JP7553064B2 - Porous granules and method for producing same - Google Patents

Description

The present invention relates to a porous granule and a method for producing the same.

Shirasu, a type of volcanic ejecta deposit mineral, is widely distributed in large quantities in southern Kyushu and can be obtained easily and at low cost. Various attempts have been made to effectively utilize this shirasu as a resource. For example, crystalline materials in shirasu, such as iron ore, feldspar, quartz, pyroxene, and amphibole, are expected to be used as fine aggregate for concrete, while glassy materials other than crystalline materials in shirasu, such as pumice, are expected to be used as lightweight aggregate and concrete admixture. However, volcanic ejecta deposit minerals generally contain a wide range of particle size distributions of the above-mentioned crystalline and glassy materials, making it difficult to separate them according to their intended use by simple sieving.

Therefore, there is a dry separation method for volcanic ejecta deposit minerals, which removes gravel with a particle size of more than 5 mm from the volcanic ejecta deposit minerals and supplies the remaining part to an air table type specific gravity difference sorting device that vibrates a perforated plate tilted at a predetermined angle from the horizontal direction and blows air from below toward the perforated plate, and separates the heavy specific gravity part, light specific gravity part, dust collection part, and perforated plate drop part (Patent Document 1). According to one embodiment of this dry separation method, the sorted heavy specific gravity part and perforated plate drop part can be used as fine aggregate for concrete, the light specific gravity part that passes through the sieve can be used as lightweight aggregate or crushed as a mineral admixture raw material, and the light specific gravity part that passes through the sieve and the dust collection part that has been classified to remove clay can be recovered as a perlite substitute, perlite raw material, shirasu balloon raw material, mineral admixture raw material, or mixed cement raw material.

In addition to the above-mentioned uses, attempts are also being made to use volcanic deposit minerals such as shirasu for new applications. As an example, slag removers that are poured onto the surface of molten cast iron, cast steel, or non-ferrous metals contained in electric furnaces or ladles during casting have traditionally been made by crushing obsidian or perlite to adjust the grain size, and proposals have also been made to use granular silica or high-silica glass fiber cloth with 80% or more silica (Patent Document 2). Therefore, instead of these conventional slag removers, a slag remover using shirasu powder is being considered.

However, a slag remover made of shirasu powder was not desirable from a work environment perspective because the shirasu powder would fly up when poured into the molten metal. Also, when pumice, which is a relatively large particle size contained in shirasu, was used as the slag remover, the powder was prevented from flying up when poured into the molten metal, but because it was granular, it could be caught in the molten metal and cause casting defects, and its poor slag removal and heat retention performance could have a negative impact on workability.

Patent No. 6458267 Japanese Utility Model Application Publication No. 5-44369

Finding new uses for volcanic deposit minerals such as shirasu and expanding their uses will enable more effective use of resources that have been little utilized up until now, which will ultimately contribute to the promotion of domestic industry, making them extremely valuable industrially. Furthermore, as volcanic deposit minerals such as shirasu are natural materials, there is a demand for processed products with low environmental impact that can be used for new purposes without adversely affecting the natural environment and that can be returned to nature after use.

The present invention aims to provide a porous granule that is made from volcanic ejecta deposit minerals, can be effectively used as a slag remover and for other new applications, and has a low environmental impact, and a method for producing the same.

The inventors of the present invention have conducted extensive research to find new uses for shirasu, and have found that porous granules containing shirasu and a biodegradable binder have a small environmental impact, do not fly up when added as a slag remover, and after addition, the granules quickly foam and dissolve on the molten metal, providing performance equivalent to that of conventional slag removers. Based on this knowledge, the inventors have conducted further research and development on porous granules containing shirasu, and have found that porous granules containing shirasu and a biodegradable binder have excellent performance in a variety of applications, such as compost treatment material, livestock feed additive, and fired foam raw material.
The present invention is based on the above findings.

The porous granules of the present invention contain a powder derived from volcanic deposit minerals, including volcanic glass, and a biodegradable binder.

The porous granules of the present invention preferably have a porosity of 45 to 55%. The powder derived from volcanic ejecta deposit minerals containing volcanic glass can be a powder obtained by removing coarse particles from shirasu, or a powder having a volcanic glass content of 80 mass% or more obtained by gravity separation from shirasu. The powder derived from volcanic ejecta deposit minerals containing volcanic glass preferably has a particle size of 0.8 mm or less.
In addition, the porous granules of the present invention, preferably having a particle size of 0.6 to 3 mm, can be used as a slag remover. Furthermore, the granules, preferably having a particle size of 1 to 20 mm, more preferably 3 to 15 mm, can be used as a compost treatment material. Furthermore, the granules, preferably having a particle size of 0.3 to 2 mm, can be used as a livestock feed additive. Furthermore, the granules, preferably having a particle size of 0.6 mm or less, can be used as a raw material for a fired foam.

