JPS63121625A - Method for recovering gold and silver from waste water - Google Patents

Abstract

PURPOSE:To efficiently recover gold and silver from waste water contg. cyan complex salts of gold and silve and to make a waste water treatment simultaneously by adding bivalent copper ions and reducing agent to said waste water, recovering gold and silver from the formed precipitate and recovering copper from the separated liquid. CONSTITUTION:The waste water contg. the gold cyan complex salt and silver cyan complex salt is introduced into a reaction vessel 1 where the bivalent copper ions, reducing agent and pH controlling agent are added to the waste water and the waste water is stirred to form the hardly soluble precipitate. The reaction liquid thus formed is introduced into a flocculating vessel 2 where a high-polymer flocculating agent is added to the water to form flocs having good settleability. The water is then introduced into a settling vessel 3 and is subjected to a solid-liquid sepn. The solid-component is recovered as the complex salts of the gold and silver. The separated liquid is introduced into a neutralizing and flocculating vessel 4 where pH is adjusted and the excess copper is settled as copper hydroxide. The precipitate is separated in a settling vessel 5. The separated copper component is returned to the reaction vessel 1 and is utilized as a copper ion source of a gold and silver recovering stage. The separated liquid is introduced into a reneutralizing vessel 6 and is reneutralized. The liquid is then released in the form of the harmless treated liquid.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for recovering gold and silver from wastewater, and in particular, a method for recovering gold and silver from wastewater containing gold cyanide complex salts and/or silver cyanide complex salts by precipitating gold and silver as cyanide complex salts. The present invention relates to a method for simultaneously recovering wastewater and treating wastewater at the same time.

[Conventional technology]

Gold plating and silver plating have characteristics such as high corrosion resistance, low electrical resistance, good thermal conductivity, and can be bonded to silicone, so they have traditionally been used for decorative items (watches, fountain pens).
In recent years, it has been applied to terminal plating of IC-related lead frames, printed circuit boards, etc., aircraft, electronic equipment parts, etc.

Gold cyanide complex salts contained in wastewater discharged from such gold plating and silver plating processes cannot be decomposed by oxidation methods such as the alkali chlorine method and the ozone method.

Although silver cyanide complex salt is slightly more unstable than gold cyanide salt, it cannot be completely decomposed, so a method of recovering gold and silver by solid-liquid separation after decomposing the cyanide complex salt has not been adopted.

Conventional methods for recovering gold and silver from gold and silver cyanide complex salts include adsorption treatment using ion exchange resins or activated carbon, but elution is generally difficult, so the adsorbed resin or activated carbon is ashed. A regeneration method has also been reported in which the cyanide complex salt is eluted from the resin, which is often recovered by converting it into a resin. Gold and silver can be recovered from recycled wastewater using zinc powder,
There are methods such as reducing it with sodium borohydride and recovering it as a metal, or recovering it as a metal through electrolysis.

In addition, as a treatment method for wastewater containing general cyanide complex salts,
A method has been proposed in which free cyanide, etc. are decomposed by an alkali chlorine method, and then complex salts of iron, copper, etc. are precipitated and separated using a reducing agent (for example, Japanese Patent Publication No. 51-29587).

[Problems to be solved by the invention] [However, the above conventional methods of recovering gold and silver using ion exchange resins, etc. all have high initial costs and running costs, and the process of recovering gold and silver from dissociating from gold and silver. There was a problem in that it could not be discharged unless free cyanide was oxidized and decomposed.

Moreover, the method of Japanese Patent Publication No. 51-29587 does not suggest the possibility of application to gold and silver, and it requires the separation of insoluble complex salts after decomposing free cyanide by an oxidation method in the first step. There were problems such as complexity.

This invention is intended to solve the above-mentioned problems. Instead of decomposition by oxidation, cyanide complex salts of gold and silver are directly dissolved in the complex form by ordinary precipitation treatment, and solid-liquid separation is carried out. The purpose of this project is to develop a method for recovering gold and silver that can be recovered as precious metals and treated as wastewater at the same time.

[Means for solving problems]

This invention provides a gold-silver recovery process in which divalent copper ions and a reducing agent are present in wastewater containing gold-cyanide complex salts and/or silver-cyanide complex salts, and a sparingly soluble precipitate is separated and recovered; A feeding recovery process in which an alkali is added to the separated supernatant liquid to separate and recover excess copper as precipitate of copper hydroxide, and a process in which the recovered copper hydroxide is returned to the gold and silver recovery process as a divalent copper ion source. This method recovers gold and silver from wastewater consisting of

The wastewater to be treated in the present invention is wastewater containing gold cyanide complex salt and/or silver cyanide complex salt. Such wastewater is discharged from processes such as gold plating and silver plating,9 and typically contains free cyanide.

