Precipitation

Description

• Add chemicals to a solution to make dissolved contaminants form insoluable precipitate
• Filter the resulting mixture to remove the precipitate
• Reuse the filtrate (clean liquid) as process bath liquid
• Two Methods
• Chemical: Reaction forms a less soluble compound (typically through a reduction or oxidation process)
• pH: The solubility of metals typically decreases as the solution become more neutral. Adjusting the pH causes many metals to precipitate out of solution.

Advantages

• Reduce the concentration of dissolved metals in the process water

Limitations

• Not typically performed in the process line

Implementation Process

Chemical

• Determine what contaminants are present in the process bath
• Identify less soluble compounds that can easily be formed, ensuring that the new compound is not a more hazardous waste
• Implement the procedure
• Train employees to operate and maintain the system, and monitor their performance

pH

• Determine what contaminants are present in the process bath
• Use a pH chart for each metal to determine its solubility
• Determine the ideal pH for treating the bath
• Implement the procedure
• Train employees to operate and maintain the system, and monitor their performance

Resources

• Cushnie, George C. Jr. Pollution Prevention and Control Technology for Plating Operations. National Center for Manufacturing Sciences, Ann Arbor, MI, 1994.