JP2021025090A - Method for cleaning filtration film - Google Patents

Abstract

To provide an efficient and productivity-improving cleaning method for a filtration film used for solid-liquid separation after neutralization of an acidic solution in a process of refining a scandium component being a valuable metal from the acidic solution including scandium and iron, and containing impurities such as aluminum, chrome, manganese or the like as ions.SOLUTION: A cleaning method for a filtration film is characterized in that the cleaning operation for the film is carried out along the procedure of an aqueous cleaning step (1), alkali cleaning step (2) and acid cleaning step (3) after at least solid-liquid separation by filtering operation using the film or during separation in a process of generating a solid of iron hydroxide by adding alkali to an acidic solution including a valuable metal ion being a scandium ion and impurity element ions including an iron ion to obtain a slurry including the valuable metal ion, iron hydroxide and impurity element ions, and then obtaining the solution including the valuable metal ion by solid-liquid separation.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for cleaning a filtration membrane used when filtering iron hydroxide from an acidic solution containing a scandium component of a valuable metal.

Scandium is extremely useful as an additive component of high-strength aluminum alloys. However, it has not been widely used due to its low production volume and high cost.
By the way, in recent years, as described in Patent Document 1, a high pressure acid leaching (HPAL) process for recovering nickel from nickel oxide ores such as laterite ore and limonite ore containing scandium has been industrialized. There is.

In this HPAL process, nickel oxide ore is charged into a pressure vessel together with sulfuric acid and heated to a high temperature of about 240 ° C. to 260 ° C. to obtain a nickel-containing leachate and a leaching residue, and then the nickel oxide ore is taken out from the pressure vessel. Solid-liquid separation. Then, a neutralizing agent such as alkali is added to the obtained leachate to separate impurities, and then a sulfurizing agent is added to separate nickel as nickel sulfide from the post-sulfurized liquid and recover it. ..
Furthermore, when the HPAL process is used, scandium contained in the oxide ore is leached into the leachate together with nickel, but sulfide is not produced even when a sulfide agent is added, and is contained in the post-sulfide liquid. Become. That is, nickel and scandium can be effectively separated by using the HPAL process.

However, scandium separated from nickel by the HPAL process exists in a dilute concentration in the solution, and a wide variety of impurities coexist. Therefore, it cannot be said that the scandium could be recovered as it is, and concentration or purification to separate impurities is required. It becomes.
By the way, as specific impurities contained in nickel oxide ore, various elements such as manganese and magnesium are known in addition to iron and aluminum, although the type and amount vary depending on the region of production.

Therefore, for example, Patent Document 2 proposes a method of concentrating or separating scandium from the above solution using an HPAL process and a chelating resin.
In the method of Patent Document 2, nickel and scandium are selectively leached into an acidic aqueous solution under a high temperature and high pressure in an oxidizing atmosphere to obtain an acidic solution, and then the pH of the acidic solution is adjusted. It is adjusted to the range of 2 to 4, and nickel is selectively precipitated and recovered as a sulfide by using a sulfide agent.

The post-sulfurized liquid obtained by this HPAL process after recovering nickel is brought into contact with the chelate resin to adsorb scandium to the chelate resin, and then the chelate resin is washed with a dilute acid to separate some impurities, and further strong acid is added. The scandium is eluted by contacting it with a chelating resin.

Further, as disclosed in Patent Documents 3 and 4, a method of recovering scandium by using a solvent extraction method has also been proposed.
For example, Patent Document 3 discloses a method for extracting scandium into an organic solvent using an organic solvent obtained by diluting 2-ethylhexylsulfonic acid-mono-2-ethylhexyl with kerosene.
Further, Patent Document 4 also discloses a method for selectively separating and recovering scandium by batch processing.

It is known that the grade of scandium recovered by these methods has a purity of about 95% to 98% in terms of scandium oxide. However, although the grade is sufficient for the above-mentioned applications such as addition to alloys, for applications such as fuel cell electrolytes, which have been in increasing demand in recent years, in order to exhibit the characteristics of fuel cells, For example, a higher purity grade of about 99.9% is required. In addition, some specific elements have an acceptable upper limit of grade, and it is necessary to remove the specific element.

