Technical Field
[0001] The present invention relates to a method for removing ferrous ions from acidic tin
baths such as tinning electrolytes which are commonly used in the tinplating industry,
and a tinning electrolyte recovery plant wherein this method is employed. More particularly,
the present invention relates to a method by which ferrous ions are separated from
acidic tinning electrolytes in the form of insoluble ferrous methanesulfonate or ferrous
phenolsulfonate in the cold.
Background of the Invention
[0002] For the deposition of tin upon a steel sheet or ribbon, mainly acidic solutions containing
fluoroborate, phenolsulfonic acid, hydrogen halides or methanesulfonic acid (hereinafter
MSA) or mixtures of these acids have been used in the tinplating industry. These acidic
electrolytes all have in common that they attack steel in the initial phase of the
electrolysis due to their strong acidity. In this initial stage, the thickness of
the deposited tin layer is not yet sufficiently high to protect the steel against
the acidic medium; thereby iron is dissolved and remains in the solution because it
is not deposited from the strongly acidic electrolyte.
[0003] Low concentrations of ferrous ions, ranging from about 1 to 5 g/ℓ can be tolerated
in these processes. However, concentrations in the order of 10 to 15 g/ℓ Fe adversely
affect the process by narrowing the range of operable current densities and by strongly
promoting the oxidation of Sn
2+ ions into Sn
4+ ions. A broad range of operable current densities is necessary for an effective tin
electrolysis. The formation of tin(IV) oxide is very disadvantageous for the tinplating
process, because this insoluble oxide drops out of the solution and is collected as
a muddy precipitate on the bottom of the tinplating bath; furthermore it may result
in porous tin deposits. Therefore suppressing the formation of insoluble tetravalent
tin (SnO
2) is a major concern in any tinplating process. As this formation is strongly enhanced
by the presence of dissolved iron, there have been several attempts to separate ferrous
ions from tinplating baths.
[0004] The Fe content can be kept constant in processes operating with hydrogen halide by
adding soluble sodium ferrocyanide to form a ferrocyanide of iron. However, a different
approach has to be taken for tinplating baths operating with a polysulfonic acid,
an acidic fluoroborate or MSA electrolyte. In such baths, a lowering of the Fe content
has been attempted by diluting the bath with fresh electrolyte and discarding part
of the old one, or by plating out tin with tungsten electrodes, and then by re-dissolving
it. Such processes, however, are very expensive.
[0005] A process of precipitating iron with organic or inorganic acids has not been successful
because the high proton concentration of the electrolyte causes a precipitation of
the acids as such or contributes to redissolving the formed iron compound. A chemical
separation of iron by means of a pH change has also proven to be unsatisfactory. At
a pH value of around 1.2, divalent tin hydroxide Sn(OH)
2 precipitates, while iron only precipitates at pH values of around 3. Even in the
best case, only mixtures of Sn(OH)
2 and an iron salt such as ferrous oxalate were obtained.
[0006] The recently published method of iron separation by means of electrodialysis may
lead to precipitates of Fe(OH)
2 and Sn(OH)
2. In general, such a method is laborious and requires well trained personnel and,
furthermore it is doubtful whether it is suitable to comply with the high amounts
of metal hydroxides which have to be processed. A typical tinplating bath may have
a volume of 100,000 to 120,000 liters. Treatment of such amounts of liquid represents
a problem of its own which this invention sets out to avoid. For such reason, a method
wherein Sn ions, Fe ions and detrimental cations are absorbed from a tinning liquid
by passing the liquid through a strong acid cation exchanger such as described in
EP-B-0 621 354 is disadvantageous as well. US-A-5 057 290 discloses processes and
apparatus for the closed-loop regeneration of spent hydrochloric acid pickle liquors
by recovering ferrous chloride from the spent pickle liquors at very low temperatures.
However, this patent does not relate to the recovery of tinning electrolytes and is
not concerned with the particular necessity of separating stannous and ferrous ions
in such an electrolyte.
[0007] In view of the above, the present invention wishes to avoid the above-mentioned problems
involved with prior art methods for removing Fe ions from tin electrolytes, particularly
from electrolytes used as tinplating baths. Moreover, the present invention aims at
providing such a separation method which is reliable, inexpensive, provides a good
separation performance and can be operated by personnel without specific education.
