U.S. patent application number 10/673203 was filed with the patent office on 2004-11-04 for method for producing an anion-exchanging mineral and use of said mineral.
Invention is credited to Beavers, Kirstin, Buhl, Josef-Christian, Bull, Claus, Kuhlmann, Hermann, Schenk, Manfred, Seward, Paul.
Application Number | 20040219089 10/673203 |
Document ID | / |
Family ID | 7844416 |
Filed Date | 2004-11-04 |
United States Patent
Application |
20040219089 |
Kind Code |
A1 |
Kuhlmann, Hermann ; et
al. |
November 4, 2004 |
Method for producing an anion-exchanging mineral and use of said
mineral
Abstract
A layered double hydroxide (LDH) includes at least one
intermediate layer, and M.sup.II surrounded by OH.sup.-, with
replacement of the bivalent metal ions by M.sup.III producing an
excess of positive charge, balanced by anions A.sup.n- in the
intermediate layer, wherein M.sup.II dennotes a divalent metal ion
or 2 LI, M.sup.III dennotes a trivalent metal ion. The LDH can be
used in mixtures and preparations such as auxiliary materials,
additives, seeds, seedlings, or propagation materials. Also it is
possible to use the LDH in a method of nitrate removal in
purification of water.
Inventors: |
Kuhlmann, Hermann; (Dulmen,
DE) ; Seward, Paul; (Munster, DE) ; Buhl,
Josef-Christian; (Wathlingen, DE) ; Beavers,
Kirstin; (Hannover, DE) ; Schenk, Manfred;
(Hannover, DE) ; Bull, Claus; (Hannover,
DE) |
Correspondence
Address: |
WHITHAM, CURTIS & CHRISTOFFERSON, P.C.
11491 SUNSET HILLS ROAD
SUITE 340
RESTON
VA
20190
US
|
Family ID: |
7844416 |
Appl. No.: |
10/673203 |
Filed: |
September 30, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10673203 |
Sep 30, 2003 |
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09509743 |
Jun 2, 2000 |
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6656382 |
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09509743 |
Jun 2, 2000 |
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PCT/DE98/02927 |
Oct 2, 1998 |
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Current U.S.
Class: |
423/395 |
Current CPC
Class: |
Y10S 71/903 20130101;
C05D 9/00 20130101; B01J 41/10 20130101; C05G 5/10 20200201; C05G
5/12 20200201; C05G 5/18 20200201; C05G 5/40 20200201; C05D 9/00
20130101; C05G 5/40 20200201; C05D 9/00 20130101; C05G 5/40
20200201; C05G 5/40 20200201; C05G 5/18 20200201; C05G 5/27
20200201 |
Class at
Publication: |
423/395 |
International
Class: |
C01F 011/36 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 2, 1997 |
DE |
197 43 606.4 |
Claims
1-8. (Cancelled)
9. A layered double hydroxide (LDH) according to claim 20, in which
M.sup.II is Ca, Mg, Fe, Ni, Zn, Co, Cu, Mn, or 2 Li, M.sup.III is
Al, Fe, Cr or Mn, A.sup.n- is nitrate, sulfate, chloride or
hydroxide.
10. The LDH of claim 9, wherein the LDH contains up to about 30% by
weight nitrate ions.
11. A mixture comprising an LDH according to claim 9 in combination
with auxiliary materials and additives.
12. A mixture comprising an LDH according to claim 9 to which is
added an ordinary mixed fertilizer and optionally other fertilizer
additives.
13. A preparation comprising an LDH according to claim 9, with at
least one selected from seeds, seedlings, or propagation
material.
14. A preparation according to claim 13, characterized in that the
propagation material, seeds, or seedlings in the preparation are
coated with the LDH and optionally with other additives.
15. A preparation according to wherein the LDH is present in liquid
form or in solid form.
16-17. (cancelled)
18. The LDH of claim 9, wherein the LDH is essentially
carbonate-free the divalent metal ion is Ca, Mg, Fe, Ni, Zn, Co,
Cu, or Mn, the trivalent metal ion is Al, Fe, Cr or Mn, the anion
is sulfate, hydroxide, chloride or nitrate.
