JP4195652B2 - Method for producing organochlorine compound remover - Google Patents

Description

  The present invention relates to a removal agent for organic chlorine compounds such as dioxins discharged from, for example, incineration facilities for municipal waste and industrial waste, steel electric furnaces and the like, and a method for producing the same.

  Conventionally, an adsorption method using activated carbon is generally performed as a method for reducing organic chlorine compounds such as dioxins generated in the combustion process. As an adsorption treatment method, an adsorption technique using a packed bed mainly using activated carbon or activated coke as an adsorbent and a powder adsorbent blowing technique have been put into practical use.

Further, instead of activated carbon, for example, a method for suppressing dioxins in a garbage incinerator using an iron oxide catalyst has been developed as disclosed in JP-A-11-267507 (see Patent Document 1). In this method, an iron oxide catalyst is blown into a combustion chamber or a reburning chamber of a garbage incinerator to suppress dioxins. The iron oxide used here is prepared from the reagent. For example, the goethite powder is a ferrous salt obtained by reacting with ferrous salt and one or more selected from alkali hydroxide, alkali carbonate, and ammonia. It can be obtained by producing goethite particles by passing an oxygen-containing gas such as air through a suspension containing an iron-containing precipitate. The hematite powder can be obtained by subjecting the goethite powder to heat dehydration in the temperature range of 200 to 800 ° C. in the air. Further, the magnetite powder is obtained by heating and reducing the hematite powder at 300 to 600 ° C. in a reducing atmosphere.
JP-A-11-267507

  In the case of the adsorption method using activated carbon, the treatment of activated carbon after adsorption of dioxins and the danger of a coal dust explosion are problems. These activated carbons adsorbing dioxins cannot be buried in landfills as waste. Therefore, high-temperature incineration that can decompose dioxins again is necessary. Even in the case of this high-temperature incineration, there is a danger that dioxins are generated again during the cooling process. In addition, it is generally known that dioxins are re-synthesized in a temperature range of 300 ° C. to 500 ° C., but there is a problem that there is a risk of a coal dust explosion if activated carbon powder is blown into this temperature range. .

Further, in the iron oxide catalyst of Patent Document 1 as described above, iron oxide is a chlorine or sulfur oxide as compared with a V ₂ O ₅ —TiO ₂ or V ₂ O ₅ —TiO ₂ —WO ₃ catalyst. The catalytic activity tends to decrease. For this reason, it cannot be used for a long time, and is used for a short time by being blown into the exhaust gas. However, in order to suppress dioxins, it is necessary to continuously blow into the exhaust gas. Moreover, since an iron oxide catalyst prepares a catalyst from a reagent through a complicated process as mentioned above, it becomes expensive. In the case of blowing such an expensive iron oxide catalyst, the used iron oxide catalyst is recovered together with dust and is poisoned by chlorine and sulfur oxides in the exhaust gas. Is discarded with dust. Furthermore, the iron oxide catalyst requires a temperature of 250 ° C. or higher in order to obtain an efficient decomposition activity, and if the blowing position is limited to the high temperature portion of the exhaust gas or the exhaust gas temperature is lower than 250 ° C., the exhaust gas Need to be heated, and the removal performance is not sufficient.
Then, an object of this invention is to provide the removal agent which removes organic chlorine compounds, such as cheap and high performance dioxins, and its manufacturing method.

The gist of the present invention is that
[1] Hydrochloric acid pickling waste liquid for hot-rolled steel sheet, sulfuric acid pickling waste liquid for hot-rolled steel sheet, and pickling process for steel sheet comprising one or more kinds of sulfuric acid pickling waste liquid for electrogalvanization process for chromate treatment The Fe ²⁺ in the effluent discharged from the reactor is oxidized to Fe ³⁺ , and the resulting ferric hydroxide and / or the composite hydroxide slurry of iron and chromium is filtered and dried to ferric hydroxide, And / or containing 70% or more of a composite hydroxide of iron and chromium, the specific surface area determined by the BET method is 150 m ² / g or more, and determined by the t-plot method against the specific surface area determined by the BET method. A method for producing an organochlorine compound remover in a gas, wherein a remover for the organochlorine compound in the gas having a specific surface area ratio of micropores having a pore radius of 1 nm or less is 70% or more .