Further, Patent Document 5 discloses a method for purifying scandium from a solution containing scandium by subjecting it to solvent extraction using an amine-based extractant and oxalis oxidation treatment.
By further roasting the obtained scandium oxalate using the method of Patent Document 5, a solid of 99.9% high-purity scandium oxide can be recovered.

In this way, it has become possible to recover high-purity scandium oxide, but there are still various problems in terms of industrial operation that reduce productivity.
As one of the specific problems, a large amount of iron often coexists in the above-mentioned post-sulfidation solution and the subsequent solution. Industrially, a neutralizing agent such as an alkali is added to a scandium-containing solution to neutralize it to generate iron hydroxide, and solid-liquid separation is performed to remove iron.
In this solid-liquid separation, the filtration membrane of a filter cloth or the like used for a solid-liquid separation device such as a filter press is often clogged with a precipitate such as iron hydroxide, and the frequency of stopping the filtration and cleaning the filtration membrane often increases. Occurs.

If the filter cloth is clogged, it is washed with water or the like to restore the filtration capacity. In the case of the above iron hydroxide, it is not easy to completely wash it with water alone, and the filter cloth has been washed with an acidic solution to dissolve the iron hydroxide.
However, in the case of neutralization of a solution containing valuable metals such as scandium and iron and impurity element ions such as aluminum, chromium, and manganese, it is not easy to recover the filtration capacity because it is quickly clogged by washing with only an acidic solution. It was one of the causes that hindered the improvement of productivity.

Japanese Unexamined Patent Publication No. 2005-350766 Japanese Unexamined Patent Publication No. 9-194211 Japanese Unexamined Patent Publication No. 9-291320 International Publication No. 2014/11216 Japanese Unexamined Patent Publication No. 2016-108664

The present invention neutralizes the acidic solution in a step of purifying a scandium component from an acidic solution containing valuable metal elements such as scandium and impurities such as aluminum, chromium, and manganese containing iron as ions, and solid-liquid. Provided is a cleaning method that contributes to the improvement of efficiency and productivity of the filter membrane used at the time of separation.

The first invention of the present invention for solving the above-mentioned problems is to add an alkali to an acidic solution containing impurity element ions containing valuable metal ions and iron ions, and the iron ions to iron hydroxide solids. In the step of obtaining a slurry containing the valuable metal ion, the iron hydroxide, and the impurity element ion, and then solid-liquid separating the slurry to obtain a solution containing the valuable metal ion.
The solid-liquid separation is a solid-liquid separation process in which the solution is filtered by a filtration membrane.
A method for cleaning a filtration membrane, which comprises performing the operation for cleaning the filtration membrane at least after or during the solid-liquid separation treatment by the following procedure.
(Record)
(1) A step of bringing water into contact with the filtration membrane and washing with water (1).
(2) A step (2) of bringing an alkaline solution having a pH of 10 to 14 into contact with the water-washed filtration membrane that has undergone the water-washing step (1) to perform alkaline cleaning.
(3) A step (3) of contacting an acidic solution having a pH of 4 to 6 with the alkali-cleaned filter membrane that has undergone the alkali-cleaning step (2) to perform acid cleaning.

The second invention of the present invention is a method for cleaning a filter membrane, characterized in that the impurity element ion in the first invention contains iron ion and is one or more of aluminum ion, chromium ion and manganese ion. ..

A third invention of the present invention is a method for cleaning a filtration membrane, characterized in that the valuable metal ion in the first and second inventions is a scandium ion.

According to the present invention, with respect to the filtration of iron hydroxide, it is possible to improve the productivity by efficiently using the filtration membrane by extending the usage time of the filtration membrane, which has a remarkable industrial effect. ..

It is a flow chart which shows an example of the application example of the scandium purification method. It is a flow chart which shows an example of the neutralization step S3 in the scandium purification method.

