Valuable metal recovery methods

Abstract

To provide a method for recovering valuable metals in a solubilized state by a simple process from water to be treated that contains valuable metals.SOLUTION: A method for recovering valuable metals includes: a step in which (a) a valuable metal-recovering composition that contains (i) a protein and / or a peptide and (ii) bicarbonate ions and / or carbonate ions, or (b) an aqueous solution thereof is added to water to be treated that contains valuable metals, thereby forming complexes of the valuable metals and the protein and / or peptide; and a step in which the complexes formed are subjected to membrane separation to recover the valuable metals as complexes with the protein and / or peptide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for recovering valuable metals from water to be treated that contains valuable metals, and relates to a method for recovering valuable metals in a solubilized state by adding a valuable metal recovery composition through membrane treatment. [Background technology]

[0002] Recovering valuable metals from wastewater containing them is important not only for the effective use of resources but also for meeting water quality standards and reducing environmental impact. As a general method for recovering valuable metals from wastewater, the neutralization coagulation sedimentation method, which insolubilizes valuable metals and separates them into solids and liquids, is widely used, and various methods using membrane treatment for solid-liquid separation are being investigated in order to obtain treated water of high quality. In the neutralization coagulation sedimentation method, the aggregates of insoluble hydroxides of valuable metals are very fine, which can lead to problems such as a decrease in sedimentation speed, which reduces the ability to separate the precipitation, and the contamination of the treated water with insoluble hydroxides. Therefore, measures are taken to increase the particle size of the aggregates of insoluble hydroxides by adding a coagulant, thereby increasing the sedimentation speed. However, the addition of a coagulant generates a large amount of aggregates of insoluble hydroxides with a high water content, which poses challenges to recovery efficiency and disposal of the aggregates. Japanese Patent Application Laid-Open No. 2010-284593 addresses the issue of suppressing the generation of large amounts of insoluble hydroxide aggregates in the neutralization coagulation sedimentation method, and improves the efficiency of metal recovery from plating cleaning wastewater by combining an RO membrane separation process and a crystallization process after solid-liquid separation. Japanese Patent Application Laid-Open No. 2006-320862 discloses a treatment method in which, instead of discharging the treated water, inorganic wastewater that has passed through a filtration device but has not yet been filtered is circulated upstream of the filtration device for a predetermined period of time, thereby depositing aggregates of insoluble hydroxides as a cake layer to capture fine impurities and improving metal removal capacity. Furthermore, Japanese Patent Application Laid-Open No. 2008-253954 addresses the issue of suppressing an increase in transmembrane pressure due to the accumulation of deposits on the inner and outer surfaces of a membrane during solid-liquid separation, and discloses a method for stable treatment over a long period of time by adding an agent that reduces the iron concentration to the iron-containing water to be treated and controlling the soluble iron concentration. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2010-284593 [Patent Document 2] Patent Publication No. 2006-320862 [Patent Document 3] Patent Publication No. 2008-253954 Summary of the Invention [Problem to be solved by the invention]

[0004] The neutralization coagulation sedimentation method requires many steps and various chemicals for neutralization and precipitation, making the process complicated and tedious.Furthermore, further treatment is required to remove the effects of the various chemicals used from the treated water, and treatment is required for the reuse of the recovered insoluble valuable metals, requiring complicated procedures even after the valuable metals are recovered. The present invention provides a method for recovering valuable metals in a solubilized state by adding a valuable metal recovery composition to a membrane treatment. The concentration of valuable metals in the aqueous solution that passes through the membrane is reduced to below the water quality standard, making it possible to use the method for treating wastewater containing metals, such as plating wastewater. [Means for solving the problem]

[0005] In order to solve the above problems, the present invention includes the following configurations. An aqueous solution containing valuable metals is mixed with a valuable metal recovery composition containing proteins or peptides and bicarbonate ions and / or carbonate ions, or with an aqueous solution of such a composition. This forms a complex containing the valuable metals and proteins or peptides, and the aqueous solution containing this complex is then subjected to membrane separation, allowing the valuable metals to be recovered in a solubilized state. This method can produce aqueous solutions with significantly increased concentrations of valuable metals, as well as aqueous solutions in which the concentrations of valuable metals have been reduced to below legally mandated water quality standards. [Effects of the Invention]

[0006] The present invention provides a method for recovering valuable metals in a solubilized state by membrane treatment. By subjecting the water to membrane separation treatment, an aqueous solution with a significantly increased concentration of solubilized valuable metals can be obtained, reducing the burden of treatment required for the reuse of valuable metals. The present invention provides a valuable metal recovery method that involves the addition of a valuable metal recovery composition and membrane separation treatment. Because the recovery process involves fewer steps, it is possible to minimize the need for new equipment when adopting a new recovery method. The valuable metal recovery composition can also contain proteins, peptides, and sodium bicarbonate, a food additive, providing a valuable metal recovery method with reduced environmental impact. Furthermore, because the concentration of valuable metals in the aqueous solution that passes through the membrane is reduced to below water quality standards, the method can also be used to treat wastewater containing metals. DETAILED DESCRIPTION OF THE INVENTION

