| 摘要 |
PURPOSE:To remarkably reduce the Pd and Cu contents in electrodeposited silver when electrolysis is carried out with a consumable anode made of crude silver and an AgNO3 soln. contg. HNO3 soln. as an electrolytic soln. to electrodeposit pure silver on a cathode, by regulating the concn. of free HNO3 in the electrolytic soln. to a specified value or below. CONSTITUTION:A cathode 7 made of a stainless steel plate and a consumable anode 5 made of a crude silver plate are suspended in an electrolytic cell 1 and electrolysis is carried out with an AgNO3 soln. contg. HNO3 as an electrolytic soln. The anode 5 is held in an anode bag 3 made of 'Tetlon(R)' so as to accumulate anode slime 9 on the bottom 3' of the bag 3 and to prevent the dropping of the slime 9 on the bottom of the cell 1. Ag electrodeposited on the cathode plate 7 is scraped down with a scraper and recovered. During the electrolysis, part of the electrolytic soln. is sent to a nitric acid treatment tank 14, where Ag2O is reacted with free HNO3 to keep the concn. of free HNO3 in the electrolytic soln. at <=2.5g/l. At the concn. Pd and Cu in the slime 9 do not dissolve in the electrolytic soln., so Pd and Cu do not electrodeposit on the cathode plate 7 and the increase of the amts. of Pd and Cu as impurities in electrodeposited Ag is prevented.
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