Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~7329 ~ ~
This invention relates to the removal of metals
from metal-containing solutions such as waste waters and
the like.
Many industries producè large quantities of waste
water which contain metals that are detrimental to the
environment and/or toxic to man and animal. Typical examples
of these metals are mercury, cadmium, copper, zinc, silver
and nickel. Waste waters, containing these metals are common-
ly produced by metal finishing electroplating, ore digestion ~ ;
and salt recovery plants. Since waste waters are being pro- ~-
duced in ever increasing quantities and since the legally ~ -
permissible levels of discharge are becoming more and more
stringent, the purification of these waters, and parti-
cularly the removal of these various metals, becomes a pro-
blem of increasing importance.
The current procedure for the removal of metals
from waste waters is precipitation of the insoluble hydroxides
with alkali or lime. In the absence of complexing agents,
a pH of 9 is sufficient to reduce the level of most of these
metals down to 1 ppm or lower. Higher pH values are only
required for some metals, such as cadmium and the attainable ; -
1 ppm level is still relatively high for cadmium in view of
its toxicity. A coprecipitation with ferric hydroxide is
also used in some cases.
However, the effluents of metal-finishing and
electroplating industries often contain organic chemicals such
.:
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.~
10~7329
as detergents or dispersing agents, which may form complexes with one or more
of these metals.
Typical examples of such chemicals are aminocarboxylic acids
~ethylenediaminotetraacetate, diethylenetriaminopentaacetate, hydroxyethyl-
ethylenediaminotriacetate, nitriloacetate), oxycarboxylic acids (citrate,
tartrate, gluconate) and amines (ammonia, triethanolamine, ethylenediamine,
trimethylamine). All these chemicals form rather stable, water-soluble
complexes with most metal ions, hampering thereby the quantitative pre-
cipitation of these metals at high pH. Under such conditions, waste waters
may carry 10 ppm or more of the metals in complexed dissolved state and
such amounts are discharged in the environment together with the waste
water.
The invention has for its object to provide a process by which,
irrespective of the presence of the aforementioned chemicals, a nearly
quantitative removal of metals from waste water and other solutions, can
be accomplished.
The present invention provides a process for the removal of metal
ions from aqueous solution characterized by treating said solution with a
cation exchanger in the presence of a polyamine, wherein said metal and said
polyamine are capable of forming with one another a stable cationic complex
and wherein during treatment said solution has a pH value of 4 to 9. Metal
`~ ions may be quantitatively removed from solutions even extremely dilute
solutions, by this process, irrespective of the presence of the aforesaid
~^ organic chemicals or other electrolytes such as sodium or calcium salts.
! Experiments leading to the invention have shown that the addition
~ of polyamines, which are capable of forming stable
.~
G -3_
1~37329
cationic complexes with most metal ions, to metal-containing -
aqueous solutions has a pronounced synergistic effect on the
adsorption of these metals by a cation exchanger. In particular,
it was found that tetraethylenepentamine in combination with
phyllosilicates such as bentonite and montmorillonite is
quite effective in reducing the concentration of copper and
mercury to very low values, sometimes down to 10 ppb (parts
per billion) or less. The phenomenon is based upon the
formation of a cationic polyamine complex which is easily
adsorbed in the cation exchanger and which is stabilized by
a factor of about one thousand as compared to the complex
stability in solution.
It should be understood that many of the
aforesaid metal-polyamine complexes are known already
se and that the formation of such complexes on mineral
cation exchangers has beén studied already before. However,
the studies on this subject have always been made from an
analytical or diagnostic point of view and the idea of
using such complex-forming and adsorption phenomena for
a substantive removal of metals from solutions has seldom,
if ever, occurred to research workers in this field. In
the few cases that a suggestion about extracting certain
metals from solution was made, these suggestions led awa~
from the present invention by starting that such extraction
is questionable or less effective. Moreover, the great
difference in stability constants between metal-polyamine
complexes in solution and in adsorbed state on a cation
exchanger has never been found before and it was especially
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7~Z9
on the basis of this surprising discovery that the present
invention could be established.
