Process of Purifying a Residue with Calcium Ions
TECHNICAL FIELD
The present invention which claims priority to EP patent application
N° 11163262.6 filed on April 20, 201 1 the whole content of which is
incorporated herein by reference for all purposes relates to a process of purifying
a residue from an industrial process using calcium ions, for the purifying
treatment, wherein the residue is particularly obtained from rice hull ashes, ashes
of wood combustion plants, ashes of coal combustion plants, cement kiln dusts,
steel industry dusts, dusts from iron sintering processes, flue dusts from furnace
such as glass furnace or cotton processing dusts. The present invention also
relates to a process of removing excess alkali earth metal ions remained in brine
and recycling the insoluble or removed species.
BACKGROUND
Residues from many industrial processes contain soluble salts, which make
the disposal of these residues more difficult and expensive. This is because such
soluble salts may leak out and contaminate subsoil of the disposal site.
Particularly, representatives of such salts are alkali metal salts, especially
potassium and/or sodium salts. The alkali metal salts often remain in the form of
a mixture of different alkali metal salts, for example, a mixture of alkali metal
chloride and alkali metal sulfate.
Thus, it would be desirable to have processes, which make it possible to
remove sulfates contained in industrial residues with high purity and low cost in
an industrial scale. It would be more desirable to have processes that make it
possible to remove two or more different salts from the residue.
International Patent Application WO 201 1048135 discloses a process that
recycles the soluble salts contained in some industrial residue, particularly to
recycle potassium chloride or sodium chloride. Said WO 201 1048135
corresponds to application N°. PCT/EP2010/065783, which was unpublished at
the date of filing of the above-mentioned EP patent application N° 11163262.6
and which was filed in the name of Solvay SA, the entire content of which is
incorporated herein by reference. It has been found that the disposal of residue,
which contains valuable raw materials for the above-mentioned industrial
processes, particularly cement manufacture, is highly uneconomical.
U.S. Patent No. 1,402,173, the entire content of which is incorporated
herein by reference, discloses a process of obtaining potassium chloride, which is
particularly applicable to the production of potassium chloride from cement kiln
dust, or other flue dust from furnaces such as glass furnaces or the like. In the
process, the sulfates of calcium and potassium form the double salt
CaSC"4 K2SO4 H2O. By agitating this double salt in water in the presence of
calcium chloride, the double salt is broken up and the potassium is obtained in
the form of potassium chloride. The potassium chloride is obtained from the
solution by fractional crystallization.
U.S. Patent No. 3,647,395, the entire content of which is incorporated
herein by reference, describes a process of recovering alkali metal salts contained
in the gases emitted by cement production furnaces. In this process, the vapours
of alkali metal salts contained in the gases emitted are condensed and then added
to water with the dust from the flue gas. The aqueous solution obtained is
separated from the insoluble particles. The latter is then subjected to a
succession of dissolving and separating steps. The aqueous solution finally
obtained is subjected to a crystallization of the soluble salts.
However, these processes, which require a large number of dissolving and
separating steps, are complex and do not make it possible to effectively remove
the sulfates. Moreover, the excess alkali earth metal ions, which existed in the
original residue or were added into the residue for removing sulfates from the
residue, can be deposited into other devices in the next processes such as
crystallization or electrolysis. However, this has an undesirable effect upon the
devices.
Thus, there is a need for simpler and cheaper processes, which can purify
industrial residue, while avoiding the above-described disadvantages of the prior
art.
SUMMARY
The present invention relates to a purification process of the residue
containing soluble salts obtained from industrial source, especially residues
obtained with the process described in International Patent Application
PCT/EP20 10/065783 to yield purified brine.
The present inventors invented a simple purification process of the residue,
which can remove sulfates initially contained in the residue and obtain a very
low concentration of alkali earth metal ions, to undergo further processing such
as crystallization or electrolysis.
Consequently, one of the essential features of the invention resides in a
process of purifying a residue comprising sulfate salts from an industrial process
using calcium ions as purifying agent to obtain a purified brine, which process
comprises :
(a) mixing the residue comprising sulfate salts from the industrial process with
calcium salts ;
(b) separating insoluble species and/or precipitates from the suspension from
(a) ;
(c) adding an agent capable to precipitate calcium salts from the filtrate from (b)
preferably selected from one or more of C0 2, carbonates, hydrogen
carbonates or fluorinated salts into the filtrate from (b) to remove excess
calcium ions ; and
(d) separating precipitates from the suspension from (c) to obtain a purified
brine.
