JP4787951B2 - Method for electrolytic purification of silver - Google Patents
Method for electrolytic purification of silver Download PDFInfo
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- JP4787951B2 JP4787951B2 JP2004100818A JP2004100818A JP4787951B2 JP 4787951 B2 JP4787951 B2 JP 4787951B2 JP 2004100818 A JP2004100818 A JP 2004100818A JP 2004100818 A JP2004100818 A JP 2004100818A JP 4787951 B2 JP4787951 B2 JP 4787951B2
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- 229910052709 silver Inorganic materials 0.000 title claims description 129
- 239000004332 silver Substances 0.000 title claims description 129
- 238000000746 purification Methods 0.000 title claims description 41
- 238000000034 method Methods 0.000 title claims description 22
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims description 125
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims description 58
- 229910052763 palladium Inorganic materials 0.000 claims description 29
- 239000003792 electrolyte Substances 0.000 claims description 24
- 238000005868 electrolysis reaction Methods 0.000 claims description 17
- SQGYOTSLMSWVJD-UHFFFAOYSA-N silver(1+) nitrate Chemical compound [Ag+].[O-]N(=O)=O SQGYOTSLMSWVJD-UHFFFAOYSA-N 0.000 claims description 6
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 5
- 229910017604 nitric acid Inorganic materials 0.000 claims description 5
- 229910001961 silver nitrate Inorganic materials 0.000 claims description 3
- 229910052751 metal Inorganic materials 0.000 description 39
- 239000008151 electrolyte solution Substances 0.000 description 30
- 238000010828 elution Methods 0.000 description 28
- 239000012535 impurity Substances 0.000 description 28
- 239000011133 lead Substances 0.000 description 27
- 239000007788 liquid Substances 0.000 description 21
- 239000002184 metal Substances 0.000 description 20
- 229910052802 copper Inorganic materials 0.000 description 17
- 239000010949 copper Substances 0.000 description 17
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 16
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 12
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 8
- 239000000243 solution Substances 0.000 description 7
- 238000003723 Smelting Methods 0.000 description 6
- 238000007670 refining Methods 0.000 description 6
- 238000006386 neutralization reaction Methods 0.000 description 5
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 4
- 229910052737 gold Inorganic materials 0.000 description 4
- 239000010931 gold Substances 0.000 description 4
- 229910052697 platinum Inorganic materials 0.000 description 4
- NDVLTYZPCACLMA-UHFFFAOYSA-N silver oxide Chemical compound [O-2].[Ag+].[Ag+] NDVLTYZPCACLMA-UHFFFAOYSA-N 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- NWUYHJFMYQTDRP-UHFFFAOYSA-N 1,2-bis(ethenyl)benzene;1-ethenyl-2-ethylbenzene;styrene Chemical compound C=CC1=CC=CC=C1.CCC1=CC=CC=C1C=C.C=CC1=CC=CC=C1C=C NWUYHJFMYQTDRP-UHFFFAOYSA-N 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 239000003795 chemical substances by application Substances 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000000151 deposition Methods 0.000 description 3
- 239000003456 ion exchange resin Substances 0.000 description 3
- 229920003303 ion-exchange polymer Polymers 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- 150000003378 silver Chemical class 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 2
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 229910001923 silver oxide Inorganic materials 0.000 description 2
- 229910001220 stainless steel Inorganic materials 0.000 description 2
- 239000010935 stainless steel Substances 0.000 description 2
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 150000001879 copper Chemical class 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000000706 filtrate Substances 0.000 description 1
- 238000002386 leaching Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000003472 neutralizing effect Effects 0.000 description 1
- -1 palladium and lead Chemical compound 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
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Description
本発明は、銀を主成分とし、銀以外の不純物金属元素を含有する金属から、銀を精製する電解精製方法に関する。 The present invention relates to an electrolytic purification method for purifying silver from a metal containing silver as a main component and containing an impurity metal element other than silver.
