JP3474526B2 - How to recover silver - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering silver from copper electrolytic deposits and industrial wastes containing at least silver and lead, and more particularly to a method for recovering silver from a wet method. The present invention relates to a method for efficiently recovering high-purity silver by combining with a dry method. 2. Description of the Related Art In many fields, it is desired to recover silver, gold, platinum group and the like from raw materials containing noble metals including silver, lead, copper and other various elements. For example, electronic equipment scraps containing noble metals, including copper electrolytic deposits in copper refining, wirings and electrodes of gold, silver, etc., copper foil circuits and solder portions and solder films are examples of such collection sources. Hereinafter, description will be made by taking a copper electrolytic deposit as an example. In electrolytic refining of copper, crude copper from a converter is refined to about 99.5% in a refining furnace, and a cast anode (anode) and a seed plate as a cathode are alternately suspended in a dozen sheets in an electrolytic cell. Then, electrolytic refining is performed. The copper electrodeposited on the seed plate is called electrolytic copper and is subsequently processed in a known manner. At the bottom of the electrolytic cell, impurities contained in the anode are deposited in a muddy state, and this is called a copper electrolytic deposit (anode slime). Copper electrolytic artifacts include gold, silver, in addition to copper,
The precious metals in the raw materials are concentrated and are the main raw materials for precious metal recovery. In addition, selenium and tellurium are also included. Lead is also included. Table 1 shows an example of the analysis of copper electrolytic deposits.
Shown in: [0003] As a method of recovering a noble metal from the copper electrolytic deposit, both a dry method and a wet method have been put to practical use. As a method of treating the electrolytic deposit by a wet method,
The following methods have been reported: For example, copper electrolytic deposits are repulped with an electrolytic solution or the like, and copper, tellurium,
It dissolves arsenic and other soluble impurities, and performs solid-liquid separation from insolubles mainly composed of noble metals including gold, silver and platinum group, selenium, etc., and performs concentration and purification of noble metals. The main components of the insolubles are silver, selenium, gold, platinum group, tellurium, lead and the like.
The residue is oxidized and dissolved with a solution containing hydrochloric acid, and the gold, platinum group,
Dissolve selenium etc. Silver, lead, and the like, which form chloride and chloride and form undissolved products, are subjected to solid-liquid separation and become a silver intermediate material in which silver is concentrated. Since silver is chloride, it is converted into silver chloride again after de-leading treatment and de-impurity treatment, and then reduced to a silver product. Since the liquid after the solid-liquid separation of silver chloride contains valuable substances such as gold, platinum group, and selenium, gold is extracted by solvent extraction.
Further, selenium is purified and separated by distillation purification, and the platinum group is purified and separated by a platinum purification step by solvent extraction to obtain a product. FIG. 2 shows a process flow sheet for recovering silver from a copper electrolytic deposit according to a conventional method. In the conventional wet processing method, silver chloride obtained in the precipitating wet processing step is further subjected to wet purification to produce high-purity silver. This method has the following problems when refining silver: In the case of a reaction using hydrochloric acid or the like in a wet refining, when processing a raw material containing lead such as a copper deposit, the method involves the addition of silver. Lead also becomes chloride, and lead chloride is mixed with silver chloride. It is necessary to strictly control the liquid temperature, suppress the precipitation of lead chloride as much as possible, and raise the quality of silver chloride. Nevertheless, pre-separation of lead is required as a pre-treatment for silver refining. Therefore, lead is converted to lead carbonate using a sodium carbonate solution. Next, lead is leached with nitric acid to separate into a lead-containing liquid and silver residue. Thus, an extra step of separating lead from silver chloride is required. The silver residue (silver chloride) subjected to solid-liquid separation is subjected to ammonia leaching to separate it from impurities other than silver chloride in order to increase its purity. This leachate is thermally decomposed to recover ammonia, and silver becomes high-purity silver chloride. After converting this silver chloride to silver oxide with caustic soda, saccharides are added and reduced,
Obtain silver powder. The use of ammonia was required. As described above, not only is the process complicated, but also various chemicals are collected.