The residue contains water-soluble salts including water-soluble sulfate
salts.
In a preferred embodiment, the sulfate-containing residue is introduced
into step a) in the form of an aqueous solution. The amount of the residue
dissolved in the aqueous solution may be high up to the saturation concentration.
For example, the concentration of the dissolved residue may be equal to or
greater than 40 % by weight of the total weight of the dissolved solution. It may
be equal to or lower than the saturation concentration. Preferably, the term
"saturation concentration" denotes the salt with the lowest solubility at a given
temperature. This allows for optimal purification of the residue because the
solution of the residue to be treated according to the invention contains no solids.
In some embodiments, the sulfate salts are selected from one or more alkali
metal salts, preferably, the sulfate salt is potassium sulfate or sodium sulfate. In
some embodiments, carbonates, hydrogen carbonates or fluorinated salts are
applied as agent to precipitate calcium salts from the filtrate, and at least one of
the carbonates, hydrogen carbonates or fluorinated salts are alkali metal salts, for
example, alkali metal carbonates such as sodium carbonate or potassium
carbonate, alkali metal hydrogen carbonates such as sodium hydrogen carbonate
or potassium hydrogen carbonate, alkali metal fluorides such as sodium fluoride
or potassium fluoride or a mixture thereof.
In some preferred embodiments, calcium salts are added with an amount of
from 1 to 20 % by weight, preferably from 2 to 15 % by weight, more preferably
from 5 to 10 % by weight of aqueous solution in step (a).
In some embodiments, the residue may contain one or more species
selected from the group consisting of alkali metal salts such as NaCl, KC1,
Na2S0 4, K2SO4, and alkali earth metal salts such as strontium or barium salts.
The strontium and/or barium salts are also removed in step (c).
In some embodiments, calcium salts are soluble in the aqueous solution.
Such salts are preferably calcium halides, and more preferably calcium chloride.
The strontium and/or barium salts also are soluble in an aqueous solution. Such
salts are preferably strontium and/or barium halides, and more preferably
strontium and/or barium chlorides. The residue may contain such calcium salts
which are soluble in the aqueous solution.
In some embodiments, calcium salts are insoluble in an aqueous solution.
Such salts are preferably selected from one or more of hydroxides, oxides or
carbonates. The strontium and/or barium salts can also be insoluble in the
aqueous solution, wherein said salts are preferably strontium and/or barium
carbonates. In such cases, the process further comprises the step of adding
hydrogen halide, preferably hydrogen chloride, into the suspension from step (a)
prior to separating. By adding hydrogen halide, insoluble calcium salts, barium
salts and strontium salts, e.g. the hydroxides, oxides and carbonates mentioned
above, are transformed into soluble halides, especially the respective chlorides,
which have a high solubility in water.
In all cases, the type of strontium and/or barium salts is independent from
the type of calcium salts.
In some embodiments, the residue originates from rice hull ashes, ashes of
wood combustion plants, ashes of coal combustion plants, cement kiln residue,
steel industry dusts or dusts from iron sintering processes, flue dusts from
furnace such as glass furnace or cotton processing dusts.
In some embodiments, the purified brine is subjected to at least one
additional process such as crystallization and electrolysis.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows a representative scheme of the purification process
according to the present invention.
DETAILED DESCRIPTION
In the present specification, the plural form and the singular form are used
interchangeably. Thus, it should be understood that the plural form also includes
the singular form and vice-versa.
In the present invention, the alkali earth metal ions used for purifying the
residue may be calcium ions. The term "alkali earth metal salt(s)" used herein
means any soluble and/or insoluble salts containing alkali earth metal, i.e.,
calcium, strontium, barium, radium or a combination thereof. The term "alkali
earth metal salt(s)" used herein may comprise one or more selected from calcium
salts, strontium salts or barium salts.
The term "soluble" and "insoluble" used herein means soluble or insoluble
in aqueous solution, unless indicated otherwise. The term "soluble" denotes salts
having solubility in water of equal to more than 0.05 g/liter at 20°C. The term
"insoluble" denotes salts having solubility in water of less than 0.05 g/liter
at 20°C.