The method for producing porous granules is characterized by kneading a powder derived from volcanic deposit minerals, including volcanic glass, with a biodegradable binder and water, passing the mixture through a porous surface to form small lumps, tumbling the mixture to granulate it, and then drying and hardening the mixture.

The present invention provides a porous granule that is made from volcanic deposit minerals and can be effectively used as a slag remover and for other new applications, and that has a low environmental impact, as well as a method for producing the same.

1 is a photograph substituting a drawing showing the particle shape of a porous granule of the present invention.

The following describes in more detail the embodiments of the porous granules and the manufacturing method thereof of the present invention.

[Porous granules]
Figure 1 shows the particle shape of the porous structure of the present invention. The porous granules contain a powder derived from volcanic ejecta deposit minerals containing volcanic glass and a biodegradable binder, and are porous particles in which the powder particles are bound by the binder. Depending on the granulation method, the density near the particle surface may be relatively higher than the density inside, but in any case, the pores of the porous granules are open pores, allowing gas and liquid to flow from the outside to the inside of the porous granules and from the inside to the outside.

The porous granules preferably have a porosity of 45 to 55%. With a porosity of 45 to 55%, the pores are open, allowing gas and liquid to flow from the outside to the inside of the porous granules and from the inside to the outside, and are highly effective in applications such as slag removal material, compost processing material, livestock feed additive, and fired foam raw material. If the porosity is 45% or less, pores that do not contribute to capillary action will begin to appear, causing poor flow. Also, if it is 55% or more, the granules will become brittle and may crumble when bagged. The porosity was measured in accordance with JIS R1634 after vacuum degassing using the Archimedes method.

The particle size of the porous granules varies depending on the application, as described below, but is generally between 0.3 mm and 20 mm. Here, particle size is synonymous with the sieve opening during sieving, and if the particles have an elliptical cross section, it refers to the short diameter.

The bulk density of the porous granules varies depending on the raw material and the application, but is approximately 1.05 to 1.25 g/ ^cm3 . By keeping the bulk density in the range of approximately 1.05 to 1.25 g/ ^cm3 , it is possible to obtain porous granules with a porosity of 45 to 55%. The bulk density was measured by the Archimedes method in accordance with JIS R1634 after vacuum degassing.

The crushing strength of the porous granules varies depending on the amount of biodegradable binder used and the application, but can be approximately 4 to 57 N. If the crushing strength is low, storage stability decreases, and if the crushing strength is high, manufacturing costs increase. The crushing strength was measured using a flat load in accordance with JIS Z8841.

Next, each component of the porous granules will be described.
(Powder derived from volcanic deposit minerals, including volcanic glass)
A representative example of the volcanic vitreous deposit mineral that is the raw material for the porous granules is shirasu. However, the present invention is not limited to shirasu. By using the volcanic vitreous deposit mineral as the raw material for the porous granules, the volcanic vitreous deposit mineral can be effectively utilized.

The powder derived from volcanic ejecta deposit minerals containing volcanic glass can be obtained by removing gravel with a particle size of more than 5 mm from the above-mentioned volcanic ejecta deposit minerals containing volcanic glass using a sieve or the like, and then removing the coarse particles. The porous granules of the present invention utilize the volcanic glass in the volcanic ejecta deposit minerals as an active ingredient, and while it is desirable to have a small amount of crystalline matter, the coarse particles contain a large amount of crystalline sand. In addition, the coarse particles make it difficult to form the granules and reduce the crushing strength of the porous granules. Increasing the proportion of biodegradable binder in the mixture increases the crushing strength of the porous granules, but this is disadvantageous in terms of granulation workability and cost.

The coarse particles to be removed are particles larger than the sieve opening of approximately 0.8 mm or less. The opening is preferably 0.2 to 0.8 mm, and more preferably 0.4 to 0.6 mm. The larger the opening, the more pumice and crystalline sand are contained in the powder that falls through the sieve, the lower the density of the porous granules and the lower the strength, and the higher the proportion of unnecessary crystalline matter in the powder. The smaller the opening, the lower the yield of the raw material, the higher the cost, and the higher the density of the porous granules and the lower the porosity. In one example, when Ito Shirasu is used as the raw material, the coarse particles were 25.4 mass% when the opening was 0.6 mm, and the powder yield was 74.6 mass%. In addition, the volcanic glass content in the powder after removing the coarse particles using a vibrating sieve with an opening of 0.6 mm was 70 mass% or more.

