【発明の詳細な説明】[Detailed description of the invention]
本発明は銀電解精製液に関し、一層詳細には、
粗銀インゴツトから銀を純度よく、かつ効率よく
精製することのできる銀電解精製液に関する。
電子部品等には銀が多量に使用されている。こ
れら銀は主としてめつきに使用されているのであ
るが、不良部品等の廃品から銀を有効に回収する
ことが、コストの面からも重要である。廃品から
の銀の回収には、一旦粗銀インゴツトとして回収
し、さらにこの粗銀インゴツトから電解によつて
銀を精製して回収するようにしている。
従来においては、上記の銀の電解精製液とし
て、硝酸10ｇ／、銀40ｇ／を含む、いわゆる
Moebius液が知られている。ところがこの
Moebius液を使用すると、陰極に電析した電析銀
が陽極側へ樹枝状に結晶成長する。このため陽極
とのシヨート防止策として、絶縁性の棒を陽極前
面で静かに往復動させ、陰極の結晶を掻き落とさ
ねばならず厄介である。
また上記精製液の場合には液の強い攪拌が行え
ず、銀イオンの陰極への移行速度が低下するた
め、銀の析出速度が遅く、しかも、粗大で形状の
整わない樹枝状の析出物しか得られない。
さらには陰極電圧も高くなる傾向にあり、結果
として不純物である銅の共析が多くなる（銀めつ
きの下地として一般に銅めつきが行われるため、
粗銀インゴツト中には不純物として銅を含んでい
る）。したがつて上記の精製液では、粗銀インゴ
ツト、ひいては液中の銅濃度を低く保たねば高純
度の銀を得ることが難しく、粗銀インゴツトには
上述のように銅を含んでしまい、現場の実情に沿
わないという難点がある。
本発明は上記難点に鑑みてなされ、その目的と
するところは、均一な高純度の電析銀を得ること
のできる、銀と遊離硝酸を含む液に、ロツシエル
塩を２ｇ／以上添加して成る銀電解精製液を提
供するにある。
本発明に係る銀電解精製液は、従来のMoebius
液、すなわち銀（40ｇ／）と遊離硝酸（10ｇ／
）を含む液にロツシエル塩（酒石酸カリウム・
ナトリウム）を２ｇ／以上添加して成る。
ロツシエル塩の添加量は、２ｇ／よりも少な
いと、従来と同様に、陰極電着面に銀が樹枝状結
晶として陽極方向へ成長してしまう傾向が残り好
ましくない。ロツシエル塩が２ｇ／以上になる
と上記の樹枝状結晶の成長がおさえられ、特に４
ｇ／以上になると陰極電着面に銀が均一に電析
して、密着性のよい、しかしながら層状に剥離性
のある（陰極板はSUS板を使用した）電析銀が
得られた。またロツシエル塩を２ｇ／以上添加
することによつて、攪拌が可能となり、電流密度
も、従来のMoebius液では２〜4A／ｄm2の範囲
でしか行えなかつたものが、本発明においては
6A／ｄm2の高電流密度で行え、高速性が達成し
得た。また得られた精製銀の純度も、Moebius液
においては99.95〜99.98％が限度であるが、本発
明においては99.999％以上の高純度のものが可能
である。
以下に実施例を示す。
実施例 １
銀40ｇ／、硝酸10ｇ／を含む液に、ロツシ
エル塩を、0.8ｇ／、1.6ｇ／、４ｇ／、８
ｇ／、12ｇ／を添加した液をそれぞれ調整
し、電流密度4A／ｄm2、浴温度60℃、攪拌の条
件の下に銀を電析させ、電析銀の状態を調べた。
結果を表１に示す。
The present invention relates to a silver electrolytic purification solution, and more specifically,
This invention relates to a silver electrolytic refining solution that can efficiently purify silver from a crude silver ingot with high purity. Silver is used in large quantities in electronic components. Although these silvers are mainly used for plating, it is important from a cost standpoint to effectively recover silver from waste products such as defective parts. In order to recover silver from waste products, it is first recovered as a crude silver ingot, and then silver is purified and recovered from this crude silver ingot by electrolysis. Conventionally, the so-called silver electrolytic purification solution containing 10 g of nitric acid and 40 g of silver has been conventionally used.
Moebius liquid is known. However, this
When Moebius solution is used, the silver deposited on the cathode grows into dendritic crystals toward the anode. Therefore, as a measure to prevent the cathode from colliding with the anode, it is necessary to gently move an insulating rod back and forth in front of the anode to scrape off the cathode crystals, which is troublesome. In addition, in the case of the above-mentioned purified liquid, the liquid cannot be stirred strongly and the transfer rate of silver ions to the cathode is reduced, so the silver precipitation rate is slow, and moreover, only coarse and irregularly shaped dendritic precipitates are formed. I can't get it. Furthermore, the cathode voltage also tends to increase, resulting in increased eutectoid deposition of copper as an impurity (copper plating is generally performed as a base for silver plating, so
Coarse silver ingots contain copper as an impurity). Therefore, it is difficult to obtain high-purity silver using the above-mentioned purification solution unless the copper concentration in the crude silver ingot and, by extension, in the solution is kept low. The problem is that it does not reflect the actual situation. The present invention has been made in view of the above-mentioned difficulties, and its purpose is to obtain uniform, high-purity deposited silver by adding 2 g/or more of Rothsiel's salt to a solution containing silver and free nitric acid. To provide silver electrolytic purification solution. The silver electrolytic refining solution according to the present invention is a conventional Moebius
liquid, i.e. silver (40g/) and free nitric acid (10g/
) in a solution containing Lotsiel's salt (potassium tartrate,
2 g/or more of sodium). If the amount of Rothsiel's salt added is less than 2 g/l, silver tends to grow as dendrites toward the anode on the cathode electrodeposition surface, which is undesirable, as in the conventional case. When the amount of Rothsiel salt is 2g/or more, the growth of the above-mentioned dendrites is suppressed, especially 4
When the electrodeposition amount exceeded 1.5 g/g, silver was uniformly deposited on the cathode electrodeposition surface, resulting in deposited silver with good adhesion but peelability in layers (a SUS plate was used as the cathode plate). Furthermore, by adding 2 g/or more of Rothsiel's salt, stirring becomes possible, and current density, which could only be achieved in the range of 2 to 4 A/dm 2 with conventional Moebius liquid, can be achieved with the present invention.
