Note: Descriptions are shown in the official language in which they were submitted.
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METHOD TO CONVERT LITHIUM IN SOLUBLE FORM FROM LITHIUM SILICATE MINERALS BY
THE USE OF AN INTRINSIC CHEMICAL HEAT SYSTEM
TECHNICAL FIELD
[0001] The present disclosure relates to the recovery of lithium from
concentrated
lithium aluminum silicate minerals using pyrometallurgical and intrinsic
chemical
heat system techniques producing lithium hydroxide and a by-product containing
calcium hydroxide and calcium silicate compounds under a desired form.
BACKGROUND
[0002] In most case, lithium-bearing minerals occurs in pegmatite mines and
include spodumene, petalite and lepidolite, such lithium aluminum silicates.
Their
respective formula are Li20.A1203.4Si02, Li20.A1203.8Si02 and
LiF.KF.A1203.3Si02. Nowadays, lithium as its major applications in batteries
and
cells, in the ceramic and glass industry and in lubricating greases trade. In
the last
decade, overall lithium consumption has increased significantly resulting in a
grow
demand. Lithium is used as a mineral concentrate or as a simple compounds,
such
carbonate or chloride. If in the past the concentrate was the main form of
lithium
sale, now the trend changes. Increasingly lithium compounds are being
consumed.
As the chief ore and with the growing interest in lithium, lithium aluminum
silicate
minerals is again taken into consideration for producing lithium products,
more
particularly lithium hydroxide.
[0003] There are two industrial processes of lithium recovery from lithium
aluminum silicate minerals: acid pathway and basic pathway. Both involve high
temperature reaction and yield salts readily interconvertible.
[0004] In the usual acid processes cited in the U.S. patent 2,020,854 and as
described in the U.S patent 2,516,109 the ore is calcined at around 1050 C to
convert the naturally occuring a-spodumene to 0-spodumene. This change in
molecular structure is accompanied by a severe decrepitation. The calcined
material is roasted at 250 C with sulfuric acid in a stoichiometric portion of
Date Recue/Date Received 2023-03-22
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hydrogen-lithium at about 40 per cent in excess. Then, the lithium sulfate is
leached out with hot water. By increasing pH, the impurities in solution are
precipitated. Insoluble portion is remove by filtration. Lithium is recovered
as a
sulfate after neutralizing treatment with same acid. Otherwise, lithium is
precipitated as a carbonate by reaction with soda ash or carbon dioxide
bubbling.
[0005] This method has some disadvantages, which make it expensive. The acid
roasting step results in a dissolution of other metals along with the lithium
and in a
significant proportion, such iron and aluminum. Although the ore is generally
concentrated initially, a content of penalty iron oxide remains with the
silicate
mineral and is thus leached. Aluminum contained in the ore is also attacked by
the
acid. To neutralize the free acid in solution and precipitate unwanted
elements,
reagent consumption is significant. Also, the calcination temperature over
1000 C
requires high energy consumption.
[0006] Lithium sulfate solution can be subject to electrochemical treatment
using
exchange membranes as presented by A. D. Ryabtsev and al. for additional
purification. Lithium hydroxide solution, diluted sulfuric acid, oxygen and
hydrogen
are reaction products.
[0007] By the other pathway, lithium bearing minerals are calcined in the
presence
of a basic oxide between 800 and 1000 C. As describe in the U.S. patent
2,020,854, calcium carbonate or calcium oxide is mixed with the ore in a
proportion
around two to one. Then, the solid is leached with hot water to solubilise
lithium
and a part of calcium too. The later in the aqueous solution is precipitated
by
adding soluble carbonate or bubbling carbon dioxide gas therethrough. The
solid-
liquid mixture is separated by known methods. Hydrochloric acid is poured into
the
lithium solution in a sufficient amount to neutralise it and convert salts to
chlorides.
After concentration of the solution, a commercially usable lithium chloride is
obtained.
[0008] By this method, calcium oxide used for calcination treatment is in a
large
amount. In addition, the calcium carbonate precipitate is not recovered, but
remove
with insoluble portion of the ore. Sadly, the authors did not specify the
efficiency of
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lithium ore conversion by its reaction with calcium material. The operational
parameters of each step are often incomplete or unspecified.