[2] Hydrochloric acid pickling waste liquid for hot-rolled steel sheet, sulfuric acid pickling waste liquid for hot-rolled steel sheet, and pickling process for steel sheet made of one or more kinds of sulfuric acid pickling waste liquid for electrogalvanizing process for chromate treatment The Fe ²⁺ in the effluent discharged from the reactor is oxidized to Fe ³⁺ , and the resulting ferric hydroxide and / or iron and chromium composite hydroxide slurry is adjusted to pH 5-11 with an alkaline aqueous solution, and It is filtered and dried to contain 70% or more of ferric hydroxide and / or a composite hydroxide of iron and chromium, the specific surface area determined by the BET method is 150 m ² / g or more, and the BET method It is possible to obtain an organic chlorine compound remover in a gas in which the ratio of the specific surface area of micropores having a pore radius of 1 nm or less determined by the t-plot method with respect to the determined specific surface area is 70% or more. Organic chlorination of Method for producing a removing agent of the object.

[3] The organochlorine compound in the gas according to [1] or [2], wherein Fe ²⁺ in the waste liquid is oxidized to Fe ³⁺ using an oxidizing agent and / or iron-oxidizing bacteria . A method for producing a remover .

  If the method for producing an organic chlorine compound remover according to the present invention is used, an organic chlorine compound remover can be economically produced using a pickling waste liquid or the like, which is a byproduct of the iron making process, and the produced remover is Since the proportion of micropores is extremely large, dioxin and the like can be efficiently adsorbed and decomposed, and the excellent effect of sufficiently removing dioxin even when the exhaust gas temperature is low, which has been difficult with conventional iron oxide catalysts, is achieved.

  In order to adsorb and decompose organic chlorine compounds such as dioxins, dioxins can be used in a temperature range of 300 to 500 ° C., which has pores for adsorbing and dioxins are re-synthesized in exhaust gas. Substances that do not cause combustion are effective in suppressing resynthesis. The present invention has focused on iron hydroxide in view of the above characteristics. As a result of various investigations on substances containing iron hydroxide, it was found that the neutralized sludge generated from steelworks has a relatively high content of iron hydroxide.

The neutralized sludge is generally by-produced in a large amount as a by-product of a pickling process when manufacturing a cold-rolled steel sheet or a surface-treated steel sheet such as galvanized or tin-plated at an ironworks. When manufacturing cold-rolled steel sheets or surface-treated steel sheets such as galvanized or tin-plated, waste liquids such as hydrochloric acid and sulfuric acid are discharged as waste liquids for pickling and washing. These acidic waste liquids contain ferrous iron, zinc, tin, nickel, chromium and the like as metal ions, and particularly ferrous ions (Fe ²⁺ ) are contained in a larger amount than other metal ions. In order to discharge these wastewaters into public water bodies, metal ions and pH are removed or adjusted below the water quality of environmental regulations. As a prior art for this purpose, alkali coagulation precipitation is used. That is, when these acidic wastewaters are mixed, the pH becomes about 2 to 4, but thereafter, an alkaline agent such as slaked lime is added, the pH is maintained at 8 to 9, and a large amount of air is blown into the wastewater. Iron is oxidized to ferric hydroxide and precipitated. At the same time, zinc, nickel, chromium, etc. are precipitated as hydroxides. These precipitates are called neutralized sludge.

The neutralized sludge obtained by the prior art is composed mainly of ferric hydroxide, but has a small specific surface area and is not suitable as a removal agent for organic chlorine compounds such as dioxin.
Therefore, as a result of intensive development, the present inventors have reached the present invention. That is, the waste liquid resulting from the pickling process of steel sheet (hereinafter referred to as pickling waste liquid) is oxidized from divalent iron ions (Fe ²⁺ ) to trivalent iron ions (Fe ³⁺ ) in a state where pH adjustment is not performed (pH 2 to 4), Subsequently, it was discovered that fine iron hydroxide with a large specific surface area can be obtained by precipitation as ferric hydroxide. Methods for oxidizing divalent iron ions under conditions of pH 2-4 include chemical oxidation methods such as hydrogen peroxide and biological oxidation methods. If divalent iron ions can be oxidized under pH 2-4 conditions, The method may be used.