The present inventors use iron hydroxide produced when an acidic solution containing scandium, which is a valuable metal, is contained in an ion form and iron ions, aluminum ions, and chromium ions are contained as impurity element ions in a neutralization step. In addition to iron hydroxide, hydroxides such as aluminum and chromium are mixed, and it was found that this is one of the causes that hinder the recovery of filterability.

Generally, polypropylene is used for the filtration membrane of the filter press, and polysulfone, polyvinylidene fluoride, or the like is used as the material for the ultrafiltration. When the filtration membrane is clogged and the differential pressure rises, acid cleaning is performed to dissolve the clog and the differential pressure is reduced.
However, in the case of a solution in which aluminum ions, chromium ions, etc. coexist with iron ions as in the present application, if the filtration membrane is clogged, it is not easy to remove the clogging of the filtration membrane only by acid cleaning, and the differential pressure is not sufficient. It was not resolved in. Therefore, the present inventors have found that the function of the filtration membrane can be returned to the initial state by further incorporating alkaline cleaning.

Specifically, by washing the clogged filtration membrane with an alkaline solution, the sediment clogged in the membrane is removed and the function of the filtration membrane is restored.
In addition, since the liquid in which the filtration membrane is immersed after alkaline cleaning has a high pH, if the filtration of the process liquid is restarted in this state, not only iron but also hydroxides such as arnimium, scandium, chromium and manganese are formed. Even metal ions form new precipitates, which in turn promotes blockage of the filtration membrane and does not lead to improvement in filtration.

Therefore, after the alkaline cleaning, cleaning is performed using a cleaning solution having an pH adjusted to 4 to 6 using acid and pure water. In this case, if the pH is too low, such as less than 4, the iron hydroxide remaining on the surface of the filter film is dissolved, the iron concentration in the solution becomes high, and the impurity concentration of the final product becomes high. If the pH is as high as more than 6, it is not preferable because the above-mentioned new precipitate formation occurs.

Hereinafter, specific embodiments of the present invention (hereinafter referred to as “the present embodiment”) will be described in detail, but the present invention is not limited to the following embodiments, and the gist of the present invention is changed. It can be implemented with appropriate changes within the range that does not apply. In this specification, the notation "X to Y" (X and Y are arbitrary numerical values) means "X or more and Y or less".

Hereinafter, scandium will be described as a valuable metal.
FIG. 1 is a process chart showing an application example of the scandium purification method according to the present embodiment.
Based on the post-sulfurization liquid obtained through the hydrometallurgical process of nickel oxide ore, the acidic solution obtained through the treatment of concentrating the scandium component of the valuable metal is subjected to solvent extraction treatment and obtained by solvent extraction. It is a figure of an example of the process of recovering scandium from a smelting residue.

Specifically, the scandium recovery process shown in FIG. 1 is a wet smelting treatment step S1 in which an acidic solution containing scandium ions is obtained by leaching nickel oxide ore with an acid such as sulfuric acid, and impurities are added to the obtained acidic solution. Scandium elution step S2 to obtain a scandium eluent in which the scandium component is concentrated, and a neutralization step to increase the concentration of the scandium component by adding a neutralizing agent to the scandium eluent and performing a neutralizing treatment. It has S3, a solvent extraction step S4 in which a specific extractant is used for solvent extraction in an acidic solution containing a scandium component as a metal ion, and a scandium recovery step S5 in which scandium is recovered from a drawing residue.
Each process will be described in detail below.

<Hydrometallurgy process>
As the acidic solution containing the scandium component to be treated for scandium purification as a metal ion, as described above, the acidic solution obtained by leaching the nickel oxide ore with sulfuric acid or the like is a nickel oxide ore. A solution obtained through a hydrometallurgy process can be used.

The acidic solution containing a specific scandium component as a metal ion is prepared in the leaching step S11 in which nickel oxide ore is leached with sulfuric acid under high temperature and high pressure to obtain a leaching solution, and neutralization containing impurities by adding a neutralizing agent to the leaching solution. By a wet smelting treatment step S1 having a neutralization step S12 for obtaining a starch and a solution after neutralization, and a sulfurization step S13 for obtaining a nickel sulfide and a solution after sulfurization by adding a sulfurizing agent to the solution after neutralization. The obtained post-sulfidation solution can be used. Hereinafter, the flow of the hydrometallurgical process step S1 will be briefly described.

