Note: Descriptions are shown in the official language in which they were submitted.
CA 02429156 2003-05-15
Henkel KGaA
Dr. Endres / KK
14.11.2000
Patent Application
H 5083
"Treatment of nickel-bearing waste water in phosphating"
This invention pertains to the field constituted by the
phosphating of metallic surfaces, as is implemented as a
widespread corrosion-preventive measure in the metalworking
industry, such as in the automobile industry and the
household-appliance industry, for example, but sometimes
also in steelworks. It relates to a process for treating
the overflow of the phosphating baths and/or the rinsing
water after phosphating with nickel-bearing phosphating
solutions. In preferred embodiments the process enables
the recycling of bath ingredients into the phosphating
bath, the re-use of active substances for the purpose of
producing replenishing solutions for phosphating baths, and
the use of the solution that has been depleted of metal
ions as rinsing water.
The phosphating of metals pursues the aim of generating
layers of metal phosphate which are firmly fused on the
surface of the metal and which, in themselves, already
improve corrosion resistance and, in conjunction with
lacquers and other organic coatings, contribute to a
substantial enhancement of the adhesion and the resistance
to infiltration in the event of corrosive stress. Such
phosphating processes have been known for a long time in
the state of the art. Suitable in particular for the
pretreatment prior to lacquering are the low-zinc
CA 02429156 2003-05-15
2
phosphating processes, in which the phosphating solutions
have comparatively low contents of zinc ions amounting to,
e.g., 0.5 to 2 g/1. A significant parameter in these low-
zinc phosphating baths is the weight ratio of phosphate
ions to zinc ions, which conventionally lies in the range
> 12 and may take values up to 30.
It has become evident that, through the concomitant use of
multivalent cations other than zinc in the phosphating
baths, phosphate layers can be formed having distinctly
improved corrosion-prevention and lacquer-adhesion
properties. For example, low-zinc processes with addition
of, e.g., 0.5 to 1.5 g/1 manganese ions and, e.g., 0.3 to
2.0 g/1 nickel ions find wide application as so-called tri-
cation processes for the preparation of metallic surfaces
for lacquering, for example for the cathodic
electrophoretic lacquering of automobile bodies.
A phosphating solution contains layer-forming components
such as, e.g., zinc ions and optionally further divalent
metal ions as well as phosphate ions. In addition, a
phosphating solution contains non-layer-forming components
such as alkali-metal ions for neutralising the free acid
and, in particular, accelerators and decomposition products
thereof. The decomposition products of the accelerator
arise by virtue of the fact that the latter reacts with the
hydrogen that is formed on the metallic surface by
corrosive reaction. The non-layer-forming components
accumulating with time in the phosphating bath - such as,
for example, alkali-metal ions and, in particular, the
decomposition products of the accelerator - can only be
removed from the phosphating solution by a portion of the
phosphating solution being discharged and discarded and
being continuously or discontinuously replaced by new
phosphating solution. Phosphating solution can, for
example, be discharged by the phosphating bath being
operated with an overflow and by the overflow being
CA 02429156 2003-05-15
3
discarded. As a rule, however, an overflow is not
required, since by virtue of the phosphated metal parts a
sufficient quantity of phosphating solution is discharged
in the form of adherent liquid film.
After the phosphating, the phosphating solution adhering to
the phosphated parts, such as automobile bodies for
example, is rinsed off with water. Since the phosphating
solution contains heavy metals and, optionally, further
ingredients that are not permitted to be released into the
environment in uncontrolled manner, the rinsing water has
to be subjected to a water treatment. This has to take
place in a separate step prior to introduction into a
biological clarification plant, since otherwise the
operational capability of the clarification plant would be
endangered.
Since both the disposal of the waste water (from
phosphating-bath overflow and/or rinsing water) and the
supply of the phosphating plant with fresh water are cost
factors, there is a need to minimize these costs. German
Patent Application DE 198 13 058 describes a process for
treating phosphating-bath overflow and/or rinsing water
after phosphating, wherein the phosphating-bath overflow
and/or the rinsing water is subjected to a nanofiltration.