精製対象の銀を主成分とし、銀以外の不純物金属元素を含有する金属から、精製対象の銀を精製する電解精製においては、銀を主成分とし銀以外の不純物金属元素を含有する金属をアノードとし、一方、準備された他の金属電極をカソードとし、当該アノードとカソードとを電解液に浸積した後に通電し、当該精製対象の銀をカソード上に析出させることがおこなわれる。 In electrolytic refining, which purifies silver to be refined from metals containing silver as the main component and containing impurity metal elements other than silver, the anode contains metal containing impurity metal elements other than silver as the main component. On the other hand, another prepared metal electrode is used as a cathode, and the anode and the cathode are immersed in an electrolytic solution and then energized to deposit silver to be purified on the cathode.
より具体的に説明すると、銀の精製は、銀を主成分とし銀以外の不純物金属元素を含有する金属（粗銀）から成る銀アノードを用い、硝酸銀溶液を電解液として電解により実施され、カソードに高純度の銀を析出させる。ところが、上述の銀の精製においては、銀アノードに不純物金属元素（例えば、パラジウムや鉛、金、白金等）が含有されているため、電解液にパラジウムや鉛が銀と共に溶出し、パラジウムの析出や、パラジウムや鉛を含む電解液の物理的な巻き込みにより、これらがカソードに混入して、析出銀の品位を低下させてしまう恐れがある。 More specifically, the refining of silver is carried out by electrolysis using a silver anode made of a metal (crude silver) containing silver as a main component and containing an impurity metal element other than silver, and using a silver nitrate solution as an electrolytic solution. To deposit high purity silver. However, in the above-described silver purification, since impurity metal elements (for example, palladium, lead, gold, platinum, etc.) are contained in the silver anode, palladium and lead are eluted together with silver in the electrolytic solution, and palladium is deposited. In addition, due to physical entrainment of an electrolytic solution containing palladium or lead, these may be mixed into the cathode and the quality of the deposited silver may be reduced.
そこで、析出銀の品位を良好に確保するために、電解液中に溶出した銀以外のパラジウムや鉛等の不純物金属元素を除去する操作（以下、浄液と記載する）が実施される。この浄液は、電解液の一部を抜き出し、水酸化ナトリウムや酸化銀などの薬剤を使用して、中和処理により不純物金属元素を沈澱させて除去したり、特許文献１に記載のように、キレート性のイオン交換樹脂を使用して、不純物金属元素であるパラジウムを除去する操作である。
ところが、精製対象である銀の品位を所定以上に保つため浄液時に使用する中和処理用の薬剤の使用量が増加すると、浄液コストが上昇してしまう。特に、薬剤として酸化銀を用いた場合には、その製造のために設備が必要となる。また、薬剤として水酸化ナトリウム以外のアルカリ添加剤を用いた場合には、その価格が高価であることなどから、浄液コストが更に上昇してしまう。 However, if the amount of the neutralizing agent used at the time of liquid purification increases in order to keep the silver quality to be purified at a predetermined level or higher, the liquid purification cost increases. In particular, when silver oxide is used as a chemical, equipment is required for its production. In addition, when an alkali additive other than sodium hydroxide is used as a chemical, the cost of the liquid purification further increases due to its high price.
また、中和処理による浄液の際には、不純物金属元素と共に精製対象である銀の一部も沈澱除去されてしまうため、この沈殿から銀を再精製しなければならずコストの上昇を招く。
更に、イオン交換樹脂を用いて浄液をおこなう場合には、このイオン交換樹脂が電解液により損傷され易いことから交換頻度が高くなり、ランニングコストが上昇してしまう。
In addition, during the purification by neutralization, a part of the silver to be refined is precipitated and removed together with the impurity metal element, so that silver must be re-purified from this precipitate, resulting in an increase in cost. .
Furthermore, when performing a liquid purification using an ion exchange resin, since this ion exchange resin is easy to be damaged by electrolyte solution, replacement frequency becomes high and a running cost will rise.