Furthermore, the method should be suitable for the treatment of large amounts of electrolyte,
particularly MSA-containing electrolyte. It would be especially advantageous if the
method was also suitable for electrolytes containing a mixture of MSA and sulfuric
acid.
[0008] A further object underlying the present invention is to provide a recovery plant
for tinning electrolytes which allows the separation of ferrous ions from iron-containing
tin electrolytes on the basis of MSA and, optionally, sulfuric acid.
Summary of the invention
[0009] The inventors found that the compound ferrous methanesulfonate precipitates from
a ferrous ions-containing acidic tin electrolyte on MSA basis at a higher temperature
than tin methanesulfonate. Thus, a separation of ferrous methanesulfonate and tin
methanesulfonate becomes possible at low temperatures. It was further found that the
separation behavior is dependent on the concentration of free methanesulfonic acid
and the total dissolved salts and that agitation of the cooled electrolyte is effective
in reducing the freezing point of the solution. The present invention was accomplished
on the basis of these findings.
[0010] More precisely, the present invention provides:
[0011] A method for separating ferrous ions from an iron-containing tinning electrolyte
on the basis of methanesulfonic acid or phenolsulfonic acid, comprising the following
steps:
(a) providing a concentrated tin and iron-containing electrolyte containing 0.75 mols/ℓ
or more methanesulfonic acid or phenolsulfonic acid
(b) cooling the concentrated electrolyte to temperatures at which an insoluble Fe-salt
precipitates while providing agitation to limit or prevent the formation of ice
(c) separating the insoluble precipitate to recover an electrolyte with a reduced
iron concentration.
[0012] In a preferred embodiment, the method according to the present invention further
comprises the steps of:
(d) washing the insoluble precipitate with a cold mixture of water and methanesulfonic
acid
(e) recovering methanesulfonic acid from said precipitate by ion exchange.
[0013] Additionally, a step (f) may be provided which comprises recycling of the recovered
concentrated electrolyte from step (c) into the original tinning electrolyte or a
tin dissolving station.
[0014] Furthermore, subject-matter of the present invention is:
[0015] A recovery plant for tinning electrolytes on the basis of methanesulfonic acid, which
comprises:
a device for concentrating the electrolyte to obtain a concentrated tin and iron-containing
electrolyte on the basis of methanesulfonic acid or phenolsulfonic acid
a device for cooling the concentrated electrolyte to temperatures at which an insoluble
Fe-salt precipitates
optionally supply means for feeding a solution of methanesulfonic acid or phenolsulfonic
acid into the concentrated electrolyte
a device for separating the iron-containing precipitate from the concentrated electrolyte
conducts for recycling the recovered concentrated electrolyte into the original tinning
electrolyte or a tin dissolving station
[0016] In a preferred embodiment, the above recovery plant, according to the present invention,
further comprises a device for recovering methanesulfonic acid or phenolsulfonic acid
from said iron-containing precipitate such as an ion exchanger and/or a device for
washing the obtained precipitate with a cold mixture of water and methanesulfonic
acid or phenolsulfonic acid.
Best mode for carrying out the Invention
[0017] According to the invention, a method for separating ferrous ions from an iron-containing
tinning electrolyte on the basis of methanesulfonic acid (or phenolsulfonic acid,
the same applies hereinafter) is provided. The tinning electrolyte can be any solution
suitable for the electrodeposition (plating) of tin on other metals, particularly
iron or iron alloys. Such electrolytes are commonly used in the tinplating industry.
The tinning electrolyte in the present invention should be on the basis of methanesulfonic
acid, i.e. it should contain an aqueous acidic solution mainly consisting of methanesulfonic
acid. Optionally, one or more further acids may be present as well. For cost reasons,
sulfuric acid is often used to replace part of the methanesulfonic acid. A particularly
suitable tinning electrolyte for use in the present invention is Ronastan® TP containing
about 20 g/ℓ Sn, 25 to 100 g/ℓ MSA, 20 g/ℓ H
2SO
4 and 7% w/v of additives (organic compounds, e.g. antioxidants). The pH value of this
electrolyte is around 0.8 at room temperature.
[0018] Commercial tinning and tinplating electrolytes are either operated with soluble or
insoluble anodes. Soluble anodes are made of metallic tin, while insoluble anodes
consist of e.g. iridium or another inert metal. The latter case usually requires an
additional tin dissolving station to bring metallic tin into the dissolved state.
