Precision Determination of Lead in High Grade Copper

Abstract

The technique of the determination of lead in copper by the dithizone and electrodeposition methods is discussed in detail. WHEN electrolytic copper is produced by the air oxidation of molten copper, it is important to determine its lead content (0 to 0.03%) because of the undesirable hardness attributed to the presence of small amounts of lead in highly refined copper metal. The most applicable chemical procedures are the lead dithizone photometric and lead dioxide electrodeposition methods. The techniques of these two methods are discussed in detail in this paper. ELECTRODEPOSITION METHODAcidity. When lead dioxide is to be deposited from a copper nitrate solution of 200-ml. volume, the nitric acid content should be (roughly) proportional to the amount of lead present: 0.15 gram of lead, 15% of nitric acid (by volume) 0.05 gram of lead, 5 to 7% of nitric acid 0.002 gram of lead, 1 to 2% of nitric acid plus ammonium ion These figures indicate the desired range of acidity, which must be kept in mind when preparing the electrolyte.Ammonium and Nitrate Ions. Ammonium nitrate is an essential reagent in the electrodeposition of small amounts of lead dioxide. The electrolyte should contain a minimum of 5 grams of ammonium ion per 100 ml.; electrolytes containing less than this amount give poorer plates than those of higher ammonium contents. Ammonium nitrate increases the conductivity of the electrolyte (decreases the resistance), which