[0009] In the U.S. patent 2,662,809, the ore is firstly calcined between 1000
and
1300 C with an oxide from the group of alkali or alkaline-earth metal or salts
forming these oxides during treatment at a temperature to partially or totally
fuse
the mass. In the mixture, the oxide material is present in a too small amount
to
bring about a sufficient solubility of the calcined product in water to
readily leach
lithium salts. Thus, the solid is mixed with a concentrate aqueous electrolyte
solution, for example sodium chloride, under super atmospheric pressure to
dissolve lithium. The slurry is filtrated to separate the insoluble residue.
Sodium
carbonate is added to lithium solution to precipitate impurities, such silico-
aluminates. After removing them, lithium is recovered under carbonate form by
addition of a further amount of reagent.
[0olo] This way to recover lithium from minerals alters its crystallized
nature and
composition by chemical reactions at elevated temperature, such calcination
and
leaching steps. More, part of the silica is solubilized and becomes an
additional
impurity that must be removed from the aqueous solution.
[0011] Overall, the methods described are regardless of the economic potential
of
silicate secondary products. Also, warmth recovery and transfer from heat
treatments are not maximized. The lithium is recovered under sulfate, chloride
or
carbonate form.
REFERENCES CITED
U.S. patent 2, 020, 854 Method of recovering lithium from its ores
U.S. patent 2, 516, 109 Method of extracting lithium values from spodumene
ores
U.S. patent 2, 662, 809 Method of recovering lithium compounds from lithium
minerals
A. D. Ryabtsev and al., Preparation of high-purity lithium hydroxide
monohydrate
from technical-grade lithium carbonate by membrane electrolysis, Applied
electrochemistry and corrosion protection of metals, Vol. 77, 2004.
Date Regue/Date Received 2023-03-22
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SUMMARY
[0012] This invention relates to a method for separate lithium from
concentrated
lithium aluminum silicate minerals by the use of a powerful reagent. Another
object
of this invention is to provide an efficient method to convert the separate
lithium in
a soluble water form. Another object of this invention is to provide a cost-
effective
method by the use of an intrinsic chemical heat system and minimize in many
different manners the energy consumption. It is a further object of the
invention to
provide a method to produce lithium hydroxide and marketable by-product
contained calcium silicate compounds under a desired form.
BRIEF DESCRIPTION OF DRAWING
[0013] Figure 1 illustrates a schematic representation of a method to produce
lithium hydroxide and a by-product contained a mixture of calcium hydroxide
and
one or more calcium silicate compounds from concentrated lithium aluminum
silicate minerals.
DETAILED DESCRIPTION
[0014] There is provided a method to produce lithium hydroxide and a by-
product
contained a mixture of calcium hydroxide and one or more calcium silicate
compounds from concentrated lithium aluminum silicate minerals comprising the
steps of mixing and pulverizing the concentrated mineral and the alkaline
calcium
reagent obtaining an ultimate mixture of the two; pre-calcining the mixture
producing calcium oxide in the blend; calcining the mixture obtaining a
calcined
mass containing calcium oxide, lithium oxide and one or more calcium silicate
compounds; cooling the calcined mass obtaining a cooled mass; hydrating the
cooled mass with water vapor producing a 5011d-H2Ovapor mixture; separating
the
solid-H2Ovapor mixture obtaining a solid containing calcium hydroxide, lithium
hydroxide and/or lithium hydroxide monohydrate, one or more calcium silicate
compounds and water vapor; dissolving soluble salts from the solid with hot
water
obtaining a slurry comprising a solid fraction and a liquid fraction;
separating from
the slurry the solid fraction containing calcium hydroxide and one or more
calcium
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silicate compounds obtaining a by-product; recovering calcium hydroxide from
the
liquid fraction by water evaporation, precipitation then separation;
introducing the
calcium hydroxide recovered at mixing-pulverizing step; crystallizing lithium
salt
from liquid fraction by partial water evaporation; separating the crystals
from the
mother liquor obtaining lithium hydroxide monohydrate and a mother liquor with
impurities; recovering and using heat released from calcining, cooling and
hydrating steps to reduce the energy demand of the process; recovering and
using
water vapor used in excess and obtained by evaporation to reduce energy demand
of the process.
[0015] The present method is effective for treating various concentrated
lithium
aluminum silicate minerals such as for examples, and not limited to,
spodumene,
petalite and lepidolite or mixtures thereof which is used as starting
material.
