you can deploy copilot To adjust the pH of a leaching solution containing calcium ions (Ca²⁺) from 1 to 7 without causing the precipitation of calcium hydroxide (Ca(OH)₂), you can consider the following approaches:

### 1. Use a Buffer Solution

Buffer solutions can help maintain a stable pH without causing precipitation. A suitable buffer system for your pH range could be a combination of a weak acid and its conjugate base, such as acetic acid (CH₃COOH) and sodium acetate (CH₃COONa). This buffer system can help control the pH without introducing hydroxide ions (OH⁻) that would precipitate Ca(OH)₂.

### 2. Gradual pH Adjustment

Instead of adding NaOH directly, you can gradually adjust the pH using a weaker base, such as sodium bicarbonate (NaHCO₃). Sodium bicarbonate will react with the acidic solution to form carbonic acid (H₂CO₃), which then decomposes into water (H₂O) and carbon dioxide (CO₂). This process helps to avoid the rapid increase in pH that causes Ca(OH)₂ precipitation.

### 3. Chelating Agents

Chelating agents, such as ethylenediaminetetraacetic acid (EDTA), can bind to calcium ions and prevent them from forming insoluble compounds. By adding a chelating agent to your solution, you can keep the calcium ions in solution while adjusting the pH.

### 4. Controlled Addition of Acid and Base

You can use a combination of a weak acid (e.g., acetic acid) and a weak base (e.g., ammonium hydroxide) to gradually adjust the pH. This method allows for more controlled pH adjustment without causing rapid changes that lead to precipitation.

### References

For more detailed information on preventing calcium hydroxide precipitation, you can refer to the following sources:

- [Calcination-free production of calcium hydroxide](https://pubs.rsc.org/en/content/articlehtml/2021/ra/d0ra08449b)

- [A pilot-process for calcium hydroxide production](http://www.seas.ucla.edu/~pilon/Publications/JEnvChemE2022-PilotProcessCa%28OH%292.pdf)

Good luck

Just to add to the excellent answer by E.A. Gawad. From my own experience in pH adjustments of the Fe(III)(aq) solutions where I needed to increase the pH of the solutions (and this may cause precipitation of hydroxide), the use of magnetic stirrer may help to prevent high and rapid local increase of pH. The addition was performed by gradually adding very small amounts of base to the center of vortex formed in the stirred solution.