Alunite has historically been used as a source of potash alum and aluminum sulfate. While its use has declined, it is being reexamined as a potential non-bauxite source of aluminum. Alunite deposits are found in the western US, Mexico, South America, Europe, Asia, and Australia. Processes have been developed to extract alumina from alunite along with potassium sulfate and sulfuric acid as byproducts, but high costs have prevented widespread commercialization.

1. METALURGIA
DE
NO METÁLICOS

2. ALUM
ALUNITE
HALOTRIQUITE

3. ALUNITE.
• Alunite, KAL3(SO4)2(OH)6 , was used from the 15th century until early in
the present century as a source of potash alum and aluminum
sulfate.
• Since early in this century its use for this purpose has declined to
virtually nil with acid treatment of bauxite or clay replacing alunite
as a source of alum.
• Durint the First World War alunite served as an emergency source of
potassium sulfate fertilizer in the United States and Australia.
• More recently, alunite has been investigated as a nonbauxite ore of
aluminum, with potassium sulfate and sulfuric acid as recoverable
byproducts.
• The US has the largest aluminum producing and fabricating industry in
the world but imports more than 90% of its aluminum-bearing raw
materials.
• This chapter reviews the status of alunite as a potencial source of
aluminum with by product fertilizer, and the resources available to
support this industry, whenever this becomes economically feasible.

4. HISTORICAL BACKGROUND
Alunite has received little attention until recently, yet for centuries it
held a higher place than many of the industrial minerals considered
essential today.

5. GEOLOGY.
• Alunite occurs in a variety of deposits ranging in size from mere
nodules and lenticles a few centimeters across to huge masses
comprising several hundreds of millions of tons of altered rocks
containing 30 to 40% alunite.
• Nearly pure alunite occurs in hypogene veins.
CLASSIFICATION OF DEPOSITS.
• Veins:
• Nodules and seams in argillaceous sedimentary rocks:
• Replacement bodies in solfatarically and hydrothermally altered
volcanic, subvolcanic, and hypabyssal intrusive rocks:

6. GEOLOGY.
MINERAL AND CHEMICAL COMPOSITION AND OTHER
CHARACTERISTICS.
– Pure alunite (KAl3(SO4)2(OH)6) theorically contains:
• 11.37% K2O
• 36.92% Al2O3,
• 38.66% SO3
• 13.05% H2O.
– Analyses of some crystals may approach this composition, but most
natural alunites contain some sodium substituting for
potassium.
• If the atomic ratio Na:K is equal to or greater than 1, the mineral
is called natroalunite.
• If the Na:K ratio is greater than 1:3, the material may be called
sodian alunite.

7. GEOLOGY.
MINERAL AND CHEMICAL COMPOSITION AND OTHER
CHARACTERISTICS.
• Typically, the alunite occurs in fine-grained altered volcanic or
subvolcanic rock, or coarser hypabyssal intrusive porphyries.
• The altered rock is composed principally of microcrystalline quartz
and rutile or anatase.
• Clays and other caustic-soluble silica minerals are common
alteration constituents and may be troublesome in the Alumet
process.
• Identification of alunite-bearing rocks in the field is not easy
because altered volcanics look very much alike whether rich in alunite
or in kaolinite, sericite, or other alteration minerals.
• Alunite has a specific gravity of 2.82, slightly higher than quartz and
clays, and so a greater heft commonly is a good clue to presence of
high alunite content in the rock.
• Vein alunite commonly is flesh-pink, but color is a poor criterion in
identifying alunitized rocks, wich may be off-white, gray, yellowish,
brownish, or pinkish, usually mottled or variegated, and iron-stained.

8. GEOLOGY.
MINERAL AND CHEMICAL COMPOSITION AND OTHER
CHARACTERISTICS.
• Microcrystaline quartz is a major contituent in typical ore-grade
rocks, which is tenacious, hard, and abrasive, with dull luster and an
uneven to subconchoidal fracture.
• Table 1 shows the composition of theoretically pure (KAl3(SO4)2(OH)6),
one sample of high-grade vein from Marysvale, UT.

10. GEOLOGY.
ZONING OF REPLACEMENT DEPOSITS.
• Four principal zones generally are recognized:
– Siliceous core or cap
– Quartz-alunite;
– Argillic;
– And propylitic.

