JP3226634B2 - Purification method of iron chloride waste liquid containing a small amount of chromium ion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying an iron chloride waste solution containing a small amount of chromium ions, and more particularly to an iron chloride waste solution containing chromium ions such as an etching solution and a plating solution. The present invention relates to a method for purifying an iron chloride waste liquid containing a small amount of chromium ions for removing chromium from water.

[0002]

2. Description of the Related Art For example, lead frames for ICs and LSIs are sometimes processed by photoetching. The etching solution used at that time usually contains high-purity ferric chloride. By the way, in the used etching solution, the components of the lead frame are eluted in the solution, and the concentration of ferric chloride in the solution is reduced to deteriorate the etching efficiency. Is being done. However, this etching waste liquid contains a considerable amount of valuable copper ions and nickel ions in addition to high-concentration iron ions. Therefore, Japanese Patent Laid-Open No. 1-1672
As disclosed in Japanese Patent No. 35, a method is known in which iron scrap is added to an etching waste liquid to adjust pH in the waste liquid, copper and nickel are recovered, and the etching liquid is reused. .

[0003]

However, in the above-mentioned conventional method for treating an iron chloride waste liquid, the quality of the recovered copper and nickel is low, and even though it is a valuable metal, its commercial value is low. Further, as a means for improving the quality of recovered metal from the past, a powder containing a valuable metal was converted into a slurry, as in the method of treating a metal-containing carbon-containing powder described in JP-A-51-120902. However, there is a known method of flotation after wet classification, but if the specific gravity of impurities to be separated is large due to physical beneficiation,
It is difficult to perform flotation. Further, when chromium ions are contained in the waste liquid, there has been no means for effectively removing chromium without contaminating iron chloride, so that iron and chromium are discarded as hydroxide by lime neutralization. Has been disposed of. For this reason, there has been a situation in which an effective component of chromium has not been conventionally utilized. The present invention has been made in view of such circumstances, and can effectively remove chromium contained in an iron chloride-based waste liquid, and can recover a small amount of valuable metals such as copper and nickel of high quality. An object of the present invention is to provide a method for purifying an iron chloride waste liquid containing chromium ions.

[0004]

In order to achieve the above object, a method for purifying an iron chloride waste liquid containing a small amount of chromium ions in accordance with the above-mentioned object comprises, in addition to ferric chloride as a main component, copper ions, nickel ions and 2 g / liter. Iron powder is added to the following chromium ion-containing iron chloride waste liquid, and ferric chloride is reduced to ferrous chloride to displace and precipitate dissolved copper chloride. The mixed waste liquid is adjusted to have a pH of 1.3 to 2.5 and an iron ion concentration of 280 g / liter or less by adjusting the addition amount of iron powder and a small amount of the iron chloride waste liquid, Chromium hydroxide is removed by coprecipitating chromium hydroxide and ferric hydroxide generated simultaneously with the precipitation of nickel.

Examples of the iron chloride waste liquid include an etching waste liquid containing ferric chloride as a main component, an etching waste liquid, a hydrochloric acid pickling waste liquid, and a plating solution. Also,
The concentration of chromium ions in the waste liquid is preferably 2 g / L or less, particularly preferably 1.5 or less, and if it exceeds 2 g / L, a high iron concentration (220 to 2
80g / liter) and low PH (PH1.2 ~ 2.5)
It is difficult to remove chromium ions in the atmosphere. Further, as the iron powder, for example, a spherical converter purified iron powder or the like can be used, and its size is preferably from 44 to 250 μm, particularly preferably from 44 to 150 μm. If it is less than 44 μm, the specific surface area is too large and the reaction occurs rapidly, so that the pH cannot be controlled (rapid rise).
When it exceeds 250 μm, the specific surface area of the spherical iron powder becomes small, and the reaction becomes slow because the reaction active area is small.
Furthermore, the iron ion concentration in the strong acid waste liquid to which the iron powder has been added is 280 g / liter or less, particularly 240 to 270 g / l.
g / liter is preferable, and if it is less than 240 g / liter, it is too thin to be suitable as a product for etching and 280 g / liter.
/ Liter, the iron ion concentration is too high and the substitution reaction of nickel is suppressed.

