FR2718735A1 - Absorbent aggregates based on Kieselguhr, their preparation and their application in particular as horticultural supports. - Google Patents

Abstract

These products are obtained, endowed with remarkable water retention according to a process which comprises a step of kneading kieselguhr, with a formaldehyde urea resin which is crosslinked between 90 and 180 degrees C. The process is made particularly economical when the source of kieselguhr consists of filter cakes from the clarification of beer or oenological products.

Description

The present invention relates to new absorbent aggregates and to

their application, especially as

horticultural supports.

  The horticultural supports used for hydroponics or for growing in pots are sand, volcanic pumice, perlites, vermiculites, expanded clays, wood bark, brown or blond peat. Expanded clay or wood bark has the disadvantage of not being very porous in the 150 lm range. Water retention in these supports is therefore very limited, which requires, in hydroponics, a

  permanent irrigation of these supports.

  Perlite or vermiculite have more porosity between 15 and 150 µm than expanded clay or wood bark. The ventilation of these supports is important because the intergranular water flows easily. These supports

  are very often used in hydroponic crops.

  Sand is capable of retaining more water than the four supports described above, essentially in the intergranular porosity, in which it leaves only a small volume of air. As a result, the sand used as a culture medium requires renewed irrigation at regular and frequent time intervals, permanent irrigation rapidly causing suffocation and decay.

roots.

  Peat is a better support for growing in pots than for hydroponics. They have water and air retention capacities which make them a popular material in horticulture. However, they should not be dried, otherwise they become hydrophobic and are then very difficult to rewet (see Soil Science, 1991, 152-2, pp. 100-107, B. Valat, C. JOUANY and LM RIVIERE: Characterization of the Wetting of Air Dried Peats and Composts). They also have the drawback of settling over time, which reduces the aeration of the roots,

and therefore the growth of the plant.

  A good horticultural support, as referred to in the present invention, must be characterized by: - a demand for water greater than or equal to 8%; - an air volume in the apparent volume of the support greater than 20%; - structural stability greater than 80%; - a pH of 3.5 to 8;

  - a very high permeability, greater than 15 darcys.

  Other characteristics are desired: - a low content of heavy metals; - good mechanical resistance to compaction; - a cation exchange capacity (Ca ++, Na +, Mg +, K +) greater than 100 milliequivalents / dm3 in pot culture or less than 100 milliequivalents / dm3 in hydroponic culture - easy rewetting after accidental drying. Good mechanical resistance to sterilization by water vapor is also highly appreciated for hydroponic culture media which are desired to be bacteriologically inert, especially if it is a question of recycling a

end of culture cycle.

  Some of these characteristics are explained more

in detail below.

  The water retention of a support is expressed in mass of water absorbed per kg of horticultural support. The water assimilable by the plant or useful reserve water is that which is retained in the porosity of between 1.5 and 150 μm. We can distinguish the demand for water, water easily extractable by the plant, which is the water contained in the porosity 15 to 150 μm. The water contained in the porosity of between 1.5 to pm is assimilable by the plant, but at the cost of a suction effort which places the plant in stress condition: here it is called stress water. The water contained in the porosity of less than 1.5 μm cannot be assimilated by the plant, and therefore of no interest for cultivation: here it is called unnecessary reserve water. For example, raw quarry natural clays contain up to 2 to 3 times their weight in water, but plants cannot grow there because all

  their porosity is less than 1.5 µm.

  The useful reserve and the water demand are expressed as a percentage between the volume occupied by the water and that occupied by the dry horticultural substrate (apparent volume of the horticultural support). They are measured according to the protocol described in D. TESSIER and J. BERRIER: Use of scanning microscopy in the observation of soils subjected to different pH,

Soil Science, 1, 67-82, 1979.

  Structural stability is an important criterion when it comes to the disintegration of a support under the effect of prolonged or frequent watering and when its stability

  with respect to water. Indeed, some argillo-

  silt disintegrate under the simple effect of the capillary rise of water in the pores and channels of the material. The material disintegrates by explosion of the trapped air pockets and then disintegrates. The material is tested by introducing into a 50 ml test tube, 5 g of dry support and then 25 ml of water. The tube is closed and inverted continuously for 30 minutes. Structural stability is represented by the percentage by mass of particles

  remaining greater than the dimension of 1 mm.

