JP4723624B2 - Disposal of chlorine-containing fine powder waste - Google Patents

Description

  The present invention relates to a dust containing a harmful substance (hereinafter referred to as “bleeding dust”) that comes out when a part of a burning gas containing chlorine, a basic substance, sulfur or the like is extracted in a cement manufacturing apparatus or the like. ) And incineration ash, etc.

  Extracted dust contains harmful substances such as lead, cadmium, selenium, copper and zinc in addition to chlorine, basic substances and sulfur. Therefore, if the extracted dust is used for landfill as it is or discarded, it causes environmental pollution. Therefore, conventionally, the solid content obtained after washing the extracted dust to remove chlorine and basic substances has been used as a part of the raw material for cement. On the other hand, the harmful substances are dissolved in the water used for washing. The drainage water must conform to the drainage standards of the Water Pollution Control Law when draining. Therefore, a treatment method for removing those harmful substances from the washing water so that the concentration is not more than the concentration specified in the drainage standard of the Water Pollution Control Law has been studied and implemented.

  Patent Document 1 discloses a method for treating cement kiln bleed dust, which includes four solid-liquid separation steps. Patent Document 2 discloses a method of treating cement apparatus bleed dust, which includes three solid-liquid separation steps. In order to carry out these methods in a continuous manner, it is necessary to prepare at least four precipitation tanks (in the case of the invention described in Patent Document 1) or three groups (in the case of the invention described in Patent Document 2), Therefore, the construction of the equipment is expensive. Furthermore, since solid-liquid separation takes time, these methods are inefficient and therefore the running cost increases.

  By the way, selenium is mentioned as one of the metals that are difficult to remove in the treatment of the extracted dust washing water. Patent Literature 3 and Patent Literature 4 disclose a method for treating extraction dust for the purpose of sufficiently removing selenium from extraction dust washing water. The feature of the invention described in Patent Document 3 is that calcium polysulfide is added to treated water (supernatant) after solid-liquid separation of the extracted dust slurry. In addition, the solid-liquid separation process in this method is twice. In the method described in Patent Document 4, the solid-liquid separation process is performed only twice. Therefore, it can be said that these methods are superior to the methods described in Patent Document 1 and Patent Document 2 in terms of equipment costs and running costs.

  In the inventions described in Patent Document 3 and Patent Document 4, the polymer flocculant normally used in the treatment of the extracted dust washing water is not an essential component but an optional component. Depending on the type and amount of harmful substances in the extracted dust washing water, it may be necessary to use a polymer flocculant. However, Patent Document 3 and Patent Document 4 describe polymer aggregation suitable for use in the inventions described therein. There is no specific illustration about the agent, and there is no description of an example (Example) using the polymer flocculant. In addition, in the methods described in Patent Document 3 and Patent Document 4, in particular, when the concentration of harmful substances in the extracted dust washing water is high, all the harmful substance concentrations are the standard values defined in the drainage standards of the Water Pollution Control Law. It is also unclear whether it can be processed to be as follows.

JP 2005-103476 A JP-A-10-99817 JP2002-254049 JP 2006-347831 A

  In view of the above prior art, the present inventors are a method with a small equipment cost and running cost and a small number of solid-liquid separation steps, and the object of treatment is chlorine-containing fine powder such as extraction dust having a high content of harmful substances. In order to provide a method that can treat the concentration of toxic substances in washing water within the standard value of the wastewater standards of the Water Pollution Control Law, we have conducted intensive research. As a result, by limiting the types of polymer flocculants, inorganic flocculants, and metal scavengers used, limiting the pH of the liquid phase during use and specifying the order of use, the above object can be achieved. did it.

That is, the present invention is a first step in which water is added to a chlorine-containing fine powder waste to form a slurry, and solid-liquid separation is performed in the presence of an anionic carboxylic acid polymer flocculant at pH 12 or higher. the resulting iron-based reducing agent and the acid agent is added to the liquid phase, the second step the pH was 6.0 to 8.0, and then adding a metal scavenger, after completion of the second step, when the batch In the case of a continuous type, the liquid phase after the second step is transferred to the next water tank, and polyferric sulfate or ferric chloride and, if necessary, an alkali agent are added. After completion of the third step and the third step with a pH of 6.5 to 7.5 , the batch type is continued as it is, and in the case of the continuous type, the liquid phase after the third step is transferred to the next water tank. Te, was added anionic carboxylate polymer flocculant, characterized in that it comprises a fourth step of the solid-liquid separation It relates to a process for the treatment of chlorine-containing pulverulent waste.