In addition to the vibrating sieve with the above-mentioned openings, a wind separator can also be used to remove coarse particles from volcanic ejecta deposit minerals. In any case, a powder with the coarse particles removed can be obtained from volcanic ejecta deposit minerals with a high yield using a simple device.

The particle size of the powder derived from volcanic ejecta deposit minerals containing volcanic glass, in which the coarse particles have been removed from the volcanic ejecta deposit minerals by using a sieve with suitable openings, is 0.8 mm or less, preferably 0.2 mm or less to 0.8 mm or less, and more preferably 0.4 mm or less to 0.6 mm or less. Here, the particle size is synonymous with the sieve opening during sizing as described above, and the particle size of the powder derived from volcanic ejecta deposit minerals containing volcanic glass, in which the coarse particles have been removed, is equal to or less than the sieve openings listed above. The powder from which the coarse particles have been removed is a natural material containing a high content of volcanic glass, the main component of which is silica, and is harmless when orally ingested by livestock.

The powder derived from volcanic ejecta deposit minerals containing volcanic glass may be a powder with a volcanic glass content of 80% by mass or more, which is gravity-separated from shirasu using the dry separation method for volcanic ejecta deposit minerals described in Patent Document 1 from the above-mentioned volcanic ejecta deposit minerals containing volcanic glass. In one specific example, gravel with a particle size of more than 5 mm is removed from the volcanic ejecta deposit minerals, and the remaining portion is fed to an air table-type gravity difference sorting device that vibrates a perforated plate tilted at a predetermined angle from the horizontal direction and blows air from below toward the perforated plate, and the powder is sorted into a heavy specific gravity portion, a light specific gravity portion, a dust collection portion, and a perforated plate drop portion. The light specific gravity portion is sieved through a sieve with a mesh size of 0.8 mm, and the dust collection portion is classified and removed with a cyclone classifier to remove fine clayey matter. The powders recovered respectively have a volcanic glass content of 80% by mass or more and a particle size of 0.8 mm or less. By using the dry separation method for volcanic deposit minerals described in Patent Document 1, it is possible to obtain a powder with a high content of volcanic glass.

(Biodegradable Binder)
The biodegradable binder binds the powder derived from volcanic deposit minerals, including glass. By using a biodegradable binder, it is possible to produce porous granules that are harmless during use and return to nature after use, resulting in a small environmental impact.

When the porous granules are used as a slag remover, the binder is biodegradable, so that the biodegradable binder is easily incinerated by the high temperature of the molten metal, causing the porous granules to foam and dissolve, effectively acting as a slag remover, and not remaining as inclusions in the molten metal.

When the porous granules are used as compost treatment material, the binder is biodegradable, so that the binder biodegrades after treatment and the porous granules return to the soil as volcanic deposit minerals, so no special post-treatment is required and the environmental burden is small.

When the porous granules are used as livestock feed additives, the binder is biodegradable, so they are harmless to livestock when ingested orally.

When the porous granules are used as a raw material for a fired foam, only CO ₂ and H ₂ O are generated by the thermal decomposition and firing of the binder, and no harmful substances are generated, making it possible to obtain porous granules with a small environmental impact.

As the biodegradable binder, various types developed as biodegradable plastics can be used. They are classified into three types according to the production method: microbial, natural, and chemically synthesized. Examples of microbial binders include polyester and bacterial cellulose, a polysaccharide, natural products include cellulose and starch, and chemically synthesized products include polyvinyl alcohol (hereinafter abbreviated as "PVA") and fatty acid polyesters. From the viewpoints of production volume and safety, PVA is preferred.
PVA is a type of synthetic polymer that is soluble in water and is used in a wide range of applications, such as adhesives and binders for the manufacture of ceramic products. PVA is extremely low in toxicity and is listed in the pharmaceutical additives standard and cosmetics standard. It is also listed as a government-designated soil improvement material in the Soil Fertility Improvement Law. Furthermore, PVA is a chemically synthesized biodegradable plastic that is eventually decomposed into water and carbon dioxide by microorganisms in nature. Therefore, by using PVA as a binder for porous granules, it is possible to obtain porous granules that have a small environmental impact.