The concentrate of the nanofiltration can be resupplied to
the phosphating bath. The filtrate of the nanofiltration
constitutes waste water which has to be subjected to
further treatment, optionally prior to being introduced
into a biological clarification plant. German Patent
Application DE 198 54 431 describes a process for saving
rinsing water in the course of phosphating. In this
process the phosphating-bath overflow and/or the rinsing
water after phosphating is subjected to a treatment process
such as, for example, a reverse osmosis, an ion-exchange
process which is not characterised in any detail, a
nanofiltration, an electrodialysis and/or a heavy-metal
CA 02429156 2003-05-15
4
precipitation, and the aqueous phase which in each given
case has been depleted of metal ions is employed as rinsing
water for the purpose of rinsing the metal parts to be
phosphated after they have been cleaned. The treatment of
rinsing water after phosphating by ion-exchange processes
is known from DE-A-42 26 080. In this case, use is made of
strongly acidic canon-exchange resins on the basis of
sulfonic-acid groups. Said cation-exchange resins bind all
canons in non-selective manner. Since it also contains
non-layer-forming cations in addition to the layer-forming
cations, the regenerated material cannot be used for
replenishing the phosphating solution, as this would lead
to an excessive increase in salinity of the phosphating
solution.
DE 199 18 713 describes an improved process for treating
phosphating-bath overflow and/or rinsing water after
phosphating. In this process it is at least intended to be
guaranteed that a waste water for disposal ultimately
arises, the contents of which in respect of zinc ions
and/or nickel ions lie below the permissible waste-water
limits. However, instead of a disposal by virtue of a
clarification plant, the waste water is also intended to be
capable of being used for the purpose of rinsing the metal
parts to be phosphated after the degreasing thereof. The
process is preferably to be operated in such a way that
layer-forming components of the phosphating bath, in
particular zinc ions and/or nickel ions, can be recovered
and employed again for phosphating purposes.
The object that is formulated in the aforementioned patent
is achieved by a process for treating phosphating-bath
overflow and/or rinsing water after phosphating,
phosphating being effected with an acidic aqueous
phosphating solution that contains 3 to 50 g/1 phosphate
ions, reckoned as PO43-, 0.2 to 3 g/1 zinc ions, optionally
further metal ions as well as, optionally, accelerators,
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whereby the phosphating-bath overflow and/or the rinsing
water after phosphating is conducted across a weakly acidic
ion-exchanger after a membrane filtration or without
upstream membrane filtration.
5
An example of a weakly acidic ion-exchanger is LewatitR TP
207 or TP 208 produced by Bayer AG, In a company
publication relating to this product (Bayer AG: LewatitR-
Selektivaustauscher, Eigenschaften and Anwendung von
Lewatit TM 207) it is reported that in the majority of
cases Lewatit TP 207 is employed after pre-exhaustion
(conditioning) with alkali ions or alkaline-earth ions. In
a few exceptional cases, which do not involve nickel, the
use of the hydrogen form is also possible. The
decomplexing pH value for nickel is specified as 2.1. This
pH value indicates the hydrogen-ion concentration at which
the metal ion is just desorbed from the Lewatit TP 207.
This company publication further states that the maximum of
the exchange capacity is attained in general if the pH
value of the exhausting solution is at least 2 units above
the decomplexing pH value. Accordingly, as reported in
this statement, nickel is only bound to a sufficient extent
at a pH value above 4.1. Consequently in the embodiment
examples of the already cited DE-A-199 18 713 the ion-
exchanger is employed in the monosodium form. According to
the aforementioned company publication produced by Bayer
AG, the outflow of the ion-exchanger in the monosodium form
has a pH value that lies between 6 and 9.
Japanese Patent Application P 62287100 (cited as stated in
Derwent Abstract 1988-0-25811) describes the binding of
nickel ions from phosphoric-acid solution to an ion-
exchanger, the acidic groups of which are neutralised with
sodium ions to an extent amounting to 25 to 75 0.
