JPH0910773A - Treatment of waste acid - Google Patents

Abstract

PURPOSE: To efficiently form sulfur oxide to recover the same, in a method mixing and reacting iron oxide with waste acid in the case of the treatment of waste acid containing org. matter and a sulfate group to obtain a solid product and heating the solid product to form sulfur oxide and heating the residue to higher temp., by specifying heating temps. in respective processes. CONSTITUTION: When waste acid containing org. matter and a sulfate group and/or a bisulfate group is treated, at first, iron oxide is mixed with the waste acid containing the org. matter and the sulfate group and/or the bisulfate group to be reacted therewith in a process (i). The solid product obtained in the process (i) is heated to 550-750 deg.C in a process (ii) to form sulfur oxide. The residue in the process (ii) is heated to 800 deg.C) in a process (iii). At this time, iron oxide regenerated in the process (iii) is circulated to the process (i) to be used and the content of sulfur trioxide in sulfur oxide formed in the process (ii) is set to 70% or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for treating an organic substance and a waste acid containing a sulfuric acid group and / or a bisulfate group. In the case of the treatment method of the present invention, the organic substance contained in the waste acid is completely removed. In addition, it can be removed smoothly and smoothly, and the sulfur oxide mainly consisting of sulfur trioxide can be efficiently produced and recovered from the waste acid, and the sulfur oxide produced thereby can be absorbed by water or sulfuric acid. By this, sulfuric acid or concentrated sulfuric acid can be efficiently formed.

[0002]

2. Description of the Related Art Effluents discharged from the process of treating organic compounds with sulfuric acid such as the ε-caprolactam manufacturing industry and the acetone cyanohydrin method methyl methacrylate manufacturing industry, petroleum refining waste liquid, and flue gas desulfurization treatment. In the waste liquid usually called "waste acid" such as waste liquid,
It contains a large amount of organic substances, sulfate groups and bisulfate groups. As a treatment method of the waste acid as described above, conventionally, there is a method of neutralizing the waste acid with ammonia to form ammonium sulfate (ammonium sulfate), a method of neutralizing the waste acid by adding an alkali such as sodium hydroxide. Are known. And in that case, ammonium sulfate produced by neutralization with ammonia is mainly used as a fertilizer, but in recent years, ammonium sulfate has become over-supplied, and its handling has been difficult. Sulfate obtained by neutralization with alkali such as sodium hydroxide is subjected to heat treatment to generate sulfur oxides, and the sulfur oxides produced there are mainly recovered from sulfur dioxide. Therefore, it is necessary to further oxidize the generated sulfur oxides into sulfur trioxide, and to absorb it into water or sulfuric acid to form sulfuric acid or concentrated sulfuric acid, which increases the number of steps and requires more equipment. There is a problem that it becomes complicated and large.

[0003]

The object of the present invention is to obtain ε-
Waste liquor discharged from the process of treating organic compounds with sulfuric acid, such as the caprolactam manufacturing industry and the acetone cyanohydrin method methyl methacrylate manufacturing industry, petroleum refining waste liquor, waste liquor discharged from flue gas desulfurization, and other organic substances It is possible to smoothly and efficiently generate and recover sulfur oxides mainly composed of sulfur trioxide from a waste liquid containing sulfuric acid groups and / or bisulfate groups (that is, a waste liquid called “waste acid”). Accordingly, it is an object of the present invention to provide a waste acid treatment method capable of omitting a process or equipment for oxidizing sulfur dioxide to sulfur trioxide and downsizing the apparatus. It is an object of the present invention to provide a waste acid treatment method capable of completely and smoothly carrying out the organic matter contained in the waste acid at the same time as the production of sulfur oxides mainly consisting of sulfur trioxide.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted various studies to achieve the above object, and mixed iron oxide with waste acid containing an organic substance and a sulfate group and / or a bisulfate group, When the solid product thus obtained is subjected to heat treatment in two steps at a specific temperature, sulfur oxide having a very high content of sulfur trioxide can be efficiently produced and recovered, and moreover, it is contained in the waste acid. The present invention has been completed by finding out that the removal of the organic substances that are present can be completely achieved.

