JP2008264687A - Recovery method of iron from waste liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recovery method of iron from a waste liquid which treats a divalent iron ion-containing acidic waste liquid at a low cost to convert it into iron-containing slurry having improved dewaterability. <P>SOLUTION: The divalent iron ion-containing acidic waste liquid is supplied into a first reaction tank which is loaded with iron-oxidizing bacteria and microorganism carriers and aerated, to oxidize divalent iron ions to trivalent iron ions, and the pH of the first reaction tank is adjusted to 3 or more and 5 or less to generate iron hydroxide (III) particles. Slurry containing the iron hydroxide (III) particles and microorganism carrier after the treatment are settled and separated in a first settling tank, and settled microorganism carriers are returned to the first reaction tank. A polymer coagulant is added to slurry containing the iron hydroxide (III) particles after the treatment in a flocculation tank to generate flocs of the iron hydroxide (III) particles. Slurry containing the flocs of the iron hydroxide (III) particles after the treatment is settled and separated in a second settling tank, and settled slurry containing the iron hydroxide (III) particles is recovered. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for recovering iron in a waste liquid by treating a waste liquid containing a plurality of metals such as pickling waste liquid and plating waste liquid of a steel sheet or a metal mine drainage that is acidic and contains heavy metals.

  When surface treatment or the like is performed on the surface of the steel plate, pickling treatment or alkali treatment is performed as pretreatment to remove scale generated on the surface of the steel plate. In this pickling treatment, an acidic liquid containing sulfuric acid, nitric acid, nitric hydrofluoric acid, etc. is used. In the case of a steel sheet, an acidic waste liquid in which a metal such as iron or nickel in the steel sheet is dissolved is generated. In some cases, waste liquid is generated in which metals such as nickel and zinc contained in the plating solution and iron in the base material are dissolved. That is, these waste liquids become acidic waste liquids containing metal ions such as nickel ions and zinc ions in addition to divalent iron ions and trivalent iron ions.

  Such an acidic waste liquid is usually neutralized by adding an alkaline liquid, and then a flocculant is added to precipitate a metal hydroxide using a sedimentation basin such as a thickener to form a slurry. Is dewatered and processed into a sludge cake. Therefore, the sludge cake contains metal hydroxides such as nickel and zinc in addition to iron, which is a component problem for recycling as an iron source. In addition, since these metal hydroxides have small particles, the moisture content of the sludge cake is high, and in order to recycle as an iron source, the drying cost of the sludge cake becomes high. Furthermore, since the moisture content of the sludge cake is high, it is transported in a state containing a large amount of water, which causes problems such as an increase in transportation costs.

  In addition, as acid waste liquid containing divalent iron ions, there is mine waste water generated from metal mines. Metal mines mainly mine sulfide minerals, and after mining, minerals such as pyrite, chalcopyrite, sphalerite remain, and these react with oxygen in groundwater and air to produce acidic divalent iron ions, Mine wastewater containing heavy metals is generated.

In patent document 1 and patent document 2, the processing method of the acidic waste_water | drain containing these bivalent iron ions is disclosed. In these patent documents, the above-mentioned waste liquid is put into a reaction tank holding iron-oxidizing bacteria to oxidize divalent iron ions to trivalent iron ions, and the pH is adjusted to 3 to 5, and trivalent. A method is proposed in which iron ions are precipitated as iron (III) hydroxide, and then a floc is created by adding a polymer flocculant, which is recovered in a sedimentation basin and a part thereof is returned to the reaction vessel. . In order to oxidize the divalent iron ions in the acidic waste liquid, it is necessary to maintain the total amount of iron-oxidizing bacteria (bacterial concentration x volume) in the reaction tank. In addition, the iron-oxidizing bacteria adhere to the precipitated iron hydroxide (III), and the total amount of iron-oxidizing bacteria in the reaction tank is maintained. Is to hold. Increasing the solids concentration in the reaction tank increases the buffering frequency between the particles and decreases the sedimentation rate, so the precipitation tank must be enlarged, while if the solids concentration in the reaction tank is reduced, the particles Although the frequency of buffering between each other is reduced and the sedimentation rate is increased, there is a problem that the reaction tank capacity is increased and a large amount of stirring power is required.
JP 2004-202488 A JP 2005-296866 A

  In view of the above-mentioned problems of the prior art, the present invention reduces an acidic waste liquid containing divalent iron ions at a low cost while suppressing the equipment cost and suppressing the stirring power in the reaction tank and the amount of the polymer flocculant used. It is a first object to provide a method of processing.

  Further, a method of reducing the water content of an iron-containing dehydrated cake obtained by dehydrating an iron-containing slurry having improved dehydration property from a slurry containing flocs of recovered iron (III) hydroxide particles. The second object is to provide the above.

  Furthermore, when the acidic waste liquid containing divalent iron ions contains at least one of nickel ions and zinc ions, a third object is to obtain a cake having a high nickel or zinc concentration.

  In order to solve the above-mentioned object, the present inventor supplies an acidic waste liquid containing divalent iron ions into a first reaction vessel in which a microorganism carrier with good sedimentation is previously introduced and stirred by aeration. The pH of the waste liquid is adjusted to 3 or more and 5 or less by adding an alkaline agent while oxidizing divalent iron ions by iron-oxidizing bacteria to produce particles mainly composed of iron (III) hydroxide. After recovering the carrier, a method of adding a polymer flocculant to aggregate iron (III) -based particles, separating and recovering the aggregate from the liquid, and dehydrating to produce an iron-containing dehydrated cake. We studied diligently. As a result, a microbial carrier with good sedimentation is introduced into the first reaction tank in advance, and then the microbial carrier with good sedimentation is recovered downstream of the waste liquid treatment. On the other hand, the slurry containing iron (III) -based particles that did not settle in the first sedimentation tank was introduced into the coagulation tank, and flocs were formed by the polymer coagulant to improve sedimentation. Then, the iron hydroxide (III) -based particles are recovered in the second sedimentation tank, or a part of the recovered iron hydroxide (III) -based particles is charged again into the first reaction tank. Thus, the slurry becomes dense iron (III) hydroxide-based particles, the slurry dewaterability is improved, and the remaining iron (III) hydroxide-based particles can be dehydrated to produce a dehydrated cake with a low water content. I found.

  In addition, by adopting a microbial carrier having a high sedimentation rate, the microbial concentration in the first reaction tank can be increased, and as a result, the first reaction tank can be made smaller and, accordingly, the stirring power can be suppressed. It was.