On the other hand, Japanese Patent Application JP 63057799
A2 (cited as stated in Patent Abstracts of Japan) discloses
CA 02429156 2003-05-15
6
that nickel from a plating solution can also be bound to
the H-form of an ion-exchanger with chelating
iminodiacetic-acid groups (which constitute weakly acidic
groups). This cannot be applied to the problem as
formulated in the present invention, since plating
solutions have substantially higher contents of metal ions
than phosphating-bath overflow diluted with rinsing water
or rinsing water after phosphating. The nickel contents of
the last-named solutions lie, as a rule, within the range
between 5 and 100, in particular between 10 and 50 ppm.
These solutions have to be treated in such a way that the
nickel contents of the treated solutions are below 1 ppm.
This is possible with the process according to
DE-A-199 18 713. However, the use of a weakly acidic ion-
exchanger, preferably one having chelating iminodiacetic-
acid groups, in the monosodium form, which is disclosed
therein entails several disadvantages. On the one hand,
for the regeneration of the ion-exchanger after eluting the
bound metals with acid it is necessary to convert the ion-
exchanger into the monosodium form with caustic-soda
solution. This contributes to the chemical consumption of
the overall process and compels the user of this process to
hold supply vessels and pipelines in store for the caustic-
soda solution. This complicates the overall process and
makes it more expensive. Moreover, this process has the
disadvantage that when the ion-exchanger is employed for
the purpose of treating the stated phosphating-bath waste
waters a waste water arises that has been subjected to an
increase in salinity by virtue of sodium salts and that can
only be re-used to a limited extent. In the course of
regeneration of the exhausted ion-exchanger with acid, in
which a nickel-bearing solution of valuable material is
preferably to be ejected, residual sodium in the ion-
exchanger is likewise eluted. The nickel-bearing solution
of valuable material is therefore contaminated with sodium
ions and so can only be re-used to a limited extent.
CA 02429156 2003-05-15
The present invention sets itself the object of avoiding
the aforementioned disadvantages. It is based on the
surprising perception that weakly acidic ion-exchangers of
the type represented by LewatitR TP 207, contrary to what is
stated by the manufacturer, bind nickel from dilute
solutions (nickel contents between 5 and 100, in particular
between 10 and 50 ppm) to a sufficient extent and in
particular selectively in relation to manganese and,
partially, zinc, also at a pH value no higher than 4.
The invention accordingly provides a process for treating a
nickel-bearing aqueous solution consisting of phosphating-
bath overflow and/or of rinsing water after phosphating,
wherein phosphating is effected with an acidic aqueous
phosphating solution that contains 3 to 50 g/1 phosphate
ions, reckoned as PO93, 0.2 to 3 g/1 zinc ions, 0.01 to
2.5 g/1 nickel ions, optionally further metal ions as well
as, optionally, accelerators, whereby the phosphating-bath
overflow andlor the rinsing water after phosphating is
conducted across a weakly acidic ion-exchanger,
characterised in that the acid groups of the ion-exchanger
are neutralised with alkali-metal ions to an extent
amounting to no more than 15 o and in that when it is fed
to the ion-exchanger the nickel-bearing aqueous solution
has a pH value within the range from 2.5 to 6.0, preferably
from 3 to 4.1.
Thus in accordance with the invention a weakly acidic ion-
exchanger is to be employed, the acid groups of which are
neutralised with alkali-metal ions to an extent amounting
to no more than 10 0. However, the aim is that the acid
groups of the ion-exchanger are neutralised with alkali-
metal ions to an extent amounting to no more than 5 0,
preferably no more than 3 o and in particular no more than
1 0. In the optimal case the ion-exchanger contains no
CA 02429156 2003-05-15
8
alkali-metal ions at all. However, since equilibrium
processes play a role in the regeneration of an exhausted
ion-exchanger, this desired ideal state of the ion-
exchanger cannot always be obtained.
A simple criterion as to whether the acid groups have been
neutralised with alkali-metal ions to a sufficiently small
extent is constituted by the bed volume (abbreviated as BV
in the following) of the ion-exchanger. The term 'bed
volume' is to be understood to mean the total volume of the
ion-exchange particles together with the liquid between the
particles. The bed volume of weakly acidic ion-exchangers
usually depends on the degree of neutralisation of the acid
groups. For example, if the disodium form of a weakly
acidic ion-exchanger with iminodiacetic-acid groups -
LewatitR TP 207 for example - with a bed volume of 500 ml is
washed out with acid to such an extent that the sodium ions
are removed as extensively as possible, the bed volume
shrinks to 400 ml. The bed volume of the monosodium form
amounts to around 450 ml. Such an ion-exchanger is in the
state to be used in accordance with the invention if the
bed volume of the ion-exchanger, which in the disodium form
amounts to 500 ml, is not above 415 ml.