  It is preferable to use ferrous chloride or ferrous sulfate as the iron-based reducing agent.

  As the anionic carboxylic acid polymer flocculant, it is preferable to use a copolymer of (meth) acrylamide- (meth) acrylate.

  As the metal scavenger, it is preferable to use a dithiocarbamic acid polymer metal scavenger.

  Ferrous chloride is used as an iron-based reducing agent, and in the second step, iron powder having a passage of 95 μm or more of sieve (JIS Z8801-1) having a mesh opening of 45 μm is used in combination with ferrous chloride. It is preferable.

  In the method for treating chlorine-containing pulverized waste according to the present invention, the solid-liquid separation process is performed only twice, so that the treatment equipment and the site for the treatment are small, and therefore the construction cost of the treatment equipment can be reduced. Furthermore, since the method of the present invention is a simple method having only two solid-liquid separation steps, the working efficiency is high, and therefore the running cost in carrying out the method of the present invention is low.

  Only by carrying out the method of the present invention, the concentration of harmful substances in the washing water of chlorine-containing fine powder waste can be within the drainage standard value of the Water Pollution Control Law. Since no further treatment is required, the cost of chlorine-containing fine powder waste treatment can be reduced from this point as well by implementing the present invention.

  The present invention will be specifically described below.

  The chlorine-containing pulverized waste that is the object of the method of the present invention refers to, for example, dust (chlorine bypass dust), electrostatic dust collection dust, incineration ash, and the like that come out when extracting the calcination gas in a cement manufacturing apparatus. . The method of the present invention is particularly suitable for treating bleed dust such as chlorine bypass dust.

  The first step is a step in which water is added to a chlorine-containing fine powdery waste to form a slurry, and solid-liquid separation is performed in the presence of an anionic carboxylic acid polymer flocculant at pH 12 or higher. The amount of water added to the chlorine-containing fine powder waste is not particularly limited as long as a slurry can be formed. For example, the amount of the solid content (dust) of the slurry is about 5 to 20% by weight, preferably 8 to 15 The amount is about wt%. When water is added to the chlorine-containing fine powder waste and stirred, a slurry is formed. Since this slurry is generally highly basic, the pH of the slurry is 12 or more without adding an alkali agent. However, when the pH of the slurry is less than 12, an alkaline agent such as sodium hydroxide, potassium hydroxide or sodium hydroxide is added to adjust the pH to 12 or more. In addition, preferable pH is 12.5 or more, and more preferable pH is 13 or more.

  The polymer flocculant used in the first step is an anionic carboxylic acid flocculant. Specific examples of such flocculants include acrylamide-acrylate copolymers, methacrylamide-methacrylate copolymers, and acrylamide-methacrylamide-acrylate-methacrylate copolymers. It is done. Examples of the salt are sodium salt and ammonium salt. In the following, such copolymers are collectively referred to as “(meth) acrylamide- (meth) acrylate copolymer”. The copolymer of (meth) acrylamide- (meth) acrylate is partially hydrolyzed poly (meth) acrylamide to produce a (meth) acrylic acid portion, and the acrylic acid portion is converted to a sodium salt or an ammonium salt. Is. The polymer flocculant preferably has a number average molecular weight of 5 million to 30 million, more preferably 10 million to 20 million. The anionic degree of anionicity is 0% for poly (meth) acrylamide, 100% for poly (meth) acrylic acid salt, and a copolymer of (meth) acrylamide- (meth) acrylate As the ratio of the (meth) acrylate moiety increases, the anionic degree increases. In the first step, a polymer flocculant having an anion degree of about 10 to 30% is preferable, and a polymer flocculant of about 15 to 25% is more preferable. The amount of the polymer flocculant added is preferably such that the amount of the polymer flocculant itself in the water slurry is 0.1 to 50 ppm, more preferably 0.5 to 20 ppm. The amount is preferably 1 to 10 ppm, and still more preferably.