(1) Leaching Step In the leaching step S11, for example, using a high-temperature pressure vessel (autoclave) or the like, sulfuric acid is added to a slurry of nickel oxide ore and stirred at a temperature of 240 ° C. to 260 ° C. to form a leaching solution. This is a step of forming a leaching slurry composed of a leaching residue. The treatment in the leaching step S11 may be performed according to a conventionally known HPAL process, and is described in, for example, Patent Document 1.

Here, examples of the nickel oxide ore include so-called laterite ores such as limonite ore and saprolite ore. The nickel content of the laterite ore is usually 0.8-2.5% by weight and is contained as a hydroxide or magnesium silicate mineral. In addition, these nickel oxide ores contain scandium.

In the leaching step S11, while washing the leaching slurry composed of the obtained leaching solution and the leaching residue, the leaching solution containing nickel, cobalt, scandium and the like as metal ions and the leaching residue which is hematite are solid-liquid separated. This solid-liquid separation treatment can be performed, for example, by mixing the leaching slurry with the cleaning liquid and then using a solid-liquid separation facility such as a thickener using a coagulant supplied from a coagulant supply facility or the like.

(2) Neutralization Step The neutralization step S12 is a step of adding a neutralizing agent to the obtained leachate to adjust the pH to obtain a neutralized starch containing an impurity element and a neutralized liquid.
By the neutralization treatment in this neutralization step S12, valuable metals such as nickel, cobalt, and scandium are contained in the neutralized liquid as metal ions, and most of the impurity element ions such as iron and aluminum are contained. It forms a precipitate and becomes a neutralized starch.

As the neutralizing agent, conventionally known ones can be used, and examples thereof include calcium carbonate, slaked lime, sodium hydroxide and the like.

(3) Sulfide Step The sulfurization step S13 is a step of adding a sulfurizing agent to the neutralized liquid obtained in the above-mentioned neutralization step S12 to obtain nickel sulfide and a post-sulfide liquid.
By the sulfurization treatment in the sulfurization step S13, nickel, cobalt, zinc and the like become sulfurized, and scandium is contained in the post-sulfurized liquid as metal ions.

Specifically, in the sulfurization step S13, a sulfurizing agent such as hydrogen sulfide gas, sodium sulfide, and sodium hydride sulfide is added to the obtained after neutralization liquid, and nickel and cobalt having less impurity components are used as metal ions. A sulfide containing (nickel-cobalt mixed sulfide) and a post-sulfurization liquid containing scandium ions are produced by stabilizing the nickel concentration at a low level.

In the sulfurization treatment in the sulfurization step S13, the nickel-cobalt mixed sulfide slurry is subjected to a sedimentation separation treatment using a sedimentation separator such as a thickener, and the nickel-cobalt mixed sulfide is separated and recovered from the bottom of the thickener. On the other hand, the post-sulfurization liquid, which is an aqueous solution component, is recovered by overflowing.

[Purification of valuable metals (purification of scandium)]
In the scandium refining method according to the present embodiment, the post-sulfurized solution obtained through each step of the hydrometallurgy step S1 of nickel oxide ore as described above is subject to scandium refining treatment, such as scandium and other substances. It can be used as an acidic solution containing impurities as ions.

However, in addition to scandium ions, the post-sulfurization solution, which is an acidic solution containing scandium ions, includes, for example, aluminum, chromium, and a wide variety of other substances that remain in the solution without being sulfurized by the sulfurization treatment in the above-mentioned sulfurization step S13. Sulfide element ion is contained. For this reason, when subjecting this acidic solution to solvent extraction, it is preferable to remove impurity element ions contained in the acidic solution in advance as the scandium elution step S2 to concentrate the scandium component.