The thus obtained solution containing stannous ions is then transferred into the tinplating
bath. The expression "tinning electrolyte" should be understood here as including
both a tinning or tinplating electrolyte with soluble and insoluble anodes. In the
latter case it is, however, more advantageous to recirculate the recovered electrolyte
into the tin dissolving station rather than into the tinning electrolyte itself.
[0019] During the tinning or tinplating process, the MSA dissolves part of the iron out
of the steel ribbon or sheet, which accumulates in the tinning electrolyte. Typical
iron content values in a tinning electrolyte after some time in use are 10 - 25 g/ℓ
Fe. As iron forms salts with methanesulfonic acid, MSA is bound in the electrolyte.
If part of the electrolyte is removed and replaced with fresh electrolyte, as was
the industrial practice in the state of the art, relatively large amounts of expensive
MSA must be supplemented to maintain the acid content of the electrolyte. This is
disadvantageous both from an economical and ecological point of view. One of the objects
of the invention therefore is to find a convenient method for recovering the methanesulfonic
acid from its ferrous salt so that it may be reused in a tinning electrolyte.
[0020] In view of the above, the invention comprises a multi-step method which is essentially
based on the different solubilities of tin methanesulfonate and ferrous methanesulfonate
in the cold, which were heretofore unknown.
[0021] In step (a) of the method according to the present invention, a concentrated tin
and iron-containing electrolyte containing 0.75 mols/ℓ (corresponding to approx. 75
g/ℓ) or more methanesulfonic acid, more preferably 150 g/ℓ or more, is provided. The
term "concentrated tin and iron-containing electrolyte" means any electrolyte wherein
the concentration of methanesulfonic acid and, preferably, also of tin and iron is
higher than in a normal electrolyte used for tinning or tinplating. Such a concentrated
electrolyte can be prepared by concentrating a normal tinning electrolyte to about
50% of its original volume or less, more preferably 40% or less, most preferably about
1/3. This concentration can be carried out by conventional means, e.g. by applying
a vacuum, by distillation or by a combination thereof. Particularly preferable is
a cautious heating of the electrolyte to about 40°C under a pressure of about 2130
Pa (16 Torr). Increasing the concentration, particularly the MSA concentration, serves
to lower the freezing point of the electrolyte. Conventional electrolytes for tin
plating processes have an MSA concentration of about 2.5 - 10% by weight. The freezing
point of e.g. a solution containing about 20 g tin methanesulfonate, 12 g iron as
methanesulfonate and 7% w/v Ronastan® additives would be around -1 to -5°C in static
conditions. If the concentration of free MSA in the electrolyte is increased to 15
- 18%, the freezing point is lowered even more. Agitating the solution lowers the
freezing point still further.
[0022] The concentrated electrolyte used in step (a) can also be provided just by adding
methanesulfonic acid to a regular tinning electrolyte, without a concentration process.
MSA is commercially available as a 70% aqueous solution having a freezing point of
about -60°C. However, in view of the high costs of methanesulfonic acid, this is a
less preferred embodiment of the invention.
[0023] The most favorable way to prepare a concentrated tin and iron-containing electrolyte
containing 0.75 mols/ℓ or more methanesulfonic acid is to concentrate a commercial
tinning electrolyte. The addition of further methanesulfonic acid can optionally be
performed before or during the cooling (step (b)). By vigorously agitating the solution
the freezing point of the concentrated electrolyte can be decreased. Preferably the
electrolyte is stirred during the cooling process by conventional means. According
to the present invention, a 0.75 mols/ℓ or higher concentration of methanesulfonic
acid in the electrolyte, preferably about 1 mol/ℓ or more, is favorable in view of
the desirable lowering of the freezing point on the one hand and overall costs on
the other. Furthermore, the MSA contributes to a better crystallization of the ferrous
methanesulfonate.
[0024] The concentrated tin and iron-containing electrolyte as provided in step (a) is an
electrolyte on the basis of methanesulfonic acid or phenolsulfonic acid and may, optionally,
contain further acids such as sulfuric acid, and additives. This concentrated electrolyte
is cooled in step (b) to temperatures at which an insoluble Fe-salt precipitates.
