GB2330138A

GB2330138A - Aggregates from fly ash

Info

Publication number: GB2330138A
Application number: GB9821749A
Authority: GB
Inventors: Koji Kawamoto; Shingo Sutoh
Original assignee: Sumitomo Metal Mining Co Ltd
Current assignee: Sumitomo Metal Mining Co Ltd
Priority date: 1997-10-07
Filing date: 1998-10-07
Publication date: 1999-04-14
Also published as: CN1218014A; GB9821749D0

Abstract

Fly ash is mixed with a melting point lowering agent, a caking agent comprising bentonite, and with either a foaming agent comprising iron oxide, silicon carbide and carbonaceous material, or a material for adjusting the degree of reduction comprising carbonaceous material. The mixture is crushed so that the average particle size is up to 15 microns which is pelletized after which the pellets are baked within a temperature range of 1000‹C # 1250‹C. The melting point lowering agent is made by mixing an alkali metal compound with Fly ash so that the total amount of Na 2 O and K 2 O respectively or both is within the range of 30 to 50 wt% in the mixture, melting the mixture at 1000‹ to 1200‹C to form a glassy material and cooling and crushing the glassy material.

Description

Title of the Invention Artificial Lightweight Aggregate and Manufacturing Metho4.Therefdre Field of the Invention The present invention relates to a method of effectively using fly ash produced from coal fired boilers of coal fired power plants or the like, by recycling as an artificial lightweight aggregate for buildings, and d for englneering public works, and to an artificial lightweight aggregate made thereby.

Background of the Invention The effective use of fly ash produced from coal fired boilers of coal fired power plants or the like is a big problem.

As an effective use of fly ash, the use as an artificial lightweight aggregate which is in great demand, is suitable from the point of bulk disposal.

However, the use of fly ash produced from coal fired boilers of coal fired power plants as an aggregate, where part is aggregated by a sinter grate method, is still very limited.

The reason for this is that with coal fired boilers of coal fired power plants or the like, in order to reduce adhesion of the ash to the boiler pipes or the boiler wall, a coal which produces a high melting point ash is selected and used. That is to say, the fly ash generated from coal fired boilers of coal fired power plants or the like is in general of a high melting point, and in order to make this into a lightweight aggregate this must be mixed with a large amount of low melting point clay or shale and baked. Securing this clay and shale in large amounts is difficult, and the mining, transportation, pre-processing, and mixing ofthis clay and shale, require a large expenditure, so that the manufacturing costs for the artificial lightweight aggregate are increased. Furthermore, since the utilization ratio of fly ash per unit product is low, then from the point of effective utilization of fly ash such use is not desirable.

Moreover, the absolute dry specific gravity of the artificial lightweight aggregate using fly ash is approximately 1.2 - 1.4, and techniques for manufacturing a light artificial lightweight aggregate of an absolute dry specific gravity of 1.0 - 0.5 do not exist. Hence use is limited.

Summary of the Invention An object of the present invention is to provide a technique for producing at low cost a high specific strength high quality artificial lightweight aggregate at a comparatively low temperature, by adding a low cost additive which is easy to procure.

Furthermore, it is an object to increase the utilization ratio of fly ash per unit product and thus increase the utilization efficiency of fly ash, by reducing the amount of additive used.

Moreover, it is an object to increase the lightness and thus provide an extremely light artificial lightweight aggregate, to thereby extend its use.

Description ofthe Preferred Embodiments The artificial lightweight aggregate of the present invention is manufactured by mixing fly ash produced from a coal fired boiler with a melting point lowering agent, a caking agent, and a foaming agent to obtain a mixture, crushing the mixture so that the average particle size is up to 15 microns to obtain a pulverized product, adding water to the pulverized product and pelletizing to obtain pellets, and then baking the pellets in a rotary kiln within a temperature range of 10000C 12500C to give an absolute dry specific gravity of 1.0 - 0.5. Furthennore, the method of manufacturing artificial lightweight aggregate according to the present invention involves; ining fly ash produced from a coal fired boiler with a melting point lowering agent, a caking agent, and a foaming agent or a material for adjusting the degree of reduction, to obtain a mixture, crushing the mixture so that the average particle size is up to 15 microns to obtain a pulverized product, adding water to the pulverized product, pelletizing to obtain pellets, and then baking the pellets in a rotary kiln within a temperature range of 1000"C - 12500C. Here, drying may be carried out as required prior to baking.

The foaming agent comprises iron oxide in an amount such that the amount of Fe203 in the fly ash is within the range of 1 wt. % - 10 wt. %, carbonaceous material in an amount within the range of 0.2 wt. % - 10 wt. % ofthe fly ash, and silicon carbide in an amount within the range of 0 wt % ~ 1 wt. % of the fly ash. In particular, in the case of baking to give an absolute dry specific gravity of 1.0 - 0.5, then preferably iron oxide in an amount such that the amount of Fe2O3 in the fly ash is within the range of 3 wt. % - 10 wt. %, silicon carbide in an amount of 0.1 wt % ~ 1 wt. % of the fly ash, and carbonaceous material in an amount of 0.2 ~ 10 wt. % of the fly ash is added. The carbonaceous material is typically coal or coke.

The melting point lowering agent is made by mixing an alkali metal compound with fly ash so that the total amount of Wa.,O and K20 respectively or both is within the range of 30 wt % - 50 wt. %, heating and melting within a temperature range of 10000C - 12000C to form a glass7 and then cooling and crushing.

The melting point lowering agent is then preferably added to the fly ash so that the total weight of the Na2O and the RO is within the range of 2 wt. % - 6 wt.

% in the baked product. Here the alkali metal compound is preferably sodium carbonate or potassium carbonate.