  In the first step, an aqueous slurry of chlorine-containing fine powdery waste is formed, the pH is measured, an alkaline agent is added as necessary, and then a polymer flocculant is added.

  In the first step, the polymer flocculant forms a floc in which dissolved metals other than selenium and lead are bonded. This floc aggregates and settles. The solid-liquid separation method after the coagulation sedimentation is not particularly limited, but for example, filtration using a filter cloth or a membrane, centrifugal dehydration, filter press dehydration, belt press dehydration, screw press dehydration, etc. Examples include separation into liquid.

In the second step, first, an iron reducing agent and an acid agent are added to the liquid phase obtained in the first step, and the pH is adjusted to 6.0 to 8.0. The iron-based reducing agent is used to reduce and precipitate dissolved hexavalent selenium to tetravalent. As iron-based reducing agent, it is preferred to use the ferrous chloride (FeCl ₂₎ or ferrous sulfate (FeSO _4). Ferrous chloride is easily oxidized by air (oxygen). Since ferric chloride (FeCl ₃ ) after oxidation does not show the ability to reduce selenium, in order to return ferric chloride to ferrous chloride, it passes through a sieve (JIS Z8801-1) having an opening of 45 μm. It is preferable to use iron powder having a content of 95% by weight or more in combination.

  The amount of the iron-based reducing agent added to the liquid phase obtained in the first step depends on the amount of iron ions in the iron-based reducing agent, although it depends on the amount of dissolved selenium. It is preferably 20 ppm or more, more preferably 500 ppm or more, and even more preferably 700 ppm or more. Note that the upper limit is an amount that is not wasted and is about 10,000 ppm (1 wt%). The amount of iron powder used is preferably about 5 to 20% by weight based on the weight of iron ions in the iron-based reducing agent.

  The pH of the liquid phase when reducing the hexavalent selenium dissolved to tetravalent is 5.0 to 12.0, preferably 6.0 to 8.0. The acid agent used to obtain such a pH value is hydrochloric acid, sulfuric acid or the like. In addition, when using ferrous chloride, it is preferable to use hydrochloric acid, and when using ferrous sulfate, it is preferable to use sulfuric acid.

  In the second step, a metal scavenger is added to collect tetravalent selenium. The metal scavenger is also referred to as a metal fixing agent. As the metal scavenger, it is preferable to use a dithiocarbamic acid-based metal scavenger, and it is more preferable to use a dithiocarbamic acid-based polymer metal scavenger. Here, the dithiocarbamic acid-based metal scavenger refers to a compound having a carbodithioic acid group, and the dithiocarbamic acid-based polymer metal scavenger is a compound having a carbodithioic acid group, for example, a low molecular weight dithiocarbamic acid. A high molecular weight compound such as a high molecular weight polyamine salt of the compound. The amount of the metal scavenger added is preferably such that the amount of the metal scavenger itself in the liquid phase is 0.3 to 200 ppm, preferably 1 to 100 ppm, on a weight basis. preferable.

  After the second step, the batch process is continued as it is, and in the case of the continuous process, the liquid phase after the second process is transferred to the next water tank and the third process is performed. In the third step, the liquid phase obtained in the second step is added with ferric sulfate or ferric chloride, which is an inorganic flocculant, and an alkali agent, if necessary, to a pH of 6.5. To 7.5, preferably 6.8 to 7.2.

  The amount of ferric sulfate (example of iron ion content of liquid product: 11%) and ferric chloride (example of iron ion content of liquid product: 13%) is the amount of those in the liquid phase. However, the amount of iron ions is preferably 0.1 to 70 ppm on a weight basis, and more preferably 0.3 to 50 ppm.

  Addition of polyferric sulfate or ferric chloride lowers the pH of the liquid phase. In particular, when ferric chloride is used, the degree of pH decrease is large. Therefore, when the pH of the liquid phase is not within the range of 6.5 to 7.5, or when it is within this range but it is desired to further increase the pH within this range (that is, when necessary), alkaline Add agent. Examples of the alkali agent include sodium hydroxide, potassium hydroxide, and calcium hydroxide.