The oxidation-reduction potential of the strong acid waste liquor to which the iron powder has been added is -520 to -400 mV, especially -460.
When it is less than -520 mV, the addition amount of iron powder becomes excessive, and a load is applied to the stirrer to make the operation impossible, and when it exceeds -400 mV, the progress of the nickel substitution reaction (cementation) becomes slow. Further, the pH value of the strong acid waste liquid to which the iron powder has been added is 1.3 to 2.
5, particularly preferably 1.5 to 1.7, and when the pH is less than 1.3, chromium hydroxide is hardly hydrolyzed in a low PH region and the amount of hydroxide generated is reduced. If the pH exceeds pH 2.5, the amount of hydroxide generated will be too large, the iron powder consumption will increase, and the load on the solid-liquid separator used in the next process will be large. Becomes Further, the hydroxide sticks to the periphery of the iron powder and hinders the contact between the solution and the iron powder, resulting in a poor reaction (particularly a poor nickel cementation reaction).

Further, the amount of the ferric hydroxide produced in the waste liquid is 13 to 30 g / liter, particularly 15 to 20 g / liter.
Liter is preferred, and less than 13 g / liter is insufficient to coprecipitate chromium hydroxide and insufficient to include suspended impurities (insoluble solids (SS) such as C and SiO ₂ ). On the other hand, if it exceeds 30 g / liter, the hydroxide will cling to the periphery of the iron powder and hinder contact between the solution and the iron powder, resulting in poor reaction (particularly nickel cementation). Furthermore, the amount of hydroxide is too large, so that the separation in the next solid-liquid separation step becomes poor, and the SS in the product liquid becomes poor.
Increase.

[0008]

In the method for purifying an iron chloride waste liquid containing a small amount of chromium ions according to the present invention, iron powder is contained in an iron chloride waste liquid containing copper ions, nickel ions and chromium ions of 2 g / l or less. In addition, the residual ferric chloride is reduced to ferrous chloride to displace and precipitate the dissolved copper chloride. Next, iron powder and a small amount of iron chloride waste liquid were mixed into the mixed waste liquid thus decoppered, and the pH of the obtained liquid was adjusted to 1.
Ferric hydroxide is produced by adjusting the concentration to 3 to 2.5 and controlling the iron ion concentration to 280 g / liter or less. On the other hand, chromium hydroxide and the ferric hydroxide, which are produced simultaneously when nickel is precipitated by adding iron powder to the decoppered mixed waste liquid, are co-precipitated to effectively remove the chromium hydroxide. Can be removed.

Incidentally, chromium ions have a higher ionization tendency than iron, and therefore cannot be removed by cementation (substitution reaction) like copper and nickel. Therefore, as a normal dechroming treatment, PH is raised to cause hydrolysis, and chromium hydroxide: Cr (O
H) ₃ to form a precipitate, where PH ≧ 4
is necessary. Therefore, as in the present invention, PH = 1.3.
If chromium is removed in the low region of ~ 2.5, it is considered that the following reaction or action is working. (1) That is, under the reaction conditions, PH = 1.3 to
Chromium gate sites generated under conditions of a low PH of 2.5 are generated as deposits. CrCl ₃ + 2H ₂ O → CrOOH + 3HCl (PH> 1.3) (2) Further, ferric hydroxide: Fe (OH) ₃ is generated as a precipitate due to the incorporation of trivalent iron ions into the nickel bath. At this time, a coprecipitation phenomenon in which a small amount of trivalent chromium ions are simultaneously precipitated (adsorption, occlusion, and compound formation) occurs. Chromium ions are removed by the synergistic action of (1) and (2).

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will now be described with reference to the accompanying drawings to provide an understanding of the present invention. Here, FIG. 1 is an overall process diagram showing a method for purifying an iron chloride waste liquid containing a small amount of chromium ions according to one embodiment of the present invention.

In one embodiment of the present invention, a method for purifying an iron chloride waste liquid containing a small amount of chromium ions comprises a step of removing the iron chloride waste liquid from a copper removal step, a nickel removal step, and a suspension impurity (SS) removal step. Become. First, a 100 m ³ waste liquid tank 1 in which an etching waste liquid 10 which is a kind of the iron chloride waste liquid is stored.
From 1, the waste liquid 10 is supplied into the copper removal reaction tank 12 by the slurry pump 13 at 0.9 to 1.3 m ³ / Hr. The copper removal reaction tank 12 is replenished with dilution water as needed. In the waste liquid 10, in addition to ferric chloride as a main component, metals such as copper, nickel, and chromium are dissolved and ionized during the etching process, and trivalent iron ions are reduced.
Valent iron ions are mixed.

