JP2009101359A - Cement kiln extraction dust treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the content of selenium and heavy metals contained in a dechlorination water-washing solution for cement kiln extraction dust to a level of not higher than 0.1 mg/l which is a fluent standard according to Water Pollution Control Act. <P>SOLUTION: A cement kiln extraction dust treatment method includes the following processes. The method includes (1) the first process of adding water to cement kiln extraction dust to form a slurry before executing solid/liquid separation, (2) the second process of controlling the pH of a liquid phase (raw water) obtained after solid/liquid separation in the first process to 5-10, adding a chelating agent for removing heavy metals, adding a ferric salt compound before controlling the pH of the liquid phase to 5-10 again and adding a polymer flocculating agent to execute solid/liquid separation, (3) the third process of adding a first ferrous salt compound to the liquid phase obtained after solid/liquid separation in the second process and controlling the pH to 8-12 before adding a polymer flocculating agent to execute solid/liquid separation, and (4) the fourth process of adding a ferric salt compound to the liquid phase obtained after solid/liquid separation in the third process and controlling the pH to 8-12 before adding a polymer flocculating agent for executing solid/liquid separation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  In order to reduce the circulation of chlorine, alkali, and sulfur in a cement kiln, the present invention is a dust containing selenium (hereinafter, extracted air) that is accompanied when a part of the calcination gas is extracted using an extraction device such as a chlorine bypass. (Referred to as dust).

When a cement raw material containing a large amount of chlorine, alkali, and sulfur is used, the amount of chlorine, alkali, and sulfur contained in the cement clinker increases, which adversely affects cement quality.
In addition, chlorine, alkali, and sulfur form a compound with high vapor pressure, and before it is gasified and circulated in the cement kiln, it is condensed at a relatively low temperature in the equipment to form a coating. It is also the cause of the above trouble.
In order to solve this problem, a part of the firing gas is extracted from the kiln bottom portion of the cement kiln to reduce the amount of chlorine, alkali, and sulfur circulating in the cement kiln.

  However, when such a calcination gas is extracted, extraction dust having a large content of chlorine, alkali, and sulfur is inevitably accompanied, and the processing method of this extraction dust becomes a new problem. In other words, in addition to chlorine, alkali and sulfur, extracted dust contains lead, cadmium, chromium, manganese, iron, selenium and other harmful substances regulated by the Water Pollution Control Law, and the extracted dust remains untreated. Landfilling and disposal can cause environmental pollution and should be handled in an appropriate manner. Even when the extracted dust is not discarded but reused as a cement raw material, it is necessary to reduce the amount of alkali and chlorine contained in the extracted dust and then return to the raw material system.

Since alkali and chlorine compounds contained in the bleed dust are water-soluble, washing with water is most suitable for removal, and already known (for example, Patent Documents 1 and 2). However, in this document, there is no report regarding a method for treating harmful substances including heavy metals that are eluted together with alkali and chlorine compounds during water treatment.
As a method for treating heavy metals, Patent Document 3 reports a method for treating tetravalent selenium and hexavalent selenium (hereinafter referred to as all selenium). In this document, wastewater with a total selenium content of 1.6 mg / l is mixed with ferrous sulfate heptahydrate 2832 times the total selenium amount and ferric chloride hexahydrate with total selenium. It has been reported that the total selenium concentration of the remaining filtrate after addition of 945 times the amount, adjusting the pH to 9 and stirring for 30 minutes and filtering off with a filter press is 0.04 mg / l. . However, in this method, in the case of selenium-containing water in which a large amount of hexavalent selenium is dissolved, a large amount of ferrous and ferric iron is required, so that coagulation and precipitation are difficult, and the processing cost is expensive, so that it can be put into practical use. It can be difficult.

  In Patent Document 4, ferrous sulfate is added in an amount of 40 to 80 times the amount of dissolved selenium in terms of the amount of divalent iron ions, the pH is adjusted to 8.5 to 10 and stirred for 20 to 30 minutes, It has been reported that all selenium is adsorbed and immobilized on ferrous hydroxide. However, the total selenium content of the treated water is 0.2 to 0.4 mg / l, and the wastewater standard value of 0.1 mg / l or less according to the Water Pollution Control Law cannot be achieved.

