Summary for muriatic acid pickle bath Discussion
Filtering a muriatic acid pickle bath is unlikely to extend bath life if the iron is dissolved, not particulate. In the thread, Dawn Baeckeroot asks whether filtering a straight 22° Bé HCl pickle used to descale DOM steel tubes before plating could remove iron and delay dumping; she notes the bath is titrated with permanganate to track iron. Mark Baker replies that Dawn’s understanding is correct: filtering will not buy much unless there are visible particulates, which can be checked by holding a beaker sample to the light. He also cautions that filter pumps do not last long in HCl dips and that other contaminants, such as cleaning solutions or surfactants dragged in over time, are another reason to keep a regular dump-and-recharge schedule.
Q. There is a debate going on with my co-workers whether filtering an acid pickle bath will extend the life. This bath is used to remove scale from DOM steel tubes prior to plating. We know that we can (and do) titrate the solution to identify the amount of iron. We are trying to establish the correct iron concentration cut-off point for when to dump and recharge.
A question has been raised as to whether or not filtering the acid solution would be a way to extend the bath (by potentially filtering the iron). As I understand it, this iron concentration is dissolved iron, not free, solid iron particulate. Filtering should not alter the iron concentration (in the way they think it will).
I’m fairly new to this operation and haven’t dealt with true chemistry issues like this in a few years. I’m just looking to make sure my understanding of the process is correct.
We are titrating with a permanganate solution. The bath is straight Muriatic 22 ° Bé and the bath is not heated.
What are your thoughts?
Thanks!
Dawn
Dawn Baeckeroot
Engineer – Bellaire, Michigan USA
October 13, 2014
A. Hello Dawn,
I think you are correct in your summation that filtering the bath will not buy you much. I could see the advantage if you had particulates, which you could determine by taking a beaker sample of the bath and holding the sample up to the light. Filter pumps don’t last very long in HCl dips either. After changing filter tubes from city rinse water supply lines over the years, I’ve noticed a buildup of iron on the filter tubes, but this is usually after a month or more of a new installation of the filter. As we know, city water cannot dissolve iron. HCl dips do. There are also other considerations of dumping the bath on a regular basis. There is always a chance that cleaning solutions/ surfactants could be dragged into the bath over time. To ensure a quality product I would keep the dump schedule you have in place. As the old saying goes, if it ain’t broke, don’t fix it…
Mark Baker
Process Engineer – Phoenix, Arizona USA