JPH07188793A - Method for recovering valuable metal and calcium fluoride from waste liquid of pickling stage - Google Patents

Abstract

PURPOSE:To efficiently recover sludge contg. a sulfur-component at a lower ratio and contg. valuable metal oxides at a high concn. by adding CaCl2 and inoculating agent to a waste liquid of pickling, adjusting this waste liquid to correct pH and neutralizing and dehydrating a supernatant from which formed precipitate is removed. CONSTITUTION:Part 5 of the precipitate is supplied as the inoculating agent together with the waste liquid 2 of a pickling stage contg. metal ions of Fe, Ni, Cr, etc., and Fe<+>, sulfuric acid or sulfurous acid ions, etc., and an alkali 4 contg. CaCl2, 3, Ca into a pH adjusting vessel 1. The pH of the waste liquid 2 is adjusted to 1.0 to 3.0 in this vessel to form the precipitate contg. F and S. This precipitate is separated by a thickener 7 and part thereof is added as the inoculating agent 5 to the waste liquid 2 to promote the formation of the precipitate. The remaining part is sent to a floation separating machine 13 where CaF2 is recovered as floating ore 19. On the other hand, the supernatant 8 of the thickener 7 is neutralized by the alkali 14 in a neutralizing vessel 9. The metal hydroxide 15 formed in such a manner is dehydrated and heat treated in a dehydrating stage 17, by which the high-concn. sludge 18 of the valuable metal oxides, such as Ni and Cr, contg. the S-component at a lower ratio is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is mainly applied to iron, such as waste liquid discharged in the pickling process of stainless steel.
Nickel and chromium metal ions and fluorine ions, sulfate ions and / or sulfite ions (hereinafter “sulfate ions”)
A method for recovering valuable metals such as nickel and chromium, which are useful as steel materials, in the form of oxide sludge with a low sulfur content concentration from an acidic waste liquid containing
Further, it relates to a method for recovering calcium fluoride from the liquid.

[0002]

2. Description of the Related Art As a method for industrially recovering a metal component from an acidic liquid containing metal ions and sulfate ions, such as waste liquid discharged from a pickling process, an alkali is added to the acidic liquid. There is a method of precipitating the metals in the liquid all at once by saccharifying, or a method of gradually precipitating various metal ions by adding alkali little by little and separating and recovering them. It is conventionally known. An inexpensive calcium salt such as slaked lime is generally used as the alkali to be added.

Here, Japanese Patent Application Laid-Open No. 506574/1975 discloses a treatment method for producing a valuable solid molded product from waste acid containing chromium and sulfuric acid and hydrofluoric acid by using slaked lime or quick lime. In addition, Japanese Patent Publication No. 51-19439
In Japanese Patent Publication No. 1994-242242, there is disclosed a method of synthesizing a calcined gypsum raw material for gypsum board from a solution of ammonium sulfate acid using calcium salt and calcium chloride. Furthermore, in Japanese Patent Application No. 4-296577 filed by the present applicant, the sulfate ion and sulfite ion in the liquid are previously fixed and removed as a compound having a low solubility such as calcium sulfate, and then the supernatant is neutralized. A method for obtaining a low-sulfur sludge having a low sulfur content by applying the above has been filed.

In addition, metals or metals having a low content of impurities such as sulfur are obtained by individually separating those metals from an acidic liquid containing metal ions such as nickel and cobalt by solvent extraction or back extraction. A method of recovering the oxide is also conceivable.

[0005]

In order to save resources, it is desirable that the precipitates and sludges recovered by the above treatment method can be reused as resources. However,
When an alkali is added to a liquid containing metal ions such as iron, nickel, and chromium and fluorine ions, sulfate ions, etc. to precipitate the metal components all at once, the precipitate is calcium sulfate (gypsum plaster). ), Calcium fluoride, etc. will be obtained in a mixed form. The precipitate thus obtained contains valuable nickel and chromium as raw materials for steel and calcium fluoride which can be used as a flux in refining operation in some cases, but at the same time, it is harmful. Since it contains a large amount of various sulfur components, there is a problem in that desulfurization treatment is required to reuse it as a steel raw material or flux, which causes a cost increase. In addition, there is also a problem that the amount of sulfur used is severely limited due to the large amount of sulfur.