The reduction degree adjustment material is for adjusting the degree of reduction inside the aggregate, and is preferably made from carbonaceous material in an amount within the range of0.2 wt. % ~ 10 wt. % of the fly ash. The carbonaceous material is typically coal or coke.

The present inventors added to fly ash as a melting point lowering agent, a product made by mixing an alkali metal compound with fly ash so that the total amount of Ai a20 and KO respectively or both was 30 wt. % ~ 50 wt. %, heating and melting at 10000C ~ 1200cC to form a glass, and then cooling and crushing, so that the total amount of the converted amount of Na2O and K20 was 2 wt. % ~ 6 wt. % of the baked product. As a result the melting point ofthe fly ash was lowered to a temperature of 1000 C ~ 12000C at which industrial wise, baking is relatively easy.

Then, by adding iron oxide, silicon carbide, and carbonaceous material such as coal or coke with an average particle size of 10 microns or less as a foaming agent, a first artificial lightweight aggregate with a high specific strength and low water absorption at an absolute dry specific gravity of about 0.5 - 1.5 was baked.

Alternatively, by adding carbonaceous material such as coal or coke with an average particle size up to 10 microns as a reduction degree adjustment material in an amount of 0.2 - 10 wt. % of the fly ash, a second artificial lightweight aggregate with a high specific strength and low water absorption at an absolute dry specific gravity of about 1.5 ~ 2.0 was baked.

The iron oxide was added to the fly ash so that the amount of Fe203 in the fly ash was 1 wt. ~ 10 wt. %. In particular, in the case where the absolute dry specific gravity was 0.5 ~ 1.0, the FeO3 was made at least 3 wt. % and silicon carbide was added to the fly ash to give 0.1 wt. ~ 1 wt. %. Furthermore, carbonaceous material in an amount of 0.2 wt. % ~ 10 wt. % of the fly ash was used. Here the carbonaceous material also fUnctions to adjust the reduction condition within the granulated pellet at the time of baking.

With a specific working example, the melting point lowering agent is produced by mixing sodium carbonate, potassium carbonate and carbonaceous material and then heating and melting at 1000 C ~ 1200 C to form a glass where the total weight of the NaO and the KO respectively or both was 30 wt. % ~ 50 wt. % and then cooling and crushing.

According to a method of manufacturing artificial lightweight aggregate of the present invention, at first, with respect to 1 iso parts by weight of fly ash being the raw material, bentonite being the caking material, is added to give 0.2 - 5 parts by weight in all external proportion, and the beforementioned melting point lowering agent is added so that the total of the converted amount of NO and K20 is 2 wt. % - 6 wt. % in the baked product.

Furthermore, in the case where the first artificial lightweight aggregate is obtained, the foaming agent is added in the beforementioned proportion.

Alternatively, in the case where the second artificial lightweight aggregate is obtained, 0.2 wt. % - 10 wt. % of carbonaceous material such as coal or coke is added as the material for adjusting the degree of reduction inside the aggregate.

The mixture obtained in this way is then crushed to give an average particle size of up to 15 microns. The pellets are then obtained by pelletizing the pulverized product with water added. Subsequently, and after drying as necessary, the pellets are baked at 10000C - 12500C.

The method of pelletizing used in the present invention, may be one which enables to give the pellets a predetermined diameter, being simply achieved using a pan pelletizer or an extrusion pelletizing machine. Moreover, for the baking, if continuous operation and uniformity of quality are considered, then use of a rotary kiln is preferable.

The melting point lowering agent is discussed hereunder.

With fly ash, it is commonly the case where the temperature at which a liquid phase is produced to Initiate sintering is extremely high at 1400CC 1500 C. Baking tile artificial lightweight aggregate at 14000C ~ 1 500 C is not practical due to difficulties with fire resistance of the baking equipment, energy costs, and the selection of the foaming agent. Heretofore, in the case of baking such a raw material with a high degres of fire resistance, in general there is a method where natural minerals such as clay or shale with a low degree of fire resistance and including a large amount of alkaline metal, or waste glass such as bottle glass etc. are added in large amounts as a melting point lowering agent. The various investigated results of the present inventors of the effect of adding clays, and shales, verified that in the constituents forming these clays and shales, the liquid phase forming temperature was remarkably low with alkali metals in a small amounts.

However, if an industrial chemical having a high included amount of alkali metals was added to the fly ash, only the surface of the pellet of granulated fly ash was melted, and the interior could not be baked. This is because the sodium and potassium salts being the industrial products of the alkali metals which are effective in lowering the melting point are mostly those which are water soluble, and in the step of drying the granulated pellet, the alkali metals are concentrated on the pellet surface so that at the time of baking, only the pellet surface is melted and the interior cannot be baked.

From the results of an investigation into a method of preventing concentration of the industrial alkali metals compounds on the pellet surface, it was found that when a compound of an alkali metal such as sodium carbonate or potassium carbonate, was mixed with fly ash and heated and melted at 1000 C - 12000C to form a glass state so that the total amount of Na,O and LO respectively or both was 30 wt. % - 50 wt. %, and then cooled and crushed, and added to the fly ash so that the total amount of Na20, K2O was 2 wt. O/O ~ 6 wt. % of the baked product, and Ihen baked at 1 000C - 1250 & C, a high strength artificial lightweight aggregate foamed uniformly from the center was obtained.

With the present invention, the alkali metal compound such as sodium carbonate, or potassium carbonate used in the melting point lowering agent, is mass produced at low cost as an industrial chemical, and hence the present invention is advantageous cost wise. Furthermore, when the carbonate or the hydrogen carbonate of the alkali metal group is heated, har gas is not produced, and hence this is desirable. By adding this alkali metal compound to the fly ash, a glass which is difficult to dissolve in water is produced from the alkali metal group and silica.

