GB2101108A

GB2101108A - Granular substrate comprising kieselguhr

Info

Publication number: GB2101108A
Application number: GB08213939A
Authority: GB
Inventors: Werner Zyla
Original assignee: GEISS CHEM FAB
Current assignee: GEISS CHEM FAB
Priority date: 1981-05-25
Filing date: 1982-05-13
Publication date: 1983-01-12
Also published as: NL8201854A; GB2101108B; FR2506119A1; DK232182A; SE8203212L; IT1151770B; BE893298A; IT8221455A0; ES8304047A1; ES512532A0; ZA823608B; JPS57202229A; DE3120782A1

Abstract

The preparation of a granular substrate comprises making a mixture of a bonding agent and kieselguhr in a proportion of from 70 to 50 parts by weight of bonding agent to from 30 to 50 parts by weight of kieselguhr, adding 50 parts by weight of water, with reference to the weight of the said mixture, to create a wet mixture, preparing grains or pellets from the wet mixture, drying the grain or pellets and heat treating the grains or pellets at temperatures of 750 DEG C or more for from 0.3 to 2 hours. The mixture can have added to it organic substances and the bonding agent may be clay and/or water- glass. The pellets are especially suitable for use as a hydroponics substrate.

Description

SPECIFICATION Improvements in or relating to a process for the preparation of a granular substrate THE INVENTION relates to a process for the preparation of a granular substrate, particularly for use as a hydroponics base.

In hydroponics, the missing earth is often replaced by a substrate which can consist of natural substances, such as granite, chippings or pumice gravel or an artificial product prepared synthetically by the firing of expanded clay in the form of pellets. The aim of these substrates is to provide, in association with appropriate nutrient solutions, appropriate living conditions for the plant roots.

The preparation of expanded clay grain calls for the use of a special expandable clay which is fired after preparation in a rotary kiln. The resulting expanded-clay members have pores which take up the nutrient salt solution used for hydroponics and release it over a varying time to the plants. The pores vary in size in dependence upon the nature of the clay and upon the firing conditions.

According to this invention, there is provided a process for the preparation of a granular substrate comprising the steps of making a mixture of a bonding agent and kieselguhr in a proportion of from 70 to 50 parts by weight of bonding agent to from 30 to 50 parts by weight of kieselguhr, adding 50 parts by weight of water, with reference to the weight of the said mixture, to create a wet mixture, preparing grains or pellets from the wet mixture, drying the grain or pellets and heat treating the grains or pellets at temperatures of 750"C or more for from 0.3 to 2 hours.

The bonding agent is preferably a clay, but may also, or alternatively, comprise waterglass.

Thus, in the preferred embodiment, the pore structure is produced not by means of expanding agents in the clay but by the incorporation of kieselguhr, the clay basically functioning only as a bonding agent.

Since kieselguhr starts to sinter at the temperatures specified, firing can proceed at lower temperatures than are conventional for clay firing. If the clay is replaced by another bonding agent, such as waterglass, it has been possible to achieve a further reduction in the difficulties arising in the firing because the variations in quality, especially regarding salt content, associated with clays are reduced.

If the granular substance in accordance with the invention is prepared by taking 40 parts by weight of salt-free kieselguhr to 60 parts by weight of clay and mixing 50 parts by weight of water with the mixture, by reference to the weight of the dry mixture, it has been possible to produce in a pelleting or granulating device, such as a vibrating dish, grains which have long-term strength after being dried and heat-treated at temperatures as low as 750"C. The presence of the kieselguhr has been found to ensure that the resulting grains have the very fine micropores typical of kieselguhr, with a high uniform capillary action and a high water absorption capacity. A water absorption capacity of from 4 to 6 times that of grains of expanded clay of the same size was found.However, not only is a greater quantity of water or nutrient solution stored, but also, because of the consistent micropore structure, drying-out has been very satisfactory, with a slow release of liquid which provides a 6-fold or more increase in the nutrient solution storage time.

Also, the kieselguhr content has led to an increased and lasting mobility of the trace elements; plant growth has been increased and, in relatively poor growth conditions, there are fewer shortages of nutrients.

The grains of the substrates in accordance with the invention can be given further adsorption properties if a structure having finely divided carbon particles is produced by the application or introduction of organic substances before firing. A very advantageous way of introducing the organic substances has been to use those kieselguhr residues which, for example, arise as filter residue and which therefore have an organic content. Advantageously, therefore, kieselguhr residues, for example the yeast-loaded filter residues associated with the production of beverages, which would otherwise be a nuisance in sewage systems, are used.

Thus, this invention has been found to provide a process for the preparation of a granular substrate, more particularly for hydroponics, which, by virtue of a predetermined pore structure, makes it possible, using conventional non-expanding kinds of clay, to have a high storage capacity for the nutrient solution with slow release over relatively long periods of time and to improve growth conditions by increased mobility of the trace elements.