[0006] Further, according to the method of gradually precipitating various metal ions by adding alkali little by little to the liquid and gradually separating and recovering them, any metal and sulfur are coprecipitated. By doing so, a precipitate in which the sulfur content and the metal content are mixed is generated, and the same problem as described above occurs.

When the treatment method of JP-A-50-6574 is carried out on a liquid containing a metal component such as iron, chromium or nickel, the solid molded product obtained is a mixture of the metal component and calcium sulfate. It is impossible to use the solid molded product as it is as a raw material for steel. Furthermore, since the method of Japanese Patent Publication No. 51-19439 is intended for ammonium sulfate acid solution, it has a high iron content and cannot be applied to liquids containing metal components such as chromium and nickel. However, this method cannot be applied to liquids containing a large amount of valuable metals as raw materials for steel.

On the other hand, Japanese Patent Application No. 4-
According to the method of 296777, the sludge is obtained after fixing and removing the sulfate ion or the like in the liquid as a compound having a low solubility such as calcium sulfate or calcium sulfite in advance, so that the sludge is obtained. Compared with the method described in JP-B No. 51-19439 and the method disclosed in JP-B-51-19439, there is an advantage in that loss of valuable metal as a steel raw material can be reduced and sludge with a low sulfur content can be obtained. However, in this method, when the concentration of sulfate ions etc. in the liquid is low, it is necessary to add an excessive sulfur content fixing agent such as calcium chloride, which increases the treatment cost and chlorine concentration. This causes a problem that the precipitation efficiency of metal ions is reduced. In addition, when a large amount of iron ions are present in the liquid, the content of iron in the obtained sludge becomes high, and there is a drawback that useful steel raw materials having high chromium and nickel concentrations cannot be efficiently recovered.

In addition, the method of individually separating and recovering metals such as nickel and cobalt from the liquid by solvent extraction or back extraction can reduce the content of impurities such as sulfur, but the chemicals used for extraction are expensive. However, it has the drawbacks of high cost and difficulty in industrial use.

Therefore, according to the present invention, an acidic liquid containing metal ions of iron, nickel, chromium and fluorine ions, sulfate ions and the like, such as waste liquid discharged from the pickling process of stainless steel, is converted into valuable metals such as nickel and chromium. The purpose is to efficiently recover sludge containing a high concentration of metal oxides with a low sulfur content.

[0011]

According to the present invention, mainly metal ions of iron, nickel and chromium and fluorine ions,
Calcium chloride is added to the waste liquid of the pickling step containing sulfate ions and / or sulfite ions, and the pH of the waste liquid is adjusted to the range of 1.0 to 3.0 to remove the fluorine content and the sulfur content. Forming a precipitate containing and separating into a supernatant and a precipitate, and then neutralizing the supernatant,
A method for recovering sludge containing nickel and chromium metal oxides having a low sulfur content concentration, wherein a part of the precipitate obtained in advance is used as an inoculant in the waste liquid when forming the precipitate. A method for recovering valuable metals from the waste liquid of the pickling step, which is characterized by being added to promote the generation of the precipitate, is provided.

Further, in this method, a method in which calcium fluoride in the precipitate is recovered by subjecting the pulp in which the precipitate obtained by separating the supernatant and the precipitate is suspended to flotation Then, in the flotation process, the pH of the pulp is adjusted to a range of 9.0 to 11.0, and an anionic scavenger is added,
And in the flotation, the pulp pH is adjusted to 5.5 to 9.5.
And the addition of a cationic scavenger.