Beneficiation of lithium aluminum silicate minerals are known in the art and
aims
to concentrate the lithium value.
[0016] At high temperature in the presence of calcium oxide (CaO), lithium
oxide
(Li2O) from spodumene is replaced to form a calcium aluminum silicate molecule
(Ca2Al2Si07) or liberated to obtain calcium silicates (CaSiO3, Ca2SiO4), but
not
restricted too. According to the lithium aluminum silicate mineral used, other
silica
compounds may be obtained. The reactions are evidenced by the fact that
lithium
oxide may next be converted by water vapor in hydroxide form, then dissolved
with
hot water such as described below.
[0017] Calcium oxide's specific surface area improve the yield of solid-phase
reactions. A correlation is found between structural properties of calcium
hydroxide
(Ca(OH)2) and the product of its thermic treatment. When calcium hydroxide is
decomposed at intermediate temperatures, such between 375 and 525 C, the
calcium oxide shows a higher specific surface area. This enhancement is
considered at the pre-calcination stage. To promote the reaction with a
concentrated mineral, the use of calcium hydroxide or a mixture of calcium
hydroxide and calcium oxide is recommended. Calcium hydroxide comes from the
reagent recovery step and the new quantity introduced.
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[0018] Particle size influences exchange capacity by accessible surface. In
the
present method, thermal substitutions and reformulation reactions are
accomplished in a solid phase. Hence they require fine grinding ore and
reagent
to give large surface area and facilitate the further reactions. The
concentrate
mineral and calcium hydroxide are mixed and pulverized together to obtain an
ultimate mixture of the two 1. A particle size smaller than 400 m is
considered
efficient, more precisely a grain size spread between 25 and 354 Th. If a
blend of
calcium oxide and calcium hydroxide is used as reagent, the same procedure is
applied to reach an optimum mixture.
[0ots] The effective CaO-concentrated mineral mass ratio to separate lithium
is
less than 3.0, more particularly between 0.5 and 2Ø The total calcium
reagent is
expressed on an oxide base. Calcium is added in excess to the lithium content.
The ratio is also selected according to the composition of the desired by-
product:
the more calcium, the more aluminum remains attached to silica.
[0020] The mixture is then fed into a continuous or discontinuous heating
apparatus, for examples a rotary kiln or a furnace, to be heated within 375 to
525 C
2. According to the fixed temperature, the roasted time varies between 5 to 30
minutes for complete decomposition of calcium hydroxide. Hot gas emitted from
the calcination treatment may be used for example to carry out the pre-
calcination.
[0021] If a blend of calcium hydroxide and calcium oxide is mixed with
concentrated mineral, same residence time is applied for a given temperature
at
pre-calcination step to promote structure development of calcium oxide.
[0022] The CaO-concentrated lithium aluminum silicate mineral is next
subjected
to a thermal treatment at a temperature between 800 to 1000 C for 15 to 120
minutes 3. Any of the well know types of continuous or discontinuous heating
apparatus is used, for examples direct fired rotary calciner or furnace.
Temperature
and time are fixed according to the liberation rate of lithium. The method
promotes
the avoidance of the fused mass at these temperatures improving a secondary
product more easily recoverable.
Date Recue/Date Received 2023-03-22
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[0023] The calcined mass contained mostly one or more calcium silicate
compounds, lithium oxide and calcium oxide is cooled at a temperature between
80 and 200 C 4. The hot feed is chilled in any well know granulate cooling
device
where thermal energy is restored. This energy may be used for example to
drying
by-product or additionally drying calcium hydroxide recovered at later stage.
If a
coarse portion is formed during heat treatment, the calcined mass may be
ground
with a rotating ball mill equipped with a cooling device. Heat released is
also
recovered and introduced into the process.
[0024] The present method includes an intrinsic chemical heat loop, such
dehydration-hydration alternating reaction using Ca(OH)2-CaO adding to Li2O
hydration at pre-calcination and hydrating steps. The dehydration of calcium
hydroxide discussed previously is called charge stage since energy is consumed
by the following endothermic reaction.
Ca(OH)2s ¨> CaO s + H20 g (1)
[0025] Through the hydration process carried out with water vapor, also called
the
discharge stage, exothermic reactions take place (reactions 2 to 5) and heat
is
released 5.