The residue, which is purified according to the process of the present
invention, is obtained by, for example, treating by-products from metallurgical
manufacture, preferably from steel manufacture, or by treating cement kiln dust
from cement production. Cement kiln dust (CKD) is preferably a fine-grained,
solid, highly alkali metal waste removed from cement kiln exhaust gas by air
pollution control devices. Other residue from an industrial process such as rice
hull ashes, ashes of wood combustion plants, ashes of coal combustion plants,
cement kiln residue, steel industry dusts, dusts from iron sintering processes, flue
dusts from furnace such as glass furnace or cotton processing dusts can be
purified using the present process. A suitable treatment may comprise, for
example, contacting the residue with aqueous solution to provide a suspension of
solids in a solution of water soluble impurities.
The process of the present invention can remove sulfates contained in the
residue to make the resulting brine having a high purity. The residue may
contain various impurities, including polyvalent metals, inorganic compounds
and/or organic compounds as well as sulfates. Such residue may contain
impurities from 2 to 99 %, preferably from 5 to 99 %, more preferably from 10
to 99 % by weight of the residue. Further, the sulfate salts may be contained
from 1 to 95 %, preferably from 3 to 90 %, more preferably from 10 to 90 % by
weight of the residue.
According to the present invention, the amount of aqueous solution needed
to dissolve salts is brought into contact with the residue. The aqueous solution
may be prepared with substantially pure water or water recycled from an
industrial process. The aqueous solution may contain an excess amount of
calcium salts. In any case, an excess amount of calcium ions may be needed to
obtain the best removal yield. In the process of the present invention, the
amount of calcium salts included in the aqueous solution is generally from 1
to 20 %, preferably from 2 to 15 %, more preferably from 5 to 10 % by weight of
aqueous solution.
The temperature of the aqueous solution may be adapted to the solubility
of soluble salts. It has been observed that the process of the present invention
functions especially well when the dissolving step is carried out at a temperature
between 5 and 99°C, and preferably between 10 and 80°C. Temperatures
between 15 and 60°C, particularly temperatures close to 20°C, e.g., between 18
and 22°C, are suitable.
The aqueous solution may be brought into contact with the residue in
various ways as follows.
According to a first embodiment of the invention, the aqueous solution is
brought into contact with the residue by introducing the aqueous solution and the
residue into a reactor, which is preferably equipped with stirring means to ensure
homogeneous mixing. The soluble salts then dissolve in the aqueous solution.
The amount of aqueous solution and the residence time in the reactor must be
sufficient to obtain the most complete dissolution possible of soluble salts to be
regenerated. In the first embodiment, it is recommended that at least 95 %,
advantageously at least 98 %, preferably 99 % of these salts are dissolved. It is
pointless to add an excessive amount of aqueous solution. It is recommended
that this amount does not exceed 1.5 times, preferably 1.25 times the minimum
amount of solution needed to dissolve at least 99 % of the salts.
According to a second embodiment of the invention, the aqueous solution
is brought into contact with the residue by leaching. In this embodiment, the
aqueous solution is percolated through a layer constituted with the residue. This
layer is generally placed on a filter layer that can prevent the residue particles
from being entrained during the percolation into the resulting aqueous
suspension. In the second embodiment, it is advantageous for said filter layer to
possess separation properties that can perform the separation of the insoluble
particles carried out in the second step of the process according to the present
invention. It is then possible to carry out the contacting step and the separation
step using a single device. It is recommended that the leaching allows the
dissolution of at least 50 %, advantageously 75 %, preferably at least 95 %,
particularly preferably at least 99 % of the salts to be regenerated that are present
in the residue. In certain cases, it is possible for the leaching step to be carried
out at an industrial site different from that where the rest of the process is carried
out.
After dissolving soluble salts and mixing them with residue, the
undissolved, mainly insoluble, species and/or precipitates are separated from the
aqueous suspension to form the product solution. Any separation means known
in the field may be used. Filtration, decantation or centrifugation can be
preferably used. When an average diameter of the particles in the suspension is
equal to at least 10 (as measured by laser diffraction, for example, using a
SYMPATEC apparatus), it is possible to use vacuum filters such as rotary filters
or belt filters. These filters are recommended when the average diameter of the
particles exceeds 50 . When the average diameter of the particles is less
than 10 , horizontal or vertical frame filter presses, cartridge filters or bag
filters are preferably used. These filters are also recommended when the average
diameter of the particles ranges from 10 to 50 . The separation may be
preceded by a settling step in order to thicken the suspension to be filtered. The
settling step is preferably preceded by a flocculation step.