19. The LDH of claim 15, wherein the solid form is a granulate, a
powder or a prill.
20. An LDH comprising at least one intermediate layer, and M.sup.II
surrounded by OH.sup.-, with replacement of the bivalent metal ions
by M.sup.III producing an excess of positive charge, balanced by
anions A.sup.n- in the intermediate layer, wherein M.sup.II denotes
a divalent metal ion or 2 Li, and M.sup.III denotes a trivalent
metal ion.
21. The LDH of claim 20, wherein the LDH is essentially
carbonate-free, and in which the divalent metal ion is Ca, Mg, Fe,
Ni, Zn, Co, Cu or Mn; the trivalent metal ion is Al, Fe, Cr or Mn;
the anion is sulfate, hydroxide or chloride.
22. A method of nitrate removal in purification of water followed
by a method of uniform supplying arable land with nitrogen in form
of nitrate, comprising the steps of contacting the water with
layered double hydroxides (LDHs) that reversibly exchange nitrate
wherein the LDHs comprise at least one intermediate layer, and
M.sup.II surrounded by OH.sup.-, with replacement of the bivalent
metal ions by M.sup.III producing an excess of positive charge,
balanced by anions A.sup.n- in the intermediate layer, wherein
M.sup.II denotes a divalent metal ion or 2 Li, M.sup.III denotes a
trivalent metal ion, A.sup.n- denotes an anion bound in the
intermediate layer; and applying the LDHs that reversibly exchange
nitrate as fertilizer and soil conditioner for the uniform
supplying of arable land with nitrogen in the form of nitrate,
wherein both the contacting and applying steps are performed using
the same LDHs.
23. A composition comprising layered double hydroxides (LDHs)
according to claim 20, wherein the LDHs contain anions exchangeably
bound in intermediate layers.
24. The composition of claim 23, wherein the LDHs are substantially
carbonate-free, and in which the divalent metal ion is Ca, Mg, Fe,
Ni, Zn, Co, Cu or Mn; the trivalent metal ion is Al, Fe, Cr or Mn;
the anion is sulfate, hydroxide, chloride or nitrate.
25. The LDH of claim 20, wherein A.sup.n- is nitrate.
26. The LDH of claim 20, wherein A.sup.n- is sulfate.
27. The LDH of claim 20, wherein A.sup.n- is chloride.
28. The LDH of claim 20, wherein A.sup.n- is hydroxide.
Description
[0001] The invention concerns a process for preparing an
anion-exchanging mineral and the use of such minerals which
reversibly bind (exchange) anions such as NO.sub.3.sup.-, among
others, as improvements for fertilizers and soil, or for purifying
and treatment of water, especially to remove nitrate.
[0002] In a broader sense, the invention concerns the intentional
addition and removal of nitrates.
[0003] Optimal nutrition of crop plants, both in the open air and
in the greenhouse, requires, among other things, an adequate
nitrogen supply timed to match the plant growth. As a general
guideline, one can assume that about 200 kg N/hectare is needed
during one vegetation phase, with plants having different needs,
depending on the species and variety and on their stage of
development.
[0004] Supplying nitrogen to plants in the proper amount at the
right time is not simple, for various reasons. Nitrogen can be made
available in the form of ammonium ions (NH.sub.4.sup.+) or nitrate
ions (NO.sub.3.sup.-). In the soil, there is a complex equilibrium
between the various forms of bound nitrogen. There are
microorganisms in the soil--in various proportions--which can
convert ammonia into nitrate.
[0005] Because the soils on which we grow crops do not have much
anion-exchange ability, though, the nitrate is easily washed out
into surface water and ground water. Nitrification inhibitors are
often used at times to inhibit the soil microorganisms so as to
avoid excessive conversion of ammonium into nitrate.
[0006] Washing out of cations, by comparison, is of secondary
importance, because they can be bound to the exchange sites of the
clay minerals normally present in the soil. Therefore ammonium ions
and the other cations important for plant culture, such as
potassium, magnesium, and calcium, can be held well enough in our
crop soils. The extremely sandy soils with very low clay content
are exceptions, where cation washout is also a problem.