Described below are phosphating baths which are
conventional in the state of the art, the bath overflow or
rinsing water of which can be treated with the process
according to the invention:
The zinc contents preferably lie within the range from 0.4
to 2 g/1 and in particular from 0.5 to 1.5 g/1, as
conventional for low-zinc processes. The weight ratio of
phosphate ions to zinc ions in the phosphating baths may
fluctuate within wide limits, provided that it lies within
the range between 3.7 and 30. A weight ratio between 10
and 20 is particularly preferred. Moreover, the
phosphating baths contain 0.01 to 2.5 g/1, preferably 0.3
CA 02429156 2003-05-15
9
to 2.0 g/1, nickel ions. In addition, the phosphating
solution may contain 0.1 to 4 g/ml, in particular 0.5 to
1.5 g/1, manganese ions, as is conventional for tri-ration
processes. Moreover, in addition to the zinc ions and
nickel ions and optionally manganese ions, the phosphating
solution may contain by way of further metal ions:
0.2 to 2.5 g/1 magnesium(II),
0.2 to 2.5 g/1 calcium(II),
0.002 to 0.2 g/1 copper(II),
0.1 to 2 g/1 cobalt(II).
The form in which the rations are introduced into the
phosphating baths is basically of no importance. One
I5 possibility which presents itself in particular is to use
oxides and/or carbonates as a ration source. On account of
the risk of an increase in salinity of the phosphating
baths, salts of acids other than phosphoric acid should
preferably be avoided.
In the case of phosphating baths that are to be suitable
for differing substrates, it has become conventional to add
free and/or coordinated fluoride in quantities up to
2.5 g/1 of total fluoride, thereof up to 750 mg/1 of free
fluoride, in each case reckoned as F-. In the case where
fluoride is absent, the aluminium content of the bath is
not to exceed 3 mg/1. In the case where fluoride is
present, higher A1 contents are tolerated as a consequence
of the complexing, provided that the concentration of the
non-complexed A1 does not exceed 3 mg/1.
Besides the layer-forming divalent rations, phosphating
baths additionally contain, as a rule, sodium ions,
potassium ions and/or ammonium ions for the purpose of
adjusting the free acid.
Phosphating baths that serve exclusively to treat
CA 02429156 2003-05-15
galvanised material do not necessarily have to contain a
so-called accelerator. However, accelerators that are
required in the phosphating of non-galvanised steel
surfaces are also frequently employed concomitantly in the
5 state of the art in the phosphating of galvanised material.
Accelerator-containing phosphating solutions have the
additional advantage that they are suitable both for
galvanised materials and for non-galvanised materials.
This is particularly important in the phosphating of
10 automobile bodies, since the latter frequently contain both
galvanised and non-galvanised surfaces.
Various accelerators are available in the state of the art
for phosphating baths. They accelerate the formation of
layers and facilitate the formation of closed phosphate
layers, since they react with the hydrogen arising in the
course of the corrosive reaction. This process is
described as "depolarisation". The formation of hydrogen
bubbles on the metallic surface, which interfere with the
formation of layers, is prevented by this means. If,
within the scope of the process according to the invention,
a membrane process (reverse osmosis or nanofiltration) is
employed prior to the ion exchange, those accelerators are
preferred, the by-products or decomposition products of
which (reaction products with hydrogen) are able to
penetrate the membrane. By this means it is guaranteed
that these by-products and decomposition products of the
accelerator do not accumulate in the phosphating bath but
are discharged from the system at least partially via the
filtrate of the membrane filtration.
