JP4785438B2 - Heavy metal recovery from cement manufacturing process - Google Patents

Description

The present invention relates to Omokin Shokukai yield method of cement production process, in particular, from the kiln exhaust gas passage from the kiln ass cement kiln up to the bottom cyclone, chlorine and sulfur, etc. to bleed a portion of the combustion gas to remove relates to a method of heavy metal yield efficiency good Ku times such as thallium and lead from dust or the like contained in the extracted combustion gas.

  Focusing on chlorine, sulfur, alkali, etc. that cause problems such as blockage of preheaters in cement production equipment, focusing on the problem of chlorine, from the kiln bottom of cement kilns to bottom cyclones Chlorine bypass equipment is used for extracting chlorine from a kiln exhaust gas passage to remove chlorine.

  In this chlorine bypass facility, for example, as described in Patent Document 1, since chlorine is unevenly distributed on the fine powder side of the dust generated by cooling the extracted exhaust gas, the dust is divided into coarse powder and fine powder by a classifier. Separated, the coarse powder was returned to the cement kiln system, and the separated fine powder (chlorine bypass dust) containing potassium chloride and the like was recovered and added to the cement grinding mill system.

  However, in recent years, as the recycling of wastes into cement raw materials or fuels has been promoted, and the amount of waste processed increases, the amount of volatile components such as chlorine, sulfur, and alkali brought into the cement kiln also increases. The amount of bypass dust is also increasing. For this reason, all of the chlorine bypass dust could not be used in the cement crushing process and was washed with water. However, heavy metals are expected to exceed the allowable concentration of cement in the future, so the development of an effective utilization method is required. It was done.

  From this point of view, the cement raw material processing method described in Patent Document 2 desalinates chlorine bypass dust that has been conventionally washed with water, and adds chlorine to the waste containing chlorine to remove chlorine in the waste. Elution and filtration, use the resulting desalted cake as a raw material for cement, and purify wastewater to remove heavy metals such as selenium, effectively using chlorine bypass dust without causing environmental pollution ing.

  Patent Document 3 describes the purpose of reducing the amount of chemicals used when separating and recovering lead, chlorine, and calcium from waste such as chlorine bypass dust. Then, a waste containing chlorine and water for slurrying are mixed to form a slurry, the slurry is classified into a coarse part and a fine part, and an alkali agent such as sodium hydroxide is added to the fine part, Solid-liquid separation is performed to obtain a filtrate containing solid content including calcium hydroxide, lead and chlorine, and a sulfurizing agent such as sodium hydrosulfide is added to the filtrate, followed by solid-liquid separation and lead sulfide. And a technique of obtaining a filtrate containing a chlorine component and using the obtained filtrate as water for slurrying.

  Furthermore, in Patent Document 4, when the waste containing lead content such as chlorine bypass dust and slurry water are mixed and the lead content in the waste is eluted in water, the elution rate of the lead content in water In order to increase the pH, waste containing lead and water for slurrying are mixed to form a slurry, the pH of the slurry is adjusted to 7.0 to 11.5, the oxidation-reduction potential is adjusted to 400 mV or more, and lead The slurry containing lead is obtained, the slurry containing lead is separated into solid and liquid, the filtrate containing solid and lead is obtained, and the sulfur containing agent is added to the filtrate containing lead, followed by solid-liquid separation. A technique is described in which lead sulfide and a filtrate are obtained and a part of the obtained filtrate is used as water for the slurrying.

  On the other hand, in the cement manufacturing process, in addition to the above selenium, lead, etc., a small amount of thallium (Tl) is produced from coal as fuel and waste tires. For example, pulverized coal supplied to kilns and calcining furnaces contains about 1 ppm of thallium and waste tires contain about 8 ppm of thallium. Since this thallium has a low boiling point, it volatilizes between the kiln and the preheater of the cement baking apparatus, and most of it is concentrated in the preheater.

International Publication No. WO97 / 21638 Pamphlet Japanese Patent Laid-Open No. 11-100343 JP 2003-236497 A JP 2003-236503 A

  As described above, when thallium is concentrated in the preheater and the cement kiln combustion exhaust gas is cooled, it is absorbed by the cement raw material, and is therefore mixed into the chlorine bypass dust. Therefore, when desalinating the chlorine bypass dust and effectively using it as a cement raw material, it is necessary to remove thallium together with selenium, lead, etc., and to effectively use the chlorine bypass dust without causing environmental pollution.

