JP2014051737A - Noble metal recovery method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which a minute amount of a noble metal included in cyanogen-containing waste liquor, in particular plating waste liquor can be effectively recovered, and to provide a method for effectively treating the cyanogen-containing waste liquor.SOLUTION: There is provided the noble metal recovery method which includes: a step in which cyanogen is treated under alkaline condition; and a step in which noble metal oxide obtained by the above treatment is reacted with hydrogen disulfide or a metal sulfide salt under acidic condition, thereby precipitating noble metal sulfide and the precipitated noble metal sulfide is filtered or a step in which the noble metal oxide is reacted with metals such as zinc under acidic condition, thereby precipitating noble metal and the precipitated noble metal is filtered. There is also provided the cyanogen-containing waste liquor treatment method which includes a step in which cyanogen waste liquor is contacted with chlorine gas under heating condition of 60°C or higher in a step in which cyanogen waste liquor is subjected to oxidation treatment under alkaline condition.

Description

  The present invention relates to a method for recovering noble metal from a cyan waste liquid containing noble metal, and a method for treating the cyan waste liquid.

In the method for recovering a valuable metal from a cyanide-containing liquid in which a cyanide of at least one valuable metal selected from the group consisting of nickel, copper, zinc, gold and silver is dissolved, the cyanide-containing liquid is alkaline. In addition, hypochlorite is continuously added under the condition of a temperature range from 60 ° C. to less than the boiling point, and among the valuable metals, silver is precipitated as chloride, and nickel, copper and zinc are precipitated as oxide or hydroxide. In addition, a method for recovering valuable metals from a cyanide-containing solution is known, in which gold is dissolved in a solution as a chloroaurate. (See Patent Document 1)
However, there is no description about a method for efficiently recovering a gold component from an aqueous solution present as a chloroaurate.

Gold chalcogenide ions formed by adding a chalcogenide to a gold compound solution are brought into contact with the carrier to adsorb the gold-chalcogen ions to the carrier, or the solution is acidified to form gold chalcogenide on the surface of the carrier. A method of dispersing and immobilizing gold fine particles on a carrier is known, in which gold fine particles are precipitated on the surface of the carrier by precipitating and then separating the carrier and heating. (See Patent Document 2)
More specifically, the following method is described. Take 10 mL from 1000 ppm Au (5 mmol / L) tetrachloroauric acid aqueous solution and adjust to 500 mL to prepare 20 ppm Au (0.1 mmol / L) gold (III) aqueous solution. When 6 drops (0.3 mL, equivalent to 0.3 mmol) of an aqueous sodium solution were added and stirred well, a yellow-orange solution was obtained. To this was added 1 g of molybdenum trioxide (manufactured by Kanto Chemical Co., Ltd.), and then 5 mL of concentrated hydrochloric acid ( After about 1 hour, the reaction was stopped, washed with repeated decantation, and a filtered product was obtained by suction filtration. The filtered product was dried at 80 ° C. overnight. After that, the gold concentration of the liquid (filtrate) obtained by calcination in an electric furnace at 300 ° C. for 4 hours and separation is determined by using ICP-AES, and gold is supported from the difference from the original gold solution. Estimate quantity The amount of gold supported was 1% by weight, and this weight almost coincided with the amount of gold contained in the gold (III) aqueous solution used at the beginning. It was supported on.

  That is, a chalcogenide such as sodium sulfide or hydrogen sulfide is added to a gold compound solution in which the carrier is dispersed, and the formed gold-chalcogen ion is adsorbed on the carrier, or an acid is added to make the dispersion acidic. This promotes rapid precipitation of chalcogenide gold, thereby precipitating and precipitating gold chalcogenide on the surface of the carrier, and then heating to precipitate gold-chalcogen ions, such as gold-chalcogen complex ions or chalcogenide gold. It has been found that gold fine particles can be supported on an acidic carrier by precipitation and heating to precipitate gold.

  However, this is a method of supporting gold fine particles on a carrier, and it is not described whether gold contained in a trace amount can be efficiently recovered.

On the other hand, when recovering the noble metal dissolved in the aqueous alkali hydroxide solution, the aqueous alkali hydroxide solution is characterized in that the noble metal is reduced and precipitated by adding an amphoteric metal or an alloy of the amphoteric metal to the solution. A method for recovering precious metals from is known. (See Patent Document 3)
As a method for recovering the noble metal from the aqueous alkali hydroxide solution in which the noble metal is dissolved, a method in which a mineral acid is added to the aqueous solution to make the aqueous solution acidic, and sodium borohydride (SBH) is further added to reduce the noble metal. Is also known. Since this method uses expensive SBH as a reagent, it is not suitable as an industrial production method.

  A noble metal characterized by adding a base metal and a mineral acid selected from magnesium, aluminum, zinc, iron, tin and lead to an organic solvent in which the noble metal compound is dissolved, reducing the noble metal and precipitating, and filtering the precipitate. A method of recovery is known. (Refer to Patent Document 4) Although this method is a suitable method for recovering a relatively high concentration of noble metal dissolved in an organic solvent, whether or not a noble metal contained in a trace amount in an aqueous solution can be recovered. Not suggested.