Next, from a 2 m ³ OGP hopper feeder 14, a 1 m particle diameter,
m or less (250-44 μm: 90-100%, 150-
While dropping a spherical converter purified iron powder 15 (hereinafter referred to as OGP iron powder) of 74 μm: 50 to 70%), the stirring device 16
With stirring. At this time, the amount of the OGP iron powder 15 added is such that the iron ion concentration in the waste liquid 10 is 280 g / liter or less, the oxidation-reduction potential (ORP) is -300 to -100 mV, and the PH is 0.5 to 1.5. To adjust. As a result, the following reaction occurs and copper powder is deposited. 2FeCl ₃ + Fe → 3FeCl ₂ (1) CuCl ₂ + Fe → FeCl ₂ + Cu ↓ (2) 2HCl + Fe → FeCl ₂ + H ₂ ↑ (3) The OGP iron powder 15 contains Fe ³⁺ ,
The solid flow rate is 70 to 12 by an amount equivalent to Cu ²⁺ and HCl.
It is injected into the waste liquid at 0 kg / Hr. Further, the temperature of the waste liquid 10 rises to 70 to 100 ° C. due to its own heat of reaction, so that the reaction actively occurs, and copper precipitates on the surface of the OGP iron powder 15.

A mixed solution 10a of the waste liquid 10 and the OGP iron powder 15 overflowing from the copper removal reaction tank 12 is once stored in a cone tank 17 and then pumped up by a slurry pump 18 so that a wet cyclone 19 on the upper part is removed.
Further, it is supplied with a cyclone 20. Since this wet cyclone 19 is set to a concentration (coarse particle classification) condition,
The unreacted OGP iron powder 15, the OGP iron powder 15 to which the reaction-produced copper particles have adhered, and the large-grown copper particles are separated and returned into the copper removal reaction tank 12. Here, the solid flow rate is 120 to 150 kg / Hr, and copper occupies 80% or more, and the remainder is a few percent of iron and a small amount of suspending impurities such as carbon and silicon dioxide (hereinafter sometimes referred to as SS). And the particle size is 60-150 μm.

Next, the remaining medium-grained powder and fine-grained solid that cannot be captured by the wet cyclone 19 are further sent to the next wet cyclone 20 via the cone tank 21 and the slurry pump 22. This wet cyclone 20
Since the collection (fine-grain classification) condition where the collection particle size is 20 μm or more is set, the medium-sized unreacted OGP iron powder 15, the OGP iron powder 15 to which the reaction-generated copper particles are attached, and the medium-sized The copper particles that have grown into the copper are separated and returned into the copper removal reaction tank 12. Here, the solid flow rate is 10 to 40 kg / Hr, occupying 70% or more of copper, and the balance is a few% of iron and a small amount of SS.
The particle size is between 20 and 80 μm. The OGP iron powder 15 to which the copper particles have adhered and the grown copper particles are returned to the copper removal reaction tank 12 again, so that the reaction formulas (1), (2),
The reaction of (3) is promoted, and by continuing this copper removal treatment continuously for 6 hours or more (usually about 10 hours), the OGP iron powder 15 is almost completely eliminated, and large-grain copper is generated. .

After that, as shown by a broken line in FIG. 1, the produced copper is drained by a drainer Akins 23, then washed by showering clean water by a washing Akins 24, and recovered in a recovery box. You. The recovered copper particles are dried and commercialized. The recovered copper particles have a grade (purity) of 80 to 95%.

Next, the copper-removed mixed waste liquid 10b containing fine solids of 5 to 19 μm is sent into a 12-m ³ denickelization reaction tank 27. The solid flow here is 6-10
kg / Hr, copper 30-70%, iron 15% or less, SS
A few percent. The nickel removing reaction tank 27 has a stirring device 2
8 is provided, and a steam pipe is provided so as to keep the liquid temperature at 70 to 100 ° C.