These temperatures depend on the exact state and composition of the electrolyte. Typically,
the electrolyte is cooled to temperatures of about 0°C or less. At temperatures below
about 0°C, an insoluble iron salt (Fe salt) precipitates which essentially consists
of ferrous methanesulfonate or phenolsulfonate and, optionally, other ferrous salts
such as ferrous sulfate. The concentration of tin methanesulfonate in the precipitate
is fairly small, about 2% by weight or less, and may, in a preferable embodiment of
the invention, be further reduced by washing the ferrous methanesulfonate crystals
with a cold mixture of water and MSA (about 25% by volume), step (d).
[0025] In step (c), the iron-containing precipitate is separated from the concentrated electrolyte
by conventional means, preferably by centrifugation or filtration techniques. Most
preferable is centrifugation. The concentrate still contains approx. 7% of the original
Fe concentration, whereby account has been taken for the volume change. In step (e),
which is a further preferred embodiment of the present invention, the methanesulfonic
acid is recovered from said iron-containing precipitate, e.g. by means of ion exchange.
The recovered methanesulfonic acid may be reused to provide the electrolyte used in
step (a) or for other purposes, e.g. to be supplemented into a tinning electrolyte.
[0026] In the present invention a step (f) may be additionally provided which comprises
the recycling of the concentrated electrolyte into the original tinning electrolyte
or a tin dissolving station. Thus, the present invention allows a complete method
for recovering a Fe-containing tinning electrolyte by removing the undesirable iron
component and recycling the valuable tin and MSA component.
[0027] Furthermore, the present invention provides a recovery plant for tinning electrolytes
on the basis of methanesulfonic acid, which is suitable for conducting the above process.
This plant may comprise:
- a device for concentrating the electrolyte. Such a device may be a conventional distillation
apparatus which can preferably be operated under vacuum;
- a device for cooling the concentrated electrolyte to temperatures at which an insoluble
Fe-salt precipitates. This device may be a container equipped with agitating means
which is filled with the concentrated electrolyte and can be cooled with an external
cooling fluid. In such a cooled container, a precipitate is obtained which consists
essentially of ferrous methanesulfonate and, optionally, other ferrous salts such
as ferrous sulfate or mixed salts thereof;
- optionally, supply means for feeding methanesulfonic acid or phenolsulfonic acid,
preferably a 70% aqueous solution thereof, into the concentrated electrolyte.
- a device for separating said iron-containing precipitate from the concentrated electrolyte
- conducts for recycling the recovered concentrated electrolyte into the original tinning
electrolyte or a tin dissolving station and, preferably,
- an ion exchanger for recovering methanesulfonic acid or phenolsulfonic acid from said
iron-containing precipitate.
[0028] In a preferred embodiment, the above apparatus according to the present invention
further comprises a device for washing the obtained precipitate with a cold mixture
of water and methanesulfonic acid or phenolsulfonic acid.
[0029] The invention is further illustrated in the following examples wherein all percentages
are weight percentages unless indicated otherwise.
Example 1
[0030] 3700 ml tinning electrolyte Ronastan® TP-Sn-electrolyte (Fa. Rasselstein) were concentrated
to 1200 ml by cautious distillation under vacuum. The concentrated electrolyte was
poured into a glass reactor and put into a methanol bath. The methanol bath was gradually
cooled by adding dry ice. The original electrolyte had an acid content (MSA) of 55
g/ℓ, a content of ferrous ions of 10 g/ℓ and a content of stannous ions of 18-19 g/ℓ.
After the concentration, the respective values were 165 g/ℓ acid, 33 g/ℓ Fe and 55
g/ℓ Sn.
[0031] After cooling to a temperature of -7°C under stirring, some ice crystals started
to form as well as a solid precipitate. The solid matters were removed by filtration,
and contained primarily Fe MSA and a negligible amount of Sn.
[0032] Thereafter 30 ml of 70% MSA were added and the cooling was continued to a temperature
of -17.4°C. The electrolyte could now be separated by filtration into a solid portion
containing 60 g/ℓ Fe and a liquid containing 14 g/ℓ Fe and 70 g/ℓ Sn (the increased
Sn concentration is due to the removal of some water in the form of ice and hydration
water in the Fe MSA-crystals). The cooling was continued and at -23°C (external bath
temperature) further 30 ml 70% MSA were added and a further filtration process was
carried out. The slightly green filtrate now contained 3.4 g/ℓ Fe and 67 g/ℓ Sn and
the filtration residue proved to be a paste-like solid phase without a tendency to
melt.
