JP3773467B2 - Method for treating substances containing calcium and heavy metals - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for treating a substance containing calcium and heavy metals, and more particularly to a treatment method for separating and collecting heavy metals such as calcium and lead from dust collected from exhaust gas generated in a cement kiln or the like.
[0002]
[Prior art]
In recent years, technology has been developed to recover heavy metals from non-ferrous smelting raw materials by collecting heavy metals from dust (kiln dust collection dust) containing heavy metals generated from cement kilns etc. using waste as part of the raw materials. .
For example, Japanese Patent Application Laid-Open No. 2000-212654 discloses that a substance (for example, fly ash) containing a heavy metal component such as zinc and chlorine is added with a mineral acid to be slurried, and the pH is adjusted to 5 or less to dissolve chlorine. A chlorine dissolving step to be performed, and an alkali agent is added to the slurry of the chlorine dissolving step to adjust the pH to 12 or more, and then the heavy metal containing starch is separated and recovered from the chlorine containing filtrate by solid-liquid separation. A method for recovering heavy metals from a material containing heavy metals and chlorine, characterized in that it comprises a starch recovery step is described.
[0003]
[Problems to be solved by the invention]
In the technique described in the above publication, an alkali agent is added to the slurry of the chlorine dissolution step to adjust the pH to 12 or higher, and then solid-liquid separation is performed to convert heavy metals such as zinc into heavy metal-containing starches (hydroxides). ).
However, this technique has the following problems.
That is, the heavy metal-containing starch (hydroxide) obtained by the technique of the above publication contains not only heavy metals such as zinc, but also calcium hydroxide and the heavy metal-containing starch in the production process of the heavy metal-containing starch. Because it contains components such as sodium and potassium that are incorporated into the steel, the quality as a non-ferrous refining raw material is not high. That is, by adjusting the pH of the slurry to 12 or more, the solid content includes not only heavy metal hydroxides but also calcium hydroxide and the like, so the content of heavy metal compounds in the solid content is It becomes low and the value as a nonferrous smelting raw material falls.
[0004]
Therefore, the present invention specifies a heavy metal compound that can be suitably used as a non-ferrous refining raw material with a low content of calcium, sodium, potassium, etc. from a substance containing calcium and heavy metals (for example, kiln dust collection dust) and zinc It is an object of the present invention to provide a treatment method that can be separated and recovered from calcium compounds that do not contain heavy metals and can be suitably used as a cement raw material.
[0005]
[Means for Solving the Problems]
As a result of diligent studies to solve the above-mentioned problems, the present inventor has made it possible to elute calcium into the liquid by adjusting pH with hydrochloric acid and then use an alkalinizing agent when processing a substance containing calcium and heavy metals. By adjusting the pH and adding a sulfiding agent, a precipitate containing heavy metal sulfide can be obtained while maintaining the state in which calcium is dissolved in the liquid, and thus the above object is achieved. The present invention has been completed.
[0006]
That is, according to the method for treating a substance containing calcium and heavy metal of the present invention (Claim 1), (A) a substance containing calcium and heavy metal (for example, copper, lead, zinc) and water are mixed to obtain a slurry. Thereafter, hydrochloric acid is added to the slurry to adjust the pH of the slurry to 2.0 to 4.0, and a calcium elution step of eluting calcium into the liquid from the substance containing calcium and heavy metals, (B ) An alkalizing agent (for example, sodium hydroxide) is added to the slurry from which calcium is eluted to adjust the pH of the slurry to 6.5 to 8.0, and then a sulfiding agent (for example, sodium hydrosulfide). Thereafter, the slurry is subjected to solid-liquid separation, and a heavy metal recovery step for obtaining a solid content including a heavy metal sulfide (for example, copper sulfide, lead sulfide, zinc sulfide) and a liquid content including calcium , ( C) Heavy metal After adding the ferrous compound to the liquid containing calcium obtained in the recovery step (B), the pH of the liquid is adjusted to 8.0 to 12.0, and then the liquid is solid-liquid. Selenium to obtain a solid content containing each component of selenium and / or chromium derived from ferrous hydroxide, calcium hydroxide, a substance containing calcium and heavy metals, and a liquid from which heavy metals have been removed, And a chromium removal step .
