Explain with an Example, How Precipitation Reactions Can Be Used

Explain with an example, how precipitation reactions can be used to recover precious metals for recycling.
Student examples may vary.
Precipitation reactions can be used to recover silver from solutions that are used to develop conventional photographic films. Silver bromide turns black when exposed to light and this reaction is used by the photographers to capture images in shades of grey. The washing of unexposed silver bromide using sodium thiosulfate solution generates a dilute silver waste solution. Instant photo operations can generate more than a hundred gallons of dilute silver waste solution per day. The silver from these solutions can be recovered by first removing the thiosulfate by oxidation and then precipitating Ag⁺ ions with excess chloride ions.