本発明の目的は、上述の事情を考慮してなされたものであり、電解精製法により精製される精製対象である銀の品位を所定以上に保つと共に、電解液の浄液量を減少して浄液コストを低減できる銀の電解精製方法を提供することにある。 The object of the present invention has been made in consideration of the above-mentioned circumstances, and while maintaining the quality of silver to be purified to be purified by the electrolytic purification method at a predetermined level or more, the amount of the electrolytic solution is reduced. An object of the present invention is to provide a silver electrolytic purification method capable of reducing the cost of liquid purification.
上述の課題を解決するための第１の手段は、電解液中において、銀を主成分とするアノードを電解し、カソードに銀を析出させる電解精製方法であって、
上記アノードの電解により溶出する銀の量の制御によって、アノード近傍の電解液中の遊離の電解質濃度を低下させながら電解精製をおこなうことを特徴とする銀の電解精製方法である。
The first means for solving the above-mentioned problem is an electrolytic purification method in which an anode mainly composed of silver is electrolyzed in an electrolytic solution and silver is deposited on the cathode.
The silver electrolytic purification method is characterized in that the electrolytic purification is performed while the free electrolyte concentration in the electrolytic solution in the vicinity of the anode is reduced by controlling the amount of silver eluted by the electrolysis of the anode.
第２の手段は、電解液中において、銀を主成分とするアノードを電解し、カソードに銀を析出させる電解精製方法であって、
上記アノードの電流密度を５００Ａ／ｍ２以上に設定することを特徴とする銀の電解精製方法である。
The second means is an electrolytic purification method in which an anode mainly composed of silver is electrolyzed in an electrolytic solution and silver is deposited on the cathode.
A method for electrolytically purifying silver, wherein the current density of the anode is set to 500 A / m 2 or more.
第１の手段によれば、電解精製によるアノードの電解により、アノードから溶出する銀の量を制御しながら、当該アノードから溶出する銀と当該アノード近傍の電解液中に含まれる遊離の電解質との反応により、当該遊離の電解質濃度を低下させながら電解精製をおこなうことで、アノードに含まれる銀以外の不純物金属元素のイオン化が抑制され、これら不純物金属元素の電解液への溶出率を低減できる。この結果、電解液中の上記不純物金属元素がカソードへ析出、および付着巻き込みすることを抑制でき、カソードに析出させる銀の品位を向上させることができる。 According to the first means, the amount of silver eluted from the anode is controlled by electrolysis of the anode by electrolytic purification, while the silver eluted from the anode and the free electrolyte contained in the electrolyte near the anode. By performing electrolytic purification while reducing the concentration of the free electrolyte by the reaction, ionization of impurity metal elements other than silver contained in the anode is suppressed, and the elution rate of these impurity metal elements into the electrolytic solution can be reduced. As a result, it is possible to suppress the impurity metal element in the electrolytic solution from depositing on and adhering to the cathode, and to improve the quality of silver deposited on the cathode.
第２の手段によれば、アノードの電流密度が５００Ａ／ｍ２以上に設定されたことから、アノードの酸化状況が強くなって当該アノードから銀が溶出する溶出速度を上昇できるので、この溶出した銀によりアノード近傍の電解液中の遊離の電解質濃度が低下して、アノードに含まれる銀以外の不純物金属元素のイオン化が抑制され、これら不純物金属元素の電解液への溶出率を低減できる。この結果、電解液中の上記不純物金属元素がカソードへ析出、および付着巻き込みすることを抑制でき、カソードに析出させる銀の品位を向上させることができる。 According to the second means, since the current density of the anode was set to 500 A / m 2 or more, the oxidation state of the anode became stronger and the elution rate at which silver was eluted from the anode could be increased. Silver reduces the concentration of free electrolyte in the electrolyte near the anode, suppresses ionization of impurity metal elements other than silver contained in the anode, and reduces the elution rate of these impurity metal elements into the electrolyte. As a result, it is possible to suppress the impurity metal element in the electrolytic solution from depositing on and adhering to the cathode, and to improve the quality of silver deposited on the cathode.