  The pH measurement is carried out after contacting, for 15 minutes, a portion of granules with 5 times their

  weight in water. Plants do not accept a basic support.

  The acceptable heavy metal content in a support

  horticulture has been defined in standard AFNOR NFU 44-041.

  The cation exchange capacity of a horticultural support mainly depends on the use of the substrate either in hydroponic culture or in pot culture. A zero ion exchange capacity is not a handicap in hydroponics while it is important for a pot culture. A value greater than 100 milliequivalents (meq.) Of ions / dm3 is satisfactory for culture in pots. For a value less than 100 meq / dm3, the culture medium

  should be regularly amended with a little fertilizer.

  The permeability of the support must allow rapid passage and drainage of the water through the substrate. It is commonly measured in darcys, i.e. 0.987.10-12 m2 in MKSa units, according to the method described in the French patent.

FR 2,367,282.

  Kieselguhr has so far found no practical application as horticultural supports. Yet it's a powder

  able to absorb almost twice its weight in water.

  The study of its moistening shows that it is saturated with 1.8 kg of water / kg, but its water demand is close to 4%. Water is mainly absorbed in pores less than 1.5 µm, and the water-saturated porosity is not accessible to air, the free volume of which after moistening the substrate is less than 0.5% : wet kieselguhr is a mud impractical to use, in which, without air at the level of

roots, plants die.

  There is indeed a German patent DE 31 20782 which cites the manufacture of horticultural supports by granulation of used kieselguhrs coming from filter cakes of

  brewery. The cakes were agglomerated with clays.

  However, this process leads to dry products with water demands of between 4 and 7% of the apparent volume (to be compared with 20 to 40% for different varieties of peat). The structural stability of the dried and calcined products, between 50 and 80%, depending on the origin of the filter cakes, is insufficient to make it a good hydroponic horticultural support. Whatever clay is used, the filter cake granules have a pH

  between 8 and 10 when calcined.

  We have now found that it is possible to form absorbent granules, useful in particular as horticultural supports, by agglomerating 100 parts of the kieselguhr with 20 to 50 parts of a urea-formaldehyde resin, which may be a melamine-formaldehyde resin. , counted by dry weight. This is an unexpected result, when it is known that binders in general block the porosity of a material, which is not disadvantageous for a fuel or a building material, but which would be prohibited in the case of the manufacture of horticultural yarns which are highly demanding

water demand.

  The method of the invention consists in mixing a kieselguhr, the water content of which is adjusted to around 40%, with a urea-formaldehyde resin containing an acid catalyst, for example NH4Cl. The whole is carefully kneaded, then spun on a press, for example a Kahl type press. The dough is then forced through a die, which can be operated by means of rubbing rollers on a grid. It can also be pressed on a Pinette press with the addition of a spinning agent of the carboxymethylcellulose type to the dough. The yarns are then dried between 95 and 180 C to crosslink the resin, and if necessary crushed to meet the size requirements of users, generally between 1

and 4 mm.

  Resins are of the type used as a binder to make combustible materials or to make agglomerated wood panels. The resin is produced by the condensation of formalin and urea. It is found commercially, either in aqueous form containing from 50 to

  % of dry resin, either in dry form.

  The kieselguhr usable in the present invention must have undergone the calcination treatment to adjust its permeability between 0.03 and 15 darcys. It is such a treatment that kieselguhr undergoes precisely when it is made to make it into filtration agents. This condition of permeability of the kieselguhr is necessary to achieve a sufficient open porosity in the material, but it is not sufficient. Shaping the powdered kieselguhr ensures an intergranular permeability essential for root respiration. The order of magnitude of this permeability is not comparable to that of the intrinsic material. The permeability increases as a function of the power squared of the diameter of the open pores, from a few millimeters in the stack of granules to

  a few tens of micrometers in the kieselguhr.

  Kieselguhr is, however, an expensive raw material for making ordinary horticultural support. Its quality of permeability is not exhausted by the ordinary use which is made of the filtering agent and it is found in the material of used filter cakes, for example those of the brewery or of the wine industry, which constitute an economical source of materials for the production of the absorbent aggregates of the present invention. The use of these filter cakes is all the more advantageous for the present invention that not only are they raw materials of zero value, but that their landfill becomes more and more expensive. The only constraint is to have to partially dry them to bring the humidity from 65% to

40%.

