JP2001039710A - Production of aluminum-based chemical and silica-based chemical from coal ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique to produce aluminum sulfate from Al2O3, and water glass (sodium silicate) and white carbon from SiO2 in coal ash. SOLUTION: Sulfuric acid is added to coal ash essentially consisting of SiO2 and Al2O3, and the mixture is heated. A chemical agent of aluminum sulfate is produced from the filtrate of the reaction. Or, a chemical agent of water glass (sodium silicate) or white carbon is produced from the residue of filtration. The aluminum sulfate, water glass or white carbon obtained from the reaction is preferably used for paper making. The sulfuric acid is preferably the waste sulfuric acid from the producing device of chlorine dioxide used as a bleaching agent for pulp.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing aluminum sulfate, water glass (sodium silicate) or white carbon from coal ash.

[0002]

2. Description of the Related Art Coal has abundant reserves compared with other fossil fuels, and is an important energy that can be supplied stably in the long term. Japan is also one of the world's leading coal consumers, and it is expected that reliance on coal energy will continue to increase in the future due to measures to diversify energy resources. According to the data of the Ministry of International Trade and Industry's Agency for Natural Resources and Energy,
Coal ash generated from coal-fired power plants accounted for about 72
It is expected to reach 100,000 tonnes and about 13.7 million tonnes in 2005.

The effective utilization rate of coal ash was about 70% in 1996
The main fields are cement, civil engineering, construction, agriculture, forestry and fisheries, and others. Among them, utilization as a cement raw material occupies a large weight. Use as a cement raw material is used as a substitute for clay, which is one of the raw materials for cement.However, except for JIS fly ash (JIS A 6201), in most cases, it is treated as industrial waste and contracted to a cement manufacturer. Processing costs must be paid, and companies that own thermal power plants are burdened with the cost of processing coal ash. For this reason, the development of other utilization fields of coal ash, particularly the development of valuable material production technology from coal ash, is desired.

[0004] Existing technologies for considering coal ash as SiO ₂ , Al ₂ O ₃ and other secondary resources and recovering valuable materials from coal ash include Japanese Patent Application Laid-Open No. 03-90523, “Valuable components from inorganic powders”. Recovery method '', JP-A-03-88710 JP `` Method of recovering valuable components in coal ash '', JP-A-04-169709 JP `` Method of treating coal ash '',
There is Japanese Patent Publication No. Hei 08-8872, "Biological extraction method".

Japanese Patent Application Laid-Open No. 03-90523 discloses a method in which a mixed acid of hydrogen fluoride and hydrochloric acid is added to coal ash and heated to extract and separate Si from volatile components and Al and other metal compounds from the remaining liquid. Since hydrogen fluoride, which is highly toxic, is used, its practical application is difficult.

[0006] Japanese Patent Application Laid-Open No. 03-88710 discloses a method of obtaining a SiC production raw material by adding a carbon source to a residue obtained by recovering a valuable metal component. Japanese Patent Application Laid-Open No. 04-169709 discloses a method for efficiently extracting metals by adding sulfuric acid to coal ash, and aims at extracting rare metals in coal ash.

[0007] Japanese Patent Publication No. 08-8872 discloses a method of extracting useful metals by a special method called thiovacsyl-thiooxydance. As described above, the technology of industrially producing aluminum sulfate from Al ₂ O _{3 in} coal ash and simultaneously producing water glass (sodium silicate) and white carbon dioxide from SiO ₂ has not been established.

[0008] At present, aluminum sulfate is industrially produced by dissolving bauxite, which is generally imported, in sulfuric acid. The pure product is obtained by reacting aluminum hydroxide with sulfuric acid. However, the method of producing the Al ₂ O ₃ minutes aluminum sulphate in the coal ash has not been established in yet industrially.

[0009] An industrial production method of cullet (sodium silicate) includes:
There are a dry method and a wet method. In the dry method, high-purity silica sand and sodium carbonate are melted in a furnace and then cooled and solidified. However, a method for producing cullet from SiO _{2 in} coal ash has not yet been established industrially.

An industrial method for producing water glass (sodium silicate) is obtained by pulverizing a cullet into an autoclave, adding water and heating and dissolving the cullet, and using a silicate raw material that easily reacts with an alkali such as diatomaceous earth. It is obtained by placing it in an autoclave and reacting with caustic sodium. However, a method for producing a water glass using cullet produced from SiO _{2 in} coal ash as a raw material has not yet been established industrially.