更に、第１、第２の手段によれば、アノードに含まれる銀以外の不純物金属元素が電解液中へ溶出する溶出率を減少できるので、電解液から上記不純物金属元素を取り除く電解液の浄液量を減少できる。このため、浄液時における薬剤の使用量を減少でき、また、浄液時に沈澱して除去されてしまう銀の再精製量を減少できるので、浄液に伴うコストを低減できる。 Furthermore, according to the first and second means, the elution rate at which impurity metal elements other than silver contained in the anode elute into the electrolyte solution can be reduced, so that the electrolyte solution that removes the impurity metal elements from the electrolyte solution can be reduced. The amount of liquid can be reduced. For this reason, since the usage-amount of the chemical | medical agent at the time of liquid purification can be reduced, and the repurification amount of silver which precipitates and is removed at the time of liquid purification can be reduced, the cost accompanying liquid purification can be reduced.
以下、本発明を実施するための最良の形態を図面に基づき説明する。
図１は、本発明に係る銀の電解精製方法の一実施形態例を含む非鉄金属製錬工程を示すフローチャートである。図２は、図１の製錬工程のうち、銀の精製工程を示すフローチャートである。
The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is a flowchart showing a non-ferrous metal smelting process including an embodiment of the silver electrolytic purification method according to the present invention. FIG. 2 is a flowchart showing a silver refining step in the smelting step of FIG.
非鉄金属製錬工程では、一般に、鉱石等より、銅、銀、金、白金などを順次精製する。このうち、銅は、図１に示すように銅溶錬工程（ステップＳ１）での処理を経て粗銅とした後、この粗銅を鋳造して銅アノードとし、この銅アノードを用いて銅電解（ステップＳ２）を実施すると、カソードに銅が析出し電気銅として得られる。このとき、銅が精製されると同時に銅スライムが生ずる。 In a non-ferrous metal smelting process, copper, silver, gold, platinum, etc. are generally refined sequentially from ore or the like. Among these, as shown in FIG. 1, copper is made into crude copper through the treatment in the copper smelting step (step S <b> 1), and then the crude copper is cast into a copper anode, and copper electrolysis is performed using the copper anode (step 1). When S2) is carried out, copper is deposited on the cathode and obtained as electrolytic copper. At this time, copper slime is produced at the same time copper is refined.
この銅スライムには銀、金、白金、パラジウム、鉛等の有用な金属が含有されている。このため、まず、この銅スライムを硫酸浸出処理（ステップＳ３）して、銅スライム中の銅を溶解して取り除き、未浸出残留物を乾式処理（ステップＳ４）し、銀分が９７〜９９重量％の銀アノードとし、この銀アノードを用いて銀電解（ステップＳ５）を実施してカソードに銀を析出させる。析出した銀は、銀分が９９．９９重量％以上である。また、この析出と同時に銀スライムが生成する。 This copper slime contains useful metals such as silver, gold, platinum, palladium and lead. Therefore, first, the copper slime is leached with sulfuric acid (step S3), and the copper in the copper slime is dissolved and removed, and the unleached residue is dry-processed (step S4), and the silver content is 97 to 99 weight. % Silver anode, and using this silver anode, silver electrolysis (step S5) is performed to deposit silver on the cathode. The precipitated silver has a silver content of 99.99% by weight or more. Simultaneously with the precipitation, silver slime is produced.
尚、上述の銀の精製は、銅スライムを塩酸浸出し、銀を塩化物として分離し、この銀含有塩化物に上述と同様な乾式処理を実施して銀アノードを得、この銀アノードを用いて銀電解を実施して銀を析出させ、精製する場合であってもよい。 In addition, the above-mentioned silver purification is carried out by leaching copper slime with hydrochloric acid, separating silver as a chloride, and subjecting this silver-containing chloride to a dry treatment similar to the above to obtain a silver anode, and using this silver anode. In this case, silver electrolysis may be performed to precipitate and purify silver.
