EP1068279A1

EP1068279A1 - METHOD FOR INCREASING THE pH VALUE IN ACIDIC SOILS

Info

Publication number: EP1068279A1
Application number: EP99915700A
Authority: EP
Inventors: Aloys HÜTTERMANN; Moitoba Zomorrodi
Original assignee: Stockhausen GmbH and Co KG; Chemische Fabrik Stockhausen GmbH
Current assignee: Stockhausen GmbH and Co KG
Priority date: 1998-03-26
Filing date: 1999-03-24
Publication date: 2001-01-17
Also published as: WO1999048998A1; US6484441B1

Abstract

The invention relates to a method for increasing the pH value in acidic soils in which acidic soils are treated with cross-linked polyacrylates or polymethacrylates.

Description

Process for raising the pH in acidic soils

The present invention relates to a method for increasing the pH in acidic soils, in particular in soils with a pH in the aluminum buffer range, that is to say less than 5 than 4.2. The aluminum buffer range is the pH range in which at higher pH values than oxide resp. Hydroxide, i.e. Non-ionic aluminum, which comes from the weathering of the clay minerals, changes into cationic solution.

To raise the pH, such soils have previously been treated with lime, e.g. B. by 0 sprinkling on or mixing into the soil. Existing crops were limed at around 3 tons per hectare every five years to stop further acidification. In the case of initial afforestation, the recommended liming quantities are considerably higher depending on the acidification of the soil, up to 15 t per hectare due to the higher sensitivity of the young plants to acidification. Because acid emissions have now decreased considerably, acidification of the soil is no longer to be expected Old stocks will no longer be so important in the future. However, the problem of leaving afforestation at problem locations will continue to exist because the acid present in the soil will not be neutralized so quickly.

o To improve the soil quality, attempts have already been made to use alkaline sand and

Mixing clay soils with poly (meth) acrylates (Arid-Soil-Research-and-Rehabilitation, 1996, 10; 3, 277-285). An increase in the pH was observed. This effect of raising the pH, which is actually undesirable in alkaline soils, can be explained by the binding of protons to the acrylate, whereby metal cations, such as potassium, are released from the acrylate.

Different conditions exist in acidic soils. Soil slurries in pure water have a pH about 0.6 units higher than a slurry in CaCl ₂ solution. This is due to the fact that in such soils the exchange sites at the clay-humus complex are mostly occupied with protons and cationic acids and the pH of the

Soil solution sets only very slowly, ie, the balance between the clay-humus complexes of the soil and the soil solution takes place very slowly (see: "Soil Ecology", Georg Thieme Verlag Stuttgart 1997, p. 125). Becomes one Soil slurry KC1 or CaCl ₂ added, the counterions on the exchange complex are released immediately and the pH value is reduced accordingly.

If poly (meth) acrylates are added to an acidic soil by the process according to the invention, the protons in the soil solution are trapped by the negatively charged carboxyl groups of the poly (meth) acrylates, so that a higher pH value is established in the soil solution. This effect persists over a long period of time, surprisingly even over a period of many months. This was not to be expected for the expert and enables a long-term increase in the pH value of acidic soils.

The acidic soils are treated with the crosslinked poly (meth) acrylates, e.g. B. by

Sprinkle on or preferably by mixing. When mixing, amounts of 0.1% to 2.5%, based on the total soil mass, are used, preferably about 0.5 to 2% by weight. -%, particularly preferably about 0.2 to 0.8 wt. -%, e.g. B. 0.4%.

The bottom is excavated to a depth of approximately 50 cm, preferably 30 cm and in particular approximately 40 cm, and mixed with the poly (meth) acrylates.

Suitable poly (meth) acrylates to be used according to the invention are all crosslinked, carboxylate-containing poly (meth) acrylates which form hydrogels.