Hereinafter, the chemical oxidation method will be described. If a chemical (oxidizing agent) is used, oxidation from divalent iron ions (Fe ²⁺ ) to trivalent iron ions (Fe ³⁺ ) in a low pH region becomes possible. Examples of the oxidizing agent include hydrogen peroxide, hypochlorous acid, ozone, and calcium dioxide. When the oxidizing agent is reduced, divalent iron ions (Fe ²⁺ ) are oxidized to trivalent iron ions (Fe ³⁺ ). The reaction formula is as follows.

2Fe ²⁺ + H ₂ O ₂ + 2H ⁺ → 2Fe ³⁺ + 2H ₂ O
2Fe ²⁺ + NaOCl + 2H ₂ O → 2Fe ³⁺ + NaCl + 2OH ⁻
2Fe ²⁺ + O ₃ + 2H ⁺ → 2Fe ³⁺ + 2H ₂ O + O ₂
2Fe ²⁺ + CaO2 + H ₂ O → 2Fe ³⁺ + CaO + 2OH ⁻

  Specifically, by mixing and stirring an oxidizing agent having a concentration corresponding to the concentration of divalent iron ions in an iron oxidation tank filled with the waste liquid discharged from the pickling process, trivalent iron ions are converted into trivalent iron ions. Until stable oxidation to form an iron hydroxide slurry.

Moreover, as a bio-oxidation method, for example, there is a method using iron-oxidizing bacteria that are active at pH 2-4. That is, there is a method using an iron-oxidizing bacterium that grows using energy generated when oxidizing a divalent iron ion to a trivalent iron ion. Iron oxidizing bacteria are classified into neutral, filamentous bacteria and the acid-non-filamentous bacteria, bacteria to be used herein is the latter acidic and non-filamentous bacteria, for example, Chiobachirasu-ferrooxidans (Thiobachillus ferrooxidans) representative Bacteria. If waste water containing divalent iron ions is treated using iron oxidizing bacteria that have a pH of 2 to 4 and are active or active among these iron oxidizing bacteria, divalent iron ions are converted to trivalent iron ions at a low pH stage. Can be rapidly oxidized.

  Specifically, first, activated sludge collected from a sewage treatment plant was put into an iron oxidation tank, and the pH was adjusted to 2.0 or more and less than 3.0 with an alkaline aqueous solution, for example, NaOH. Then, after leaving still for 2 hours and throwing away the supernatant liquid of activated sludge, the waste liquid discharged | emitted from a pickling process was thrown in until the iron oxidation tank became full. Furthermore, air was supplied by a blower so that the dissolved oxygen in the iron oxidation tank was 2 mg / l or more. Thereafter, the oxidation-reduction potential (ORP) of the iron oxidation tank was monitored, and when ORP rose to +550 mV, it was judged that the oxidation was completed, the supply of air was stopped, the mixture was left to stand for 2 hours, and the supernatant was poured . Sludge of iron-oxidizing bacteria accumulated at the bottom of the iron oxidation tank. Thereafter, the plating wastewater was again poured until the iron oxidation tank became full, and the same operation was repeated to grow iron-oxidizing bacteria.

  When the weight concentration of iron-oxidizing bacteria in the iron oxidation tank reached 2000 mg / l, the plating waste water was continuously supplied so that the residence time (HRT) of the pre-iron oxidation tank was 60 minutes. In the continuous treatment, aeration was performed by controlling the rotation speed of the blower so that the oxidation-reduction potential (ORP) of the iron oxidation tank was maintained at +550 mV or higher.

By this method, divalent iron ions in the waste liquid discharged from the pickling process were stably oxidized to trivalent iron ions, and a ferric hydroxide slurry could be formed.
The ferric hydroxide obtained by this method has a large specific surface area and has a very large proportion of micropores (pore radius of 1 nm or less) effective for adsorption and decomposition of organic chlorine compounds such as dioxin.
It is considered that when oxidized at a low pH of 2 to 4 to form ferric hydroxide, it becomes extremely amorphous iron hydroxide having many micropores.

