KR20020094482A - Method of recovering silver - Google Patents

Abstract

PURPOSE: A method for efficiently recovering high purity silver from copper anode slime or industrial waste comprising at least silver and lead by combining wet type process with dry type process is provided. CONSTITUTION: In a method for recovering silver from raw materials comprising at least lead and precious metal such as silver, the method for recovering silver comprises the steps of forming anode slime comprising chlorides of silver and lead by chloridation leaching the raw materials and recovering anode slime comprising chlorides of silver and lead by solid-liquid separating the raw materials; repulping the anode slime comprising chlorides of silver and lead, reducing the anode slime comprising chlorides of silver and lead by adding iron to the anode slime, and recovering a mixture comprising metallic silver and lead; oxidizing the mixture comprising silver and lead in a drying furnace at a high temperature, and forming slag comprising coarse silver and lead oxide; and producing high purity silver by separating the coarse silver and electrolyzing the residual silver.

Description

Recovery method of silver {METHOD OF RECOVERING SILVER}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering silver from copper electrolytic materials or industrial waste containing at least silver and lead, and more particularly, to a method for efficiently recovering high purity silver by combining wet and dry methods. .

In many fields, recovery of silver, gold, platinum groups, and the like from raw materials containing precious metals including silver, lead, copper and various other elements is required. Examples of such a recovery source include, for example, copper electrolytic materials in copper refining, electronic wire scraps including precious metals including wires, electrodes, copper foil circuits, and solder parts and solder films such as gold and silver. to be.

Hereinafter, a copper electrolytic material is demonstrated as an example. In electrolytic refining of copper, the crude silver from the converter is refined to about 99.5% in a refinery furnace, and a dozen sheets of the positive electrode (anode) and the end plate as the negative electrode are crossed in the electrolytic cell. It is suspended in two tanks and electrolytic purification is performed. Copper electrodeposited on the end plates is called electric copper and is subsequently treated in a known embodiment. At the bottom of the electrolytic cell, impurities contained in the anode are immersed in the form of mud, which is called a copper electrolyte (anode slime). In addition to copper, precious metals in the raw material, including gold and silver, are concentrated in the copper electrolytic material and are the main raw materials for the recovery of precious metals. In addition, selenium (Se) and tellurium (Te) are also included. Lead is also included. An analysis example of the copper electrolytic material is shown in Table 1 below:

Copper Electrolyte Analysis Example (Unit:%) Au Ag Cu Pt Pd As Bi Sb Pb Se Te 1.9 17.5 25.7 0.03 0.2 3.7 0.4 2.0 4.7 8.4 4.5

As for the method of recovering the noble metal from this copper electrolytic material, all the treatment methods of the dry method and the wet method are put to practical use. The following method is reported as a method of wet treating an electrolytic material. For example, copper electrolyte is repulped with an electrolyte solution to dissolve copper, selenium, arsenic, and other soluble impurities remaining in the precursor, and insoluble mainly containing precious metals, selenium, and the like including gold, silver, and platinum groups. Seafood and solid solution are separated and concentrated precious metals are purified. The main components of the insoluble matter are silver, selenium, gold, platinum group, tellurium, lead and the like. This residue is oxidized and dissolved in a solution containing hydrochloric acid to dissolve gold, platinum group, selenium and the like. Silver, lead, etc., which form chlorine and chloride and form undissolved products, are solid-liquid separated, and silver becomes a concentrated silver intermediate. Since silver is a chloride, it is treated with silver chloride, reduced, and then reduced to a silver product after the deoxidation treatment and the impurity treatment. In the liquid after solid-liquid separation of silver chloride, valuables such as gold, platinum group, and selenium are contained. Therefore, gold is purified by solvent extraction, selenium by distillation purification and platinum group by solvent extraction. The product is purified by separation.

Fig. 2 shows a treatment process flow sheet for recovering silver from the copper electrolytic material by the conventional method.

In the conventional wet treatment method, the silver chloride obtained in the whole wet treatment process is further wet-purified to produce high purity silver. In this method, the following problems were encountered when refining silver:

(1) In wet refining, in the case of a reaction using hydrochloric acid or the like, in the case of treating a raw material containing lead, such as copper, lead and chloride also become silver and lead chloride is mixed in silver chloride.