Since the fly ash is provided as silica source for producing the glass, then the fly ash can also be used in the melting point lowering agent. Hence the disposal rate of the fly ash can be improved, and new resources are not necessary, and hence this is desirable.

With the melting point lowering agent, with the total amount of NaaO or K2O respectively or both 30 wt. % or less, the melting point temperature for glassification exceeds 12000C and hence the equipment and maintenance cost becomes high, and energy cost is also high. Furthermore, since the included percentage of alkali also drops, the amount of melting point lowering agent used becomes great, and hence this is undesirable. Moreover, if the total amount of nazi or K2O respectively or both exceeds 50 wt. %, then the water solubility of the formed glass increases so that only the surface of the granulated pellet is easily softened, and the interior of the pellet cannot be baked. Hence this is undesirable With the artificial lightweight aggregate of the present invention, the reason for adding a melting point lowering agent so that the total weight ofthe conversion amount of neo and K2O becomes 2 wt. % ~ 6 wt % in the baked product, is because the chemical composition of the fly ash differs depending on the type of carbonaceous material, and comprises SiO2: 50 wt. % ~ 55 wt %, AO,: 25 wt. % 30 wt. %, Na2O: 0.2 wt. % ~ 2 wt %, K2O: 0.2 wt. % ~ 1 wt. %, arld by adding the alkali metal group in the beforementioned amount, the melting point is greatly reduced, and the melting temperatwo range extended.

If the total amount of ?4a,0 and KO in the artificial lightweight aggregate falls below 2 wt %, the baking temperature becomes 12500C or greater, so this is not practical. Furthermore, if increased above 6 wt %, the reduction effect on the melting point is minimal, and manufacturing costs are increased due to the increase in additives. Hence this is undesirable.

Next is a description of the foaming agent for obtaining the first artificial lightweight aggregate When water is added to the fly ash for pelletization, then depending on the pelletization method also, the bulk specific gravity ofthe dried pellet becomes 1.5 1.9 approximately. When this pellet is baked at 1000 C - 125O0C, the absolute dry specific gravity becomes approximately 1.5 - 2.0. Consequently, in order to make the absolute dry specific gravity ofthe artificial lightweight aggregate 0.5 - 1.5 approximately, a foaming agent is added to the fly ash.

For the iron oxide of the foaming agent, a hematite with a high degree of oxidation is desirable. The reason for having the particle size ofthe iron oxide 10 microns or less is to promote the deoxidization reaction due to the carbonaceous material and silicon carbide during baking. Furthermore, the reason for making the amount of Fe O3 in the artificial aggregate 1 wt. % or more during baking is because if less than this, the effect as a foaming agent is minimal, and the absolute dry specific gravity of the artificial aggregate cannot be reduced to 1.0 - 1.5 approximately. Furthermore, in order to make the absolute dry specific gravity 0.5 1.0, the Foe203 amount must be made 3 wt. % or greater so that the silicon carbide is adequately reacted. Due to the foaming action from the carbon produced by dissociation of the silicon carbide, the lightening is considerable. On the other hand, even if the amount of Foe203 in the baked aggregate exceeds 10 wt %, the lightening effect due to the foaming does not increase. Here the specific gravity of the iron oxide is very much greater than that of the fly ash, and if foaming is not promoted, the absolute dry specific gravity of the artificial lightweight aggregate is increased.

When liquid phase is produced in large amounts by heating granulated pellets, the silicon carbide reacts with iron oxide (FeaO;) with good efficiency to produce CO and CO, gas. This CO and CO. gas is captured and promotes the swelling of the bubbles in the pellet. With the amount of silicon carbide less than 0.1 wt%, then the lightening effect for an absolute dry specific gravity is 0.5 - 1.0 is not sufficient, and an absolute dry specific gravity of 1.0 or less cannot be attained. On the other hand, even if this exceeds 10 wt%, the lightening effect is not increased.

With the carbonaceous material, the effect of adjusting the degree of reduction inside the pellet during sintering as discussed later is great, and also this reacts with the iron oxide to achieve a foaming action.

Next is a description of a material for adjusting the degree of reduction in order to obtain a second artificial lightweight aggregate.

The reason for maintaining the interior ofthe granulated pellet in a reducing atmosphere due to the added carbonaceous material is to reduce the hematite, being the iron oxide contained in the fly ash, to wustite or magnetite to thus lower the melting point of the matrix, to oxidize the pellet surface, and to increase the fire resistance to mitigate the elision ofthe pellet at the time of heating, to increase the baking temperature, and to promote the intering of the interior to increase the aggregate strength and reduce water absorption.

With the added proportion of the carbonaceous material of 0.2 wt % or less, conditions for reducing the interior ofthe pellet cannot be maintained so that the effect of lowering the melting point inside the pellet cannot be obtained.

Furthermore, ifthe added proportion ofthe carbonaceous material exceeds 10 wt%, then unburned carbon will remain in the pellet interior, and since the reactivity of this residual carbon with silicates is poor, there is the possibility of a reduction in the strength ofthe artificial lightweight aggregate and an increase in water absorption.

Hence this is undesirable.

When water is added to the fly ash for pelletization, then depending on the pelletization method also, the bulk specific gravity of the dried pellet becomes 1.5 1.9 approximately. If the pellet is baked at 1000 C - 1250C together with a material for adjusting the degree of reduction, then a high strength aggregate of an absolute dry specific gravity about 1.5 - 2.0 is obtained with some baking shrinkage.

Examples The present invention will now be described using the following working examples.

Working examples 1 - 65 are for the first artificial lightweight aggregate, while working examples 66 - 94 are for the second artificial lightweight aggregate.