PVA is synthesized by polymerizing vinyl acetate to make polyvinyl acetate, and then replacing the acetate groups with hydroxyl groups through a saponification reaction using an alkali. The properties of PVA are greatly affected by the degree of polymerization and the degree of saponification. The degree of polymerization is the number of vinyl acetate molecules connected in the PVA, and the degree of saponification is the percentage of hydroxyl groups relative to the total number of acetate groups and hydroxyl groups in the PVA. Depending on the degree of saponification, they are called fully saponified poval, intermediately saponified poval, and partially saponified poval, in descending order of degree of saponification. poval stands for PVA.

The degree of polymerization of PVA greatly affects the viscosity of the PVA aqueous solution and the strength of the applied PVA film. Specifically, as the degree of polymerization increases, the water solubility decreases, and the viscosity of the aqueous solution also increases, resulting in poor workability. Conversely, as the degree of polymerization decreases, the water solubility improves, but the bonding strength decreases. The degree of saponification of PVA also affects the solubility in water and the water resistance of the PVA film. Specifically, the partially saponified type is more water soluble than the fully saponified type, but the water resistance of the film decreases accordingly. The porous granules need a certain degree of strength to prevent collapse during transportation and processing, and also need a certain degree of water resistance to prevent collapse due to dissolution of the PVA on contact with water. Therefore, a PVA with an appropriate degree of polymerization and saponification is selected according to the use and purpose of the porous granules. One example is a fully saponified (98% or more) PVA with a degree of polymerization of 1300 to 2000, preferably 1600 to 1800, and more preferably 1500 to 1800.

Although PVA is water-soluble, it does not dissolve easily at room temperature, so when preparing an aqueous PVA solution in advance to facilitate kneading during the production of porous granules, it is preferable to heat it to about 90°C.

The proportion of PVA in the porous granules depends on the size of the powder derived from the volcanic deposit minerals, including the volcanic glass mentioned above, but is preferably about 0.8 to 2.0 mass% relative to the shirasu that has passed through a 0.6 mm sieve using a vibrating sieve, and more preferably about 0.9 to 1.1 mass%. If the proportion of PVA is too low, the strength of the granules will be weak, and if the proportion is high, the strength of the granules will increase, but the mixture will be sticky during production, making workability difficult and increasing material waste.

In addition to the components mentioned above, the porous granules may contain other components depending on the application, purpose, and function.

[Method of manufacturing porous granules]
Next, a method for producing the porous granules will be described.
The manufacturing method includes the steps of kneading a powder derived from volcanic ejecta deposit minerals, including volcanic glass, with a biodegradable binder, and water, passing the mixture through a porous surface to form small lumps, tumbling to granulate the mixture, and then heating and drying the mixture.

(Raw materials)
In one example, the powder derived from volcanic ejecta deposit minerals containing volcanic glass is obtained by removing gravel particles having a particle size of more than 5 mm from the raw material volcanic ejecta deposit minerals, such as shirasu, using a sieve, as described above, and then removing the remaining coarse particles using a sieve. Depending on the moisture content of the shirasu, the moisture content in the shirasu can be reduced to a predetermined amount or less using a heating device such as a rotary kiln, if necessary, before or after removing the gravel particles having a particle size of more than 5 mm. However, the moisture content can also be reduced by naturally drying the raw material in the sun without using a heating device.

The coarse particles can be removed by a vibrating sieve with the specified mesh size (0.8 mm or less, preferably 0.2 to 0.8 mm, more preferably 0.4 to 0.6 mm) as mentioned above. Instead of a vibrating sieve, a wind sorter can also be used to remove the coarse particles. The wind sorter may be a circulation type wind sorter, a blow-up type wind sorter, or a suction type wind sorter. Among these, a closed type or an outside air introduction type circulation type wind sorter is preferred because it requires less power than a blow-up type wind sorter or a suction type wind sorter.