上述のステップＳ５で示す銀電解の工程を含む銀精製工程を、図２を参照して更に詳説する。
図２において、銀精製工程は、銀電解工程と浄液工程とを有する。
The silver refining process including the silver electrolysis process shown in step S5 will be described in more detail with reference to FIG.
In FIG. 2, the silver refining process includes a silver electrolysis process and a liquid purification process.
まず、銀電解工程について説明する。
銀電解工程では、銀分が９７〜９９重量％の銀アノードと、ステンレス製のカソードとが、電解槽の電解液中に装入される。これらの銀アノード、カソードに整流器を経て直流電流が通電される。これにより、銀アノードから電解液中へ銀が溶出してカソードに銀が析出し、銀アノード表面には銀スライムが生成する。カソードに析出した銀（電気銀）は、洗浄・乾燥処理（ステップＳ８）を受けた後、そのまま、または所定形状に鋳造されて各種製品となる。一方、銀スライムには、金、銀、白金、等の有用金属が含有されているので、適宜、次工程にて処理される。
First, the silver electrolysis process will be described.
In the silver electrolysis step, a silver anode having a silver content of 97 to 99% by weight and a stainless steel cathode are charged into the electrolytic solution in the electrolytic cell. A direct current is applied to these silver anode and cathode through a rectifier. As a result, silver is eluted from the silver anode into the electrolytic solution, silver is deposited on the cathode, and silver slime is generated on the surface of the silver anode. Silver (electrical silver) deposited on the cathode is subjected to a cleaning / drying process (step S8), and is then cast as it is or into a predetermined shape to form various products. On the other hand, since silver, slime contains useful metals such as gold, silver, platinum, etc., it is appropriately treated in the next step.
次に浄液工程について説明する。
浄液工程は、銀アノードから電解液へ溶出してくる銀以外の不純物金属元素（パラジウムや鉛等）の濃度を低減して、カソードに析出する析出銀の品位を良好に確保するために実施される。
Next, the liquid purification process will be described.
The liquid purification process is performed to reduce the concentration of impurity metal elements (palladium, lead, etc.) other than silver that are eluted from the silver anode to the electrolyte, and to ensure a good quality of the silver deposited on the cathode. Is done.
図２に示すように、浄液工程においては、電解槽からの排液を循環槽を介して、一部を中和槽へ送り、ここで水酸化ナトリウム等を添加して中和処理する（ステップＳ９）。この中和処理によりパラジウム、鉛等の不純物金属元素を沈澱させ、フィルタープレス等を用いて固体と液体を分離（固液分離）して沈澱物を除去し（ステップＳ１０）、ろ液を循環槽へ戻し、再び電解液として電解槽へ送り再使用する。このような浄液工程により、電解液中の銀以外の不純物金属元素（パラジウムや鉛等）の濃度を低減させる。 As shown in FIG. 2, in the liquid purification process, a part of the effluent from the electrolytic cell is sent to the neutralization tank through the circulation tank, and sodium hydroxide or the like is added here for neutralization treatment ( Step S9). By this neutralization treatment, impurity metal elements such as palladium and lead are precipitated, the solid and liquid are separated (solid-liquid separation) using a filter press or the like to remove the precipitate (step S10), and the filtrate is circulated in a circulation tank. To the electrolytic cell again as an electrolytic solution for reuse. By such a liquid purification process, the concentration of impurity metal elements (palladium, lead, etc.) other than silver in the electrolytic solution is reduced.