(Detailed Description of the Invention) For example, in a pickling facility for stainless steel, pickling of the steel surface is performed using an acid such as sulfuric acid, hydrofluoric acid or nitric acid. The waste liquid discharged from the pickling equipment is a liquid containing mainly metal ions of iron, nickel, and chromium, fluorine ions, sulfate ions, and the like.
The present invention relates to a method for recovering valuable metal oxide-containing sludge having a low sulfur content and calcium fluoride from a liquid containing metal ions, fluorine ions, sulfate ions and the like. Hereinafter, the configuration of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, a waste liquid 2 containing metal ions, fluorine ions, sulfate ions and the like is introduced into a pH adjusting tank 1. The waste liquid 2 is a liquid mainly containing metal ions of iron, nickel, chromium and fluorine ions, sulfate ions and the like, such as the waste liquid discharged from the pickling equipment of stainless steel. In this waste liquid 2, as the first step,
Add calcium chloride 3 and alkali 4 if necessary
Is added to adjust the pH of the waste liquid 2 to be in the range of 1.0 to 3.0, and a precipitate containing a fluorine content and a sulfur content is produced. Further, a part 5 of the precipitate separated by a thickener 7 described later is added to the waste liquid 2 as an inoculant to accelerate the formation of the precipitate. Calcium chloride 3 is used as a sulfur content fixing agent, and may be used in either powder form or aqueous solution form. Further, the alkali 4 is used as necessary in order to adjust the pH of the waste liquid 2 within the range of 1.0 to 3.0. As the alkali 4, alkalis containing calcium components such as lime milk, slaked lime, and quick lime, and carbonates that generate carbon dioxide gas such as calcium carbonate and magnesium carbonate are preferably used.

In the first stage, the pH of the waste liquid 2 is adjusted to 1.
The reason for adjusting to the range of 0 to 3.0 is as follows. That is, when the pH of the waste liquid 2 exceeds 3.0, the amount of precipitation of the chromium component remarkably increases, and along with the precipitation of the chromium component, a large amount of other metals such as nickel may also precipitate. . On the other hand, the higher the pH, the better the precipitation of calcium fluoride, and the pH of the waste liquid 2 is 1.0.
In the range below the range, the precipitation rate of calcium fluoride is low, and the fluorine content cannot be removed sufficiently. Further, in order to increase the metal oxide concentrations of chromium and nickel in the metal oxide-containing sludge finally recovered in the method of the present invention, it is preferable to precipitate iron as much as possible in the operation of the first step, In order to form an iron precipitate, the pH needs to be in the range of more than 1.0. On the other hand, if the iron content in the waste liquid 2 is sufficiently oxidized by mixing air into the waste liquid 2 in advance, the pH will be 3.
In the range of 0 or less, 95% or more of iron can be precipitated. Therefore, in this first step aimed at producing a precipitate containing fluorine and sulfur, the pH of the waste liquid 2 was adjusted to the range of 1.0 to 3.0.

In this first step, in order to sufficiently precipitate and remove the sulfur content and the fluorine content existing as ions in the waste liquid 2, the addition amount of calcium chloride 3 (if the alkali having calcium content is When 4 is added, the addition amount of calcium chloride 3 and alkali 4 having a calcium content) is such that the calcium content contained in them is combined with all the sulfur content and fluorine content contained in the waste liquid 2. It is desirable that the amount is equal to or more than the reaction equivalent amount required for precipitation to form calcium fluoride and / or calcium sulfite (hereinafter referred to as “calcium sulfate etc.”) and calcium fluoride. However, if the addition amount of these is too large, the cost rises, and by adding a large amount of calcium chloride 3, the chlorine concentration in the waste liquid 2 rises, and in the next second step, metal hydroxide of chromium and nickel is added. There arises a problem that the efficiency of precipitating the substance is lowered. Therefore, the addition amount of calcium chloride 3 and alkali 4 should be minimized within a range where the calcium content contained therein is equal to or more than the reaction equivalent of the sulfur content and the fluorine content in the waste liquid 2.

Further, since the solubility of calcium sulfate and the like decreases as the temperature increases, in order to increase the removal rate of sulfur,
The first stage operation is preferably carried out at a temperature as high as possible. For example, since the temperature of the waste liquid immediately after being discharged from the annealing pickling equipment for stainless steel is 50 ° C. or higher, it is introduced into the pH adjusting tank 1 before the temperature of the waste liquid discharged from the annealing pickling equipment decreases. It is efficient to adjust the pH to a range of 1.0 to 3.0 and add calcium chloride 3 to carry out the precipitation reaction.