  In the third step, harmful substances dissolved in the liquid phase, such as lead, are collected with an inorganic flocculant. There are various inorganic flocculants, but in this third step, polyferric sulfate or ferric chloride is used. Ferric chloride is more preferred.

  After the third step, the batch process is continued as it is, and in the case of the continuous process, the liquid phase after the third process is transferred to the next water tank, and the fourth process is performed. In the fourth step, an anionic carboxylic acid polymer flocculant is added to the liquid phase obtained in the third step, and solid-liquid separation is performed.

  The anionic carboxylic acid type polymer flocculant is as described in the explanation relating to the first step. Also in this step, a polymer flocculant having an anion degree of about 10 to 30% is preferable, and a polymer flocculant of about 15 to 25% is more preferable. In the fourth step, the same one used in the first step may be used, or a different one (for example, one having a different anion degree or molecular weight) may be used. The amount added is preferably an amount such that the amount of the polymer flocculant itself in the liquid phase is 0.1 to 50 ppm, and more preferably 0.5 to 10 ppm.

  The polymer flocculant forms a floc in which the dissolved metal collected by the inorganic flocculant is bound. This floc aggregates and settles. The solid-liquid separation method after the coagulation sedimentation is not particularly limited, but for example, filtration using a filter cloth or a membrane, centrifugal dehydration, filter press dehydration, belt press dehydration, screw press dehydration, etc. Examples include separation into liquid.

  The method of the present invention does not exclude the addition of optional substances and other steps not described in this specification. However, water that conforms to the drainage standards of the Water Pollution Control Law can be obtained only by performing the first to fourth steps using only essential components. As a matter of course, the method of the present invention includes a method in which the first to fourth steps are carried out substantially using only the essential components.

(Experimental example 1) Examination of water washing conditions of kiln dust 200 g of kiln dust having the composition shown in Table 1 was put into a 2 liter beaker, and pure water was added thereto to make the total amount of 2,000 g. This was stirred for a certain time to obtain a slurry. When this slurry was allowed to stand for several days, the supernatant became colorless and transparent. Then, the water quality analysis of this supernatant liquid was performed. The results are shown in Table 2. In addition, the metal content in kiln dust was quantified according to the bottom sediment investigation method (Showa 63 ring water pipe No. 127), the metal content in water was quantified according to JISK0102, and the chlorine ion concentration was quantified according to the sewage test method. The results are shown in Table 2.

  As is clear from Table 2, zinc was found to be below the drainage standard even by natural sedimentation alone.

Experimental Example 2 Addition of Polymer Flocculant to Slurry After forming a slurry in the same manner as in Experimental Example 1, polyacrylamide polymer flocculant (SKF-A553; manufactured by Sekisui Aqua System Co., Ltd .; anion degree: 5 ppm of 20% (medium anion); molecular weight 12 million) was added, stirred, and allowed to stand to cause aggregation precipitation. The pH was not adjusted, but the pH was about 13. A water quality analysis was performed on the supernatant liquid after the formation of the aggregated precipitate. The results are shown in Table 3.

  As is clear from Table 3, the concentrations of selenium and cadmium were lower than those of water washing alone (Table 2 of Experimental Example 1), but the concentrations of lead and selenium were not yet compatible with the wastewater standards.

(Experimental example 3) Secondary flocculation treatment of supernatant water after primary flocculation The supernatant liquid of experimental example 2 (corresponding to the liquid phase after the first step of the present invention) is treated as follows to cause secondary flocculation. The water quality of the supernatant was analyzed. The results are shown in Table 4.