  Furthermore, by introducing a microbial carrier having a high sedimentation rate into the first reaction tank, iron oxidation is performed in the first reaction tank having the first precipitation tank or the sedimentation section without adding a polymer flocculant. Since the microbial carrier to which bacteria are attached can be recovered, the slurry concentration in the iron (III) hydroxide-based slurry sent to the second sedimentation tank can be reduced, and the amount of polymer flocculant added can be reduced. It was found that the second sedimentation tank can be made compact while the sedimentation speed in the second sedimentation tank can be increased.

  Furthermore, in the case where nickel ions and / or zinc ions are contained in the acidic waste liquid containing divalent iron ions, the supernatant after the precipitation of the flocs of iron (III) hydroxide particles in the second settling tank (hereinafter, “ The first treatment water ”may be supplied to the third reaction tank, and the treatment liquid in the third reaction tank is stirred to adjust the pH of the treatment liquid to 6 or more and 10 or less. To produce nickel and / or zinc metal hydroxide particles, solid-liquid separation and concentration of the slurry containing the metal hydroxide particles, and then dehydrating to obtain a cake, whereby nickel and / or It has been found that a cake with a high zinc concentration can be obtained.

  That is, the present invention has been made based on the above findings, and the gist thereof is as follows.

(1) Iron-oxidizing bacteria and any one or more selected from the group consisting of coke powder, activated carbon, coal powder, pumice powder, and foamed slag, and a microbial carrier of the iron-oxidizing bacteria that settles in water An acidic waste liquid containing divalent iron ions is supplied into the first reaction tank that is charged and stirred by aeration, and the divalent iron ions are oxidized into trivalent iron ions by the iron oxidizing bacteria. And the production | generation process of the iron (III) hydroxide particle | grain which adjusts the pH in the said 1st reaction tank to 3-5 and produces | generates an iron (III) hydroxide particle,
The slurry containing the iron (III) hydroxide particles and the microbial carrier discharged from the production step of the iron (III) hydroxide particles is settled and separated in a first settling tank, and the settled microbial carrier is converted into the first microbial carrier. Sedimentation and separation step of the microbial carrier to be returned to the reaction tank,
The slurry containing the iron (III) hydroxide particles discharged from the sedimentation and separation step of the microorganism carrier is fed to a coagulation tank, and a polymer flocculant is added to flock the iron (III) hydroxide particles. A flock forming step to be formed;
The slurry containing the flocs of the iron (III) hydroxide particles discharged from the floc forming step is settled and separated in a second settling tank, and the slurry containing the flocs of the precipitated iron (III) particles is recovered. And a method for recovering iron from a waste liquid.

  (2) A sedimentation part of the microbial carrier is provided at a subsequent stage in the tank in the first reaction tank, the microbial carrier is sedimented in the sedimentation part, and the iron (III) hydroxide particles separated by sedimentation are included. The method for recovering iron from the waste liquid according to (1), wherein the slurry is discharged from the first reaction tank so that the first reaction tank also serves as the first precipitation tank.

  (3) In the first reaction tank, the mass of the microbial carrier relative to the total mass of the microbial carrier and the iron (III) hydroxide particles is 70% by mass to 95% by mass. A method for recovering iron from waste liquid according to (1) or (2) above.

  (4) A part of the slurry containing flocs of the iron (III) hydroxide particles settled in the second sedimentation tank in the iron recovery step is returned to the first reaction tank. It is a method for recovering iron from the waste liquid according to any one of 1) to (3).

(5) In the method for recovering iron content from the waste liquid according to any one of (1) to (4), the acidic waste liquid containing the divalent iron ions is further at least one of nickel ions and zinc ions. The supernatant after the flocs of iron (III) particles are settled and separated in the second precipitation tank of the iron recovery step is supplied to the third reaction tank, and the pH is 6 or more and 10 Adjusting to the following, the production step of metal hydroxide particles to produce metal hydroxide particles containing at least one of nickel or zinc, and
A metal hydroxide particle recovery step of settling and separating the slurry containing the metal hydroxide particles discharged from the production step of the metal hydroxide particles and recovering the slurry containing the precipitated metal hydroxide particles; And a method for recovering iron from waste liquid.

  (6) In the method for recovering iron content from the waste liquid according to any one of (1) to (5), a slurry containing flocs of the recovered iron hydroxide (III) particles, or the recovered water A method for recovering iron from waste liquid, characterized in that a slurry containing flocs of iron (III) oxide particles and a slurry containing metal hydroxide particles are further dehydrated to form a cake.

According to the method of the present invention, it is possible to treat an acidic waste liquid containing divalent iron ions at a low cost while suppressing the equipment cost and suppressing the stirring power in the reaction tank and the amount of the polymer flocculant used. .
Moreover, according to the method of the present invention, the slurry containing iron hydroxide (III) particles to be recovered is made into an iron-containing slurry having improved dewaterability, and the water content of the iron-containing dehydrated cake obtained by dehydrating the slurry. Can be reduced.
Furthermore, according to the method of the present invention, it is possible to obtain a cake having a high nickel or zinc concentration when the acidic waste liquid containing divalent iron ions contains at least one of nickel ions and zinc ions. Become.

The overall process of the present invention will be described.
An iron waste bacterium and a microbial carrier of the iron oxidization bacterium are charged in advance, and an acidic waste liquid containing divalent iron ions is supplied into a first reaction tank that is stirred by aeration. Among these, the microorganism carrier is composed of any one or more selected from the group consisting of coke powder, activated carbon, coal powder, pumice powder, and foamed slag, all of which have a high sedimentation rate and settle in water. . In the first reaction tank, iron oxide bacteria oxidize divalent iron ions to trivalent iron ions, and by adding alkali to the first reaction tank, the pH in the first reaction tank is 3 or more. Adjust to 5 or less to precipitate iron ions as iron (III) hydroxide. Then, a slurry containing iron (III) hydroxide particles and the microbial carrier is sent to the first precipitation tank, the microbial carrier is recovered in the first precipitation tank, and the recovered microbial carrier is put into the first reaction tank. To do. On the other hand, an overflow slurry containing iron hydroxide (III) -based particles overflowed from the first sedimentation tank is sent to the aggregation tank, and a polymer flocculant is added to form a floc. Thereafter, the slurry containing the flocs of iron (III) hydroxide particles is subjected to solid-liquid separation in a second precipitation tank to concentrate the slurry, and the slurry containing the flocs of the precipitated iron (III) hydroxide particles is recovered. At this time, preferably, a part of the slurry containing flocs of precipitated iron hydroxide (III) particles is returned to the first reaction tank, and the excess slurry is dehydrated to obtain an iron-containing dehydrated cake. Good.