Accordingly, an object of the present invention to provide a method for yield efficiency good Ku times these heavy metals from chlorine bypass dust or the like generated in the cement manufacturing process.

To achieve the above object, the present invention provides a Omokin Shokukai yield method of cement production process, from the cement manufacturing process, bled part of 300 ° C. or higher 900 ° C. or less of the cement kiln combustion gas, bled The combustion gas is cooled without dust removal, the heavy metal-containing dust contained in the combustion gas is collected, water is added to the collected heavy metal-containing dust to form a primary slurry, and then the primary cake and primary filter are collected. And a sulfurizing agent is added to the primary filtrate so that the equivalent ratio of S / (Tl + Pb) is 2.0 to 2.5 to separate into a secondary cake and a secondary filtrate. , characterized by yield one or more times selected in the secondary cake side thallium, lead, selenium.

Then, according to the present invention, to bleed part of cement kiln combustion gas, and thallium from chlorine bypass dust or the like contained in the extracted combustion gas, lead and, be yield efficiency good Ku times heavy metals comprising selenium it can.

The present invention also relates to a method for recovering heavy metals from a cement manufacturing process, wherein from the cement manufacturing process, a step of removing a part of a cement kiln combustion gas of 300 ° C. or higher and 900 ° C. or lower to extract only the gas, after solidifying of the gas is cooled, and the dust collecting heavy metals containing dust contained in 該Ga scan, by adding water to the dust collecting heavy metal-containing dust, sulfuric acid, hydrochloric acid, one or more selected from nitric acid After making the primary slurry, it is separated into a primary cake and a primary filtrate, and a sulfurizing agent is added to the primary filtrate so that the equivalent ratio of S / (Tl + Pb) is 2.0 to 2.5. and then separated into a second cake and secondary filtrate, and recovering an Tariu arm to said secondary cake side. The cement kiln combustion gas of 300 ° C or more and 900 ° C or less contains a large amount of thallium compared to other heavy metals, so a part of the cement kiln combustion gas in this temperature range is extracted and cooled. Thallium can be efficiently recovered from the obtained dust.

The sulfurizing agent can be either sodium hydrosulfide or sodium sulfide .

  Moreover, after adding a pH adjuster and a ferrous iron compound to the secondary filtrate to reduce the selenium concentration, the secondary filtrate is separated into a tertiary filtrate containing a tertiary cake and selenium. The subsequent filtrate may be passed through an electrodialyzer and separated into concentrated brine and demineralized water containing selenium.

As described above, according to the present invention, it is possible to cement manufacturing process thallium, lead, to yield efficiency good Ku times of heavy metals, including selenium.

  As an example of the heavy metal recovery method from the cement manufacturing process according to the present invention, as shown in FIG.

  The water washing step is a step of removing chlorine by washing the chlorine bypass dust, and in order to carry out this step, a boiler 1, a hot water tank 2, a dissolution tank 3, and a belt filter 4 are provided.

  Warm water generated in the boiler 1 is supplied to the dissolution tank 3 through the warm water tank 2 and mixed with chlorine bypass dust. In the dissolution tank 3, the water-soluble chlorine content contained in the chlorine bypass dust is dissolved in warm water. The slurry discharged from the dissolution tank 3 is solid-liquid separated by the belt filter 4, and the primary cake from which the chlorine content has been removed is returned to the cement kiln and used as a cement raw material. On the other hand, the primary filtrate containing chlorine and heavy metals such as thallium, lead and selenium is temporarily stored in the storage tank 5.

  The wastewater treatment step is a step of removing the heavy metals and calcium from the primary filtrate. In order to carry out this step, the storage tank 5, the chemical reaction tanks 7, 9, 11 and the solid-liquid separation device are used. Filter presses 6, 8 and 10, an iron removal tower 12, a chelate resin tower 13, a filtration device 14, and an electrodialysis device 15.

A sulfiding agent is added to the primary filtrate containing chlorine, heavy metals such as thallium and lead, and calcium stored in the storage tank 5, and thallium (Tl ⁺ ) in the filtrate contains sulfide ions (S ^2- ) reacts with thallium sulfide (Tl ₂ S), and lead (Pb ²⁺ ) reacts with sulfide ions (S ^2- ) to produce lead sulfide (PbS). Can also be precipitated as a solid and can be recovered as a secondary cake via the filter press 6.