The residue to be purified according to the present invention may comprise
one or more species selected from the group consisting of alkali metal salts,
alkali earth metal salts and sulfates. The term "alkali metal salt(s)" used herein
means any soluble/insoluble salt(s) containing alkali metal ion, i.e., sodium,
potassium, lithium, caesium or francium. By way of example, the alkali metal
salts contained in the residue may be selected from : alkali metal halide such as
sodium chloride, potassium chloride, sodium fluoride, potassium fluoride,
sodium bromide, potassium bromide, sodium iodide and potassium iodide,
preferably sodium chloride and potassium chloride ; and alkali metal sulfates
such as sodium sulfates and potassium sulfates. The alkali earth metal salts
contained in the residue may be selected from : alkali earth halide such as
calcium chloride, strontium chloride, barium chloride, calcium fluoride,
strontium fluoride, barium fluoride, calcium bromide, strontium bromide, barium
bromide, calcium iodide, strontium iodide and barium iodide ; alkali earth metal
sulfates such as calcium sulfates, strontium sulfates and barium sulfates ;
alkaline earth metal hydroxide such as strontium hydroxide or barium
hydroxide ; and alkaline earth metal oxide such as strontium oxide or barium
oxide. The residue generally may further contain any soluble salts other than
those described above.
In some embodiments of the present invention, the residue containing
sulfates is suitable and may be removed from the residue by reaction with
calcium ions to precipitate calcium sulfates. The excess amount of calcium ions
can be removed by reaction with, for example, C0 2, carbonates, hydrogen
carbonates or fluorinated salts to precipitate calcium carbonates or calcium
fluorides. Strontium and/or barium ions typically contained in the residue can be
removed simultaneously by precipitation of strontium carbonates, barium
carbonates.
Figure 1 shows a representative scheme of purification process of the
present invention. In some embodiments, the residue is highly concentrated with
sulfate salts such as K2S0 4 or Na2S0 4. The residue may also comprise other
alkali metal salts such as KC1 or NaCl, or other alkali earth metal salts such as
strontium or barium salts.
To separate salt and insoluble species, the residue (1) is brought into
contact with aqueous solution comprising calcium salts (a) in a dissolver (2). At
the same time, anions of sulfate salts contained in the residue react with calcium
ions contained in the aqueous solution. In any case, an excess amount of
calcium salts can be added into the residue to achieve the best removal yield.
In one embodiment, the reaction mechanism is as follows :
CaCl2 + H20 Ca2+ + 2C1 + H20 (1-1)
S0 4
2-+ Ca2+ + 2Cr + 2H20 CaS0 4-2H20 + 2Cr (1-2)
If insoluble calcium salt may be present in the residue, they may also be
removed using the present process. In this case, for example, calcium salts can
be hydroxides, oxides or carbonates. If the insoluble calcium salts are used, then
hydrogen halides (b) selected from hydrogen chloride, hydrogen fluoride,
hydrogen bromide, hydrogen iodide or a mixture thereof, preferably hydrogen
chloride, can be added into the suspension to react with insoluble calcium salts.
In one embodiment, the reaction mechanisms are as follows :
2HC1 + Ca(OH) 2 + H20 Ca + + 2C1 + 3H20
2HC1 + CaO + H20 Ca2+ + 2C1 + 2H20
2HC1 + CaC0 3 + H20 Ca2+ + 2C1 + 2H20 + C0 3
S0 4
2 + Ca2+ + 2C1 + 2H20 CaS0 4 2H20 + 2C1
In the reaction (1-2), insoluble calcium sulfates are precipitated and
removed through using a separating method such as filtration, decantation or
centrifugation (3). Other insoluble species and/or gypsum produced by the
dissolution and reaction may also be removed in this step. Any separating
method in this field can be used in lieu of decantation and/or filtration and/or
centrifugation.
The dissolution and sulfate precipitation steps can be separated. For
example, salts are dissolved into the residue, the suspension is decanted and/or
filtrated to remove insoluble species, calcium salts are added, and the suspension
is decanted and/or filtrated again to separate gypsums from the residue.
At this step, the clear brine () has a low concentration of sulfates and an
excess amount of calcium ions. Since the excess amount of calcium ions may
cause undesirable effects such as crusting or scaling in the subsequent processes,
they need to be removed from the final brine.