According to the method of the present invention, in the calcium elution step (A), calcium contained in the substance containing calcium and heavy metal can be eluted in the liquid, and only the heavy metal is removed in the heavy metal recovery step (B). Since it can be recovered as a sulfide, calcium (a component that can be used as a cement raw material) and heavy metal such as copper can be separated and recovered without being mixed with each other. According to the method of the present invention, a series of operations for separating calcium and heavy metals such as copper can be performed in one reaction tank without using a plurality of reaction tanks. Furthermore, according to the method of the present invention, since the selenium and chromium removing step (C) is provided, the liquid after removing a specific heavy metal such as copper (that is, a heavy metal capable of forming an insoluble sulfide) is removed. Further, selenium and chromium can be effectively removed, and the concentration of selenium and chromium in the liquid can be reduced below the environmental standard value .
[0008]
In the method for treating a substance containing calcium and heavy metal, phosphoric acid and / or a liquid component obtained in (D) the heavy metal recovery step (B) can be used as a pre-step of the selenium and chromium removal step (C). Alternatively, a phosphate is added, and an alkalinizing agent (for example, slaked lime) is added as necessary to adjust the pH of the liquid to 6.0 to 10.0, and a substance containing calcium and heavy metals. The fluorine removal process which produces | generates the sparingly soluble fluorine phosphate compound formed by the reaction of the fluorine derived from this and the said phosphoric acid and / or a phosphate can be included (Claim 2 ).
By providing the fluorine removal step in this manner, fluorine can be precipitated as a solid component from the liquid after removing a specific heavy metal such as copper, and the concentration of fluorine in the liquid can be reduced to an environmental standard value or less. it can.
Examples of the object to be treated in the present invention include soot collected from an exhaust gas generated in a kiln such as a cement kiln for producing eco-cement (Claim 3 ).
Since the soot dust has a high content of calcium and heavy metals, it is suitable as an object of the method of the present invention.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail. FIG. 1 is a flowchart showing an example of a method for treating a substance containing calcium and heavy metal according to the present invention, and FIG. 2 is a flowchart showing another example of a method for treating a substance containing calcium and heavy metal according to the present invention.
One example of the method for treating a substance containing calcium and heavy metal according to the present invention is as shown in FIG. 1, in which (A) a substance containing calcium and heavy metal and water are mixed to obtain a slurry, and then hydrochloric acid is added to the slurry. To adjust the pH of the slurry to 2.0 to 4.0 and to elute calcium into the liquid from a substance containing calcium and heavy metals, and (B) obtained in step (A). An alkalinizing agent is added to the slurry to adjust the pH of the slurry to 6.5 to 8.0, and then a sulfiding agent is added. Thereafter, the slurry is subjected to solid-liquid separation to contain heavy metal sulfide. A heavy metal recovery step for obtaining a solid and a liquid containing calcium; and (C) after adding the ferrous compound to the liquid containing calcium obtained in step (B), the pH of the liquid is adjusted. Adjusted to 8.0 to 12.0, and then the liquid was solid-liquid Separately, selenium and chromium to obtain a solid content containing each component of selenium and / or chromium derived from a substance containing ferrous hydroxide, calcium hydroxide, calcium and heavy metals, and a liquid component from which heavy metals have been removed A removal step.
[0010]
Moreover, in addition to each process shown in FIG. 1, as shown in FIG. 2, the other example of the processing method of the substance containing calcium and heavy metal of the present invention is between the process (B) and the process (C). (D) Phosphoric acid and / or phosphate are added to the liquid obtained in step (B), and an alkalinizing agent is added as necessary to adjust the pH of the liquid to 6.0-10. And a fluorine removal step of producing a phosphoric acid phosphate compound formed by reacting fluorine derived from a substance containing calcium and heavy metals with phosphoric acid and / or phosphate.
[0011]
Hereinafter, each process will be described in detail.
[(A) Calcium elution step]
In this step, first, a substance containing calcium and heavy metals and water are mixed to obtain a slurry.
Examples of the substance containing calcium and heavy metal to be treated in the present invention include incineration ash remaining as an incineration residue at the bottom of an incinerator and soot and soot.
Here, as dust, for example, fly ash generated from an incinerator (incineration fly ash), fly ash generated from a melting furnace such as incineration ash (molten fly ash), or chlorine bypass extracted from a cement manufacturing process Examples thereof include dust and bag filter dust obtained during the production of ecocement.