  Alternatively, a sedimentation section for precipitating the microbial carrier may be provided at the latter stage in the first reaction tank (downstream of waste liquid treatment in the reaction tank), and the first reaction tank may also serve as the first sedimentation tank. . That is, the acidic waste liquid containing divalent iron ions is any one or more microorganism carriers selected from the group consisting of iron-oxidizing bacteria, coke powder having a high sedimentation rate, activated carbon, coal powder, pumice powder, and foamed slag. Is added to the first reaction tank / precipitation tank which is previously stirred and aerated by aeration, and the iron-oxidizing bacteria oxidize divalent iron ions to trivalent iron ions, and further, alkali is used as the first reaction tank / precipitation tank. By introducing it into the precipitation tank, the pH in the first reaction tank / precipitation tank is adjusted to 3 or more and 5 or less to precipitate iron ions as iron (III) hydroxide, and the microorganism carrier is used as the first reaction tank / The slurry containing iron (III) hydroxide-based particles from the first reaction tank / precipitation tank while being held in the precipitation tank is added to the coagulation tank, and after adding a polymer flocculant to form a floc, Solid-liquid separation in 2 precipitation tank and concentrate slurry Then obtain a cake dewatering the slurry the concentration.

  By the way, as a method for oxidizing divalent iron ions, there is a chemical treatment using ozone, hydrogen peroxide, or the like. However, since the cost is increased, in the present invention, a microbial treatment is performed.

First, the effect of using a microorganism carrier having a high sedimentation rate will be described.
An important factor for the ability to oxidize divalent iron ions in the first reaction tank is the total amount of iron-oxidizing bacteria in the reaction tank (microorganism concentration x reaction tank capacity). In Patent Document 1, it is necessary to separate and collect a slurry containing iron (III) -based particles to which iron-oxidizing bacteria are attached in a sedimentation tank, and to return a large amount of slurry to the reaction tank. For this purpose, it is necessary to use a large amount of a polymer flocculant, and since the slurry concentration is high, the sedimentation rate is reduced, and the size of the sedimentation tank is increased accordingly.

  On the other hand, in the first embodiment of the present invention, a microbial carrier having a high sedimentation rate is introduced into the first reaction tank, and iron-oxidizing bacteria are attached to the microbial carrier, thereby introducing the polymer flocculant. The microbial carrier can be retained in the first reaction tank by collecting it in the first sedimentation tank without returning to the first reaction tank, and the required divalent iron ions. Can retain oxidation ability. The sedimentation rate of the microorganism carrier in the sedimentation tank is preferably 200 to 2000 m / D. When it is replaced with the size of the microbial carrier, it becomes about 300 to 2000 μm, although it depends on the specific gravity of the microbial carrier. If it is less than 300 μm, the sedimentation speed becomes small and it cannot be recovered in the first sedimentation tank. If it exceeds 2000 μm, the stirring power required for fluidizing the microorganism carrier in the first reaction tank becomes large, which is not economical.

  Examples of the material for the microbial carrier include activated carbon, coke powder, coal powder, pumice, and foamed slag that have good adhesion to iron (III) hydroxide and precipitate in water. You may mix and use these.

In the acidic region, iron (III) hydroxide is positively charged, whereas the microbial carrier is negatively charged, so it has good adhesion and has a large specific surface area. Can be attached. The specific surface area of the microbial carrier is preferably 0.5 to 500 m ² / g (BET value). If it is less than 0.5 m < ² > / g, the oxidation rate of the bivalent iron ion per unit mass will become small, and the oxidation capability of the bivalent iron ion in a 1st reaction tank will fall. This is considered to be because the amount of iron (III) hydroxide per unit mass of the microbial carrier is reduced and iron oxidizing bacteria are reduced. Moreover, when it exceeds 500 m < ² > / g, the oxidation rate of the bivalent iron ion per unit mass does not become so large, and the oxidation capability of the divalent iron ion in the first reaction tank does not improve. This is presumed that the ultrafine pores are not easily contributed to the ability to oxidize divalent iron ions because they are likely to be blocked by the iron (III) hydroxide phase deposited on the surface of the microorganism carrier.

  In order to fluidize the microbial carrier in the first reaction tank, the microbial carrier concentration is suitably 60% by mass or less. For example, FIG. 2 shows the relationship between the sedimentation speed of coke powder selected with a 500 to 1000 μm sieve and the coke powder concentration. As the coke powder concentration increases, the coke powders interfere with each other, so the sedimentation rate decreases. As the iron-oxidizing bacterium itself, a separately conditioned one may be added, or the iron-oxidizing bacterium present in the waste liquid to which the present invention is applied may be grown and used.

  Although the divalent iron ions are oxidized to trivalent iron ions by the iron oxidizing bacteria in the first reaction tank, they are precipitated as iron (III) hydroxide in the pH 3-5 region. Iron-oxidizing bacteria also adhere to the precipitated iron hydroxide (III) -based particles. The precipitated iron hydroxide (III) is improved in the sedimentation rate by the granulation operation and polymer flocculant addition described later. FIG. 3 shows the relationship between the slurry concentration and the sedimentation speed. As is apparent from FIG. 3, the smaller the slurry concentration, the less the interference between particles and the greater the sedimentation speed.

  By adding a microbial carrier having a high sedimentation rate in the first reaction tank, the microbial carrier to which iron-oxidizing bacteria adhere in the first precipitation tank can be recovered without adding a polymer flocculant. Particles mainly composed of iron hydroxide (III) precipitated in the first precipitation tank hardly precipitate in the first precipitation tank. The overflow slurry containing particles mainly composed of iron hydroxide (III) that has not settled in the first settling tank is added with a polymer flocculant in the coagulation tank to form aggregates. Sedimentation in 2 sedimentation tanks. By setting the slurry concentration of the overflow slurry from the first sedimentation tank to 3.5% by mass or less, the sedimentation speed can be increased to 100 to 350 m / D.

Next, the amount of iron (III) -based particles recovered in the second sedimentation tank is returned to the first reaction tank.
The iron hydroxide (III) -based particles precipitated and recovered in the second sedimentation tank are aggregated alone or by van der Waals force, and further loosely aggregated by the polymer flocculant added in the aggregation tank. Yes. When a part of the recovered iron hydroxide (III) -based particles (slurry containing flocs of iron (III) hydroxide particles) is returned to the first reactor, the iron hydroxide (III) -based particles Iron (III) hydroxide precipitates on the surface and the respective particles become larger, or the aggregated particles are integrated to become dense particles and the particle diameter is increased. As the particle size becomes larger and the particle size becomes larger, the dewaterability of the slurry drawn from the lower part of the second sedimentation tank is improved, and the remaining iron (III) -based particles not returned to the first reaction tank are dehydrated to reduce the water content. Rate dehydrated cake can be produced.