That is, the present invention relates to a method for treating a waste acid containing an organic substance and a sulfate group and / or a bisulfate group, which comprises (i) a waste acid containing an organic substance and a sulfate group and / or a bisulfate group. And (ii) a step of heat-treating the solid product obtained in the above step (i) at a temperature of 550 to 750 ° C. to produce sulfur oxides; and ( iii) The above step (i
i) a step of heat-treating the residue at a temperature of 800 ° C. or higher;

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The present invention is a method for treating a waste acid containing an organic substance and a sulfate group and / or a bisulfate group, which is referred to herein as "a waste acid containing an organic substance and a sulfate group and / or a bisulfate group" (hereinafter This may be simply referred to as "waste acid") means a waste (exhaust) containing at least one of a sulfate group and a bisulfate group as an acid component together with an organic substance,
The waste acid may be in any form such as waste liquid (liquid substance), its concentrate, slurry, paste, and solid substance. Also,
The discharge source (source) of the waste acid is not limited at all, and may be discharged from any of a chemical plant, a petroleum refinery, various flue gas desulfurization facilities, and other facilities.

Further, the kind and amount of the organic substances contained in the waste acid are not particularly limited. Furthermore, the sulfate group and bisulfate group contained in the waste acid may be in the form of ions such as sulfate ion and bisulfate ion, or in the form of salt such as sulfate and bisulfate. Alternatively, it may be in the form of an acid such as sulfuric acid or bisulfate, and the existing forms of the sulfate group and the bisulfate group in the waste acid are not limited at all. Further, the content of the sulfate group and / or the bisulfate group in the waste acid is not particularly limited. Further, the waste acid may contain other inorganic substances in addition to the organic substance and the sulfate group and / or the bisulfate group.

Although not limited, examples of waste acids to which the treatment method of the present invention can be applied smoothly include the above-mentioned ε-caprolactam production industry and the acetone cyanohydrin method methyl methacrylate production industry. Such as waste liquid discharged from the process of treating organic compounds with sulfuric acid, organic waste discharged from petroleum refining and waste containing sulfuric acid groups and / or bisulfate groups, organic waste discharged from flue gas desulfurization and sulfuric acid Liquids containing radicals and / or bisulfate groups, concentrated liquids of these waste liquids, slurries, pastes, solids, etc. containing organic substances and sulfate groups and / or bisulfate groups recovered from these waste liquids can be mentioned. .

Further, in the present invention, in step (i), iron oxide is mixed or mixed / reacted with an organic substance and a waste acid containing a sulfate group and / or a bisulfate group. As the iron oxide used in this step (i), ferrous oxide which is an oxide of divalent iron, ferric oxide which is an oxide of trivalent iron,
It is possible to use iron oxide (Fe ₃ O ₄ ) containing both divalent iron and trivalent iron, a mixture of two or more of the above-mentioned iron oxides, and the like. Among them, ferric oxide or a mixture of ferric oxide and ferrous oxide is used to smoothly generate sulfur oxide having a high sulfur trioxide content in the next step (ii). It is preferable because it can

The iron oxide used in the step (i) does not necessarily have to be of high purity, and low purity iron oxide can be used. Generally, any iron oxide having a purity of about 60% or more can be used smoothly. . Further, the manufacturing method, particle size, crystal morphology, etc. of the iron oxide used in step (i) are not particularly limited. By the way, as will be described later, in the case of the method of the present invention, iron oxide is regenerated as a residue after the heat treatment in step (iii), but a part of the iron oxide regenerated in step (iii) or If the whole amount, preferably the whole amount, is repeatedly circulated in this step (i) and repeatedly used, the treatment of the present invention can be carried out very efficiently and economically while suppressing the addition of new iron oxide from the outside. It is desirable because it can be implemented.