[0011] There are a dry method and a wet method as an industrial production method of white carbon. In the dry method, it is obtained by a method such as heating a mixture of silica sand and coke by an arc, and in the wet method, it is obtained by a method such as acid decomposition of sodium silicate. However, a method of producing white carbon using cullet produced from SiO _{2 in} coal ash as a raw material has not yet been established industrially.

On the other hand, the paper balm industry consumes a large amount of resources and energy. Purification of large amounts of water and CO in wastewater
A large amount of aluminum sulfate is used as a coagulant sedimentation treatment for removing D and as a fixing agent for sizing agent in papermaking. Also, in the production process of deinking halves, which are the raw materials for newsprint,
Water glass (sodium silicate) is used as a deinking agent, and a large amount of white carbon is used as a filler for the purpose of improving the opacity of newsprint and the like. In recent years, the necessity of environmental protection on a global scale has led to a remarkable increase in recycling, and there has been a tendency to increase the use rate of deinked bulbs.
(Sodium silicate) and the amount of white carbon used are increasing. These aluminum sulfate, water glass (sodium silicate), white car
At present, most paper balm mills purchase products in the form of commercial products.

As described above, the technology for producing on-site aluminum sulfate, water glass (sodium silicate), and white carbon using a large amount of coal ash generated in a factory having a coal boiler has not yet been established. Absent.

The sulfate and water glass obtained by the present invention can be used.
(Sodium silicate) and white carbon are not limited to use in the paper balm industry, but can be used for existing uses of each chemical. In most cases, chlorine dioxide is used as a bleaching agent in the craft half bleaching process to prevent pollution. Although there are various types of chlorine dioxide generators, many devices that generate sulfuric acid as a by-product of chlorine dioxide generation are currently operating in Japan. Some of this sulfuric acid is recovered and used for the purpose of replenishing the sulfur content in the cooking chemicals of Kraft Hall.
The remainder is drained and often uses a large amount of alkaline chemicals for this neutralization.

In the step of eluting Al ₂ O ₃ from coal ash according to the present invention, the waste sulfuric acid solution from the chlorine dioxide generator can be used. The three reaction formulas for generating chlorine dioxide that generate this waste sulfuric acid are shown below. NaClO ₃ + HCl + 1 / 2H ₂ SO ₄ → ClO ₂ + 1 / 2Cl ₂ + 1 / 2Na ₂ SO ₄ + H ₂ O NaClO ₃ + 1 / 2H ₂ O ₂ + 1 / 2H ₂ SO ₄ → ClO ₂ + 1 / 2O ₂ + 1 / 2Na ₂ SO ₄ + H ₂ O NaClO ₃ + 1 / 4CH ₃ OH + 2 / 3H ₂ SO ₄ → ClO ₂ + 1 / 4HCOOH + 1 / 3Na ₂ H (SO
₄ ) 2 + 3 / 4H ₂ 0

[0016]

SUMMARY OF THE INVENTION The present invention aims to convert coal ash, which is expected to increase in the future, into a valuable secondary resource mainly composed of SiO ₂ and Al ₂ O ₃ in Japan, a resource-small country. Assuming, aluminum sulfate from coal ash Al ₂ O ₃ and water glass from SiO ₂
(Sodium silicate), which provides a technique for producing white carbon.

[0017]

The present invention relates to a method for producing aluminum sulfate, water glass (sodium silicate) and white carbon from coal ash as described below.

(1) Sulfuric acid is added to coal ash mainly composed of SiO ₂ and Al ₂ O ₃ and heated. Aluminum sulfate is obtained from the filtrate of this reaction, and water glass (sodium silicate) is obtained from the filtration residue. , How to manufacture white car horn chemicals.

(2) A method for producing a chemical, wherein the aluminum sulfate, water glass (sodium silicate) and white carbon obtained by the reaction according to the above (1) are for papermaking. (3) The sulfuric acid used in the above (1) and (2) is waste sulfuric acid from a generator of chlorine dioxide which is a bleaching agent.
Manufacturing method of chemicals.