It is necessary to strictly control the liquid temperature, to suppress the precipitation of lead chloride as much as possible, and to improve the quality of silver chloride. However, pretreatment of lead is required as a pretreatment for silver tablets. Therefore, lead is converted into lead carbonate using a sodium carbonate solution. Next, lead is leached by nitric acid and separated into lead-containing liquid and silver residue. As such, an extra step of separating lead from silver chloride is required.

(2) The silver liquid material (silver chloride) separated from the solid-liquid is subjected to ammonia leaching in order to increase its purity, and is separated from impurities other than silver chloride. The leaching solution is thermally decomposed and ammonia is recovered to make silver a high purity silver chloride. The silver chloride is converted to silver oxide by caustic soda, and then sugar is added to reduce silver powder. Use of ammonia is necessary.

③ As described above, not only the process is complicated, but also the cost of construction and chemicals, including the chemical recovery process, is increased in order to recover various chemicals. In addition, in order to use ammonia and the like, explosive nitriding requires careful attention to prevention of production, thus entailing difficulties in operation.

An object of the present invention is to completely solve the above problems and to develop an efficient process for recovering silver from copper electrolyte and scrap.

1 is a flow sheet showing a process using the copper electrolyte of the present invention as an example.

2 is a process flow sheet of the conventional method.

(Means to solve the task)

The inventors of the present invention pointed out that the source of the problem in the silver chloride refining process containing silver and lead containing silver at least is the coprecipitation of lead chloride with silver, and in order to facilitate operation of the silver chloride refining process, It was necessary to use a process that does not cause coprecipitation with silver. For this purpose, it was judged to be advantageous to introduce a dry oxidation process into the treatment of silver chloride obtained in the silver refining process. It has also been found that the use of iron is beneficial as a reducing agent. This is because in addition to the direct desalination reaction with iron, hydrogen generated by the reaction between iron and an acidic solution can also be used effectively, and iron is useful for forming slag in a dry oxidation process.

Thus, this invention is a method of recovering silver from the raw material containing at least the noble metal containing silver and lead,

(1) chlorinating the raw material to form a whole containing a chloride of silver and lead, and recovering the whole containing a chloride of silver and lead by solid-liquid separation;

(2) repulping the whole containing chlorides of silver and lead with water, reducing by adding iron, and recovering a mixture containing metallic silver and lead;

(3) subjecting the mixture containing silver and lead to high temperature oxidation in a dry furnace, forming a slag comprising crude silver and silver oxide;

(4) separating the silver and electrolyzing to produce high purity silver

It provides a recovery method of silver comprising a.

In a preferred embodiment, when the raw material contains gold and platinum groups, the whole material is sufficiently washed to minimize the involvement of gold and platinum groups into the solid-liquid separated thing of step (1). In the gold extraction process from the chloride leaching solution after the chloride leaching and solid-liquid separation, only gold is extracted with the solvent using a DBC (dibutylcarbitol) solvent. In the case where the raw material contains copper, a decopper step of leaching and removing copper contained in the stock solution from the sulfuric acid solution before chloride leaching is carried out.

(Embodiment of the Invention)

The present invention is directed to scraps of electronic devices containing noble metals including copper electrolytic materials in copper refining, wires such as gold and silver, electrodes, copper foil circuits, solder parts and solder films.

Here, a copper electrolytic material is demonstrated as an example.

As shown in Table 1, in the copper electrolyzed material, in addition to copper, precious metals in the raw material including gold are concentrated, and are the main raw materials for recovering precious metals. In addition, selenium and tellurium are also included. The problem is that lead is also included.

First, a copper electrolytic material is dissolved using a copper electrolytic process liquid, and impurities such as copper, tellurium, and arsenic are leached. The leaching residue is dissolved using a hydrochloric acid solution and an oxidizing agent, and then silver and the like are separated into solids as chlorides. Gold is separated from the thickened solution after separation by solvent extraction.