Particularly suitable are those accelerators which form as
by-products or decomposition products either water or
monovalently charged ions which are able to penetrate a
nanofiltration membrane. For example, the phosphating
solution may contain one or more of the following
accelerators:
- CA 02429156 2003-05-15
11
0.3 to 4 g/1 chlorate ions
0.01 to 0.2 g/1 nitrite ions
0.1 to 10 g/1 hydroxylamine
0.001 to 0.15 g/1 hydrogen peroxide in free or bound
form
0.5 to 80 g/1 nitrate ions.
In the course of the depolarisation reaction on the
metallic surface, chlorate ions are formed from chloride
ions, nitrate ions and ammonium ions are formed from
nitrite ions, ammonium ions are formed from nitrate ions,
ammonium ions are formed from hydroxylamine, and water is
formed from hydrogen peroxide. The anions or ammonium ions
that are formed are able to pass through a nanofiltration
membrane, so that in the process according to the invention
they are discharged at least partially from the
phosphating-bath overflow or from the rinsing water after
phosphating.
Together with, or instead of, chlorate ions, use may
advantageously be made of hydrogen peroxide by way of
accelerator. This can be employed as such or in the form
of compounds that form hydrogen peroxide under the
conditions of the phosphating bath. However, preferably no
multivalent ions are to arise as by-products in this case,
since they would be enriched in the phosphating bath in the
event of recycling of the concentrate of the
nanofiltration. Therefore alkali-metal peroxides, in
particular, present themselves as an alternative to
hydrogen peroxide.
An accelerator that is likewise preferably to be used
within the scope of the process according to the invention
is hydroxylamine. If the latter is added to the
phosphating bath in free form or in the form of
hydroxylammonium phosphates, hydroxylammonium nitrate
and/or hydroxylammonium chloride, likewise only
- CA 02429156 2003-05-15
12
decomposition products or by-products are formed that are
able to penetrate a nanofiltration membrane.
The process according to the invention can be operated in
such a way that the phosphating-bath overflow and/or the
rinsing water after phosphating is conducted directly
(optionally after removal of sludge and/or of organic
constituents, which can be effected, for example, by a
screen filtration or bag filtration or a filtration across
a particle bed such as a sand filter, for example) across
the weakly acidic ion-exchanger. As an alternative to
this, the phosphating-bath overflow and/or the rinsing
water after phosphating (likewise optionally after the
removal of sludge and/or of organic constituents) may be
subjected to a membrane filtration in the form of an
ultrafiltration, a nanofiltration or a reverse osmosis.
After the filtration the aqueous solution is subsequently
conducted across the weakly acidic ion-exchanger. By
virtue of the weakly acidic ion-exchanger, metal ions that
constitute valuable materials of a phosphating solution are
removed selectively from the aqueous solution. By this
means, on the one hand the reliability is increased that
the waste-water limits for these can ons will be observed.
Moreover, these can ons can be employed again for
phosphating purposes after regeneration of the ion-
exchanger.
Various types of membrane are available in the state of the
art for an ultrafiltration, a nanofiltration or a reverse
osmosis. Since phosphating baths and also the
corresponding rinsing waters react acidically, the membrane
that is employed should be acid-resistant. Suitable, for
example, are inorganic membranes such as, e.g., ceramic
membranes. Moreover, organic polymer membranes can be
employed. In particular, a polyamide membrane is suitable
as a nanofiltration membrane.
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13
If one of the stated membrane-filtration processes is
employed prior to the ion exchange, the process is
preferably operated in such a way that the retentate of the
membrane filtration is recycled into the phosphating
solution. By this means, some of the layer-forming cations
that are present in the overflow of the phosphating bath or
in the rinsing water are already recycled into the
phosphating solution. This results in a more economical
mode of operation of the phosphating bath, since fewer
ingredients have to be freshly supplied.
Irrespective of whether the phosphating-bath overflow
and/or the rinsing water after phosphating is conducted
directly to the ion-exchanger or whether one of the stated
membrane-filtration processes is employed beforehand, it is
preferred to free the phosphating-bath overflow and/or the
rinsing water after phosphating from sludge and/or from
organic constituents. Blocking of the filtration membranes
or of the ion-exchanger is prevented by this means. Sludge
can be removed by bag filtration, for example. The filter
Lofclear 523 D produced by Loeffler GmbH, for example, is
suitable here by way of filter. It removes 95 0 of the
particles having a size below 1.5 um and 99.9 0 of the
particles having a size below 5.5 Vim. Organic constituents
in the phosphating bath (for example, organic accelerators
and/or decomposition products thereof or any organic
polymers that are present in the phosphating bath) can be
removed by activated carbon or by synthetic resins.