As the sulfiding agent, sodium hydrosulfide (NaHS), sodium sulfide (Na ₂ S), sodium polysulfide (Na ₃ S ₄ , Na ₂ S ₄ ) or the like can be used. The obtained thallium sulfide can be used as a raw material for magnetic tapes, metal halide lamps, optical lenses, etc., and lead sulfide can be used as a raw material for refining.

  FIG. 3 shows the analysis result of the filtrate when sodium hydrosulfide is added to the storage tank 5 and stirred and then filtered. From the graph, the concentration of Tl and Pb in the filtrate is approximately 0 mg / l with the addition amount of sodium hydrosulfide so that the equivalent ratio of S / (Tl + Pb) is 2.0 to 2.5. From this, it can be seen that substantially all of Tl and Pb in the storage tank 5 can be precipitated as Tl2S and PbS, respectively, at this equivalent ratio. The Tl concentration of the solid obtained after drying the cake collected at this time was 29%, and the Pb concentration was 49%.

FIG. 4 shows that after adding sodium hydrosulfide to the storage tank 5 and stirring it, adding hydrochloric acid and ferrous sulfate to the secondary filtrate after filtering it, adjusting the pH with calcium hydroxide and stirring The analysis result of the tertiary filtrate after filtering is shown. The amount of sodium hydrosulfide added is 1.6 or more in the equivalent ratio of S / (Tl + Pb), and the concentration of Tl and Pb in the filtrate is 0.3 mg / l or less. It can be seen that Tl in 5 precipitates as Tl ₂ S and Pb precipitates as Pb ₂ S or Pb (OH) ₂ .

  A secondary filtrate is supplied to the chemical reaction tank 7 shown in FIG. 1, and hydrochloric acid as a pH adjuster is added to adjust the pH of the chemical reaction tank 7 to 4 or less. The reason for supplying hydrochloric acid is to dissolve ferrous sulfate or the like as a reducing agent, thereby enhancing the effect as a reducing agent.

  With ferrous sulfate, selenium as a heavy metal contained in the waste water is reduced and deposited. Here, in order to suppress the addition amount of ferrous sulfate as a reducing agent, the selenium concentration of the tertiary filtrate is set to about 0.8 mg-Se / l. Next, calcium hydroxide is added to raise the pH to 8 to 11, and the ferrous hydroxide produced by the addition of ferrous sulfate is condensed and precipitated. The reason why the pH is adjusted to 8 to 11 is that ferrous hydroxide and a selenium compound and / or selenium metal precipitate as products in such a pH range. In place of calcium hydroxide, sodium hydroxide, potassium hydroxide or the like may be used.

  And the slurry discharged | emitted from the chemical | medical solution reaction tank 7 is solid-liquid separated by the filter press 8, and a tertiary cake is returned to a cement kiln etc. and used as a cement raw material, and a tertiary filtrate is potassium carbonate in the chemical | medical solution reaction tank 9. And calcium in the tertiary filtrate is removed. The reason why calcium in the tertiary filtrate is removed is to prevent clogging between the exchange membranes due to the calcium scale in the electrodialysis apparatus 15 in the subsequent stage. In addition, you may use sodium carbonate instead of potassium carbonate.

  Next, the slurry discharged from the chemical reaction tank 9 is solid-liquid separated by a filter press 10, the quaternary cake is returned to the cement kiln and used as a cement raw material, and the fourth filtrate is hydrochloric acid in the chemical reaction tank 11. After adjusting the pH by adding iron, the iron removal tower 12, the chelate resin tower 13, and the filtration device 14 remove iron, residual heavy metals, and suspended substances (SS).

The waste water from the filtration device 14 is supplied to the electrodialysis device 15 where the selenic acid (SeO ₄ ²⁻ ) in the waste water is included in the desalted water and the chlorine content is included in the concentrated salt water. The electrodialyzer 15 functions to include monovalent anions and cations in the secondary filtrate from the filtration device 14 on the concentrated salt water side. This will be described with reference to FIG.