In another example, powder derived from volcanic ejecta deposit minerals containing volcanic glass is obtained by using the dry separation method for volcanic ejecta deposit minerals described in Patent Document 1 as described above, removing gravel with a particle size of more than 5 mm from the raw volcanic ejecta deposit minerals, such as shirasu, using a sieve, then feeding the raw material volcanic ejecta deposit minerals, for example, shirasu, to an air table type specific gravity difference sorting device that vibrates a perforated plate tilted at a predetermined angle from the horizontal direction while blowing air from below toward the perforated plate, and sorting into a heavy specific gravity fraction, a light specific gravity fraction, a dust collection fraction, and a perforated plate drop fraction, and recovering a powder of the light specific gravity fraction sieved through a sieve with a mesh size of 0.8 mm and a powder of fine clay particles classified from the dust collection fraction using a cyclone classifier. The recovered powder has a volcanic glass content of 80% by mass or more and a particle size of 0.8 mm or less. Instead of removing gravel with a particle size of more than 5 mm using a sieve as a pretreatment, it can also be crushed using a machine that crushes the particles to a particle size of 5 mm or less. Before or after removing gravel with a particle size of more than 5 mm, the moisture content of the shirasu can be reduced to a specified amount or less using a heating device such as a rotary kiln, if necessary, depending on the moisture content of the shirasu. However, even if a heating device is not used, the moisture content can be reduced by drying the raw material in the sun.

The aforementioned PVA can be suitably used as the biodegradable binder.

When kneading powder derived from volcanic deposit minerals, including volcanic glass, with a biodegradable binder and water, since PVA, which is preferably used as a biodegradable binder, does not dissolve easily in water at room temperature, it is preferable to mix the PVA with water heated to about 90°C to prepare an aqueous PVA solution.

The mixing ratio of powder derived from volcanic deposit minerals including volcanic glass, biodegradable binder, and water is preferably about 0.8 to 2.0 mass% of PVA relative to the shirasu, more preferably about 0.9 to 1.1 mass%, and about 18 to 25 mass% of water relative to the shirasu, more preferably about 20 to 23 mass%, in the case of shirasu from which coarse particles have been removed using a 0.6 mm mesh sieve, PVA, and water. If the water ratio is too low, the kneaded material in small lumps that have been passed through the porous surface will not come together and will be difficult to granulate. If the water ratio is too high, the raw materials will adhere heavily to the container wall of the rolling granulator after passing through the porous surface, and the kneaded material in small lumps will adhere to each other, making it difficult to obtain granules of the desired size.

(Kneading)
The kneading can be carried out for a period of time sufficient for the raw materials to be kneaded using a known kneading device.

(Smaller nodules)
After kneading, the kneaded material is passed through a porous surface to form small lumps. According to the inventor's new findings, it has been difficult to efficiently produce granules of a predetermined particle size directly from the kneaded material, but by first forming the kneaded material into small lumps smaller in particle size than the granules of the predetermined particle size and granulating the small lumps of the kneaded material, the small lumps of the kneaded material serve as the cores of the granules, making it possible to efficiently produce granules of the predetermined particle size. The pore size of the porous surface is preferably smaller than the particle size of the granules to be produced. Depending on the particle size of the granules depending on the application of the granules, the pore size of the porous surface is approximately 1 to 8 mm. When producing granules for livestock feed additives, the pore size of the porous surface is preferably 1 to 2 mm, and when producing granules for slag removal material or compost treatment material, the pore size of the porous surface is preferably 2 to 8 mm.

Small lump-shaped kneaded material is efficiently obtained by applying the pressure required for passing the kneaded material through the holes in the porous surface while scraping the kneaded material off at the outlet side of the porous surface. If necessary, the obtained small lump-shaped kneaded material can be roughly crushed to a particle size smaller than that of the granules.

(Granulation)
Granulation can be performed using a known rolling granulator, for example, a granulator that supplies powder to an inclined circular container and rotates the container to granulate. By rolling granulation, the shape of the particles is adjusted and the shirasu density on the particle surface is higher than that of the inside. The size and particle size distribution of the granules can be adjusted by adjusting the rolling rotation speed and rotation time.

(Drying and hardening)
The granules obtained by the tumbling granulator are fed to a heating device to remove moisture and completely harden the biodegradable binder. Known devices such as dryers and rotary kilns are used as the heating device. The heating temperature may be 80 to 150°C to remove moisture from the granules and solidify the PVA. Specifically, drying and hardening can be performed at 105°C for ease of use. If the heating temperature is too high, there is a risk of thermal decomposition of the PVC. If the heating temperature is low, it takes a long time to dry and harden.

The granules can also be naturally dried before heating. The granules can be sieved before or after heating to adjust the particle size according to the application. Furthermore, the granules can be rubbed together in a dry barrel to remove fine powder adhering to the surface of the granules and to smooth the surface.