JP 49-86419 A JP-A-62-252351 JP 2002-273455 A JP-A-6-79286

  The present invention is a waste water treatment method for water pollution treatment, in which cement kiln extraction dust is washed with water, solid content is reused as a cement raw material, and selenium containing selenium that cannot be treated with normal trivalent iron ions is contained. It aims at providing the processing method which makes it possible to discharge and discard by removing below a reference value.

As a result of intensive studies, the present inventors have found that the above object can be achieved.
That is, this invention relates to the processing method of the cement kiln extraction dust characterized by including the following processes.
(1) A first step in which water is added to cement kiln extraction dust to form a slurry, followed by solid-liquid separation,
(2) The pH of the liquid phase after solid-liquid separation obtained in the first step (hereinafter referred to as raw water) is adjusted to 5-10, a chelating agent for removing heavy metals is added, and a ferric salt compound is added. After that, the second step of re-adjusting the pH of the liquid phase to 5-10, adding a polymer flocculant, and solid-liquid separation,
(3) The ferrous salt compound is added to the liquid phase after solid-liquid separation obtained in the second step, the pH is adjusted to 8 to 12, and then the polymer flocculant is added to perform solid-liquid separation. A third step to perform,
(4) A ferric salt compound is added to the liquid phase after solid-liquid separation obtained in the third step, the pH is adjusted to 8 to 12, and then a polymer flocculant is added to perform solid-liquid separation. 4th process to perform.

When the cement kiln extraction dust processing method of the present invention is carried out, hexavalent selenium, which is extremely difficult to remove, is reduced to tetravalent and collected as a solid phase, and all selenium (tetravalent selenium in the liquid phase after solid-liquid separation) is collected. , Hexavalent selenium) can be reduced to a level that sufficiently satisfies the drainage standard value according to the Water Pollution Control Law, and can be discharged.
Moreover, since the addition amount of the ferrous salt compound used as the reducing agent is small, sedimentation separation is facilitated in a short time by adding a small amount of the polymer flocculant. Therefore, the amount of sludge that is a solid phase is reduced and the sludge is easily dewatered.
Furthermore, the solid content can be reused as a cement raw material.

FIG. 1 is a flowchart showing a method of treating cement kiln bleed dust according to the present invention.

The present invention is described in detail below. Moreover, the flow of the processing method of the cement kiln extraction dust which concerns on this invention is shown in FIG.
The first step of the present invention is a step of solid-liquid separation after adding water to the cement kiln bleed dust to form a slurry. In this step, alkali metal salts such as potassium chloride, sodium chloride, and calcium chloride are eluted and collected as a solid phase. Since the main component of the extracted dust is an alkali metal salt, the resulting slurry exhibits a high pH value. The amount of water added is such that the concentration of chlorine in the liquid phase after solid-liquid separation is 2% by mass or less. Generally, the chlorine concentration of seawater is 0.005 to 2% by mass, and the treated wastewater can be discharged as it is if the chlorine concentration of the liquid phase is 2% by mass or less.

  In the second step of the present invention, after adjusting the pH of the liquid phase (raw water) separated in the first step to 5 to 10, adding a chelating agent for removing heavy metals, and adding a ferric salt compound, Further, the pH of the liquid phase is readjusted to 5 to 10, a polymer flocculant is added, and solid-liquid separation is performed. In this step, heavy metals such as lead, cadmium, and chromium, and some tetravalent selenium are co-precipitated with iron hydroxide and collected as a solid phase.

Examples of the raw water pH adjuster include hydrochloric acid, sulfuric acid, and nitric acid. The pH is adjusted to 5-10, preferably 6-8.
Examples of the liquid phase pH adjuster after addition of the chelating agent for heavy metal removal include sodium hydroxide and calcium hydroxide. The pH is adjusted to 5-10, preferably 6-8.

