Coprecipitation

Coprecipitation is a scalable technique for atomic-level mixing of reactants. In one example, soluble transition metal salts are dissolved in water, and then added to a concentrated solution of potassium hydroxide, causing the rapid precipitation of insoluble metal hydroxides, now uniformly mixed. Often, a chelating agent such as ammonium hydroxide is added to the potassium hydroxide solution to encourage uniform nucleation. Careful control of the pH will result in a significantly more uniform distribution of the reagents.

Equipment

Tank reactor for large scale coprecipitation

A highly primitive coprecipitiation can be performed simply using a burette, erlenmeyer flask, stir plate, and magnetic stir bar. A more advanced version of this technique relies upon a tank reactor, which enables careful control over both pH and the concentration of the chelating agent.

Simplified Synthesis

Synthesis of Ni_0.25Mn_0.75(OH)₂

1. Create 10ml of a 0.5M NiSO₄-6H₂O and 1.5M MnSO₄-H₂O solution in water. (Water content of these hydrates salts can be measured using TGA)
2. Add this solution dropwise to 100ml of a 2M KOH 0.05 NH₄OH solution in water.
3. Collect and wash the precipitate via vacuum filtration or centrifiguation until the pH of the filtrate is neutral and all residual K₂SO₄ is removed.