In addition, if it is desired to precipitate and remove a large amount of iron while keeping the precipitation loss of chromium and nickel metal ions small in the operation of the first step, the waste liquid 2 should be added before adding calcium chloride 3. It is advisable to perform oxidation treatment such as aeration by introducing air into the waste liquid 2 to oxidize the iron ions present in the waste liquid 2 and convert them into ferric ions. Since ferric ions are easily precipitated and removed even in a low pH range, if all ferric ions are used, the pH will be as low as possible within the range of 1.0 to 3.0.
At the H value, iron can be sufficiently precipitated. The lower the pH value, the smaller the amount of chromium precipitation, and the smaller the amount of nickel precipitation that accompanies the precipitation of chromium. Therefore, it is possible to minimize the pH value for performing the first step. By doing so, it is possible to minimize the loss of chromium and nickel.

When alkali 4 is added,
Due to a local increase in pH in the waste liquid 2, there is a possibility that chromium and nickel components existing in the vicinity of the waste liquid 2 may be precipitated and a loss of valuable metal may occur. In order to prevent such a situation, it is effective to use a carbonate such as calcium carbonate or magnesium carbonate as the alkali 4 and generate a carbon dioxide gas to prevent such a situation.

In the first stage, calcium chloride 3 and, if necessary, alkali 4 are added to the waste liquid 2 of the pH neutralization tank 1, and a part of the precipitate already separated in the thickener 7 described later. 5 is added as an inoculum. As a result, a part 5 of the precipitate added to the waste liquid 2 serves as nuclei to promote the generation of the precipitate, and the concentration of iron ions, fluorine ions, sulfate ions, etc. in the waste liquid 2 is reduced. Even in such a case, the precipitate is satisfactorily formed.

In the first step, calcium hydroxide 3 and, if necessary, alkali 4 are added to the waste liquid 2 to obtain iron hydroxide precipitates, and at the same time, precipitates of calcium sulfate and calcium fluoride. Although obtained, the solubility of calcium fluoride is much lower than that of calcium sulfate and the like, so that calcium fluoride precipitates first in the waste liquid. When a calcium fluoride precipitate is generated in this way, a so-called coprecipitation phenomenon occurs with it, and calcium sulfate and the like are easily precipitated as a precipitate. in this way,
Fluorine ions are contained in the waste liquid, so that the sulfur precipitate can be efficiently generated.

Therefore, alkali 4 was added in the pH adjusting tank 1 as needed, and calcium chloride 3 was added while adjusting the pH of the waste liquid 2 to the range of 1.0 to 3.0, and the pH was previously obtained. The precipitate 5 containing a fluorine content and a sulfur content was sufficiently generated by adding a part 5 of the precipitate, and then the waste liquid 2 in the pH adjusting tank 1 was pumped by the pump 6.
Is introduced into the next thickener 7 in a slurry state in which the precipitate and the supernatant liquid are mixed.

Then, in the thickener 7, solid-liquid separation of the precipitate and the supernatant liquid is performed, and the supernatant liquid 8 is the neutralization tank 9
Will be introduced to. Also, a part 5 of the precipitate separated in the thickener 7 is re-pHed by the operation of the pump 10.
By returning to the adjusting tank 1 and being added to the waste liquid 2 introduced into the pH adjusting tank 1 to be subsequently processed, it serves as an inoculant for promoting precipitation generation in the subsequent process. On the other hand, the remaining 11 of the precipitate is the pump 12
Is introduced into the flotation machine 13.

Next, in the neutralization tank 9, as a second step, the alkali 14 is added to the supernatant liquid 8 to perform a neutralization treatment. By this neutralization treatment, the metal components of nickel and chromium dissolved in the supernatant liquid 8 as ions are precipitated as metal hydroxides and recovered. As described above, in the first step, an amount of calcium chloride 3 that makes the calcium content equal to or more than the reaction equivalent in advance (if alkali 4 having calcium content is added, calcium chloride 3
In addition, since the sulfur and fluorine components have already been sufficiently precipitated and removed by the addition of the alkali having a calcium content and 4), in this second step, nickel and chromium metals with a low sulfur content concentration are used. A hydroxide can be obtained. As the alkali 14 added to the supernatant 8 in the second step, a strong alkali such as magnesium hydroxide or caustic soda can be used in addition to calcium salts such as calcium hydroxide and quick lime. In the illustrated example, the first
In the stage, the alkali 4 and the alkali 14 added to the pH adjusting tank 1 are shared. In addition, if the kind of alkali 14 is selected so that the filtrate remaining after the precipitation of the metal hydroxide in the second step becomes an aqueous calcium chloride solution, the concentrated filtrate is adjusted in the first step. It can be reused as a sulfur fixing agent added to the tank 1.