According to the present invention, after combining the wet method and the dry method, if necessary, after preliminary treatment including decopper and detellurization steps before chloride leaching of the copper electrolyte as a raw material,

(1) chlorinating the copper electrolyte as a raw material to form a chloride precursor of silver and lead, and solid-liquid separation to recover the chloride precursor of silver and lead;

(2) repulping all the chlorides of silver and lead with water to add and reduce iron to recover the metallic silver and lead mixture;

(3) subjecting the silver and lead mixture to high temperature oxidation in a dry furnace and forming a slag comprising crude silver and lead oxide;

(4) separating the silver and electrolyzing to produce high purity silver

Silver is recovered by carrying out in order.

The solution after chloride leaching and solid-liquid separation, slag containing lead oxide, and silver electrolysate are provided in a separate gold recovery process.

BRIEF DESCRIPTION OF THE DRAWINGS The flowchart of the process at the time of processing a copper electrolyte in this invention is shown.

(1) Decopper and De Tellurium Pretreatment Process

The decopper process is a process in which about 25% of the copper contained in the whole product is leached out of the sulfuric acid solution of the copper electrolysis step and is 1% or less. The telomerization step is a process for removing the tellurium in the leach solution in advance by copper substitution, because telure is also leached into the solution leaching copper, and returning it directly to the copper electrolysis process contaminates the quality of copper. The whole material sent from the electrolytic process is repulped with the electrolytic return liquid after Ni removal, for example from the copper electrolytic semen process. This releases the mold release agent contained in whole thing with a wet sieve, and sends it to a decopper leaching tank. Decopper leaching is carried out under normal pressure and air injection and at 70 to 85 ° C., especially at 80 ° C., and the copper quality in the whole product decreases from about 25% to about 0.5% for 18 to 24 hours. . In addition, Te and As in whole thing elute 50% and 85%, respectively.

The scheme is shown below:

Cu + 1 / 2O ₂ + H ₂ SO ₄ → CuSO ₄ + H ₂ O

Cu ₂ Se + O ₂ + 2H ₂ SO ₄ → 2CuSO ₄ + Se + 2H ₂ O

The leachate contains about 1 g / l of Fe and the following reactions also contribute to decopper leaching:

4FeSO ₄ + O ₂ + 2H ₂ SO ₄ → 2Fe ₂ (SO ₄ ) ₃ + 2H ₂ O

Cu ₂ Se + 2Fe ₂ (SO ₄ ) ₃ → 2CuSO ₄ + Se + 4FeSO ₄

After decoppering, solid-liquid separation is carried out by a filter press. The leaching after-liquid precipitates tellurium as copper telluride by a copper plate and copper powder in a tal tellurium bath. Sulfuric acid concentration is 230-450 g / l, temperature is 70-90 degreeC, and reaction time is 16-24 hours. The end point of the reaction is confirmed by analyzing the Te concentration in the rear solution. The scheme is as follows:

H ₂ TeO ₃ + 4Cu + 2H ₂ SO ₄ → Cu ₂ Te + 2CuSO ₄ + 3H ₂ O

The precipitated copper telluride is separated into solids in a filter press and then sent to a tellurium recovery process. The thick liquid is returned to the copper electrolytic solution process.

The entirety of the decopper and the taltellurhu is sufficiently washed to minimize the involvement of the gold and platinum groups (the total amount of the platinum group is limited to an amount less than 1/100 of the silver), and then repulped with hydrochloric acid in a repulp bath. Send it to the chloride leaching tank.

(2) Chloride leaching process

The chloride leaching step is a step of mainly separating silver and the like as chlorides from the whole product after decoppering.

In the chloride leaching tank, basically, the copper leaching precursor degreased with hydrochloric acid is leached. It is preferable to use hydrogen peroxide together. The dissolution reaction involves a reaction of consuming hydrochloric acid and hydrogen peroxide, a reaction consuming only hydrochloric acid, and a reaction consuming only hydrogen peroxide, as shown below.