(Grain size adjustment)
The particle size of the granules can be adjusted, for example, by sieving granules larger than the particle size required for each application before drying. The sieved large granules are returned to the mixed raw material and reused. In addition, the required particle size of the porous granules for livestock feed additives is smaller than that of the granules for slag removal materials and compost treatment materials, so that after drying, they can be sieved into livestock feed additives, slag removal materials, and compost treatment materials. Furthermore, those with a particle size of 0.3 mm or less are not sufficiently granulated or have become fragments or powder after granulation, and are not required for livestock feed additives, slag removal materials, or compost treatment materials, so they can be sieved using a sieve with an opening of 0.3 mm. For slag removal materials, sieved to a particle size of 0.6 mm or less, for compost processing materials, sieved to a particle size of 1.0 mm or less and then sieved to a particle size of 0.6 mm or less, and for livestock feed additives, sieved to a particle size of 0.3 mm or less can be used as raw materials for fired foams such as shirasu balloons. By adjusting the particle size in this way, the produced granules can be used without waste.

[Application]
Next, applications of the porous granules will be described.
(Slag removal material)
Conventionally, silica-based powder has been used as a slag remover. However, the powder is scattered on the high-temperature molten metal, which causes the powder to fly around, which is undesirable for the work environment. To address this issue, fine pumice is used to prevent the powder from flying around, but fine pumice is difficult to dissolve and can affect the quality and workability.

Here, by using the porous granules of the present invention as a slag removal material, no dust was generated, there were no problems with solubility, and the slag removal performance was good. The reason for this is that when the porous granules come into contact with the molten metal, the biodegradable binder (organic matter) burns, causing the granules to quickly disintegrate and disperse, while the shirasu powder foams and reacts with the slag, making the slag highly viscous, which is thought to contribute to slag removal. In addition, slag removal materials need to have a certain degree of heat resistance, and the porous granules of the present invention preferably use shirasu with a size of 0.6 mm or less as the raw material, and the fact that they are porous is thought to contribute to their heat resistance.

When used as a slag remover, the particle size of the porous granules is preferably about 0.6 mm to 3 mm so that they do not fly around as dust.

(Compost treated material)
The use of bio-bacteria to promote fermentation has been considered as a method to deodorize livestock manure through fermentation. Conventionally, bio-bacteria have been planted on porous bodies such as pumice, which have been spread on barn floors or used for treatment at manure collection sites. However, while there is a need to increase the proliferation of bio-bacteria to enhance fermentation, there are limitations to the conventional porous bodies such as pumice. In addition, the treated manure is used as compost for pastures and fields, but pumice does not weather easily and ends up becoming soil mixed with pumice.

Here, when the porous granules of the present invention were used as a compost treatment material and as a carrier for bio-bacteria, the bio-bacteria proliferated, and the same fermentation was achieved with one-third the amount used in the past. The reason for this is not clear, but it is thought that the reason for the active proliferation is that the pores of the porous granules of the present invention are through-holes, which make it easy to take in water-soluble nutrients from the outside by capillary action, providing many spaces for the bio-bacteria to proliferate, and that the organic binder serves as nutrition for the bio-bacteria. Furthermore, when the treated manure is used as compost, the porous granules of the present invention use a water-soluble and biodegradable binder, so it ultimately returns to the soil as shirasu powder.

When used as a compost treatment material, the particle size of the porous granules is preferably about 1 to 20 mm, more preferably about 3 to 15 mm, because they need to be spread over a wide area on the compost and can reach far, and from the viewpoint of workability, such as not creating dust when spread.

(Livestock feed additives)
By ingesting biobacteria along with feed, it is possible to promote fermentation in the intestines, making feces and urine odorless, and also increasing resistance to pathogenic bacteria.

When the porous granules of the present invention are used as a carrier for bio bacteria as a livestock feed additive, the porous granules have through holes, providing many spaces for the proliferation of bio bacteria, and because an organic binder is used, the granules are easy for the proliferation of bio bacteria, so they can be orally ingested by livestock with a small amount added. In addition, the porous granules of the present invention are made of ingredients that are harmless to livestock when ingested orally.

When used as a livestock feed additive, the particle size of the porous granules is preferably about 0.3 mm to 2 mm. More preferably, it is 1 mm or less. However, since pig intestines are similar to those of humans, it is also possible to use porous granules with a size of 0.6 mm or less.

(Baked foam raw material)
Shirasu is foamed by instantaneously exposing it to a high temperature of about 1000°C to obtain shirasu balloons. Shirasu balloons are spherical foams that are lightweight and have low thermal conductivity, and are non-flammable and have a high melting point due to their composition of aluminosilicate, and are non-toxic and inert, and are used as concrete building materials, etc. Shirasu balloons are preferably large in size with a high water flotation rate. In addition, when producing shirasu balloons, there are products in which the obtained shirasu balloons are floated on water and hollow shirasu balloons are selected and collected. However, depending on the type of shirasu and the firing conditions, the balloons may burst, making it difficult to increase the water flotation rate, in other words, the size and yield of the shirasu balloons.