The chemical compositions ofthe fly ash, bentonite, hematite, silicon carbide, and coke used in the experiments are shown in Table 1. Furthermore, the melting point lowering agent was made by mixing the fly ash shown in Table 1 with a reagent first grade product of sodium carbonate and potassium carbonate as the alkali metal raw material, heating in an electric firmace under the conditions shown in Table 2, at a predeterimned temperature for 10 minutes, removing from the flirnace and cooling, and then pulverizing.

Oh orlsing Examples 1 - 31; foaming with hematite and carbonaceous material] The beforementioned raw materials were collected and weighdd in the composition shown in Table 3, and then pulverized and mixed in a ball mill. The particle size distribution of the pulverized raw material was measured by a laser diffraction type particle size distribution meter, and is shown in Table 3.

With the addition of water to the obtained pulverized raw matenal, this was pelletized to a spherical shape of approximately 5 ~ l5mm diameter in a pan pelletizer, and then dried, after which the pellets were fed to a rotary kiln crick lining internal diameter SO()mm and length 4800mm) and baked. The chemical composition of the alkali metal in the post baked artificial lightweight aggregate is shown in Table 3.

The absolute dry specific gravity and the water absorption ofthe baked artificial lightweight aggregate was measured based on JIS A 1110, and the crushing strength was measured for an artificial lightweight aggregate of approximately 1 Omm m diameter. The obtained results and baking temperatures are shown in Table 4. The absolute dry specific gravity was approximately 1.0 - 1.5, and hence an artificial lightweight aggregate of almost the same 1.2 - 1.4 absolute dry specific gravity of commercial artificial lightweight aggregate was obtained. Furthermore, the crushing strength at an absolute dry specific gravity of 1.2 - 1.3 was 11?\i ~ 15N compared to 5N - 6N for the commercial artificial lightweight aggregate, and even with the absolute dry specific gravity close to 1.0, was still 7N - 8N, giving an extremely high specific strength artificial lightweight aggregate. Twenty four hour water absorption was also shown low at approximately 5%.

[Comparative Examples 1, 7, 13] In the case where the melting point lowering agent was minimal. and the total weight of the alkali metal compound in the baked artificial lightweight aggregate was less than 2 wt. %, even if the baking temperature was increased to 12100C 12600C, baking of the pellet was insufficient so that the absolute dry specific gravity exceeded 1.55, being higher than the target value (1.5), the crushing strength was low, and the water absorption was high [Comparative Examples 2, 8, 14] In the case where the melting point lowering agent was abundant and the total weight of the alkali metal compound in the baked artificial lightweight aggregate exceeded 6 wt. %, the pellet surface melted at a low temperature and the baking temperature dropped to 1050C ~ 11200C so that the pellet interior could not be adequately baked. Hence the crushing strength dropped to 2N - 4N and the water absorption increased to 10% - 11%.

[Comparative Examples 3, 9, 15] Even with the total weight of the alkali metal compound at 2 - 6 wt. %, in the case where the added amount of the hematite was minimal, while the strength was increased and the water absorption also reduced, the absolute dry specific gravity exceeded 1.55, being higher than the target value (1.5). Hence lightening was inadequate.

[Comparative Examples 4, 10, 16] With a total weight of alkali metal compound of 2 ~ 6 wt. %, even if the added weight ofthe hematite exceeded 10 wt. %, there was no improvement effect for the specific gravity, the strength, or water absorption.

[Comparative Examples 5, 11, 17] In the case where carbonaceous material was not added, sintemg was not promoted so that the absolute dry specific gravity was high, giving high water absorption at low strength.

[ComparativeExample6, 12,18] If the added amount of carbonaceous material exceed 10 wt%, the absolute dry specific gravity increased to approximately 1.65 and the specific strength dropped to 6N - 8N.

[Working Examples 32 ~ 65 65: carbonaceous matenal and silicon carbide syiiergistic lightening] The beforernentioned raw materials were collected and weighed in the composition shown in Table 5, and then pulvensed and mixed in a ball mill. The particle size distribution of the pulverised raw material was measured by a laser diffiaction type particle size distribution meter, and is shown in Table 5.

With the addition of water to the obtained pulverized raw material, this was pelletized to a spherical shape of approximately 5 - 1 5mm diameter in a pan pelletizer, and then dried, after which the pellets were fed to a rotary kiln (brick lining internal diameter 500mm and length 4800mm) and baked. The included amount of the alkali metals and the included amount of iron converted Fe203 in the post baked artificial lightweight aggregate is shown in Table 5.

The specific gravity and the water absorption ofthe baked artificial lightweight aggregate was measured based on JIS A 1110, and the crushing strength was measured for an artificial aggregate of approximately 1 Omm in diameter. The obtained results and baking temperatures are shown in Table 6. The absolute dry specific gravity was approximately 0.5 - 1.0, and hence an extremely light artificial lightweight aggregate was obtained. Furthermore, the crushing strength close to an absolute dry specific gravity of 0.5 was 3N, however at close to an absolute dry specific gravity of 1 0, this was 7N - 8N, giving an extremely high specific strength artificial was less than 2 wt. %, even if the baking temperature was increased to 13O00C, baking of the pellet was insufficient so that irrespective of addition of foaming agent, the absolute dry specific gravity was high at 1.21, the crushing strength was low at 2.2N, and the water absorption increased to 14.2.

[Comparative Example 20] In the case where the melting point lowering agent was abundant and the total weight of the alkali metal compound in the baked artificial lightweight aggregate exceeded 6 wt. %, the pellet surface melted at a low temperature and the baking temperature dropped to 10000C so that the pellet interior could not be adequately baked. Hence the absolute dry specific gravity increased to 1.37 being above the target value (1.0), the crushing strength dropped to 2.7N and the water absorption increased to 13.1%.