(A) Reactions consuming bases and hydrogen peroxide:

Au: 2Au + 3H ₂ O ₂ + 8HCl → 2HAuCl ₄ + 6H ₂ O

Ag: Ag ₂ Se + 3H ₂ O ₂ + 2HCl → 2AgCl + H ₂ SeO ₃ + 3H ₂ O

Pt: Pt + 2H ₂ O ₂ + 6HCl → H ₂ PtCl ₆ + 4H ₂ O

Pd: Pd + H ₂ O ₂ + 4HCl → H ₂ PdCl ₄ + 2H ₂ O

Cu: Cu + H ₂ O ₂ + 2HCl → CuCl ₂ + 2H ₂ O

(B) reactions that consume only hydrochloric acid:

Pb: PbSO ₄ + 2HCl → PbCl ₂ + H ₂ SO ₄

Bi: BiAsO ₄ + 3HCl → BiCl ₃ + H ₃ AsO ₄

(C) reactions that consume only hydrogen peroxide:

Se: Se + 2H ₂ O ₂ → H ₂ SeO ₃ + H ₂ O

Te: Te + 2H ₂ O ₂ → H ₂ TeO ₃ + H ₂ O

Sb: H ₃ SbO ₃ + H ₂ O ₂ → H ₃ SbO ₄ + H ₂ O

The chloride leaching reaction is preferably performed by gradually adding hydrogen peroxide. In order to suppress decomposition due to disproportionation of hydrogen peroxide, it is necessary to appropriately control the reaction temperature. By chloride / oxidation reaction, chloride and oxide respectively dissolve or precipitate by solubility. Silver chloride precipitates because of its low solubility in hydrochloric acid and separates it from other precious metals. Most lead chlorides also precipitate. In addition, most antimony compounds and tellurium compounds precipitate.

After the leaching of chloride, the solids are separated by a filter press, and the solid of the silver chloride is sent to the silver reduction and purification process after repulping with water, and the solution is sent to an acid concentration adjusting tank equipped with cooling means.

The silver purification process which is the subject of this invention is a wet + dry process which reduces silver from silver chloride, refine | purifies and commercializes by an oxidation furnace and silver electrolysis.

(3) Iron reduction process

According to the present invention, in a silver reduction bath, iron is added to a solid slurry of a silver main body to reduce silver. The reaction is promoted in the oxidizing solution, but since the chloride leaching residue has adhered hydrochloric acid, the slurry becomes acidic due to repulpation with water. The reactor may take into account direct reduction reactions with iron and hydrogen reduction of generators produced by hydrolysis of iron as follows:

2AgCl + Fe → 2Ag + FeCl ₂

2AgCl + 2H → 2Ag + 2HCl

The reaction starts at room temperature, but increases to the boiling point by the heat of reaction. The lead chloride in the leach residue also becomes metal lead, and the chlorine in reducing silver is about 0.5%.

The iron amount used is 1.5 to 2 times the equivalent (as Ag / Fe = 2/1).

Iron is not a problem because it will remain in the slag in the following dry tablets. The temperature is 80 ° C. or higher and exothermic when iron is dissolved in the remaining hydrochloric acid. Hydrochloric acid concentration is 0.1-2 mol, about 0.2 mol is preferable. The reaction time is sufficient for about 4 hours, but in practice it takes about 10 hours to suppress boiling in the heat of melting of iron.

After reduction, solid-liquid separation is performed by filter press, and the rear liquid is reduced by hydrazine and then waste liquid.

(4) oxidation process

In dry oxidizers, impurities such as lead are effectively oxidized and removed, and lead, tin, antimony, and unreacted iron of reducing agents separated by silver slag are separated by slag, and the noble metals that are condensed are concentrated in silver to make silver.

(5) silver electrolysis process

Zo-eun is cast in a circular silver plate and silver electrolytic tableting is performed. Electrodeposition is cast with electrolytic silver after silver cleaning dissolution. All precious metals containing gold, platinum group, etc. generated are treated separately. Since a conventional process is performed, description is abbreviate | omitted.

Although not directly related to the present invention, the gold extraction and reduction process from the chlorine leaching liquor will be described by reference.

Gold Extraction and Reduction Process

After chloride leaching, the solution is sent to an acid concentration adjusting tank equipped with cooling means. In an acid concentration adjustment tank, it cools to 5 degreeC in order to prevent the impurity precipitation by solubility in a gold extraction process. In addition, the concentration of hydrochloric acid is adjusted under gold extraction conditions. After the adjustment, after solid-liquid separation by filter press, the solution is sent to the gold extraction process. Precipitation precipitates, mainly lead chloride, are returned to the smelting process.