In the scandium elution step S2, the post-sulfurized liquid obtained in the sulphurized step S13 in the wet smelting treatment step S1 is passed through an ion exchange resin using, for example, a chelate resin, and scandium ions or other sulphurized liquid in the post-sulfurized liquid is passed. After adsorbing the impurity element ions on the ion exchange resin, only the scandium ions are eluted from the ion exchange resin with a strong acid such as sulfuric acid, whereby a scandium eluent in which the scandium component is concentrated can be obtained. After elution of the scandium component, air purge and water washing are performed to remove strong acids and prevent the resin from solidifying.

The scandium eluent obtained in the scandium elution step S2 obtains scandium hydroxide through a neutralization step S3 using a neutralization precipitation method for the purpose of removing impurity components and concentrating the scandium components. By performing this treatment, it is possible to improve the operation efficiency in the solvent extraction treatment in the next step.
In the solvent extraction treatment, the higher the concentration of the target component in the extraction starting solution to be treated, the better the separation performance from the unintended impurity element ions. Further, if the amount of scandium ions to be treated is the same, the higher the concentration of scandium ions in the extraction starting solution, the smaller the amount of solution to be used for solvent extraction, and as a result, the extractant to be used The quantity is also small. Further, there are various merits such as improvement of operation efficiency such that the equipment required for the solvent extraction process can be made more compact.

Therefore, the specific contents of the neutralization step S3 will be described below.
FIG. 2 is a flow chart showing an example of the neutralization step S3 of the scandium eluent, which is an acidic solution obtained by concentrating the scandium component obtained by using an ion exchange resin.
In the neutralization step S3, a neutralizing agent is added to the scandium eluent to adjust the pH within a predetermined range.
First, in FIG. 2, in Neutralization 1, iron hydroxide is mainly precipitated and filtered to form a scandium solution from which impurities have been removed, and then the solution is sent to the next Neutralization 2.
Neutralization 2 concentrates scandium by forming a scandium precipitate.

The hydroxide containing iron hydroxide produced by the neutralization treatment in Neutralization 1 contains a large amount of impurity components such as iron, aluminum, and chromium that were contained in the scandium eluent in large amounts, and is filtered by a filter. It is discharged to the outside of the system. By this impurity separation, the concentration of scandium hydroxide obtained in the next neutralization 2 is increased, and the treatment efficiency of solvent extraction is improved.

As the filter used in this neutralization 1, specifically, a filter press, an ultrafiltration machine, a precision filter, or the like can be used. When these filters are used, if the filter is used for a long time, sediment accumulates on the filtration membrane and the "differential pressure" shown in the following equation (1) rises, that is, the precipitate is clogged and filtered. The characteristics deteriorate.
In particular, when ultrafiltration is used for the filter, when the hollow fiber membrane is clogged and exceeds 50 kPa, it is difficult to remove the solid content that clogs the membrane unless it is washed, so the "differential pressure" becomes 50 kPa or more. The state was regarded as a blockage.

Therefore, as described above, acid cleaning is often performed for cleaning the filter membrane, but even if acid cleaning is performed and the filter membrane is restored, the differential pressure immediately rises again and the filtration characteristics deteriorate. In particular, when an acidic solution containing impurity element ions including scandium ions and iron ions is neutralized and filtered, if the acidic solution contains a large amount of aluminum or chromium ions, the acid cleaning is sufficient in removing the precipitate. It has been found that cleaning with an alkaline solution is more effective in improving the removal efficiency.
That is, it is considered that the chromium hydroxide starts to dissolve in the alkaline region.

In neutralization 2, the pH of the scandium solution treated and formed in neutralization 1 is adjusted to obtain a scandium hydroxide precipitate (see FIG. 2).
Then, by adding an acid to the obtained scandium hydroxide precipitate and dissolving it again, a solution having a high scandium concentration with reduced impurities can be obtained. As described above, the solvent extraction treatment efficiency can be improved by going through the neutralization step S3 in which the scandium eluate is neutralized to concentrate the scandium prior to the solvent extraction step S4. In such a neutralization step S3, an effect of separating impurities that did not become a precipitate can be expected by once forming a scandium-containing precipitate from the scandium eluate and separating it into a solid solution.