As a chelating agent for removing heavy metals, a dithiocarbamic acid group (> N-CS ₂ X, where X represents H, Li, Na, K, Ca / 2, Mg / 2) and / or a thiol group ( -SY, where Y represents H, Li, Na, or K) can be used. For example, a solid polymer in which a dithiocarbamic acid group and / or a thiol group is introduced into a base resin such as a styrene-divinylbenzene-based resin or a phenol resin, and a dithiocarbamic acid group and / or a thiol group is introduced into a polyalkylene polyamine. A liquid polymer that forms a floc by combining with a heavy metal can be used.
In particular, it is particularly preferable to use a liquid water-soluble polymer chelating agent having polyethyleneimine as a base polymer and having a sodium dithiocarbamate group and a sodium mercaptide group in the molecule. It can be used as it is or as a diluted aqueous solution.

The addition amount of the chelating agent for removing heavy metals is 0.2 to 3 equivalents, preferably 0.5 to 2 equivalents with respect to lead ions dissolved in the raw water.
Examples of the ferric salt compound include ferric chloride, ferric chloride and hexahydrate, ferric sulfate, ferric sulfate and trihydrate, ferric sulfate and hexahydrate, Examples thereof include ferric sulfate heptahydrate, polyferric sulfate and the like.
The addition amount of the ferric salt compound is 5 to 15 times by weight, preferably 7 to 13 times by weight, with respect to the heavy metal removing chelating agent.

The third step is a step of performing solid-liquid separation by adding a ferrous salt compound to the liquid phase solid-liquid separated in the second step and adjusting the pH to 8 to 12 and then adding a polymer flocculant. It is. In this step, hexavalent selenium (selenic acid) that has not been collected in the second step is reduced to tetravalent selenium (selenite) that is likely to coprecipitate with trivalent iron hydroxide.
Examples of ferrous salt compounds include ferrous chloride, ferrous chloride and dihydrate, ferrous sulfate, ferrous sulfate and tetrahydrate, ferrous sulfate and pentahydrate, Examples thereof include ferrous sulfate and heptahydrate, polyferrous sulfate and the like.
The addition amount of the ferrous salt compound is 50 to 300-fold mol amount, preferably 100 to 200-fold mol amount in terms of iron ion, with respect to the hexavalent selenium amount dissolved in the raw water.
Examples of the liquid phase pH adjuster include sodium hydroxide and calcium hydroxide as in the second step. The pH is adjusted to 8-12, preferably 9-11.

In the fourth step of the present invention, the ferric salt compound is added to the liquid phase separated in the third step and the pH is adjusted to 8 to 12, followed by the addition of the polymer flocculant and the solid-liquid separation. It is a process of performing.
Examples of the ferric salt compound include ferric chloride, ferric chloride, hexahydrate, ferric sulfate, ferric sulfate, trihydrate, ferric sulfate, hexahydrate, And ferric sulfate heptahydrate and polyferric sulfate.
The ferric salt compound is added in an amount of 30 to 120 times, preferably 50 to 100 times, the molar amount of iron ions with respect to the total amount of selenium dissolved in the raw water.
Examples of the liquid phase pH adjuster include sodium hydroxide and calcium hydroxide as in the second and third steps. The pH is adjusted to 8-12, preferably 9-11.

The polymer flocculant added to the second to fourth steps of the present invention has an effect of facilitating the aggregation of the precipitate mainly composed of iron hydroxide and facilitating solid-liquid separation. As the polymer flocculant, any polymer flocculant containing polyacrylamide or sodium polyacrylate may be used, regardless of nonionic, cationic or anionic. The addition amount of the polymer flocculant is 0.2 to 4 mg / l, preferably 0.5 to 2 mg / l.
As a method for solid-liquid separation performed in the first to fourth steps of the present invention, a generally used method such as a filtration method, a centrifugal separation method, a sedimentation separation method, or the like can be used.
The liquid phase in which heavy metal and selenium are reduced to below the drainage standard value by solid-liquid separation in the fourth step can be discharged after the pH is lowered to near neutrality. Moreover, since the solid phase obtained in the first to fourth steps contains iron, it can be reused as a raw material for cement as an iron source.