In the nickel removal reaction tank 27, a small amount of etching waste liquid (a ferric chloride new liquid may be used because trivalent iron ions in the waste liquid are useful) 10 in a waste liquid tank 11;
The OGP iron powder 15 collected from the converter in the OGP hopper feeder 29 of 2 m ³ is charged to form a mixed waste liquid 10c. At this time, the temperature of the liquid in the tank is 40 ° C. or more (70 to 10
0 ° C) and the ORP of the mixed waste liquid 10c is -52.
Nickel is deposited by adjusting the addition amounts of the etching waste liquid 10 and the OGP iron powder 15 so that 0 to -400 mV, PH is 1.3 to 2.5, and iron ion concentration is 280 g / liter or less. NiCl ₂ + Fe → FeCl ₂ + Ni ↓ (4) At this time, the OGP iron powder 15 is added as a bed material from an initial stage in an excessive amount (several tens of equivalents of the contained Ni to be treated). Further decoppered mixed waste liquid 1
0b and 1.5% of Fe ³⁺ , Cu ²⁺ , HCl and Ni contained in a small amount of etching waste liquid 10.
The OGP iron powder 15 is added up to several times. The solid flow rate at this time is usually 60 to 120 kg / Hr,
kg / Hr.

In this case, a nickel film is deposited on the surface of the iron powder of the OGP iron powder 15, but the surface of the unreacted portion of the iron powder is formed by the adhesion of hydroxides described later or the generation of hydroxides. The hydrochloric acid further passivates due to the adhesion of hydrogen gas generated when the hydrochloric acid reacts with the iron powder, which hinders the progress of the reaction. Therefore, a small amount of trivalent iron ions is mixed in, and this portion is subjected to a chemical conversion treatment to activate the portion, thereby promoting a smooth reaction. It is conceivable to add a small amount of hydrochloric acid instead of the etching waste liquid 10, but the surface of the iron powder is similarly passivated due to adhesion of hydrogen gas generated when hydrochloric acid reacts with the OGP iron powder 15.

The effluent 10 contains chromium ions. If the chromium ion content is as small as 2 g / liter or less, the above-described conditions (PH is 2 or less) in the denickelization reactor 27 are used. However, chromium ions can be formed as hydroxides by the following reaction formula simultaneously with the precipitation of nickel. The production of chromium hydroxide is
This is promoted by the formation of ferric hydroxide described below. CrCl ₃ + 3H ₂ O → Cr (OH) ₃ + 3HCl (PH> 4) (5) CrCl ₃ + 2H ₂ O → CrOOH + 3HCl (PH> 1.5) (6) 2HCl + Fe → FeCl ₂ + H ₂ ↑ (7)

Next, the reaction when a small amount of trivalent iron ions is mixed in the denickelization reaction tank 27 is as follows under the condition of PH of 1.3 to 2.5. Reaction rate when PH = 1.3 (8) 70%; (9), (10) 30% Reaction rate when PH = 2.0 (8) 50%; (9), (10) 50% (8) 40%; (9), (10) 60% 2FeCl ₃ + Fe → 3FeCl ₂ (8) FeCl ₃ + 3H ₂ O → Fe (OH) ₃ + 3HCl (9) 2HCl + Fe → FeCl ₂ + H ₂ ↑ (10) In other words, when the pH is 2.0, about half of the trivalent Fe ions are chemically converted to the surface of the passivated OGP iron powder 15 with the iron powder surface. To promote the nickel deposition reaction. On the other hand, the other half of the trivalent Fe ion forms a ferric hydroxide precipitate. By generating a small amount (suitable amount) of the precipitate, a flocculant effect of adsorbing and covering SS or coprecipitating and capturing the chromium hydroxide can be obtained. As described above, the OGP iron powder 15 is added to the iron chloride waste liquid 10 containing 2 g / liter or less of chromium ions, and the pH of the waste liquid 10 is adjusted to 1.3 to 2.5 to adjust the ferric hydroxide. Chromium hydroxide can be effectively removed by coprecipitating the ferric hydroxide and chromium hydroxide.

The mixed waste liquid 10c overflowing from the nickel removal reaction tank 27 is temporarily stored in a cone tank 30, pumped up by a slurry pump 31, and sent to a wet cyclone 32 and further to a wet cyclone 33. At this time, similarly to the copper removal step, this wet cyclone 3
2 is set to the condensation (coarse particle classification) condition, the unreacted OGP iron powder 15 and the OGP iron powder 15 to which the nickel particles generated by the reaction adhere are separated, and the nickel removal reaction tank 27 is removed.
Will be returned within. The solid flow rate here is usually 40 to 90
In kg / Hr, iron accounts for half, the balance being nickel and copper and traces of SS, with a particle size of 60-150 μm.