[0007] The method for recovering valuable metals from water to be treated according to the present invention will be described in detail below. The composition for recovering valuable metals is characterized by containing proteins or peptides and bicarbonate ions and / or carbonate ions. Iron, a valuable metal, is known to form complexes with proteins or peptides in the presence of bicarbonate ions and / or carbonate ions. An aqueous solution containing a protein or peptide and hydrogen carbonate ions and / or carbonate ions dissolved therein is prepared as a composition for recovering valuable metals. An aqueous solution of a valuable metal recovery composition is added to water to be treated that contains valuable metals. This causes the valuable metals to form complexes with proteins or peptides. When a solution containing these complexes is subjected to membrane separation, the valuable metals do not pass through the membrane and remain in the concentrate. To maintain the solubilization of the valuable metals, the aqueous solution obtained after adding the valuable metal recovery composition to the water to be treated has a protein or peptide material concentration of 0.025 to 10%, preferably 0.05 to 4%, and more preferably 0.125 to 2%, and a sodium bicarbonate concentration of 0.5 to 13.4 g / L, preferably 1.0 to 6.7 g / L, and more preferably 1.7 to 3.4 g / L. To prevent the permeation of valuable metals, an ultrafiltration membrane may be used for the water to be treated containing the valuable metals and the valuable metal recovery composition. The pore size of the ultrafiltration membrane used should be 500 kDa or less, preferably 300 kDa or less, and more preferably 100 kDa or less. Examples of the material of the membrane to be used include hydrophilic membranes such as polysulfone, polyethersulfone, tetrafluoroethylene, ceramic, cellulose acetate, nitrocellulose, polyacrylonitrile, and aromatic polyamide, and charged membranes. The membrane treatment method for recovering valuable metals of the present invention may be any method commonly used in valuable metal recovery, water purification, production, etc., and examples thereof include cross-flow filtration treatment, etc. This method makes it possible to obtain an aqueous solution with a significantly increased concentration of valuable metals and an aqueous solution with a reduced concentration of valuable metals below the water quality standards set by law. The temperature of the solution during membrane treatment may be adjusted to a temperature that is compatible with the type of membrane used. In addition to iron, valuable metals to be recovered include copper, zinc, silver, etc. The state of these valuable metals may be an aqueous solution containing the valuable metals in a solubilized state, and even if they are in an insolubilized state, they may be solubilized in advance with hydrochloric acid, sulfuric acid, or the like. The protein of the present invention may be derived from any protein-containing material, including animal-derived proteins, plant-derived proteins, and bacterial-derived proteins. Peptides obtained by enzymatic hydrolysis of these proteins can also be used. The bicarbonate ions and / or carbonate ions may be generated using any components and methods that generate carbonate ions and / or bicarbonate ions in an aqueous solution. Carbonate ions and / or bicarbonate ions may be generated by combining one or more compounds and / or methods exemplified below. Examples of the method include a method of adding carbon dioxide such as blowing in gaseous carbon dioxide or adding liquid or solid carbon dioxide; a method of adding a bicarbonate such as sodium bicarbonate, potassium bicarbonate, calcium bicarbonate, or ammonium bicarbonate; and a method of adding a carbonate such as sodium carbonate, potassium carbonate, ammonium carbonate, or calcium carbonate. [Example]

[0008] Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.

[0009] [Example 1] An aqueous solution of ferric chloride with an iron concentration of 100 mg / L was used as the water to be treated, and the same amount of an aqueous solution of a valuable metal recovery composition was added. The concentration of the valuable metal recovery composition after addition was 1.7 g / L of potassium bicarbonate and 0.125% of a milk protein material (WPI8855 (Fonterra)). It was confirmed that adding the valuable metal recovery composition to the aqueous iron solution formed a complex containing iron and protein, and no iron precipitates were formed. 4 mL of the water to be treated containing this complex was centrifuged at 4000×g using a centrifugal 50 kDa membrane to obtain 2 mL of concentrate, which was then subjected to membrane separation treatment (2-fold concentration). The iron concentrations in the water to be treated before membrane separation, the concentrate after membrane separation, and the permeate were then measured. No iron was detected in the permeate. In the present invention, iron was measured by the nitroso-PSAP method.

[0010] [Comparative Example 1] Solution addition and membrane separation treatment were carried out under the same conditions as in Example 1, except that potassium bicarbonate was not added. Iron concentration was measured, and 17 mg / L of iron was detected in the permeate, with a recovery rate of 77.1%.