Suitable by way of activated carbon is, for example, the
type Lofsorb LA 40 E-3-Ol produced by Loeffler GmbH. By
way of organic resins, use may be made of Lewatit VP OC
1066 or Dowex OPTL 285, for example, with a view to
removing organic constituents.
A Desal DK membrane, for example, is suitable for the step
of nanofiltration. With a pressure difference of 7 bar and
at a temperature of 35 ~C it provides a membrane flow of the
CA 02429156 2003-05-15
14
order of 35 to 40 1 per m2 per hour at a volume ratio of
concentrate . filtrate = 1 . 1. A Filmtec SW 30 membrane
produced by Rochem, for example, can be employed for the
step of reverse osmosis. With a pressure difference of 25
bar and at a temperature of 45 °C it yields a membrane flow
of approximately 30 1 per m2 per hour at a volume ratio of
concentrate . filtrate = 5 . 1.
By way of weakly acidic ion-exchanger, preferably such a
type is employed that is selective in respect of nickel
ions and/or zinc ions. Under operational conditions the
weakly acidic ion-exchanger preferably binds nickel ions
more strongly than zinc ions. This means that nickel ions
from the solution that has been fed are able to displace
zinc ions from the ion-exchanger. Monovalent can ons are
to be bound as little as possible. For this purpose, in
particular such weakly acidic ion-exchangers are suitable
that bear chelate-forming iminodiacetic-acid groups. A
suitable product is LewatitR TP 207 or TP 208 produced by
Bayer. Other suitable ion-exchangers are IRC 718/748
produced by Rohm & Haas, as well as S-930 produced by
Purolite.
The process is preferably operated in such a way that the
weakly acidic ion-exchanger is regenerated with a weakly
acidic acid after exhaustion. The selectively bound nickel
ions, optionally together with zinc ions still remaining,
are eluted in the process and can be re-used for
phosphating purposes. Through the use of the process
according to the invention these rations do not have to be
disposed of in the form of heavy-metal-containing sludge
but can - optionally after suitable treatment - be employed
again for phosphating. As a result, resources are spared.
For the regeneration of the exhausted weakly acidic ion-
exchanger it is particularly preferred to make use of an
acid that constitutes a valuable material for the
phosphating solution. Phosphoric acid is particularly
CA 02429156 2003-05-15
suitable. Phosphoric acid may contain, relative to the
overall quantity of acid, up to a total of 10 mol.o nitric
acid, hydrochloric acid and/or hydrofluoric acid.
5 In order, after the regeneration with acid, to keep the
ion-exchanger in the acid form but largely to wash out the
free acid that was used for the purpose of regeneration,
after the regeneration with a strong acid the ion-exchanger
is washed with water or with a quantity of lye that
10 corresponds to a maximum of 0.5 bed volumes of 4-o caustic-
soda solution. This rinsing process is carried out until
such time as the pH value of the rinsing solution running
off from the ion-exchanger lies between 2.1 and 4.5,
preferably between 3.0 and 4.1. In this connection a
15 rinsing water is employed, the temperature of which lies
within the range between approximately 5 and approximately
50 ~C and in particular between approximately 15 and
approximately 45 °C. For the rinsing, caustic-soda solution
may be dispensed with entirely. However, this presupposes
an appropriately long rinsing with water. The rinsing
operation can be shortened if a quantity of lye is admixed
to the rinsing water that corresponds to a maximum of 0.5
bed volumes of 4-% caustic-soda solution. With this
quantity of lye the residual acid in the free volume
between the ion-exchange particles is neutralised, but the
acid groups of the exchanger itself are not. This means
that sodium ions scarcely bind to the ion-exchanger with
this low quantity of lye. Rather, sodium ions are
predominantly present between the ion-exchange particles in
the form of dissolved salts in the aqueous phase and are
therefore rapidly displaced in the course of feeding the
solution to be treated to the exchanger.
