Neerslag en coprecipitatie

Precipitation and coprecipitation techniques can be applied to separate a mixture of ions.

When different ions form sparingly soluble salts with the same reagent, they can be separated by precipitation if their solubility products differ significantly.

In an acidic solution of hydrogen sulfide, the product of copper and sulfide ion concentrations exceeds the solubility product. So, copper sulfide is precipitated while the ferrous ions remain in solution.

However, when the solution acidity is decreased to promote the sulfide ion concentration, iron sulfide is precipitated.

Coprecipitation is a phenomenon where the precipitate is contaminated by species soluble in the mother liquor.

For instance, water contaminated by arsenic is purified by a process based on coprecipitation called gathering.

Here, iron particles are added to arsenic-contaminated water, and oxidized to obtain a precipitate of ferric hydroxide.

Arsenic coprecipitates with ferric hydroxide and can be filtered to produce non-toxic drinking water.