On the other hand, as a method for treating a cyan waste liquid containing a noble metal, an alkaline agent is added to the cyan waste liquid to adjust the pH value to about 10 to 11, and an oxidizing agent is added to the solution at a temperature of about 80 to 95 ° C. A method for decomposing cyan waste liquid characterized by reacting is known, and hypochlorite is exemplified as an oxidizing agent. (See Patent Document 5)
In addition, when treating the waste water discharged from the combustion exhaust gas of an explosive compound having an N—O bond, the pH of the waste water is set to 11 or higher, and hypochlorous acid is injected to maintain the redox potential of the waste water at 700 mV or higher. Then, after maintaining the pH at 11 or higher and the residual chlorine at 100 ppm or higher and heating to 80 ° C. or higher to oxidatively decompose cyanide in the wastewater, persulfate is added to the wastewater. There is known a method for treating cleaning waste water of combustion exhaust gas of an explosive compound having an N—O bond, which is characterized by decomposing a COD load component therein. (See Patent Document 6)

  Further, a waste liquid containing at least one of free cyanide, complex cyanide and a reduced compound exhibiting volatility in an aqueous alkaline solution under an alkaline condition is in a temperature range from room temperature to the boiling point and including a high temperature range of 80 ° C. or higher. The temperature is then maintained, and the oxidation-reduction potential of the waste liquid is measured from room temperature, and hypochlorite is continuously added to the waste liquid from room temperature until the oxidation-reduction potential of hypochlorite is detected. There is known a method for treating cyan waste liquid, which is characterized by being added periodically or intermittently. (See Patent Document 7)

In addition, chlorine gas is introduced into cyanide-containing wastewater in advance under alkaline conditions or hypochlorite is added to perform a first stage treatment for oxidative decomposition of cyanide, and then cyanide remaining in the wastewater. A second stage treatment in which the compound is treated with a ternary system of formaldehyde, a manganese compound and / or a copper compound, and chlorine gas or hypochlorite to remove the cyanide as a decomposition product and / or a water-insoluble salt. Cyanogen-containing wastewater treatment methods characterized by performing are known. (See Patent Document 8)
None of these methods is satisfactory because the operation is complicated, the decomposition of cyanide ions is not satisfactory, and the amount of reagents used is large.

JP 2003-147444 A JP 2009-240951 A JP 07-258758 A JP 2002-111501 A Japanese Patent Laid-Open No. 50-118962 Japanese Patent Laid-Open No. 01-107893 International Publication Number WO03 / 040045 JP 2005-279571 A

  In view of the above situation, the present invention aims to provide a method for efficiently recovering a trace amount of noble metal contained in a cyan-containing waste aqueous solution, particularly plating waste solution, and a method for efficiently treating the cyan-containing waste water. And

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have conducted a process of oxidizing a cyan waste solution under alkaline conditions and a noble metal sulfide which is precipitated by reacting with hydrogen sulfide or a metal sulfide salt under acidic conditions. The inventors have found that a trace amount of noble metal can be recovered almost quantitatively by the step of filtering a substance or the step of filtering a noble metal that precipitates by reacting with a metal such as zinc under acidic conditions, and the present invention has been completed. It was. Furthermore, in the step of oxidizing the cyan waste liquid under alkaline conditions, it was found that the cyanide can be efficiently decomposed by contacting chlorine gas under heating conditions of 60 ° C. or higher, and the present invention has been completed.

That is, the present invention
In a method for recovering a noble metal from a cyan waste solution containing a noble metal, a step of oxidatively decomposing a cyanide compound with an oxidant under alkaline conditions, and a noble metal compound obtained in the above step under conditions of hydrogen sulfide or metal A step of filtering the precious metal sulfide precipitated by reacting with a sulfide salt, or reacting with at least one metal selected from the group consisting of magnesium, aluminum, zinc, iron, tin, and lead under acidic conditions; Regarding a method for recovering precious metals, including a step of filtering the precious metal that has precipitated,
The noble metal is preferably gold, the oxidant is preferably hypochlorite or chlorine, and the acidic condition is preferably in the range of pH 0 to 3, and more preferably in the range of pH 0 to 1. Preferably, the step of oxidatively decomposing a cyanide compound with an oxidizing agent under alkaline conditions is performed by adding an oxidizing agent in the range of pH 10-12, and then adding an oxidizing agent in the range of pH 4-9. It is preferable that the step is performed, and the step is preferably performed at a temperature of 80 to 95 ° C.

  The present invention also relates to a gold recovery method in which a solution containing a chloroaurate salt is reacted with hydrogen sulfide or a metal sulfide salt under acidic conditions to collect gold sulfide. Is preferably in the range of ~ 3, more preferably in the range of pH 0-1.

  In addition, as a method for efficiently treating cyan waste liquid, the cyan waste liquid is brought into contact with chlorine gas under alkaline conditions and under heating conditions of 60 ° C. or higher, and the alkaline condition is pH 10 or higher. Preferably, the alkaline condition is controlled at pH 10 or more until the oxidation-reduction potential of the treatment liquid reaches about 600 to about 800 mV, and after the oxidation-reduction potential of the treatment liquid becomes about 600 to about 800 mV, the pH is less than 10 It is preferable to control, and after setting the pH to less than 10, it is preferable to perform the treatment until the oxidation-reduction potential of the treatment liquid reaches 800 mV or more, and the heating condition is more preferably 80 ° C. or more.