[0012]
Among soot dust, soot generated from combustibles including incinerated ash and / or fly ash (also referred to as “kiln dust collection dust” in this specification) contains calcium and heavy metals at a relatively high content. It is suitable as a processing object of the present invention.
Examples of the kiln dust collection dust include cement kiln for producing eco-cement using incineration ash and fly ash as a part of raw materials, fly ash discharged from kiln for high temperature treatment of incineration ash and fly ash, etc. Can be mentioned.
The component ratio of the kiln dust collection dust generated in the cement kiln for eco-cement manufacture is, for example, the weight ratio in terms of oxide, 2% calcium, 13% potassium, 32% sodium, 2% lead, 1% zinc, copper 2% and chlorine 38%.
[0013]
In this step, the solid-liquid ratio (the mass of the substance containing calcium and heavy metal in 1 liter of slurry) when the substance containing calcium and heavy metal and water are mixed is preferably 600 g / liter or less. When the solid-liquid ratio exceeds 600 g / liter, calcium, water-soluble chlorine and the like contained in the substance containing calcium and heavy metal may not be sufficiently eluted in the liquid.
[0014]
Next, hydrochloric acid is added to the resulting slurry to adjust the pH of the slurry to 2.0 to 4.0, preferably 2.5 to 3.5. From the substance containing calcium and heavy metals, Elute calcium.
When the pH is less than 2.0, silicon and aluminum contained in the substance containing calcium and heavy metal are eluted in the liquid to form a gel-like substance, which causes a decrease in filtration rate during solid-liquid separation. On the other hand, when the pH exceeds 4.0, the elution amount of calcium contained in the substance containing calcium and heavy metal into the liquid decreases, and separation of heavy metal and calcium becomes insufficient.
Note that it is not preferable to use nitric acid or an organic acid instead of hydrochloric acid because the load on the wastewater treatment process increases and the treatment cost increases. In addition, it is not preferable to use sulfuric acid instead of hydrochloric acid because calcium contained in a substance containing calcium and heavy metal generates calcium sulfate (gypsum) and does not elute into the liquid.
[0015]
[(B) Heavy metal recovery process]
In this step, first, an alkalizing agent is added to the slurry obtained in the calcium elution step (A) to adjust the pH of the slurry to 6.5 to 8.0, preferably 6.8 to 7.7. To do.
Here, examples of the alkalizing agent include sodium hydroxide and potassium hydroxide. The alkalizing agent is usually added in the form of an aqueous solution.
When the pH of the slurry is less than 6.5, the sulfurization reaction of zinc in the liquid becomes insufficient, the amount of zinc sulfide produced decreases, and the zinc recovery rate decreases.
When the pH of the slurry exceeds 8.0, the amount of calcium remaining as a solid (hydroxide) without being eluted in the liquid increases, and separation of heavy metal and calcium becomes insufficient. Also, since heavy metals are present in the solids as hydroxides instead of sulfides, the heavy metal hydroxides are dissolved in the water-soluble chlorine (chloride ions), sodium ions, potassium ions Incorporating components such as water-soluble chlorine in the solid content increases. Thus, when content of components other than the heavy metal compound contained in solid content increases, since the value of solid content as a nonferrous refining raw material falls, it is unpreferable.
[0016]
Next, a sulfurizing agent is added to the slurry whose pH has been adjusted.
Here, examples of the sulfiding agent include sodium hydrosulfide (NaSH), sodium sulfide (Na ₂ S), and the like. By adding a sulfiding agent, copper, lead, and zinc contained in a substance containing calcium and heavy metal become copper sulfide (CuS), lead sulfide (PbS), and zinc sulfide (ZnS), respectively. These sulfides are sparingly soluble and remain in the solids.
The addition amount of the sulfiding agent may be appropriately determined according to the content of heavy metal (copper, lead, zinc) in the substance containing calcium and heavy metal.
The slurry after the addition of the sulfiding agent is subjected to solid-liquid separation by filtration or the like to obtain a solid containing heavy metal sulfide and a liquid containing calcium.
Among these, since solid content (dehydrated cake) has water-soluble chlorine attached thereto, it is washed with water to remove water-soluble chlorine. After washing, the solid content can be used as a non-ferrous refining raw material.
On the other hand, the liquid component containing calcium is sent to the selenium and chromium removal step.
[0017]
[(C) Selenium and chromium removal step]
In this step, first, the ferrous compound is added to the liquid containing calcium obtained in the heavy metal recovery step (B).