[0007] Various ways are known at the state of the art by which
useful nitrogen can be made available to plants for long periods.
Known fertilizers and soil improvers with depot action, for
instance, work with fertilizer mixtures from which nitrogen is
supposed to be released at different times in a vegetation
period.
[0008] For example, a fertilizer with long-term action and
programmed nutrient release for providing the nutrient requirements
of a plant during a culture period, in the form of a mixture of an
initial release, a long-term release, and a final release, is known
from DE 33 21 053 C2. The long-term releaser and the final releaser
comprise particles of fertilizer of certain particle sizes with
coatings which prevent immediate release of nitrogen.
[0009] Furthermore, soil substrates are also known which can be
used directly for growing crops--in greenhouses, for instance--or
as soil improvers. They are reported to consist for the most part
of neutral porous materials such as zeolites and the like, and
their physical adsorption and filtering actions are utilized.
[0010] The known fertilizing and soil-improving agents also have
the disadvantage that they do not release nutrients as they are
required by the plants. Rather, the release is a result of the
action of soil factors (temperature, water, microorganisms). It
follows that nutrients which are released because of soil factors,
with simultaneous low requirement of the plants for nutrients, are
potentially exposed to washout and can cause pollution.
[0011] Thus the invention is based on the problem of finding an
environmentally acceptable anion exchanger with particularly good
exchange capacity for nitrate ions.
[0012] With respect to a fertilizer improver and soil improver, the
objective is to find such an agent that has a buffering action on
the nitrate content in the soil solution. Thus it can provide the
nitrogen requirement of the plants through continuous release of
nitrate as needed; On the other hand, it can bind again any excess
nitrate in the soil and in the ground water flowing through it.
Thus the agent can simultaneously supply crop soils with nitrogen
in the form of nitrate.
[0013] With respect to an agent for purifying and treating water,
the objective is to remove nitrate efficiently and economically
from drinking water or waste water.
[0014] These objectives are attained through the process according
to the invention for preparing an anion exchanging mineral and the
use of anion-exchanging minerals which exchange NO.sub.3.sup.-,
among others, reversibly, as fertilizer and soil improvers and for
purifying and treating water.
[0015] Experiments by the inventor have shown that certain mineral
double salts can be used well as anion exchangers in the sense of
this invention. A special precipitation process is recommended here
to prepare such anion-exchanging minerals as are suitable to attain
the objective.
[0016] The process according to the invention comprises
[0017] coprecipitation from a highly carbonate-free aqueous
alkaline solution
[0018] of at least one metal salt from the group: Ca.sup.2+,
Mg.sup.2+, Fe.sup.2+, Ni.sup.2+, Zn.sup.2+, Co.sup.2+, Cu.sup.2+,
Mn.sup.2-, Li.sup.+, nitrate, sulfate, chloride or hydroxide
[0019] and at least one metal salt from the group Al.sup.3+,
Fe.sup.3+, Cr.sup.3+, Mn.sup.3+, nitrate, sulfate, chloride, or
hydroxide, with the precipitation reaction controlled over an
extended period;
[0020] separation of the precipitated product, and
[0021] heat-treating the precipitated product, i. e., carrying out
a thermal treatment at up to 350.degree. C., preferably up to
250.degree. C.
[0022] The carbonate content during the precipitation should be as
low as possible, as carbonate is not exchangeably bonded in the
material, so that anion exchange is severely reduced by any
carbonate content. On precipitation over an extended period, one
gets a well-crystallized laminar double hydroxide (LDH) which, as
described below, exhibits good exchange characteristics under soil
conditions and which, charged with the appropriate anions, is also
well suited for water purification.
[0023] The precipitation reaction should take place over a long
period. After precipitation, a heat treatment up to 300.degree. C.,
preferably up to 250.degree. C., is carried out to improve the
crystallinity and exchange behavior.