Therefore, the amount of solid matter mainly composed of iron (III) hydroxide in the first reaction tank is set to A (kg), and the acidic waste liquid contains at least one of nickel ions and zinc ions in addition to divalent iron ions. The amount of divalent iron ions contained therein is oxidized by iron-oxidizing bacteria, an alkali agent is added, and the amount of iron (III) -based particles newly precipitated, that is, the divalent charged in the first reaction tank. In the dehydrated cake when dehydrated at A ÷ B (day) and a dehydration pressure of 0.5 MPa, where B (kg / day) is the total amount of divalent iron ions and trivalent iron ions in the acidic waste liquid containing iron ions FIG. 4 shows the relationship between the water content and water content. FIG. 4 shows that when A ÷ B is 0.6 days or more, a dehydrated cake having a low water content can be obtained. Also, even if A ÷ B is 2.0 days or more, there is not much difference in moisture in the dehydrated cake, and A ÷ B is 2.0 days or more because the amount of returned slurry from the second settling tank is Increased and not economical.
A (kg) = Fe concentration in first reaction tank (kg / m ³ ) × first reaction tank liquid amount (m ³ )
B (kg / day) = Fe concentration of acidic waste liquid (kg / m ³ ) × Amount of acidic waste liquid input (m ³ / day)
And

  Next, it was returned from the microbial carrier existing in the first reaction tank and the second sedimentation tank, taking as an example the case where a 300-2000 μm microbial carrier previously screened was put into the first reaction tank. The oxidation ability of divalent iron ions by iron-oxidizing bacteria adhering to the surface of iron (III) hydroxide-based particles will be described.

The slurry obtained from the inside of the first reaction vessel was sieved with an opening of 300 μm, and the microorganism carrier on the sieve was recovered. Further, the under-slurry slurry was sieved with an aperture of 74 μm, and the slurry composed of iron (III) -based particles under the sieving was recovered. In a state in which a slurry composed of microbial carrier and iron (III) hydroxide-based particles is added to an acidic waste liquid containing divalent iron ions and adjusted to pH 4 with a sodium hydroxide solution while stirring by aeration, 2 The change with time in the iron ion concentration was measured, and the oxidation rate of divalent iron ions per unit mass was examined. As a result, the average for microbial carriers was 0.12 g-Fe ²⁺ / g-dry / day, and the average for iron (III) hydroxide particles was 0.15 g-Fe ²⁺ / g-dry / day. .

  From the above findings, the oxidation rate per unit mass is 20 to 30% larger for the iron (III) hydroxide-based particles than the microbial carrier, but the sedimentation rate at the same slurry concentration is 50 to 50 for the microbial carrier. It was found to be 300 times larger. Therefore, by setting the ratio of the microbial carrier mass to 70-95% by mass in the solid matter in the first reaction tank, that is, the total mass of the microbial carrier mass and the iron (III) hydroxide-based particles. The slurry concentration of the overflow slurry from the first sedimentation tank can be reduced. By setting the slurry concentration to 3.5% by mass or less, after the addition of the polymer flocculant in the coagulation tank, the sedimentation rate can be increased to 100 to 350 m / D, and the second precipitation tank can be made compact. If it exceeds 3.5% by mass, the sedimentation rate becomes small, and the second sedimentation tank cannot be made compact. If A ÷ B is 0.6 to 2.0 days, there will be no significant difference in dewaterability, so the amount of slurry returned from the second settling tank to the first reaction tank can be further reduced. It was found that the concentration of particles mainly composed of iron (III) in the first reaction tank can be reduced to about 1% by mass and the second precipitation tank can be further reduced. When it is less than 1% by mass, the dehydrating property is deteriorated. It was also found that the amount of the polymer flocculant added in the coagulation tank can be reduced by reducing the solid matter mainly composed of iron (III) flowing from the coagulation tank to the second precipitation tank.

Next, element separation will be described.
The relationship between the pH of solutions containing 400 mg / L, 400 mg / L, 30 mg / L, and 30 mg / L of divalent iron ions, trivalent iron ions, nickel ions, and zinc ions and the residual ratio of elements in wastewater was shown. This is shown in FIG. From FIG. 1, trivalent iron ions are precipitated at pH 3 to 5, and zinc ions, nickel ions and divalent iron ions are precipitated at pH 6 to 10.

In order to separate zinc ions and nickel ions from iron ions, divalent iron ions are first oxidized to trivalent iron ions by chemical oxidation or biological oxidation, and then the pH is adjusted to 3-5. Thus, iron (III) hydroxide precipitates. The solid part and the liquid part are separated from the slurry by solid-liquid separation operation, and the solid part is recovered. Then, zinc hydroxide and nickel hydroxide precipitate by making pH of a liquid part into 6-10. Only the liquid part is separated from the slurry by solid-liquid separation, and the solid part is recovered. By doing so, iron ions can be separated from nickel ions and zinc ions.
In other words, in the process of precipitating the metal compound, the element separation can be performed by controlling the pH to several stages and extracting the metal compound precipitated at each stage.

Next, an embodiment embodying the present invention will be described.
In FIG. 5, an example of the processing apparatus which concerns on the manufacturing method (the recovery method of the iron content from a waste liquid) of the iron containing dehydrated cake from the waste liquid of this invention is shown. As shown in FIG. 5, a wastewater treatment apparatus 10 applied to a method for producing an iron-containing dehydrated cake according to an embodiment of the present invention includes, for example, a thin steel plate made of an acid solution such as sulfuric acid, nitric acid, or nitric hydrofluoric acid. Pickling wastewater that is an example of waste liquid after pickling treatment, pickling plating wastewater consisting of plating waste liquid after surface treatment, or acid and heavy metal-containing mine drainage generated after mining a metal mine, etc. A first reaction tank 12 for treating an acidic waste liquid containing divalent iron ions, an air diffuser 14 for stirring the inside of the first reaction tank 12 by aeration and supplying oxygen to the iron-oxidizing bacteria, and iron-oxidizing bacteria A microbial carrier 13 for adhering, a pH meter 15 for measuring the pH in the first reaction tank 12, and a neutralizing agent for controlling the input of a neutralizing agent 17 for adjusting the pH of the liquid in the first reaction tank 12. Valve 16 and the first to recover the microorganism carrier , The microbial carrier return pump 19 for returning the recovered microbial carrier to the first reaction tank 12, and the iron (III) hydroxide-based particles in the overflow slurry from the first precipitation tank 18 are flocked. The polymer flocculant 21 to be received, the agglomeration tank 20 to receive it, the stirrer 22 to stir, the second sedimentation tank 23 to precipitate the slurry flocked in the aggregation tank 20, and the precipitated slurry as the return slurry 27 The slurry pump 24 is returned to one reaction tank 12 or drawn out as a drawn slurry 26 to a dehydrator.