電解実施中の電解液は、上述した浄液工程により、電解液量や組成が適切な範囲に確保される。この電解液は、銀濃度が５５〜１１０ｇ／ｌ、遊離硝酸濃度が２〜１０ｇ／ｌの硝酸銀溶液であり、液温が１９〜２９℃に調整されている。このとき、銀アノードの電流密度は、従来２００〜３００Ａ／ｍ２に設定されていた。その理由は、銀アノードから銀以外の不純物金属元素、特にパラジウムや鉛を電解液中に溶出させにくくするためには、一般に、銀アノードの電流密度を減少させて、銀アノードの酸化状況を弱くする必要があると考えられていたためである。 The amount of the electrolyte and the composition of the electrolyte during the electrolysis are ensured within an appropriate range by the above-described cleaning process. This electrolytic solution is a silver nitrate solution having a silver concentration of 55 to 110 g / l and a free nitric acid concentration of 2 to 10 g / l, and the liquid temperature is adjusted to 19 to 29 ° C. At this time, the current density of the silver anode has been conventionally set to 200 to 300 A / m 2 . The reason is that in order to make it difficult to elute impurity metal elements other than silver, particularly palladium and lead, from the silver anode into the electrolyte, the current density of the silver anode is generally decreased to weaken the oxidation state of the silver anode. It was because it was thought that it was necessary to do.
ところが、本発明者等は、種々の実験の結果、銀アノードの電流密度を上昇させていくと、銀アノードの酸化状況が強くなって当該銀アノードからの銀の溶出速度が上昇し、この溶出した銀と、銀アノード近傍の電解液中の遊離の電解質である遊離硝酸との反応により、当該銀アノード近傍の遊離硝酸濃度が低下して、銀アノード中の銀以外の不純物金属元素、特にパラジウムや鉛のイオン化が抑制されることを見出した。即ち、電解精製によるアノードの電解により、アノードから溶出する銀の量を制御しながら、当該アノードから溶出する銀と当該アノード近傍の電解液中に含まれる遊離の電解質との反応により、当該遊離の電解質濃度を低下させながら電解精製をおこなうことで、アノードに含まれる銀以外の不純物金属元素のイオン化が抑制され、これらの不純物金属元素の電解液への溶出率を低減できる。
さらに、本発明者等は、電解精製法により精製される精製対象である銀の品位を所定以上に保つと共に、電解液の浄液量を減少して浄液コストを低減できるアノードの電流密度が、５００Ａ／ｍ２以上、好ましくは７００Ａ／ｍ２以上、さらに好ましくは１０００Ａ／ｍ２以上であることを見出した。当該知見を、図３（イ）（ロ）を参照しながら説明する。
However, as a result of various experiments, the present inventors have increased the current density of the silver anode. As a result, the oxidation state of the silver anode became stronger and the elution rate of silver from the silver anode increased. The concentration of the free nitric acid in the vicinity of the silver anode decreases due to the reaction between the oxidized silver and free nitric acid, which is a free electrolyte in the electrolyte near the silver anode, and impurity metal elements other than silver in the silver anode, particularly palladium. And found that ionization of lead is suppressed. That is, by controlling the amount of silver eluted from the anode by electrolysis of the anode by electrolytic purification, the free elution is caused by the reaction between the silver eluted from the anode and the free electrolyte contained in the electrolyte near the anode. By performing electrolytic purification while reducing the electrolyte concentration, ionization of impurity metal elements other than silver contained in the anode is suppressed, and the elution rate of these impurity metal elements into the electrolyte can be reduced.
Furthermore, the present inventors have maintained the silver quality to be purified by the electrolytic purification method at a predetermined level or more, and the anode current density capable of reducing the liquid purification cost by reducing the liquid purification amount of the electrolytic solution. 500 A / m 2 or more, preferably 700 A / m 2 or more, and more preferably 1000 A / m 2 or more. The knowledge will be described with reference to FIGS.