[0024] In a further development of the invention, the precipitated
or separated mineral can, after washing and drying, be treated with
acid and/or phosphate solution. The post-treatment with biphosphate
salts causes coagulation (flocculation of the individual
particles). The post-treatment with acid is done for further
deliberate influence on the crystallinity.
[0025] Preferably the pH of the solution is held constant in the
alkaline range during the precipitation, preferably at pH 12.+-.2.
Accurate control of the pH also improves the crystallinity of the
product. For that reason the precipitation should be monitored, as
with a pH-stat.
[0026] Potassium hydroxide (KOH) is used preferably as the base to
adjust the alkaline medium.
[0027] Particularly good results for the purpose of the invention
have been achieved if the first group of metal salts comprises
magnesium nitrate and the second group of metal salts comprises
Al.sup.3+ or Fe.sup.3+ nitrate. Minerals obtained from these salt
combinations are particularly suitable as fertilizer and soil
improvers. The exact composition of cations and anions can be made
dependent on the particular area of application, i. e., on the
nature of the soil and the crop species, as they affect the
exchange behavior.
[0028] One the other hand, minerals synthesized from Ca.sup.2+,
Mg.sup.2+, sulfate, chloride and hydroxide as salts of the first
group and from Al.sup.3+, Fe.sup.3+, Cr.sup.3+, Mn.sup.3+, sulfate,
chloride, and hydroxide as salts of the second class are preferred
for water treatment and purification. These materials are also
suitable as soil improvers.
[0029] The minerals prepared by the process according to the
invention, which exchange NO.sub.3.sup.-, among others,
reversibly--or corresponding natural or synthetic minerals--are
usable as fertilizers and soil improvers.
[0030] These are preferably natural or synthetic mixed-valence
basic metal-metal salts and preferably essentially carbonate-free
laminar double hydroxides (LDHs) which have exchangeable anions
bound in the intermediate layers and which can be represented by
the following formulas:
[M.sup.II.sub.(1-x)
M.sup.III.sub.x(OH).sub.2].sup.x+(A.sup.n-.sub.x/n-).m H.sub.2O
[0031] in which
[0032] M.sup.II is a bivalent metal ion such as Ca, Mg, Fe, Ni, Zn,
Co, Cu, Mn, or 2 Li, preferably Ca, Mg or Fe,
[0033] M.sup.III is a trivalent metal ion, preferably Al, Fe, Cr or
Mn,
[0034] A.sup.n- is a n-valent anion bound in the intermediate
layer, such as nitrate, sulfate, chloride or hydroxide.
[0035] LDHs comprise bivalent metal ions (M.sup.II) surrounded by
OH.sup.-. Replacement of the bivalent metal ions in the lattice by
trivalent metal ions (M.sup.III) produces an excess of positive
charge, which can be balanced by anions (A.sup.n-) in the
intermediate layer. Hydrotalcite and pyroaurite have structures
like those of the LDHs.
[0036] The anions of the minerals obtained according to the
invention can be exchanged appropriately for the particular
purpose. For use as a fertilizer, as much nitrate as possible is
put into the mineral and thus into the soil. That can be done
directly in the synthesis, or it can be done later by saturation
with a flowing nitrate solution (on a column, for instance), with
the other ions being displaced by nitrate.
[0037] For use as an agent for purifying and denitrifying water,
the mineral should initially contain as little nitrate ion as
possible; that is, practically none. Then the anions are preferably
chloride ions. One could also consider SO.sub.4.sup.2-.
[0038] Corresponding natural LDH-like minerals can also be used
according to the invention as fertilizers and soil improvers.
[0039] When it is produced as a fertilizer, the mineral, however
obtained, is given the highest possible nitrate content. Preferably
the fertilizer and soil improver should be almost completely
charged with nitrate when they are produced. That is, at least 80%
of the exchangeably bound anions in the mineral can be nitrate
ions. The complete charging with nitrate ions, with which at least
80% of the anions in the mineral are nitrate ions, corresponds to
up to 30% by weight of nitrate anions in the minerals in question,
usually between about 10% and 25% by weight. It can also be
desirable to add ions other than nitrate to the soil. In this case,
the nitrate ion concentration is optionally less than 80% of the
anions, depending on what proportion is chosen for the other
anions.