[0011] [Example 2] 500 mL of water to be treated containing the complex prepared in the same manner as in Example 1 was subjected to membrane separation treatment using a cross-flow 50 kDa membrane to obtain 450 mL of permeate (10-fold concentrated). After that, the iron concentrations in the water to be treated before membrane separation treatment, the concentrated liquid after membrane separation treatment, and the permeate were measured. Iron was not detected only in the permeate.

[0012] [Example 3] A 0.5% aqueous solution of yeast-derived peptide material (BD) was prepared and used as the aqueous peptide solution for the valuable metal recovery composition. The valuable metal recovery composition was added to an aqueous ferric chloride solution to achieve the same concentration conditions as in Example 1, thereby preparing a solution containing a complex of yeast-derived peptide and iron, and it was confirmed that no precipitation occurred. 4 mL of the water to be treated containing the complex was concentrated twice using a centrifugal 3 kDa membrane under the same conditions as in Example 1, and the iron concentration was measured. No iron was detected in the permeate.

[0013] [Example 4] An aqueous solution of zinc acetate with a zinc concentration of 100 mg / L was used as the water to be treated, and an aqueous solution of a valuable metal recovery composition was added. The concentration of the valuable metal recovery composition after preparation was 3.4 g / L of sodium carbonate and 2% of a milk protein material (WPI8855 (Fonterra)). This resulted in the formation of a complex containing zinc and protein, and it was confirmed that no zinc precipitation occurred. When 4 mL of the water to be treated containing this complex was concentrated twice using a centrifugal 10 kDa membrane under the same conditions as in Example 1 and the zinc concentration was measured, the zinc recovery rate was 98.9%. In the present invention, zinc is measured by a direct method using 5-Br-PAPS.

[0014] [Example 5] An aqueous solution of copper sulfate with a copper concentration of 100 mg / L was used as the water to be treated, and an aqueous solution of a valuable metal recovery composition was added. The concentration of the valuable metal recovery composition after preparation was 3.4 g / L of sodium bicarbonate and 2% soy protein material (Rocket Co.). This resulted in the formation of a complex containing copper and protein, and it was confirmed that no copper precipitation occurred. When 4 mL of water to be treated containing copper complexes was concentrated twice using a centrifugal 10 kDa membrane under the same conditions as in Example 1 and copper concentration was measured, the copper recovery rate was 99.5%. In the present invention, copper was measured by a direct method using DiBr-PAESA.

[0015] [Example 6] 50 L of water to be treated containing the complex prepared by the same method as in Example 1 was subjected to membrane separation treatment using a cross-flow 50 kDa membrane, and 45 L of permeate was obtained (10-fold concentrated). After that, the iron concentrations in the water to be treated before membrane separation treatment, the concentrated liquid after membrane separation treatment, and the permeate were measured, and iron was only detected in the permeate.

[0016] [Example 7] An aqueous solution of silver nitrate with a silver concentration of 100 mg / L was used as the water to be treated, and an aqueous solution of a valuable metal recovery composition was added. The concentration of the valuable metal recovery composition after preparation was 1.7 g / L sodium bicarbonate and 0.25% protein material (WPI8855 (Fonterra)). This resulted in the formation of a complex containing silver and protein, and it was confirmed that no silver precipitation occurred. When 4 mL of water to be treated containing a silver complex was concentrated twice using a centrifugal 50 kDa membrane under the same conditions as in Example 1 and the silver concentration was measured, the silver recovery rate was 91.6%. In the present invention, silver is measured by a direct method using PAN.

Claims

1. A preparation for recovering valuable metals, comprising a protein and / or a peptide, and bicarbonate ions and / or carbonate ions.

2. 2. A valuable metal recovery composition according to claim 1, which comprises an aqueous solution in which proteins and / or peptides and bicarbonate ions and / or carbonate ions are dissolved.

3. A method for recovering valuable metals contained in an aqueous solution, comprising the steps of: obtaining an aqueous solution of a composition for recovering valuable metals in which proteins and / or peptides and bicarbonate ions and / or carbonate ions are dissolved; adding the composition for recovering valuable metals to the aqueous solution containing the valuable metals, or adding the aqueous solution containing the valuable metals to the composition for recovering valuable metals, thereby forming a complex containing the valuable metals and the proteins and / or peptides; and treating the aqueous solution containing the complex with a 10 kDa membrane.

4. A method for recovering valuable metals contained in an aqueous solution, comprising the steps of: adding a protein and / or a peptide to an aqueous solution containing the valuable metal, and then adding an aqueous solution in which bicarbonate ions and / or carbonate ions have been dissolved; or adding an aqueous solution containing the valuable metal and the protein and / or peptide to an aqueous solution in which bicarbonate ions and / or carbonate ions have been dissolved, thereby forming a complex containing the valuable metal and the protein and / or peptide; and treating the aqueous solution containing the complex with a 10 kDa membrane.