[Comparative Example 21] Even with the total weight of the alkali metal compound at 2 - 6 wt. %, and the added amount of the hematite abundant such that the included proportion of Fez after baking exceeded 10%, there was no significant change in the absolute dry specific gravity or the strength, and the effect of increasing the amount of hematite was not apparent.

[Comparative Example 22] In the case where silicon carbide was not added, the absolute diy specific gravity became 1.15, not falling to the target value (1.0). Here this example belongs to the working example where deoxygenation of the hematite was carried out with carbonaceous material only.

[Comparative Example 23] Even if the additive amount of silicon carbide exceeded 1 wt. %, the effect of lowering the absolute dry specific gravity was not improved.

[Comparative Example 24] In the case where coke (carbonaceous material) was not added at all, oxidation inside the artificial lightweight aggregate progressed so that swelling of the bubbles was minimal and the absolute dry specific gravity became 1.44, falling short of the target value (1.0).

[Comparative Example 25] If coke (carbonaceous matenal) was added at more than more than 1.0 wt. %, the degree of oxidation of the surface of the artificial lightweight aggregate became minimal so that the baking temperature could not be increased. Hence the specific gravity increased and the strength dropped. working Examples 66 - 94] The beforementioned raw materials were collected and weighed in the composition shown in Table 7, and then pulverized and mixed in a ball mill. The particle size distribution ofthe pulverized raw material was measured by a laser diffraction type particle size distribution meter, and is shown in Table 7.

With the addition ofwater to the obtained pulverized raw material, this was pelleiized to a spherical shape of approximately 5 - 15mm diameter in a pan pelletizer, and then dried, after which the pellets were fed to a rotary kiln (brick lining internal diameter 500mm and length 4800mm) and baked. The chemical composition of the alkali metal in the post baked artificial lightweight aggregate is shown in Table 7. The specific gravity and the water absorption of the baked artificial lightweight aggregate was measured based on JIS A 1110, and the crushing strength was measured for an artificial lightweight aggregate of approximately loom in diameter. The obtained results and baking temperatures are shown in Table 8. The absolute dry specific gravity was approximately 1.5 - 2.0.

Furthermore, the crushing strength was 15N - 40N compared to SN - 6N for the commercial artificial lightweight aggregate, giving an extremely high specific strength artificial lightweight aggregate. Twenty four hour water absorption was also shown low at approximately 0.3% -4%.

[Comparative Examples 26, 30, 34] In the case where the melting point lowering agent was minimal and the total weight of the alkali metal compound in the baked artificial lightweight aggregate was less than2 wt. %, even ifthe baking temperature was increased to 12500C 127O0C, baking of the pellet was insufficient so that the crushing strength was low and the water absorption high.

[Comparative Examples 27, 31, 35] In the case where the melting point lowering agent was abundant and the total weight of the alkali metal compound in the baked artificial lightweight aggregate exceeded 6 wt. %, the pellet surface melted at a low temperature so tbat the baking temperature could not be increased to approach 1000 C. Hence since the pellet interior could not be adequately baked, the crushing strength dropped to SN - 9N and the water absorption increased to 5% - 8%.

[Comparative Examples 28, 32, 36] Even with the total weight of the alkali metal compound at 2 - 6 wt. %, in the case where carbonaceous material (coke) was not added, the interior of the pellet was not in a reducing state and hence the formation of a liquid phase was not promoted, so that adequate strength was not obtained.

[Comparative Examples 29, 33, 37] With a total weight of alkali metal compound of 2 - 6 wt. %, if the added weight ofthe hematite was more than 10 wt. %, there was no improvement effect for the absolute dry specific gravid the strength, or water absorption, being a little worse.

With the present invention, since this is constructed as described above, a high quality artificial lightweight aggregate oflow cost can be efficiently produced using fly ash produced from coal fired boilers as the raw material. Consequently, the fly ash can be recycIed for building materials or the like where light weight is required, instead of disposal as industrial waste in reclamations. Hence the contribution to environmental maintenance and a stable supply of energy is significant.