  By using the method of the present invention, a trace amount of noble metals contained in a cyan-containing waste aqueous solution typified by plating waste liquid can be efficiently recovered without performing work such as energy-intensive concentration. It is a useful invention. In addition, the method of the present invention is an industrially useful invention that can efficiently decompose cyanide compounds that cause environmental problems.

(1) Noble metal recovery method The noble metal recovery method of the present invention includes the following steps (A) and (B).
(A) Process
Step (B) Step of Oxidizing Decomposition of Cyanide Waste Solution Containing Noble Metal with Oxidizing Agent under Alkaline Conditions The following step (B-1) or (B-2) is included.
(B-1) A step (B-2) in which the precious metal compound obtained in the step (A) is reacted with hydrogen sulfide or a metal sulfide salt under acidic conditions to precipitate the precious metal sulfide deposited. The step of reacting the noble metal compound obtained in step A) with at least one metal selected from the group consisting of magnesium, aluminum, zinc, iron, tin, and lead under acidic conditions, and filtering the deposited noble metal Below, each process is explained in full detail.

1) Step (A) The “cyan waste liquid containing noble metal” used in the present invention is not particularly limited, and specific examples include salt bath nitriding waste liquid, general waste water, plating waste liquid and the like. Among these, the method of the present invention is preferably used for the treatment of plating waste liquid.

  Specific examples of the precious metal contained include gold, silver, ruthenium, rhodium, palladium, osmium, iridium, or platinum, and these may include one or more. The concentration of the precious metal contained is not particularly limited, but the present invention can be used to recover the precious metal effectively even at a low concentration. A range of 0.01 to 1000 ppm is preferable, a range of 0.01 to 500 ppm, a range of 0.01 to 200 ppm, a range of 0.01 to 50 ppm, and a range of 0.01 to 500 ppm. A range of 10 ppm is preferred. In addition, the method of the present invention can also be applied to a waste liquid having a low concentration of noble metal after initially treating a waste liquid containing a high amount of noble metal by a known method to recover another noble metal.

In addition, metals other than precious metals may be included, such as zinc, iron, chromium, cadmium, lead, arsenic, mercury, sodium, copper, aluminum, potassium, magnesium, nickel, silicon Etc. can be illustrated.
These metals may be contained in the waste liquid in any form, specifically, organic acids such as chlorides, oxides, sulfates, phosphates, nitrates, borates, and acetates. Salt, Na ₃ Au (CN) ₄ , Na ₃ Ag (CN) ₄ , Na ₂ Zn (CN) ₄ , Na ₂ Cd (CN) ₄ , Na ₂ Ag (CN) ₄ , Na ₂ Ni (CN) ₄ , Examples include complex compounds such as cyan complex compounds such as Na ₂ Cu (CN) ₄ , Na ₂ Au (CN) ₄ , K ₄ Fe (CN) _{6, and the} like.
Further, cyan contained in the cyan waste liquid may be contained in the waste liquid in any form. Specifically, cyan ions such as sodium cyanide, the above-described cyan complex compound, or complex ions thereof may be used. It can be illustrated.

When recovering a noble metal from a cyan waste liquid, particularly when a cyan complex is formed, it is necessary to decompose the cyano group first because it is stable as a compound.
As a method for decomposing cyano group, a thermal hydrolysis method, a wet oxidation method, a bitumen method, a zinc white method, a boiled high temperature combustion method, and an alkali chlorine method are known, and any of these methods can be used. In the present invention, a method is preferred in which an oxidant is allowed to act under alkaline conditions to oxidatively decompose a cyano group into cyanic acid, and further into carbonic acid and nitrogen. Although it does not restrict | limit especially as an oxidizing agent, It is preferable to use a hypochlorite or chlorine. The salt of hypochlorite is not particularly limited, and specific examples include sodium salt, potassium salt, calcium salt, and the like, but sodium salt is preferable from the viewpoint of availability.

As a step of oxidatively decomposing a cyanide compound with an oxidizing agent under alkaline conditions, a method by the alkali chlorine method is specifically exemplified. At pH 10 to 12, until the oxidation-reduction potential becomes 300 to 350 mV, sodium hypochlorite or A two-stage method in which chlorine is added and sodium hypochlorite or chlorine is further added until the oxidation-reduction potential reaches 600 to 650 mV at pH 4 to 9 can be preferably exemplified.
The treatment temperature is not particularly limited as long as it is in the range of room temperature to the waste liquid boiling point temperature, but in order to further promote oxidative decomposition, it is preferably carried out at a high temperature, and it is preferred to carry out the treatment in the range of 80 to 95 ° C. . The process of oxidative decomposition involves adding chlorine or hypochlorite and then raising the temperature, adding chlorine or hypochlorite while raising the temperature, or adding chlorine or hypochlorite after raising the temperature. Can be done in any way.
When the treatment is performed at 80 ° C. or higher, the redox potential is preferably 700 to 900 mV in the pH 10 to 12 region and 1000 mV or higher in the pH 4 to 9 region, unlike the case described above.

2) (B) Process (B) Process consists of the following (B-1) or (B-2) processes.
(B-1) A step (B-2) in which the precious metal compound obtained in the step (A) is reacted with hydrogen sulfide or a metal sulfide salt under acidic conditions to precipitate the precious metal sulfide deposited. The step of reacting the noble metal compound obtained in step A) with at least one metal selected from the group consisting of magnesium, aluminum, zinc, iron, tin, and lead under acidic conditions, and filtering the deposited noble metal

2-1) (B-1) Step After the oxidation step (A), the obtained noble metal compound is reacted with hydrogen sulfide or a metal sulfide metal salt under acidic conditions and collected as a noble metal sulfide.
The step is preferably performed after the step of oxidatively decomposing the cyanide compound described above, but may include another step between the oxidative decomposition step and the step.