For the regeneration of the exhausted ion-exchanger the
procedure is preferably such that a concentrate fraction is
ejected that contains at least 0.5 wt.o nickel ions, and
said fraction is re-used immediately or after replenishment
CA 02429156 2003-05-15
16
with further active substances for the purpose of
replenishing a phosphating solution. In this connection it
is particularly preferred to replenish the regenerated
material with further zinc ions andlor nickel ions and also
with further active substances of a phosphating solution in
such a way that a conventional replenishing solution for a
phosphating bath is formed. This replenishing solution can
then be used as conventionally for the purpose of
replenishing the phosphating bath.
The solution that has been depleted of can ons and that
leaves the weakly acidic ration-exchanger in the exhaustion
phase thereof can, depending on ingredients, be supplied to
a simplified waste-water treatment or introduced directly
into a biological clarification plant. However, it is more
economical to use this solution as rinsing water for the
metal parts to be phosphated after the degreasing thereof.
This embodiment of the process according to the invention
has the additional advantage that rinsing water is saved.
If the phosphating-bath overflow or the rinsing water after
phosphating is subjected to a membrane filtration prior to
being fed to the weakly acidic ion-exchanger, the outflow
from the ion-exchanger can be employed directly for rinsing
purposes. If the membrane filtration arranged upstream is
dispensed with, it is advisable to subject the outflow from
the ion-exchanger to a membrane filtration before it is
used as rinsing water. A nanofiltration is particularly
suitable for these processes.
Embodiment Examples
Example 1:
The activity of the weakly acidic ration-exchanger
according to the invention Lewatit TP 207 (Bayer) in the H+
form was examined in comparison with a fully synthetic
CA 02429156 2003-05-15
17
aqueous phosphating rinsing solution. To this end, ion-
exchange columns were filled with, in each case, 500 ml of
resin (in the supplied form as the disodium form; in the
course of exchange with acid for the purpose of forming the
H+ form the volume shrinks to 400 ml) and charged with 648
bed volumes of rinsing solution, and the eluate solution
emerging from the columns was continuously analysed in
respect of its residual metal content. The fully synthetic
rinsing solutions that were employed (pH value 4.0)
contained 25 ppm nickel, 25 ppm manganese and 50 ppm zinc.
Table 1 indicates the exhaustion volumes and the
corresponding nickel concentrations.
CA 02429156 2003-05-15
18
Table 1
Eluate BV ppm Nickel
(bed volume = 0.5 1)
24 0.33
48 0.30
72 0.25
96 0.28
120 0.30
144 0.29
168 0.27
192 0.34
216 0.38
240 0.21
264 0.26
288 0.30
312 0.44
336 0.44
360 0.56
384 0.69
408 0.88
432 1.08
456 1.32
480 1.51
504 1,84
528 2.01
552 2.31
576 2.63
600 2.95
624 3.41
648 3.77
- CA 02429156 2003-05-15
19
Comparative Example 1:
In a manner analogous to Example l, the activity of the
weakly acidic cation-exchanger according to the invention
Lewatit TP 207 (di-Na+ form) was investigated. To this end,
the resin was conditioned after the regeneration with 2.4
BV NaOH (4 0) and subsequently rinsed with 2.0 BV of
desalinated water (in each case with 4 BV/h). The
phosphating rinsing solutions that were employed
corresponded to the data in Example 1. Table 2 indicates
the exhaustion volumes and the corresponding nickel
concentrations. The breakthrough behaviour for nickel is
virtually identical in both Examples.
CA 02429156 2003-05-15
Table 2
Eluate BV ppm Nickel
(bed volume = 0.5 1)
24 0.10
48 0.11
72 0.14
96 0.18
120 0.28
144 0.24
168 0.21
192 0.36
216 0.30
240 0.33
264 0.28
288 0.31
312 0.39
336 0.55
360 0.69
384 0.85
408 1.05
432 1.23
456 1.32
480 1.44
504 1.68
528 1.86
552 2.17
576 2.54
600 2.71
624 3.16
648 3.46
CA 02429156 2003-05-15
21
Example 2:
In order to document the regenerative power of the
exhausted ion-exchange resins, after exhaustion with 648
bed volumes of rinsing water (corresponds to 8.1 g nickel)
said ion-exchange resins were re-extracted with phosphoric
acid. To this end, the resins that were exhausted in
accordance with Example 1 were eluted with 40-o phosphoric
acid, and a concentrate fraction having the following
composition was collected: nickel 1.8 wt. o, phosphate
10 wt.%.