[0040] In the following culture period, the nitrate is slowly
released by ion exchange. As the nitrate anions, like any anions,
have a certain affinity with the mineral to be used according to
the invention because of the excess of positive charge in the
mineral lattice, there is no simple wash-out of the nitrate.
Instead, the nitrate content is in an equilibrium between
"mineral-bound" and "in solution (in the natural soil water) so
that the nitrate concentration is considerably lower than in soils
fertilized in the usual manner, but is still enough to meet the
requirements of the plants.
[0041] The mineral is very stable, and is retained for a long time
during the growth phase. Thus the mineral, after an initial phase
of nitrate release, be recharged with nitrate derived from
fertilization or mineralization. The nitrate can again be released
slowly.
[0042] Thus the mineral acts as a soil improver by buffering the
nitrate content. That is, it takes up nitrate in times of greater
NO.sub.3.sup.- availability and releases it when there is a nitrate
deficiency. In this way, the nitrate concentration in the ground
solution is maintained at a low level when the plants need little
or no nitrate (that is important especially in fallow times, as in
the Fall and Winter). Then the mineral makes the bound nitrate
available again for the next crop. Therefore the minerals according
to the invention are nitrate ion exchangers, and nitrate buffers
under soil conditions.
[0043] The mineral obtained is this or other ways can also be given
the lowest possible nitrate content when it is produced as a soil
improver and nitrate buffer.
[0044] Thus, the mineral used according to the invention or in the
fertilizer or soil-improvement agent reduces the nitrate wash-out
from crop soils into the ground water, making a substantial
contribution to environmental protection.
[0045] The invention assures a nitrate concentration in the soil
solution which will be enough to provide for the absorption rate of
the roots in optimal development of the plants, and is
substantially lower than when the usual nitrate fertilizers are
used. The exchangeably bound nitrate is released slowly and as
needed, as described above. The release is controlled by the
nitrate requirement of the plants. Thus the invention involves a
fertilizer with depot action (a "triggered-release
fertilizer").
[0046] The mineral is stable in the soil for a long time. In
contrast to anion exchangers found in the soil in some situations,
the exchange capacity is quite independent of the pH. That makes
the action reliable under crop conditions. The extremely low anion
exchange capacity which soil is known to have is based essentially
on amorphous and crystalline iron compounds. Their exchange
capacity increases as the pH decreases. Thus the iron compounds are
significant only in soils with decidedly acid pH, and otherwise
ineffective.
[0047] The invention makes it possible to apply the amount of
nitrogen needed by a crop in a single application when the crop is
started, without the plants being damaged by excessive salt
concentration in the soil. The nitrate is held in the upper layer
of the soil where roots are thickly developed, so that it is
completely available for the plants, particularly for plants which
do not have deep roots. Therefore the invention can also be applied
advantageously in production of sod, so as to provide the thin
layer of soil with anion exchange capability. At the final
location, the fertilizing nitrogen is protected from being washed
out, as could otherwise easily happen with the very shallow-rooted
grass. The invention is also particularly suited for improving the
soil of intensively used lawn areas, such as golf courses, sports
fields, etc., by giving it anion exchange capacity and thus
preventing washout of nitrate.
[0048] The invention can be applied in substrates and potting soil
as a slow-releasing nitrogen fertilizer. For instance, the
invention can be used in commercial gardening for open-air crops,
such as Calluna or Erica; for container plants or the like; and in
the hobby area for flower beds and balcony plants. The invention is
also suitable for lawn fertilization as a slow nitrogen releaser.
With this invention, the nitrogen requirement is met continuously
over a long period without plant damage by overfertilization.
[0049] The invention is also well suited for meeting the nitrogen
requirement of crops in hydroponic systems over long periods, and
to contribute to stabilization of the salt concentration.
[0050] The mineral to be used according to the invention, as a
fertilizer and soil improver can also be used with other nutrients
in multi-ingredient fertilizers, as in combination with an ordinary
mixed fertilizer or with various other fertilizer components and/or
other additives.