The process described in this application is
suitable for the removal from aqueous solutions of all
dissolved metals capable of forming stable cationic complexes
with polyamines. In general, these are elements from the
groups III B, IV B, V B, VI B, VII B, VIII, I B, II B,
III A, IV A, V A, VI A and VII A of the Periodic System
to the extent that they belong to the periods 4, 5, 6,
7 of that System and insofar certain oxydation states of
these elements lead to complex formation. Evidently, not
all metals from this series will be present in the solution
to be purified nor have all metals necessarily to be removed
from it. The choice of metals to be removed ~ith the process
3 of this invention depends on various factors such as the
s~; toxicity and detrimental effect of the metal in question,
~ the cost of the pure metal and of the method used, the ~ -
"". . . .
stability of the complex to be formed and so on. In practice,
one of the chief interests lies in the removal of mercury,
cadmium, copper, zinc, silver, nickel and cobalt which are
o~ten present in industrial waste waters and are detrimental ~ ~
to the environment while the recovery of silver is also ~ -
~, desirable by reason of its high price.
In carrying out the invented process, one may use
any type of aqueous solution containing one or more valuable
metals from the above groups m a dissolved state. Thus,
the starting material is not restricted to waste waters but
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1~373Z9
it may include solutions of various origin, for example
solutions derived from reclaiming low-grade ores. No limits
need be set to the concentration of metal to be removed from
the starting solution. If desired, the bulk of the metal may
be removed from solution by means of some other method such as
precipitation of metal hydroxide with lime or alkali and the
residual metal be removed then by the invented process.
In case the concentration of the metal to be removed ;~
- is rather low, then the efficiency of the process can be
estimated in advance on the basis of the equilibrium concen~
tration of free metal in the presence of the polyamine complex. ~ -
The cationic complexes of polyamines with most metal ions are
well known and the corresponding stability constants are
easily found in handbooks. In this way, one may check whether
the use of the present invention is worthwhile or not.
.. - :
Should anionic complexing agents be present in the
~,:;,
aqueous solution, then this presence does not necessarily
have a negative effect on the efficiency of the process.
In may cases, these chemicals can form anionic complexes with
~; 20 the metals to be removed but an addition of polyamines
will lead to a displacement of the metals from such complexes
~ , .
to form the more stable polyamine complexes which, upon adsorp-
tion into the ion exchanger are further stabilized and removed.
Accordingly, the presence of anionic complexing agents presents
little problems in most cases.
Should the solution contain other complexing agents
which can form cationic complexes, then there is evidently
no negative effect on the efficiency of the process,
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:
since their presence can only enhance the effect of the polyamine to be
added. The invented process can therefore be carried out irrespective of
the presence of complex forming chemicals.
The acidity of the aqueous solution is not critical but in most
cases the removal of metals from solution by means of a polyamine and a
cation exchanger proceeds satisfactorily between a pH of 4 to 9 and preferably
between 6.5 and 9. For some elements such as mercury which form extremely
stable complexes, the process can be carried out even at lower pH values.
In general, however, no complexes will be formed at very acid pH and difficult-
ies in processing may occur at very alkaline pH.
As to the polyamine, any type of organic chemical carrying twoor more amino groups can be used provided it forms cationic complexes with
these metals. Typical examples of these chemicals are ethylenediamine, propy-
- lenediamine, triaminotriethylamine, diethylenetriamine, triethylenetetramine,
~ tetraethylenepentamine, tetra-2-aminoethylethylenediamine etc. If desired, ~ - -
3~ carboxyl groups, hydroxyl groups and/or other substituents may be present in
the molecule provided they do not weaken the complex-forming effect of the
polyamine. In practice, one should choose a polyamine which forms a metal
complex of sufficiently high stability with the metal to be removed so as to
exceed the stability of complexes of the metal with other complexing agents
which may already be present. In general, the best results are obtained ~ -
with polyamines containing four or more amino groups.