Example 3:
The activity of the weakly acidic can on-exchanger
according to the invention Lewatit TP 207 (Bayer) in the H+
form was examined in comparison with a fully synthetic
aqueous phosphating rinsing solution. To this end, ion-
exchange columns were filled with, in each case, 500 ml of
resin (supplied form: di-Na+, in the H+ form that was
employed approximately 400 ml) and charged with 480 bed
volumes of rinsing solution, and the eluate solution
emerging from the columns was continuously analysed in
respect of its residual metal content. The fully synthetic
rinsing solutions that were employed (pH value 3.5; for
comparison, in Ex. 1 pH value 4.0) contained 25 ppm nickel,
25 ppm manganese and 50 ppm zinc. Table 3 indicates the
exhaustion volumes and the corresponding nickel
concentrations.
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22
Table 3 (rinsing solutions pH value 3.5; column in H+ form)
Eluate BV ppm Nickel
(bed volume = 0.5 1)
24 0.19
48 0.07
72 0.10
96 0.15
120 0.20
144 0.34
168 0.41
192 0.76
216 0.78
240 0.85
264 1.09
288 1.24
312 1.47
336 1.74
360 2.06
384 2.42
408 2.89
432 3.31
456 3.83
480 4.35
CA 02429156 2003-05-15
23
Comparative Example 2:
In a manner analogous to Example 3, the activity of the
weakly acidic cation-exchanger Lewatit TP 207 (di-Na+ form)
was investigated. To this end, after the regeneration the
resin was conditioned with 2.4 BV NaOH (4 0) and
subsequently rinsed with 2.0 BV of desalinated water (in
each case with 4 BV/h). The phosphating rinsing solutions
that were employed corresponded to the data in Example 3.
Table 4 indicates the exhaustion volumes and the
corresponding nickel concentrations. The breakthrough
behaviour for nickel is very similar in both examples.
CA 02429156 2003-05-15
24
Table 4 (rinsing solutions pH value 3.5; column in di-Na+
form
Eluate BV ppm Nickel
(bed volume = 0.5 1)
24 0.16
48 0.19
96 0.28
144 0.35
168 0.55
192 0.71
216 0.93
240 1.10
264 1.28
288 1.18
312 1.50
336 1.45
360 1.72
384 1.95
408 2.35
432 2.67
456 3.02
480 3.82
The following Example 4 shows that nickel is more firmly
bound to LewatitR TP 207 than zinc and manganese. (The
initially high nickel contents are based on residual nickel
in the experimental arrangement, as a result of a preceding
experimental cycle.) Manganese is only bound initially by
CA 02429156 2003-05-15
the column but runs freely through after exhaustion with
approximately 500 bed volumes of solution. In the course
of this exhaustion the breakthrough of zinc also begins,
whereas nickel is still almost completely bound up to
5 approximately 1,000 bed volumes. Although nickel is bound
increasingly poorly above this degree of exhaustion, it is
still clearly bound, whereas the zinc content of the
emerging solution is higher than that of the solution that
has been fed. This means that not only no further zinc is
10 bound but that nickel in the solution displaces the zinc
that is bound to the exchanger.
Example 4:
Two columns in series, both columns in H+ form, the column
15 in position 2 from a preceding cycle already partially
exhausted with Ni. The fully synthetic rinsing solutions
that were employed (pH value 4.0) contained 25 ppm nickel.
25 ppm manganese and 50 ppm zinc.
BV ppm Ni ppm Zn ppm Mn
48 0.6 1.1 3.5
192 0.2 0.5 17
384 0.1 0.2 21
576 0.1 2.1 23
720 0.1 7.8 25
864 0.1 18 27
1056 0.2 34 28
1248 0.9 50 29
1440 3.2 59 28
1632 6.6 61 28