It was possible to perform the process at a high current density of 6 A/dm 2 and achieve high speed. Further, the purity of the obtained refined silver is limited to 99.95 to 99.98% in Moebius solution, but in the present invention, high purity of 99.999% or more is possible. Examples are shown below. Example 1 Add Rothsiel's salt at 0.8 g/, 1.6 g/, 4 g/, 8 to a solution containing 40 g/silver and 10 g/nitric acid.
Silver was electrodeposited under conditions of a current density of 4 A/dm 2 , a bath temperature of 60° C., and stirring, and the state of the deposited silver was examined. The results are shown in Table 1.
【表】
なお上記の各液で電流密度を変化させて電析銀
の状態を調べたところ、電流密度が6A／ｄm2ま
では、ロツシエル塩濃度が４〜12ｇ／のものは
良好な電析銀が得られたが、6A／ｄm2以上にな
るといずれのものも陰極のコーナー部で樹枝結晶
状となり、好ましい結果が得られなかつた。
実施例 ２
銀40ｇ／、硝酸10ｇ／、ロツシエル塩８
ｇ／を含む基本液に、硝酸銅を銅濃度として１
ｇ／、10ｇ／を添加した液をそれぞれ調整
し、浴温60℃、攪拌の条件の下に、電流密度を１
〜6A／ｄm2の範囲で変化させて、電析銀中の銅
の共析量を調べた。なお陽極の粗銀インゴツトは
銀96.93％のものを用い、陰極にはSUS板を使用
した。結果を第１図に示す。
いずれも銅の共析量は6ppm以下であり、良好
な結果を得た。
なお実施例１、２共、均一な、良好な電析銀が
得られた際の銀純度は99.999％であり、Moebius
液よりも高純度のものが得られた。
以上のように本発明に係る銀電解精製液によれ
ば、均一な、密着性のよい、しかしながら陰極板
から層状に剥離可能な電析銀を、不純物の共析な
く高純度で得ることができるという著効を奏す
る。しかも従来のごとく樹枝状結晶でないから、
掻き落とし作業も必要でなく、作業性よく行える
という効果も有する。
以上本発明につき好適な実施例を挙げて種々説
明したが、本発明はこの実施例に限定されるもの
ではなく、発明の精神を逸脱しない範囲内で多く
の改良を施し得るのはもちろんのことである。[Table] When we investigated the state of deposited silver by changing the current density with each of the above solutions, we found that when the current density was up to 6 A/dm2, the Rothsiel salt concentration was 4 to 12 g/dm, which resulted in good electrodeposition. Although silver was obtained, when the concentration exceeded 6 A/dm 2 , the corners of the cathode became dendrite-like, and favorable results could not be obtained. Example 2 Silver 40g/, nitric acid 10g/, Rothsiel salt 8
Copper nitrate was added to the base solution containing 1 g as a copper concentration of 1
10g/ and 10g/ were prepared respectively, and the current density was set to 1 at a bath temperature of 60°C and under stirring conditions.
The amount of copper eutectoid in deposited silver was investigated by changing the amount in the range of ~6 A/dm 2 . Note that a coarse silver ingot containing 96.93% silver was used for the anode, and a SUS plate was used for the cathode. The results are shown in Figure 1. In both cases, the amount of copper eutectoid was less than 6 ppm, and good results were obtained. In both Examples 1 and 2, when uniform and good deposited silver was obtained, the silver purity was 99.999%, and Moebius
A product with higher purity than the liquid was obtained. As described above, according to the silver electrolytic purification solution of the present invention, it is possible to obtain highly pure electrodeposited silver that is uniform, has good adhesion, and can be peeled off in layers from the cathode plate without eutectoidation of impurities. It has a remarkable effect. Moreover, it is not a dendrite like the conventional one,
There is also the effect that scraping work is not necessary and the work can be performed with good work efficiency. Although the present invention has been variously explained above with reference to preferred embodiments, the present invention is not limited to these embodiments, and it goes without saying that many improvements can be made without departing from the spirit of the invention. It is.
【図面の簡単な説明】[Brief explanation of drawings]
第１図は不純物として浴中に銅を混入させた場
合の、電流密度変化と銀膜中の銅共析量との関係
を示すグラフである。
FIG. 1 is a graph showing the relationship between the current density change and the amount of copper eutectoid in the silver film when copper is mixed into the bath as an impurity.