Preferably, the amount of polyamine used is sufficient to provide `~
a molar ratio of polyamine to metal which is equal to or greater than the
molecular ratio of polyamine to metal in the complex formed. For example,
the amount of polyamine to be used should at least
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10~373Z9
be equal to the amount of the metal - on a molar basis - in the case of the
formation of 1-1 complexes, as for example with copper and tetramine or
pentamine. In case complexes of the type 1-2 are formed, as for copper with
diamines and triamines, then at least a two-fold excess of palyamine is to
be added with respect of the amount of metal present. The question which
type of complex will be formed, is dependent from the nature of metal and
polyamine and the exact type of complex may be readily be established before-
hand by consulting available handbooks on this subject.
When a large excess of anionic complex forming agents is present in
the solution, somewhat higher doses of polyamine may be needed to obtain ~
optimum results. Such higher doses have an additional advantage in that they ~ ;
mostly lead to a better flocculation of the cation exchanger which-may settle
more rapidly and be filtered off more easily.
: . .
Any organic or inorganic material having cation-exchange properties
can be taken as a cation exchanger. Among the inorganic cation exchangers
- the most suitable materials are synthetic or natural tectosilicates and
synthetic or natural phyllosilicates (clay minerals).
~ Examples of useful tectosilicates are ultramarines and zeolites,
-~ both synthetic (zeolite A, zeolite X, zeolite Y, zeolite L, zeolite Q) and
natural (chabazite, erionite, heulandite, mordenite, clinoptilolite). Ex-
amples of useful phyllosilicates are attapulgite, vermiculite, montmorillonite,
- bentonite, illite, micas and hydromicas, kaolinite, chrysotyle. These ion
exchangers may be used as such or mixed with conventi~nal additives such as
for instance organic or inorganic granulates, agglomerants, diluters and
binders.
Which type of cation exchangers will be used depends on various
circumstances such as the molecular volume of the metal complex to be adsorbed,
the pore structure of the ion exchanger, the initial concentration of the
metal in solution, the exchange capacity of the ion exchanger, the desired
efficiency and the cost of the materials.
10i~7329
For the removal of copper and mercury from aqueous solutions, best
results were obtained with montmorillonite and bentonite as ion exchangers
combined with tetraethylenepentamine as polyamine. The efficiency was then
in~ariably better than 99%.
The amount of cation exchanger to be used is not critical. In
general, this amount will depend on various factors such as the ion capacity
- of the ion exchanger and the concentration of the metal ion to be removed from
solution. In practice, amounts of cation exchanger of about 20 gram per
. . ~.
gram of metal turned out satisfactory though one may use doses of 3 to 30
gram of cation exchanger per gram of metal with equally good result. ~ -
Regarding the order of addition of polyamine and cation exchanger, ~-
1 various embodiments are possible.
;i~ In a first embodiment, the polyamine is added to the aqueous solu- ;~
`i tion first, so as to form a cationic complex of the polyamine with the metal
present in solution, and then the solution is contacted with the cation
i exchanger so as to adsorb the previously formed complex onto the ion exchanger.
... . .
After separation of the ion exchanger and the liquid, a residual solution
is obtained from which the metal has been removed to a sufficient extent. ;
The contact between cation exchanger and polyamine-added liquid may
be effected in any appropriate way. Both continuous and discontinuous methods
."
are possible. In the case of small volumes of solution, one may use a simple
column through which the liquid percolates in a continuous fashion; in case
of large volumes of liquid to be treated, a discontinuous method seems prefer-
able.
Using this embodiment, it is often possible to obtain efficiencies
of 99% or better in one single treatment, the residual metal content in the
aqueous solution bring then around 1 ppm. A repetition of this treatment
may easily reduce the residual metal content in aqueous solution to about 1
ppb or less. If desired, a counter-current treatment may be used.