The neutralizing agent is not particularly limited, and for example, sodium hydroxide or the like can be used. The acid for dissolving the neutralized starch is not particularly limited, but sulfuric acid is preferably used. When sulfuric acid is used, the redissolved solution is a scandium sulfate solution.

In the solvent extraction step S4, the redissolved solution obtained through the neutralization step S3 in which the scandium eluent is neutralized is brought into contact with a specific extractant to perform the solvent extraction treatment. As described above, the scandium eluent and redissolve solution used for solvent extraction are acidic solutions containing impurity elements such as thorium and uranium in addition to scandium, and these are hereinafter referred to as "scandium-containing solutions". Refer to.

The embodiment in the solvent extraction step S4 is not particularly limited, but as shown in FIG. 1, for example, after extraction, a scandium-containing solution is subjected to solvent extraction using a specific extractant to extract impurities and a small amount of scandium. Extraction step S41 that separates the extractant and the extract residue with the solvent left, and the post-extraction extractant mixed with a sulfuric acid solution, and the small amount of scandium extracted by the extractor after extraction is separated into an aqueous phase and washed. It is preferable to perform a solvent extraction treatment having a scrubbing step S42 for obtaining a post-liquid and a back extraction step S43 for back-extracting impurities from the organic solvent after washing by adding a back-extracting agent to the organic solvent after washing.

Next, in the scandium recovery step S5, scandium is recovered from the extraction residual liquid obtained in the extraction step S41 in the solvent extraction step S4, and when scrubbing is performed in the scrubbing step S42, the scandium is recovered from the cleaning liquid after scrubbing. To do.

The scandium recovery method is not particularly limited, and a known method can be used. For example, a method of adding alkali to neutralize and recover as a starch of scandium hydroxide, or a method of precipitating oxalate with an oxalic acid solution. Examples thereof include a method of recovering as a product (oxalate treatment).

In the recovery method using the oxalate treatment, a precipitate of scandium oxalate is produced by adding oxalic acid to the extraction residue and the washing liquid, and then the scandium oxalate is dried and roasted. It is recommended to recover it as scandium oxide.
As a condition for roasting the obtained scandium oxalate, for example, it may be placed in a tube furnace and heated at about 900 ° C. for about 2 hours. Industrially, it is preferable to use a continuous furnace such as a rotary kiln so that drying and roasting can be performed with the same apparatus.

The method for cleaning the filtration membrane according to the present invention can be applied to any of the filtration membranes used for solid-liquid separation in the above neutralization step S3.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

The post-sulfurization solution obtained in the sulfurization step S13 in the hydrometallurgical process S1 described above using nickel oxide ore containing scandium, aluminum and chromium as a raw material is passed through an ion exchange resin of a chelate resin having iminodiacetic acid as a functional group. After the liquid is sulphurized and the scandium and other impurities in the liquid are adsorbed on the ion exchange resin, the scandium is eluted from the ion exchange resin using a sulfuric acid solution of 0.5 definition, and the scandium concentration is 194 m [g / L]. ], Aluminum concentration: 194 [mg / L], Chromium: 62 [mg / L].

Next, the pH of the eluent obtained above was adjusted to 3.8 to 4.2 using a sodium hydroxide solution to obtain a slurry in which iron hydroxide was produced. Next, this slurry was filtered using an ultrafiltration machine using a hollow fiber membrane as a filtration membrane. The suspension concentration of the solution at this time was 100 to 200 mg / l.
By observing the differential pressure during filtration, the filtration membrane in which the differential pressure exceeded 50 kPa and reached 68 kPa was considered to be clogged, and the washing according to the present invention was carried out.

This washing was carried out once by washing a sulfuric acid solution having a sulfuric acid concentration of 2 for 1 hour. Then, when the washing was performed with a sodium hydroxide solution having a concentration of 1% by weight for 1 hour, the differential pressure of the filtration membrane after washing returned to 20 kPa.
After the washing, the liquid was passed again, and the difference pressure and the time for the difference pressure to rise to 50 kPa were measured to confirm the effect of the washing. It was 162 hours later that the differential pressure reached 50 kPa after resuming use.

