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Closed-loop water recycling cause of salt spray failure

 

We have 12 process tanks each with their own dragout tank and 5 final rinses. All of our waste water is treated through the following 4 steps:
1 - heavy metals removed
2 - pH adjusted
3 - processed through carbon filtration unit
4 - processed through deionizing unit

Then stored in a tank and used as need to replenish and remake our baths/rinses.

My question is this: Is there a chance that a system such as this could eventually build up contaminants that would not be removed by any of the steps mentioned and the contaminants cause salt spray failures for our colored Alodine?

Does anyone else out there operate a closed loop system similar to ours and has experienced no problems? How long has it been in operation?

Thank you for your time in posting a reply to this query, it is greatly appreciated!

Benjamin J. Curto
- Ponderay, Idaho, USA

To directly answer your question, it is highly possible that there could be contaminants still in the deionized water that could cause salt spray failure on the Alodine parts. Identifying them, however, is another story.

What are you using to gauge when your system requires regeneration? What chemicals are you using to regenerate and in what concentrations? What are your flows and the specific mechanical and hydraulic criteria of the system?

There are certain ions that will bleed from an IX system during it's operation service cycle that contribute to small fractions of the effluent TDS or conductivity that could cause adherence or surface anomalies on your parts prior to the Alodine step, which, even though the parts might look fine, they will not pass a salt spray.

Careful consideration of the design of the system to address all the ions must be done. I am concerned that you are treating the water prior to the DI system, as this adds a significant amount of salt to the solution that is unnecessary, and only shortens the time between regeneration cycles. Further, your adjusting the pH also adds ions to the system that normally do not need to be added. We have installed and refurbished dozens of water recycling systems in the last few years on applications such as yours, and in particular, by carefully looking at each of your rinses, most of the applications were amenable to direct recycling with no treatment, and then batch treatment to remove the metals from the salty regenerant solution.

Your incoming water make-up for regeneration losses may be an area to look at, especially in your geographical location.

Tom Baker
wastewater treatment specialist - Warminster, Pennsylvania

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Yes there is a chance. I purchased a DI system that failed within four months of operation. Iron and zinc were my build-up problems. I recommend at least monthly detail water analysis of your DI water.

Good Luck!

Karl Weyermann
- Lebanon, Kentucky