DK171408B1 - Plant growth medium based on diatomaceous earth and method of preparation thereof - Google Patents

Description

in DK 171408 B1

The present invention relates to novel absorbent granules and their use, especially as plant growth medium.

Plant growth media used for hydroponic cultivation 5 or as a substrate in pots is based on sand, pumice or volcanic lava, perlite, vermiculite, expanded clay soil, tree bark, lignite or light peat.

Expanded clay soil or tree bark has the disadvantage of not being particularly porous in the range of 15 to 150 pra. The retention of water in these substrates is thus very limited, which necessitates a permanent irrigation of such substrates by hydroponic cultivation.

15 Perlite or vermiculite have higher porosity between 15 and 150 µm than expanded clay soil or tree bark. Aeration of the substrate is important as the intergranular water flows easily. These substrates are often used as hydroponic culture media.

20

Sand can retain more water than the four substrates described above, mainly in the intergranular porosity where only a small volume of air can be maintained. For this reason, the use of sand as a culture medium will necessitate a renewed irrigation at frequent and regulated intervals of time, since permanent irrigation would cause rapid swelling and rot of the roots.

Peat is the best adapted substrate for herbal pots for 30 hydroponic cultivation. It has the ability to retain water and air and is therefore sought after for plant cultivation. It should never dry out as it will then become hydrophobic and then difficult to re-moisturize (see Soil Science, 1991, 152-2, pp. 100-107, B. Valat, C. JOUNANY 35 AND lm RIVIERE: Characterization of the Wetting or Air Dried Peats and Composts). It also has the disadvantage that 2 DK 171408 B1 sink together over time, which impairs aeration of the roots and thus the growth of the plant.

DE-publication 3,220,137 discloses a plant-5 growth medium consisting of calcined silica and which exhibits high capillarity. The preparation of the granules by calcination is uneconomical and energy intensive and the starting material itself is expensive.

The present invention, on the other hand, relates to an excellent growth medium for plants, characterized by the characterizing part of claim 1. This growth medium can, surprisingly, be prepared from used silica gel in the form of filter cakes from the fermentation industry.

15

In addition, the invention relates to a process for the preparation of the subject plant growth medium which is characterized by the characterizing part of claim 2. In addition, the invention relates to the use of the growth medium as claimed in claims 6 and 7.

Other features which are particularly advantageous are the following: 25 - a low content of heavy metals; good mechanical resistance to sinking; an ion exchange capacity for cations (Ca +, Na +, Mg ++, K) exceeding 100 milliequivalents / dm in herbal pots o or less than 100 milliequivalents / dm in hydroponic cultures; slight rewetting after accidental drying.

Good mechanical resistance to water vapor sterilization is also appreciated for the hydroponic plant cultures, which must be bacteriologically inert, especially when it comes to recycling a substrate after its use for cultivation.

Certain properties will be explained in more detail below.

The retention of water by a substrate is expressed by the amount of water absorbed per kg of plant growth medium.

The water-assimilable plant or useful water-10 reserve is the amount retained in pores of a size between 1.5 and 150 μπι. The amount of water retained in the pores of a size between 1.5 and 150 μπι is assimilable by the plant, but at the expense of a suction force that puts the plant in a state of stress: it is called stress water. The water in pores of a size below 1.5 μπι is not assimilable by the plant and is therefore of no interest to the growth: it is termed useless water reserve. For example, natural raw samples from clay-digging water contain up to 2 to 3 times their weight, but the plants cannot grow or thrive there because the entire porosity is less than 1.5 μπι.

The useful reserve and the need for water are expressed as a percentage between the volume filled with water and the volume of the dry plant substrate (the apparent volume of the plant substrate). It is measured according to a protocol described by D. TESSIER and BERRIER: Utilization de la microscopy to balance dance in obervation de sols soumis a différents pH, Science du So, 67-82, 1979.

30

Structural stability is an important criterion as to the irrigation properties of a substrate during prolonged or frequent irrigation and the stability to water. Thus, certain types of clay soil will degrade under the simple influence of capillary rise of water in the pores and channels of the material. The material is decomposed by explosion of the pockets due to entrapped air, and then it is cleaved. The material is tested by introducing 5 g of dry carrier medium into a 50 ml test tube and then 25 ml of water. The tube is closed and turned continuously for 30 minutes. The structural stability is indicated by the percentage of the mass of the particles remaining at dimensions above 1 mm.

The measurement of the pH is carried out after a portion of granulate has been contacted within 5 minutes with 5 times its weight of water. The plants poorly tolerate a basic substrate.