To remove the undesired calcium ions, C0 2, carbonates, hydrogen
carbonates or fluorinated salts, for example, alkali metal carbonates such as
sodium carbonate or potassium carbonate, alkali metal hydrogen carbonates such
as sodium hydrogen carbonate or potassium hydrogen carbonate, alkali metal
fluorides such as sodium fluoride or potassium fluoride, or a mixture thereof can
be added into the brine in the reactor (4). Adding C0 2, carbonates, hydrogen
carbonates or fluorinated salts can initiate precipitation of calcium carbonates or
calcium fluorides, thereby causing highly purified brine from calcium ions. In
this step, the strontium and/or barium ions, which have been contained in the
residue, may also be removed from the brine.
The reactions between alkali earth metal cations and C0 2 or carbonate
anions are as follows :
Ca2+ + C0 3
2 CaC0 3 (3-1)
Ba2+ + C0 3
2 BaC0 3 (3-2)
Sr2+ + C0 3
2 SrC0 3 (3-3)
The reactions between calcium cations and fluorine anions are as follows :
Ca2+ + 2F CaF2 (4)
The precipitates ( ) are separated by, for example, decantation and/or
filtration (5). Any separating method in this field can be used in lieu of
decantation, filtration or centrifugation.
The purified brine has a Ca salt concentration of equal to or lower than
0.015 g/liter solution.
The final purified brine () is ready to be sent to its further application (6)
such as crystallization to recover, for example, KC1 and/or NaCl, or to
electrolysis.
The separated solids can be reused for :
Both salts : electrolysis uses, high quality salts applications such as food, feed,
electronics, pharmaceuticals, water remineralisation, water treatment, food
preservatives, ceramic glaze, metallurgy, water softeners, regeneration of ion
exchange resins, photography, nuclear reactors, etc ;
NaCl : soda ash plant raw material ; and
KC1 : fertilizers, plant nutriments, buffer solutions.
Should the disclosure of any patents, patent applications, and publications
which are incorporated herein by reference conflict with the description of the
present application to the extent that it may render a term unclear, the present
description shall take precedence.
EXAMPLES
The following examples are intended to illustrate the present invention
without limiting the scope of the present invention.
Example 1 and 2
STEP l a
Two tests have been performed with industrial cement kiln dusts. Cement
kiln dusts were dissolved in water at 50°C and then CaCl2 was added in the
suspension. The test conditions are shown in Table 1.

STEP l b
After CaCl2 addition and a residence time of about 30 min, suspension
filtered on a Buchner filter equipped with a Millipore 0.45 membrane.
Compositions of clear solution after filtration are shown in Table 2 .

Composition of clear solution after dissolution and CaCl2 addition
Ca Na K CI S0 4 Ba Sr
DN/kg solution 196 1716 2264 3993 46 0.114 1.393
Test 1
g/kg solution 3.930 39.468 88.522 141.752 2.213 0.0082 0.061
DN/kg solution 177 1551 2047 3610 42 0.108 1.258
Test 2
g/kg solution 3.553 35.684 47.079 83.033 0.957 0.0074 0.0551
STEP l c
Clear solutions were warmed up to 50°C and 31.1 1 g ofa 300 g
Na2C0 3/ g solution was mixed into the clear solution. After 35 minutes,
colloidal precipitates were identified. The solutions were filtered and the new
clear solutions were analyzed again. The compositions of the final brines are
shown in Table 3 .

Note : n.d. = non determined

Balance on N 2C0 3 during the tests
Na2C0 3 balance
Concentration amount of Introduce
g kg solution solution, g , g
Na C0 introduced 300 0.0312 9.36
Mass of brine treated kg 0.905
Species to remove Ca Ba Sr
Concentration g/kg 3.93 0.0082 0.06
Test 1 Amount to remove g 3.56 0.01 0.06
Na C0 needed at
stoichiometric g 9.41 0.01 0.07
Total Na C0 needed
at stoichiometric g 9.48
Na C0 excess 0.99
Na2C0 3 balance
Concentration amount of Introduce
g/kg solution solution g g
Na C0 introduced 300 0.0312 9.36
Mass of brine treated kg 0.905
Species to remove Ca Ba Sr
Concentration g/kg 3.553 0.0074 0.06
Test 1 Amount to remove g 3.22 0.01 0.05
Na C0 needed at
stoichiometric g 8.50 0.01 0.06
Total Na C0 needed
at stoichiometric g 8.57
Na C0 excess 1.09
More than 99.8 % of Ca, 95.9 % of Ba and 97.2 % of Sr were removed
with a stoichiometric between 0.99 and 1.09.