図３（イ）（ロ）は、横軸に銀アノードの電流密度をとり、縦軸に（イ）はパラジウム溶出率、（ロ）は鉛溶出率をとったグラフである。
ここで、パラジウム、鉛の溶出率は、次式で示すように、銀アノード中のパラジウム、鉛が電解液へ溶出（移行）したそれぞれの割合を示す。
パラジウムの溶出率（％）＝（電解液に溶出したパラジウム量／電解前の銀アノード中のパラジウム量）×１００
鉛の溶出率（％）＝（電解液に溶出した鉛量／電解前の銀アノード中の鉛量）×１００
これらのパラジウム溶出率を示す実曲線Ａ、鉛溶出率を示す実曲線Ｂは、後述の実施例における実験値をプロットした点を結んだ折れ線Ｃ、Ｄからそれぞれ求めたものである。
3A and 3B are graphs in which the horizontal axis represents the current density of the silver anode, the vertical axis represents (a) the palladium elution rate, and (b) the lead elution rate.
Here, the elution rates of palladium and lead indicate the respective proportions of palladium and lead in the silver anode eluted (transferred) to the electrolyte solution, as shown by the following formula.
Elution rate of palladium (%) = (amount of palladium eluted in the electrolyte / amount of palladium in the silver anode before electrolysis) × 100
Elution rate of lead (%) = (amount of lead eluted in electrolyte / lead amount in silver anode before electrolysis) × 100
The real curve A indicating the palladium elution rate and the real curve B indicating the lead elution rate are respectively obtained from the broken lines C and D connecting the points where the experimental values in the examples described later are plotted.
図３（イ）（ロ）より、電流密度が５００Ａ／ｍ２を越えると、パラジウム、鉛の溶出率が顕著に減少し、７００Ａ／ｍ２を越えるとパラジウムの溶出がほぼ止まり、１０００Ａ／ｍ２を越えると鉛の溶出も低い値に抑制されることが判明した。
即ち、アノードの電流密度を５００Ａ／ｍ２以上に設定する制御をおこなうことで、これらの不純物金属元素（パラジウムや鉛等）によるカソードへの析出および付着巻き込みを防止でき、析出銀の品位を確保することが可能となった。
3 (A) and 3 (B), when the current density exceeds 500 A / m 2 , the elution rate of palladium and lead decreases remarkably, and when it exceeds 700 A / m 2 , the elution of palladium almost stops, and 1000 A / m. When it exceeded 2 , it became clear that the elution of lead was also suppressed to a low value.
In other words, by controlling the anode current density to 500 A / m 2 or more, it is possible to prevent deposition and adhesion of these impurity metal elements (palladium, lead, etc.) to the cathode, and to ensure the quality of the deposited silver. It became possible to do.
また、銀アノードの電流密度を５００Ａ／ｍ２以上に設定することにより、カソードに銀を短時間で析出できるので、精製時間の短縮が可能となるという効果も得ることができた。 In addition, by setting the current density of the silver anode to 500 A / m 2 or more, silver can be deposited on the cathode in a short time, so that the effect of shortening the purification time can be obtained.
加えて、本実施の形態では、前述の如く銀アノードの電流密度が、銀アノード中の銀以外の不純物金属元素（パラジウムや鉛等）が電解液中へ溶出する溶出率を低減できるものとなっている。この結果、浄液工程において電解液から上記不純物金属元素を取り除くための電解液の浄液量を減少できる。このため、浄液時に使用する水酸化ナトリウム等の薬剤の使用量を減少でき、また、浄液時に沈澱して電解液から除去される銀の再精製量を減少できるので、浄液に伴うコストの低減が可能となった。
尚、銀アノード中のパラジウム、鉛は、電解液への溶出率が低下したことで、電解の進行に伴いスライムへ移行し、電解終了後、次工程にて回収される。
In addition, in the present embodiment, as described above, the current density of the silver anode can reduce the elution rate at which impurity metal elements (palladium, lead, etc.) other than silver in the silver anode are eluted into the electrolytic solution. ing. As a result, the amount of the electrolyte solution for removing the impurity metal element from the electrolyte solution in the solution purification step can be reduced. For this reason, the amount of chemicals such as sodium hydroxide used at the time of liquid purification can be reduced, and the amount of silver repurified that is precipitated at the time of liquid purification and removed from the electrolyte can be reduced. Can be reduced.