[0033] Further 30 ml of 70% MSA solution were added and a further filtration was carried
out while gradually cooling the mixture down to -30°C and agitating heavily. The final
liquid electrolyte had a concentration of 1.5 g/ℓ Fe and 65 g/ℓ Sn and an acid content
of about 255 g/ℓ. This concentrated recovered electrolyte was diluted to an Fe concentration
of 0.5 g/ℓ and then reused in the original tinning electrolyte.
[0034] The solid ferrous methanesulfonate crystals were dissolved in warm water and passed
through an acidic ion exchanger to recover MSA in very good yields.
Examples 2-4
[0035] Each 35 liters of a concentrated Ronastan® TP-Sn electrolyte were treated according
to the procedure of example 1. The final temperature of the cooling liquid was -30°C,
and the corresponding temperature of the electrolyte was -29°C. The content of ferrous
ions was determined by atomic absorption spectroscopy. The initial and final Fe contents
in the electrolyte were recorded.
[0036] The results are shown in the following Table:
Ex. No. |
Initial Fe content (g/ℓ) |
Final Fe content (g/ℓ) |
2 |
33 |
4 |
3 |
33 |
6 |
4 |
33 |
3 |
1. A method for separating ferrous ions from an iron-containing tinning electrolyte on
the basis of methanesulfonic acid or phenolsulfonic acid, comprising the following
steps:
(a) providing a concentrated tin and iron-containing electrolyte containing 0.75 mol/ℓ
or more methanesulfonic acid or phenolsulfonic acid
(b) agitating and cooling the concentrated electrolyte to temperatures at which an
insoluble Fe-salt precipitates
(c) separating the insoluble precipitate to recover an electrolyte with a reduced
iron concentration.
2. The method according to claim 1, which further comprises at least one of the following
steps:
(d) washing the insoluble precipitate with a cold mixture of water and methanesulfonic
acid or phenolsulfonic acid
(e) recovering methanesulfonic acid or phenolsulfonic acid from said precipitate by
ion exchange.
3. The method according to claims 1 or 2, further comprising a step (f) which comprises
recycling of the recovered concentrated electrolyte from step (c) into the original
tinning electrolyte or a tin dissolving station.
4. The method according to any one of the preceding claims, wherein the electrolyte contains
methanesulfonic acid or a mixture of methanesulfonic acid and sulfuric acid as acidifying
agent.
5. The method according to any one of the preceding claims, wherein the concentrated
tin and iron-containing electrolyte used in step (a) is prepared by concentrating
a tinning electrolyte to 1/3 of its original volume by vacuum distillation and optionally
adding methanesulfonic acid or phenolsulfonic acid.
6. The method according to any one of the preceding claims, wherein in step (b), the
electrolyte is cooled to temperatures of +5°C or less.
7. The method according to any one of the preceding claims, wherein the concentration
of methanesulfonic acid or phenolsulfonic acid in the tin and iron-containing electrolyte
used in step (a) is 1 mol/ℓ or more.
8. The method according to any one of the preceding claims, wherein the electrolyte is
on the basis of methanesulfonic acid.
9. A recovery plant for tinning electrolytes on the basis of methanesulfonic acid or
phenolsulfonic acid, which comprises:
a device for concentrating the electrolyte to obtain a concentrated tin and iron-containing
electrolyte on the basis of methanesulfonic acid or phenolsulfonic acid
a device for cooling and agitating the concentrated electrolyte to temperatures at
which an insoluble Fe-salt precipitates
optionally supply means for feeding a solution of methanesulfonic acid or phenolsulfonic
acid into the concentrated electrolyte
a device for separating the iron-containing precipitate from the concentrated electrolyte
conducts for recycling the recovered concentrated electrolyte into the original tinning
electrolyte or a tin dissolving station
10. The recovery plant according to claim 9, which further comprises a device for recovering
methanesulfonic acid or phenolsulfonic acid from said iron-containing precipitate.
11. The recovery plant according to claim 9, which further comprises a device for washing
the obtained precipitate with a cold mixture of water and methanesulfonic acid or
phenolsulfonic acid, and an ion exchanger for recovering methanesulfonic acid or phenolsulfonic
acid from said iron-containing precipitate.