(Table 1) Component - Fly Ash Bentonite Hematite Silicon Carbide Coke SiOr 56.2 65.8 1.03 14325 756 Al2O3 32.1 13.2 97.8 3.24 Fc,O, 3.57 155 CaO 059 055 MgO 1.4 1.8 Na2O 0.22 159 K2O 0.48 1.7 SO3 0.48 0.61 C 29.06 883 I.L. 13.42 Total 94.56 100.09 98.S3 172.31 99.71 Table 2 Melting Point fly Ash Sodium Potassium Alkali Metal Temparature of Lowering (W.%) Carbonate Carbonate aftcr Heat Ueat treatment Agent No. (w.%) treatment (W.%) treat=eut(W.%) ( C) 1-1 70 30 0 21.0 1200 1-2 58 42 0 31.9 1200 1-3 50 50 0 38.1 1100 14 40 60 0 48.0 1000 1-5 30 70 0 58.9 1000 2-1 70 0 30 23.8 1200 2-2 60 0 40 32.6 1200 2-3 50 0 50 41;9 1100 2-4 45 0 55 46.9 1000 2-5 30 0 70 62.7 1000 31 70 15 15 22.7 1200 3-2 60 20 20 31.1 1200 3-3 50 25 25 40.2 1100 3-4 44 28 28 46.1 1000 3-5 30 35 35 61.0 1000 (Table 31 Material Composition Pellct Particle Size fly Ash Melting Point Bentonite Hematite Coke Na1O+K1O (W.%) Lowing Agent (W.R) (W.%) (W.%) (W.%) ( m) No. Ratio Example 89 4 1 3 3 2.1 - 9 2 83 1-2 10 1 3 3 4 13 - 3 78 15 1 3 3 5.6 9 Comparison Examples 90 3 1 3 3 1.7 13 2 76 17 1 3 3 6.3 13 3 86 1-2 10 1 0 3 4.1 10 4 74 10 1 12 3 3.9 14 5 86 10 1 3 0 4.1 9 6 75 10 1 3 11 43 11 Example 4 89 4 1 3 3 2.4 9 5 85 8 1 3 3 4 9 6 81 12 1 3 3 5.7 12 7 87 1-3 8 1 1 3 4 13 8 78 8 1 10 3 3.9 11 9 87 8 1 3 1 3.9 8 10 78 8 1 3 10 4.2 7 C-E 7 91 2 1 3 3 1.6 11 8 79 14 1 3 3 6.4 12 9 88 S 1 0 3 4 15 10 76 1-3 8 1 12 3 3.9 10 11 88 8 1 3 0 3.9 12 12 77 8 1 3 11 4.2 12 E;xamplcll 90 3 1 3 3 23 14 12 87 14 6 1 3 3 3.8 10 13 83 10 1 3 3 5.8 10 C-E 13 91 2 1 3 3 1.8 12 14 88 12 1 3 3 6.9 10 15 90 14 6 1 0 3 3.9 12 16 78 6 1 12 3 3.7 11 17 90 6 1 3 0 3.7 7 18 79 6 1 3 11 4 10 Examplel4 89 4 1 3 3 2.1 9 15 84 2-2 9 1 3 3 3.9 10 16 78 15 1 3 3 5.9 10 (Table 3) continued.

Example17 90 3 1 3 3 2.1 12 18 86 2-3 7 1 3 3 3.9 19 82 11 1 3 3 5.6 12 Example20 90 3 1 3 3 2.2 12 21 86 24 7 1 3 3 42 11 22 83 10 1 3 3 5.7 9 Example23 89 4 1 3 3 2.1 10 24 83 3-2 10 1 3 3 4 8 25 78 15 1 3 3 5.7 11 Example26 90 3 1 3 3 2 11 27. 85 3-3 8 1 3 3 42 11 28 81 12 1 3 3 3.9 10 Example29 90 3 1 3 3 2.2 11 30 86 3-4 7 1 3 3 4.2 13 31 83 10 1 3 3 5.7 10 CE. Comparison Example [Table 4) Absolute Dry Crushing Strength (N) Water Absorption Baking Temperature Specific Gravity (24H) (D.B.%) ( C) Example 1.44 18 4.7 1230 2 1.13 10 5.8 1180 3 0.98 7 6.1 1150 Comparison Example 1.58 3 8.8 1260 2 1.61 3 10.2 1120 3 1.78 21 4.3 1200 4 1.22 12 5.4 1160 5 1.55 4 8.1 1200 6 1.63 8 5.7 1110 Example4 139 16 4.8 1200 5 1.15 10 5.7 1160 6 1.10 9 6.0 1120 7 1.26 13 5.2 1190 8 1.11 10 5.8 1140 9 1.26 12 5.3 1170 10 1.29 15 5.0 1150 C- Example7 1.62 3 9.7 1240 8 1.66 2 11.4 1070 9 1.74 4 23 43- 1180 10 1.19 11 55 1140 11 157 4 8.4 1180 12 1.65 6 6.7 1140 Example11 1.51 21 4.5 1180 12 133 15 5.0 1140 13 1.26 11 5.4 1110 C-Example13 1.60 2 11.1 1210 14 1.81 4 7.9 1050 15 159 19 4.5 1160 16 1.27 11 5.4 1120 17 158 3 9.5 1150 18 1.64 6 6.4 1130 Examplel4 1.42 18 4.7 1190 15 1.12 9 5.9 1150 16 1.05 8 6.2 lI20 17 139 17 4.7 1170 18 1.12 10 3.8 1130 (Table 4) continued.

19 0.95 9 6.0 1100 20 1.50 20 4.5 1150 21 1.23 12 5.3 1110 22 1.19 11 5.S 1070 23 1.43 19 4.6 1200 24 1.11 9 5.9 1160 25 1.06 8 6.3 1130 26 1.45 20 4.6 1180 27 1.14 10 5.8 1140 28 1.12 9 5.9 1100 29 153 23 4.4 1160 30 1.26 13 5.2 1100 31 1.21 11 5.4 1080 (Table 5) Matcrial Composition Pellet Particle Fly Ash Melting Point Bentonite H matite Slicon Coke Na2O+K2O Fesa Size (W.%) Lowing Agent (W.%) (W.%) Carbide (W.%) (W.) .(w.%) ( m) No. Ratio (w.%) E-32 865 4 4 1 3 0.5 5.0 2.1 6.8 12 33 805 1-2 10 1 3 0.5 5.0 4.1 6.7 12 34 75.5 15 1 3 0.5 5.0 5.8 6.6 14 E-35 86.5 4 1 3 05 5.0 2.4 6.8 12 36 77.9 10 1 1 0.1 10.0 5.1 4.6 12 37 825 10 1 1 0.5 5.0 4.9. 4.6 11 38 86.8 10 1 1 1.0 0.2 4.7 4.6 10 39 75.9 1-3 10 1 3 0.1 10.0 5.1 6.8 14 40 80.6 10 1 3 05 5.0 4.9 6.7 14 41 84.8 10 1 3 1.0 0.2 4.7 6.6 11 42 72.9 10 1 6 0.1 10.0 5.0 10.0 12 43 775 10 1 6 05 5.0 4.9 9.8 13 44 81.8 10 1 9 1.0 0.2 4.7 9.5 12 45 765 15 1 3 0.5 5.0 6.9 6.6 10 C-19 885 2 1 3 0.5 5.0 1.6 6.8 14 20 725 18 1 3 OS 5.0 8.2 6.5 11 21 865 10 1 7 05 5.0 4.8 10.8 11 22 81.0 1-3 10 1 3 0.0 5.0 4.9 6.7 15 23 79.8 10 1 3 1.2 5.0 4.9 6.7 10 24 855 10 1 3 0.5 0.0 4.7 6.6 12 25 73.5 10 1 3 0.5 12.0 5.2 6.8 12 S46 865 4 1 3 05 5.0 28 6.8 11 47 825 1-4 8 1 3 05 5.0 4.9 6.7 14 48 785 12 1 3 0.5 5.0 7.0 6.6 13 E49 86.5 4 1 3 0.5 5.0 - 2.1 6.8 13 50 805 2-2 8 1 3 OS 5.0 4.3 6.7 13 51 755 15 1 3 0.5 5.0 6.0 6.6 11 E-52 865 4 1 3 0.5 5.0 2.6 6.8 11 53 77.9 10 1 1 0.1 10.0 55 4.6 14 54 82.5 10 1 1 0.5 5.0 4.9 4.6 13 55 86.8 10 1 1 1.0 0.2 5.1 4.6 12 56 75.9 10 1 3 0.1 10.0 55 6.8 10 57 80.5 2-3 10 1 3 0.5 5.0 5.3 6.7 13 58 84.8 10 1 3 1.0 0.2 5.1 65 12 59 72.9 10 1 6 0.1 10.0 55 10.0 15 [Table 5] continued.