The acceptable content of heavy metals in a plant substrate depends mainly on whether the substrate is to be used as a hydroponic culture medium or a pot culture. Zero ion exchange capacity is not a handicap for a hydroponic culture, although it is important for a pot culture. A value of over 100 milliequivalents (meq) ions / dm is satisfactory for the pot cultivator. At a value below 100 mEq / dm, the growth medium should generally be improved with a little fertilizer.

The permeability of the growth medium should allow rapid dewatering through the suspension. It is usually measured in darcy 25 to be about 0.987 * 10 "12 m2 in MKSa units according to a method described in FR 2,367,282.

So far, Kieselguhr has not gained practical use as a growth medium for plants. Still, it is a powder that can absorb almost its double weight of water. Studies of its moisture content show that it is saturated with 1.8 kg of water / kg, but its need for water is close to 4%. Water is absorbed mainly in pores below 1.5 microns, and the porosity saturated with water is not available for air, where the free volume after wetting the substrate is less than 0.5%: the wetted silica is a mud or mud, 5 DK 171408 B1 which is practically useless and in which the plants would die due to lack of air at the roots.

Admittedly, there is a German patent, DE 31.20782, which discloses the production of growth media for plants by granulation of spent silica that originates from filter cakes from breweries. The cakes were agglomerated with clay. This process nevertheless leads to dry products in need of water in amounts between 4 and 7% of the 10 apparent volumes (compared to 20 to 40% for different peat species). The structural stability of the dry and calcined products, comprising between 50 and 80%, according to the original filter cakes, is insufficient to form a good hydroponic growth medium for plants. Depending on the nature of the clay used, the granules of the filter cakes will have a pH between 8 and 10 when calcined.

In general, the compounds 20 are believed to clog the porosity of the materials with which they are combined. It would not be a disadvantage for a fuel or a construction material, but it would be extremely unfortunate in connection with the production of plant fibers where there is a great need for water.

This is why the attempts to agglomerate the known absorption soils are the result of incorporating the absorption soils within the foam resins themselves (see, for example, JP-A-55125132 or JP-A-80125132 from Mitsui Toatsu Chem. Inc., DD 217795 from VEB 30 Agroch. Piesteri) reduced to the desired granulometry by crushing the polymerized mass.

It has now been investigated whether it is possible to prepare such absorbent granules, especially as growth media for 35 plants, by forming fibers of mixtures of silica and urea formaldehyde resins which are allowed to dry after polymerization and finally complete in details in the desired form. The absorption efficiency of the products obtained in this extraordinarily simple process is very unexpected. The preferred compositions are those comprising 100 parts of silica with 20 to 50 parts of a urea-formaldehyde resin which may be a melamine-formaldehyde resin, based on dry weight.

Thus, the process of the invention consists in mixing a silica gel whose water content is set at 40% with a urea formaldehyde resin containing an acidic catalyst, for example NH 2 Cl. The composition is mixed with care and spun under pressure, for example with a Kahl press. The paste is then pressed through a spinning nozzle which can be driven by means of an ironing roller over a grid. It can also be pressed with a pinette type press while adding to the paste of a carboxymethyl cellulose type spinner. Finally, the fibers 20 are dried at a temperature between 95 and 180 ° C to cross-link the resin and, if necessary, a grinding is performed to meet the user's dimensions requirements, generally between 1 and 4 mm.

The resins of are of a type used as a binder for making combustible materials or for obtaining sheets of agglomerated wood. The resin is prepared by condensation of formalin and urea. It is marketed in aqueous form containing 50 to 80% dry 30 resin, or in dry form.

The silica gel of the present invention should be subjected to calcination treatment to adjust permeability to between 0.03 and 15 darcy. It is one such treatment that silica must be subjected to when processed into filtration agents. This state of silica glue permeability is necessary to achieve sufficient open porosity in the material, but it is not sufficient. By using silica as a powder, the necessary intergranular permeability for the respiration of the roots is ensured. The size of this permeability is not comparable to the internal permeability of the material. The permeability is increased as a function of the ability with the square of the diameter of the open pores, from a few millimeters of the accumulation of the granules to some 10 half a dozen microns in the silica.

However, silica is a very expensive material to use for an ordinary plant substrate. Its permeability properties have not been depleted by general use as a filtering agent, but are still found in materials such as filter cakes, such as for breweries or in the wine industry, which provide an inexpensive source of raw materials for making the absorbent granules according to the present invention. The use of these filter cakes is so much more advantageous to the present invention because not only are raw materials of no value, but also because their disposal becomes more and more cumbersome. The only limitation is that you have to dry them partially to reduce the humidity from 65% to 40%.