  The agglomerates of the prior art exhibited a hardly acceptable basicity, which came from the ashes of combustion of organic materials retained in the cake during the filtration of beer or wine. Those of the present invention are obtained without calcination and their pH is suitable. Their water demand is between 8 and 12%, their useful reserve between 20 and 40% and their structural stability between 80 and 95%. Those with a water demand of between 8 and 12% are particularly suitable for hydroponics, even if their useful reserve does not exceed 12%. Those with a water demand of between 8 and 12% and a useful reserve of between 20 and 40% are suitable for growing potted plants, which involves the plant's resistance to inevitable water stress conditions, for example during its

transport or maintenance.

  Without departing from the scope of the invention, these products also constitute absorbents for sponging oils,

for example on garage floors.

  EXAMPLE 1 Prior Art A horticultural support is made with a clay binder

  in accordance with the description cited in the patent

  DE 31 20782. For this, a wet brewery filtration cake is mixed with a bentonite clay (CLARSOL FR4 from CECA S.A.) and carboxymethylcellulose to retain the water during spinning. The proportions used are the following proportions: filtration cake (dry) 1000 g water 650 g bentonite clay 100 g carboxymethylcellulose 20 g After mixing on a WERNER device, and spinning at a diameter of 1.6 mm on a Pinette press, the product is oven dried, and

  the yarns are cut to the length of 5 mm.

  Their characteristics are as follows: - a water demand of 5%; a useful reserve of 30%; - a volume of free air in the support of 30 to 35%; - a pH of 6 to 7; - low mechanical resistance to compaction; a structural stability close to 60%;

- very high permeability.

  Their structural stability and their water retention are however insufficient for use as a hydroponic support. They can be improved by calcination at 600 C, which sinter the clay binder and destroys organic matter by calcination, but the structural stability does not exceed 65% and the pH rises to 8.9. These products allow the growth of plants in the laboratory, but the release of fines due to the low structural stability makes them unusable due to fouling of the systems of

  recirculation of nutrient solutions.

EXAMPLE 2:

  The filter cake of Example 1 is mixed with the same bentonite clay, then compacted under 50 bars. The product is dried, crushed and sieved between 1 and 4 mm. The x composition used is as follows: filtration cake (dry) 1000 g water 650 g bentonite clay 100 g The characteristics obtained are as follows: - a water demand of 5%; a useful reserve of 25%; - a volume of free air in the support of 30 to 35%; - a pH of 6.5; - low mechanical resistance to compaction; - a structural stability close to 50%;

- very high permeability.

  After calcination at 600 C, we obtain: - a water demand of 4%; a useful reserve of 27%; - a volume of free air in the support of 30 to 35%; - a pH of 9; - average mechanical resistance to compaction; - a structural stability close to 60%;

- very high permeability.

  This material suffers from far too little structural stability.

EXAMPLE 3:

  Compacting takes place between 50 and 400 bars of the previous filter cake, but without the use of a clay binder. The composition is: filtration cake (dry) 1000 g water 650 g o the water is that of the filtration cake after

partial drying.

  After simple drying, very friable granules are obtained, the characteristics of which are: - a water demand of 1%; a useful reserve of 15%; - a volume of free air in the support of 30 to 35%; - a pH of 6; - very low mechanical resistance to compaction; - a structural stability close to 10%; - very low permeability due to the disintegration of the product. These granules are unacceptable as a culture medium. They quickly turn into mud in which the plants rot due to lack of air at the level

roots.

EXAMPLE 4:

  The bentonite clay of example 1 is replaced by an attapulgite (CLARSOL ATCNA from CECA S.A.). The dried product is obtained having the following characteristics: - a water demand of 4%; a useful reserve of 30%; - a volume of free air in the support of 30 to 35%; - a pH of 6; - low mechanical resistance to compaction; - a structural stability close to 70%; - high permeability After calcination at 600 C, these characteristics become: - a water demand of 5%; - a useful reserve of 29%; - a volume of free air in the support of 30 to 35%; - a pH of 8.1; - average mechanical resistance to compaction; - a structural stability close to 75%;

- high permeability.