  Furthermore, as a result of various investigations, the produced ferric hydroxide is treated with an alkaline aqueous solution at a pH of 5 to 11, preferably at a pH of 8 to 10, so that the proportion of finer pores is larger and the removal performance is more excellent. An agent can be obtained. In particular, it exhibits excellent performance when moisture coexists in the gas. If the pH is less than 5, the effect of increasing the pH is small and the adsorption performance is not improved. When the pH is more than 11, due to adhesion of alkali salt, the micropores are blocked, the specific surface area is reduced, and the adsorption performance is lowered. This is because ferric hydroxide is positively charged in the acidic region and strongly adsorbs negatively charged sulfate ions and chlorine ions. Since the neutralization point of the charge of ferric hydroxide is pH 8-9, raising the pH with an alkaline aqueous solution neutralizes the positive charge of ferric hydroxide and removes sulfate ions and chloride ions. It is thought that. In particular, since sulfate ions are hydrophilic, removal of sulfate ions is considered effective for adsorption removal of organochlorine compounds when moisture coexists in the gas. Here, the alkaline aqueous solution is an aqueous solution in which an alkali metal or alkaline earth metal hydroxide, alkali metal carbonate, ammonia, or amine is dissolved or suspended.

  In general, steel sheets are pickled with sulfuric acid or hydrochloric acid in order to remove scale, dirt, oxide film, acid, and the like on the surface of the steel sheet. Chemical oxidation methods or biological oxidation methods using iron-oxidizing bacteria can be applied to any of the waste liquids, but hydroxides obtained from sulfuric acid waste liquids are finer, have a larger specific surface area, and a larger proportion of micropores.

  Further, when chromium is contained in the waste liquid, a part of iron of ferric hydroxide is replaced with trivalent chromium, and a composite hydroxide of iron and chromium is formed. The composite hydroxide of iron and chromium is finer than ferric hydroxide, has a large specific surface area, and a large proportion of micropores. The waste liquid containing both iron and chromium is generated, for example, in a process having a chromate treatment step as a post treatment in an electrogalvanization step. The precipitate obtained from this waste liquid is fine, has a large specific surface area, and a large proportion of micropores. Here, the chromate treatment is to apply an aqueous solution containing chromium after electrogalvanizing the steel sheet in order to improve corrosion resistance and paintability.

As a result of measuring the content of amorphous ferric hydroxide and / or a composite hydroxide of iron and chromium, the removal agent produced in the present invention was measured by X-ray analysis and thermobalance. It was found that 70% or more of these were included. Further, the specific surface area determined by the BET method is 150 m ² / g or more, and the ratio of the area of the micropores determined by the t-plot method to the specific surface area determined by the BET method is 70% or more and has extremely fine pores. I also understood that.

  The removing agent of the present invention may be used in a packed bed or may be blown into a gas. When it is blown into the gas, it is used as a powder, and when it is used in a packed bed, it is used after forming a pellet or briquette.

  Using the substances shown in Table 1 below, the adsorption performance of dibenzofuran, which is a skeleton substance of polychlorodibenzofuran (PCDF), which is a kind of dioxins, was evaluated. Here, in Example 1, the hydrochloric acid pickling waste liquid of the hot-rolled steel sheet was oxidized and precipitated by iron-oxidizing bacteria without adjusting the pH. In Example 2, the same waste liquid as in Example 1 was oxidized with iron-oxidizing bacteria, and then the pH was adjusted to 9 with sodium hydroxide. In Example 3, the sulfuric acid pickling waste liquid of the hot-rolled steel sheet was oxidized with iron-oxidizing bacteria without adjusting the pH, and then adjusted to pH 9 with sodium hydroxide. In Example 4, the sulfuric acid pickling waste liquid in the electrogalvanizing step for chromate treatment was oxidized with iron-oxidizing bacteria without adjusting the pH, and then adjusted to pH 9 with sodium hydroxide. In Example 5, the same waste liquid as in Example 4 was oxidized with an aqueous hydrogen peroxide solution without adjusting the pH, and the pH was adjusted to 9 with sodium hydroxide. In Comparative Example 1, the same waste liquid as in Example 4 was adjusted to pH 9 with calcium carbonate and oxidized with air. All samples were washed and dried after the treatment. As a result of measuring the total content of ferric hydroxide and a composite hydroxide of iron and chromium by X-ray analysis and measurement with a thermobalance, it was confirmed that 70 to 95% of these were contained.