In the step (i), the amount of iron oxide mixed with the waste acid can be adjusted according to the content of the sulfate group or bisulfate group contained in the waste acid, the type of the waste acid, and the like. However, it is generally desirable to mix an amount of iron oxide satisfying the following formula with the waste acid because the content of sulfur trioxide in the sulfur oxide produced in the next step (ii) can be further increased.

[0012]

## EQU00002 ## A / B.gtoreq.1.5 In the formula, A = the number of moles obtained by converting the amount of iron oxide used in step (i) into iron atoms. B = the total of sulfate groups and bisulfate groups contained in the waste acid. Number of moles

If the amount of iron oxide used in step (i) is lower than that in the above formula (that is, A / B is less than 1.5), the amount of iron oxide in the sulfur oxide produced in the next step (ii) is three. The content ratio of sulfur oxide tends to be low. In the treatment method of the present invention, the value of A / B in the above formula is set to 2.0 or more so that the content ratio of sulfur trioxide in the sulfur oxide formed in step (ii) can be further increased. It is more preferable because it can. Although the upper limit of A / B in the above formula is not particularly limited, it is preferable to set A / B to 5 or less from the viewpoint of effectively using iron oxide without waste and further preventing heat loss. .

The mixing method of the waste acid and the iron oxide in the step (i) is not particularly limited, and for example, the waste acid in a liquid, paste, slurry or solid state and the solid (powder) iron oxide can be used as they are. Method of mixing; liquid, paste, slurry,
Examples thereof include a method of mixing waste acid in a solid state and iron oxide dispersed in a liquid medium such as water. Among them, it is preferable to mix at least one of the waste acid and the iron oxide in a liquid or slurry form so that the waste acid and the iron oxide can be mixed uniformly.

The mixing temperature of the waste acid and the iron oxide in the step (i) is not particularly limited, and it can be usually performed at a temperature of about room temperature to 250 ° C., but the mixing of the step (i) is performed under heating ( Preferably at a temperature of 100 to 150 ° C.), in step (i), a reaction between the sulfate group and / or bisulfate group contained in the waste acid and iron oxide occurs to give iron sulfate,
A salt such as iron bisulfate is formed, so that in the next step (ii), the production of sulfur oxide is performed more smoothly. In performing the mixing in the step (i) under heating, the mixing device may be heated, but the iron oxide regenerated by the heat treatment in the step (iii) described below is kept in the hot state in the step (i). When it is circulated and used, the process of step (i) can be carried out under heating without external heating due to the heat of iron oxide or while keeping external heating to a minimum, so that thermal efficiency, etc. It is also desirable from the point of.

Next, the solid product obtained by the above-mentioned step (i) is added in step (ii) to 550-750.
C., preferably 600 to 650.degree. C., is heat treated to form sulfur oxides. When the heat treatment temperature in this step (ii) is less than 550 ° C, it takes a long time to form the sulfur oxide, and the sulfur oxide is not smoothly generated. On the other hand, when it exceeds 750 ° C, the sulfur oxide is not contained in the sulfur oxide. Since the content ratio of sulfur trioxide is decreased, it becomes impossible to smoothly recover sulfur oxide as sulfuric acid or concentrated sulfuric acid. Moreover, if the heat treatment in the step (ii) is performed at a temperature higher than 750 ° C., the device will be consumed quickly, and it is uneconomical in terms of fuel consumption. When performing the step (ii), if the solid product obtained in the step (i) is a paste-like material, a slurry-like material, or a solid-like material having a low liquid content, they are not deliquored. Can be used as it is in step (ii) for heat treatment. When the product obtained in step (i) is a slurry or dispersion having a high liquid content, it is necessary to remove liquid to reduce the liquid content and then perform the heat treatment in step (ii) to improve thermal efficiency and reaction time. Is preferable in terms of shortening The deliquoring method for deliquoring the product obtained in the step (i) is not particularly limited, and an appropriate method such as filtration, decantation, centrifugation or sedimentation can be employed.