In a second embodiment, the polyamine and cation exchanger are com-
10~732g ~ ~
bined in advance to form a solid adsorbent which is subsequently contacted ;
with the aqueous solution. The metal ions from the solution will then
react with polyamine in the adsorbent to form a complex, thereby being fixed -
onto the exchanger simultaneously. After separation of the adsorbent and
the liquid, the result is a solution from which the metal is removed to a
sufficient extent.
In the case of using a clay material such as bentonite or montmoril-
lonite in combination with tetraethylenepentamine Ccalled-tetren hereafter~
the solid adsorbent may be prepared as follows:
A solution of the polyamine is adjusted to a pH of about 7 with
acid and mixed with an aqueous suspension of the clay~mineral in such a propor-
tion that 0.3 millimoles of tetren per gram of clay mineral are used. At
this pH, tetren occurs as a tri~alent cation which is strongly adsorbed onto
the clay. When the clay is saturated completely with polyammonium ions, the
slurry is filtered and dried and finally ground.
In the case of combining bentonite or montmorillonite~with diethy-
lenetetramine (hereafter called dien), the procedure will be the-same, with
the exception that 0.5 millimoles of dien per gram of clay~mineral are used. ~ -
When the adsorbent, prepared are just deseribed, is used in the
removal of metals from solutions - even extremely dilute sol~tions with a
metal content of only a few milligrams per liter - the procedure is-as follows.
A certain amount of solid adsorbent, dependent from the metal content of the
solution~ is contacted with the solution and maintained in contact therewith
for some time. At the surface of the adsorbent, an exchange reaction between
metal ions from solution and protons from the adsorbed polyammonium ions will
occur. Thus, metal ions from solution are bonded to the clay-as a stable
amine complex. The liberated protons will cause a decrease in pH of the
solution and therefore, it is advisable to neutralise these protons by addi-
tion of alkali. The exchange process is diffusion-controlled and the contact
time should be sufficiently long to ensure good results: in general, a
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contact time of two hours will be sufficient.
Contact of the adsorbent with the solution may be effected in
different ways but a discontinuous method is preferred on account of the
extended contact time.
In this embodiment, a single treatment is generally sufficient to
reduce the metal content of the solution by a factor of about I00 or somewhat
less, de~ending on the initial concentration of the metal ions and the nature
and concentration of other complex forming chemicals which might be present.
This embodiment is completely insensitive to the presence of alkalimetal or
al~aline earth metal ions. Such cations, which are not to be removed, may
be present in fairly large excess without any detrimental effect. The pre-
sence of anionic complexing agents such as citrate or tartrate does reduce
the treatment efficiency to some extent but a residual metallcontent of less
than 1 ppm is easily accomplished. In some cases, it is possible to reduce
the metal content to a few parts-per-billion, even in the presence of ethylene-
diaminetetraacetate which forms extremely stable anionic complexes.
The liquid which has been treated by the invented process comprises
only a fraction of the initial content of undesired metals and may be dis-
; charged into a sewer or surface water or, optionally be processed to recover
other components.
The metal which has been fixed onto the cation exchanger or adsor~
bent during the process may be desorbed by a treatment with acids such as ~`
concentrated hydrochloric acid or nitric acid. However, such a recovery is
only useful when dealing with costly or rarely available metals such as silver.
; In other cases, the ion-exchanger loaded with the metal-polyamine complex may -~
simply be discharged and this is a safe procedure because the metal is no
; longer apt to have any detrimental effect.
Example 1
A natural aluminosilicate (montmorillonite from Camp Berteau,
Moroccol was mixed with a series of aqueous solutions containing the following
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.~ ,
amounts of metal and polyamine:
a) 20 ppm of mercury and 42 ppm of ethylenediamine.
~) 20 ppm of mercury and 33 ppm of propylenediamine.
c) 20 ppm of mercury and 50 ppm of diethylenetriamine.
d) 20 ppm of mercury and 24 ppm of triethylenetetramine.
e) 20 ppm of mercury and 30 ppm of tetraethylenepentamine.