Examples of ferrous compounds (divalent iron compounds) include ferrous sulfate, ferrous chloride, and ferrous nitrate.
The ferrous compound becomes divalent iron ions in the liquid. The divalent iron ions reduce hexavalent selenium ions and hexavalent chromium ions present in the liquid. As a result, most of the hexavalent selenium ions in the liquid become tetravalent selenium ions, and most of the hexavalent chrome ions become trivalent chromium ions.
The amount of ferrous compound added is 2,500 mg / liter or more as ferrous ions when the selenium content in the liquid is 1 mg / liter, and ferrous iron when the selenium content in the liquid is 10 mg / liter. The ion is preferably 6,000 mg / liter or more.
[0018]
After adding the ferrous compound, the pH of the liquid is adjusted to 8.0 to 12.0, preferably 8.5 to 11.5 by adding an alkalizing agent such as slaked lime as necessary. To do. By adjusting the pH within this numerical range, iron hydroxide derived from the ferrous compound, calcium hydroxide generated by the reaction of calcium in the liquid with hydroxide ions, calcium and heavy metals are included. Selenium and / or chromium derived from the substance can be co-precipitated.
If the pH is less than 8.0, the production of iron hydroxide becomes insufficient, the coprecipitation of selenium and / or chromium with iron hydroxide does not occur sufficiently, and the amount of selenium and / or chromium remaining in the liquid Is unfavorable because it increases. If the pH exceeds 12.0, selenium remains in the liquid, which is not preferable.
[0019]
Next, the liquid containing the precipitate after pH adjustment is subjected to solid-liquid separation by filtration or the like to obtain a solid (dehydrated cake) and a liquid.
Among these, solid content contains selenium and / or chromium co-precipitated with ferrous hydroxide, calcium hydroxide, and their hydroxides as described above. Since this solid content is mainly composed of calcium hydroxide and does not contain heavy metals such as copper, it can be used as a cement raw material after washing with water.
On the other hand, since the liquid does not contain heavy metals and contains a lot of sodium ions, chloride ions, etc., it can be drained into the environment outside the system after passing through the pH adjustment step and the chloride recovery step.
[0020]
[(D) Fluorine removal step]
When the liquid containing calcium obtained in the heavy metal recovery step (B) contains fluorine exceeding the drainage standard (for example, 15 mg / liter), the fluorine removal step is performed before the selenium and chromium removal step (C). It is desirable to provide (D).
In this step, first, phosphoric acid and / or phosphate is added to the liquid obtained in the heavy metal recovery step (B). The addition amount of phosphoric acid and / or phosphate (when phosphoric acid and phosphate are used in combination) is usually about 3 to 30 mol with respect to 1 mol of fluorine in the liquid.
When phosphoric acid and / or phosphate is added to lower the pH of the slurry to less than 6.0, an alkalizing agent such as slaked lime is added to adjust the pH of the slurry to 6.0 to 10.0. Preferably, it is adjusted to 6.5 to 9.5. In addition, when the pH of the slurry after adding phosphoric acid and / or phosphate is within the above numerical range, it is not necessary to add an alkalizing agent.
[0021]
By adjusting the pH within this numerical range, fluorine derived from a substance containing calcium and heavy metals, added phosphoric acid and / or phosphate, and calcium present in the liquid react to react with each other. An oxyfluorine compound can be produced. When the pH is less than 6.0 or exceeds 10.0, the amount of fluorine phosphate compound produced decreases, and fluorine cannot be removed sufficiently.
Phosphoric acid (H ₃ PO ₄ ) is usually added as a phosphoric acid aqueous solution having an appropriate concentration.
Examples of the phosphate include sodium phosphate, potassium phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, and the like.
[0022]
Specifically, the phosphoric acid fluorine compound is fluoroapatite (Ca ₁₀ (PO ₄ ) ₆ F ₂ ). Fluoroapatite is a hardly soluble substance and precipitates in the liquid.
When slaked lime (Ca (OH) ₂ ) is used as the alkalizing agent, the slaked lime becomes a calcium source for the fluorine phosphate compound (Ca ₁₀ (PO ₄ ) ₆ F ₂ ).
After the pH adjustment, the liquid containing the precipitate of the fluorine phosphate compound is treated in the selenium and chromium removal step (C) described above.