The main reaction that takes place during the heat treatment in this step (ii) is the reaction of forming iron oxide and sulfur oxides due to the thermal decomposition of iron sulfate, and as a result of such reaction, this step Sulfur oxide is formed in (ii). In the present invention, it is desirable that the heat treatment in step (ii) is carried out while supplying an oxidizing gas such as air or oxygen gas, whereby the sulfur oxide contained in the sulfur oxide produced in step (ii) is contained. The rate can be increased. At that time, the oxygen concentration in the reaction system of the step (ii) can be adjusted according to each situation, but if the oxygen concentration in the system is set to 10% or more, sulfur oxidation having a high sulfur trioxide content is obtained. It is more desirable because it can generate things.

According to the present invention, in this step (ii), a gas containing a large amount of sulfur trioxide and a small amount of sulfur dioxide and having a high sulfur trioxide content is produced, and in this step (ii), a gas is usually produced. The content ratio of sulfur trioxide in the sulfur oxide contained in the generated gas is 70% or more. That is, as described in the Examples section below,
SO ₃ selectivity is 70% or more. Therefore, a gas having a high sulfur trioxide content produced in this step (ii) is passed through water or sulfuric acid so that most of the sulfur trioxide in the gas and a predetermined amount (dissolved amount) of sulfur dioxide (SO ₂ ) are contained. When absorbed in water or sulfuric acid, preferably sulfuric acid, sulfuric acid or concentrated sulfuric acid is formed, and the sulfur oxide generated in step (ii) can be recovered very easily and efficiently. The sulfur dioxide that is discharged without being absorbed by water or sulfuric acid may be treated with a conventionally known desulfurization device, or may be recovered by adding ammonia to obtain ammonium sulfate (ammonium sulfate). In any case, according to the method of the present invention,
Since the amount of sulfur dioxide discharged out of the system is small,
It is possible to downsize the desulfurization equipment, downsize the manufacturing equipment for ammonium sulfate, and reduce the amount of ammonia used for manufacturing ammonium sulfate.

By the heat treatment in this step (ii), various decomposed gases derived from organic substances contained in the waste acid together with sulfur oxides, and the heat treatment in this step (ii) can be performed with air or oxygen gas. When oxidizing gas is used, those oxidizing gases may be discharged at the same time. In that case, if the difference in solubility between sulfur oxide and other gases such as water and sulfuric acid is used, , Sulfur oxides can be selectively separated from other gases and recovered.

Next, in the present invention, the residue obtained after the sulfur oxide is generated in the above step (ii) is treated with the step (iii).
At 800 ° C. or higher, heat treatment is performed. The organic substances contained in the waste acid may be partially decomposed and gasified in the above step (ii) and discharged together with the sulfur oxide gas, but the heat treatment in the step (ii) In many cases, it is not completely decomposed and remains as a solid or carbonized and remains. In the present invention, the residue produced in step (ii) is heat-treated at a temperature of 800 ° C. or higher in step (iii) to completely decompose or burn the organic matter and its carbides attached to the residual portion. Can be removed. The temperature of the heat treatment in step (iii) is 8
The temperature may be 00 ° C. or higher, and the upper limit temperature is not particularly limited, but the temperature is preferably 800 to 1100 ° C. from the viewpoint of thermal efficiency, corrosion prevention of the device, improvement of durability, and the like.

The heat treatment in step (iii) may be carried out by simply heating the residual portion from step (ii) to a temperature of 800 ° C. or higher as it is, but under the supply of an oxidizing gas such as air or oxygen gas. And / or while supplying fuel such as heavy oil, it is possible to more completely decompose and combust the remaining organic substances and their carbides.
desirable.

The gas discharged by the heat treatment in the step (iii) is subjected to an appropriate exhaust gas purification treatment known in the related art or in the exhaust gas, depending on the kind and amount of the components contained in the exhaust gas. If no harmful substances are contained, they can be directly discharged into the atmosphere. For example, the process (ii
If the exhaust gas from i) contains only harmless substances such as carbon dioxide and water vapor, it can be directly discharged into the atmosphere, and the exhaust gas from step (iii) If a component regulated by law is included, remove it before purifying it before discharging.