Operation costs for chemicals etc. increase. In addition, since ammonia and the like are used, care must be taken to prevent the formation of explosive silver nitride, which involves operational difficulties. It is an object of the present invention to completely solve the above problems and to develop an efficient process for recovering silver from copper electrolytic deposits and scrap. The present inventors have found that the root of the problem in the silver chloride refining step containing at least lead and a noble metal containing silver is co-precipitation of lead chloride with reduced silver. In order to facilitate the operation of the refining process, it is necessary to adopt a process that does not cause co-precipitation of lead chloride with reduced silver. For that purpose, a dry oxidation process is used for the treatment of silver chloride obtained in the silver refining process. It was determined that it would be advantageous to introduce them. It has also been found that the use of iron as a reducing agent is beneficial. This is because, in addition to the direct desalination reaction with iron, hydrogen generated by the reaction between iron and an acidic solution can be effectively used, and iron is useful for forming slag in the dry oxidation step. Thus, the present invention provides a method for recovering silver from a raw material containing at least a noble metal containing silver, gold, and a platinum group, copper, and lead: (1) leaching copper from the raw material with a sulfuric acid solution; Silver, gold, platinum
To form a copper removal buttocks comprising a family and lead, (2) dehydration copper buttocks was exudate and silver and lead chloride containing leach to gold and platinum group chloride slurry formed by repulping with hydrochloric acid chloride (3) Gold is extracted from the chlorinated leachate collected in step (2) by DB.
Only gold is solvent-extracted and recovered using a C (dibutyl carbitol) solvent, and (4) the deposit containing silver and lead chlorides recovered in step (2) is washed and accompanied by the deposit. And (5) adding iron powder to a slurry formed by repulping silver and lead chloride-containing deposits washed in step (4) with water. The mixture containing silver and lead in a metallic state is recovered by reducing the product, and (6) the mixture containing silver and lead in step (5) is oxidized at high temperature in a dry furnace to remove slag containing coarse silver and lead oxide. Let it form
Then, (7) a method of recovering silver including a step of separating the coarse silver from the slag and subjecting the separated coarse silver to silver electrolysis to produce high-purity silver is provided. In a preferred embodiment, when the raw material contains gold and platinum group, the residue is sufficiently washed so as to minimize the entrainment of the gold and platinum group to the solid-liquid separated residue in step (1). In the step of extracting gold from the chlorinated leachate after the chlorination leaching and solid-liquid separation, only gold is extracted into the solvent using a DBC (dibutyl carbitol) solvent. In the case where the raw material contains copper, a decoppering step of leaching out copper contained in the raw material with a sulfuric acid solution before chlorination leaching is included. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic equipment scrap containing a noble metal, including a copper electrolytic deposit, wiring and electrodes of gold and silver, a copper foil circuit, a solder portion and a solder film in copper refining. set to target. Here, a copper electrolytic deposit will be described as an example. As shown in Table 1 above, the copper electrolytic
In addition to copper, gold and other precious metals in the raw materials are concentrated and are the main raw materials for precious metal recovery. In addition, selenium and tellurium are also included. The problem is that lead is also included. First, a copper electrolytic deposit is dissolved using a copper electrolytic process solution, 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 subjected to solid-liquid separation using silver or the like as chloride. Gold is separated from the post-separation solution by solvent extraction. According to the present invention, the wet method and the dry method are combined to remove copper prior to chloride leaching of the copper electrolytic deposit as a raw material.
After carrying out pretreatment including the tellurium removal step as required, (1) chloride and leach copper oxide deposits as a raw material to form silver and lead chloride deposits, solid-liquid separation, silver and lead (2) repulping the silver and lead chloride deposits with water, adding iron powder and reducing to recover a metallic silver and lead mixture, (3) high-temperature oxidation of the silver and lead mixture in a dry furnace to form coarse silver and slag containing lead oxide; and (4) separating the coarse silver and subjecting it to silver electrolysis to obtain high-purity silver. The silver is recovered by sequentially performing the steps of: The solution after chloride leaching and solid-liquid separation, the slag containing lead oxide, and the silver electrolytic deposit are separately subjected to a gold recovery step. FIG. 1 shows a process flow sheet for treating a copper electrolytic deposit in the present invention. (1) Copper removal and tellurium removal pretreatment step The copper removal step is a step of leaching and removing about 25% of copper contained in the residue with a sulfuric acid solution in a copper electrolysis step to make it 1% or less.
In the tellurium removal process, tellurium is also leached in the copper leached solution, and if this is directly returned to the copper electrolysis process, the quality of electrolytic copper is contaminated, so that tellurium in the leaching solution is removed in advance by copper replacement. It is a process of. The deposit sent from the electrolysis step is repulped with, for example, an electrolytic return solution after removing Ni from the copper electrolytic cleaning step. The mold release agent contained in the residue is removed by a wet sieve and sent to a copper removal and leaching tank. Copper removal leaching is performed at 70 to 85 ° C., especially at 80 ° C. under normal pressure and air blowing.