(1) Sulfuric acid was added to the supernatant to adjust the pH to 7.8.
(2) To the liquid phase obtained in (1), a dithiocarbamic acid polymer metal scavenger (Epofloc L-1; manufactured by Miyoshi Oil & Fats Co., Ltd .; molecular weight: 80,000 to 120,000; pH (1%) 5 to 12.5; specific gravity: 1.19 to 1.23; total concentration of dithiocarbamic acid-based compound and sodium hydrogen sulfide: about 35%) in solid form at 100 ppm (volume basis) (polymer metal scavenger) About 42 ppm) and stirred for 10 minutes.
(3) To the liquid phase obtained in (2), polyferric sulfate (liquid product; Fe content: 11%) was added in an amount of 33 ppm in terms of Fe ions, and the mixture was stirred for 5 minutes.
(4) When pH was measured, it was pH = 6.33, so sodium hydroxide was added to make pH = 7.0.
(5) Polyacrylamide polymer flocculant (A-110; manufactured by MT Aqua Polymer Co., Ltd .; anion degree: 20% (medium anion); molecular weight of 19 million) is added to the liquid phase obtained in (4). After adding 5 ppm and stirring, the mixture was allowed to stand to cause aggregation and precipitation.

  As is clear from Table 4, the concentrations of lead, selenium, cadmium and zinc were within the effluent standard values. However, for selenium, it was the same as the upper limit of the effluent standard, so the conclusion was reached that some treatment to reduce the selenium concentration in the liquid phase was necessary.

(Experimental example 4) Examination of selenium removal conditions The kiln dust was washed with water and the water was treated under the following conditions.

1. Primary aggregation (first step)
Pure water was added to 200 g of the same kiln dust as used in Experimental Example 1 to make a total amount of 2,000 g, and stirred to obtain a slurry. To this slurry, 5 ppm of polyacrylamide polymer flocculant (SKF-A553; manufactured by Sekisui Aqua System Co., Ltd .; anion degree: 20% (medium anion); molecular weight: 12 million) was added and stirred, and then allowed to stand. Thus, agglomeration precipitation was generated. The pH was not adjusted, but the pH was about 13. The supernatant liquid (primary flocculated water) after the formation of the flocculated precipitate was collected.

2. Addition of reducing agent and metal scavenger (second step)
Ferrous sulfate or ferrous chloride, which is a reducing agent, was added to the primary flocculated water and stirred. Thereafter, sulfuric acid or hydrochloric acid was added to obtain pH = 7.8. Thereafter, for Invention Examples 1 to 7 and Comparative Example 1, a metal scavenger (Epofloc L-1; manufactured by Miyoshi Oil & Fat Co., Ltd.) is 100 ppm on a volume basis as a solid (as the amount of the polymer metal scavenger, About 42 ppm) was added and stirred for 10 minutes.

  Here, as shown in Table 5, an experiment was conducted on seven types of cases in which the type, amount of addition, and stirring time of the reducing agent were changed. In addition, a system without a reducing agent was also tested in two cases (whether or not an acid agent and a metal scavenger were added). The system without addition of the reducing agent, the acid agent and the metal scavenger is a blank, and the system without addition of the reducing agent and the addition of the acid agent and the metal scavenger is Comparative Example 1.

3. Addition of inorganic flocculant and alkali agent (third step)
Following the second step, polyferric sulfate, which is an inorganic flocculant (liquid product; Fe content is 11%), in an amount of 33 ppm in terms of Fe ion, or ferric chloride, which is also an inorganic flocculant (ferric chloride) A liquid product having a ferric content of 38%; the iron content being 13%) was added in an amount of 39 ppm in terms of Fe ions, sodium hydroxide was further added to adjust the pH to 7.0, and the mixture was stirred for 5 minutes. In addition, the inorganic flocculant was not added to the blank, while poly ferric sulfate was added to Comparative Example 1.

4). Addition of polymer flocculant (fourth process)
Following the third step, for Invention Examples 1 to 7 and Comparative Example 1, 5 ppm of polyacrylamide polymer flocculant (A-110; manufactured by MT Aqua Polymer Co., Ltd.) was added, stirred, and then allowed to stand. Thus, agglomeration precipitation was caused.

  The selenium concentration was measured for the supernatant (secondary flocculated water). The results are shown in Table 5. In addition, as is clear from the above, the blank is obtained by performing only the first step, and the comparative example 1 is obtained by performing only the first and third steps.

  As is clear from the results shown in Table 5, the selenium content of the secondary flocculated water was within the drainage standard value by first performing the selenium removal step (second step) for the primary flocculated water. . About other components, as shown in Table 4 of Experimental Example 4, it was within the drainage standard value without performing the selenium removal step (second step). It became clear that the washing water of waste can be treated so that the concentration of harmful substances meets the effluent standards.