The previously known agglomerates exhibited a poorly acceptable basicity derived from combustion ash from organic matter retained in the cake during the filtration of beer or wine. The agglomerates of the present invention are obtained without calcination and their pH value is appropriate. Their need for water is between 8 and 12%, their useful reserve is between 20 and 40%, and their structural stability is between 80 35 and 95%. Those with a water demand of between 8 and 12% are particularly suitable for hydroponic culture, although their useful reserve does not exceed 12%. Those having a water requirement located between 8 and 12% and a useful reserve between 20 and 40% are suitable for plant cultures in pots, resulting in the plant's resistance to unavoidable 5 water stress conditions, for example during transport or storage.

Without departing from the scope of the invention, these products also constitute absorbent materials for absorbing 10 oils, for example from garage floors.

EXAMPLE 1: Prior Art

A plant substrate with a clay binder is prepared in accordance with that disclosed in patent specification DE 3120782. To this is added a moist filtration cake from a brewery with a bentonite clay (CLAR-SOL® FR4 from CECA S.A.) and carboxymethyl cellulose to retain water during spinning. The quantity ratios used are as follows:

Filter cake (in dry state) 1000 g water 650 g bentonites 100 g carboxymethyl cellulose 20 g

After mixing in a WERNER apparatus and spinning to a diameter of 1.6 mm in a Pinette press, the product is dried on a steam bath and the fibers are cut to lengths of 5 mm.

The properties of the fibers are as follows: 30 - a water requirement of 5%; an exploitable water reserve of 30%; a free air volume in the substrate of 30 to 35%; A pH of from 6 to 7; a mechanical resistance of weak compression; a structural stability in the neighborhood of 60%; a very powerful permeability.

5

However, the structural stable and water retention is insufficient for use as a hydroponic carrier or substrate. They can be improved by calcination at 600 ° C, whereby the clay binder is sintered and the organic substances destroyed by calcination, but the structural stability does not exceed 65% and the pH again rises to 8.9. These products allow the growth of plants laboratory-wise, but the salting out of fine material due to the poor structural stability makes them useless due to clogging of the nutrient fluid recirculation systems.

EXAMPLE_2; The filter cake of Example 1 is mixed with the same bentonite particles and then compressed to 50 bar. The product is dried, crushed and sieved to between 1 and 4 mm. The composition used is as follows: filter cake (dry state) 1000 g water 650 g bentonitles 100 g 25

The properties obtained are as follows: - a water requirement of 5%; - an exploitable water reserve of 25%; 30 - a free air volume in the substrate of 30 to 35%; a pH value of 6.5; - mechanical resistance to weak compression; - structural stability close to 60%; 10 DK 171408 B1 - a very powerful permeability.

After calcination at 600 ° C: 5 - a water demand of 4%; - a utilizable water reserve of 27%; a free air volume in the substrate of 30 to 35%; - a pH value of 9; - mechanical resistance to weak compression; 10 - a structural stability in the vicinity of 60%; - a very strong permeability.

This material still suffers from too weak structural stability.

EXAMPLE 3

Compression between 50 and 400 bar of the previous filter cake is used, but without the use of clay binder. The composition is: 20 filter cake (in dry state) 1000 g water 650 g where the water comes from the filter cake after a partial drying.

After simple drying, brittle granules are obtained with the following properties: - a water requirement of 1%; - an exploitable water reserve of 15%; 30 - a free air volume in the substrate of 30 to 35%; a pH value of 6; - mechanical resistance at very weak compression; - structural stability in the neighborhood of 10%; DK 171408 B1 π - a very weak permeability due to the cleavage of the product.

These granules are unacceptable as a culture medium. The 5 quickly turn into a scent in which the plants rot due to lack of air at the roots.

EXAMPLE, "4; The bentonites used in Example 1 are replaced with at-tapulgite (CLARSOL® ATCNA from CECA S.A.). A dry product is obtained with the following properties: - a water demand of 4%; 15 - an exploitable water reserve of 30%; a free air volume in the substrate of 30 to 35%; - a pH value of 6; - mechanical resistance to weak compression; - structural stability close to 60%; 20 - a very powerful permeability.

After calcination at 600 ° C, the following properties are obtained: - a water requirement of 5%; 25 - an exploitable water reserve of 29%; a free air volume in the substrate of 30 to 35%; a pH of 8.1; - mechanical resistance to moderate compression; - a structural stability in the neighborhood of 75%; 30 - a powerful permeability.