The gold extraction step is a step of extracting only gold as a solvent from a chlorine leaching solution. After extraction of the gold solvent, in the gold product forming step, gold is reduced and precipitated from the solvent from which the gold is extracted to be commercialized.

As a solvent for gold extraction, a known one is used, but the use of DBC (dibutylcarbitol; (C ₄ H ₉ OC ₂ H ₄ ) ₂ O) is preferred. Since DBC is easy to form a compound with gold (HAuCl ₄ or AuCl ₃ ), gold can be extracted from an aqueous solution. The DBC has very high selectivity for gold, and the distribution coefficient for gold is as high as 1000.

Gold extraction is carried out in a continuous operation using a mixer settler because the reaction is fast. In the DBC after extraction, a very small amount of an aqueous solution or a precipitate is present, which finally causes deterioration or variation in the quality of the product gold, and is thus removed from the DBC by a centrifuge. The DBC after centrifugation is scrubbed by continuous operation with a mixer setler using a weak hydrochloric acid solution. Scrub removes impurities such as Fe extracted in the DBC. The DBC after scrubbing is sent to the gold reducing aid after the removal of impurities by a centrifugal separator. The scrubbing after-liquid is used as washing water and dilution water in the chloride leaching process.

Since the gold extract is dissolved in about 3 g / l of solubility in water phase, DBC is distilled off with about 20% water in a distillation tank. The gold extraction after removal of DBC is sent to the reduction process using sulfurous acid gas. The distilled DBC is repeated in the gold extraction process.

In the gold reduction aid, gold in DBC is directly reduced by mixing oxalic acid aqueous solution and DBC. The scheme is as follows:

2HAuCl ₄ + 3 (COOH) ₂ → 2Au + 6CO ₂ + 8HCl

The reduction reaction is carried out at 80 to 90 ° C. for 2 hours with stirring. After reduction, DBC sediments and separates the aqueous solution, and returns to the gold extraction step for circulation. The reduced gold and aqueous solution are vacuum filtered, and the reduced gold is washed, dried, melted and cast to form a gold ingot or gold short. Since the filtered after-liquid contains a small amount of gold and unreacted oxalic acid, hydrazine reduction and deoxalic acid treatment are performed to waste the liquid. The oxalic acid residue is repeated for the smelting process, and the rear liquid is discarded. The oxalic acid treatment is a method of fixing oxalic acid as calcium oxalate with calcium hydroxide by the following reaction:

(COOH) ₂ + Ca (OH) ₂ → Ca (COO) ₂ + 2H ₂ O

(Example)

The copper electrolyte having the analytical value shown in Table 1 was leached using the sulfuric acid solution of the copper electrolysis process in the decopper process. Decopper leaching was carried out at 80 ° C under atmospheric pressure and air injection, and the copper quality in the whole product decreased to about 0.5% for 18 to 20 hours. The decopper leaching rates were Cu: 98.5%, Te: 50%, Sb: 3%, Bi: 2%, As: 85%, and none of Au, Ag, Pt, Pd, Se, and Pb contained in the whole material. It was not leached and the leaching rate was 0%.

The decopper leaching liquor was treated by using a copper plate and a copper powder in a detellurizing bath under conditions of sulfuric acid concentration: 25 g / l, temperature: 80 ° C, and reaction time: about 18 hours to precipitate copper telluride.

The whole thing after decoppering was repulsed with hydrochloric acid, and it sent to the chloride leaching tank. The chloride leaching reaction was performed by gradually adding hydrogen peroxide. Cooling was performed so that reaction temperature might be 60-70 degreeC. After leaching the chloride, solid-liquid separation was carried out by a filter press, and the solids of the silver chloride were sent to a silver reduction process after repulping with water, and the solution was sent to an acid concentration adjusting tank equipped with a cooling means for gold extraction.