The coal ash to be treated in the present invention is:
Domestic, without distinction of imported coal, and the SiO ₂ and Al ₂ O ₃ produced by burning the ordinary coal ash as a main component, other components Fe, Ca, Ti, Mg, P, Na, It may contain K, V, Cd, Cu, Pb, S, C, and the like. In addition, as the shape of coal ash, fly ash, clinker, fluidized bed ash, etc. are all targets. Also, the type of coal boiler is not limited.

The aluminum sulfate, water glass (sodium silicate) and white carbonate obtained in the present invention are Al ₂ (SO ₄ ) ₃ and Na ₂ O · n, respectively.
SiO ₂ , a compound containing SiO ₂ as a main component, and other impurities may be present.

As the sulfuric acid used in the present invention, there can be used sulfuric acid which is a general industrial chemical, and waste sulfuric acid coming out of a chlorine dioxide generator which is a bleaching agent in a bleaching step of paper varnish.

In the present invention, first, sulfuric acid is added to coal ash in order to dissolve Al ₂ O ₃ in the coal ash. Normal aluminum silicate clay minerals mainly composed of SiO ₂ and Al ₂ O ₃ have a dense crystal structure, so it is difficult to easily dissolve Al ₂ O ₃ even with sulfuric acid, but coal ash is Since it is ash in petrified plants, it is amorphous, and Al ₂ O ₃ can be easily dissolved by addition of sulfuric acid. Al ₂ O ₃ , one of the main components of coal ash, becomes Al ₂ (SO ₄ ) _{3 by} the reaction with sulfuric acid, and dissolves in the liquid. At this time, Fe, Ca, Mg, Na, K, etc. which are soluble in the sulfuric acid solution also dissolve in the solution. In this state, filtration is performed to separate the filtrate into a residue.

Regarding the method of adding sulfuric acid, concentrated sulfuric acid and water may be mixed in advance, and coal ash may be added to the diluted solution. The conditions in this case are as follows. To avoid bumping due to heat of dilution, the sulfuric acid concentration needs to be 50% by weight or less. When waste sulfuric acid from the chlorine dioxide generator is used, the concentration of sulfuric acid is not particularly limited because the temperature of the liquid has already been lowered in the generator. The addition ratio of sulfuric acid (pure content) to coal ash is preferably 20% or more, and more preferably 20 to 100% by weight. Elution of Al ₂ O _{3 and the} like with sulfuric acid is performed under stirring. Elution time is 1-5
Time is preferred.

After adding and mixing coal ash to water to form a slurry, concentrated sulfuric acid may be added. The conditions in this case are as follows. The concentration of coal ash slurry must be less than 50% by weight. If it exceeds 50% by weight, the coal ash slurry becomes highly viscous, and as a result of insufficient stirring, Al ₂ O
Elution of ₃ etc. becomes insufficient. Sulfuric acid for coal ash (pure)
Is preferably 20% by weight or more, more preferably 20 to 100% by weight. The elution time is preferably 1 to 5 hours.

The main component of the filtrate after the reaction between coal ash and sulfuric acid is aluminum sulfate, but contains other impurities. This filtrate can be used as a coagulant for coagulation and sedimentation of wastewater, for example, without problems even if it contains impurities.

Further, after removing impurities by a purification treatment described later, the Al component is taken out as Al (OH) ₃ , and is further purified into aluminum sulfate by reaction with sulfuric acid. It can be used as a fixing agent for Sais II agent. 2Al (OH) ₃ + 3H ₂ SO ₄ → Al ₂ (SO ₄ ) ₃ + 6H ₂ O A specific method of the purification treatment is described below. Of the impurities, a particular problem is Fe which causes coloring. When Fe is present, it is gradually oxidized to produce a colored compound of iron oxide. Therefore, from the filtrate obtained by treating coal ash with sulfuric acid, Fe content and
It is necessary to separate the Al content. Formation pH of Fe (OH) ₃ and Al (OH) ₃
Is different from the sulfuric acid filtrate,
Al content can be separated. However, divalent Fe is contained in the filtrate.
The presence of ions makes it difficult to separate Fe and Al because the production pHs of Fe (OH) ₂ and Al (OH) ₃ are close to each other. For this reason, an oxidizing agent is added to the filtrate to convert divalent Fe ions into trivalent Fe ions. NaOH is added to the sulfated filtrate containing trivalent Fe ions, Al ions, and other metal ions, and the pH is maintained at 3.0 to 3.9.
(OH) ₃ precipitates. Desirably, pH = 3.1-3.8. This precipitate is removed by filtration or the like to obtain a liquid containing no Fe component.

