Chemical Precipitation Description

Like neutralization, chemical precipitation is a pH adjustment process. To achieve precipitation, an acid or base is added to a solution to adjust the pH to a point where the constituents to be removed reach their lowest solubility. Chemical precipitation facilitates the removal of dissolved metals from aqueous wastes. Metals may be precipitated from solutions by the following methods.

Alkaline agents, such as lime or caustic soda, are added to waste streams to raise the pH. The solubility of metals decreases as pH increases, and the metal ions precipitate out of the solution as hydroxide (Figure 11.15.9).

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