Particularly suitable as the carboxylate-containing poly (meth) acrylates to be used according to the invention are those which are primarily and preferably composed of the monomers acrylic acid, acrylamide, methacrylic acid and methacrylamide, but also other water-soluble monomers, such as acrylonitrile, methacrylonitrile, N, N -Dimethylacrylamide,

Vinylpyridine and other water-soluble polymerizable acids and their salts, in particular maleic, fumaric, itaconic, vinylsulfonic or acrylamidomethylpropanesulfonic acid; also hydroxyl-containing esters of polymerizable acids, especially the hydroxyethyl and hydroxypropyl esters of acrylic and methacrylic acid; further amino group-containing and ammonium group-containing esters and amides of polymerizable acids such as the dialkylamino esters, in particular the dimethyl and diethylamino alkyl esters of acrylic and methacrylic acid, and also the trimethyl and trimethyl ammonium alkyl esters and the corresponding amides. The poly (meth) acrylates to be used according to the invention can

REPLACEMENT BUTT (RULE 26) to be formed exclusively from the abovementioned monomers containing carboxylate groups or else to be combined in a copolymer with the monomers bearing no carboxylate groups. The proportion of carboxylate monomers in the copolymers is 90 to 10 mol%, preferably 60 to 30 mol%.

5

In small amounts, even slightly or completely water-insoluble monomers can be copolymerized with the above monomers, such as vinyl esters and the esters of acrylic and / or methacrylic acid with Cj-Cjo alcohols, styrene and alkylated styrenes. In general, the proportion of water-soluble monomers is 80 to 100% by weight, based on the total of the monomers. The water-insoluble (hydrophobic) monomers generally make up 0 to 20% by weight of the monomers.

The acidic monomer components can be neutralized before the polymerization, the degree of neutralization preferably being between 10 and 95 mol%, in particular between 50 5 and 90 mol%, and in particular between 70 and 95 mol%. Suitable bases for the neutralization are all common inorganic and organic compounds, in particular sodium hydroxide solution, potassium hydroxide solution and ammonia (ammonium hydroxide) are preferred.

0 Together with the above Monomers are cross-polymerized in small proportions with cross-linking monomers with more than one reactive group in the molecule. This produces partially cross-linked polymers that are no longer soluble in water but only swellable. Crosslinking monomers include, for example, bi- or polyfunctional monomers, e.g. Amides such as methylene bisacryl or methacrylamide or ethylene bisacrylamide, furthermore 5 allyl compounds such as allyl (meth) acrylate, preferably alkoxylated allyl (meth) acrylate

1 to 30 moles of ethylene oxide reacted, triallyl cyanurate, maleic acid diallyl ester, polyallyl ester, tetraallyloxiethan, triallyl amine, tetraallyl ethylenediamine, allyl ester of phosphoric acid or phosphorous acid, further crosslinkable monomers, such as the N-methylol compounds of amides such as methacrylamide or acrylamide and the derivatives derived therefrom o esters of polyols and alkoxylated polyols, such as diacrylates or triacrylates, for example butanediol or ethylene glycol diacrylate, polyglycol di (meth) acrylates, trimethylolpropane triacrylate, di- and triacrylate esters of the (preferably ethoxylated) trimethylolpropane which is alkoxylated with 1 to 30 mol of alkylene oxide and methacrylate esters of glycerin and Pentaerythritol, as well as glycerol and pentaerythritol, which is preferably ethoxylated with 1 to 30 mol ethylene oxide. Methylene or ethylene bis (meth) acrylamide, N-methylolacrylamides and triallylamine are preferably used. The proportion of the crosslinking comonomers is from 0.01 to 2.5% by weight, preferably from 0.01 to 1.0% by weight and particularly preferably from 0.01 to 0.1% by weight, based on the total of Monomers.

The carboxylate group-containing polymers to be used according to the invention can contain water-soluble polymers as the graft base, with amounts of up to 30% by weight being preferred. These include partially or fully saponified polyvinyl alcohols, starch 0 or starch derivatives, lignin or lignin derivatives, cellulose or cellulose derivatives, polyacrylic acids, polyglycols or mixtures thereof.