When NaOH is further added to the solution and the pH is maintained at 4.0 to 10.5, Al (OH) ₃ precipitates. Desirably pH = 4.5
~ 9.0 is preferred. This precipitate can be separated to obtain Al (OH) ₃ containing no other impurities. Sulfuric acid was added to the Al (OH) _3, to obtain the Al ₂ (SO _{4) 3} was purified. The ratio of sulfuric acid to Al (OH) ₃ is preferably 1.0 to 1.2 molar ratio.

The oxidizing agent to be added is preferably oxygen, oxygen, hydrogen peroxide, chloric acid, hypochlorous acid or the like. Mangan dioxide,
Other oxides such as permancapnic acid and chromic acid are not preferred because the reaction solution is colored.

On the other hand, the residue is obtained by neutralizing the remaining H ₂ SO ₄ with NaOH.
Filter again and dry. The main components of this residue are SiO ₂ insoluble in sulfuric acid and unburned carbon generated in the boiler furnace. From the residue, cullet can be produced through a dry production process similar to the existing technology for producing cullet (solid sodium silicate) from silica sand. That is, this residue is mixed with a sorter ash, put into a melting furnace and heated with heavy oil or electric power (1300-1500 ° C),
It is completely melted, taken out, cooled and solidified to obtain cullet. During high-temperature melting, the unburned carbon dioxide in the residue is completely burned and CO ₂
Becomes a gas and is released to the atmosphere. The addition ratio of the residue to the sorter ash is preferably 2.1 to 3.5 mol ratio, similarly to the commercially available cullet. Na ₂ CO ₃ + nSiO ₂ → Na ₂ O · nSiO ₂ + CO ₂ n = 2.1 to 3.5 The cullet and water are placed in a low-pressure autoclave and heated to produce a water glass (liquid sodium silicate). The conditions of the autoclave are as follows: pressure 2.5 to 5.0 kg / m ² , temperature 110 to 250
C. and a treatment time of 40 to 120 minutes are preferred.

In addition, white carbon is obtained by an existing technique (dry method) of pulverizing cullet with a pulverizer. As the pulverizer, a ball mill, a sunscreen liner or the like can be used. From water glass, white carbon can be manufactured by the existing technology (wet process). That is, an inorganic acid such as sulfuric acid is added to a water glass to decompose it, followed by pulverization, filtration, washing with water and drying to obtain a white carbon. However, in the production of white car horn on-site,
The drying step can be omitted. The reaction formula is as follows. Na ₂ CTAB specific surface area of the _{O · nSiO 2 + H 2 SO} 4 → nSiO 2 + Na 2 SO 4 + H 2 O White car Ho Bu emissions may have 100 to 500 m ² / g, especially 150~350m ² / g is desirable. Aluminum sulfate obtained in the present invention is a flocculant and size fixing agent in the paper balm industry, a mordant,
Can be used for applications such as water purification.

The water glass (sodium silicate) obtained in the present invention is
It can be used in the paper balm industry, such as deinking agents, adhesives for corrugated wheels, soap additives, glass molding agents for castings, acid-resistant cement, fire-resistant mortar, water softeners, raw materials for silica gel, and water purifiers.

The white carbon obtained by the present invention can be used in the paper balm industry, as a filler in white paper (especially synthetic comb), a pigment suspending agent, a dispersant, a quenching agent, a matting agent, and a pesticide. Agent, Chris viscosity regulator, plastic filler, toothpaste, printing ink, paint, etc.

[0034]

EXAMPLES Example 1 Table 1 shows the chemical composition of the coal ash tested.

[0035]

[Table 1]

The following is an experimental example of obtaining aluminum sulfate, cullet, water glass, and white carbon using the coal ash of Table 1 as a starting material. 100 g of commercially available concentrated sulfuric acid (98% product) and 120 g of water are mixed to obtain a solution having a sulfuric acid concentration of 45%. 180 g of coal ash shown in Table 1 is added to the diluted sulfuric acid solution. At this time, the concentration of coal ash in the slurry was 45% by weight. The coal ash slurry is kept under stirring for 5 hours to perform an elution treatment. After completion of the elution treatment, the mixture is filtered through No. 5C filter paper to obtain a residue (1) and a filtrate (1-1).