The noble metal compound obtained in the step (A) represents a noble metal compound oxidized in the oxidative decomposition step of the step (A), specifically, NaAuCl ₂ , NaAuCl ₄ , NaPtCl ₆ , HAuCl ₂ , HAuCl ₄ , Examples thereof include HPtCl _{6 and the} like. The other metal contained at the beginning can be recovered from the waste liquid as a metal hydroxide or a metal oxide after the oxidation treatment step (A), for example.

Specific examples of the metal sulfide salt to be used include alkali metal sulfides or alkaline earth metal salts such as Na ₂ S, K ₂ S, MgS, and CaS, and polysulfides such as Na ₂ Sx, K ₂ Sx, MgSx, and CaSx. Examples include alkali metal or alkaline earth metal salts.
The amount of hydrogen sulfide or metal sulfide salt to be used is not particularly limited as long as it is equal to or more than an equivalent equivalent to the sulfur content necessary for the sulfide formed by the metal with respect to 1 mol of the metal contained. 1 to 20 molar equivalents, 1 to 10 molar equivalents, 1 to 5 molar equivalents, 1.5 to 3 molar equivalents, 1.8 to 2.2 molar equivalents It is preferable to use in the range.

The acidic condition is not particularly limited as long as the pH is 7 or less, but is preferably in the range of pH 0 to 3, and more preferably in the range of pH 0 to 1. When the pH exceeds 1, the precious metal recovery rate may decrease. The method for adjusting the waste liquid to the pH range is not particularly limited, and specifically, a method of adding an appropriate amount of acid can be exemplified. The acid to be used is not particularly limited, and specifically, mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, trifluoromethanesulfonic acid, fluorosulfonic acid, a mixture of antimony pentafluoride and fluorosulfuric acid, or five Examples include super strong acids such as a mixture of antimony fluoride and hydrogen fluoride. As a method of performing the reaction under acidic conditions, after adjusting the pH in advance, a method of adding hydrogen sulfide or the like while adjusting the pH, hydrogen sulfide or the like while adjusting the pH by adding hydrogen sulfide or the like and an acid simultaneously or alternately Any method can be used, such as a method of adding pH, a method of adjusting pH after adding hydrogen sulfide or the like.
The temperature of the reaction with hydrogen sulfide or the like is not particularly limited in the range from room temperature to the boiling point of the waste liquid, but it is preferably performed in the range of 40 to 60 ° C.

In addition, this invention also includes the case where (A) process is not taken about the collection | recovery method of gold | metal | money.
That is, a solution containing chloroaurate such as NaAuCl ₂ and NaAuCl ₄ can be reacted with hydrogen sulfide or a metal sulfide salt under acidic conditions to collect gold sulfide.
In that case, the range of pH 0-3 is preferable with acidic conditions, and the range of pH 0-1 is more preferable.

2-2) Step (B-2) In the method of the present invention, the noble metal compound obtained after the oxidation step (A) is selected from the group consisting of magnesium, aluminum, zinc, iron, tin, and lead. And reacting with at least one kind of metal, and collecting the precious metal deposited by filtration.

  Examples of the metal used for the reduction include at least one metal selected from the group consisting of magnesium, aluminum, zinc, iron, tin, and lead, and alloys containing them can also be used, and are particularly effective and economical. From the surface, zinc is preferred. Although the property of the metal used for reduction is not particularly limited, it is preferable to use a powder of 5 to 200 μm. Although the amount of metal used depends on the metal compound contained, it is 1.0 to 50 molar equivalents, more preferably 1.0 to 20 molar equivalents, and further 1.0 to 1.0 moles per mole of the contained metal. The range is preferably 10 molar equivalents, more preferably 1.5 to 4.0 molar equivalents.

  The acidic condition is not particularly limited as long as the pH is 7 or less, but is preferably in the range of pH 0 to 3, and more preferably in the range of pH 0 to 1. The method for adjusting the waste liquid to the pH range is not particularly limited, and specifically, a method of adding an appropriate amount of acid can be exemplified. The acid to be used is not particularly limited, and specifically, mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, trifluoromethanesulfonic acid, fluorosulfonic acid, a mixture of antimony pentafluoride and fluorosulfuric acid, or five Examples include super strong acids such as a mixture of antimony fluoride and hydrogen fluoride. Among them, concentrated hydrochloric acid or concentrated sulfuric acid is preferably used.

As a reaction for reducing a noble metal compound under acidic conditions using zinc or the like, specifically, a predetermined amount of powder such as zinc is added to a solution in which the noble metal compound is dissolved, and then an acid is added. Method of adjusting pH, adjusting pH by adding acid in advance, then adding powder such as zinc under stirring, operation of adjusting pH by adding acid, etc. and adding powder of zinc, etc. The method etc. which perform the operation to perform simultaneously or alternately can be illustrated.
In addition, after the oxidation step which is the previous step, the reduction step of the subsequent step can be performed as it is, but a metal such as zinc is adjusted after adjusting the oxidation-reduction potential lower than the reduction in a state where the oxidation-reduction potential of the solution is high. It is more efficient and preferable to carry out the reduction using. The method for adjusting the oxidation-reduction potential to be low is not particularly limited, and specifically, a method for adjusting by adding a reducing compound such as sodium sulfide can be exemplified.