  The solid concentration of the particles mainly composed of iron (III) and the microorganism carrier in the first reaction tank 12 is 10 to 30% by mass. The mass of the microbial carrier with respect to the total mass of the microbial carrier and the iron (III) hydroxide mass is 70 to 95% by mass. The remaining solid matter is contained in the return slurry 27 returned to the first reaction tank 12 by the iron (III) hydroxide-based particles generated during the neutralization treatment of the acidic waste liquid 11 containing divalent iron ions and the slurry pump 24. 1 to 3.5% by mass in the slurry in the reaction vessel 12. The size of the microbial carrier is activated carbon, coke powder, coal powder, pumice, foamed slag, etc., which is sieved to 300 to 2000 μm and has good adhesion to iron-oxidizing bacteria, depending on the specific gravity of the microbial carrier. The OFR (over flow rate, treated water amount / precipitation tank water area) in the first sedimentation tank 18 is preferably set in the range of 200 to 2000 m / D. Moreover, since the slurry density | concentration which flows in into a 2nd sedimentation tank is 1-3.5 mass%, OFR in the 2nd sedimentation tank 23 can be set in 50-350 m / D. From FIG. 3, although it becomes OFR100m / D or more, it is set to 50m / D in consideration of a margin rate. The microbial carrier concentration in the first reaction tank 12 can be managed by measuring the mass of the microbial carrier charged into the first reaction tank 12 in advance. Alternatively, the suspended solid substance in the first reaction tank 12 can be managed by separating a particle group of 300 μm or more with a sieve having an opening of 300 μm and measuring the amount of the solid matter.

Next, based on FIG. 5, one Embodiment of the manufacturing method of the iron containing dewatering cake which is this invention is described.
Acid waste liquid 11 containing divalent iron ions, such as pickling wastewater or pickling wastewater after pickling treatment of a thin steel plate, or mine wastewater is continuously supplied into the first reaction tank 12. . The general acidic waste liquid 11 has a pH of 2 or less and dissolves 0.01 to 1 mass% of metals such as Fe, Zn, and Ni, and most of these metals exist as metal ions. However, a small amount is present as suspended particles.

In the 1st reaction tank 12, it added so that the microorganisms carrier 13 density | concentration in a slurry might be 7-28 mass%, the acclimatized iron oxidation bacterium was added, and the acidic waste liquid 11 was continued in it. And stirred by the air diffuser 14 in the first reaction tank 12. The divalent iron ions contained in the acidic waste liquid 11 are oxidized by iron-oxidizing bacteria to produce iron (III) hydroxide. While continuously measuring the pH in the first reaction tank 12 with the pH meter 15, the neutralizer valve 16 is adjusted to neutralize the neutralizer 17 made of NaOH, Ca (OH) ₂ or Mg (OH) ₂ solution. Is added to the 1st reaction tank 12, and pH in the 1st reaction tank 12 is adjusted to 3-5. Here, when the pH is less than 3, precipitation of trivalent iron ions in the acidic plating waste liquid becomes worse. On the other hand, when the pH exceeds 5, metal hydroxides such as nickel and zinc are likely to be precipitated, and it becomes difficult to separate iron metal hydroxides. That is, by the first neutralization treatment, as shown in FIG. 1, particles mainly composed of iron (III) hydroxide are precipitated, and trivalent iron ions can be separated from the acidic waste liquid 11.

  Microorganism carrier 13 and iron (III) hydroxide-based particles flow from first reaction tank 12 to first precipitation tank 18. Since no polymer flocculant is added, it is not flocked, and the particles mainly composed of iron (III) hydroxide have a very low sedimentation speed of 10 m / D or less. Moreover, since the OFR of the first sedimentation tank 18 is 200 to 2000 m / D, the microbial carrier having a high sedimentation rate is precipitated in the first sedimentation tank 18, but the particles mainly composed of iron (III) hydroxide are used. Most of the liquid does not settle and is sent to the next agglomeration tank 20. The microorganism carrier 13 precipitated and collected in the first sedimentation tank 18 is returned to the first reaction tank 12 together with a part of the slurry in the first sedimentation tank 18 by a microorganism carrier return pump 19.

  By adding a polymer flocculant 21 to an overflow slurry containing particles mainly composed of iron (III) hydroxide that has overflowed from the first sedimentation tank 18 to the coagulation tank 20, and stirring with a stirrer 22, floc having good sedimentation To form. The flocs formed in the aggregation tank 20 are sent to the second precipitation tank 23 and settled in the precipitation tank 23. The primary treated water 25 is discharged from the upper part of the precipitation tank. The primary treated water 25 has a pH of 3 to 5 and contains metal ions such as nickel and zinc. The flocs mainly composed of iron (III) hydroxide deposited in the lower part of the second sedimentation tank are returned to the first reaction tank 12 as the return slurry 27 by the slurry pump 24. The return amount is set such that A ÷ B is 0.00 when the Fe amount in the first reaction tank 12 is A (kg) and the Fe amount in the acidic waste liquid containing divalent iron ions is B (kg / day). 6 to 2.0 days are preferred. The surplus slurry of iron (III) hydroxide is withdrawn intermittently as a drawing slurry 26 and dehydrated by a method described later.

  Although the primary treatment water 25 from the second sedimentation tank 23 is not shown in the drawing, a neutralizing agent is introduced into the subsequent neutralization tank to adjust the pH to 6 to 10, and nickel, zinc, etc. in the primary treatment water After the metal ions are precipitated as hydroxides, a polymer flocculant is added to the floc state in a subsequent agglomeration tank, and further, a slurry containing hydroxides such as nickel and zinc is separated in the subsequent agglomeration tank. The separated slurry is dehydrated by the method described below.