After the residue (1) was dried, it was ashed at 975 ° C. for 2 hours, and the amount of unburned carbon was measured. Hydrofluoric acid was added to the residue to decompose metals such as SiO ₂ in the residue, and the metal concentration was measured with an atomic absorption spectrophotometer.

The residue (1) was dried after neutralization.
52 g of Na ₂ CO ₃ was added to 00 g, and the mixture was heated and melted at 1400 ° C. for 1 hour in an electric melting furnace. The melt was cooled to obtain cullet (1). Cullet
(1) 100 g and water (75 g) were put into a low-pressure autoclave, steam was blown therein, the pressure was kept at 4.0 kg / m ² , the temperature was kept at 150 ° C. for 1 hour, and then blown to obtain a water glass (1) weight of 50%. The cullet (1) was subjected to a dry pulverizer to obtain a white carbon (1-A). Concentrated sulfuric acid in 100 g of water glass (1)
(98% by weight) was gradually added to obtain white carbon (1-B).
The CTAB specific surface area of the obtained white carbonate was measured.

After adding hydrogen peroxide to the filtrate (1-1), the pH was adjusted to 3.5 by adding NaOH, and the brown precipitate of Fe (OH) ₃ formed was filtered through N0.5C filter paper. 1-2) was obtained. N in the filtrate (1-2)
aOH was added and the resulting white precipitate of Al (OH) ₃ was filtered through NO.5C filter paper. Equimolar sulfuric acid was added to the Al (OH) ₃ which are separated by the filter paper, the precipitate was dissolved in Al (OH) _3, to obtain an aluminum sulfate (1).
The metal concentration in the obtained aluminum sulfate solution was measured with an atomic absorption spectrophotometer.

[0040]

[Table 2]

(Coagulation and sedimentation test of wastewater) Filtrate (1-1) or a commercial product of aluminum sulfate (manufactured by Nippon Light Metal Co., Ltd.) was added to the wastewater of a paper factory, and after coagulation and sedimentation treatment, the COD of the supernatant was measured. And the performance as a flocculant was compared. Table 3 shows the results.
Shown in The performance of the filtrate (1-1) as a flocculant is equivalent to that of a commercial product. Untreated wastewater: pH = 8.4, COD = 89ppm Filtrate (1-1), aluminum sulfate addition rate: 500 ppm as Al ₂ O ₃
(For drainage)

[0042]

[Table 3]

(Fixing test of Saisei agent) CSF = 400 ml of hardwood bleached varnish (hereinafter referred to as L-BKP) and a pulp made of talc (valve / talc = 75% by weight / 25% by weight) and aluminum sulfate (1) Or a commercially available aluminum sulfate product (manufactured by Nippon Light Metal Co., Ltd.) was added and mixed, and then a rosin sizing agent was added. Using this stock, basis weight 64
g / m ² paper was hand-manufactured, the size of the paper was measured and compared, and the fixing of the size agent was compared. The results are shown in Table-4. Aluminum sulfate (1), which uses coal ash as a starting material, has the same sizing agent fixing performance as a commercial product. Addition rate of rosin sizing agent: 0.3% by weight (based on stock) Addition rate of aluminum sulfate: 1.0% by weight (based on stock)

[0044]

[Table 4]

(Deinking test of waste paper) Newspaper waste paper is dissolved in water, and NaOH, hydrogen peroxide and a higher alcohol-based surfactant are added thereto. Further, a water glass (1) or a commercially available water glass No. 3 (manufactured by Hokkaido Soda Co., Ltd.) was added, and the newspaper ink was separated using a flotation tester. The whiteness of the completed deinking half was measured and the deinking performance was compared. The results are shown in Table-5. The deinking performance of the water glass (1) is equivalent to that of the commercially available water glass No. 3. NaOH addition rate: 2.0% by weight (vs. used paper) Hydrogen peroxide addition rate: 2.0% by weight (vs. used paper) Higher alcohol-based surfactant addition rate: 0.5% by weight (vs. used paper) Water glass (1), commercial water glass 3 No. addition rate: 0.5% by weight (vs. used paper)