Next, the remaining medium-grained powder and fine-grained solid that could not be captured by the wet cyclone 32 are transferred to the cone tank 3.
4. It is sent to the second-stage wet cyclone 33 via the slurry pump 35. Since the wet cyclone 33 is set to the collection (fine-grain classification) conditions and the collection particle size is 20 μm or more, the medium-sized unreacted OGP iron powder 15 and the OGP to which the reaction-generated nickel particles adhere are attached. The iron powder 15 is separated and returned to the lower part of the denickelization reaction tank 27. Here, the solid flow rate is 5 to 15 kg / Hr, the iron content is half, the balance is nickel and copper and a trace amount of SS, and the particle size is 10 to 60 μm.

At this time, the unreacted OGP iron powder 15 and the OGP iron powder 15 to which the nickel particles adhere are returned to the nickel removal reaction tank 27 again, so that the reactions (4) to (10) are promoted, 12 hours or more continuously (about 24 hours)
By continuing this processing step, nickel quality is improved. In this nickel removal step, the stirring device 28
Alternatively, the phenomenon of mechanical exfoliation and grinding caused by recycling using the wet cyclones 32 and 33 does not occur.

After performing the above steps for about 24 hours, the continuous supply of the waste liquid is stopped, and the nickel iron powder is taken out together with the mixed waste liquid 10c from the lower discharge port of the denickelization reaction tank 27 to remove the liquid. The supernatant is sent to an Akins (classifier) 36, and the supernatant is temporarily stored in a cone tank 37 and then returned to the denickelization reaction tank 27 by a slurry pump 38.
On the other hand, the drained nickel iron powder is sent to the next washing Akins 39. Here, the water is washed and drained by a shower ring of purified water, and the nickel iron powder 40 (wet powder) is collected in the collection box 41. Thereafter, the wet nickel iron powder 40 is dried and commercialized. The obtained nickel iron powder 40 has a grade of 10 to 20%. The supernatant of the cleaning Akins 39 is stored in the cone tank 4.
After being temporarily stored in the cleaning tank 2, it is returned to a cleaning tank (not shown) by the pump 43.

Next, a mixed solution 10 containing fine solids of 5 to 19 μm of SS and hydroxide (mainly ferric hydroxide) of unnecessary solids overflowing from the cyclone 33 is used.
d is sequentially sent to a high-speed stirring tank 44 and a low-speed stirring tank 45 to which a coagulant (a small amount of chromium hydroxide) is added. Each stirring tank 44, 45 is provided with a stirring device 46, 47,
A coagulant solution 50 in a coagulant dissolution tank 49 stirred by a stirrer 48 is pumped into the high-speed stirring tank 44.
1 added. The solid flow rate here is 30 to 50
kg / Hr, the majority of which is ferric hydroxide deposits, the balance being nickel, copper, M-Fe a few percent and SS a few percent.

By the way, in the solution of the mixed waste liquid 10d overflowed from the wet cyclone 33, the hydroxide adsorbed and the SS adsorbed and entrapped therein contain a small amount of nickel particles, copper particles and iron particles in a fine particle state. Contains. The mixed waste liquid 10d is sent to the high-speed stirring tank 44, and the coagulant solution 50 (concentration: 1,000 mg / liter) is added from the coagulant dissolution tank 49, and first, the coagulant solution 5
0 is diffused, and then flocculated floc is slowly formed by the low-speed stirring tank 45. If the aggregate floc has too small a shape, the solid-liquid separation ability is reduced. Next, a suspended impurity removing step of removing suspended impurities in the denickelized mixed waste liquid 10e containing the flocculated floc will be described.