In a preferred embodiment, the polymers to be used according to the invention are post-crosslinked. For post-crosslinking, which leads to a significant improvement in gel stability, the liquid absorption under pressure and the absorption speed

Compounds used which generally have at least two functional groups and which can crosslink the functional groups of the polymer on the surface of the polymer particles. Alcohol, amine, aldehyde, glycidyl and epichlor functions are preferred, crosslinker molecules with several different functions also being usable. The following post-crosslinking agents may be mentioned as examples: ethylene glycol,

Diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, diethanolamine, triethanolamine, polypropylene oxide, block copolymers of ethylene oxide and propylene oxide, sorbitan fatty acid esters, ethoxylated sorbitan fatty acid esters, trimethylol propane, ethoxylated trimethylol propylene glycol, 5-ethylenediethylphroxyphenol, pentethylene, pentitole, ethoxylated trimethylol propylene, pentethylene, pentitone, pentitole, pentitone, pentitone approximately

Ethylene glycol diglycidyl ether. Ethylene carbonate is preferably used as the post-crosslinking agent. The post-crosslinking agent is used in an amount of 0.01 to 10 percent by weight, preferably 0.1-5 percent by weight, particularly preferably 0.1-1 percent by weight, based on the polymer to be post-crosslinked. 0

The poly (meth) acrylates to be used according to the invention can be prepared by customary processes, preferably in aqueous solution, batchwise in a polymerization vessel or continuously, for example on an endless belt. The

REPLACEMENT BUTT (RULE 26) Polymerization is triggered using conventional initiators or redox systems which trigger free-radical polymerization. In the case of a practically adiabatic course of the polymerization, with an appropriate initial concentration of 15 to 50% by weight of the monomers, an aqueous polymer gel is formed. By choosing the initial monomer concentration and the corresponding low starting temperature in the temperature range from 0 to 50 ° C., preferably from 5 to 25 ° C., the polymerization can be carried out in such a way that the maximum temperature in the resulting aqueous polymer gel is easy to control. After the polymerization has ended, the polymer gel is mechanically comminuted, dried, ground and optionally subjected to surface crosslinking. 0

The suspension polymerization process is also suitable for the production of the poly (meth) acrylates, in which the discrete polymer particles are already formed during the polymerization.

5 When adding the surface postcrosslinker, ensure that the polymer particles are thoroughly mixed. Suitable mixing units for applying the post-crosslinking agent are e.g. Patterson-Kelley mixers, DRAIS turbulence mixers, Lödige mixers, Ruberg mixers, screw mixers, plate mixers and fluidized bed mixers, as well as continuously operating vertical mixers, in which the powder is mixed at a fast frequency using rotating knives (Schugi mixer). After the postcrosslinker has been mixed with the polymer particles, preferably in the form of a solution, the postcrosslinking reaction is heated to temperatures of 80 to 250 ° C., preferably to 135 to 250 ° C. and particularly preferably to 150 to 200 ° C. The optimal duration of the reheating can easily be determined 5 for the individual types of crosslinker with a few tests. It is limited by the point at which the desired property profile of the superabsorber is destroyed again as a result of heat damage. For example, the crosslinking times for temperatures of 180 ° C are usually less than 30 minutes.

The poly (meth) acrylates can also contain processing and conditioning aids such as potassium stearate, polyglycol, silicas, bentonites.

The residual monomer content of the poly (meth) acrylates to be used according to the invention is low and is less than 1000 ppm, preferably less than 500 ppm and particularly preferably

REPLACEMENT BUTT (RULE 26) less than 250 ppm. In particular, the residual content of ecotoxicologically questionable monomers such as acrylamide is preferably below 250 ppm.

The absorption capacity of the poly (meth) acrylates to be used according to the invention for water 5 and aqueous solutions can vary within wide limits and is affected by

Monomer components, the crosslinkers and, if necessary, the postcrosslinkers set. Poly (meth) acrylates are preferably used which absorb more than 30 g / g, more than 50 g / g and particularly preferably more than 65 g / g polymer of a synthetic soil solution with a conductivity of 2.5 μS. The synthetic soil solution 0 contains 0.71 g NaCl, 0.065 g NaN ₃ , 1.676 g KCl, 0.353 NH ₄ C1, 3.363 g MgCl ₂ 6H ₂ O, 10.5 g CaCl ₂ 2H ₂ O and 0.019 g FeCl per 10 1 water ₃ 6H ₂ O. 1 g of poly (meth) acrylate in 200 ml of this solution is stirred for 15 min with a magnetic stirrer, left to stand for 45 min and then filtered through a 100 mesh sieve. The absorption value results from the quotient of the amount of liquid absorbed and the weight of polymer. 5

Poly (meth) acrylate copolymers which have been prepared using comonomers which are free from carboxylate groups, in particular acrylamide, have a higher long-term stability of the absorption against frequently changing wet and dry phases during use. 0

The soluble proportions of the poly (meth) acrylates to be used according to the invention are usually below 20% by weight, preferably below 15% by weight and very particularly preferably below 10% by weight.