The amount of clay used in all cases was 2.5 gram per liter and the
pH values were 6.9, 6.6, 7.3, 6.2 and 6.2, respectively. After reaching
equilibrium the mercury concentration in the solutions was found to be reduced
to the following values:
a) .1 ppm of mercury, efficiency 99.5%.
b~ .1 ppm of mercury, efficiency 99.5%.
c) .13 ppm of mercury, efficiency 99.4%.
d) .05 ppm of mercury, efficiency 99.8%.
el .02 ppm of mercury, efficiency 99.9%.
Example 2
~ natural aluminosilicate ~Wyoming ~entonite) was mixed with aqueous
solutions containing the following concentrations of metal and polyamine:
a) 50 ppm of mercuryJ 200 ppm of calcium and 150 ppm of tetraethylenepent-
amine.
~ol 100 ppm of mercury and 380 ppm of tetraethylenepentamine.
The amount of clay as used was always 2.5 gram~per liter and the
pH was 7.1 after reaching equilibrium, the mercury concentration was found
; to be reduced to .08 ppm and .5 ppm resp. which correspond to efficiencies
of 99.8 and 99.5% respectively.
Example 3
An aqueous solution containing 10 ppm of mercury and 20n ppm of
calcium with, in addition, onè of the following:
a~ no complexing agent.
bl 190 ppm of citrate.
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73Z9
. .
c) 325 ppm of EDTA,
was mixed with 20 ppm of tetraethylenepentamine and 250 ppm of natural alumino~
; silicate (montmorillonite from Camp Berteau, Morocco). The pH value was 8.
After 2 hours, the mercury concentration had been reduced to ~a) 56 ppb, (b) -~
50 ppb and (c) 52 ppb. A second treatment with 400 ppm of the same clay in the
presence of 20 ppm tetraethylenepentamine reduced the mercury concentration
further to 8-11 ppb in all three cases, which correspondedto an overall
efficiency of about 99.9%.
Example 4
A natural aluminosilicate ~montmorillonite from Camp Berteau,
Morocco) was mixed with a series of aqueous solutions containing 200 ppm of
calcium and in addition: -
a) 16 ppm of copper with 40 ppm of ethylenediamine.
b) 32 ppm of copper with 70 ppm of ethylenediamine.
c) 48 ppm of copper with 100 ppm of ethylenediamine.
d) 64 ppm of copper with 130 ppm of ethylenediamine.
In each case, the pH was adjusted to about 7, and the amount of clay
as used was 2.5 gram/liter. After equilibrium, the copper concentration was
33 ppb (a~, 82 ppb (b), 141 ppb (c) and 181 ppb, respectively, which corres-
- 20 ponded to efficiencies of 99.6 to 99.8 %. In the absence of ethylenediamine,
the efficiency varied between 35 and 40%.
Example 5
A synthetic aluminosilicate (zeolite Y, Union Carbide) was mixed
with a series of aqueous solutions containing the following amounts of metal ~`
and polyamine:
a) 32 ppm of copper and 70 ppm of ethylenediamine.
b) 64 ppm of copper and 130 ppm of ethylenediamine.
c) 96 ppm of copper and 190 ppm of ethylenediamine. ~
The pH was about 7 and the zeolite content about 3 gram per liter. ~ -
After equilibrium, the copper concentration had been reduced to 35 ppb (a),
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1~87329
.~
120 ppb (b) and 0.56 ppm (c) respectively which corresponded to efficiencies
of at least 99.5%. In the absence of ethylenediamine, the equilibrium -~
concentration of copper was at least 5-10 times larger. The equilibrium
concentration of ethylenediamine varied between 1 and 2 ppm which means that -~
99% of the amine has been co-adsorbed.
Example 6
The same material as in example 4 is mixed with a series- of aqueous
solutions containing 32 ppm of copper and in addition:
a) 70 ppm of ethylenediamine.
b) 100 ppm of propylenediamine. -
c) 100 ppm of diethylenetriamine
d) 100 ppm of triethylenetetramine.
e) 100 ppm of tetraethylenepentamine.