11. RESOURCES
US ALUNITE RESOURCES.
– Utah,
– Nevada,
– Arizona,
– New Mexico,
– Colorado,
– Other:
• California,
• Washington
• Texas.

12. RESOURCES
FOREING ALUNITE RESOURCES.
• USSR
• Asia
– Republic of China
– Japan
– Korean
• Europe
– Italy
– France
– Spain
– Greece
– Bulgary.
• Mexico and South America
– Mexico
– During the 1950s,, a nationwide investigation of alunite deposits in
Mexico was undertaken.

13. RESOURCES
FOREING ALUNITE RESOURCES.
• Mexico and South America
– Alunite was recognized as a common constituent in hydrothermal
kaolin deposits in Mexico during the 1940s.
– Experiments were conducted at the University of Guanajuato,
and several processes were developed on a laboratory scale for
extraction of potassium fertilizers and alumina from mexican
alunitic rock.
– In the 1970s an alunite-processing plant was projected for
construction at Salamanca, Guanajuato, to be fed by material
from deposits in the Juventino Rosas district northwest of
Celaya, Guanajuato, but the projects was suspended.
– Probably the most promising alunite resources recognized in
Mexico so far are in Guanajuato, but occurrences are numerous in
other states, although no single deposits has yet been proven to be
of a size and grade that would support a plant of economic scale.

14. RESOURCES
FOREING ALUNITE RESOURCES.
– Mexico and South America
– Argentina
– Bolivia
– Perú
– El Salvador and Chile

15. RESOURCES
FOREING ALUNITE RESOURCES.
– Australia.
– Other countries.
• Iran
• Turkey
• Pakistan
• Israel
• Tanzania
• New Zealand
• Sumatra
• Philippines.

16. TECHNOLOGY
• The technique for making potash alum and aluminum sulfate from
alunite was developed at Tolfa, Italy, during the 15th century and was
used with little change into the 20th century.
• The importance of alunite today lies not in its historical use as a raw
material for making alum, but in its potential for becoming a non-
bauxite ore of aluminum with fertilizer by-products.
ALUMINA FROM ALUNITE PROCESSES.
• KALUNITE PROCESS.
• UG PROCESSES.
• ALUMET PROCESS.

17. TECHNOLOGY
ALUMINA FROM ALUNITE PROCESSES.
• KALUNITE PROCESS:
– The Kalunite process involves reaction of dehydrated alunite
with a solution of sulfuric acid and potassium sulfate to produce
potassium alum (K2SO4.Al2(SO4)3).24H2O
– The potassium alum is heated under pressure to make water-
insoluble basic alum (K2SO4.3Al2O3.4SO3.9H2O, with liberation of
K2SO4 and H2SO4 in solution.
– Calcination of the basic alum in a multiple muffled-hearth furnace
produces a mixture of K2SO4 and Al2O3.
– The sulfate is precipited from solution as potash fertilizer; the
insoluble aluminous residue is calcined to Bayer grade alumina.
– The Kalunite process represented a significant technological
development in the utilization of alunite as an ore of aluminum,
but was plagued with problems of materials handling, high costs,
high energy use, and impurities in the alumina.

18. TECHNOLOGY
ALUMINA FROM ALUNITE PROCESSES.
• UG PROCESSES:
– Three methods for extracting alumina from alunitic rock with
simultaneous production of fertilizer byproducts have been
developed on a laboratory and small pilot-plant scale at the
University of Guanajuato, state of Guanajuato, Mexico.
– The three methods differ only in details.
– The basic UG process commences with dehydroxylation of
crushed alunite ore at temperatures below 700º C, followed by
reaction with ammonia gas in a boiling aqueous suspension.
– The filtrate from this treatment is a solution of potassium and
ammonium sulfates; the filter cake is said to be boehmite, an
aluminum monohydrate.
– The syntetic boehmite (Al2O3.H2O) is reacted with SO2 in an
aqueous suspension at temperatures below 75º C, forming soluble
aluminum sulfite (Al2O3(SO2)3(H2SO3)n, n>1.

19. TECHNOLOGY
ALUMINA FROM ALUNITE PROCESSES.
• UG PROCESSES:
– Treatment of unreacted sludge with added H2SO4 makes a
solution of aluminum sulfate (Al2(SO4)3), which is reacted with the
previously obtained aluminum sulfite solution, precipitating a mixture
of nearly pure aluminum hydrate and aluminum sulfate; SO2 off
gas is recycled in the process.
– The mixed aluminum sulfate-hydrate precipitate then is calcined
driving off SO3, SO2, and O2, leaving a Bayer-grade alumina residue.
– The offgases are recycled to make the H2SO4 used in the previous
steps.
– Valuable byproducts are potassium and ammonium sulfate
fertilizers.