The metal hydroxide 15 thus recovered is sent by the operation of the pump 16 and undergoes a dehydration process 17 such as filter pressing, drying and heating to obtain a metal oxide-containing sludge 18. The metal oxide-containing sludge 18 thus obtained has a low sulfur content and is suitably used as a nickel and chromium source in the steelmaking process. Thus, it becomes possible to recover and reuse valuable metal resources from waste liquid containing metal ions, fluorine ions, sulfate ions, etc., like waste liquid discharged from the pickling process of stainless steel, thus saving resources. It comes off.

Next, in the flotation machine 13, calcium fluoride is recovered by flotation as a third step. That is, when the balance 11 of the precipitate concentrated in the thickener 7 is introduced into the flotation machine 13, the balance 11 of the precipitate is first suspended in water, whereby pulp is produced. Then, fine air bubbles are introduced into this pulp to carry out flotation. Thus, the calcium fluoride particles attached to the surface of the bubbles float on the liquid surface of the pulp, and the calcium fluoride is collected as flotation ore 19.

Here, the balance 11 of the precipitate is composed of a mixture containing iron hydroxide, calcium sulfate and the like, and calcium fluoride. As a means of recovering calcium fluoride in this third step, it is possible to perform specific gravity separation utilizing the difference in specific gravity of each mixing element, but strictly speaking, these iron hydroxide, calcium sulfate, etc., and calcium fluoride Since the conditions for forming the precipitates are different from each other, the balance 11 of the precipitates is composed of mixed particles having a non-uniform composition, and a concentrated part of each compound is present. Therefore, in the present invention, it was decided to recover the calcium fluoride concentrated portion by carrying out flotation.

In addition, a scavenger is added to the pulp in order to facilitate adhesion of calcium fluoride particles to air bubbles during flotation, but calcium fluoride and calcium sulfate contained in the precipitate are included. , And the surface potential of iron hydroxide, the p-value of pulp when an anionic scavenger is used
By adjusting H to the range of 9.0 to 11.0, and when using a cationic scavenger, the pH of the pulp is adjusted to the range of 5.5 to 9.5 to efficiently fluorinate. It is possible to recover the calcium enriched portion as floating ore 19.

Although the calcium fluoride recovered in the third stage contains some calcium sulfate and iron as impurities, it can be sufficiently used as a smelting flux. On the other hand, the rest of the precipitate from which calcium fluoride has been recovered in this way is recovered as the ore 20. The ore 20 contains a large amount of calcium sulfate and iron hydroxide, and if it is further separated to recover calcium sulfate, it can be used as a plaster for building materials. The ore 20 may be discarded.

[0030]

EXAMPLES Examples of the present invention will be described below. (Example 1) A mixed liquid (Fe: 3) of the waste liquid discharged from the sulfuric acid pickling equipment and the waste liquid discharged from the nitric hydrofluoric acid pickling equipment
0.2 g / liter, Ni: 2.7 g / liter, Cr:
5.7 g / liter, SO ₄ ^2- : 8.6 g / liter,
F ⁻ : 2.5 g / liter, NO ₃ ⁻ : 3.3 g / liter) was introduced into a pH adjusting tank, and a CaCl ₂ aqueous solution (35
%) While adding 1.1 times the reaction equivalent amount, lime milk (Ca
(OH) ₂ ) was added and the pH of the waste liquor was adjusted to 1.1 to form a precipitate. At this time, a part of the precipitate, which had already been concentrated with a thickener, was circulated as an inoculant into the pH adjusting tank to form a precipitate.

Next, the supernatant liquid separated from the precipitate in the thickener was introduced into a neutralization tank, and lime milk was added to neutralize it to adjust the pH to 8 to precipitate the metal hydroxide. This was dehydrated, collected as a dehydrated cake, and dried to obtain a metal oxide-containing sludge. Table 1 shows the composition of the obtained metal oxide-containing sludge and the Cr and Ni recovery rates.

[0032]

[Table 1]

The metal oxide-containing sludge of Example 1 had a low sulfur content and a low CaF ₂ content, and the Cr concentration and N
The i concentrations were all high. Further, both the Cr recovery rate and the Ni recovery rate were high values of 90% or more.