The slurry in which the eluate was neutralized under the same conditions as in Example 1 was filtered using the same type of ultrafiltration machine.
The filtration membrane whose differential pressure reached 72 kPa by filtration was washed with a sulfuric acid solution having a sulfuric acid concentration of 2 for 1 hour. Then, when washing was carried out with a sodium hydroxide solution having a concentration of 1% by weight for 4 hours, the differential pressure after washing returned to 15 kPa.
Almost no increase in the differential pressure was observed after resumption of use, and the differential pressure reached 50 kPa after 312 hours.

(Comparative Example 1)
The slurry in which the eluate was neutralized under the same conditions as in Example 1 was filtered using the same type of ultrafiltration machine.
The filtration membrane having a differential pressure of 67 kPa was washed with a sulfuric acid solution having a sulfuric acid concentration of 2 for 1 hour, and then alkaline washing was not performed.
The differential pressure after washing at the time of resuming use returned to 30 kPa, but after 12 hours, the differential pressure increased to 50 kPa.

(Comparative Example 2)
The slurry in which the eluate was neutralized under the same conditions as in Example 1 was filtered using the same type of ultrafiltration machine.
The filtration membrane having a differential pressure of 60 kPa was repeatedly washed twice with a sulfuric acid solution having a sulfuric acid concentration of 2 for 1 hour. No alkaline cleaning was performed.
The differential pressure after washing returned to 25 kPa, but after 12 hours, the differential pressure increased to 50 kPa.

(Comparative Example 3)
The slurry in which the eluate was neutralized under the same conditions as in Example 1 was filtered using the same type of ultrafiltration machine.
The filtration membrane having a differential pressure of 63 kPa was washed twice with a sulfuric acid solution having a sulfuric acid concentration of 2 for 1 hour.
Then, alkaline washing was carried out for 0.5 hours using a sodium hydroxide solution having a concentration of 0.1% by weight.
The differential pressure after washing returned to 22 kPa, but the cleaning effect was not sustained because the alkaline component was thin and the pH was too low below the appropriate cleaning range, and the differential pressure increased to 50 kPa after 22 hours.

As described above, the conventional acid cleaning alone requires a total cleaning time of 3 hours twice a day, and the operating rate is only 88%. On the other hand, by carrying out cleaning in which the alkaline solution of the present invention and acid cleaning are combined, it is possible to perform filtration for 162 to 312 hours, which greatly exceeds one day, and the frequency of cleaning can be significantly reduced. ..
Estimating from the results of Example 2, since the cleaning time is 4 hours after the lapse of 312 hours, the operating rate in the neutralization step reaches 99%, and the productivity is greatly improved.

Claims (3)

An alkali is added to an acidic solution containing an impurity element ion containing a valuable metal ion and an iron ion to generate a solid iron hydroxide from the iron ion, and the precious metal ion, the iron hydroxide and the impurity element are produced. In the step of obtaining a slurry containing ions and then solid-liquid separating the slurry to obtain a solution containing valuable metal ions.
The solid-liquid separation is a solid-liquid separation process in which the solution is filtered by a filtration membrane.
A method for cleaning a filtration membrane, which comprises performing the operation for cleaning the filtration membrane at least after or during the solid-liquid separation treatment by the following procedure.
(Record)
(1) A step of bringing water into contact with the filtration membrane and washing with water (1).
(2) A step (2) of bringing an alkaline solution having a pH of 10 to 14 into contact with the water-washed filtration membrane that has undergone the water-washing step (1) to perform alkaline cleaning.
(3) A step (3) of contacting an acidic solution having a pH of 4 to 6 with the alkali-cleaned filter membrane that has undergone the alkali-cleaning step (2) to perform acid cleaning. The method for cleaning a filter membrane according to claim 1, wherein the impurity element ion contains iron ion and is one or more of aluminum ion, chromium ion, and manganese ion. The method for cleaning a filtration membrane according to claim 1 or 2, wherein the valuable metal ion is a scandium ion.

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