  The slurry from the precipitation tank separating the slurry mainly composed of iron hydroxide (III) separated in the second precipitation tank 23 and the slurry containing hydroxides such as nickel and zinc (not shown) are dehydrated, respectively. Process into sludge cake. Examples of the dehydration method include a method of dehydrating using a dehydrator such as a filter press, a vacuum dehydrator, and a centrifugal dehydrator, and a method of dehydrating by sun drying. Each dehydrated sludge cake can be effectively used as a resource. Although the moisture after dehydration varies greatly depending on the dehydration method, when dehydrated with a filter press, the dehydrated cake mainly composed of iron (III) hydroxide recovered from the second settling tank 23 has a moisture content of 40 to 50% by mass. In addition, the dehydrated cake made of metal hydroxide such as nickel and zinc recovered from a precipitation tank (not shown) has a moisture content of 65 to 85% by mass. The large difference in moisture occurs because the recovered metal hydroxide contains crystal water.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and all changes in conditions and the like that do not depart from the gist are within the scope of the present invention.

  For example, in FIG. 5, the microbial carrier 13 is recovered by the first sedimentation tank 18 and the microbial carrier return pump 19 and returned to the first reaction tank 12, but as shown in FIG. A first reaction / precipitation tank 30 in which the tank is integrated can be used. That is, the first reaction / precipitation tank 30 has a reaction part 31 and a sedimentation part 32, and there is an aeration device 34 for stirring the reaction part 31 at the lower part of the reaction part 31. 13 is mixed. Since the OFR of the sedimentation section 32 is 200 to 2000 m / D and is set to be equal to or less than the sedimentation end speed, only the microorganism carrier 13 having a large sedimentation speed is sedimented and automatically returns to the reaction section 31 again.

  In FIG. 5, a pump 19 and a return pipe are installed in the lower part of the first sedimentation tank 18 for recovering the microorganism carrier. Instead, a device for lifting the sediment, such as a screw type or a conveyor type, is used. A device may be installed. Further, as the mixing in the first reaction tank 12, a diffuser and a stirrer may be used in combination instead of the diffuser 14.

  Further, in the case where trivalent chromium ions are contained in the acidic waste liquid containing divalent iron ions, the trivalent chromium is precipitated in the first reaction tank 12 together with the trivalent iron ions oxidized by the iron-oxidizing bacteria. A floc is formed in the coagulation tank 20 to which the coagulant 21 is added, and the flocs are precipitated and separated in the second precipitation tank 23.

[Example]
Next, although the Example of the manufacturing method of the iron containing dehydrated cake from the waste liquid of this invention is given, this invention is not limited to a following example.
In addition, a present Example is an Example conducted by the indoor experiment, taking a correlation with actual wastewater, and this experimental result is a desirable result on sludge recycling, and is considered to be no different from actual wastewater.

Example 1
A solution containing divalent iron ions, nickel ions, and zinc ions shown in Table 1 was used as the pickling plating waste solution, and this pickling plating simulated waste water was processed using the processing apparatus of FIG. Further, coke powder (40 kg) whose particle size was adjusted to 500 to 1000 μm as the microbial carrier 13 was added to the first reaction vessel. The sedimentation speed of the coke powder was approximately 1700 m / D.

The capacities of the first reaction tank 12 and the coagulation tank 20 are 270 L and 15 L, respectively, the water surface area of the first precipitation tank 18 is 154 cm ² , the OFR is 800 m / D, and the water surface area of the second precipitation tank 23 is The OFR is 227 m / D at 324 cm ² . Note that iron-oxidizing bacteria are previously introduced into the first reaction tank 12.

  While pickling plating waste liquid is continuously supplied to the first reaction tank 12 at 5.1 L / min, an aqueous caustic soda solution is added as a neutralizing agent 17, and the pH in the first reaction tank 12 is controlled at 4. Furthermore, air was blown at a rate of 20 NL / min from an air diffuser 14 installed at the bottom of the first reaction tank 12 to stir the first reaction tank 12.

  The divalent iron ions in the pickling plating wastewater charged into the first reaction tank 12 are particles of iron hydroxide (III) mainly contained on the coke powder surface and in the slurry returned from the second settling tank 23. The iron-oxidizing bacteria adhering to the surface oxidize almost the entire amount to trivalent iron ions, and precipitate as iron hydroxide (III) on the surface of iron hydroxide (III) -based particles and on the surface of coke powder. Was made larger. The coke powder settles in the first sedimentation tank 18 and is returned to the first reaction tank 12 by the microorganism carrier return pump 19, and the supernatant water containing iron (III) hydroxide-based particles is charged into the aggregation tank 20, The particles mainly composed of iron (III) hydroxide formed flocs by the polymer flocculant 21 (anionic), and were separated in the second precipitation tank 23. The slurry concentration of the separated slurry is 9 to 11% by mass, and the slurry concentration in the first reaction tank 12 is 16% by mass (15.5 to 16.5% by mass). The returned slurry 27 was returned to the first reaction / precipitation tank 30 at about 0.7 L / min. Of the slurry in the first reaction vessel 12, the amount resulting from the coke powder is about 92% by mass. The surplus slurry was intermittently drawn as a drawn slurry 26 and dehydrated with a filter press dehydrator having a pressure of 0.5 MPa to obtain a dehydrated cake. The above-mentioned A ÷ B was about 0.72 days.

  The supernatant water (primary treated water 25) separated in the second sedimentation tank 23 contains nickel ions and zinc ions. Although not shown in the figure, a neutralizing agent is introduced into the subsequent neutralization tank to adjust the pH to 9, and the nickel / zinc metal ions in the primary treated water 25 are precipitated as hydroxides. A polymer flocculant (anionic) was added in the tank to form a floc state, and a slurry containing nickel / zinc hydroxide was separated in a subsequent precipitation tank.

  The components in the primary treated water 25 at this time are shown in Table 1, and the components of the dewatered cake after the drawing slurry 26 drawn from the second settling tank 23 is dehydrated are shown in Table 2. Divalent iron ions are mainly precipitated from the quality of the primary treated water in Table 1. The cake component in Table 2 is also a component mainly composed of iron (III) hydroxide, and the water content is 48% by mass (hydrous cake). Since the ratio of the amount of water in [wet] is low, it can be used as an iron source by adding operations such as kneading with other raw materials having low water content. Moreover, although C content in a cake component is contained a little, it is substantially the same level as the comparative example mentioned later, and the coke powder added as a microorganisms carrier has flowed out little.

  In addition, although it implemented also when not returning to the 1st reaction tank 12 with the slurry pump 24, in that case, the filter press which has the applied pressure of 0.5 Mpa for the slurry isolate | separated with the 2nd sedimentation tank 23 The water content in the dewatered cake dehydrated by the dehydrator became 57% by mass, and the dewaterability decreased compared with the case where the slurry pump 24 returned to the first reaction tank 12.