Chloride leaching rates were as follows: Au: 97.5%, Ag: 1%, Pt: 99%, Pd: 98%, Se: 93%, Te: 70%, Pb: 5%, Sb: 30%, Bi: 69%

Chloride, including silver and lead, repulped in water, was reduced to iron. The amount of iron used was 1.5 to 2 times the equivalent (as Ag / Fe = 2/1). The temperature was at least 90 ° C. and exothermic when iron was dissolved in the remaining hydrochloric acid. The hydrochloric acid concentration was about 0.2 mol. The reaction time was sufficient for about 4 hours, but in fact it required about 10 hours to suppress boiling in the heat of melting of iron. A reduction rate over 97% was obtained.

The obtained reduced silver is oxidized to remove impurities such as lead efficiently in a dry oxidation furnace, and the lead which is attached to silver chloride and unreacted iron of the reducing agent are separated by slag, and the attached precious metal is concentrated in silver to be crude silver. Electrolytic purification. When it exceeds 99.99%, high purity silver product, ie, silver, was obtained.

The intermediate composition (%) and product silver composition (ppm) of each process are shown.

Ag Cl Pb Pd Au Se Te chloride 40.8 - 7.41 0.082 0.09 1.12 1.09 Reduction 49.5 1.16 10.9 0.012 0.13 1.55 1.90 Jo Eun (Won Eun Edition) 98.52 0.17 0.27 0.28 - 0.06 Product (ppm) > 99.99 1 ppm 2 ppm <1 ppm - <1 ppm

The combination of wet and dry methods has successfully established an efficient process for silver recovery.

(1) Since the process does not cause coprecipitation of silver chloride and lead chloride, the operation of the silver chloride refining process is facilitated. In order to obtain high-purity silver by wet refining, incorporation of impurities into lead and the like must be avoided as much as possible. To this end, strict operation management such as temperature control of the silver chloride generation process is required, and the facilities are complicated, but the operation method can be greatly simplified because the silver recovery process of the present invention does not cause lead copulation.

(2) By using iron as a dechlorination agent, silver and iron are simultaneously reduced. This is because the introduction of a dry oxidation step to the treatment of silver chloride obtained in the silver refining step makes it easy to treat even a mixed raw material of lead and silver. The reason for focusing on iron as a reducing agent is that in addition to the direct desalination reaction with iron, hydrogen generated by the reaction between iron and an oxidizing solution also effectively contributes to the reaction.

In the conventional process, the dechlorination process is carried out in two stages of lead and silver, but the present invention can perform all dechlorination in one step, greatly simplifying the process, and not only reduce the equipment cost, but also operate. Significant reduction in costs is now possible.

③ In the dry oxidation furnace, impurities such as lead are oxidized and removed efficiently, and unreacted iron of lead and reducing agent attached to silver chloride is separated by slag. . In this way, not only high-purity silver but also other precious metals can be concentrated and recovered. In addition, silver quality is also stabilized because there are very few platinum groups impurity in the electrolytic purification.

(4) Since no ammonia is used to produce silver as in the prior art, there are no problems such as generation of silver nitride and complex ion in the wastewater treatment process, and the effect on safety and environment is great.

Claims (4)

A method for recovering silver from a raw material containing at least a noble metal containing silver and lead, (1) chlorinating the raw material to form a whole containing a chloride of silver and lead, and recovering the whole containing a chloride of silver and lead by solid-liquid separation; (2) repulping the whole containing chlorides of silver and lead, adding iron to reduce the contents, and recovering the mixture containing metallic silver and lead; (3) subjecting the mixture containing silver and lead to high temperature oxidation in a dry furnace and forming a slag comprising crude silver and lead oxide; (4) separating the silver and electrolyzing to produce high purity silver. 2. The method for recovering silver according to claim 1, wherein when the raw material contains gold and platinum groups, the whole material is sufficiently washed to minimize the involvement of gold and platinum groups in the solid-liquid separated whole material of step (1). 2. The method of recovering silver according to claim 1, further comprising a gold solvent extraction step of extracting only gold as a solvent using a DBC (dibutylcarbitol) solvent in a gold extraction process from a chlorine leaching solution after chloride leaching and solid-liquid separation. . The method for recovering silver according to claim 1, further comprising a decoppering step of leaching and removing copper contained in the raw material with sulfuric acid solution before chloride leaching.