Electroplating and metal finishing

Common types of dangerous waste from electroplating and metal finishing

Common wastes within these industries include:

• Aerosol cans
• Metal cleaning and plating wastes (such as sludges, acid/alkaline solutions, or metal-bearing and cyanide bearing solutions)
• Solvents (waste methylene chloride paint thinner or paint sludge, toluene or MEK, sludge or “bottoms” from solvent stills that recycle gun cleaner or thinner)
• Absorbent materials, such as kitty litter contaminated with dangerous waste
• Used shop towels
• Fluorescent bulbs and PCB-containing light ballasts
• Paint booth filters and masking tape
• Used oil (metalworking oils, coolants, and debris)

Pollution prevention

There are many ways to reduce pollution. Reduction and using alternative products can lower upfront costs and long-term fees. Try these ideas in your shop:

Rinse-water reduction

• Flow rinse water counter-current to part processing. Plus, using two or three rinse tanks in a series gives the most economical results.
• Add rinse water 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 (such as plating). Chemicals can be recovered without compromising part quality.
• Never use rinse water from a cleaning process, such as an acid or alkaline etch, 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. This improves rinse efficiency and encourages evaporation.
• Use heat baths to promote evaporation.

Drag-out reduction

• Use a "drag-out recovery tank." This is a tank that acts as a pre-rinse to the counter current rinses. It concentrates rinsed-off process chemicals so they can be added back to the tank.
• Drip parts over tanks. 30 seconds is optimum.
• Place drain boards between tanks. This keeps drips running into the right bath.
• Rack parts. This lowers the amount of solution "carried out" of the bath.
• Withdraw parts slowly. This keeps 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 to keep excess in the process bath.

Wastewater treatment

• Reuse spent nitric baths for pH adjustment in wastewater treatment process.
• Reuse spent alkaline cleaning solutions for neutralization in wastewater treatment process.
• Separate 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. Use pure water 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 alternatives

• 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.