The denicked mixed waste liquid 10e is 2
It is divided and supplied equally to a pair of solid-liquid separators (decanters) 53 driven by a motor 52. Here, the mixed waste liquid 10e is separated into a hydroxide 54 (hereinafter, referred to as SS precipitate) containing and trapping suspending impurities composed of, for example, carbon and silicon dioxide, and a supernatant liquid 10f, and the solid-state SS precipitate is separated. The object 54 is collected in the collection box 55.
In this manner, the SS deposit 54 that has absorbed and included the suspended impurities, such as carbon and silicon dioxide, in the etching waste liquid 10 can be effectively recovered. Now, since the pH of the separated supernatant liquid is about 2, there is a possibility that a hydroxide may be generated as it is. Therefore, the pH needs to be 1 or less. For this reason, the supernatant liquid 10f is temporarily stored in the cushion tank 56, and is stored in the hydrochloric acid tank 57.
A small amount of hydrochloric acid 59 is added from
Is adjusted, and stored in a product tank 61 of 100 m ³ by the pump 60. The product liquid 62 in the product tank 61 is taken out by the pump 63 and reused.

The present invention is not limited to the above-described embodiment, but includes any changes within a scope not departing from the gist of the present invention.

[0029]

The method for purifying an iron chloride waste liquid containing a small amount of chromium ions according to the present invention is characterized in that the hydroxide produced simultaneously with the addition of iron powder to the iron chloride waste liquid to precipitate nickel. Chromium is coprecipitated with ferric hydroxide generated by adding iron powder to the iron chloride waste liquid to adjust the pH of the iron chloride waste liquid to 1.3 to 2.5. Therefore, the chromium hydroxide in the waste liquid can be effectively removed. Further, by adding iron powder to the iron chloride waste liquid, valuable metals such as copper and nickel in the waste liquid can be recovered with high quality. Furthermore, suspending impurities such as carbon and silicon dioxide in the iron chloride waste liquid are adsorbed and included in the ferric hydroxide to separate and remove the suspending impurities.

[Brief description of the drawings]

FIG. 1 is an overall process diagram of a method for purifying an iron chloride waste liquid containing a small amount of chromium ions according to an embodiment of the present invention.

[Explanation of symbols]

10: etching waste solution, 10a: mixed solution, 10b: mixed waste solution, 10c: mixed waste solution, 10d: mixed waste solution, 10e:
Mixed waste liquid, 10f: supernatant liquid, 11: waste liquid tank, 1
2: Copper removal reaction tank, 13: Slurry pump, 14: OGP
Hopper feeder, 15: OGP iron powder, 16: stirrer, 17: cone tank, 18: slurry pump, 1
9: Wet cyclone, 20: Wet cyclone, 21: Cone tank, 22: Slurry pump, 23: Akins for draining, 24: Akins for cleaning, 27: Denickelization reaction tank, 28: Stirrer, 29: OGP hopper feeder , 30: cone tank, 31: slurry pump, 3
2: wet cyclone, 33: wet cyclone, 34: cone tank, 35: slurry pump, 36: draining Akins, 37: cone tank, 38: slurry pump, 39: washing Akins, 40: nickel iron powder, 4
1: collection box, 42: cone tank, 43: pump, 44: high-speed stirring tank, 45: low-speed stirring tank, 46: stirring apparatus, 47: stirring apparatus, 48: stirring apparatus, 49: flocculant dissolving tank, 50: Flocculant solution, 51: pump, 52: motor, 53: solid-liquid separator, 54: hydroxide, 55: collection box, 56: cushion tank, 57: hydrochloric acid tank, 58: pump, 59: hydrochloric acid, 60 : Pump, 61:
Product tank, 62: Product liquid, 63: Pump

──────────────────────────────────────────────────続 き Continued on the front page (72) Eiji Inoue 1-3-1, Otani, Yawata-Higashi-ku, Kitakyushu-shi, Fukuoka Prefecture Astec Irie Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) C23F 1/46 C25D 21/18 C01G 49/10

Claims (1)

(57) [Claims] 1. In addition to ferric chloride as a main component, copper ions,
Iron powder is added to an iron chloride waste liquid containing nickel ions and chromium ions of 2 g / l or less, and the ferric chloride is reduced to ferrous chloride to displace and precipitate dissolved copper chloride. The amount of iron powder and a small amount of the iron chloride waste liquid added to the mixed waste liquid thus decopperized so that the pH of the mixed waste liquid is 1.3 to 2.5 and the iron ion concentration is 280 g / l or less. Chromium hydroxide and secondary hydroxide formed simultaneously with the precipitation of nickel.
A method for purifying an iron chloride waste liquid containing a small amount of chromium ions, wherein the chromium hydroxide is removed by coprecipitation with iron.