The present invention will be described in detail with reference to specific examples. The results of the following examples and comparative examples are shown in Table 1.
Example 1
2500 g of water was added to 250 g of extracted dust and stirred for 3 hours to form a slurry. The slurry was subjected to solid-liquid separation with a membrane filter having a pore size of 1 μm. The pH of the obtained filtrate (hereinafter referred to as raw water 1) was 13.2.

Heavy metals such as lead contained in the raw water 1 were quantified by hydrogen compound ICP emission spectroscopic analysis in accordance with JIS K 0102.
Further, total selenium was quantified by the following method.
That is, sulfuric acid and nitric acid were added to the raw water 1 and heated to generate sulfuric acid white smoke, then allowed to cool to room temperature, hydrochloric acid was added, heated at 90 to 100 ° C. for 10 minutes, allowed to cool, and used as a sample solution. This sample solution was quantified with a hydrogen compound generation atomic absorption spectrometer. Tetravalent selenium was quantified with a hydrogen compound generation atomic absorption spectrometer without pretreatment of raw water 1. Hexavalent selenium was obtained by subtracting tetravalent selenium from all selenium.
The contents of total selenium (tetravalent selenium and hexavalent selenium), hexavalent selenium and lead were 13, 12, and 130 mg / l, respectively.

  Add sulfuric acid to the above 250 ml of raw water 1 to adjust the pH to 7.5, and then add 51.8 mg (1 equivalent to lead) of chelating agent for heavy metal removal (Epoflex L-1 made by Miyoshi Oil & Fats). And stirred for 10 minutes. Next, 1.9 ml of 1 mol / l ferric chloride hexahydrate (10 times the amount of chelating agent for heavy metal removal) was added, the pH was adjusted to 7.5 with sodium hydroxide, and the mixture was stirred for 5 minutes. Mixed. Next, 1 mg / l of a polymer flocculant (Diatrinics Diafloc NP800) was added and stirred and mixed for 10 minutes, and after standing for 10 minutes, the treatment liquid was filtered with 5 types A filter paper.

  Add 1.58 g of ferrous sulfate heptahydrate to the above filtrate (150 times molar amount of 12 mg / l of hexavalent selenium dissolved in raw water 1), add sodium hydroxide to adjust the pH to 10 And stirred and mixed for 30 minutes. Next, 1 mg / l of the above polymer flocculant was added and stirred and mixed for 10 minutes, and after standing for 10 minutes, the treatment liquid was filtered with 5 types A filter paper.

  2.9 ml of 1 mol / l ferric chloride hexahydrate (70 times mol amount of 13 mg / l of total selenium in raw water 1) was added to the filtrate, and sodium hydroxide was added to adjust the pH to 10. The mixture was stirred and mixed for 30 minutes. Next, 1 mg / l of the above polymer flocculant was added and stirred and mixed for 10 minutes, and after standing for 10 minutes, the treatment liquid was filtered with 5 types A filter paper.

  The filtrate was quantified by the raw water 1 analysis method. Total selenium was 0.05 mg / l, which cleared the wastewater standard value of 0.1 mg / l according to the Water Pollution Control Law. Lead was 0.05 mg / l (detection limit) or less, which also cleared the wastewater standard value of 0.1 mg / l according to the Water Pollution Control Law.

