Compositions – Absorptive – or bindive – and chemically yieldive
Reexamination Certificate
2000-06-02
2003-12-02
Medley, Margaret (Department: 1714)
Compositions
Absorptive, or bindive, and chemically yieldive
C071S058000, C071S059000, C071S061000, C071S063000, C071S064030, C071S064010, C071S064070, C071S903000, C210S683000, C210S684000, C210S688000
Reexamination Certificate
active
06656382
ABSTRACT:
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
3
−
, among others, as improvements for fertilizers and soil, or for purifying and treatment of water, especially to remove nitrate.
In a broader sense, the invention concerns the intentional addition and removal of nitrates.
IS 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.
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
4
+
) or nitrate ions (NO
3
−
). 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.
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.
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.
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.
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.
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.
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.
Thus the invention is based on the problem of finding an environmentally acceptable anion exchanger with particularly good exchange capacity for nitrate ions.
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.
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.
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
3
−
, among others, reversibly, as fertilizer and soil improvers and for purifying and treating water.
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.
The process according to the invention comprises
coprecipitation from a highly carbonate-free aqueous alkaline solution
of at least one metal salt from the group:
Ca
2+
, Mg
2+, Fe
2+
, Ni
2+
, Zn
2+
, Co
2+
, Cu
2+
, Mn
2+
, Li
−
, nitrate, sulfate, chloride or hydroxide
and at least one metal salt from the group Al
3+
, Fe
3+
, Cr
3+
, Mn
3+
, nitrate, sulfate, chloride, or hydroxide, with the precipitation reaction controlled over an extended period;
separation of the precipitated product, and
heat-treating the precipitated product, i.e., carrying out a thermal treatment at up to 350° C., preferably up to 250° C.
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.
The precipitation reaction should take place over a long period. After precipitation, a heat treatment up to 300° C., preferably up to 250° C., is carried out to improve the crystallinity and exchange behavior.
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.
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.
Potassium hydroxide (KOH) is used preferably as the base to adjust the alkaline medium.
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
3+
or Fe
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.
One the other hand, minerals synthesized from Ca
2+
, Mg
2+
, sulfate, chloride and hydroxide as salts of the first group and from Al
3+
, Fe
3−
, Cr
3+
, Mn
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.
The minerals prepared by the process according to the invention, which exchange NO
3
−
, among others, reversibly—or corresponding natural or synthetic minerals—are usable as fertilizers and soil improvers.
These are preferably natural or synthetic mixed-valence basic metal-metal salts and preferably essentially carbonate-free laminar double hy
Beavers Kirstin
Buhl Josef Christian
Bull Claus
Kuhlmann Hermann
Schenk Manfred
Hydro Agri Deutschland GmbH
Medley Margaret
Whitham Curtis & Christofferson, P.C.
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