The temperature during the reaction is not particularly limited as long as it is in the range of room temperature to the boiling point of the solution, but it is preferable to suppress a rapid temperature increase during the reaction. When the temperature rises suddenly, the precipitated noble metal particles become fine and the filterability may deteriorate. When the pH is adjusted in advance by adding an acid or the like, and then a metal powder such as zinc is mixed and added, it is preferable to gradually add the metal powder. When added all at once, hydrogen gas may be rapidly generated.
The end point of the reduction reaction can be confirmed by the completion of the generation of hydrogen and the stable pH.

After the reduction reaction, it is possible to filter without neutralization and recover the precipitated precious metal, but it is necessary to manufacture the equipment with an acid-resistant material. It is preferred to do so. Neutralization varies somewhat depending on the type of metal used, and for example, it can be exemplified by adding an aqueous caustic soda solution and adjusting the pH to 3 to 5, preferably 4 to 4.5. Moreover, it is preferable to adjust to pH 4 to 4.5 when zinc is used, pH 4 to 6 when aluminum is used, pH 4 to 6 when magnesium is used, and pH 3 to 5 when iron powder is used. Even if the pH is higher than these, the quality of the precious metal recovered by precipitation of the reducing metal may be lowered, but the recovery rate of the precious metal is hardly affected. The adjusted solution with adjusted pH is filtered and separated into a precipitate and a filtrate. A normal method can be employed for filtration, and a Nutsche or a centrifuge can be employed.
The obtained precipitate can be washed with water as necessary to obtain a recovered precipitate. In the recovered precipitate, the precious metal is normally concentrated to 10 to 30% by mass in terms of a dry state. Various ordinary methods can be employed to recover the precious metal from the recovered precipitate obtained. For example, it can be baked at about 700 ° C. to remove moisture and remaining organic substances, and further concentrated.

(2) Treatment method of cyan waste liquid Furthermore, in the present invention, cyan waste liquid is efficiently detoxified by contacting it with chlorine gas under alkaline conditions and heating conditions of 60 ° C. or higher. Can do.
The “alkaline condition” is not particularly limited as long as the pH is higher than 7, but is preferably pH 10 or higher.
In order to maintain alkaline conditions, an alkaline substance or an aqueous solution thereof, specifically, an alkaline substance such as sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, or an aqueous solution thereof can be exemplified. When the pH value is lowered as the treatment proceeds, an alkaline substance or an aqueous solution thereof can be added as appropriate.

  Under alkaline conditions, the pH needs to be maintained in a range greater than 7, preferably in the range of 10 or more, but the pH value does not need to be constant during processing and may vary, especially It is preferable to control at a pH of 10 or more until the oxidation-reduction potential of the treatment liquid reaches about 600 to about 800 mV, and to control at a pH of less than 10 after the oxidation-reduction potential of the treatment liquid reaches about 600 to about 800 mV.

  “Controlling at a pH of 10 or more until the oxidation-reduction potential of the treatment liquid reaches about 600 to about 800 mV” means that when the cyan-containing waste liquid is contacted with chlorine gas under the condition of pH 10 or more, the oxidation-reduction potential gradually increases. It means that an alkaline substance or an aqueous solution thereof is appropriately added so that the value rises to about 600 to about 800 mV, and during that time, the pH becomes 10 or more. Here, the oxidation-reduction potential of “about 600 to about 800 mV” means a numerical value in a range that is rounded off to 600 to 800 mV. These values increase or decrease depending on the progress of the process in relation to the process temperature.

  “After the oxidation-reduction potential of the treatment liquid becomes about 600 to about 800 mV, control is performed at a pH lower than 10” means that after the oxidation-reduction potential of the treatment liquid becomes about 600 to about 800 mV, an alkaline substance or its It means that the pH is controlled to less than 10 by bringing the solution into contact with chlorine gas without adding an aqueous solution and gradually lowering the pH, or by adding an acidic substance to lower the pH. As less than pH 10, it is preferably greater than pH 7 and 9 or less. Further, at that time, it is preferable to carry out the treatment until the oxidation-reduction potential of the treatment liquid becomes 800 mV or more by further contacting with chlorine gas, and it is more preferred to carry out the treatment until it becomes 900 mV or 1000 mV or more. .

The temperature of the treatment liquid is not particularly limited as long as it is 60 ° C. or higher, but is preferably 80 ° C. or higher, more preferably 90 ° C. or higher, and the temperature does not have to be constant during the treatment, and is appropriately 60 ° C. or higher. It may be varied within the range. Specifically, the temperature may be gradually raised from 60 ° C. to finally reach a temperature of 90 ° C. or higher. In addition, when the cyan waste liquid is contacted with chlorine gas, the cyan waste liquid is heated to 60 ° C. or higher and then gradually heated from the room temperature in contact with the chlorine gas. The temperature may be 60 ° C. or higher.
Further, as a method of bringing the cyan waste liquid into contact with the chlorine gas, any method may be used as long as the chlorine gas is taken into the cyan waste liquid. Specifically, the chlorine gas is directly blown into the cyan waste liquid using a gas introduction pipe. Examples thereof include a method, a method in which chlorine gas is filled in the processing container space, and the chlorine gas is taken into the processing liquid by stirring.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to the examples.
The cyanide concentration in the system is determined according to JIS K 0102: 2008 Factory Wastewater Test Method. It measured based on the method as described in a cyanide compound.
COD in the system was measured based on the method described in JIS K 0102: 2008 Factory Drainage Test Method 17. Oxygen Consumption by Potassium Permanganate at 100 ° C. (CODMn).