[0051] The fertilizer and soil improver can be applied in strips or
rows, or at points, to improve the nitrogen efficiency. Loss of
gaseous nitrogen (N.sub.2, N.sub.2O, NO) and nitrate wash-out are
minimized.
[0052] The fertilizer can also appear in a preparation with seeds,
seedlings, or other propagation material. It is particularly suited
for coating seeds with a nitrogen-containing shell to assure the
initial nutrition of the seedlings.
[0053] The fertilizer and soil improver can be prepared and
applied, alone or in combination with other fertilizers, in liquid
form, such as an emulsion, gel or paste, or in solid form, as a
power, granulate or prills.
[0054] The material used as a soil improver according to the
invention is also suited for improving areas with high potential
for nitrate washout, even if it is not charged with nitrate. This
is particularly true for areas with a long history of intensive
cultivation, such as with vegetables or special crops, or soils
with low water-storage capacity. In general, the invention can be
used in all soils where nitrate washout must be expected or is to
be prevented.
[0055] The special properties pointed out here for nitrate also
apply in part for sulfate and similar anions.
[0056] The application according to the invention for water
purification and treatment, especially for removal of nitrate, is a
reversal of the processes that have been presented. With a choice
of suitable counterions, such as chloride, it is possible to trap
nitrate, by exchange for those counterions, from waters which, for
example, have flowed through a mineral layer according to the
invention. That can be done, for instance, on an ordinary column,
or on a larger scale in a tower. The equilibrium must be maintained
so that re-release of nitrate is avoided. Therefore the mineral
must be regenerated at certain intervals, as is the case with other
industrial ion-exchange processes.
[0057] The invention is suitable for purification of wastewater and
for purification and treatment of drinking water.
[0058] At the same time, the mineral exerts a filtering action, so
that large particles and suspended materials can be retained.
[0059] The mineral to be used for water treatment can be produced
relatively economically. It makes a particularly environmentally
favorable treatment process possible, as no synthetic
ion-exchangers which would present eventual disposal problems need
be used.
[0060] With this invention, rather, both applications can favorably
be combined, as the ion exchange mineral used for water
purification is, when in the charged state (charged with nitrate)
is itself a soil improver according to the invention and thus is
easily disposed of. It can be added to the compost from city
composting plants or even used for fertilization in some other
place.
[0061] Certain aspects of the invention are explained below by
means of diagrams which show:
[0062] FIG. 1: The structure of an LDH, using
Mg.sub.6Fe.sub.2(OH).sub.16(- NO.sub.3).sub.2 as the example;
[0063] FIG. 2: Nitrate release from a Mg--Al-LDH as it depends on
various extracting solutions;
[0064] FIG. 3: Nitrate release from a Mg--Al-LDH as it depends on
the initial KCl concentration;
[0065] FIG. 4: The pH stability of a Mg--Al-LDH;
[0066] FIG. 5: Nitrate release and uptake of a
Mg--Fe(III)--NO.sub.3.sup.-- -LDH as it depends on various exchange
solutions.
[0067] FIG. 1 shows the structure of an LDH, with
Mg.sub.6Fe.sub.2(OH).sub- .16(NO.sub.3).sub.2 as the example. As
described above, there are also other natural and synthetic laminar
minerals with other cations, mostly bivalent and trivalent, and
with other counterions. The laminar structure allows relatively
problem-free exchange with other anions such as nitrate, sulfate,
chloride or hydroxide. Nevertheless, there is binding, which is
strong enough that these ions cannot easily leave the lattice.
Thus, instead of simple "flushing out" there is deliberate release
of the anions, especially the nitrate ions. It is driven, among
other things, by the shift in equilibrium due to consumption.
[0068] FIG. 2 shows how the nitrate release from a Mg--Al-LDH
depends on various extraction solutions. With a nitrate content of
160 meq [milliequivalents]/100 g mineral, equivalent to a nitrate
content of scarcely 10%, based on the mineral, only 30 mg is
released into the solution if deionized water is used as the
extraction solution. But only 21 meq of nitrate is released into a
solution containing 5 mM potassium nitrate. This shows a definite
buffer action by the mineral with respect to the nitrate content of
the surrounding medium. When 5 mM KCl is used, the nitrate release
is 61 meq. The nitrate release is clearly increased over deionized
water because the chloride and nitrate ions can exchange.