The pH was always between 7 and 8 while the amount of clay as used
was 3 gram per liter. After equilibrium, the copper concentration had been
reduced to less than 10 ppb in all cases which corresponded to an efficiency
of at least 99.95%. In the absence of polyamine, the equilibrium concen-
; tration of copper was always higher by a factor of 20 or more.
Example 7
A natural aluminosilicate (Wyoming Bentonite) was mixed with a
,
solution containing 32 ppm of copper, 200 ppm of calcium and 190 ppm of
tetraethylenepentamine at a pH of 8. After equilibrium, the copper concen-
tration in solution was 40 ppb which corresponds to an efficiency of 99.8%.
The efficiency in the absence of polyamine was 35%.
Example 8
A natural aluminosilicate (montmorillonite from Camp Berteau,
Morocco) was mixed with a series of aqueous solutions containing 3.2 ppm of
copper, 200 ppm of calcium, 19 ppm of tetraethylenepentamine and in addition
(a) 150 ppm of tartrate, (b) 190 ppm of citrate, (c) 325 ppm of ethylene-
diamine tetraacetate. The clay content was 200 ppm and the pH 7.5. After -
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:~ 10~7329
equilibrium, the copper concentration was .29 ppm ~a), .26 ppm (b) and .21
ppm ~c) respectively which corresponded to efficiencies of 92-94%. No
copper was adsorbed in the absence of polyamine.
Example 9
A natural aluminosilicate (montmorillonite from Camp Berteau,
Morocco~ was mixed with two solutions containing each 200 ppm of calcium and
in addition (a~ 3.3 ppm of zinc and 19 ppm of tetraethylenepentamine; (b) 3.3
ppm of zinc, 19 ppm of tetraethylenepentamine and 190 ppm of citrate. The
amount of ion exchanger as used was 200 ppm and the pH was 7. After equili- ~ -
brium, the zinc concentration was 70 ppb (a) and 60 ppb, respectively. In -
this way, about 50% of the ion exchange capacity of the clay was used. A
second treatment of the supernatant liquid with clay and polyamine reduced the -~
zinc content in both cases to 1 ppb.
Example 10
A natural aluminosilicate (montmorillonite from Camp Berteau, ,
Morocco) was mixed with two solutions containing each 200 ppm of- calcium and
in addition ~a~ 3 ppm of nickel and i9 ppm of tetraethylenepentamine, (b) 3
ppm of nickel, 19 ppm of tetraethylenepentamine and 190 ppm of citrate,
respectively. The amount of ion exchanger as used was 200 ppm and the pH
was 7. After equilibrium, the nickel concentration was 100 ppb (a) and 65
ppb (b~ respectively. In this way, about 5% of the ion exchange capacity of
the clay was used. A second treatment of the supernatant liquid with clay
and polyamine reduced the nickel content further to 2-3 ppb in both cases.
Example 11
A solution of 2 x 10 M EDTA which contained Fe was neutralized
to pH 7 with alkali and the precipitate was separated off.
The clear supernatant was diluted by a factor Qf two and tetra-
ethylenepentamine and zinc were added in such quantities as to obtain a solu-
tion containing 0.3 gram of EDTA, 20 ppm of tetraethylenepentamine, 3 ppm of
zinc and some Fe . -
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,:
1087~;~9
This solution was mixed with 40 mg of montmorillonite. After
equilibrium, the pH was 7 and the concentration of zinc ions had been reduced ~ -
to 0.3 ppm. In this way, about 50% of the exchange capacity of the ion ex-
changer was used. A second treatment led to a further reduction of the zinc
concentration to 10 ppb,
_xample 12
A solution containing 10 ppm of mercury and 200 ppm of calcium and
in addition: ~a~ no complex forming chemicals, (b) 190 ppm of citrate or (c)
320 ppm of EDTA is treated with 400 mg per liter of a solid absorbent compris-
ing tetren and bentonite, and prepared as described above. After agitating
for two hours and neutralising with sodium hydroxide, the mercuy concentration
was found to be reduced to ~a) 45 ppb, (b~ 83 ppb and (c) 65 ppb which corres-
ponded to an efficiency of at least 99%. A second treatment of"the super-
natant solution with 400 ppm of tetrenbentonite reduced the mercury content
further to 2-4 ppb in all three cases.