The electrodialysis apparatus 15 includes an anode 15a and a cathode 15b at both ends, and a cation exchange membrane 15c as an ion exchange membrane and an anion exchange membrane 15d are alternately arranged between the electrodes 15a and 15b. A desalting chamber 15e or a concentration chamber 15f is formed between the cation exchange membrane 15c and the anion exchange membrane 15d. The treatment liquid (the filtrate of the filtration device 14) is supplied to the desalting chamber 15e, and K ⁺ contained in the treatment liquid passes through the cation exchange membrane 15c and moves to the concentration chamber 15f, and Cl ⁻ is an anion. It moves through the ion exchange membrane 15d to the concentration chamber 15f. On the other hand, if the anion exchange membrane has monovalent ion selectivity, selenic acid (SeO ₄ ²⁻ ) is divalent, and therefore remains in the desalting chamber 15e. As a result, an anion having a valence of ² or more such as SeO ₄ ²⁻ remains in the desalting chamber 15e, and K ⁺ and Cl ⁻ move to the concentration chamber 15f, and these become KCl and are included in the concentrated salt water. , SeO ₄ ^2- is included in the demineralized water.

  The desalinated water from the electrodialyzer 15 is returned to the hot water tank 2 in the water washing process via a circulation route (not shown) (see reference A). Thereby, the selenium concentration of concentrated salt water is reduced to 0.1 mg-Se / l or less which is an allowable value in the case of sewage discharge, for example.

  The salt recovery process is a process for recovering the salt from the concentrated salt water to obtain industrial raw materials. In order to carry out this process, the boiler 16, the heater 17, the crystallizer 18, the condenser 19, and the filtrate tank are used. 20 and a centrifuge 21 are provided.

  The concentrated salt water is heated in the heater 17 by the steam from the boiler 16, and crystallization is performed in the crystallizer 18. In the crystallizer 18, the solute in the concentrated salt water is precipitated as crystals, and the industrial salt is recovered through the centrifugal separator 21 and used as an industrial raw material. On the other hand, the water evaporated in the crystal unit 18 is cooled in the condenser 19 to recover the drain, and this drain is returned to the water washing step. The filtrate separated by the centrifuge 21 is returned to the crystallizer 18 through the filtrate tank 20. In addition, it is also possible to discharge the salt without recovering the salt from the concentrated salt water.

  Next, a recovery method specialized in thallium among the heavy metals will be described.

  FIG. 5 shows an example of a cement baking apparatus. The cement baking apparatus 31 includes a preheating machine 32, a calcining furnace 33, a kiln 34, a clinker cooling machine 35, and the like.

  Since the preheater 32 preheats the raw material with the high-temperature gas from the calciner 33, the preheater 32 includes a plurality of cyclones 32a to 32d, and between each cyclone, between the third-stage cyclone 32b and the calciner 33, and Raw material chutes 37 to 41 are provided between the lowermost cyclone 32a and the kiln 34, and a main exhaust wind turbine 36 for discharging exhaust gas discharged from the uppermost cyclone 32d to the outside of the system is disposed.

  The calciner 33 is provided with a burner 33a for blowing pulverized coal in order to calcine the raw material preheated by the preheater 32. The calciner 33 is extracted from the clinker cooler 35 via a cooler bleed duct 42. Is introduced. The calciner 33 is connected to the kiln 34 via the rising duct 43.

  The kiln 34 includes a burner 34a for blowing pulverized coal in order to produce a cement clinker by firing the raw material calcined by the calcining furnace 33. The clinker cooler 35 is disposed on the downstream side of the kiln 34 in order to cool the clinker fired as described above.

  Here, at points A to D in FIG. 5, the raw material was collected and the concentration of each heavy metal was measured.

  As is clear from Table 1, Tl becomes higher as the concentration in the raw material approaches the first stage cyclone, while other metals become lower as they approach the first stage, and Tl is different from other heavy metals. It can be seen that it is concentrated in the temperature range. Therefore, Tl can be removed from the cement manufacturing process by extracting the combustion gas in the temperature range of 300 to 900 ° C. above the preheater 32 and collecting the dust after cooling the extracted combustion gas.

  Further, at points E to F in FIG. 5, the combustion gas is extracted by extracting the dust, and the obtained dust and the dust-removed gas are separated and collected, and the results of measuring Tl are shown in Table 2. Shown in The dust generated by cooling at this time was dissolved in nitric acid, and the Tl concentration of the product recovered by adding sodium hydrosulfide was 89%.