(Example 2) As in Example 1, a mixed solution of the waste liquid discharged from the sulfuric acid pickling equipment and the waste liquid discharged from the nitric hydrofluoric acid pickling equipment (Fe: 30.2 g / liter, N
i: 2.7 g / liter, Cr: 5.7 g / liter, S
O ₄ ^2- : 8.6 g / liter, F ⁻ : 2.5 g / liter,
NO ₃ ^-: a 3.3 g / l) was introduced into the pH adjustment tank,
The Fe ions in the waste liquid were oxidized by previously introducing air into the waste liquid in the pH adjusting tank. While keeping this waste liquid at 80 ° C with a heat retaining agent and an electric heater,
Cl ₂ (35%) was added in an amount 1.1 times the reaction equivalent, and
The pH was adjusted to 2.8 by adding CaCO ₃ and a precipitate formed. At this time, a part of the precipitate, which had already been concentrated with a thickener, was used as an inoculant and returned to the pH adjusting tank to form a precipitate.

Next, the supernatant liquid separated from the precipitate in the thickener was introduced into a neutralization tank, and lime milk was added to neutralize the solution to adjust the pH to 8 to precipitate the metal hydroxide. This was filtered in a dehydration facility, collected as a dehydrated cake, and dried to obtain metal oxide-containing sludge. Table 1 shows the composition of the obtained metal oxide-containing sludge and the Cr and Ni recovery rates.

The metal oxide-containing sludge of Example 2 had low sulfur content, CaF ₂ content, and Fe concentration,
Both the Cr concentration and the Ni concentration became high. Also, C
Both the r recovery rate and the Ni recovery rate were high values of 90% or more. The metal oxide-containing sludge of Example 2 was the same as that of Example 1.
It is characteristic that the Fe concentration is lower than that of the metal oxide-containing sludge.

Example 3 In Example 1, after increasing the concentration of the precipitate in the pH adjusting tank, a part of the slurry-like precipitate separated from the supernatant liquid in the thickener was introduced into the flotation machine. . In a flotation machine, the pulp concentration was adjusted to 10% and NaOH was added to adjust the pH to 10%.
Adjusted to. Then, bubbling (introduction of bubbles) was carried out for 30 minutes using sodium oleate as an anionic scavenger and pine oil as a foaming agent to carry out flotation. The obtained floating ore (floss) was collected, dried, and then analyzed for composition. It was found that CaF ₂ powder having a purity of 90% was obtained.

(Embodiment 4) Similar to Embodiment 3, Embodiment 1
The slurry-like precipitate separated from the supernatant liquid in Thickener was introduced into the flotation machine. In the flotation machine, the pulp concentration was adjusted to 10% and the pH was 7.
Adjusted to 0. Then, using dodecylamine as a cationic scavenger, bubbling was performed for 30 minutes to perform flotation. The obtained floating ore was collected, dried, and then analyzed for composition. It was found that CaF ₂ powder having a purity of 85% was obtained.

(Comparative Example 1) As in Example 1, the pH of the mixed liquid (the components are the same as those in Example 1) of the waste liquid discharged from the sulfuric acid pickling equipment and the waste liquid discharged from the nitric hydrofluoric acid pickling equipment was used. Introduce CaCl ₂ (35%) into the adjusting tank to a reaction equivalent of 1.1
Lime milk was added while adding twice the amount, and the pH was adjusted to 0.5 to form a precipitate. The reaction was carried out under the condition that the waste liquid temperature was 30 ° C. Then, the supernatant liquid separated from the precipitate in the thickener was introduced into a neutralization tank, and lime milk was added to neutralize the solution to adjust the pH to 8 to precipitate the metal hydroxide. This metal hydroxide was filtered in a dehydration facility, collected as a dehydrated cake, and dried to obtain a metal oxide-containing sludge. Table 1 shows the composition of the obtained metal oxide-containing sludge and the Cr and Ni recovery rates.

Cr of the metal oxide-containing sludge of Comparative Example 1
Although both the recovery rate and the Ni recovery rate were high values of 90% or more, the sulfur content and the CaF ₂ content also increased.
Moreover, the Fe concentration was also 40% or more.

