 4360 A, Pet
5890 A, Pet
Electrochem ical Equivalents
Viscosity
~-
Ga· , '. Mg per coulomb
G peramp-hr
Lb per 1000 amp-hI'
77"C . Dyne-sec per sq cnl
11000C. Dyne-sec per sq em
1014
259
1.0
100
760
0.0926
0.0977
1.8xlO-:'
56.8
3.04
28.4
0.24x10-il
75.6
71.3
0.24083
0.86698
1.91137
0.01612
0.00578
lack of availability of quartz glass tubing in the required bores and OD sizes. It is understood that
some thermometers have been produced but the
cost has been exceedingly high and the results far
from satisfactory.
The use of gallium as a backing material for
optical mirrors has been suggested, as it reflects a
high percentage of the incident light: For certain
purposes in atomic and astrophysical spectrum research work the gallium lamp has proved quite useful. The Bureau of Standards reported satisfactory
service from quartz vacuum lamps using Ga-Zn and
Ga-Cd mixtures to replace mercury.
The Atomic Energy Commission has investigated
gallium as a possible heat-exchange medium." Its
favorable thermal characteristics, particularly the
long liquid range and low vapor pressure, encourage
consideration of its use in extracting heat from a
high level, since any atomic energy power plant
must use temperatures considerably above those of
conventional steam-power plants if even a small
part of the potential energy is to be utilized. However, gallium's considerable reactivity as expressed
in terms of attack on possible container materials
thus far has delayed its application in this field.
The addition of a small percentage of gallium
oxide to relatively high grade uranium-base material in the form of the oxide, and subsequent
fractional distillation in the dc arc, has made it
possible to determine 33 volatile impurity elements
at concentrations as low as a fraction of a part per
million.' This procedure is said to have been employed by the Manhattan Project for control and
inspection in the production of high-purity uranium
metal, oxides, and salts.
.
One principal use of gallium reported by the Germans is in organic synthesis: Its chloride salts act
as catalysts in the Friedel-Crafts reaction. In some
cases a smaller amount of catalyst is required than
when other chloride salts are used; in other cases a
94-JOURNAL OF METALS, FEBRUARY 1951
higher yield is obtained or the reaction time is
shortened.
Low-melting point alloys are formed by gallium
with indium, tin, and aluminum," and may find use
in fire alarm systems. The addition of 2 to 4 pet
gallium improves the mechanical properties of
aluminum. Gallium increases the hardness of
aluminum ternary alloys. An iron alloy containing
3 pct gallium and 14 pct nickel resembles beryllium
and titanium steels in hardenability. The addition
of 4.5 pct gallium will harden magnesium on heat
treating. Gallium also may find a place in electrical
contact alloys.
Prior to 1932 gallium was available only in small
quantities for laboratory research purposes at about
$250 per g. In 1932 the Chemical Manufacturers'
Assn. of Leopoldshall (Germany) began to recover
gallium from the residue from the Mansfeld copper
schists. By 1937, the annual production had risen
to about 50 kg and the price had dropped to about
$2.50 per g.' Directly prior to World War II, German
production was about 300 lb per year:
During the period 1943 to 1945, the Anaconda
Copper Mining Co. in connection with its recovery
of indium, produced several thousand grams of gallium but have reported no output since then. l l The
price is said to have been about $3 per g. In 1946,
The Eagle-Picher Co. was the only producer. In
1947, Aluminum Co. of America entered the field lJ
and in 1948 the Saratoga Laboratories, Inc., started
production." In 1948 the price for 99.9 pct gallium
metal was $2.50 to $5.00 per g or $1135 to $2270 per
lb, and U. S. production was estimated to have been
about 200 lb." Actual shipments probably did not
exceed 100 lb. Since 1946, a license has been required for the export of the metal.
References
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(1934). 217. Easton, Pa. Mack Printing Co.
'L. H. Ahrens: Occurrence of the Elements. South
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W. F. Hildebrand and J. A. Scherrer: Recovery of
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Ind. & Eng. Chem., 8, 225 (1916).
• Richard N. Lyon et al: Liquid Metals Handbook
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5 Erich Einecke: Das Gallium (1937). 127. Verlag von
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