At 18 ° C for 18-24 hours, the copper quality in the artifacts is about 25
% To about 0.5%. Also, Te in the treasure,
As elutes 50% and 85%, respectively. The reaction formula 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 + 2
H ₂ O The leach liquor contains about 1 g / l Fe and the following reaction also contributes to the 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 [0015] copper removal after the solid-liquid separated through a filter press. After the leaching, tellurium is precipitated as copper telluride by a copper plate and copper powder in a tellurium removal tank. Sulfuric acid concentration is 230 ~
450 g / l, temperature 70-90 ° C and reaction time 16
~ 24 hours. The end point of the reaction is confirmed by analyzing the Te concentration in the post solution. The reaction formula is as follows: H ₂ TeO ₃ + 4Cu + 2H ₂ SO ₄ → Cu ₂ Te + 2Cu
SO ₄ + 3H ₂ O The precipitated copper telluride is sent to a tellurium recovery step after solid-liquid separation by a filter press. The post-solution is returned to the copper electrolytic cleaning process. After removing copper and tellurium, the residue is sufficiently washed to minimize the entrainment of gold and platinum group (restrict the total amount of platinum group to 1/100 or less of silver), and then in a repulp tank. After repulp with hydrochloric acid, it is sent to the chloride leaching tank. (2) Chloride leaching step The chlorination leaching step is a step of mainly separating silver and the like as chlorides from the deposit after copper removal. In the chlorination leaching tank, chlorination leaching is basically performed on the decoppered product slurry repulped with hydrochloric acid. It is preferable to use hydrogen peroxide in combination. As described below, the dissolution reaction involves a reaction consuming hydrochloric acid and hydrogen peroxide, a reaction consuming only hydrochloric acid, and a reaction consuming only hydrogen peroxide. (B) the reaction consumes the hydrochloric acid 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) Reaction consuming only hydrochloric acid: Pb: PbSO ₄ + 2HCl → PbCl ₂ + H ₂ SO ₄ Bi: BiAsO ₄ + 3HCl → BiCl ₃ + H ₃ AsO ₄ (c) ) reaction Se consumes only hydrogen _{peroxide: 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 chlorination leaching reaction is preferably carried out by gradually adding hydrogen peroxide. The reaction temperature must be appropriately controlled in order to suppress the decomposition of hydrogen peroxide due to the disproportionation reaction. Chloride and oxides dissolve or precipitate due to their respective solubilities due to the chloride / oxidation reaction. Since silver chloride has low solubility in a hydrochloric acid solution, it precipitates and is separated from other noble metals. Most of the lead chloride also precipitates. Most of the antimony compound and tellurium compound also precipitate. After the chloride leaching, the solid is separated into solid and liquid by a filter press, the solid mainly composed of silver chloride is sent to a silver reduction / purification step after repulping with water, and the solution is sent to an acid concentration adjusting tank equipped with a cooling means. The silver refining process which is the subject of the present invention is a wet + dry process in which silver is reduced from silver chloride, purified by an oxidation furnace and silver electrolysis, and commercialized. (3) Iron Reduction Step According to the present invention, silver is reduced by adding iron powder to a silver slurry-based solid slurry in a silver reduction tank. Although the reaction is promoted in an acidic solution, the slurry becomes acidic due to repulp with water because of the presence of attached hydrochloric acid in the chloride leaching residue. The reaction mechanism can consider a direct reduction reaction with iron powder and a reduction reaction with nascent hydrogen generated by dissolving iron powder in hydrochloric acid as follows: 2AgCl + Fe → 2Ag + FeCl ₂ 2AgCl + 2H → 2Ag + 2HCl It starts but rises to near the boiling point due to the heat of reaction. Lead chloride in the chloride leaching residue also becomes metallic lead, and the chlorine in the reduced silver is about 0.5%. The amount of iron powder used is 1.5 to 2 equivalents (assuming Ag / Fe = 2/1).