Example 1
To a solution containing 200 ppm of chloroauric acid tetrahydrate (HAuCl ₄ .4H ₂ O), 2.0 molar equivalent (38 mg) of sodium sulfide nonahydrate per 1 mol of gold was added, and hydrochloric acid was further added. Was added at room temperature until the pH reached 0.5, and black crystals were precipitated and collected by filtration.
When the recovery rate was calculated by measuring the gold concentration contained in the filtrate, it was 99.0%, and it was found that gold could be recovered almost quantitatively.

(Example 2)
The same procedure as in Example 1 was conducted except that sodium chloroaurate dihydrate (NaAuCl ₄ .2H ₂ O) was used instead of chloroauric acid tetrahydrate. As a result, the recovery rate of gold was 99.8%.

(Example 3)
To a solution containing 200 ppm of chloroauric acid tetrahydrate (HAuCl ₄ .4H ₂ O), 1.6 molar equivalent (8 mg) of zinc (powder having a particle size of 100 μm or less) is added to 1 mole of gold, Furthermore, when hydrochloric acid was added at room temperature until the pH reached 0.5, golden crystals were precipitated and collected by filtration.
When the recovery rate was calculated by measuring the gold concentration contained in the filtrate, it was 98.9%, and it was found that gold could be recovered almost quantitatively.

(Examples 4 to 6)
Implemented except that sodium chloroaurate dihydrate (NaAuCl ₄ .2H ₂ O) was used instead of chloroauric acid tetrahydrate, and the amount of zinc shown in Table 1 (molar equivalent to 1 mol of gold) was used. It carried out like Example 3 and calculated | required the recovery rate. The results are shown in Table 1. From the results, it was found that gold can be recovered quantitatively.

(Comparative Example 1)
The recovery rate was determined in the same manner as in Example 1 except that 4.1 mole equivalent of sodium sulfide nonahydrate was used per mole of gold and pH adjustment with sulfuric acid was not performed. Yes, many of the precious metals remained in solution.

(Comparative Example 2)
The sodium sulfide nonahydrate was used in the same manner as in Example 2 except that 69 molar equivalents per 1 mol of gold and pH adjustment with sulfuric acid was not performed, and the recovery rate was determined to be 2.2%. Yes, most of the gold could not be recovered.

(Example 7)
Place 100 g of cyanide waste solution containing 10 ppm or less of gold into a 4-neck flask equipped with a pH meter, stirrer, thermometer, reflux condenser, dropping funnel, chlorine gas inlet tube, and ORP meter, and heat to 90 ° C. in an oil bath. did.
The pH of the solution was confirmed to be 11.2 with a pH meter, and chlorine gas was introduced. A 2N sodium hydroxide aqueous solution was appropriately added dropwise from a dropping funnel so that the pH was maintained between 11 and 12. When the oxidation-reduction potential measured with the ORP meter exceeded 750 mV, dropping of the aqueous caustic soda solution was interrupted, and the pH meter was adjusted to be between 7 and 8. Then, when the oxidation-reduction potential measured with the ORP meter exceeded 1000 mV, the introduction of chlorine gas was stopped and cooled to room temperature. At this time, the CN concentration in the system was measured and found to be 0.01 mg / L or less, and it was found that cyan could be decomposed quantitatively. Further, the COD of the solution was 0.3 g / L or less, and the organic matter was also decomposed.
To this solution was added 3.0 g of sodium sulfide nonahydrate at room temperature (corresponding to 3 molar equivalents per 1 mol of the total amount of metals contained in the solution), hydrochloric acid was added, and the pH was adjusted to 0.5. Adjusted.
The crystals precipitated in the system were filtered, and the recovery rate was calculated from the concentration of the noble metal contained in the filtrate. As a result, the recovery rate of Au was 100%.

(Example 8)
To the oxidative decomposition solution by chlorine as in Example 7, 3.0 g of zinc powder (10 molar equivalents per 1 mol of the total amount of metals contained in the solution) was added, and hydrochloric acid was added to adjust the pH. Was adjusted to 0.5.
The recovered crystals were filtered and the recovery rate was calculated by measuring the metal contained in the filtrate. As a result, the recovery rate of Au was 100%, and it was found that gold could be recovered quantitatively.

Example 9
A 4-neck flask equipped with a cyan waste solution of 500 mg / L of cyanide and 100 g of cyan waste liquid with a COD of 11.2 g / L, equipped with a pH meter, stirring device, thermometer, reflux condenser, dropping funnel, chlorine gas inlet tube, and ORP meter And heated to 90 ° C. in an oil bath.
A pH meter was used to confirm that the pH of the solution was 10.5, and chlorine gas was introduced. A 2N aqueous sodium hydroxide solution was appropriately added dropwise from a dropping funnel so that the pH was maintained between 10.3 and 10.7. Further, the temperature of the cyan waste liquid was adjusted to be in the range of 88 to 92 ° C. When the oxidation-reduction potential measured with the ORP meter exceeded 855 mV, the introduction of chlorine gas was stopped and cooled to room temperature. At this time, when the CN concentration in the system was measured, it was 0.3 mg / L, and it was found that cyan could be decomposed quantitatively. Further, the COD of the solution was 0.3 g / L, and the organic matter was also decomposed. The solution after treatment was a clear yellow solution.