EXAMPLE 5:

  Composition of granules according to the invention produced with the same filter cake of Example 1, by agglomeration with a urea-formaldehyde resin (Caurite 110, from Elf Atochem SA, a resin in aqueous form at 33% water) according to : filter cake (dry) 1000 g water 650 g urea-formaldehyde resin 450 g NH4Cl catalyst 4.5 g The product is spun on a Kahl press, dried between 95 and 180 C in order to crosslink the resin. It is crushed to reduce the size of the yarns between 1 and 4 mm. The granules have the following characteristics: - a water demand of 12%; - a useful reserve of 25%; - a volume of free air in the support of 30 to 35%; - a pH of 5.5; - strong mechanical resistance to compaction; - a structural stability close to 95%; - due to granulation, high permeability

27 darcys.

  The content of heavy metals in the granule was analyzed and compared with the values authorized in the standard

NFU 44-041:

  Metal Content in Content in Content in Content in mg / kg in mg / kg in mg / kg mg / kg the cake of the authorized authorized granule filtration. (NFU 44-041) (NFU 44-041) sec. in them in the soil. spreading sludge Cd 0.6 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 Il Pellet has heavy metal contents compatible with those authorized in agricultural soils or those admissible in sludges from treatment plants for agricultural spreading. Heavy metal contents higher than this standard would prohibit their use in

hydroponics or in pots.

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

  This property can be used to absorb spills of liquids in both domestic premises

  than industrial, for example garage floors.

  Note. If 150 g of Caurite resin is used, the water demand is 15%, but the structural stability decreases towards 35%. With 300 g of Caurite resin, the water demand decreases around 12%, the structural stability is around 55% against 80% to 95% desired. Beyond 550 g of Caurite resin, the cost price of the granules is increased, the water demand is reduced to around 8% without improving the structural stability. Products made with parts of Caurite resin per 100 parts of filter cake are economical and optimal for hydroponics. These products, after drying, can be very easily rewetted.

EXAMPLE 6

  The previous test is repeated with a dried, uncharred, crushed diatomite in place of cake of

  filtration; a urea-formaldehyde resin is used as a binder.

  Granules are obtained before drying, the characteristics of which are as follows: - a water demand of 1%; a useful reserve of 9%; - a volume of free air in the support of 30 to 35%; - a pH of 5.8; - strong mechanical resistance to compaction; - a structural stability close to 90%;

- high permeability.

  These granules, although of appearance fairly close to the product of Example 5, are of no interest as a support for hydroponics. A water demand of 1% makes it a product 12 times less efficient than that of Example 5 with a substantially identical production cost.

EXAMPLE 7:

  Granules were made from brewery filter cake (not calcined) and CPJ55 cement, with the composition: filter cake 1000 g water 500 g cement CPJ55 300 g The granules are shaped on a Kahl press, then crushed between 1 and 4 mm. Their characteristics are as follows: - a water demand of 5%; a useful reserve of 35%; - a volume of free air in the support of 30 to 35%; - a pH of 9.6; - strong mechanical resistance to compaction; - a structural stability close to 30%;

  - high permeability before disintegration.

  These cement granules, because of their low structural stability and because of their high pH, are not

  acceptable as horticultural supports.

Claims (8)

  1. Absorbent granules consisting essentially of kieselguhr and of an agglomeration binder, characterized in that they comprise as agglomeration binder a urea-formaldehyde resin present in an amount of 20 to 50 parts (dry) per 100 parts of kieselguhr.   2. absorbent granules according to claim 1, characterized in that their water demand is greater than or equal to 8%, - their volume of air in the apparent volume of the support is greater than 20%, - their structural stability is greater than 80%, - their pH is between 3.5 to 8, their permeability is greater than 15 darcys,   preferably greater than 25 darcys.   3. Process for obtaining granules as described   in claims 1 or 2, characterized in that one   knead the wet kieselguhr with a urea-formaldehyde resin containing an acid catalyst, that it is shaped, for example by spinning, and that it is dried at a temperature between 95 and 180 C.   4. Method according to claim 3, characterized in that the source of kieselguhr is constituted by a precalcined kieselguhr whose permeability is between 0.030 darcy and 15 darcys.   5. Method according to claim 3, characterized in that the source of kieselguhr consists of cakes of   filtration of breweries or wine industries.   6. Application to hydroponics of aggregates according to claim 2.   7. Application to the cultivation of aggregates in pots according to the   claims 1 to 2, including further useful reserve water is greater than 20%.   8. Application of the aggregates according to claims 1 or 2   to the absorption of puddles of liquids, aqueous or oily   in domestic or industrial premises.