GB2083088A - Aluminium hydroxide-based building materials and method for manufacturing same - Google Patents

Abstract

Lightweight building materials with high mechanical strengths are obtained from an otherwise noxious or difficulty-disposable sludge of gel-like aluminium hydroxide produced in large quantities in the process of the anodization treatment of aluminium shaped articles. The aluminium hydroxide sludge is first mixed with a calciferous material, which is preferably a combination of calcium oxide and gypsum, so that a reaction takes place between them to form etteringite and the thus obtained etteringite-containing mixture is blended with a fibrous reinforcing material such as a cellulosic pulp or asbestos and, optionally, hydraulic setting material such as a Portland cement to form a blend which is shaped into a desired form of, for example, wall or ceiling board followed by curing and drying.

Description

SPECIFICATION Aluminum hydroxide-based building materials and method for manufacturing same The present invention relates to building materials such as ceiling and wall boards and, more particularly, to a building material formed of aluminum hydroxide as the main component and reinforced with a fibrous material, as well as to a method for manufacturing such a building material.

Needless to say, there are currently in use in the building industry a great variety of building materials depending on the requirements for the particular building and the locality. The requirements for the building materials are so diversified that a material suitable for one building is not always useful for another. Several characteristics are, however, almost always important in all types of building materials among which, for example, mechanical strength, non-inflammability or flame retardancy and heat and sound insulation as well as cheapness may be mentioned.

In relation to the cost of the building materials, there may be obtained two-way advantages if an industrial waste can be processed or fabricated into a building material having satisfactory characteristics, namely the solution of the problem caused by the burdensome waste material such as environmental pollution and the commercial benefit obtained with the building materials produced therefrom at low cost.

Accordingly there have been made various attempts to utilize industrial waste materials for the production of building materials. Unfortunately there are known very few examples of success in which good building materials suitable for practical use are manufactured from an otherwise useless or rather harmful industrial waste as the main starting material.

Turning now to give an overview of the industries involving a serious problem of waste disposal to avoid environmental pollution, the works of aluminum fabrication are typically notorious due to the difficulties of waste disposal. As is well known, aluminum articles in recent years are used rarely as shaped by extrusion, casting or other shaping means with the metallic aluminum surface exposed but are almost always used after surface finishing.

The method of surface finishing most widely undertaken in the aluminum industry is, of course, surface anodization in which the surface of the aluminum article is electrolytically oxidized in an acidic electrolyte bath to be covered with a thin but dense layer of aluminum oxide and imparted with increased chemical and physical stability as well as an attractive finish. A problem in the anodization treatment of aluminum articles is that a considerable amount of aluminum metal is unavoidably dissolved in the electrolyte bath and the thus dissolved aluminum finally precipitates in the form of amorphous aluminum hydroxide when the electrolyte solution is neutralized for sewage disposal.

The aluminum hydroxide thus precipitated usually forms a gel-like sludge containing considerable amounts of impurities coming from several steps of the aluminum fabrication such as sulfates, e.g.

aluminum sulfate, aluminum hydroxysulfate, sodium sulfate and the like, and sodium aluminate.

The gel-like sludge usually contains large volumes, e.g. 70 to 90% by weight, of water but is hardly filterable so that drying up of such an aluminum hydroxide sludge is practically impossible. Therefore, the only way in the prior art for the disposal of the aluminum hydroxide sludge is to discard it on reclaimed land or in the ocean in the gel-like form as such.

Such a method of waste disposal is, of course, not wholly acceptable even by setting aside the problem of the large cost for the transportation of such a watery waste material to the reclaimed land or to the ocean. For example, reclaimed land filled with such a gel-like sludge is natu rally weak in the yield strength of the ground resulting in a decreased utilizability of the land. Discarding the sludge in the ocean is also not free from regulations to prevent pollution of water. Thus the waste disposal of the gel-like aluminum hydroxide sludge has been the most troublesome problem in the industry of aluminum fabrication.

An object of the present invention is to provide a novel building material composed mainly of an amorphous aluminum hydroxide converted at least partly to ettringite by reaction with a calciferous material and shaped into the desired form with the aid of a fibrous reinforcing material. The mechanical properties of the shaped body may be further improved by the combined use of a hydraulic setting material such as a Portland cement.

Another object of the present invention is to provide a novel and improved method for the manufacture of the above mentioned building material starting with the above mentioned gel-like aluminum hydroxide sludge produced in the process of surface anodization of aluminum articles.

In the method of the invention, the gel-like sludge of amorphous aluminum hydroxide is first admixed with a calciferous material, such as lime or gypsum, whereby to be reacted at least partly with the calciferous material to form ettringite, 6CaO.