  In the experiment, a glass tube prepared by adjusting the particle size of the removing agent to 0.5 to 1.0 mm was filled and kept at 100 ° C. in a thermostatic bath. A gas having a dibenzofuran concentration adjusted to 20 ppm using nitrogen as a carrier was passed through a glass tube filled with a removing agent, and the mass change of the removing agent was examined. A portion of the gas exiting the glass tube was taken and supplied to the FID gas chromatograph via an autosampler to analyze the concentration of dibenzofuran. Experiment until the outlet dibenzofuran concentration is the same as the supplied dibenzofuran concentration. The adsorption amount was obtained from the integrated value of the difference between the supply concentration and the outlet concentration (adsorption concentration). Table 2 below shows the specific surface area, the micropore area ratio, and the amount of adsorption of each remover. The specific surface area was calculated by the BET method from the adsorption isotherm of the sample at the liquid nitrogen temperature, and the specific surface area of the micropore was calculated by the t-plot method from the adsorption isotherm of the sample at the liquid nitrogen temperature. The ratio of the micropore area was determined as the ratio of the specific surface area of the micropore by the t-plot method to the specific surface area by the BET method. As compared with Comparative Example 1, both the specific surface area, the ratio of the micropore area, and the amount of adsorption increased in all the samples of the examples.

Using the removal agents of Examples 1 to 5 and Comparative Example 1, the dioxin removal experiment in the waste incinerator exhaust gas was performed. Was separated exhaust gas of 100 Nm @ 3 / hr from the exhaust gas after the bag filter passage of waste incinerators, the removing agent was 0.01 m ³ filled, and introduced into a fixed bed which is kept at 0.99 ° C., after continuous operation for 100 hours fixed The dioxin removal rate was determined from the dioxin concentration before and after the layer.

Here, the dioxin removal rate is expressed by the following formula:
(1-fixed-bed outlet dioxin concentration / fixed-bed inlet dioxin concentration) × 100 (%)
Defined by

  The results are shown in Table 3 below.

  All the samples of Examples 1 to 5 greatly exceed the removal rate of the sample of Comparative Example 1. In Example 1 where the waste gas from the refuse incinerator contains about 20 to 30% of moisture and thus the alkali treatment is not performed, the removal rate is slightly low, but in Examples 2 to 4 where the alkali treatment is performed, The removal rate was improved. Thus, it can be seen that the present invention has an effect of sufficiently removing dioxins even at an exhaust gas temperature as low as 150 ° C., which was difficult with a conventional iron oxide catalyst.

Claims (3)

It is discharged from the pickling process of steel plate consisting of one or more kinds of hydrochloric acid pickling waste liquid of hot rolled steel sheet, sulfuric acid pickling waste liquid of hot rolled steel sheet, and sulfuric acid pickling waste liquid of electrogalvanizing process for chromate treatment. The Fe ²⁺ in the waste liquid is oxidized to Fe ³⁺ , and the resulting ferric hydroxide and / or composite hydroxide slurry of iron and chromium is filtered and dried to obtain ferric hydroxide and / or And a pore radius determined by the t-plot method with respect to the specific surface area determined by the BET method, including a composite hydroxide of iron and chromium of 70% or more, a specific surface area determined by the BET method of 150 m ² / g or more A method for producing an organic chlorine compound remover in a gas, wherein the organic chlorine compound remover in the gas has a ratio of the specific surface area of micropores of 1 nm or less of 70% or more . It is discharged from the pickling process of steel plate consisting of one or more kinds of hydrochloric acid pickling waste liquid of hot rolled steel sheet, sulfuric acid pickling waste liquid of hot rolled steel sheet, and sulfuric acid pickling waste liquid of electrogalvanizing process for chromate treatment. The Fe ²⁺ in the waste liquid is oxidized to Fe ³⁺ , and the resulting ferric hydroxide and / or iron / chromium composite hydroxide slurry is adjusted to pH 5-11 with an alkaline aqueous solution and filtered and dried. Then , ferric hydroxide and / or a composite hydroxide of iron and chromium containing 70% or more, the specific surface area determined by the BET method is 150 m ² / g or more, and the ratio determined by the BET method Organochlorine in gas, characterized in that a removal agent for organochlorine compounds in gas having a ratio of the specific surface area of micropores having a pore radius of 1 nm or less determined by the t-plot method with respect to the surface area is 70% or more Compound Manufacturing method of Sa agent. The method for producing an organic chlorine compound remover in gas according to claim 1 or 2, wherein Fe ²⁺ in the waste liquid is oxidized to Fe ³⁺ using an oxidizing agent and / or iron oxidizing bacteria. .