Top Tips for Pollution Prevention in Electroplating and Metal Finishing

Washington State Department of Ecology

Top Tips for Pollution Prevention in Electroplating and Metal Finishing

Rinse-water reduction

Have rinse water flow counter-current to part processing and use several rinse tanks for each process tank, usually the most economical results are obtained by using two or three rinse tanks in series.
Add rinse water automatically only when needed. Use either rinse bath pH or conductivity to activate rinse water addition. Whenever possible, add rinse water directly onto the parts as they leave the rinse.
Use rinse water from the most concentrated rinse (the first rinse) to make up the process bath in processes (such as plating) where chemicals can be recovered without compromising part quality. Never use rinse water from a cleaning process, such as an acid or alkaline etch, to make up the process bath because the rinse water will contaminate the bath.
Place flow restrictors on rinse flows that are not automatically controlled by pH or conductivity.
Use oil-free air to agitate rinse baths to improve rinse efficiency and to encourage evaporation.
Use heat baths to promote evaporation.

Drag-out reduction

Use a "drag-out recovery tank." This tank functions as a pre-rinse to the counter current rinses and concentrates rinsed-off process chemicals so they can be added back to the tank.
Allow parts to drip over tanks for a period of time, usually around 30 seconds is optimum.
Place drain boards between tanks so that drips run back into the bath the part just left.
Rack the parts to minimize the amount of solution 'carried out' of the bath. To do this, rack the part to minimize horizontal surfaces, so depressions open downward and slant parts to provide a drip tip.
Withdraw the part slowly from the solution. This allows the surface tension of the solution to keep more of the solution in the tank.
Lower bath chemistry concentrations to the minimum effective concentration. Rinses will be contaminated less by an equal amount of drag in.
Use air knives, squeegees, or rollers on the part so excess will run into the process bath to remove excess solution from the part.

Waste Water Treatment

Reuse spent nitric baths for pH adjustment in waste water treatment process.
Reuse spent alkaline cleaning solutions for neutralization in waste water treatment process.
Segregate cyanide bearing solutions for treatment.
Use electrolytic cyanide destruction (oxidation to carbon and nitrogen) and metal recovery.
Evaporate rinse water and neutralized process baths (except for chrome and cyanide baths).

Bath Maintenance

Use ion exchange to treat incoming process water so pure water is used to make up baths and for rinsing.
Use porous pot extraction of iron from hard chrome tanks.
Freeze-crystallize copper sulfate baths to purify them.
Freeze-crystallize to remove ferrous sulfate and reclaim spent sulfuric acid.
Plate unwanted metals onto dummy electrode to purify tank (electrolysis).

Chromium and Cyanide Reduction / Elimination

Substitute boric sulfuric acid anodize for chromic acid anodize.
Substitute non-cyanide Nickel-Zinc in place of cyanide.
Use alkaline zinc instead of cyanide zinc.
Use alkaline copper instead of cyanide copper.
Substitute Alodine 600 for Alodine 1200S.

Related information

Toxic Metals Prevention Project is a joint effort between the Department of Ecology and Washington’s larger businesses that participate in Pollution Prevention Planning. Technical Assistance may be available.