[0046]

[Table 5]

(Making of newsprint paper) A raw material for newsprint consisting of newspaper deinking jars / thermomechanical jars / softwood kraft jars = 60/30/10 (weight%) was prepared using white carbon (1-A) or white Car horn (1-B) or commercially available white car horn (Heobo Chemical Co., Ltd.
# 55) was added in an amount of 1.0% by weight (based on raw materials), and an ultralight newsprint having a basis weight of 40 g / m ² was hand-made. The opacity of this paper was measured and the opacity improving effect was compared. The results are shown in Table-6. The effect of improving the opacity of a wort carphone made from coal ash is
It is equivalent to a commercially available white car phone. CTAB specific surface area of test white car phone (1-A): 240 m ² / g (1-B): 267 Commercial product: 260

[0048]

[Table 6]

Example 2 In place of commercially available concentrated sulfuric acid, 204 g of waste sulfuric acid and 14 g of water were used, using waste sulfuric acid from a ClO ₂ generator (R2P method) manufactured by Nippon Carlit Co., Ltd.
The mixture was mixed to obtain a solution having a sulfuric acid concentration of 45%, and the same experiment as in Example 1 was performed. The residue (2), filtrate (2-1), filtrate (2-2), cullet (2), and water Crow (2), White car phone (2-A), White car phone (2-B)
I got

Table 7 shows the chemical composition of the waste sulfuric acid. Residue
Table 2 shows the chemical compositions of (2), filtrate (2-1), filtrate (2-2), cullet (2), water glass (2), white carbon (2-A), and white carbon (2-B). FIG.

[0051]

[Table 7]

[0052]

[Table 8]

(Effluent Coagulation Sedimentation Treatment) The same treatment as in Example 1 was performed. The results are shown in Table-9. The performance of the filtrate (2-1) as a flocculant is equivalent to that of a commercially available product.

[0054]

[Table 9]

(Fixing Test of Size II Agent) The same test as in Example 1 was conducted. The results are shown in Table-10. The fixing ability of the aluminum sulfate (2) for the sizing agent is equivalent to that of a commercially available aluminum sulfate.

[0056]

[Table 10]

(Deinking Test of Used Paper) The same test as in Example 1 was performed. The results are shown in Table-11. The deinking performance of the water glass (2) is equivalent to that of the commercially available water glass No. 3.

[0058]

[Table 11]

(Newspaper Paper Making Test) The same test as in Example 1 was conducted. The results are shown in Table-12. White car phone (2-A),
The effect of improving the opacity of the white car phone (2-B) is equivalent to that of a commercially available white car phone.

[0060]

[Table 12]

[0061]

According to the present invention, coal ash, which is conventionally treated as industrial waste and is expected to increase in the future, is regarded as a secondary resource mainly composed of SiO ₂ and Al ₂ O ₃ , An object of the present invention is to provide a method for industrially producing aluminum sulfate, water glass (sodium silicate), and white carbon, which are valuable resources.

This is a highly practical technology that not only benefits Japan, which relies on imports for most of its resources, but also contributes to global environmental protection through the use of coal ash.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Minoru Matsubara Minoru Matsubara 143 Yufutsu, Tomakomai-shi, Hokkaido F-term in the Yufutsu Mill of Nippon Paper Industries Co., Ltd. 4D004 AA36 BA09 CA13 CA22 CA34 CA35 CA36 CA41 CA42 CC11 CC12 4G072 AA28 CC13 GG01 GG03 HH40 JJ15 MM01 UU25 4G073 CB09 FB18 FC01 UB21 4G076 AA14 AB28 BA25 DA30

Claims (3)

[Claims] 1. Coal ash containing SiO ₂ and Al ₂ O ₃ as main components is heated by adding sulfuric acid to produce a chemical of aluminum sulfate from a filtrate of the reaction and / or water from a filtration residue. A method for producing glass or white carbohydrate chemicals. 2. The method for producing a chemical according to claim 1, wherein the aluminum sulfate, water glass, or white carbon obtained by the reaction is used for papermaking. 3. The method for producing a chemical according to claim 1, wherein the sulfuric acid is waste sulfuric acid from a generator of chlorine dioxide, which is a halogen bleaching agent.