Hereinafter, the present invention will be explained with reference to the drawings. Drawing 0 is a system diagram showing an embodiment of the present invention, and l is a reaction tank.

2 is a flocculation tank, 3 is a sedimentation tank, 4 is a neutralization flocculation tank, 5 is a sedimentation tank, and 6 is a re-neutralization tank.

In the treatment method, wastewater is first introduced into a reaction tank 1 as a gold-silver recovery step, where a copper salt, a reducing agent, and a pH adjuster are added to the wastewater and stirred to form a hardly soluble precipitate.

The copper salt to be used in wastewater may be any water-soluble salt, and may be monovalent copper salt or divalent copper salt, but monovalent copper salts are generally sparingly soluble and easily oxidized by air. It is difficult to obtain it industrially, and divalent copper salts such as copper (II) sulfate, copper (II) chloride, and steel (II) nitrate can be used.

The reducing agent is a reducing agent that can reduce divalent copper ions to monovalent ones, such as sulfites, hydrosulfides, iron salts (n
), hydrazine, etc., but sulfites and hydrosulfides are recommended from the viewpoint of reducing the amount of sludge generated and being easily available.

Generally, when various reducing agents such as sulfite, hydrosulfide, iron(II) sulfate, and hydrazine are added to divalent copper salts such as copper sulfate, apparently monovalent copper ions are generated even though P[12-11 is used. However, when divalent copper salts and reducing agents are added to wastewater containing free cyanide and gold disilver cyanide complex salts, monovalent copper cyanide compounds precipitate as sparingly soluble salts.

This is thought to be because monovalent copper ions and cyanide react with each other and precipitate, creating an atmosphere where monovalent copper ions cannot exist in the system, resulting in a change in the apparent redox potential and reduction progressing. Ru.

It is assumed that the above reaction proceeds according to the following formula.

Cu”10N-→CuCN↓-(1
)Cu” +Au(CN)2− →CuAu(CN)2
↓ ・(2) Cu"+Ag(CN)2--+CuA
g(CN)2↓ -(3) Among these, equation (1) is a reaction of free cyanide, and equations (2) and (3) are reactions of a cyanide complex salt, both of which are due to the presence of monovalent copper ions: This produces a poorly soluble precipitate, which is then treated all at once.

The amount of copper salt present in the reaction system may be the reaction equivalent in equations (1) to (3) above, but in order to cope with fluctuations in the cyanide concentration in the wastewater and to promote the reaction, the cyanide concentration in the wastewater should be adjusted. 2 to 5 times the amount is preferred.

In this case, copper and cyanide complex react stoichiometrically and precipitate, so if the cyanide complex is precipitated and separated in the p and H regions where hydroxide steel does not precipitate even if copper salt is added in excess, precipitation will occur. Since the composition of the product is only the compounds shown by formulas (1) to (3), the noble metal content of the recovered product is high. The copper salt added in excess here is recovered in the next silver recovery step.

The amount of reducing agent is the total amount of the theoretical amount required to reduce divalent copper ions to monovalent and the amount consumed by dissolved oxygen, etc. 1 Usually 100 to 300 ml (about #I). If the reducing agent already exists in the wastewater, just add the missing amount.When adding the copper salt and reducing agent, it is preferable to add them at the same time, but they may be added separately before and after the addition.

PH region 4 to 9 in which gold and silver cyanide complexes precipitate,
At pH 4 or lower and pi (9 or higher), it becomes difficult for the natural salt to precipitate. At pH 7 or higher, excess copper becomes copper hydroxide and precipitates, lowering the content of gold and silver in the precipitate, and reducing the amount of copper salt. Since it cannot be used effectively, it is preferable to form a precipitate at a pH of 4 to 6.

In a beaker test, the reaction is completed in 2 to 5 minutes, but in actual equipment, 10 to 20 minutes is appropriate to prevent short circuits in the raw water.

After a poorly soluble precipitate is thus generated in the reaction tank 1, the reaction solution is introduced into the flocculation tank 2, and a polymer flocculant is added to flocculate it to form a floc with good sedimentation properties. Then, it is introduced into a precipitation tank 3 to perform solid-liquid separation, and the solid content is recovered as a complex salt of gold and silver.

Next, as a silver recovery step, the separated liquid from the third precipitation tank is introduced into the neutralization flocculation tank 4, and a pH adjuster is added to adjust the pH to 8 to 11 to precipitate excess copper as copper hydroxide. Then, the precipitate is separated in the precipitation tank 5, and the copper is returned as it is to the reaction tank 1, where it is used as a copper ion source in the gold and silver recovery process. Since the copper salt added in excess is recovered and used, the total amount of copper salt to be added may be the theoretical amount.