(Example 10)
A 4-neck flask equipped with a cyan waste solution of 500 mg / L of cyanide and 100 g of cyan waste liquid with a COD of 11.2 g / L, equipped with a pH meter, stirring device, thermometer, reflux condenser, dropping funnel, chlorine gas inlet tube, and ORP meter And heated to 90 ° C. in an oil bath.
A pH meter was used to confirm that the pH of the solution was 10.5, and chlorine gas was introduced. A 2N aqueous sodium hydroxide solution was appropriately added dropwise from a dropping funnel so that the pH was maintained between 10.4 and 10.7. Further, the temperature of the cyan waste aqueous solution was adjusted to be in the range of 90 ° C to 96 ° C. When the oxidation-reduction potential measured with the ORP meter reached 716 mV, dropping of the caustic soda aqueous solution was interrupted, and the pH meter was adjusted to be between 7 and 8. Then, when the oxidation-reduction potential measured with the ORP meter exceeded 1000 mV, the introduction of chlorine gas was stopped and cooled to room temperature. During the introduction of chlorine gas, the reaction temperature was adjusted to be in the range of 83 to 98 ° C. At this time, when the CN concentration in the system was measured, it was 0.1 mg / L, and it was found that cyan could be decomposed quantitatively. Further, the COD of the solution was 0.3 g / L, and the organic matter was also decomposed. Further, the solution after treatment was colorless and transparent.

(Comparative Example 3)
100 g of cyanide waste liquid having a cyanide compound of 500 mg / L and COD of 11.2 g / L is placed in a four-necked flask equipped with a pH meter, a stirrer, a thermometer, a reflux condenser, two dropping funnels, and an ORP meter. Heated to 90 ° C. in an oil bath.
A pH meter was used to confirm that the pH of the solution was 10.6, and an aqueous sodium hypochlorite solution having an effective chlorine content of 10% was added dropwise. A 2N aqueous sodium hydroxide solution was appropriately added dropwise from a dropping funnel so that the pH was maintained between 10.3 and 10.6. Further, the temperature of the cyan waste liquid was adjusted to be in the range of 86 to 94 ° C. When the oxidation-reduction potential measured with the ORP meter reached 367 mV, dropping of the sodium hypochlorite aqueous solution was stopped and the mixture was cooled to room temperature. At this point, the amount of available chlorine used was almost the same as in Example 9. At this point, the CN concentration in the system was measured and found to be 3.8 mg / L, and cyan remained without being decomposed. Further, the COD of the solution was 4.6 g / L, the organic matter was not sufficiently decomposed, and the solution after the treatment was colored brown.

(Example 11)
_Four necks equipped with 100 g of an aqueous solution of sodium ferrocyanide (Na ₄ [Fe (CN) ₆ ]) having a concentration of 3000 ppm equipped with a pH meter, stirring device, thermometer, reflux condenser, dropping funnel, chlorine gas inlet tube, and ORP meter The flask was placed and heated to 90 ° C. in an oil bath.
The solution was adjusted with a 2N sodium hydroxide aqueous solution so that the pH of the solution was 11.8, and chlorine gas was introduced. A 2N aqueous sodium hydroxide solution was appropriately added dropwise from a dropping funnel so that the pH was maintained between 10.8 and 11.8. Moreover, the temperature of aqueous solution was adjusted so that it might become the range of 89-93 degreeC. When the oxidation-reduction potential measured with the ORP meter exceeded 850 mV, the introduction of chlorine gas was stopped and cooled to room temperature. At this time, when the CN concentration in the system was measured, it was 0.1 mg / L, and it was found that cyan could be decomposed quantitatively. The solution after treatment was a clear yellow solution.

(Example 12)
_Four necks equipped with 100 g of an aqueous solution of sodium ferrocyanide (Na ₄ [Fe (CN) ₆ ]) having a concentration of 3000 ppm equipped with a pH meter, stirring device, thermometer, reflux condenser, dropping funnel, chlorine gas inlet tube, and ORP meter The flask was placed and heated to 93 ° C. in an oil bath.
The solution was adjusted with a 2N sodium hydroxide aqueous solution so that the pH of the solution was 12.6, and chlorine gas was introduced. A 2N sodium hydroxide aqueous solution was appropriately dropped from the dropping funnel so that the pH was maintained between 10.6 and 12.6. Moreover, the temperature of aqueous solution was adjusted so that it might become the range of 74-93 degreeC. When the oxidation-reduction potential measured with the ORP meter became 678 mV, the dropping of the caustic soda aqueous solution was interrupted, and the pH was adjusted so as to be between 7 and 8. Then, when the oxidation-reduction potential measured with the ORP meter exceeded 1100 mV, the introduction of chlorine gas was stopped and cooled to room temperature. During the introduction of chlorine gas, the reaction temperature was adjusted to be in the range of 83 to 91 ° C. At this time, when the CN concentration in the system was measured, it was 0.9 mg / L, and it was found that cyan could be decomposed quantitatively. Further, the solution after treatment was colorless and transparent.

