Date sent:              Wed, 19 Aug 1998 19:09:34 -0500
Send reply to:          TechNet <[log in to unmask]>
From:                   Automatic digest processor <[log in to unmask]>
Subject:                Re:Subject: solder strippers
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> Date:    Wed, 19 Aug 1998 17:47:16 -0400
> From:    Adeodato Vigano
> Subject: solder strippers
>
> Ladies and Gentlemen,
> my company is evaluating conveyorized solder stripping equipment/chemistry
> and I'm facing a problem.  Our water treatment system is a selective IX
> system and the resin that we are using to extract lead requires a pH
> adjustment to approx 4 pH to be effective.  Now, the problem is that at
> about 3 pH the iron that is in most nitric based solder  stripping
> chemistries precipitates creating a huge mess. The chemistry that we are
> using now (in a vertical batch system) is iron free but I am told that a
> horizontal conveyorized system needs a ferric chemistry to be effective.
> Two questions: 1. is there a chemistry that is iron free AND will perform
> well in a horizontal setup? 2. is there a lead treating resin for ion
> exchange water treatment that works well at approximately 2.5 pH? Any help
> will be greatly appreciated Kiko Vigano
>
> ------------------------------------------------------------------------
> Adeodato Vigano Production Manager Compunetics, Inc. - PCB Division
(412)
> 858-6115 [log in to unmask]
> ------------------------------------------------------------------------



Welcome to the well known can of worms.  Under NO circumstances run iron
into a chelated resin that you are using for the whole shop.  Chelated resins
LOVE iron and like to form eternal relationships with iron.  Regeneration
chemistry changes dramatically and you may start generating lots of sludge.

You can put a small system (single column) just for lead and run it at pH 2.5.
The capacity will be reduced but it will remove the lead.  The best chelated resin
for lead has a phosphate group or in this case, a standard strong cation resin
(high preference for lead) would work.

The problem is, nitric acid is an oxidizer.  The equation is:

Nitric + resin = EXOTHERMIC REACTION

Only dilute rinse should be used on the resin.  My suggestion would be a strong
cation resin (US$50-70/cu. ft), run the rinse through it, regenerate it with HCl
for about 5 to 10 cycle then replace the resin.  Use a small column holding 1-2
cu. feet of resin.  You can check capacity loss with samples to determining
when to replace.  The strong cation resin will remove, tin, lead, and iron, and
copper efficiently, even at a pH of 1.  DO NOT TRY TO PURIFY YOUR NITRIC
SOLDER STRIPPER BATH WITH ORGANIC ION EXCHANGE RESINS.  This
is one instance where sludge is better than the alternative.


Best Regards,

Bob Mesick
Remco Engineering
Water and Wastewater Treatment Systems
http://www.remco.com
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