Then, the above step (ii
After the heat treatment of i), a solid substance remains, but this solid substance mainly consists of iron oxide, and there is almost no residue of organic matter or its carbide in the iron oxide, and the sulfate group or bisulfate is present. Has excellent reactivity with groups. Therefore, if a part or all, preferably all, of the (regenerated) iron oxide produced in step (iii) is circulated to step (i) and repeatedly used, iron oxide newly added from the outside is added. It is possible to reduce the amount of waste iron, and it is possible to perform the above-described series of treatment steps of the present invention extremely smoothly and without waste and at low cost while preventing the use of useless iron oxide. In that case, as described above, the step (ii
When the iron oxide generated (regenerated) in i) is recirculated to the step (i) in a hot state, the mixed system of the step (i) is heated by the heat of the iron oxide and is heated without external heat or external heat. The step (i) can be smoothly carried out while reducing heating from the above, which is extremely advantageous in terms of thermal efficiency and the like. Although not limited thereto, when a series of steps of the present invention described above is shown in the drawings, a step diagram as shown in FIG. 1 can be given, for example. In addition, in FIG. 1, a solid line or a portion indicated by a solid arrow means the above-described steps (i) to (iii) in the present invention, and a portion indicated by a dotted arrow means an arbitrary step.

As long as the above-mentioned steps (i) to (iii) are adopted, the present invention may be carried out in any form and operation, and the reaction form, kind of reactor, structure, scale, etc. are not limited at all. . That is, the method of the present invention may be carried out batchwise or continuously. Also, for example, even if the step (i) is carried out by one apparatus and the step (ii) and the step (iii) are carried out by using one apparatus equipped with a heating means different from them, the steps (i) to (Iii) may be performed using different devices. Further, examples of the apparatus that can be used in the present invention include a batch type or continuous type rotary furnace, a tunnel furnace, a muffle furnace, a rotary kiln, and the like, and in the case of large-scale operation, a rotary kiln or the like is preferably used.

The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. In the following examples, the selectivity of sulfur trioxide (SO ₃ selectivity) in the gas obtained (exhausted) in step (ii) means the value obtained by the following formula.

[0027]

## EQU00003 ## SO ₃ selectivity (%) = {D / (C + D)} × 100 where C = sulfur dioxide (SO ₂ ) concentration (%) in the product gas (exhaust gas) of step (ii) , or the concentration of SO ₃ ^2-amount of water imbibed with the product gas (moles) D = sulfur trioxide in the product gas (exhaust gas) in step (ii) (SO ₃₎ (%), or the product SO ₄ ^2- amount (mol) in water that has absorbed gas

Example 1 (1) Iron oxide (particle size 100 μm to 1 mm; in a stainless steel first rotary furnace having an inner diameter of 780 mm and a length of 248 cm);
The waste acid discharged from the pickling step in the plating industry [sulfate ion content 58%; organic matter content, while supplying iron oxide regenerated in the third rotary furnace described below, which was circulated) at a rate of 42 kg / hr. (Total organic carbon content "TOC")
3.2%] was supplied at a flow rate of 50 kg / hr for reaction. Note that A / B =
2.1 (that is, the ratio of the number of moles of iron oxide converted to iron atoms / the mole of sulfuric acid group is 2.1), and the average residence time of waste acid and iron oxide in the first rotary furnace is It was 30 minutes. (2) Then, the slurry-like product obtained in (1) above is continuously supplied as it is to a stainless steel externally heated second rotary furnace having an inner diameter of 128 cm and a length of 268 cm without deliquoring. While further supplying air at a flow rate of 15 m ³ / min, the maximum temperature in the furnace is 650 ° C, the outlet temperature in the furnace is 600 ° C,
Heat treatment (roasting treatment) was performed with an average residence time of 80 minutes. The composition of the gas discharged from the outlet of the second rotary furnace is gas chromatograph ("GC-8AT" manufactured by Shimadzu Corporation)
When analyzed with, N ₂ 53%, O ₂ 13%, SO ₃
Is 32%, SO ₂ is 1.5%, and CO is 0.5%. Therefore, the SO ₃ selectivity of the exhaust gas determined by the above equation was 96%. (3) Next, the black solid residue (mainly composed of iron oxide) obtained in (2) above
It was continuously sent to a third rotating furnace made of stainless steel having a length of 8 cm and a length of 255 cm, and when heavy oil was supplied and burned under the conditions of a furnace temperature of 1000 ° C. and a residence time of 30 minutes, the color of the residue was black. Since it turned brown and the carbon adhering to the iron oxide was burned and removed, the whole amount of the brown iron oxide obtained thereby was circulated to the above (1) in a hot state, and the same process was repeated thereafter. ..

