Electroplating operations use a lot of water in their processes, and the purer it is, the better. It's used for mixing chemicals and then rinsing the products between plating process steps. It's critical for the rinse water to be clean to prevent cross contamination between processes and for producing clean substrate. A clean active substrate is necessary to prevent delamination of the plated layers.
This point is especially critical for plating operations that use platinum group metals. Their final finishes are expensive, so rejects are very costly to the manufacturer. Additionally, platinum plating operations lose platinum group metals as waste runoff in the rinse and drag out rinse waters in the plating process. Reusing electroplating process wastewater allows the manufacturer to control the quality of each process step. This prevents rejects, saving the manufacturer money. Additionally, a metals recovery system can be easily integrated with a water reuse system so that when the platinum group metals are filtered out of the wastewater, they are actually available for return to the process tank. A separate metals recovery system should be used for each rinse step. For example, the drag out water (the stagnant rinse right after the plating bath) should have its own recovery system. That system should constantly scavenge metals from the stagnant water. The most commonly used methods for platinum recovery systems are:
- Activated carbon (the platinum group metals are absorbed by the carbon).
- Selective ion-exchange resin (the platinum group metals are bonded to the resin). This is effective for both rinse and drag out water.
- A combination of carbon and metal selective resin.
- Electrowinning (the metals are absorbed into a porous metal cathode). This is best for drag out water.
Integrating metals recovery with water reuse
Water reuse systems have two main treatment protocols:
- Purification. For example, lowering the conductivity using ion-exchange resins.
- Filtration. For example, reverse osmosis.
To integrate metals recovery into a reuse system, all the wastewater that may contain precious metals must flow through the metals recovery system before flowing through the water purification step in the reuse system. In other words, the whole treatment process looks like this:
Directing rinse lines to the water reuse system
Because the drag out water requires periodic dumping through the water reuse system, after it flows through the metals recovery system, it is collected in a tank just before the reuse purification step. All the other rinse waters on the plating process line are counter flow, and the last one is the cleanest. The most concentrated rinse water will first flow to a collection tank before circulating through the metals recovery system. The drag out and post-plating ones (less concentrated) will flow through the precious metal recovery module first and then to the collection tank. All flowing rinse waters can be set up to circulate constantly or based upon its conductivity. The reuse collection tank should contain a level sensor that will trigger a pump to add city water to the tank when the level drops. This setup helps to maintain fresh water levels in the systems that is lost due to the evaporation and spillage.
Benefits of platinum recovery and water reuse
- Better rinsing (higher purity)
- Fewer rejects
- Decreased amount of water purchased
- Decreased amount of water discharged
- Decrease in F006 waste
- Increased precious metal recovery
ProChem strives to help their customers establish the highest level of credibility and a positive reputation within the regulatory community. Their goal is to significantly reduce the amount of fresh water that manufacturers require by providing sustainable solutions that will also benefit the customer’s bottom line.