A1203-3SO3-31 H2O, and the aluminum hydroxide sludge containing ettringite is then blended with a fibrous reinforcing material and, optionally, a hydraulic setting material such as a Portland cement and shaped into the desired form followed by drying.

The inventive building material described above is very advantageous in the building industry, in addition to the outstanding cheapness, with high mechanical strength by virtue of the entrammeling structure of the fibrous reinforcing material and the aluminum hydroxide andlor ettringite and excellent flame retardancy or non-inflammability due to the large amount of the water of crystallization contained in the ettringite.

As described above, the principal starting material used in the invention is a gel-like sludge of amorphous aluminum hydroxide such as is produced in large quantities as a waste material in the anodization treatment of aluminum articles. The sludge usually contains from 70 to 90% by weight of water or, in other words, only 10 to 30% by weight of solids and is fluid. The sludge contains several kinds of impurities originating in various steps ofthe anod ization treatment including pre-treatment and posttreatment.For example, the alkaline waste solution containing sodium aluminate formed in the degreas ing pretreatment with sodium hydroxide and follow ing washing with water is combined with the acidic waste solutions formed in the anodization in an acidic electrolyte bath and subsequent washing with water of the aluminum articles containing sulfuric acid, aluminum sulfate, aluminum hydroxysulfate and the like according to the conditions of neutralization.

The aluminum hydroxide sludge above described is admixed with a suitable amount of a calciferous material which can be reacted with the aluminum hydroxide to form ettringite cooperatively with the sulfate constituents contained in the sludge. Various kinds of calciferous materials are suitable for the purpose including quick or slaked lime, i.e. calcium oxide or calcium hydroxide, calcium carbonate, gypsum, i.e. calcium sulfate, and the like. Limes are preferred due to their relatively high reactivity with the aluminum hydroxide. For example, the calcium hydroxide residue produced by the reaction of calcium carbide with water to evolve acetylene gas is suitably used.Calcium oxide is sometimes preferred, however, because calcium oxide is effective in controlling the water content of the resultant sludge by reaction with the water content of the sludge to form calcium hydroxide as well as in elevating the temperature of the mixture with the heat of reaction with water to accelerate the formation of ettringite. It is of course optional that the sludge may be further diluted with an additional amount of water but no additional water is usually required because of the large water content in the starting aluminum hydroxide sludge. Calcium sulfate, i.e. gypsum, is also an inexpensive calciferous material obtained, for example, in the desulfurization of exhaust gases from petroleum combustion. Dihydrated gypsum is preferred although anhydrous and calcined gypsums may be used.It is sometimes advantageous to use two kinds or more of the calciferous materials in combination. In particular, the combined use of calcium oxide and dihydrated gypsum is recommended when the balance between the aluminum, calcium and sulfate ions should be taken into consideration to facilitate formation of the ettringite.

The amount of the calciferous material to be added to the aluminum hydroxide sludge naturally depends on the composition of the sludge as well as the kind of the calciferous material though not particularly limitative. It should be noted that the use of an excessively large amount of calcium oxide or hydroxide is undesirable because the free unreacted lime remaining in the resultant product is detrimental to the stability of the inventive building material.

A preferred formulation in this respect is that 100 kg of the aluminum hydroxide sludge is first admixed with 15 to 20 kg of calcium oxide and the mixture is further admixed with dihydrated gypsum in an amount of 1.0 to 1.2 times or, more preferably, from 1.15to 1.20 times by weight per dry amount of the mixture of calcium oxide and the sludge.

The aluminum hydroxide sludge thus uniformly blended with the calciferous material still retains fluidity with increased temperature when calcium oxide is used as the calciferous material by the heat of reaction with water. The mixture is then kept standing at room temperature or above for 24 to 48 hours so that reaction takes place between the amorphous aluminum hydroxide and the calciferous material to form ettringite of the formula r 6CaO-AI203 3SO3 31 H2O. It is optional that the reaction may be further accelerated by heating the mixture when a suitable heating means is available. The formation of the ettringite is readily detectable by X-ray diffractometric analysis and the reaction is continued until substantial stability of the reaction mixture has been attained.As is indicated by the X-ray analysis, the reaction mixture after completion of the reaction almost always contains several other crystalline compounds such as calcite, gibbsite, woodfordite and the like in addition to the ettringite depending on the composition of the starting sludge as well as the kind of the calciferous material.

The next step is blending of a fibrous reinforcing material with the above obtained slurry-like aluminum hydroxide sludge at least partly converted to ettringite. When a fibrous material is admixed and well blended with the sludge, coagulation takes place in the mixture as the fibers are entrameled by the gel-like mass of the aluminum hydroxide andlor ettringite in the sludge.