(Comparative Example 1)
To raw water 1 used in Example 1, 2.815 g of ferrous sulfate heptahydrate (267 times mole amount of 12 mg / l of hexavalent selenium dissolved in raw water 1) was added to adjust the pH to 10 The mixture was stirred and mixed for 30 minutes. Next, 2 mg / l of the polymer flocculant used in Example 1 was added, and the mixture was stirred and mixed for 10 minutes. After standing for 10 minutes, the treatment liquid was filtered with 5 types A filter paper.
2.9 ml of 1 mol / l ferric chloride hexahydrate (70 times molar amount of 13 mg / l of total selenium in raw water 1) was added to the above filtrate, and the pH was adjusted to 10 and stirred for 30 minutes. Mixed. Next, 2 mg / l of the above polymer flocculant was added and stirred and mixed for 10 minutes. After 10 minutes of standing, this treatment liquid was filtered with 5 types A filter paper.
The filtrate was quantified by the raw water 1 analysis method. The total amount of selenium was 0.29 mg / l, and the effluent standard value of 0.1 mg / l according to the Water Pollution Control Law could not be cleared. Moreover, lead is 0.05 mg / l (detection limit) or less, which cleared the wastewater standard value of 0.1 mg / l according to the Water Pollution Control Law.

(Comparative Example 2)
2500 g of water was added to 250 g of extracted dust and stirred for 3 hours to form a slurry. The slurry was subjected to solid-liquid separation with a membrane filter having a pore size of 1 μm. The pH of the obtained filtrate (hereinafter referred to as raw water 2) was 12.2. The contents of total selenium and hexavalent selenium contained in raw water 2 were 45 and 4 mg / l, respectively.
15.5 ml of 1 mol / l ferric chloride hexahydrate (109 times mole amount of 45 mg / l of total selenium in raw water 2) was added to 250 ml of raw water 2 to adjust the pH to 10 and 30 Stir and mix for a minute. Next, 1 mg / l of the polymer flocculant used in Example 1 was added and mixed with stirring for 10 minutes. After 10 minutes of standing, the treatment liquid was filtered with 5 types A filter paper.
The filtrate was quantified by the raw water 1 analysis method. The total amount of selenium was 1.0 mg / l, and the wastewater standard value of 0.1 mg / l according to the Water Pollution Control Law could not be cleared.

1 First Step 2 Second Step 3 Third Step 4 Fourth Step 5 Extracted Dust 6 Cement Raw Material 7 Effluent Water

Claims (8)

A method for treating dust containing chlorine and selenium, comprising the following steps.
(1) A first step in which water is added to a dust containing chlorine and selenium to form a slurry, followed by solid-liquid separation,
(2) A second step of adding a chelating agent for heavy metal removal to the liquid phase after solid-liquid separation obtained in the first step (hereinafter referred to as raw water), adding a ferric salt compound, and then performing solid-liquid separation. Process,
(3) A third step of adding a ferrous salt compound to the liquid phase after the solid-liquid separation obtained in the second step and performing solid-liquid separation;
(4) The 4th process which adds a ferric salt compound to the liquid phase after solid-liquid separation obtained at the 3rd process, and performs solid-liquid separation. The method for treating dust containing chlorine and selenium according to claim 1, wherein in the second step, the pH is adjusted to 5 to 10 and a chelating agent for removing heavy metals is added. The method for treating dust containing chlorine and selenium according to claim 1 or 2, wherein in the second step, after adding the ferric salt compound, the pH of the liquid phase is readjusted to 5 to 10 and solid-liquid separation is performed. . The dust of chlorine and selenium-containing dust according to any one of claims 1 to 3, wherein in the third step, a ferrous salt compound is added and the pH is adjusted to 8 to 12, followed by solid-liquid separation. Processing method. The dust of chlorine and selenium-containing dust according to any one of claims 1 to 4, wherein in the fourth step, a ferric salt compound is added and the pH is adjusted to 8 to 12, followed by solid-liquid separation. Processing method. The method for treating dust containing chlorine and selenium according to any one of claims 1 to 5, wherein the dust containing chlorine and selenium is cement kiln extraction dust. The method for treating dust containing chlorine and selenium according to any one of claims 1 to 6, wherein in the first step, water is added so that the chlorine concentration of the raw water is 2% by mass or less. The treatment of dust containing chlorine and selenium according to any one of claims 1 to 7, wherein the solid phase after solid-liquid separation obtained in any one of the first to fourth steps is reused as a cement raw material. Method.

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