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Pollution Prevention
Ask the Expert Question-and-Answer Archive

by George Cushnie
January, 2008

Reducing Iron in Hard Chrome Solution

Q. I am a hard chrome plater who is always facing an iron impurity which causes my plating speed to slow down. One of the suppliers suggested an ion exchanger which he claimed can be put into the plating line and run the chrome solution while Im running my production.

Do you have any experience using an ion exchanger and how efficient is the system?

A. Your problem is very common.  Hard chrome plating baths work well until the contamination level of metal cations (mainly Cr+3 and iron) reaches about 10 g/l.  Above this point, you will notice a decline in the plating rate and quality problems may occur.  Also, you will be wasting energy since you need to use more power to plate your parts in a contaminated bath.

The best course of action is to avoid getting iron into your plating bath by using a dedicated reverse etch tank.  In this bath, use the same concentration of chromic acid as in your plating tank, but do not add sulfate.  Although this bath will become contaminated with iron, it will continue to perform the reverse function well beyond the concentration of iron that affects plating (i.e., 10 g/l).

Regarding your decision on whether or not to buy an ion exchange unit, Id suggest you investigate it fully.  Not all ion exchange systems are designed to treat contaminated chromium baths.  There are some units that are designed specifically for this purpose (see:
http://www.eco-tec.com/products/chromic_acid_recovery.php).  Ask your vendor to provide the names of companies that use his technology and call or visit these facilities to find out about their experience with it.

Although ion exchange can be an effective method of chromium bath treatment, you should be aware that an ion exchange system used for this purpose generates a large volume of chromium wastewater during the regeneration cycle.  Therefore you will need a chromium wastewater treatment system (chromium reduction and precipitation) or you will need to ship many barrels of waste to an off-site treatment/disposal system.

Good luck.

George Cushnie



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