The fibrous material may be either organic or inorganic according to need. Organic fibrous materials suitable for use include wood pulp, unentangled cellulosic fibers obtained by beating scrapped papers and various kinds of fibrous flues originating in fiber-processing factories such as spinning and weaving plants. These organic fibrous materials are preferred when lightweight building materials with good heat insulation are desired. On the other hand, inorganic fibrous materials suitable for use include asbestos, rock wool, glass fibers and the like and are preferred when high non-inflammabilityorflame retardancy is desired of the inventive building material.

The amount of the fibrous material is naturally determined with consideration of various factors. It should be noted that no satisfactory mechanical strengths or, in particular, bending strength, can be imparted to the finished building material of the invention when the amount otthe fibrous reinforc ing material is too small. The thus obtained blend ofthe ettringitecontaining reaction mixture and the fibrous reinforc- - ing material may be shaped into a desired form of a ceiling or wall board and the like by a suitable shaping method in accordance with the consistency of the blend. It is noteworthy that the blend is further admixed with a hydraulic setting material, i.e. a material curable by the reaction with water, such as a Portland cement or gypsum. Various kinds of hydraulic cements are also suitable in place of Portland cement such as alumina cement, blastfurnace cement, silica cement and the like. When an industrially advantageous shaping process is desired, it is recommended that a high early strength cement is used as combined with gypsum.

Although the additional admixture of the hydraulic setting material is optional, the preferred proportions by weight of the ettringite-containing reaction mixture, fibrous reinforcing material and hydraulic setting material are as follows in a typical formulation: from 20 to 80% or, preferably, from 40 to 60% of the ettringite-containing reaction mixture; from 15 to 55% or, preferably, from 30 to 50% of the hydraulic setting material; and from 10 to 55% or, preferably, from 15 to 25% of the fibrous reinforcing material.

The addition of the hydraulic setting material is effective in improving the moldability of the blend as well as in improving the mechanical strengths and the dimensional stability of the finished building material.

The blend of the ettringite-containing reaction mixture and the fibrous reinforcing material with or without admixture of the hydraulic setting material is then shaped into a desired form such as a ceiling orwall board in a suitable shaping method, for example, in just the same manner as in the manufacture of asbestos cement boards. The inventive building material manufactured in the above described manner has usually at least 80 kg/cm2 of the bending strength or up to 150 kg/cm2 or more of the bending strength in some cases with an apparent density of about 0.9 to 1.3 g/cm3 after complete curing and drying.Accordingly, the inventive building materials are very useful with these advantageous characteristics not onlyforthe buildings of factories and warehouses but also living houses in general when attractive or decorative surface finishing is provided.

It is noteworthy that, when lime, i.e. calcium oxide or hydroxide, is used as the calciferous material, the presence of the free lime in the finished building material is undesirable due to the decreased mechanical strengths and stability of the material in the lapse of time so that the free lime should desirably be converted into a stable form such as gypsum. In this respect, it is sometimes advantageous to admix a sulfate such as aluminum sulfate into the mixture before shaping so that the free lime is converted to gypsum, i.e. calcium sulfate, by a double decomposition reaction.

It is further noteworthy that some improvement in the mechanical strength, e.g. bending strength, is obtained by partly replacing the aluminum hydroxide constituent of the gel-like aluminum hydroxide sludge with a commercial grade aluminum hydroxide, which is more or less crystalline. In some most favorable cases, the bending strength of the resultant building material may be increased by 20 to 35% over the value obtained without the replacement of the aluminum hydroxide sludge with the crystalline aluminum hydroxide. The amount of this replacement, however, should not exceed 20% of the overall amount of the aluminum hydroxide constituent in the mixture since the mechanical strengths of the building material rather decrease by an excessive amount of the crystalline aluminum hydroxide in addition to the economic disadvantage caused by the use of such a relatively expensive material.

Therefore, the amount of the replacement is preferably 15S6 or below or, more preferably, in the range from 3 to 10%.

Following are the examples to illustrate the present invention in further detail but not to limit the scope of the invention in any way.

Example 1.

A gel-like aluminum hydroxide sludge obtained from a plant for the anodization treatment of aluminum articles was admixed with calcium oxide and dehydrated gypsum, which was a by-product obtained in the desulfurization of exhaust gas of petroleum combustion. The lime and the gypsum were added in amounts of 5 kg and 35 kg, respectively, per 40 kg of the dry material in the sludge. On blending the calcium oxide, the temperature of the mixture was markedly increased and, after thorough mixing, the mixture, still having fluidity, was kept standing for 48 hours. X-ray diffractometric analysis of the mixture after 48 hours of standing indicated that the calcium constituent had almost completely reacted and was converted to ettringite.