20. ALUMINA FROM ALUNITE PROCESSES.
• UG PROCESSES:
– The second UG process is reported to be a simplification of the
first intended for use on higher-grade ores, where several reaction
and filtration steps can be bypassed.
– The third UG process entails treatment of the impure synthetic
boehmite (Al2O3.H2O), produced as filter cake in the first an
basic UG process, by a Bayer-type alkaline (NaOH) leach
instead of with sulfur dioxide gas.
– The resulting sodium aluminate solution is seeded to
precipitate synthetic gibbsite (Al2O3.·H2O) as in Bayer process.
– The alumina trihydrate is washed and calcined to produce Bayer-
grade alumina sand..
TECHNOLOGY

21. TECHNOLOGY
ALUMINA FROM ALUNITE PROCESSES.
• ALUMET PROCESS:
Principal steps in the process are:
– Crush and grind quartz-alunite ore to minus 20 mesh;
– Dehydrate in a fluidized-bed reactor at 500 to 600º C;
– Roast dehydrated ore in reducing atmosphere in fluidized bed
reactor, driving off SO2, which is passed to a sulfuric acid plant for
conversion to H2SO4;
– Leach roasted product in an aqueous solution to remove K2SO4;
– Filter, pass K2SO4 liquor to crystallizer-compactor-dryer unit for
production of fertilizer-grade potassium sulfate;
– Pass filter cake, which consists mainly of fine quartz sand and
amorphous alumina to Bayer-type caustic (NaOH) leach ;
– Filter and pass silica sand residue to tailing;
– Desilicate and filter sodium aluminate solution;
– Seed and precipitate aluminum trihydrate;
– And calcine precipitate to Bayer-grade alumina. FIG. 4

22. TECHNOLOGY

23. TECHNOLOGY
MINING.
• Alunite veins at Marysvale, UT were mined by underground drifts and
adits and also by small open pits and trenches during the First World
War, when the high-grade vein matter was used to provide potassium
sulfate fertilizer.
• Alunite at Tolfa, Italy, was mined for nearly five centuries by large
open trenches and quarries.
• Although alunite is not presently mined in the United States, open pits
on a scale comparable to the porphyry copper mines in America`s
Southwest would appear to be the only economically feasible mining
method at the +100 Mt low-grade alunite deposits. There is little barren
overburden at these deposits, but saving here could be offset by the
need to selectively remove subore-grade material to waste.

24. RELATION TO ALUNITE TO
HYPOGENE ORE DEPOSITS.
• Apart from consideration of alunitic rock as a possible ore of alunite with
hypogene examples have been reported of associated with
metalliferous deposits.
• Alunite occurs with auriferous veins at Rodalquilar in southeastern
Spain. And at the old Rattlesnake Jack prospect near Lead, SD.
• The huge Red Mountain alunite deposit near Lake City in Hinsdale
County, Colorado, is flanked on the north and east by numerous base-
and precious-metal deposits, especially along Henson Creek.
• Extensive alunitization in the volcanic complex of the Marysvale district,
Piute and Sevier counties, Utah, appears to be related genetically to
base-and precious metal deposit.
• Many additional examples could be cited. The presence of alunite,
especially in a large pervasively altered area of volcanic rock, may be
interpreted as a red flag marketing a favorable target for further
exploration for possible metalliferous deposits, nearby or at depth.

25. PROSPECTING FOR ALUNITE
DEPOSITS
• Any pervasively altered and bleached iron stained area in a volcanic
setting may contain alunite. Whitish bleached zones normally grade
outward into characteristically dull greenish-gray propylitized rock. It is
difficult to identify alunite-bearing rock by visual examination alone, but
slightly greater heaving rock can be a clue.
• A simple test using pH paper to measure acidity a powdered sample
has been strongly heated detects alunitic rock, but should be used with
caution.
• Powder X-ray diffractometry is the most reliable identification method.
• Geologists of Earth Sciences, Inc. Have been very successful in
identifying large potentially alunitized bodies from aircraft flying over
rugged volcanic terrains.