Here, by using the porous granules of the present invention as a raw material for a sintered foam, when producing shirasu balloons, the granules in which the shirasu particles are bound with a biodegradable binder are sintered to form a foam in which the expanded particles are adhered to each other. As a result, even if the balloons of the shirasu particles are partially broken, they can float on water because the balloons are aggregated together. Therefore, shirasu balloon-aggregated expanded particles with a high water floatation rate and high yield can be obtained. It is possible to obtain water-floating expanded particles with large particle sizes that cannot be obtained with conventional shirasu balloons. The obtained shirasu balloons can be used as a concrete building material, etc., like conventional shirasu balloons, and can also be used as a carrier for bio-bacteria as a livestock feed additive.
In the application as a raw material for a fired foam, the particle size of the porous granules is preferably 0.6 mm or less.

(Other uses)
The porous granules of the present invention can be impregnated with pesticides for pest control, and used as a sustained-release carrier for the drug to gradually dissolve and function for a long period of time. By using the porous granules of the present invention as a sustained-release carrier in this way, the number of times the pesticide is sprayed can be reduced, which contributes to reducing labor and the amount of pesticide used. In addition, even if the porous granules are sprayed on farmland, the binder in the sustained-release carrier is biodegraded and returned to the soil.

In addition, instead of using pesticides to control pests, the porous granules of the present invention can be impregnated with growth supplements, allowing the supplements to gradually dissolve, resulting in a long-term administration effect.

(Production of Porous Granules in Examples)
The shirasu was sieved to remove gravel of 5 mm or more, and then the moisture content was reduced to 4% or less in a rotary kiln, and the coarse particles were removed using a vibrating sieve with a mesh size of 0.6 mm. PVA was dissolved in 1% by mass of the shirasu powder after the removal of the coarse particles in water equivalent to 22% by mass of the shirasu powder at a water temperature of 90°C to obtain an aqueous PVA solution, and the aqueous PVA solution and the shirasu powder after the removal of the coarse particles were kneaded in a mixer. The resulting kneaded product was passed through a porous surface with a hole diameter of 5 mm to form small lumps. The resulting small lump-shaped kneaded product was fed to a rolling granulator and granulated. The resulting granulated product was passed through a sieve with a mesh size of 5.6 mm to remove large granules, then dried indoors, and then heated in a dryer at 105°C overnight to dry and harden. The dried and hardened porous granules were sieved through a sieve with a mesh size of 4.75 mm and a sieve with a mesh size of 4.00 mm to obtain porous granules of the present invention having particle sizes of 4.00 to 4.75 mm.

(Characteristics evaluation)
This manufacturing process was carried out in two lots, and seven granule samples were taken from each lot, and the porosity was measured by Archimedes' method to find that it was 52%. The bulk density was 1.13 g/ ^cm3 .

Furthermore, when the crushing strength was examined, the average for the first lot was 26N, and for the second lot it was 12N. The shapes of the sample particles varied, and the crushing strength varied from 4 to 38N.

The advantage of the porous granules being lower in crushing strength than pumice is that when used as a compost processing material and spread on the floor of a livestock house, they are easily crushed by livestock when stepped on, without causing damage to the livestock's hooves. Also, even if they remain as granules in compost made from fermented livestock manure, they are easily crushed and do not cause damage to workers or agricultural machinery.

(Use as a slag remover)
Next, in the production of the porous granules of the above-mentioned examples, the porous granules after drying and hardening were passed through a sieve with a mesh size of 3 mm and a sieve with a mesh size of 0.6 mm. The same process was repeated to obtain the porous granules of the examples having a particle size of 0.6 to 3 mm.
When this porous granule was added to a ladle during the casting of pig iron, it quickly foamed and melted on the surface of the molten pig iron, turning the slag into a high viscosity material and making it easy to remove the slag.