[0069] FIG. 3 shows the dependence of nitrate release from a
Mg--Al-LDH on the initial KCl concentration. From this we see that
the amount of nitrate released is related to the amount of chloride
provided. Similar relations can be established for other
anions.
[0070] FIG. 4 shows the pH stability of a Mg--Al-LDH. It shows what
percentage by weight of the mineral goes into solution at a
particular pH. As the minerals are largely stable down to pH 3, the
mineral remains in the soil through a crop phase and longer, and
can be charged with nitrate in another phase. The nitrate can come
from fertilization or mineralization.
[0071] FIG. 5 shows the exchange behavior of a
Mg--Fe(III)--NO.sub.3.sup.-- -LDH in various solutions. As can be
seen, the exchange of nitrate with sulfate goes very much slower
than with chloride. That makes it possible to apply the LDHs as
fertilizers with simultaneous application of fertilizers containing
sulfate, which could otherwise cause overly rapid nitrate release.
The figure also shows that the LDH can be recharged well with
NO.sub.3.sup.-.
EXAMPLES
Preparation of a Me(II)--Me(III)--NO.sub.3.sup.--LDH
[0072] 1. Coprecipitation:
[0073] 300 ml of a solution containing 0.4 molar iron(III) nitrate
and 1.6 molar magnesium nitrate is prepared. This solution is added
slowly, with stirring, to 120 ml distilled water which has been
adjusted to pH 11.+-.0.1 with 4 molar potassium hydroxide solution
containing 0.6 molar potassium nitrate The pH is held constant with
a pH-stat during the precipitation.
[0074] Conditions:
[0075] The precipitation reaction should take place over a long
period. That is, less than 12 ml/hour, for example, 4 ml/hr, of the
solution specified in (1) should be added slowly to the container
with a peristaltic pump. The solutions should be handled in the
absence of CO.sub.2 and should be essentially free of
carbonate.
[0076] 2. Treatment of the Precipitated Product:
[0077] After termination of the precipitation reaction, the mineral
product obtained is filtered off by suction and then subjected to
heat treatment at 200.degree. C.
[0078] 3. Options:
[0079] The heat-treated product can next be treated with a hydrogen
phosphate solution. That is done, for example, by stirring 10 g of
the LDH in 1 liter of a 5 millimolar solution of potassium
dihydrogen phosphate for 3 hours, then filtering and drying it.
[0080] An appropriate acid treatment is also possible.
[0081] The product obtained is finally washed in water and
dried.
[0082] 4. Alternatives:
[0083] Calcium nitrate can be used instead of magnesium nitrate.
Aluminum nitrate can also be used instead of iron (III)
nitrate.
[0084] The product is an LDH with a nitrate content of at least 9%
by weight.
[0085] 5. Advantages:
[0086] The Mg--Fe-NO.sub.3.sup.--LDHs have the following
advantageous properties:
[0087] The bound nitrate is not completely exchangeable in the
first extraction step, even in a highly concentrated salt solution
(1 M KCl). The slow, gradual nitrate exchange is advantageous with
respect to a slowly releasing nitrate fertilizer.
[0088] Exchange with sulfate ions is more difficult than with
chloride ions. That is an advantage because many fertilizers have a
high sulfate content. Slow nitrate exchange from the LDHs
recommended here is assured even after such fertilizers are
applied.
[0089] After complete nitrate exchange, for example, the remaining
Mg--Fe--Cl-LDH is capable of renewed nitrate adsorption. After
applying 10 mM KNO.sub.3 three times, the LDH has a nitrate content
which can, for example, be 70% of the initial content.
[0090] All the LDHs reported are quite tolerable to plants and are
not environmental pollutants.
[0091] To prepare a means for purifying wastewater, it is
advantageous to use the corresponding chloride salts.
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