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Q. We manufacture ceramic capacitors for the communications industry and then we plate them with sulfamate nickel and tin (methane sulfonic acid base). After the nickel plating, the parts pass through two nickel dragouts and three cascade DI water rinses and then they get in the tin plating bath for the tin plating. To minimize water expenses, we recycle our water and remove the metals with resin exchangers bottles (Anion and Cation), however, after a few days of use the water becomes cloudy and with high pH even at very low conductivity (50 micromhos/cm max.)

We are assuming that is due to algae or other kind of organic formation. We are planing to add to the system one UV unit to purify the water. I also would like to add some hydrogen peroxide to sanitize the system but I am afraid that this chemical might interfere with the resin of the DI water bottles.

Is that correct or is there any other suggestions?

Reynaldo Arrroyo
- Valencia, California


A. You may have biological problems, or you may have colloidal tin precipitates in your water. The ability of colloidal tin to pass through a DI system is not unusual; we have seen it many times. You may want to have the water tested for the number of Colony Forming Units (CFU) per 100 ml. If you have a biological problem that you can actually see, they will be too numerous to count! If you have < 100 per 100 ml, then you don't have a significant biological problem.

As far as sanitizing your system, a small amount of peroxide or bleach (<25 mg/l) will not significantly harm the IX resins provided that the contact time is short. If there is activated carbon before the DI resins, then this will decompose most of it before it gets to the resins. However, if you have a biological problem, then your activated carbon is now probably a breeding ground and needs to be replaced in conjunction with the system sanitization. The IX resins are not usually a significant breeding ground unless there is a long time period between regenerations.

Good Luck!

Lyle Kirman
consultant - Cleveland Heights, Ohio


A. If the pH is climbing in recycled di water after a few days, the problem is likely that there is not enough cation exchange capacity.

As contaminated water passes through a cation column it is acidified (H+ replaces other cations like sodium, copper, nickel, etc.). As the now acidified water passes through the anion column it is neutralized (OH- replaces other anions like chloride and sulfate, then reacts with the H+ to form neutral water).

If the cation column is exhausted it has no more H+ to release and will usually begin to let go of Na+. When the Na+ combines with the OH- from the anion column it makes NaOH, sodium hydroxide, a.k.a. caustic soda.

Increase the number or size of cation columns in the system. Then watch out for running out of anion capacity (usually more common)! Best monitoring is to do both conductivity and pH.

bill vins
Bill Vins
microwave & cable assemblies - Mesa (what a place-a), Arizona



A. Hydrogen peroxide will likely be destroyed by ultraviolet treatment, but keep in mind if you have enough dissolved solids in the water to color it, the transmission of the ultraviolet will be adversely affected, thus reducing the effectiveness of the ultraviolet units' sanitary or peroxide reducing qualities.

As mentioned before, be certain you have enough anion exchange contact. DI water has a pH which is neutral or very slightly acidic. Have you considered ozonating the water? Ozone will rapidly oxidize colloidal metals; after treatment with ozone, place a polishing filter (x<1 micron) inline before the ultraviolet unit to keep the water clear; if the u.v. unit is sized correctly for the flow of water, the u.v will effectively destroy the ozone. There are quite a few ozonation & u.v. equipment manufacturers out there who will be happy to help you size the apparatus you need.

It is unlikely algae & bacterial blooms are responsible for your troubles here, as there are not a lot of nutrients available in D.I. water. Add in the oxidizing ozone and the advanced oxidation process the u.v. unit would provide, and your system would be downright inhospitable for aquatic life.

Dale Woika
- Bellefonte, Pennsylvania, US

Ed. note: For more recent Q&A's on the subject of algae/fungus bio-fouling of rinse tanks please see thread 5358 and thread 34242.

For your amusement, this forum already existed as an electronic BBS before the Internet even existed; see www.finishing.com/heardhot/goldplat.html for a discussion of this topic back in 1991 :-)

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