EXAMPLE 5:

Granule compositions according to the invention are obtained with the same filter cake as in Example 1 by agglomeration with a 12 DK 171408 B1 urea formaldehyde resin (Caurite 110 from Elf Atochem AA, which is an aqueous resin with 33% water) as follows: filter cake (calculated as dry matter) 1000 g of water 650 g of urea formaldehyde resin 450 g of catalyst, NH 4 Cl 4.5 g 5 The product is spun in a Kahl press, dried between 95 and 180 ° C after cross-linking of the resin. It is ground to obtain a fiber size between 1 and 4 mm. The granules have the following properties: 10 - a water requirement of 12%; - an exploitable water reserve of 25%; a free air volume in the substrate of 30 to 35%; a pH value of 5.5; - mechanical resistance to moderate compression; 15 - a structural stability in the vicinity of 95%; - as a result of the granulation, a strong permeability of 27 darcy.

The content of heavy metals in the granulate was analyzed and compared with the authorized values of the standard NU 44-041.

13 DK 171408 B1

The Real The Real

Contents of content in content in mg / kg in file- Content in mg / kg (NFU (NFU 44-041) terkagen in mg / kg in 44-041) i in spread

Metal dry state granulate, soil__slam_

Cd__0j_6__0,45__2__20_

Cr__57__45__150__1000_

Cu__33__25__100__1000_

Hg__0,02__0,02__1__10_

Ni__30__23__50__200_

Pb__9__7__100__800_

Zn 63 50 300 3000

^ —— b —- p »—4 — i ————. U I - [I .M.I. I. - 'T

The granulate has a content of heavy metals which is compatible with the real content of the agricultural soil or 5 permissible for dispersed sludge from wastewater treatment plants. Content of heavy metals above this normal content would preclude any use for hydroponic or pot culture.

10 100 g of this product absorb 110 g of water or oil.

This property can be utilized to absorb liquid waste in houses or industrial premises, for example from garage floors.

Remark. If 150 g of Caurite resin is used, the need for water is 15%, but the structural stability is reduced to 35%. With 300 g of Caurit resin the water demand is reduced to 12%, the structural stability is between 55% against the desired 80% to 95%. With more than 550 g of Caurite resin, the price of the granulate is increased and the need for water is reduced to 8% without any improvement in structural stability. The products made with 45 parts of Caurit resin for 100 parts of filter cake are economical and optimal for hydroponic cultures.

After drying, these products can easily be re-wetted.

5 EESfiMFEl · ¢:

The previous study was repeated with dried non-calcined crushed diatomite instead of a filter cake; 10 a urea formaldehyde resin is used as a binder.

Before drying, a granulate is obtained with the following properties: - a water requirement of 1%; - a utilizable water reserve of 9%; 15 - a free volume of air in the substrate of 30 to 35%; a pH value of 5.8; - mechanical resistance to moderate compression; - structural stability in the neighborhood of 90%; - a strong permeability.

20

Although these granules are very similar to the product of Example 5, they are of no interest as substrates for hydroponic cultures. A water requirement of 1% gives a product with 12 times as poor properties as the product of Example 5 with substantially the same production price.

EESEMP-EL li

Granules were prepared from filter cakes from a brewery (not calcined) and a cement CPJ55 of the following composition: filter cake 1000 g water 500 g cement CPJ55 300 g 15 DK 171408 B1

The granules are formed by means of a Kahl type press, then ground to a particle size of 1 to 4 ram. Their properties are as follows: - a water requirement of 5%; 5 - an exploitable water reserve of 35%; a free air volume in the substrate of 30 to 35%; a pH of 9.6; - mechanical resistance to moderate compression; - structural stability in the neighborhood of 30%; 10 - a strong permeability before cleavage.

Due to their poor structural stability and their elevated pH, these cement granules are not acceptable as growth media for plants.

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Claims (7)

1. Plant growth medium, characterized in that it consists of 5 fibers of urea formaldehyde resin and silica with the following physical / chemical properties: - a water demand greater than or equal to 8%, - an air volume relative to the medium's apparent volume of more than 20 - a structural stability greater than 80%, - a pH between 3.5 and 8, - a permeability above 15 darcy, especially above 25 darcy, the urea formaldehyde resin being present in 20 to 15 50 parts (based on dry matter) per . 100 parts silica. Process for preparing a plant growth medium according to claim 1, characterized in that moist silica is mixed with a urea formaldehyde resin containing an acidic catalyst, that the mixture is formed into fibers and that the fibers are dried at a temperature between 95 and 180 ° C. Process for producing a plant growth medium 25 according to claim 2, characterized in that the silica is pre-calcined silica and has a permeability between 0.030 darcy and 15 darcy. Process for the preparation of a plant growth medium 30 according to claim 2, characterized in that the silica gel consists of partially dried filter cake from the breweries or the wine industry. Use of the hydroponic granule of claim 1 as growth medium. DK 171408 B1 Use of a growth medium according to claim 1 with a water requirement greater than 20% in the form of a herbal potato granule. Use of a plant growth medium according to claim 1 for the suction of aqueous or oily liquid waste in private homes or industrial premises.