(Experimental example 5) Experiment 1 under various processing conditions Primary aggregation (first step)
Pure water was added to 300 g of the same kiln dust as used in Experimental Example 1 to make a total amount of 2,000 g, and stirred to obtain a slurry. To this slurry, polyacrylamide polymer flocculant (SKF-A553; manufactured by Sekisui Aqua System Co., Ltd .; anion degree: 20% (medium anion); molecular weight 12 million) was added in the amount shown in Table 6 and stirred. Then, the mixture was allowed to stand to cause aggregation precipitation. Although pH adjustment was not performed, pH was about 13.5. The supernatant liquid (primary flocculated water) after the formation of the flocculated precipitate was collected.

2. Addition of reducing agent and metal scavenger (second step)
As shown in Table 6, ferrous sulfate or ferrous chloride, which is an iron-based reducing agent, was added to primary agglomerated treated water and stirred for 20 minutes. In addition, for some of the systems to which ferrous chloride was added, iron powder having a passage of a sieve having a mesh size of 45 μm (JIS Z8801-1) of 95% by weight or more was also used. Thereafter, an acid agent (sulfuric acid or hydrochloric acid) was added to obtain the pH shown in Table 6.

  Thereafter, a metal scavenger (Epofloc L-1; manufactured by Miyoshi Oil & Fat Co., Ltd.) was added in an amount shown in Table 6 and stirred for 10 minutes.

3. Addition of inorganic flocculant and alkali agent (third step)
Following the second step, inorganic flocculant (polyferric sulfate (liquid product; Fe content is 11%) or ferric chloride (liquid product with 38% ferric chloride content; Fe content is 13%) )) Was added in the amounts shown in Table 6 and the pH was measured. If necessary, sodium hydroxide was also added to bring the pH to 6.5 to 7.5, and then stirred for 5 minutes.

4). Addition of polymer flocculant (fourth process)
Following the third step, polyacrylamide polymer flocculant (A-110; manufactured by MT Aqua Polymer Co., Ltd.) was added in the amount shown in Table 6, stirred, and then allowed to stand to cause coagulation precipitation. .

  The metal concentration was measured for the supernatant (secondary flocculated water). The results are shown in Table 7.

  As is apparent from the results shown in Table 7, it has been clarified that the washing water of the chlorine-containing fine powdery waste can be treated by the method of the present invention so that the concentration of harmful substances meets the drainage standard.

Claims (5)

The liquid phase obtained in the first step and the first step, in which water is added to a chlorine-containing fine powdery waste to form a slurry, and solid-liquid separation is performed in the presence of an anionic carboxylic acid polymer flocculant at pH 12 or higher. Add iron-based reducing agent and acid agent to adjust the pH to 6.0 to 8.0, then add the metal scavenger, then after the second step, continue in the case of batch type, continuously In the case of the formula, the liquid phase after completion of the second step is transferred to the next water tank, and polyferric sulfate or ferric chloride and, if necessary, an alkali agent are added, and the pH is adjusted to 6.5 to After completion of the third step and the third step to 7.5, in the case of a batch type, continue as it is, and in the case of a continuous type, transfer the liquid phase after the completion of the third step to the next water tank, Chlorine-containing fine powder, characterized by including a fourth step of adding an acid polymer flocculant and performing solid-liquid separation Method of processing wastes. The processing method of the chlorine containing fine powder waste of Claim 1 whose iron type reducing agent is ferrous chloride or ferrous sulfate. The method for treating a chlorine-containing fine powdery waste according to claim 1 or 2, wherein the anionic carboxylic acid polymer flocculant is a (meth) acrylamide- (meth) acrylate copolymer. The processing method of the chlorine containing fine powdery waste as described in any one of Claims 1 thru | or 3 whose metal scavenger is a dithiocarbamic-acid type polymer metal scavenger. The iron-based reducing agent is ferrous chloride, and in the second step, ferrous chloride is used in combination with iron powder having a mesh passage of 45 μm and having a passage of 95% by weight or more (JIS Z8801-1). The processing method of the chlorine containing fine powder waste as described in any one of Claims 2 thru | or 4.