Example 13
A solution containing 1 mg/l of mercury was treated with 30 mg/l of
tetrenbentonite. After two hours of agitation with simultaneous addition of
' sodiumhydroxide to keep the pH at 7, the mercury concentration had been
~, 20 reduced to 45 ppb. A second treatment with 20 ppm of tetrenbentonite reduced
the mercury content further to 2-3 ppb. '~
Example 14 '
' A solution containing 6 ppm of nickel was treated with 500 ppm of
tetrenmontmorillonite. After two hours of agitation and occasional addition ~'
of NaOH to keep the pH at about 7, the nic~el concentration had'been reduced
to 60 ppb. A second treatment with 300 ppm of tetrenmontmorillonite reduced
the nickel conentration further to 7 ppb.
Example 15
A solution containing 3 ppm of nickel and 200 ppm of calcium with
(a~ no complex forming chemicals ~b) 190 ppm of citrate, was shaked for two
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1~7329
hours with 400 ppm of tetrenbentonite. After two hours of shaking, wherein
the pH was kept constant at a value of 7, through NaOH-addition, the nickel
concentration had been reduced to 100-120 ppb. A second treatment with 400
ppm of tetrenbentonite reduced the nickel concentration further to 15 ppb in
both cases~ i
Example 16
A solution containing 5.6 ppm of cadmium and 200 ppm of calcium and
in addition ~a) no complex forming chemicals, (b) 190 ppm of citrate, was
agitated for two hours with 400 ppm of tetrenbentonite, keeping the pH at
about 7 by NaOH-addition. After 2 hours the cadmium concentration was found
to be reduced to .45 ppm (a) and .95 ppm (b). A second treatment with 400
ppm of tetrenbentonite reduced the cadmium content further to 18 ppb (a) and
25 ppb (b).
Example 17
A solution containing 3.25 ppm of silver and 20n ppm of calcium was
mixed for two hours with tetrenbentonite, keeping the pH constantly at a
value between 7 and 8 by NaOH-addition. After two hours, the silver concen-
tration was found to be reduced to 22 ppb which corresponds to an efficiency
of 99.4%.
Example 18
A solution containing 3.3 ppm of zinc and 200 ppm of calcium and in
addition; (a) no further complexing agent, (b) 190 ppm of citrate, (c) 325
ppm of EDTA, was mixed with 400 ppm of tetrenbentonite. After 2 hours of
mix mg, keeping the pH at about 8, by NaOH-addition, the zinc concentration ;~
was found to be reduced to (a) 95 ppb, (b) 100 ppb or (c) 540 ppb respectively.
A second treatment with 400 ppm of tetrenbentonite reduced these concentrations
further to (a) 16 ppb, (b) 23 ppb and (c) 65 ppb respectively, which corres-
` ponded to an overall efficiency of 98% or better.
Example 19
: -
A solution containing 3.2 ppm of copper, 3.3 ppm of zinc, 3 ppm of
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'1~8~329
nickel and 5.6 ppm of cadmium was treated with 1000 ppm solid adsorbent made
from tetren and bentonite. After 2 hours of mixing, keeping the pH constant-
ly at a value of about 8, the concentrations of these metals were found to
be reduced to respectively 20 ppb in ~u, 64 ppb in Zn, 7 ppb in nickel and
250 ppb in Cd, which corresponded with efficiencies varying between 95% ~Cd~
: and 99.7% (Ni3. A second treatment with 1000 ppm of tetrenbentonite reduced
these concentrations further to 4 ppb in Cu, 5.5 ppb in Ni, 4 ppb in Zn, and
6.5 ppb in Cd, which corresponded with overall efficiencies of about 99.9%.
,
; ,;
',
`
, .
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