60 775 10 1 6 05 5.0 5.3 9.8 13 61 81.8 10 1 6 1.0 02 5.1 9.5 14 62 75.5 15 1 3 0.5 5.0 7.5 6.6 10 E-63 86.5 4 1 3 05 5.0 2.8 6.8 12 64 825 24 8 1 3 0.5 5.0 4.8 6.7 12 65 785 12 1 3 05 5.0 68 6.6 12 E: Example C: Comparison Example [Table 6] Absolute Dry Crushing Strcngth(N) Water Absorption Baking Temperature Specific Gravity (24H) (D.B.%) (t) Example32 0.69 4.8 9.2 1250 33 051 3.0 11.8 1050 34 - 056 3.5 10.9 1020 Example35 0.72 5.1 8.8 1190 36 0.97 7.6 6.3 1070 37 0.88 6.4 7.2 1070 38 0.75 5.2 9.0 1080 39 0.89 6.2 8.1 1030 40 053 3.2 115 1030 41 052 3.0 12.7 1030 42 0.91 7.0 8.9 1020 43 0.48 2.9 123 1020 44 050 2.8 13.0 1030 45 0.54 33 11.4 1020 C-E 19 1.21 2.2 14.2 1300 20 1.37 9.7 3.1 1000 21 056 35 11.1 1030 22 1.15 10.1 4.7 1030 23 053 32 115 1030 24 1.4S 5.0 16.7 1030 25 0.67 3.4 11.6 1030 Example46 0.85 6.6 7.3 1130 47 0.63 4.3 10.1 1030 48 0.78 5.3 85 1020 Example49 0.64 4.2 9.0 1250 50 0.50 3.2 11.0 1040 51 057 3.6 12.0 1020 ExampleS2 0.72 53 8.6 1160 53 0.97 6.6 6.7 1070 54 0.88 6.6 7.2 1070 55 0.75 4.2 9.0 1070 56 0.89 5.7 8.1 1020 57 0.53 3.2 11.5 1030 58 0.52 2.8 12.7 1030 59 0.91 5.9 6.9 1020 60 0.48 2.9 12.1 1020 [Table 6) continued, 61 0.50 2.6 13.0 1020 62 054 33 11.4 1020 Example63 0.79 - 6.0 8.4 1130 64 0.62 4.0 10.1 1030 65 0.72 4.7 8.6 1020 *C-E: Comparison Example [Table 71 Material Composition Pellct Particle Size Fly Ash Melting Point Bentonite Coke Na:O+K2O (W.%) Lowing Agent (W.%) (W.%) (w.%) (S m) No Ratio Example66 92 4 1 3 2.1 11 67 86 1-2 10 1 3 4.1 12 68 81 15 1 3 5.7 10 C- 26 93 3 1 3 1.8 9 27. 79 17 1 3 6.2 11 28 89 1-2 10 1 0 4 9 29 78 10 1 11 4.3 10 Example69 92 4 1 3 2.4 9 70 88 8 1 3 4 9 71 84 12 1 3 5.7 10 72 90 1-3 8 1 1 4 11 73 81 8 1 10 4.2 8 C-E 30 94 2 1 3 1.6 11 31 82 14 1 3 6.5 12 32 91 8 1 0 4 11 33 80 1-3 10 1 11 4.3 9 Example74 93 3 1 3 23 8 75 90 1-4 6 1 3 3.9 8 76 86 10 1 3 5.9 7 C- 34 94 2 1 3 1.8 11 35 84 12 1 3 6.9 11 36 93 14 6 1 0 3.8 13 37 82 6 1 11 4.1 14 Examples 92 4 1 3 . 2.2 7 78 87 2-2 9 1 3 3.9 7 79 81 15 1 3 5.9 9 Example80 93 3 1 3 22 11 81 89 2-3 7 1 3 3.9 10 82 35 11 1 3 5.6 8 Example83 90 3 I 3 22 8 84 89 24 7 1 3 43 14 85 86 10 1 3 5.8 8 Example86 92 4 1 3 2.1 10 87 86 3-2 10 1 3 4 10 88 81 15 1 3 5.7 9 (Table 7) continued.