  As is clear from Table 2, it can be seen that a large amount of Tl is present in the dust generated by extracting the combustion gas and cooling the gas after dust removal. Therefore, in the temperature range of 300 to 900 ° C. above the preheater 32, Tl can be recovered at a high concentration by collecting the dust generated by extracting the combustion gas and cooling it after dust removal.

It is a flowchart which shows an example of the system for enforcing the heavy metal collection | recovery method from the cement manufacturing process concerning this invention. It is the schematic for demonstrating the principle of the electrodialysis apparatus used for the processing system of FIG. It is a graph which shows the analysis result of the filtrate at the time of filtering, after adding and stirring sodium hydrosulfide to the storage tank of the processing system of FIG. After adding sodium hydrosulfide to the storage tank of the treatment system of FIG. 1 and stirring, add hydrochloric acid and ferrous sulfate to the secondary filtrate after filtration, adjust the pH with calcium hydroxide, and stir It is a graph which shows the analysis result of the tertiary filtrate after filtering. It is a flowchart for demonstrating the collection | recovery method of thallium from the preheater of a cement baking apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Boiler 2 Hot water tank 3 Dissolution tank 4 Belt filter 5 Storage tank 6 Filter press 7 Chemical liquid reaction tank 8 Filter press 9 Chemical liquid reaction tank 10 Filter press 11 Chemical liquid reaction tank 12 Iron removal tower 13 Chelate resin tower 14 Filtration apparatus 15 Electrodialysis apparatus 15a Anode 15b Cathode 15c Cation exchange membrane 15d Anion exchange membrane 15e Desalination chamber 15f Concentration chamber 16 Boiler 17 Heater 18 Crystallizer 19 Capacitor 20 Filtrate tank 21 Centrifuge 31 Cement calciner 32 Preheater 32a Bottom cyclone 32b 3 Stage cyclone 32c Second stage cyclone 32d Uppermost cyclone 33 Calciner 33a Burner 34 Kiln 34a Burner 35 Clinker cooler 36 Main exhaust wind turbine 37-41 Raw material chute 42 Cooler bleed duct 43 Rising duct

Claims (4)

From the cement manufacturing process, part of the cement kiln combustion gas of 300 ° C or higher and 900 ° C or lower is extracted,
Cool the extracted combustion gas without removing dust,
Collecting heavy metal-containing dust contained in the combustion gas;
After adding water to the collected heavy metal-containing dust to form a primary slurry, it is separated into a primary cake and a primary filtrate,
A sulfurizing agent was added to the primary filtrate so that the equivalent ratio of S / (Tl + Pb) was 2.0 to 2.5 to separate into a secondary cake and a secondary filtrate,
A method for recovering heavy metals from a cement manufacturing process, wherein one or more selected from thallium, lead and selenium are recovered on the secondary cake side. From the cement manufacturing process, removing a part of the cement kiln combustion gas of 300 ° C. or more and 900 ° C. or less and taking out only the gas;
After the dust-removed gas is cooled and solidified,
Collecting heavy metal-containing dust contained in the gas,
One or more selected from water, sulfuric acid, hydrochloric acid, and nitric acid is added to the collected heavy metal-containing dust to form a primary slurry, and then separated into a primary cake and a primary filtrate.
A sulfurizing agent was added to the primary filtrate so that the equivalent ratio of S / (Tl + Pb) was 2.0 to 2.5 to separate into a secondary cake and a secondary filtrate,
A method for recovering heavy metals from a cement manufacturing process, wherein thallium is recovered on the secondary cake side.   The method for recovering heavy metals from a cement manufacturing process according to claim 1 or 2, wherein the sulfiding agent is either sodium hydrosulfide or sodium sulfide. After adding a pH adjuster and a ferrous compound to the secondary filtrate to reduce the selenium concentration, the secondary filtrate is separated into a tertiary filtrate containing a tertiary cake and selenium, and a tertiary filter containing the selenium. through the liquid in an electrodialysis apparatus, a heavy metal recovery process from a cement manufacturing process according to claim 1 or 2, characterized in that the separation in demineralized water containing concentrated brine and selenium.

Images