(Use as compost processing material)
Next, in the production of the porous granules of the above-mentioned examples, the porous granules after drying and hardening were passed through a sieve with a mesh size of 20 mm and a sieve with a mesh size of 1 mm, and the same steps were followed to obtain the porous granules of the examples having particle sizes of 1 to 20 mm.
When these porous granules were loaded with bio-bacteria such as Bacillus bacteria, which are approved as feed additives by the Ministry of Agriculture, Forestry and Fisheries, and spread on the floor of livestock barns, they were able to deodorize the manure and turn it into compost. The use of porous granules stimulated the growth of the bio-bacteria, and one-third of the amount was needed compared to using pumice. This is thought to be because, although pumice is porous, it is not granulated, so it has many closed pores and there is little space for the bio-bacteria to fix, whereas porous granules have interconnected pores, so they can easily take in water-soluble nutrients from the outside through capillary action, leaving a large fixation space, and because they contain an organic binder.

After deodorizing and fermenting the compost, the material was used as organic fertilizer for pastures and fields. In this case, the pumice did not crumble and remained as stone for a long time, whereas the binder in the porous granules was decomposed by bacteria in the soil and returned to the soil.

(Use as a livestock feed additive)
In the production of the porous granules for the above-mentioned examples, the pore size of the porous surface was set to 2 mm, and the porous granules after drying and hardening were passed through a sieve with a mesh size of 2.0 mm and a sieve with a mesh size of 0.3 mm. The same process was followed to obtain porous granules for the examples having a particle size of 0.3 to 2.0 mm.

These porous granules were loaded with biobacteria such as Bacillus bacteria, a probiotic agent approved as a feed additive by the Ministry of Agriculture, Forestry and Fisheries, and were then added to chicken feed. Compared to the conventional method using pumice as a carrier, the feed effect of the biobacteria (the amount of feed given until the chickens grow to a certain size) was the same. Furthermore, compared to the feed effect of not feeding the biobacteria being 10, the feed effect of the porous granules loaded with the biobacteria was 8, meaning that feed could be reduced. This is thought to be due to the increased nutrient absorption caused by the breakdown of food by the biobacteria and the activation of intestinal bacteria.

The difference with using pumice is that pumice is a mixture of volcanic glass and hard crystalline particles, so it remains as a solid (stone) in the chicken's litter, whereas porous granules turn into sand and are excreted along with the digestive matter. Therefore, when porous granules are used, the intestines, including the litter, are clean, and the knife does not need to be used when butchering the chicken, improving workability.

(Use as a raw material for fired foam)
In the production of the porous granules for the above-mentioned examples, the dried and hardened porous granules were sieved, and the remaining porous granules were sieved through a sieve with an opening of 0.6 mm. The same process was repeated to obtain porous granules having a particle size of 0.6 mm or less.

Next, the porous granules of the above-mentioned embodiment were heated to 1050°C in an internal combustion medium fluidized bed furnace to foam, and then floated on water to select and recover hollow cohesive foams. As a result, cohesive foams were obtained with a high water floatation rate and high yield.

The porous granules of the present invention open up new uses for shirasu, such as as a slag remover, compost processing material, livestock feed additive, raw material for fired foam, pesticide carrier, and soil conditioner, and the processing of shirasu, which is in large reserves, can promote the development of industry.

Claims (10)

The porous granules contain a powder derived from volcanic ejecta deposit minerals including volcanic glass and a biodegradable binder, and have a porosity of 45 to 55% . ^2. The porous granule according to claim 1, having a bulk density of 1.05 to 1.25 g/cm3 . The porous granule according to claim 1 or 2, wherein the powder derived from volcanic ejecta deposit minerals containing volcanic glass is a powder obtained by removing coarse particles from shirasu. The porous granule according to any one of claims 1 to 3, wherein the powder derived from volcanic ejecta deposit minerals containing volcanic glass is a powder having a volcanic glass content of 80% by mass or more, which is gravity-separated from shirasu. The porous granule according to any one of claims 1 to 4, wherein the powder derived from volcanic ejecta deposit minerals containing volcanic glass has a particle size of 0.8 mm or less. The porous granules according to any one of claims 1 to 5, which have a particle size of 0.6 to 3 mm and are used as a slag remover. The porous granules according to any one of claims 1 to 5, which have a particle size of 1 to 20 mm and are used as a compost treatment material. The porous granules according to any one of claims 1 to 5, which have a particle size of 0.3 to 2 mm and are used as a livestock feed additive. The porous granules according to any one of claims 1 to 5, which have a particle size of 0.6 mm or less and are used as a raw material for fired foam. A method for producing porous granules, comprising kneading a powder derived from volcanic ejecta deposit minerals including volcanic glass with a biodegradable binder and water, passing the mixture through a porous surface to form small lumps, tumbling the mixture to granulate the mixture, and then drying and hardening the mixture to obtain porous granules having a porosity of 45 to 55% .