Add 1 times. Even if iron remains, there is no problem because it enters slag in the next dry refining. The liquid temperature is 80 ° C. or higher, and heat is generated when the remaining hydrochloric acid dissolves iron. The hydrochloric acid concentration is 0.1 to 2 mol, and preferably about 0.2 mol. A reaction time of about 4 hours is sufficient, but in practice, about 10 hours is required to suppress boiling due to heat of dissolution of iron. After the reduction, solid-liquid separation is performed by a filter press, and the post-liquid becomes a waste liquid after reduction with hydrazine. (4) Oxidation Step Impurities such as lead are efficiently oxidized and removed in a dry oxidation furnace, and lead, tin, antimony, and unreacted iron of a reducing agent, which are attached to silver chloride, are separated as slag. The noble metal used is concentrated into silver to obtain coarse silver. (5) Silver Electrolysis Step Crude silver is cast as an original silver plate and silver electrorefining is performed. Electrodeposited silver is cast into electric silver after washing and melting. Precious metal artifacts including gold, platinum group, etc. generated are treated separately. Since the conventional process is performed, the description is omitted. Although not directly related to the present invention, the step of extracting and reducing gold from the solution after leaching with chloride will be explained for reference. Gold extraction / reduction step After chlorination and leaching, the solution is sent to an acid concentration adjusting tank equipped with a cooling means. In the acid concentration adjusting tank, the temperature is cooled to 5 ° C. in order to prevent precipitation of impurities due to solubility in the gold extraction step. Also adjust the hydrochloric acid concentration to the gold extraction conditions. After the adjustment, the solution is sent to a gold extraction step after solid-liquid separation by a filter press. The precipitate mainly composed of lead chloride is returned to the smelting process. The gold extraction step is a step of extracting only gold from a chlorination leachate into a solvent. After the gold solvent extraction, in a gold product production step, gold is reduced and precipitated from the solvent from which the gold has been extracted to produce a product. As a solvent for gold extraction, a known solvent can be used, but DBC (dibutyl carbitol; (C ₄ H ₉ O
The use of C ₂ H ₄ ) ₂ O) is preferred. DBC is gold (HAu
Cl ₄ or AuCl ₃ )
Gold can be extracted from aqueous solutions. DBC has a very high selectivity for gold, and the distribution coefficient of gold is 1000
Degree and high. Gold extraction is performed in a continuous operation using a mixer settler because of the rapid reaction. Since an extremely small amount of an aqueous solution or a precipitate is present in the extracted DBC, which eventually causes the quality of the product gold to deteriorate or vary, the DBC is removed from the DBC by a centrifuge. The DBC after the centrifugation is scrubbed by a continuous operation by a mixer settler using a weak hydrochloric acid solution. By scrubbing, impurities such as Fe extracted in trace amounts into DBC are removed. The DBC after scrubbing is sent to a gold reduction tank after removing impurities by a centrifuge. The solution after scrubbing is used as washing water and dilution water in the chloride leaching step. Since about 3 g / l of DBC is dissolved in the aqueous phase after the gold extraction, the DBC is distilled off together with about 20% of water in a distillation tank. The gold-extracted liquid from which DBC has been removed is sent to a reduction step using sulfurous acid gas. The DBC separated by distillation is repeated to the gold extraction step. In the gold reduction tank, gold in DBC is directly reduced by mixing an oxalic acid aqueous solution and DBC. The reaction formula 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 time. After reduction, DBC is separated by sedimentation of the aqueous solution,
Return to the gold extraction process and recycle. The reduced gold and the aqueous solution are vacuum filtered, and the reduced gold is washed, dried, dissolved and cast to produce a gold ingot or a gold shot. Since the filtrate after filtration contains trace amounts of gold and unreacted oxalic acid, it is subjected to hydrazine reduction and oxalic acid removal treatment to be a waste liquid. The residual oxalic acid residue is repeated in the smelting process, and the after-liquid becomes waste liquid. Deoxalic 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 +2
EXAMPLE ₂ Copper electrolytic deposits having the analytical values shown in Table 1 were leached in a copper removing step using a sulfuric acid solution from the copper electrolytic step. Copper removal and leaching are carried out at 80 ° C. under normal pressure and air blowing, and the copper quality in the residue is about 0.5% in 18 to 20 hours.
Down to Copper removal leaching rate: Cu: 98.5%, T
e: 50%, Sb: 3%, Bi: 2%, As: 85%, and contained Au, Ag, Pt, Pd, Se,
No Pb was leached, and the leaching rate was 0%. The leached solution after decopperization is immersed in a tellurium-removing tank using a copper plate and copper powder, sulfuric acid concentration: 250 g / l, temperature: 80
C., reaction time: about 18 hours, to precipitate copper telluride. The copper-deposited residue was repulped with hydrochloric acid and sent to a chloride leaching tank. The chlorination leaching reaction was carried out by gradually adding hydrogen peroxide. Cooling was performed so that the reaction temperature was 60 to 70 ° C. After the leaching with chloride, the solid was separated into solid and liquid by a filter press. The solid mainly composed of silver chloride was repulped with water and then sent to a silver reduction step, and the solution was sent to an acid concentration adjusting tank equipped with a cooling means to be subjected to a gold extraction step. The chloride leaching rates were as follows: Au: 97.5%, Ag: 1%, Pt: 99
%, Pd: 98%, Se: 93%, Te: 70%, P
b: 5%, Sb: 30%, Bi: 69%. The chloride containing silver and lead, re-valved with water, was reduced with iron powder. The amount of iron powder used is equivalent (Ag / Fe = 2 /
1.5 to 2 times of (as 1). The liquid temperature was 90 ° C. or higher, and heat was generated when iron was dissolved by the remaining hydrochloric acid. The hydrochloric acid concentration was about 0.2 mol. A reaction time of about 4 hours is sufficient, but in practice, about 10 hours was required to suppress boiling due to heat of dissolution of iron. A reduction of more than 97% was obtained. The obtained reduced silver is efficiently oxidized and removed of impurities such as lead in a dry oxidation furnace, and the lead and unreacted iron of the reducing agent, which are attached to silver chloride, are separated as slag, and the attached noble metal is separated. Was concentrated in silver to obtain coarse silver, which was electrolytically purified. 99.