The separated liquid in the settling tank 5 is re-neutralized to a pH that can be discharged by adding a pH adjuster in the re-neutralization tank 6, and if necessary, the excess reducing agent is oxidized with hypochlorite, etc., and the water is discharged as treated water. do. Free cyanide, cyanide complex salts and copper salts are completely removed from this treated water, making it harmless.

In the above treatment, a filter may be installed as necessary for wastewater that contains surfactants, dispersants, etc. and has poor coagulation and sedimentation properties. Further, in place of the precipitation tank 3, filtration or other solid-liquid separation means can be used to separate the generated precipitate.

〔Effect of the invention〕

As described above, according to the present invention, copper ions and a reducing agent are present in the wastewater containing the gold cyanide complex salt and/or the silver cyanide complex salt to form a hardly soluble precipitate, thereby eliminating the dangerous oxidizing agent. Gold and silver can be efficiently recovered using conventional equipment and operations without using it, and wastewater can be treated, and excess copper can be recovered and used effectively.

〔Example〕

An embodiment of the present invention will be described below.

Example l CuSO450 mg/fl (as Cu) was added to wastewater containing 210 mg/12 (as Au) of KAu(CN) and 210 mg IQ (as Ag) of KAg(CN).
and adding hydrosulfide 200mg/Q,
When reacted for 30 minutes at pH 5 and analyzed the supernatant, Ag 0.14 mg/Q, Au < 0.1 mg IQ.
, CN<0.01mg/Q, Cu 37.1m3/+
It was 2. CuAg(CN)2 and CuAu(CN)
The amount of Cu used to generate z was 9 mgIQ, and more than the theoretical amount of Cu was dissolved. Next, the supernatant containing Cu was
Residual Cu was precipitated as hydroxide with aOH solution at pH 8.5, and Cu was measured and found to be 0.23 mg/l.Next, KAg(CN)z20mg#l (as Ag), N
aC11,000mg/Q, Na2SO350mg#
! Copper hydroxide 40 recovered as described above was added to artificial wastewater containing
mg/QCCu) and CuSO410mg#l
(as Cu) and copper hydroxide 40n+g/12 (as Cu) and C
uSO410mg/1 (as Cu) and Na2CO32
1 reaction compared with the case of adding 00mg/A 30
The analysis results of the filtrate filtered through filter paper Nci5A after 5 minutes are shown in Table 1.
The theoretical amount of is 11.8 mgIQ.

Table 1 In Table 1, when Na2SO2 is not added, the treatment is incomplete, but when 200 ng/Q is added, Ag(CN)2
was almost completely precipitated. Note that Cu and Ag (C
N)z reacts stoichiometrically, and it has been shown that with Na6, excess copper becomes hydroxide and precipitates, and with Na7, the treatment effect deteriorates if the pH is too high.

Example 2 KAu(CN) 237mH/12 (as Au), N
Copper hydroxide 40 mg, l (as Cu) and C
When uSO410mg #t (Cu) was added at °C,
These and Na25Oz Zo.

A comparison was made with the case where mg/fl was used in combination. reaction 30
The analysis results of the filtrate after 1 minute are shown in Table 2. Furthermore, KALJ (C
The theoretical amount of Cu relative to N)2 is 12.2 mg/Q.

In treated water analysis, Au(CN)z conforms to JIS KO1
In the cyan analysis method of No. 02, it was found that it did not dissociate into Au+CN and could not be measured, so cyan was not separated.

Table 2 As shown in Na 1 to 4 in Table 2, Na2S03.1
1! Upon addition, Au(CN)2− did not precipitate at all, and Na
When 2SO3 is added, A as shown in Nos. 5 to 8.
u(CN)2- can now be processed. Further, the reaction between Cu and Au(CN)2- on the weakly oxidizing side of Nα5,6 proceeds stoichiometrically.

[Brief explanation of the drawing]

The drawing is a system diagram showing an embodiment, in which 1 is a reaction tank, 2 is a flocculation tank, 3 and 5 are settling tanks, 4 is a neutralization flocculation tank, and 6 is a re-neutralization tank.

Claims (3)

[Claims] (1) Adding divalent copper ions and a reducing agent to wastewater containing a gold cyanide complex salt and/or a silver cyanide complex salt,
a gold and silver recovery process that separates and recovers the generated poorly soluble precipitate;
A copper recovery process in which an alkali is added to the supernatant liquid from which the poorly soluble precipitate has been separated to separate and recover excess copper as copper hydroxide precipitate, and a gold and silver recovery process in which the recovered copper hydroxide is used as a divalent copper ion source. A method for recovering gold and silver from wastewater, the method comprising the step of returning gold and silver to wastewater. (2) The method according to claim 1, wherein the formation of the precipitate in the gold and silver recovery step is carried out at a pH of 4 to 6. (3) The method according to claim 1 or 2, wherein the precipitation in the copper recovery step is performed at a pH of 8 to 11.