(Example 2)
A solution containing divalent iron ions, nickel ions, and zinc ions shown in Table 1 was used as the pickling plating waste liquid, and this pickling plating simulated waste water was processed using the processing apparatus of FIG. Further, coke powder (40 kg) having a particle size adjusted to 500 to 1000 μm as microbial carrier 13 was added to the first reaction / precipitation tank. The sedimentation speed of the coke powder was approximately 1700 m / D.

The capacities of the reaction section 31 and the coagulation tank 20 are 270 L and 15 L, respectively, the water surface area of the settling section 32 is 154 cm ² and OFR is 800 m / D, the water surface area of the second settling tank 23 is 324 cm ² and OFR is 227 m. / D. In addition, in the 1st reaction tank and precipitation tank 30, iron oxidation bacteria are thrown in beforehand.

  While the pickling plating waste liquid is continuously supplied to the first reaction / precipitation tank 30 at 5.1 L / min, an aqueous caustic soda solution is added as the neutralizing agent 17, and the inside of the first reaction / precipitation tank 30 is added. The pH was controlled at 4, and air was blown from the air diffuser 14 installed at the bottom of the reaction unit 31 at 20 NL / min to stir the reaction unit 31.

  The divalent iron ions in the pickling plating wastewater charged into the first reaction / precipitation tank 30 are iron hydroxide (III) contained in the slurry returned on the coke powder surface and from the second precipitation tank 23. The iron oxide bacteria adhering to the main particle surface are almost completely oxidized to trivalent iron ions and deposited as iron hydroxide (III) on the iron hydroxide (III) main particle surface and coke powder surface. The particles were made larger. The coke powder settles in the settling section 32 and returns to the reaction section 31, and the supernatant water containing particles mainly composed of iron (III) hydroxide is put into the coagulation tank 20 and is hydroxylated by the polymer coagulant 21 (anionic system). The iron (III) -based particles formed flocs and were separated in the second sedimentation tank 23. The slurry concentration of the separated slurry is 9 to 11% by mass, and the slurry pump is set so that the slurry concentration in the first reaction / precipitation tank 30 is 16% by mass (15.5 to 16.5% by mass). In 24, it returned to the 1st reaction tank and precipitation tank 30 as the return slurry 27 at about 0.7 L / min. Of the slurry in the first reaction / precipitation tank, about 92% by mass is attributed to coke powder. The surplus slurry was intermittently drawn as a drawn slurry 26 and dehydrated with a filter press dehydrator having a pressure of 0.5 MPa to obtain a dehydrated cake. The above-mentioned A ÷ B was about 0.72 days.

  The supernatant water (primary treated water 25) separated in the second sedimentation tank 23 contains nickel ions and zinc ions. Although not shown in the figure, a neutralizing agent is introduced into the subsequent neutralization tank to adjust the pH to 9, and the nickel / zinc metal ions in the primary treated water 25 are precipitated as hydroxides. A polymer flocculant (anionic) was added in the tank to form a floc state, and a slurry containing nickel / zinc hydroxide was separated in a subsequent precipitation tank.

  The components in the primary treated water 25 at this time are shown in Table 1, and the components of the dewatered cake after the drawing slurry 26 drawn from the second settling tank 23 is dehydrated are shown in Table 2. Divalent iron ions are mainly precipitated from the quality of the primary treated water in Table 1. The cake components in Table 2 are also mainly composed of iron (III) hydroxide, and the water content is 47% by mass (water-containing cake). Since the ratio of the amount of water in [wet] is low, it can be used as an iron source by adding operations such as kneading with other raw materials having low water content. Moreover, although C content in a cake component is contained a little, it is substantially the same level as the comparative example mentioned later, and the coke powder added as a microorganisms carrier has flowed out little.

  In addition, although it implemented also when not returning to the 1st reaction tank and precipitation tank 30 with the slurry pump 24, in that case, the applied pressure of 0.5 MPa is applied to the slurry separated in the 2nd precipitation tank 23. When dewatering with a filter press dehydrator, the water content in the dewatered cake becomes 57% by mass, and the dewaterability is reduced as compared with the case where the slurry pump 24 returns to the first reaction tank / precipitation tank 30. did.

(Comparative Example 1)
A solution containing divalent iron ions, nickel ions, and zinc ions shown in Table 1 was used as the pickling plating waste liquid, and this pickling plating simulated waste water was processed using the processing apparatus of FIG. No microbial carrier is added.

The capacities of the first reaction tank 12 and the coagulation tank 20 are 730 L and 15 L, respectively, the water surface area of the second sedimentation tank 23 is 2,190 cm ² , and the OFR is 34 m / D. Note that iron-oxidizing bacteria are previously introduced into the first reaction tank 12.

  While pickling plating waste liquid is continuously supplied to the first reaction tank 12 at 5.1 L / min, an aqueous caustic soda solution is added as a neutralizing agent 17, and the pH in the first reaction tank 12 is controlled at 4. Further, air was blown at 55 NL / min from the air diffuser 14 installed at the bottom of the first reaction tank 12 to stir the first reaction tank 12.

  The divalent iron ions in the pickling plating wastewater charged into the first reaction tank 12 are on the surface of particles of iron hydroxide (III) mainly contained in the return slurry 27 returned from the second settling tank 23. Almost all of the iron ions are oxidized to trivalent iron ions by the attached iron-oxidizing bacteria, and the iron ions contained in the pickling plating waste liquid become iron (III) hydroxide on the surface of the iron hydroxide (III) -based particles. Precipitates and enlarges the particles. The slurry containing the iron (III) hydroxide-based particles from the first reaction tank 12 is put into the coagulation tank 20, and the iron (III) hydroxide-based particles form flocs by the polymer flocculant 21. 2 was separated in the precipitation tank 23. The slurry concentration of the separated slurry is 9 to 11% by mass, and the slurry concentration in the slurry pump 24 is about 2.6 L / min so that the slurry concentration in the first reaction tank 12 is 5 to 6% by mass. It returned to the reaction tank 12 of 1 as the return slurry 27. The surplus slurry was intermittently drawn as a drawn slurry 26 and dehydrated with a filter press dehydrator having a pressure of 0.5 MPa to obtain a dehydrated cake. The aforementioned A ÷ B was about 9.1 days.

  The supernatant water (primary treated water 25) separated in the second sedimentation tank 23 contains nickel ions and zinc ions. Although not shown, a neutralizing agent is added in a neutralizing tank to adjust pH to 9, and after depositing nickel / zinc metal ions in the primary treated water as hydroxides, a polymer flocculant is added in the coagulating tank. In addition, a floc state was obtained, and a slurry containing nickel / zinc hydroxide was separated in a precipitation tank.