In addition, you may solid-liquid-separate the liquid part containing the deposit of a fluorine phosphate compound obtained at this process by filtration etc. previously, before processing at a selenium and chromium removal process (C). In this case, the liquid obtained by filtering the precipitate (fluorine phosphate compound) is treated in the selenium and chromium removal step (C) described above.
[0023]
【Example】
Hereinafter, the present invention will be described by way of examples.
[Example 1]
As the treatment object, soot dust obtained by collecting dust from exhaust gas discharged from a cement kiln for eco-cement production was used. This dust was a weight ratio in terms of oxide and contained 2% calcium, 13% potassium, 32% sodium, 2% lead, 1% zinc, 2% copper and 38% chlorine.
1 kg of this dust and water were stirred and mixed for 20 minutes so as to obtain a solid-liquid ratio of 400 g / liter to obtain a slurry. A hydrochloric acid solution (concentration: 35%) was added to the slurry to adjust the pH of the slurry to 3.2. Next, 2N sodium hydroxide solution was added to the slurry to adjust the pH of the slurry to 7.0, and 26 g of sodium hydrosulfide was further added and stirred.
After stirring, the slurry was filtered to obtain a liquid containing 57 g (dry weight) of solid content (sulfur of heavy metal) and calcium.
After adding 20 mL of 1N phosphoric acid solution to the obtained liquid, slaked lime was further added and stirred, and the pH of the resulting slurry was adjusted to 7.5. Next, this slurry was filtered to obtain a solid content and a liquid content composed of a fluorine phosphate compound.
After adding ferrous sulfate heptahydrate (FeSO ₄ .7H ₂ O) at a solid-liquid ratio of 15 g / liter to the obtained liquid, 2N sodium hydroxide solution was added to adjust the pH of the liquid. Adjusted to 9.4. The slurry after pH adjustment was filtered to obtain a solid content and a liquid content containing calcium hydroxide, iron hydroxide and the like.
The amounts of selenium, chromium and fluorine contained in the obtained liquid were all below the environmental standard value.
[0024]
【The invention's effect】
According to the treatment method of the present invention, from a substance containing calcium and heavy metals such as kiln dust collection dust, a low content of calcium, sodium, potassium, etc., a heavy metal compound that can be suitably used as a non-ferrous refining raw material, and zinc, etc. A calcium hydroxide-containing substance having a low heavy metal content and that can be suitably used as a cement raw material can be efficiently separated and recovered in one reaction tank.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an example of a method for treating a substance containing calcium and heavy metal according to the present invention.
FIG. 2 is a flowchart showing another example of the method for treating a substance containing calcium and heavy metal according to the present invention.

Claims (3)

(A) After mixing a substance containing calcium and heavy metals with water to obtain a slurry, hydrochloric acid is added to the slurry to adjust the pH of the slurry to 2.0 to 4.0, and the calcium and A calcium elution step of eluting calcium into the liquid from substances containing heavy metals;
(B) An alkalizing agent is added to the slurry from which calcium has been eluted to adjust the pH of the slurry to 6.5 to 8.0, and then a sulfiding agent is added. Thereafter, the slurry is solid-liquid separated. A heavy metal recovery step for obtaining a solid content containing sulfide of heavy metal and a liquid content containing calcium;
(C) After adding the ferrous compound to the liquid containing calcium obtained in the heavy metal recovery step (B), the pH of the liquid is adjusted to 8.0 to 12.0, Solid component containing selenium and / or chromium components derived from ferrous hydroxide, calcium hydroxide, a substance containing calcium and heavy metal, and liquid from which heavy metal has been removed by solid-liquid separation of the liquid component A method for treating a substance containing calcium and heavy metals, comprising the step of removing selenium and chromium to obtain As a pre-process of the selenium and chromium removal process (C),
(D) Phosphoric acid and / or phosphate are added to the liquid obtained in the heavy metal recovery step (B), and an alkalinizing agent is added as necessary to adjust the pH of the liquid to 6. Claims including a fluorine removing step of adjusting to 0 to 10.0 and generating a fluorine phosphate compound formed by a reaction between fluorine derived from the substance containing calcium and heavy metal and the phosphoric acid and / or phosphate. Item 8. A method for treating a substance containing calcium and heavy metals according to Item 1 . The method for treating a substance containing calcium and heavy metal according to claim 1 or 2 , wherein the substance containing calcium and heavy metal is soot collected from exhaust gas generated in a kiln.

Images