Ca0 s + H20 g ¨> Ca(OH)2s (2)
L120 s + H 2 0 g ¨> 2LiOH s (3)
2LiOH s + H20 g ¨> Li0H.H20 s (4)
Li2O s + 3H20 g ¨> 2Li0H.H20 s (5)
[0026] The energy balance is largely positive since the hydration enthalpy is
higher
when steam is used as a reactant instead of liquid water. Free Li2O and CaO
react
slowly in hot water but react vigorously with steam. Also the amount of oxide
to
hydrate versus the amount of hydroxide to dehydrate is much higher.
[0027] The hydration process carried out at a temperature below 200 C avoids
the
conversion of the newly formed LiOH into oxide according to the reaction
below.
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Iron oxide come from concentrated mineral is however inactive, so avoided
further
impurities dissolution at the leaching stage.
2LiOH s ¨> Li2O s + H20 g (6)
[0028] Specifically, the steam water and the hot solid mixture are brought
into
contact in a fluid bed reactor at atmospheric pressure. Steam is fed in a
sufficient
amount to act as a fluidizing gas and as a reactant with the free Li2O and CaO
contained in the mass. Otherwise, air or nitrogen could be used as a gas
carrier of
steam. Fluid bed reactor has for inherent advantages a uniform temperature
gradient and ability to operate in continuous state. A heat exchanger located
inside
the reactor extract thermal power and can exploit the high heat transfer
coefficients
typical in fluidized beds. The 5011d-H2Ovapor mixture is then separated with
the aid
of a cyclone 6. The reaction heat released may be used for example to drive
the
steam cycle. Other methods for hydrating solid can be used, for example a
conveyor belt with a chamber where water vapor is sprayed.
[0029] The solid mixture is then leached with water at a temperature between
70
and 100 C into one or more successive stirred device. This solid-liquid
extraction
is designed to dissolving soluble salts, essentially of lithium, potassium and
sodium
7. A part of calcium pass jointly into solution and is recovered at a later
stage. The
slurry is separated by know techniques 8. Countercurrent extraction method
could
be an alternative way in which small amounts of water in continuous mode are
sprayed to the mass. The residual solid consists mainly in a mixture of one or
more
calcium silicate compounds and calcium hydroxide. Traces of iron oxide and/or
unreacted mineral could be present.
[0030] The alkaline solution is evaporated partly to precipitate dissolved
calcium
hydroxide as a recovered reagent step 9. The removal of calcium is done by
filtration or other know separation techniques. The hydroxide is dried and
reintroduced at the mixing-pulverizing step. The amount to be recovered
depends
on the ratio used initially and the solubility of calcium hydroxide in water.
The
benefit of recovery is found in the production of reagent with better reaction
characteristics obtained under pre-calcination conditions.
Date Recue/Date Received 2023-03-22
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[0031] According to the CaO-concentrated mineral mass ratio, lithium aluminum
compounds may be formed during calcination and then leachable by water. In
this
case, an additional impurity is found in solution.
[0032] In the aqueous solution at a pH above 4, Al3+ ions are hydrolyzed and
the
solubility of aluminum compounds formed are influenced by Li + in the system.
In
presence of high lithium ions content, a significantly lower solubility is
observed
and promote the removal of aluminum hydroxide species from the lithium rich
solution by precipitation. At a molar ratio Li/A13+ above 0.4, the lithium
effect is
noticed. The salts concentration is adjusted by evaporation while maintaining
soluble lithium. Any of know separation equipment can be used to remove
aluminium and calcium precipitated.
[0033] Lithium hydroxide monohydrate (Li0H.H20) is obtained from rich lithium
solution by partial evaporation of water at atmospheric pressure or under
vacuum
10. The solubility of lithium hydroxide in water is much lower than that of
the
potassium and sodium hydroxides, which makes it possible to separate them. The
crystals are removed from the mother liquor by a mechanical separation
technique,
for example dewatering system. Monohydrate product can be dehydrating to
obtain lithium hydroxide.
[0034] Water vapor from solid-H2Ovapor separation, reagent recovering and
crystallizing steps is recovered and reintroduced into the process to minimize
water
consumption and energy to produce it.
[0035] The method described herein allows de production of lithium hydroxide
and
a marketable by-product which exhibits economic benefits mainly associated
with
low energy costs. By coupling heat emission and heat recovery, the energy
demand of the process is reduced and profitability is improved. Heat sources
come
from calcination of CaO-concentrated mineral, calcined mass cooling and cooled
mass hydrating.
