Lead chloride

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Lead chloride (PbCl2) is formed when alloys containing lead is dissolved in hydrochloric acid or aqua regia. It is a colorless chloride salt that is sparingly soluble in cold water and forms white needle formed crystals when crystallizing out of a solution. Heat and strong chloride concentration increases solubility a lot.

The compound lead(IV) chloride exists but breaks down at 50 °C and reacts with water so it isn't a concern for a refiner.

Contents

Chemistry

Pb + 2HCl -> PbCl2 + H2

PbCl2 + SO42- -> PbSO4 + 2Cl-

In refining

Lead chloride is formed when lead containing metal is dissolved in hydrochloric acid. For example from solders used in making or repairing carat gold or silver objects. Lead is also a common part in electronics although it is being phased out.

Gold refining

Lead contamination is especially bad for gold alloys, small amounts of lead gives alloys that easily breaks when worked. But a simple way exist to eliminate the lead before the gold is precipitated.

When lead chloride is mixed with sulfate ions a solid precipitate of insoluble lead sulfate is formed. This is easily filtered off from solutions containing values.

Any sulfate ion works but commonly a couple of drops of sulfuric acid is added to the aqua regia before the solution is filtered to remove silver chloride before precipitating the gold.

A side effect from denoxing with sulfamic acid is that sulfuric acid is formed and lead sulfate is precipitated automatically.

Silver refining

Lead chloride is encountered in silver refining when silver chlorides are formed, either when filtered from aqua regia solutions or when silver chloride is formed intentionally, for example when separating palladium from silver in recovery from MLCC:s.

The resulting silver chloride can be washed with hot water to remove lead chloride.

References

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