(Comparative Example 2) As in Example 1, the pH of the mixed solution (the components are the same as those in Example 1) of the waste liquid discharged from the sulfuric acid pickling equipment and the waste liquid discharged from the nitric hydrofluoric acid pickling equipment was used. Introduce CaCl ₂ (35%) into the adjusting tank to a reaction equivalent of 1.1
Lime milk was added while adding twice the amount, and the pH was adjusted to 3.2 to form a precipitate. The reaction was carried out under the condition that the waste liquid temperature was 30 ° C. Then, the supernatant liquid separated from the precipitate in the thickener was introduced into a neutralization tank, and lime milk was added to neutralize the solution to adjust the pH to 8 to precipitate the metal hydroxide. This metal hydroxide was filtered in a dehydration facility, collected as a dehydrated cake, and dried to obtain a metal oxide-containing sludge. Table 1 shows the composition of the obtained metal oxide-containing sludge and the Cr and Ni recovery rates.

Although the metal oxide-containing sludge of Comparative Example 2 had a low sulfur content and a low CaF ₂ content, the Cr recovery rate was 30%, and the Ni recovery rate was 40%. Was also low.

[0043]

According to the present invention, mainly iron, nickel, such as waste liquid discharged from stainless steel pickling equipment,
Chromium metal ions and fluoride ions, sulfate ions and /
Alternatively, sludge containing valuable metal oxides such as nickel and chromium, which are useful as steel materials, in high concentration can be efficiently recovered from the acidic waste liquid containing sulfite ions in a state where the sulfur content is low. .

According to the present invention, it is also possible to recover calcium fluoride that can be used as a smelting flux from the waste liquid.

[Brief description of drawings]

FIG. 1 is a block diagram for specifically explaining a method of the present invention.

[Explanation of symbols]

 1 pH adjusting tank 2 Waste liquid 3 Calcium chloride 4 Calcium-containing alkali 5 Part of precipitate (inoculant) 7 Thickener 8 Supernatant liquid 9 Neutralization tank 11 Remaining precipitate 13 Flotation machine 14 Alkali 15 Metal hydroxide 17 Dehydration Process 18 Metal oxide-containing sludge 19 Floating ore 20 Sinking

Claims (3)

[Claims] 1. Calcium chloride is added to the waste solution of the pickling step which mainly contains metal ions of iron, nickel and chromium and fluorine ions, sulfate ions and / or sulfite ions, and the pH of the waste solution is adjusted to 1. By adjusting the content in the range of 0 to 3.0, a precipitate containing fluorine and sulfur is produced and separated into a supernatant and a precipitate, and then the supernatant is neutralized to obtain a sulfur content concentration. A method for recovering sludge containing nickel and chromium metal oxides having a low content, wherein a part of the precipitate obtained in advance is added as an inoculant to the waste liquid when the precipitate is formed. A method for recovering valuable metals from the waste liquid of the pickling step, characterized in that the production of the product is promoted. 2. Calcium chloride is added to the waste solution of the pickling step which mainly contains metal ions of iron, nickel and chromium and fluorine ions, sulfate ions and / or sulfite ions, and the pH of the waste solution is adjusted to 1. A precipitate containing fluorine and sulfur is produced by adjusting the content in the range of 0 to 3.0, and the precipitate is separated into a supernatant and a precipitate, which is then suspended in the suspended pulp. A method for recovering calcium fluoride in the precipitate by performing beneficiation, wherein the pH of pulp in the flotation is 9.0 to
A method for recovering calcium fluoride from the waste liquid of the pickling step, which comprises adjusting the range to 11.0 and adding an anionic scavenger. 3. Calcium chloride is added to the waste liquid of the pickling step which mainly contains metal ions of iron, nickel and chromium and fluorine ions, sulfate ions and / or sulfite ions, and the pH of the waste liquid is adjusted to 1. A precipitate containing fluorine and sulfur is produced by adjusting the content in the range of 0 to 3.0, and the precipitate is separated into a supernatant and a precipitate, which is then suspended in the suspended pulp. A method for recovering calcium fluoride in the precipitate by performing beneficiation, wherein the pH of pulp in the flotation is 5.5 to 5
A method for recovering calcium fluoride from the waste liquid of the pickling step, which comprises adjusting the concentration to 9.5 and adding a cationic scavenger.