(Example 13)
100 g of an aqueous solution of potassium ferrocyanide (K ₃ [Fe (CN) ₆ ]) having a concentration of 4200 ppm was placed in a four-necked flask equipped with a pH meter, a stirrer, a thermometer, a reflux condenser, a dropping funnel, a chlorine gas inlet tube, and an ORP meter. It was heated to 90 ° C. in an oil bath.
The solution was adjusted with a 2N sodium hydroxide aqueous solution so that the pH of the solution was 11.6, and chlorine gas was introduced. A 2N aqueous sodium hydroxide solution was appropriately added dropwise from a dropping funnel so that the pH was maintained between 10.3 and 12.0. Moreover, the temperature of aqueous solution was adjusted so that it might become the range of 89-93 degreeC. When the oxidation-reduction potential measured with the ORP meter exceeded 817 mV, the introduction of chlorine gas was stopped and cooled to room temperature. At this time, when the CN concentration in the system was measured, it was 0.3 mg / L, and it was found that cyan could be decomposed quantitatively. The solution after treatment was a clear yellow solution.

(Example 14)
100 g of an aqueous solution of potassium ferrocyanide (K ₃ [Fe (CN) ₆ ]) having a concentration of 4200 ppm was placed in a four-necked flask equipped with a pH meter, a stirrer, a thermometer, a reflux condenser, a dropping funnel, a chlorine gas inlet tube, and an ORP meter. It was heated to 90 ° C. in an oil bath.
The solution was adjusted with 2N sodium hydroxide aqueous solution so that the pH of the solution was 11.7, and chlorine gas was introduced. A 2N aqueous sodium hydroxide solution was appropriately added dropwise from a dropping funnel so that the pH was maintained between 10.2 and 11.4. Moreover, the temperature of aqueous solution was adjusted so that it might become the range of 89-91 degreeC. When the oxidation-reduction potential measured with the ORP meter reached 740 mV, dropping of the aqueous caustic soda solution was interrupted, and the pH meter was adjusted to be between 8 and 9. Then, when the oxidation-reduction potential measured with the ORP meter exceeded 1000 mV, the introduction of chlorine gas was stopped and cooled to room temperature. During the introduction of chlorine gas, the reaction temperature was adjusted to be in the range of 86 to 91 ° C. At this time, when the CN concentration in the system was measured, it was 0.1 mg / L, and it was found that cyan could be decomposed quantitatively. Further, the solution after treatment was colorless and transparent.

Claims (15)

In a method for recovering noble metals from cyan waste liquid containing noble metals,
(A) oxidatively decomposing a cyanide compound with an oxidizing agent under alkaline conditions; and
(B-1) a step of filtering the noble metal sulfide obtained by reacting the noble metal compound obtained in the step (A) with hydrogen sulfide or a metal sulfide salt under acidic conditions, or (B-2) ) The noble metal compound obtained in the step (A) is reacted with at least one metal selected from the group consisting of magnesium, aluminum, zinc, iron, tin, and lead under acidic conditions, and the precipitated noble metal is collected by filtration. A method for recovering a noble metal including the step of: The method for recovering a noble metal according to claim 1, wherein the noble metal is gold. The method for recovering a noble metal according to claim 1 or 2, wherein the oxidizing agent is hypochlorite or chlorine. The method for recovering a noble metal according to any one of claims 1 to 3, wherein the acidic condition is in a range of pH 0 to 3. The method for recovering a noble metal according to any one of claims 1 to 3, wherein the acidic condition is in a range of pH 0 to 1. The step of oxidatively decomposing a cyanide compound by an oxidizing agent under alkaline conditions is a step of adding an oxidizing agent in the range of pH 10 to 12, and then adding and oxidizing the oxidizing agent in the range of pH 4 to 9. Item 6. The precious metal recovery method according to any one of Items 1 to 5. The method for recovering a noble metal according to any one of claims 1 to 6, wherein the step of oxidatively decomposing a cyanide compound with an oxidizing agent under alkaline conditions is performed at a temperature of 80 to 95 ° C. A method for recovering gold, in which a solution containing a chloroaurate is reacted with hydrogen sulfide or a metal sulfide salt under acidic conditions to collect gold sulfide. The method for recovering gold according to claim 8, wherein the acidic condition is in a range of pH 0 to 3. The method for recovering gold according to claim 8, wherein the acidic condition is in the range of pH 0-1. A method for treating cyan waste liquid, wherein the cyan waste liquid is contacted with chlorine gas under alkaline conditions and under heating conditions of 60 ° C. or higher. The method for treating cyan waste liquid according to claim 11, wherein the alkaline condition is pH 10 or more. The alkaline condition is controlled at a pH of 10 or more until the oxidation-reduction potential of the treatment liquid reaches about 600 to about 800 mV, and is controlled at a pH of less than 10 after the oxidation-reduction potential of the treatment liquid becomes about 600 to about 800 mV. Item 12. A method for treating cyan waste liquid according to Item 11. The method for treating a cyan waste liquid according to claim 13, wherein the treatment is performed until the oxidation-reduction potential of the treatment liquid becomes 800 mV or more after the pH is less than 10. The method for treating cyan waste liquid according to any one of claims 11 to 14, wherein the heating condition is 80 ° C or higher.