5 The particle size distribution of the polymers to be used can vary depending on the application, usually in the range of 0.2 to 3 mm.

Furthermore, the poly (meth) acrylates can be loaded with active substances which they release into the environment again in the course of the use according to the invention. These active ingredients include fertilizers, herbicides and pesticides.

In the process according to the invention, the pH of acidic soils in general can be raised by up to one unit. For example, an addition of 0.4 wt. -

REPLACEMENT BUTT (RULE 26) % By weight of copolymer to a soil with a pH of 4.11 increases the pH to 4.69.

The invention is explained in more detail below by the examples.

5

example 1

336 g of forest soil (dry weight 300 g) are distilled in 1, 2 1. Suspended water and mixed with 1.2 g of the following polyacrylates:

0 Stockosorb ^® K 400 cross-linked acrylamide / acrylic acid copolymer, partially neutralized as K-salt, particle size in the range from 200 to 1000 μm Stockosorb ^® K 410 cross-linked acrylamide / acrylic acid copolymer, partially neutralized as K-salt, particle size in the range of 1000 Up to 3000 μm Favor ^® SXM 75 re-cross-linked polyacrylic acid, partially neutralized as Na salt, particle size in the range from 200 to 800 μm

50 min after the addition of the polymer, the pH is measured with a glass electrode. The following values are obtained:

0 control pH 4.13

Stockosorb 400 K ^® pH 4.83

Stockosorb 410 K ^® pH 4.98

Favor SXM ^® 75 pH 6.06

5 Compared to untreated forest soil, the pH is increased by approx. 1 to 2 units due to the addition of polymer.

Example 2

Samples of 4 kg each (dry weight) of forest soil (from the Solling, near the o test area of the Research Center Forest Ecosystems, Göttingen) or loam soil

(taken from the Forstbotanischer Garten, Göttingen) are mixed with different amounts of Stockosorb ^® , transferred to a 6 1 plastic container and stored outdoors in summer temperatures. After 2 days, 3 samples of 5 g each

REPLACEMENT BUTT (RULE 26) removed and the pH value measured with a glass electrode. Then a spatula tip KCl is added to measure the pH again. The following results are obtained:

Soil pH value without KCl with KCl clay soil:

Control 7.78 7.52

0.2% Stockosorb 7.64 7.50 0.4% Stockosorb 7.65 7.44 0.6% Stockosorb 7.59 7.50

acid forest floor:

Control 4.09 3.45 0.2% Stockosorb 4.49 3.53 0.4% Stockosorb 4.58 3.51 0.6% Stockosorb 4.67 3.56

While no pH effect could be observed in soils with a pH around the neutral point with the Stockosorb amounts used here, the pH in the acidic soil rose by up to 0.6 units.

ERSATZBUπ (RULE 26) Example 3

As in Example 2, Waldbodcn was mixed with Stockosorb ^® K 400 and K 410, amounts of 0.1 to 1.0% by weight, based on the amount of soil, being used. After 10 days, the pH was measured on January 16, 1955. A second measurement took place about 6 months later on June 4, 1996. The following results were obtained:

Polymer content measurement date: in soil

(Wt%) 16.11. 1995 4.6. 1996 0 in water addition of KCl in water addition of KCl 0 ("Control. 4.11 3.43 4.05 3.49.

K 400

0.1 4.34 3.46 4.11 3.39

0.2 4.54 3.56 4.31 3.49 5 0..3 4.54 3.48 4.26 3.46

0.4 4.69 3.50 4.36 3.50

0.5 4.77 3.63 4.46 3.37

0.6 4.69 3.58 4.80 3.60

0.7 4.77 3.61 4.76 3.61 0 0.8 4.75 3.54 4.71 3.53

0.9 4.75 3.54 4.70 3.50 fl 4JJ_ 2 4_ LAAL

K410 5 0.1 4.39 3.48 4.19 3.48

0.5 4.58 3.51 4.64 3.62 fl 12 M UM UI.