Example 3
Another test was conducted with another solution prepared with the same
procedure as above Steps l a and lb.
At Step lc, clear solution was warmed up to 50°C and 57.5 grams of a
299 g Na2C0 3/kg solution was mixed into the clear solution. After 35 minutes,
colloidal precipitate was identified. The solution was filtered and the new clear
solution was analyzed again. The composition of the final brine is shown in
Table 5 .

Composition of clear solution after dissolution
and CaCl 2 addition
Ca Ba Sr
mg/kg solution 4000 8,3 56
Test 3 Composition of clear solution after Na2C C 3
addition
mg/kg solution 3.500 0.08 0.28
Purification
99.913 99.036 99.500
efficiency %

Balance on N 2C0 3 during the test
More than 99.9 % of Ca, 99 % of Ba and 99.5 % of Sr were removed with
a stoichiometric of 0.99.
C L A I M S
1. A method of purifying a residue from an industrial process using
calcium ions to obtain a purified brine, comprising :
(a) mixing the residue comprising sulfate salts from the industrial process with
calcium salts ;
(b) separating insoluble species and/or precipitates from the suspension
from (a) ;
(c) adding an agent capable to precipitate calcium salts from the filtrate from (b)
preferably selected from one or more of C0 2, carbonates, hydrogen
carbonates or fluorinated salts into the filtrate from (b) to remove excess
calcium ions ; and
(d) separating precipitates from the suspension from (c) to obtain a purified
brine.
2 . The method of Claim 1, wherein the sulfate salts are selected from one
or more of alkali metal salts, preferably potassium sulfate or sodium sulfate.
3 . The method of Claim 1 or 2, wherein at least one of the carbonates,
hydrogen carbonates or fluorinated salts are alkali metal salts, for example, alkali
metal carbonates such as sodium carbonate or potassium carbonate, alkali metal
hydrogen carbonates such as sodium hydrogen carbonate or potassium hydrogen
carbonate, alkali metal fluorides such as sodium fluoride or potassium fluoride,
or a mixture thereof.
4 . The method of anyone of Claims 1 to 3, wherein calcium salts are
added with an amount of from 1 to 20 %, preferably from 2 to 15 %, more
preferably from 5 to 10 % by weight of aqueous solution in step (a).
5 . The method of anyone of Claims 1 to 4, wherein the residue contains
one or more species selected from the group consisting of alkali metal salts such
as NaCl, KC1, Na2S0 4 or K2S0 4, and alkali earth metal salts such as strontium or
barium salts.
6 . The method of Claim 5, wherein the strontium and/or barium salts are
removed in step (c).
7 . The method of anyone of Claims 1 to 6, wherein calcium salts are
soluble in the aqueous solution, and wherein said salts are preferably calcium
chlorides.
8 . The method of Claim 5 or 6, wherein strontium salts are soluble in the
aqueous solution, and wherein said salt is preferably strontium chloride.
9 . The method of Claim 5 or 6, wherein barium salts are soluble in the
aqueous solution, and wherein said salt is preferably barium chloride.
10. The method of Claim 1 to 6, wherein calcium salts are insoluble in the
aqueous solution, and wherein said salts are preferably selected from one or
more of hydroxides, oxides or carbonates.
11. The method of Claim 5 or 6, wherein the strontium salts are insoluble
in the aqueous solution, and wherein said salts are preferably strontium
carbonates.
12. The method of Claim 5 or 6, wherein the barium salts are insoluble in
the aqueous solution, and wherein said salts are preferably barium carbonates.
13. The method of any one of Claims 10 to 12, further comprising the step
of adding hydrogen halide, preferably hydrogen chloride, into the suspension
from (a) prior to separating.
14. The method of anyone of Claims 1 to 13, wherein the residue
originates from rice hull ashes, ashes of wood combustion plants, ashes of coal
combustion plants, cement kiln dusts, steel industry dusts or iron sintering
processes dusts, flue dusts from furnace such as glass furnace or cotton
processing dusts.
15. The method of anyone of Claims 1 to 14, wherein the purified brine is
subjected to at least one further step selected from the group consisting of
crystallization and electrolysis.