Example 2 (1) 50 ml of water and 80 g of ferric oxide were placed in a four-necked flask having an internal volume of 1 liter and equipped with a stirrer, and the mixture was heated to 80
Heated to ° C. Under stirring, 51.7 g of a sulfuric acid solution containing p-toluenesulfonic acid as an organic substance (p-toluenesulfonic acid content of 1.7 g in the sulfuric acid solution) was added and reacted for 15 minutes (the above-mentioned formula). A / B =
2.0). (2) Collect 45 g of the slurry obtained in the above (1), charge it into a quartz tube with an inner diameter of 40 mm without deliquoring it, put the quartz tube in an electric furnace, and add 100 ml of air.
The temperature is gradually raised while supplying at a flow rate of
Heat treatment was carried out at a temperature of 0 ° C. for 30 minutes, and the gas generated during this was absorbed by sequentially passing through three gas absorption tubes containing 100 ml of water connected in series. In addition, when the gas generated in this heat treatment process is passed through water, the waste gas discharged without being absorbed by water does not contain sulfur dioxide or sulfur trioxide. All of the sulfur dioxide and sulfur trioxide therein were absorbed by water.
Therefore, the amount of sulfate ions (SO ₄ ^2- ) and sulfite ions (SO ₃ ^2- ) contained in water absorbed with sulfur dioxide and sulfur trioxide were measured by ion chromatography ("2010 type" manufactured by Dionex). As a result of measurement, the amount of SO ₄ ²⁻ was 0.12 mol and the amount of SO ₃ ²⁻ was 0.01 mol. Therefore, the SO ₃ selectivity calculated by the above formula was 94%.

(3) In (2) above, the temperature of the electric furnace was raised to 900 ° C. and heat treatment was performed for 20 minutes while the black solid residue remaining in the quartz tube was put in the same quartz tube. When taken out, brown iron oxide powder 19.
6 g was obtained, and the organic substance and its carbide were completely removed from this iron oxide.

Comparative Example 1 The steps (1) to (3) of Example 2 were the same except that the heat treatment temperature was changed from 650 ° C. to 800 ° C. in the step (2) of Example 2. And the amount of sulfate ion (SO ₄ ²⁻ ) and sulfite ion (SO ₃ ²⁻ ) contained in water when the gas generated in the step (2) is passed through water ( When measured in the same manner as in 2), the SO ₄ ²⁻ content is 0.0
8 mol, the amount of SO ₃ ²⁻ was 0.11 mol, and the SO ₃ selectivity obtained by the above formula was a very low value of 40%. Therefore, from the result of Comparative Example 1, in the step [step (ii)] for generating the sulfur oxide, when the heat treatment temperature exceeds 750 ° C., the content ratio of sulfur trioxide in the generated sulfur oxide is high. It can be seen that is greatly reduced.