Even after the very hard winter of 1995/96, when the temperature in Göttingen was -20 ° C or lower, the pH of the soil in the subsequent growing season was still significantly increased, depending on the hydrogel addition.

REPLACEMENT BUTT (RULE 26) Example 4.

Three-year-old spruces were planted in 12 L containers in an acidified clay slate floor made of resin, which was mixed with 0.6% Stockosorb K 400. Control experiments were carried out in parallel with untreated soil. The plants were kept outdoors from May to October, with routine tap watering. During this time it was found that the needles of the plants that grew in untreated soil turned yellow, while the plants that grew in the soil containing Stockosorb continued to have green needles (Fig. 1). 0

The plants were then subjected to water stress treatment, i.e. No longer watered until the needles turned gray and fell off.

For each treatment variant, the fine roots were removed from three different plants and prepared for the localization of the ions in the electron microscope using X-ray microanalysis (Godbold, DL, E. Fritz, A. Hüttermann: Aluminum toxicity and forest decline. Proc. Natl. Acad. Sci. USA 85, 3888-3892 (1988)). The analyzes of the elemental contents of the cell walls of the root cortex in mmol / dm ³ of different roots are shown in Fig. 2. In the roots, which grew in the untreated soils, there were large amounts of aluminum and only very small amounts of the important nutritional elements calcium and practically no magnesium (Fig. 2 a, control). In the cell walls of the root bark of the plants, which grew in the soil treated with Stockosorb, the conditions were exactly the opposite, there was only a little aluminum and a lot of calcium and in all cases magnesium (Fig. 2 b, 0.6% Stockosorb) . 5

The protective colloid Stockosorb was effective even under very difficult soil drying conditions, in which the concentration of ions in the nutrient solution increases by at least one order of magnitude. Substantially fewer aluminum ions were found in the plants treated with Stockosorb and instead significantly higher concentrations of the divalent nutrient ions Ca and Mg.

REPLACEMENT BUTT (RULE 26)

Claims

claims

1. A process for increasing the pH in acidic soils, characterized in that the acidic soils are treated with crosslinked polyacrylates or polymethacrylates.

2. The method according spoke 1, characterized in that the treatment of the acidic soils is carried out by sprinkling or preferably by mixing.

3. The method according to Anspmch 2, characterized in that the amount added during mixing is 0.1 to 2.5 wt.%.

4. The method according to claim 3, characterized in that the amount added during mixing is 0.5 to 2.0 wt.%.

5. The method according to claim 1, characterized in that the crosslinked poly (meth) acrylates are prepared using monoethylenically unsaturated, carboxylate group-containing monocarboxylic acids, in particular acrylic acid or salts thereof.

6. The method according spoke 5, characterized in that the poly (meth) acrylates are prepared using other monoethylenically unsaturated monomers containing no carboxylate groups, in particular using acrylamide.

7. The method according spoke 5 or 6, characterized in that the poly (meth) acrylates are obtained as crosslinkers using methylenebis (meth) acrylamide, ethylenebis (meth) acrylamide, N- 5 methylolacrylamide or triallylamine, where

Methylenebisacrylamide is preferred.

8. The method according to one or more of claims 5 to 7, characterized in that the poly (meth) acrylates treated with a post-crosslinking agent in amounts of 0.01 to 10% by weight at elevated temperature, preferably between 80 and 250 ° C become.

ERSATZBUπ (RULE 26)

9. The method according to one or more of claims 5 to 8, characterized in that the acidic monomer components of the poly (meth) acrylate are neutralized between 10 and 95 mol%, preferably between 50 and 90 mol%

10. The method according to one or melireren of claims 5 to 9, characterized in that the poly (meth) acrylates have an absorption capacity for synthetic soil solution of more than 30 g / g, preferably of more than 50 g / g and particularly preferably of more than Have 65 g / g.

11. The method according to one or more of claims 5 to 10, characterized in that the poly (meth) acrylates are incorporated into the acidic soil to a depth of about 50 cm.

ERSATZBUπ (RULE 26)