The thus obtained ettringite-containing slurry was then admixed with 8 kg of wood pulp and 12 kg of asbestos. As these fibrous materials were blended well with the slurry, the ettringite-containing solid matter in the slurry entrammeled the fibers of the pulp and asbestos and coagulated. The thus obtained mixture was relatively dry and in a condition disintegrable into lumps substantially without free water.

The mixture was shaped into a form of a board of 6.8 mm thickness by a technique similar to the manufacture of asbestos cement boards by use of a sheeting roller under a linear pressure of 35kg/cm and the thus shaped board was cured for 7 days as wrapped followed by complete drying into a finished board material. The board had an apparent density of 0.94 gleam3 and a bending strength of 82.9 kg/cm2 as the averaged values for 100 boards prepared in the same way, and was useful as a building material.

Example 2.

The experimental procedure was substantially the same as in Example 1 except that 10 kg of a Portland cement were added to the ettringite-containing slurry together with the fibrous materials of which the cellulosic fibrous material was not the wood pulp but a reclaimed pulp obtained from scrapped papers.

The resultant board material had an apparent density of 1.15 g/cm3 and a bending strength of 128.5 kg/cm2 as the averaged values for 100 boards prepared in the same way.

Example 3.

The experimental procedure was substantially the same as in Example 2 except that 3 kg of a commercial grade aluminum hydroxide were admixed with the reaction mixture of the gel-like aluminum hydroxide sludge, calcium oxide and gypsum.

The resultant board material had an apparent density of 1.17 g/cm3 and a bending strength of 176.5 kg/cm2 as the averaged values for 100 boards prepared in the same way.

Claims (19)

1. A building material formed of a uniform blend comprising an amorphous aluminum hydroxide at least partly converted to ettringite, by the reaction of a gel-like aluminum hydroxide sludge with a calciferous material, and a fibrous reinforcing material.

2. A building material as claimed in claim 1 wherein the fibrous reinforcing material is a cellulosiefibrous material.

3. A building material as claimed in claim 1 wherein the fibrous reinforcing material is asbestos.

4. A building material as claimed in any one of claims 1-3 wherein the calciferous material is calcium oxide or calcium hydroxide.

5. A building material as claimed in any one of claims 1-3 wherein the califerous material is a gypsum.

6. A building material as claimed in claim 4 which is substantially free from unreacted calcium oxide or calcium hydroxide.

7. A building material as claimed in any one of the preceding claims wherein the blend further comprises a hydraulic setting material.

8. A building material as claimed in claim 7 wherein the hydraulic setting material is a Portland cement.

9. A method for the manufacture of a building material formed of a blend comprising an amorphous aluminum hydroxide at least partly coverted to ettringite, by the reaction of a gel-like aluminum hydroxide sludge with a calciferous material, and a fibrous reinforcing material which comprises the steps of (a) admixing a calciferous material with a gel-like aluminum hydroxide sludge so as to cause a reaction to take place between the gel-like aluminum hydroxide and the calciferous material to form ettringite, (b) blending a fibrous reinforcing material with the thus obtained ettringite-containing mixture so as to have the fibres of the fibrous reinforcing material entrammeled by the solid material in the ettringitecontaining mixture, (c) shaping the mixture composed of the ettringite-containing mixture and the fibrous reinforcing material into a body in a form of building material, and (d) drying the thus formed body in the form of a building material.

10. A method as claimed in claim 9 wherein the calciferous material is calcium oxide.

11. A method as claimed in claim 9 wherein the calciferous material is a combination of calcium oxide and gypsum.

12. A method as claimed in any one of claims 9-11 wherein the fibrous reinforcing material is a pulp ofcellulosicfibres.

13. A method as claimed in any one of claims 9-11 wherein the fibrous reinforcing material is asbestos.

14. A method as claimed in any one of claims 9-13 which further comprises blending a hydraulic setting material in the mixture together with the fibrous reinforcing material.

15. A method as claimed in claim 10 or claim 11 wherein aluminum sulphate is admixed with the mixture after the reaction ofthe gel-like aluminum hydroxide and the calciferous material to convert the unreacted calcium oxide to calcium sulphate by a double decomposition reaction.

16. A method as claimed in any one of claims 9-15 wherein the amorphous aluminum hydroxide in the gel-like aluminum hydroxide sludge is partly replaced with a crystalline aluminum hydroxide.

17. A method as claimed in claim 14 wherein the hydraulic setting material is a Portland cement.

18. A building material as claimed in claim 1 substantially as hereinbefore described with reference to the examples.

19. A method as claimed in claim 9 substantially; as hereinbefore described with reference to the ' examples.