Note that palladium and lead in the silver anode move to slime as the electrolysis progresses due to a decrease in the elution rate into the electrolytic solution, and are recovered in the next step after completion of electrolysis.
銀分が９７重量％の銀アノード、ステンレス製カソード、及び銀濃度６０〜７０ｇ／ｌ、遊離硝酸濃度２〜６ｇ／ｌ、温度２６〜２９℃の電解液を用い、銀アノードの電流密度を３００Ａ／ｍ２、４００Ａ／ｍ２、５８０Ａ／ｍ２、６７０Ａ／ｍ２、２０００Ａ／ｍ２として電解精製を実施した。この結果、銀アノード中のパラジウム、鉛の電解液の溶出率の実測値例は、それぞれ図３（イ）の折れ線Ｃ、図３（ロ）の折れ線Ｄに示す結果となった。
Using a silver anode having a silver content of 97% by weight, a cathode made of stainless steel, and an electrolyte having a silver concentration of 60 to 70 g / l, a free nitric acid concentration of 2 to 6 g / l, and a temperature of 26 to 29 ° C., the current density of the silver anode is 300A. / m 2, 400A / m 2 , 580A /
上記電流密度が３００Ａ／ｍ２、４００Ａ／ｍ２、５８０Ａ／ｍ２、６７０Ａ／ｍ２、２０００Ａ／ｍ２のいずれの場合も、カソードに析出した銀は、製品とするに十分な品位であった。また、この品位を確保するために電解液を浄液するが、その浄液量は、電流密度が３００Ａ／ｍ２の場合を１００％とすると、４００Ａ／ｍ２の場合は７８％、５８０Ａ／ｍ２の場合は５６％、６７０Ａ／ｍ２の場合は２２％、２０００Ａ／ｍ２の場合は１１％であり、アノードの電流密度を５００Ａ／ｍ２以上に設定する制御をおこなうことで浄液量が大幅に低減できた。
尚、上記電流密度と銀の生産性との観点より、鉛の溶出量が１％以下となると予想される１２０００Ａ／ｍ２迄の制御が好ましい範囲と考えられる。
In either case the current density of 300A / m 2, 400A / m 2, 580A /
From the viewpoint of the current density and silver productivity, it is considered that the control up to 12000 A / m 2 where the lead elution amount is expected to be 1% or less is a preferable range.
Ａ パラジウムの溶出率の実曲線
Ｂ 鉛の溶出率の実曲線
Ｃ パラジウムの溶出率の実測値例
Ｄ 鉛の溶出率の実測値例
A Actual curve of palladium elution rate B Actual curve of elution rate of lead C Example of measured value of elution rate of palladium D Example of actual value of elution rate of lead
Claims (1)
上記アノードの電流密度を１０００Ａ／ｍ ２ 以上、１２０００Ａ／ｍ２以下に設定し、上記アノードの電解により溶出する銀の量の制御によって、アノード近傍の電解液中の遊離の電解質濃度を低下させることで、アノード中のパラジウムや鉛のイオン化を抑制しながら電解精製をおこなうことを特徴とする銀の電解精製方法。 An electrolytic purification method in which an anode mainly composed of silver is electrolyzed in a silver nitrate solution containing free nitric acid, and silver is deposited on the cathode,
The anode current density of 1000A / m 2 or more, is set lower than 12000 A / m 2, by controlling the amount of silver eluted by electrolysis of the anode, reducing the electrolyte concentration of free electrolyte in the anode vicinity A method for electrolytic purification of silver, wherein the electrolytic purification is performed while suppressing ionization of palladium and lead in the anode.
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