1. Verfahren zur Abtrennung von Eisen(II)ionen aus einem eisenhaltigen Verzinnungselektrolyten
auf Basis von Methansulfonsäure oder Phenolsulfonsäure, umfassend die folgenden Schritte:
(a) Bereitstellen eines konzentrierten zinn- und eisenhaltigen Elektrolyten, der 0,75
mol/ℓ oder mehr Methansulfonsäure oder Phenolsulfonsäure enthält,
(b) Rühren und Kühlen des konzentrierten Elektrolyten auf Temperaturen, bei denen
ein unlösliches Fe-Salz ausfällt,
(c) Abtrennen des unlöslichen Niederschlags, um einen Elektrolyten mit einer reduzierten
Eisenkonzentration wiederzugewinnen.
2. Verfahren gemäss Anspruch 1, das mindestens einen der folgenden Schritte zusätzlich
umfasst:
(d) Waschen des unlöslichen Niederschlags mit einer kalten Mischung aus Wasser und
Methansulfonsäure oder Phenolsulfonsäure,
(e) Wiedergewinnen der Methansulfonsäure oder Phenolsulfonsäure aus dem Niederschlag
mittels Ionenaustausch.
3. Verfahren gemäss Ansprüchen 1 oder 2, zusätzlich umfassend einen Schritt (f), der
die Rückführung des wiedergewonnenen konzentrierten Elektrolyten aus Schritt (c) in
den ursprünglichen Verzinnungselektrolyten oder eine Station zum Zinnauflösen umfasst.
4. Verfahren gemäss einem der vorhergehenden Ansprüche, wobei der Elektrolyt Methansulfonsäure
oder eine Mischung aus Methansulfonsäure und Schwefelsäure als ansäuerndes Mittel
enthält.
5. Verfahren gemäss einem der vorhergehenden Ansprüche, wobei der konzentrierte zinn-
und eisenhaltige Elektrolyt, der in Schritt (a) verwendet wird, durch Aufkonzentrieren
eines Verzinnungselektrolyten auf 1/3 seines ursprünglichen Volumens mittels Destillation
im Vakuum und optional Zugabe von Methansulfonsäure oder Phenolsulfonsäure hergestellt
wird.
6. Verfahren gemäss einem der vorhergehenden Ansprüche, wobei in Schritt (b) der Elektrolyt
auf Temperaturen von 5°C oder weniger gekühlt wird.
7. Verfahren gemäss einem der vorhergehenden Ansprüche, wobei die Konzentration von Methansulfonsäure
oder Phenolsulfonsäure im zinn- und eisenhaltigen Elektrolyten, der in Schritt (a)
verwendet wird, 1 mol/ℓ oder mehr beträgt.
8. Verfahren gemäss einem der vorhergehenden Ansprüche, wobei der Elektrolyt auf Methansulfonsäure
basiert.
9. Wiedergewinnungsanlage für Verzinnungselektrolyten auf Basis von Methansulfonsäure
oder Phenolsulfonsäure, umfassend:
eine Vorrichtung zum Aufkonzentrieren des Elektrolyten, um einen konzentrierten zinn-
und eisenhaltigen Elektrolyten auf Basis von Methansulfonsäure oder Phenolsulfonsäure
zu erhalten,
eine Vorrichtung zum Kühlen und Rühren des konzentrierten Elektrolyten auf Temperaturen,
bei denen ein unlösliches Fe-Salz ausfällt,
optional ein Versorgungsmittel zur Zufuhr einer Lösung aus Methansulfonsäure oder
Phenolsulfonsäure in den konzentrierten Elektrolyten,
eine Vorrichtung zur Abtrennung des eisenhaltigen Niederschlags aus dem konzentrierten
Elektrolyten,
Leitungen zur Rückführung des gewonnenen konzentrierten Elektrolyten in den ursprünglichen
Verzinnungselektrolyten oder eine Station zum Zinnauflösen.
10. Wiedergewinnungsanlage gemäss Anspruch 9, die zusätzlich eine Vorrichtung zur Wiedergewinnung
der Methansulfonsäure oder Phenolsulfonsäure aus dem eisenhaltigen Niederschlag umfasst.