Example 3 (1) 100 ml of water and 80 g of ferric oxide were placed in a four-necked flask having an internal volume of 1 liter and equipped with a stirrer to obtain 8
The mixture was heated to 0 ° C., and 52.2 g of a sulfuric acid solution containing acetonedisulfonic acid as an organic substance (the content of acetonedisulfonic acid in the sulfuric acid solution was 2.2 g) was added thereto with stirring and reacted for 15 minutes (at this time). A / B = shown in the above formula
2.0). (2) 46 g of the slurry obtained in (1) above was sampled, charged into a quartz tube with an inner diameter of 40 mm as it was without deliquoring, put the quartz tube in an electric furnace, and air 100 ml.
The heat treatment was carried out at a temperature of 590 ° C. for 45 minutes while supplying the gas at a flow rate of / min, and the gas generated during this was absorbed by sequentially passing it through three gas absorption tubes having 100 ml of water connected in series. In addition, when the gas generated in this heat treatment process is passed through water, the waste gas discharged without being absorbed by water does not contain sulfur dioxide or sulfur trioxide. All of the sulfur dioxide and sulfur trioxide therein were absorbed by water. Therefore, the amount of sulfate ion (SO ₄ ^2- ) and the amount of sulfite ion (SO ₃ ^2- ) contained in water absorbed with sulfur dioxide and sulfur trioxide were measured by the same ion chromatography as that used in Example 2. As a result, the SO ₄ ²⁻ content was 0.19 mol, S
The amount of O ₃ ²⁻ was 0.01 mol, and S calculated by the above formula was used.
The O ₃ selectivity was 95%. (3) The black solid remaining in the quartz tube after the heat treatment of (2) above is left in the same quartz tube for 100 seconds.
When heat-treated at a temperature of 0 ° C. for 15 minutes, cooled and taken out from the quartz tube, 16 g of brown iron oxide powder was obtained.
Organic substances and their carbides were completely removed from this iron oxide.

[0033]

According to the treatment method of the present invention, from the organic matter and the waste acid containing the sulfate group and / or the bisulfate group,
Since sulfur oxides can be efficiently and smoothly produced and recovered, and the sulfur oxides produced by the method of the present invention have a high sulfur trioxide content (usually 70% or more) and a low sulfur dioxide content. By directly absorbing the generated sulfur oxides directly into water or sulfuric acid,
It can be recovered very easily and efficiently in the form of sulfuric acid or concentrated sulfuric acid. And in the case of the method of the present invention,
Since the content of sulfur dioxide in the generated sulfur oxide is low, it is possible to omit the process and equipment for oxidizing sulfur dioxide to sulfur trioxide, and to simplify the process and achieve miniaturization of equipment. it can. Further, according to the method of the present invention, the organic matter contained in the waste acid is completely or almost completely removed, and the final heat treatment step [step (iii)] regenerates the iron oxide containing no organic matter or its carbide. As a result, the regenerated iron oxide can be recycled to step (i) and used repeatedly, thereby preventing wasteful use of the iron oxide and containing organic substances and sulfate groups and / or bisulfate groups. Waste acids can be treated efficiently and economically.

[Brief description of the drawings]

FIG. 1 is a process chart illustrating a series of processes of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichi Tadokoro, No. 28 Kurashiki-cho, Nakajo-cho, Kitakanbara-gun, Niigata Prefecture Kuraray Co., Ltd.

Claims (5)

[Claims] 1. A method for treating a waste acid containing an organic substance and a sulfate group and / or a bisulfate group, comprising: (i) iron oxide with respect to a waste acid containing an organic substance and a sulfate group and / or a bisulfate group. (Ii) mixing the solid product obtained in the above step (i) with 550 to 750
Heat-treating at a temperature of ℃ to produce sulfur oxides; and (iii) removing the residue of step (ii) above from 80
A step of heat-treating at a temperature of 0 ° C. or higher; 2. The treatment method according to claim 1, wherein the iron oxide regenerated in step (iii) is recycled to step (i) for use. 3. The treatment method according to claim 1, wherein the content of sulfur trioxide in the sulfur oxide produced in step (ii) is 70% or more. 4. The proportion of iron oxide used in step (i) is calculated by the following formula; A / B ≧ 1.5 where A = iron oxide is the amount of iron oxide used in step (i) The number of moles converted into atoms B = the total number of moles of the sulfate group and the bisulfate group contained in the waste acid, and the treatment method according to any one of claims 1 to 3. 5. The treatment method according to claim 1, wherein the sulfur oxide produced in step (ii) is absorbed in water or sulfuric acid.