Table 1 in the primary treated water 25 at this time shows the components of the dewatered cake after the slurry extracted from the second reaction tank 23 is dewatered. Fe ²⁺ ions are mainly precipitated from the quality of the primary treated water in Table 1. The cake components in Table 2 are also mainly composed of iron (III) hydroxide, and the water content is as low as 49% by mass. It can be used as an iron source by adding operations such as kneading with other raw materials having low moisture.

There is no difference in dehydration between the examples and comparative examples. However, the capacity of the reaction vessel and the coagulation vessel required to realize it is as follows: Examples 1 and 2: 281L, Comparative Example 1: 745L, and the water surface area of the precipitation vessel is as in Examples 1 and 2: 478 cm ² , Comparative Example 1: 2,190 cm ^{2 The} tank capacity and water surface area are smaller in the example, and the equipment cost can be suppressed.

  The amount of the polymer flocculant used is Example 1: 21 g-dry / D, Example 2: 19 g-dry / D, and Comparative Example 1: 73 g-dry / D, and the amount of the polymer flocculant used is reduced. it can.

Furthermore, the amount of air blown into the reaction tanks (12 and 30) charged as stirring power was Example 1: 20 NL / min, Example 2: 20 NL / min, and Comparative Example 1: 55 NL / min. Can also be reduced.
Table 3 (relative comparison, assuming Comparative Example 1 as 100) is a trial calculation of equipment costs and running costs when pickling waste liquid (5 m ³ / min) containing divalent iron shown in Table 1 is treated. is there. From Table 3, it can be seen that both the equipment cost and the running cost are excellent in the examples.

It is the figure which showed the relationship between the pH of a waste liquid, and the residual ratio (mass ratio) of the metal ion in a waste liquid. It is the figure which showed the relationship between the sedimentation speed | velocity | rate of coke powder (500-850 micrometers), and slurry concentration. It is the figure which showed the relationship between the sedimentation rate of the particle | grains of iron (III) main body, and slurry concentration. The amount of solid matter mainly composed of iron (III) hydroxide in the first reaction tank 12 is set to A (kg), an alkaline agent is added to an acidic waste liquid containing iron ions and other metal ions, and iron hydroxide ( III) When B (kg / day) is the amount of newly precipitated main particles, the relationship between A ÷ B (day) and the moisture in the dehydrated cake when dehydrated at a dehydration pressure of 0.5 MPa was shown. FIG. It is an example of the processing apparatus which concerns on the manufacturing method of the iron containing dewatering cake from the wastewater of this invention. It is an example of the processing apparatus which concerns on the manufacturing method of the iron containing dehydrated cake from the wastewater of this invention using a reaction tank and a sedimentation tank. It is the processing apparatus applied by the comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Waste water treatment apparatus 11 applied to the manufacturing method of an iron containing dewatering cake ... Acidic waste liquid 12 containing a bivalent iron ion ... First reaction tank 13 ... Microorganism carrier 14 ... Spatter Ventilator 15 ... pH meter 16 ... Neutralizer valve 17 ... Neutralizer 18 ... First sedimentation tank 19 ... Microbial carrier return pump 20 ... Agglomeration tank 21 ... · Polymer flocculant 22 ··· Stirrer 23 ··· Second settling tank 24 · · · Slurry pump 25 · · · Primary treated water 26 · · · Drawing slurry 27 · · · Return slurry 30 · · · 1 reaction tank / precipitation tank 31 ... reaction part 32 ... sedimentation part

Claims (6)

Iron oxidizing bacteria and any one or more selected from the group consisting of coke powder, activated carbon, coal powder, pumice powder, and foamed slag, and a microbial carrier of the iron oxidizing bacteria that settles in water are charged, In addition, an acidic waste liquid containing divalent iron ions is supplied into the first reaction vessel stirred by aeration to oxidize the divalent iron ions to trivalent iron ions by the iron oxidizing bacteria, Adjusting the pH in the first reaction tank to 3 or more and 5 or less to produce iron (III) hydroxide particles;
The slurry containing the iron (III) hydroxide particles and the microbial carrier discharged from the production step of the iron (III) hydroxide particles is settled and separated in a first settling tank, and the settled microbial carrier is converted into the first microbial carrier. Sedimentation and separation step of the microbial carrier to be returned to the reaction tank,
The slurry containing the iron (III) hydroxide particles discharged from the sedimentation and separation step of the microorganism carrier is fed to a coagulation tank, and a polymer flocculant is added to flock the iron (III) hydroxide particles. A flock forming step to be formed;
The slurry containing the flocs of the iron (III) hydroxide particles discharged from the floc forming step is settled and separated in a second settling tank, and the slurry containing the flocs of the precipitated iron (III) particles is recovered. And a method for recovering iron from waste liquid.   A settling portion of the microbial carrier is provided at a subsequent stage in the tank in the first reaction tank, the microbial carrier is allowed to settle in the settling portion, and the slurry containing the iron (III) hydroxide particles separated by settling is used. The method for recovering iron from waste liquid according to claim 1, wherein the first reaction tank also serves as the first precipitation tank by discharging from the first reaction tank.   In the first reaction tank, the mass of the microbial carrier with respect to the total mass of the microbial carrier and the iron (III) hydroxide particles is 70% by mass to 95% by mass. A method for recovering iron from the waste liquid according to claim 1 or 2.   A part of the slurry containing flocs of the iron (III) hydroxide particles settled in the second settling tank in the iron collecting step is returned to the first reaction tank. The method for recovering iron from the waste liquid according to any one of the above. The method for recovering iron from waste liquid according to any one of claims 1 to 4, wherein the acidic waste liquid containing divalent iron ions further contains at least one of nickel ions and zinc ions. The supernatant after the floc of iron (III) hydroxide particles is settled and separated in the second sedimentation tank of the iron recovery step is supplied to the third reaction tank, and the pH is adjusted to 6 or more and 10 or less, A production step of metal hydroxide particles for producing metal hydroxide particles containing at least one of nickel and zinc;
A metal hydroxide particle recovery step of settling and separating the slurry containing the metal hydroxide particles discharged from the production step of the metal hydroxide particles and recovering the slurry containing the precipitated metal hydroxide particles; And a method for recovering iron from waste liquid.   The method for recovering iron from waste liquid according to any one of claims 1 to 5, wherein the recovered iron (III) particles contain a floc slurry or the recovered iron (III) hydroxide. A method for recovering iron from a waste liquid, characterized in that a slurry containing particle floc and a slurry containing metal hydroxide particles are further dehydrated to form a cake.

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