High-purity silver products exceeding 99%, that is, mold silver, were obtained. The intermediate composition (%) and the product silver composition (ppm) of each step are shown. [Table 2] The present invention has succeeded in establishing an efficient silver recovery process by combining the wet method and the dry method. Since the process does not cause a problem of coprecipitation of silver chloride and lead chloride, the operation of the silver chloride refining process is facilitated. When high-purity silver is to be obtained by wet refining, contamination of lead and the like with impurities must be avoided as much as possible. For this purpose, strict operation control such as temperature control in the silver chloride production process is required, and the equipment becomes complicated.However, since the silver recovery process of the present invention does not pose a problem of coprecipitation of lead, the operation method is greatly simplified. Could be transformed. Silver and lead are reduced at the same time by using iron powder as a dechlorinating agent. This is due to the fact that by introducing a dry oxidation step into the processing of silver chloride obtained in the silver refining step, a mixed raw material of lead and silver can be easily processed. We focused on iron as a reducing agent because, in addition to the direct desalination reaction with iron, we thought that hydrogen generated by the reaction between iron and the acidic solution also effectively contributed to the reaction. In the conventional process, the dechlorination process was performed in two stages of lead and silver, but the present invention can perform all the dechlorination in one stage,
The process was significantly simplified, and not only the equipment cost was reduced, but also the operating cost was significantly reduced. The dry oxidation furnace efficiently oxidizes and removes impurities such as lead, separates the lead accompanying silver chloride and the unreacted iron of the reducing agent as slag, and concentrates the accompanying noble metal into silver, and removes the coarse silver. And electrolytically refining. By this method, not only high-purity silver but also other noble metals can be concentrated and separated and recovered. Further, since the amount of platinum group which is an impurity in the electrolytic refining is extremely small, silver quality is stabilized. Since ammonia is not used for the production of silver as in the prior art, there is no problem such as the production of silver nitride and complex ions in the wastewater treatment process, and the effect on safety and environment is great.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a process flow sheet using the copper electrolytic deposit of the present invention as an example. FIG. 2 shows a process flow sheet of a conventional method.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI C22B 7/00 C22B 11/02 C25C 1/20 7/02 B09B 3/00 ZAB 304J 11/02 C22B 3/00 U 13/00 J 15/00 13/04 C25C 1/20 15/12 (58) Fields investigated (Int. Cl. ⁷ , DB name) C22B 1/00-61/00 B09B 3/00 C25C 1/20

Claims (1)

(57) [Claims 1] In recovering silver from a raw material containing at least a noble metal containing silver, gold and a platinum group, copper and lead, (1) sulfuric acid is converted from the raw material to sulfuric acid Leach with solution, silver, gold, platinum
To form a copper removal buttocks comprising a family and lead, (2) dehydration copper buttocks was exudate and silver and lead chloride containing leach to gold and platinum group chloride slurry formed by repulping with hydrochloric acid chloride (3) Gold is extracted from the chlorinated leachate collected in step (2) by DB.
Only gold is solvent-extracted and recovered using a C (dibutyl carbitol) solvent, and (4) the deposit containing silver and lead chlorides recovered in step (2) is washed and accompanied by the deposit. And (5) adding iron powder to a slurry formed by repulping silver and lead chloride-containing deposits washed in step (4) with water. The mixture containing silver and lead in a metallic state is recovered by reducing the product, and (6) the mixture containing silver and lead in step (5) is oxidized at high temperature in a dry furnace to remove slag containing coarse silver and lead oxide. Let it form
Next, (7) a method for recovering silver, comprising the step of separating the coarse silver from the slag and subjecting the separated coarse silver to silver electrolysis to produce high-purity silver.