[0036] As a source of calcium and silicate, the by-product could be used as a
flux
in pyrometallurgical recovering process of platinum-group metals (PGM) from
Date Recue/Date Received 2023-03-22
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spent automotive catalysts. The classic ceramic catalysts are initially mixed
with
fluxes, collector and reductant during smelting and a PGM-collector alloy is
obtained which further undergoes purification.
[0037] For another example of industrial application, the by-product has a
potential
value as an ingredient of cement to replace basic raw materials used in its
production. In brief, cement is made by heating a carefully dosed mixture of
limestone (any rock composed mostly of calcium carbonate), clay (natural rock
based on silicates and/or aluminosilicates) and sometimes sand in a rotary
kiln to
a temperature around 1450 C. The result is an intermediate product called
clinker.
Calcination of limestone emits carbon dioxide, a greenhouse gases. Also,
quarries
exploitation requires sound management with respect to the preservation of the
environment. The use of value products helps to preserve the reserves.
[0038] The present invention will be more readily understood by referring to
the
following examples which are given to illustrate the invention rather than to
limit its
scope.
EXAMPLE 1
[0039] To demonstrate the increase of specific surface area of the calcium
oxide,
a hydration-dehydration test was carried out and this characteristic was
measured
by the BET method. A powder reagent was spread on a plate and hydrated by a
jet of water vapor. The product was leached with water at 80 C then dried to
constant weight at 120 C. The calcium hydroxide was dehydrated at 400 C for 20
minutes. This treatment represents the hydrating, leaching and pre-calcining
steps
that would occur to calcium oxide by this method. The specific surface are of
calcium oxide has increased from 1.86 m2/g initially to 18.02 m2/g, such about
10
times.
EXAMPLE 2
p040j Pre-calcination and calcination of a mixture of calcium hydroxide and
concentrated spodumene in a muffle furnace was completed to view the reaction
Date Recue/Date Received 2023-03-22
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products. The sample was analysed by x-ray powder diffraction (XRPD). The
mineral contained 5.76% Li2O.
[0041] Calcium oxide was first hydrated under a jet of water to convert it
into
hydroxide. The reagent was well mixed with the mineral. The CaO-concentrated
spodumene mass ratio was 1Ø The temperature was first fixed at 400 C for 20
minutes and next increased to 975 C for an additional 90 minutes. The mass
lost
was 15.4%.
[0042] The sample was lightly crushed and analyzed under the conditions
presented in the table 1. A search in a database indicates three crystalline
phases
as the main constituents: a calcium aluminum silicate (gehlenite: Ca2Al2Si07),
a
calcium silicate (wollastonite-2M: CaSiO3) and the portlandite (Ca(OH)2) also
called calcium hydroxide. The graph 1 beneath shows a semi-quantification on
these three phases by the Rietveld method. The result indicate that
portlandite and
gehlenite are the majority constituents of the sample. Spodumene was not
observed which suggests that it fully reacted with the reagent.
[0043] The presence of calcium hydroxide versus calcium oxide may be explained
by air exposure and moisture content prior to analysis.
Table 1
XRPD analysis experimental conditions
Instrument: Ma1vern PanAlytical Empyrean 3
Geometrie : Bragg Brentano 0 - 0
Radiation : CuKoc, = 1.54178 A
Detecteur : P IXCePD (255 canaux)
Parametres di a cquis ition 20 initial 40
20 final 90'
Pas angulaire 0.013'
Temps d'acquisition par pas angulaire 0.8 s (198 s pour 255
canaux.)
Temps total d'acquisition 1 Iheure 30
Date Regue/Date Received 2023-03-22
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cow It5 1 I 11 iii Irolimo 1 likiiii itithillid migniiiiiiiiii 11
1 1 1
CAL-2
I' ehlEn,te 5irry 412%
reoAaEtorr,V,2101, SO ioS 96
Poratioxiste, tyn 482%
20000 ¨
I
L
10000 ¨ 1
,
,
ii i k, ,
li_ .k .,,,t, ,=,.1,,,,.1' õ,:,
.,,,i ., f ' ^ ' )41111illiL
....õ.........i
20 30 40 50 60 70 80
Posftion ran (Copper (Cu))
Graph. 1
Date Regue/Date Received 2023-03-22
