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Lead, a gray heavy soft metal. Used in electronic solders and sometimes in jewellery. It is a very versatile metal and has too many technical usages to mention all here. As lead is toxic it has been phased out in areas where good alternatives exists. The RoHS directive (2003) in EU forced most electronics to use lead free solders. Similar directives have been enforced in the rest of the world too. Lead is still used in lead batteries and bullets.
Lead as a contaminant
If small amounts of lead is included in refined gold it becomes brittle and looses it's malleability. To avoid that a small amount of sulfuric acid is added to the gold chloride solution before filtering and precipitation.
Chemical reactions of lead
Lead is not attacked by sulfuric or hydrochloric acids. It dissolves in nitric acid with the evolution of nitric oxide gas to form dissolved Pb(NO3)2. The nitrate is a well-soluble solid in water. Mixed with halides, sulfate, chromate or carbonate ions the nitrate will form precipitates. Although the lead chloride forms a precipitate in water, high temperature water can dissolve a lot more lead chloride than cold water.
When lead chloride crystallizes it usually forms long thin needle-like white crystals.
Lead chloride can also be dissolved in strong hydrocloric acid via water soluble complexes.
Lead can also be dissolved in sodium hydroxide mixed with strong hydrogen peroxide. Probably by oxidize metallic lead and the oxide reacts to form sodium plumbate which is soluble in strong sodium hydroxide.
Uses for lead in refining
As lead is resistant to sulfuric acid, it is used as cathode in the Sulfuric acid cell.
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Lead in the waste stream
The EPA Limits for lead both in water and solid waste is 5ppm (mg/l)