1. A process for the preparation of a granular substrate comprising the steps of making a mixture of bonding agent and kieselguhr in a proportion of from 70 to 50 parts by weight of bonding agent to from 30 to 50 parts by weight of kieselguhr, adding 50 parts by weight of water, with reference to the weight of the said mixture, to create a wet mixture, preparing grains or pellets from the wet mixture, drying the grain or pellets and heat treating the grains or pellets at temperatures of 750cm or more for from 0.3 to 2 hours.

2. A process according to claim 1, wherein the grains or pellets are prepared by making strands of the wet mixture and then breaking up the strands.

3. A process according to claim 1 or 2,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in or relating to a process for the preparation of a granular substrate THE INVENTION relates to a process for the preparation of a granular substrate, particularly for use as a hydroponics base. In hydroponics, the missing earth is often replaced by a substrate which can consist of natural substances, such as granite, chippings or pumice gravel or an artificial product prepared synthetically by the firing of expanded clay in the form of pellets. The aim of these substrates is to provide, in association with appropriate nutrient solutions, appropriate living conditions for the plant roots. The preparation of expanded clay grain calls for the use of a special expandable clay which is fired after preparation in a rotary kiln. The resulting expanded-clay members have pores which take up the nutrient salt solution used for hydroponics and release it over a varying time to the plants. The pores vary in size in dependence upon the nature of the clay and upon the firing conditions. According to this invention, there is provided a process for the preparation of a granular substrate comprising the steps of making a mixture of a bonding agent and kieselguhr in a proportion of from 70 to 50 parts by weight of bonding agent to from 30 to 50 parts by weight of kieselguhr, adding 50 parts by weight of water, with reference to the weight of the said mixture, to create a wet mixture, preparing grains or pellets from the wet mixture, drying the grain or pellets and heat treating the grains or pellets at temperatures of 750"C or more for from 0.3 to 2 hours. The bonding agent is preferably a clay, but may also, or alternatively, comprise waterglass. Thus, in the preferred embodiment, the pore structure is produced not by means of expanding agents in the clay but by the incorporation of kieselguhr, the clay basically functioning only as a bonding agent. Since kieselguhr starts to sinter at the temperatures specified, firing can proceed at lower temperatures than are conventional for clay firing. If the clay is replaced by another bonding agent, such as waterglass, it has been possible to achieve a further reduction in the difficulties arising in the firing because the variations in quality, especially regarding salt content, associated with clays are reduced. If the granular substance in accordance with the invention is prepared by taking 40 parts by weight of salt-free kieselguhr to 60 parts by weight of clay and mixing 50 parts by weight of water with the mixture, by reference to the weight of the dry mixture, it has been possible to produce in a pelleting or granulating device, such as a vibrating dish, grains which have long-term strength after being dried and heat-treated at temperatures as low as 750"C. The presence of the kieselguhr has been found to ensure that the resulting grains have the very fine micropores typical of kieselguhr, with a high uniform capillary action and a high water absorption capacity. A water absorption capacity of from 4 to 6 times that of grains of expanded clay of the same size was found.However, not only is a greater quantity of water or nutrient solution stored, but also, because of the consistent micropore structure, drying-out has been very satisfactory, with a slow release of liquid which provides a 6-fold or more increase in the nutrient solution storage time. Also, the kieselguhr content has led to an increased and lasting mobility of the trace elements; plant growth has been increased and, in relatively poor growth conditions, there are fewer shortages of nutrients. The grains of the substrates in accordance with the invention can be given further adsorption properties if a structure having finely divided carbon particles is produced by the application or introduction of organic substances before firing. A very advantageous way of introducing the organic substances has been to use those kieselguhr residues which, for example, arise as filter residue and which therefore have an organic content. Advantageously, therefore, kieselguhr residues, for example the yeast-loaded filter residues associated with the production of beverages, which would otherwise be a nuisance in sewage systems, are used. Thus, this invention has been found to provide a process for the preparation of a granular substrate, more particularly for hydroponics, which, by virtue of a predetermined pore structure, makes it possible, using conventional non-expanding kinds of clay, to have a high storage capacity for the nutrient solution with slow release over relatively long periods of time and to improve growth conditions by increased mobility of the trace elements. CLAIMS

3. A process according to claim 1 or 2, wherein the grains or pellets are prepared on pelleting dishes or similar pelleting facilities.

4. A process according to any one of claims 1 to 3, wherein at least one organic substance is present in the mixture.

5. A process according to claim 4 wherein the kieselguhr used is in the form of kieselguhr residues containing organic material.

6. A process according to any one of the preceding claims, wherein the bonding agent comprises a clay.

7. A process according to any one of the preceding claims wherein the bonding agent comprises waterglass.

8. A process for the preparation of a granular substrate substantially as described herein.

9. A granular substrate prepared by a process according to any one of the preceding claims.

10. A substrate according to claim 9 when used as a hydroponics base.

11. Any novel feature or combination of features disclosed herein.