11. Wiedergewinnungsanlage gemäss Anspruch 9, die zusätzlich eine Vorrichtung zum Waschen
des erhaltenen Niederschlags mit einer kalten Mischung aus Wasser und Methansulfonsäure
oder Phenolsulfonsäure und einen Ionenaustauscher zur Wiedergewinnung der Methansulfonsäure
oder Phenolsulfonsäure aus dem eisenhaltigen Niederschlag umfasst.
1. Procédé pour séparer les ions ferreux d'un électrolyte d'étamage à base d'acide méthane-sulfonique
ou d'acide phénol-sulfonique, contenant du fer, comprenant les étapes consistant à
:
(a) fournir un électrolyte concentré contenant de l'étain et du fer, renfermant 0,75
moles / l ou plus d'acide méthane-sulfonique ou d'acide phénol-sulfonique
(b) agiter et refroidir l'électrolyte concentré à une température à laquelle un sel
de Fe insoluble précipite
(c) séparer le précipité insoluble pour récupérer un électrolyte avec une concentration
diminuée en fer.
2. Procédé selon la revendication 1, qui comprend, en outre, au moins une des étapes
suivantes, consistant à :
(d) laver le précipité insoluble avec un mélange froid d'eau et d'acide méthane-sulfonique
ou d'acide phénol-sulfonique
(e) récupérer l'acide méthane-sulfonique ou l'acide phénol-sulfonique dudit précipité
par échange ionique.
3. Procédé selon la revendication 1 ou la revendication 2, comprenant en outre une étape
(f) comprenant le recyclage de l'électrolyte concentré récupéré à l'étape (c) dans
l'électrolyte d'étamage d'origine ou au poste de dissolution de l'étain.
4. Procédé selon l'une quelconque des revendications précédentes, dans lequel l'électrolyte
contient de l'acide méthane-sulfonique ou un mélange d'acide méthane-sulfonique et
d'acide sulfurique comme agent d'acidification.
5. Procédé selon l'une quelconque des revendications précédentes, dans lequel l'électrolyte
concentré contenant de l'étain et du fer utilisé à l'étape (a) est préparé en concentrant
un électrolyte d'étamage à 1 / 3 de son volume d'origine par distillation sous vide
et, le cas échéant, en ajoutant de l'acide méthane-sulfonique ou de l'acide phénol-sulfonique.
6. Procédé selon l'une quelconque des revendications précédentes, dans lequel à l'étape
(b), l'électrolyte est refroidi à une température de + 5 °C ou moins.
7. Procédé selon l'une quelconque des revendications précédentes, dans lequel la concentration
en acide méthane-sulfonique ou en acide phénol-sulfonique dans l'électrolyte contenant
de l'étain et du fer utilisé à l'étape (a) est de 1 mole / l ou plus.
8. Procédé selon l'une quelconque des revendications précédentes, dans lequel l'électrolyte
est à base d'acide méthane-sulfonique.
9. Installation de récupération d'électrolytes d'étamage à base d'acide méthane-sulfonique
ou d'acide phénol-sulfonique qui comprend :
un dispositif pour concentrer l'électrolyte, afin d'obtenir un électrolyte concentré
contenant de l'étain et du fer sur la base de l'acide méthane-sulfonique ou de l'acide
phénol-sulfonique
un dispositif pour refroidir et agiter l'électrolyte concentré à des températures
auxquelles un sel insoluble de Fe précipite
le cas échéant, des moyens d'alimentation pour amener une solution d'acide méthane-sulfonique
ou d'acide phénol-sulfonique dans l'électrolyte concentré,
un dispositif pour séparer le précipité contenant du fer à partir de l'électrolyte
concentré
des conduites pour recycler l'électrolyte concentré récupéré vers l'électrolyte d'étamage
d'origine ou vers un poste de dissolution de l'étain.
10. Installation de récupération selon la revendication 9, qui comprend en outre un dispositif
pour récupérer l'acide méthane-sulfonique ou l'acide phénol-sulfonique dudit précipité
contenant du fer.
11. Installation de récupération selon la revendication 9, qui comprend en outre un dispositif
pour laver le précipité obtenu avec un mélange froid d'eau et d'acide méthane-sulfonique
ou d'acide phénol-sulfonique et un échangeur d'ions pour récupérer l'acide méthane-sulfonique
ou l'acide phénol-sulfonique dudit précipité contenant du fer.