Example89 93 3 1 3 2 10 90 88 33 8 1 3 4.2 11 91 84 12 1 3 5.9 14 Example92 93 3 1 3 2.3 11 93 89 34 7 1 3 4.2 9.

94 86 10 1 3 5.7 7; *C-E: Comparison Example [Table 8] Absolute Dry Crushing Strength (N) Slater Absorption Ba)dng Temperature Spccific Gravity (24H) (D.B.%) ( C) Example66 1.89 37 0.9 1240 67 1.78 28 1.9 1130 68 1.52 15 3.9 1000 C-B 26 1.63 10 6.0 1270 27 1.57 7 7.1 1010 28 1.80 4 3.6 1140 29 1.74 19 2.6 1140 Example69 1.97 36 03 1230 70 1.80 28 1.8 1150 71 1.61 16 3.0 1050 72 1.79 29 1.7 1140 73 1.73 2? 2.1 1130 E 30 1.84 8 45 1270 31 157 5 5.5 1000 32 1.70 4 5.0 1150 33 1.65 13 4.2 1110 Example74 1.94 37 0.5 1220 75 1.75 28 2.0 1130 76 156 18 3.6 1030 C-B 34 1.79 10 3.9 1250 35 158 9 7.8 990 36 1.78 3 4.0 1140 37 1.65 25 3.7 1130 Example 77 1.93 37 0.6 1230 78 1.76 28 2.3 1130 79 1S4 17 3.5 1020 80 l.92 36 0.7 1230 81 1.77 27 2.0 1130 82 159 19 3.3 1050 83 1.95 38 05 1230 84 1.78 31 1.7 1130 85 1.71 24 2.4 1130 86 1.97 39 0.3 1240 87 1.78 26 2.2 1140 88 1.60 22 3.1 1050 89 2.00 40 0.2 1250 [Table 8] continued.

90 1.73 27 25 1130 91 159 20 35 1030 92 1.76 27 1.7 1130 93 1.73 25 23 1120 94 1.61 19 3.2 1060 C-E: Comparison Example

Claims

Claims 1. An artificial lightweight aggregate made by mixing fly ash with a melting point lowering agent, a caking agent, and a foaming agent to obtain a mixture, crushing said mixture so that the average particle size is up to 15 microns to obtain a pulverized product, forming small bodies of said pulverized product, and then baking said small bodies within a temperature range of 1000 C ~ 1250 C to produce the aggregate with an absolute dry specific gravity of 1.0 ~ 0.5.
2. A method of manufacturing artificial lightweight aggregate comprising the steps of; mixing fly ash with a melting point lowering agent, a caking agent, and carbonaceous material to obtain a mixture, crushing said mixture to obtain a puJ-rized product with the average particle size up to 15 microns, forming small bodies of said pulverized product, and then baking said small bodies within a temperature range of 1000C - 1250CC.
3. A method of manufacturing artificial litrtreirht aggregate according to claim 2, wherein said carbonaceous material is within a range of 0.2 wt /o ~ 10 wt. % of the fly ash.
4. A method of manufacturing artificial lightweight aggregate according to claim 2, wherein in addition, iron oxide is mixed in the mixture.
5 A method of manufacturing artificial lightweight aggregate according to claim 4, wherein in addition hydrogen carbonate is mixed in the mixture.
6. A method of manufåcturing artificial lightweight aggregate according to either one of claim 4 and claim 5, involving iron oxide in an amount such that the amount of F e203 in the fly ash is within the range of 1 wt. % - 10 wt. %, carbonaceous material in an amount within the range of 0.2 wt. % - 10 wt. % of the fly ash, and silicon carbide in an amount within the range ofO wt. % - 1 wt. % of the fly ash.
7. A method of manufactunng artificial lightweight aggregate according to any one of claim 2 through claim 6, wherein the melting point lowering agent is made by mixing an alkali metal compound with fly ash so that the total amount of Na,O and K20 respectively or both is within the range of 30 wt. % - 50 wt. % in the mixture, heating and melting the mixture within a temperature range of 10000C - 12000C to form a glassy material, and then cooling and crushing the glassy material.
8. A method of manufacturing artificial lightweight aggregate according to any one of claim 2 through claim 6, wherein said melting point lowering agent is made by mixing an alkali metal compound with fly ash so that the total amount of nazi and K20 respectively or both is within a range of 30 wt. 50 ~ 50 wt % in the mixture, heating and melting the mixture within a temperature range of 1000 C ~ 1200 C to form a glassy material, and then cooling and crushing the glassy material, and said melting point lowering agent is added to the fly ash so that the total amount of NazO and K20 is within the range of2 wt % - 6 wt. % of the baked product.
9. A method of manufacturing artificial lightweight aggregate according to either one of claim 7 and claim 8, wherein said alkali metal compound is sodium carbonate and potassium carbonate.
10. A method of manufacturing artificial lightweight aggregate according to claim 2, wherein said small bodies are pellets, and a rotary kiln is used as the baking furnace.
11. A melting point lowering agent for an artificial lightweight aggregate made by mixing an alkali metal compound with fly ash so that the total amount of NO and K-O respectively or both is within a range of 30 wt. % - 50 wt. % in the mixture, heating and melting the mixture within a temperature range of 10000C - 12000C to form a glassy material, and then cooling and crushing the glassy material.
12. A melting point lowering agent for an artificial lightweight aggregate according to claim 11, wherein said alkali metal compound is sodium carbonate and potassium carbonate.
13. An artificial lightweight aggregate as hereinbefore described.
14. A method of manufacturing an artificial lightweight aggregate as hereinbefore described.