Electrowinning is a much more complicated process in some ways than plating
in general.  When you plate copper, the bath is predefined and you just
maintain those parameters as defined by the bath vendor.  No one builds
there own plating bath anymore, at least not anyone I've heard of in the
last 20 years.  

With electrowinning, you are building your own plating bath and it has a
different composition each time.  You're shooting at a moving target so the
results are not as uniform nor even obtainable at times.

The trick with electrowinning is to keep it simple.  The fewer things in the
bath, the easier it is to get results.  

You CAN build an efficient electrowinning system yourself.  You need to
decide on the type of cell.  Parallel plate cells recover high volumes of
quality copper from high copper concentration baths.  High surface area
cells, using copper mesh or wool can recover copper from dragouts or very
low concentration dumps but the copper will not be recovered efficiently
(i.e., you will spend a lot on equipment and electricity to recover a small
amount of copper).

I feel the  most efficient way to recover copper (each metal is a little
different but copper is pretty straight forward) is as follows:

Dumps under 500 ppm copper and rinses up to 300 ppm.  Recover on chelated
ion exchange resin and ewin regenerant.
 
If the solution is over 500 ppm copper up to about 3000 ppm copper, use a
copper wool cathode and precious metal anode.  Assume the cathode will plug
long before it is fully loaded so change it regularly.  These copper levels
will load up the IX resin pretty quick if you have much volume so doing a
first cut with e-winning is appropriate.

If the solution is over 3000 ppm, do a hull cell test and see what works
best.  Copper wool and any other expanded mesh high surface area cathode
material (like steel wool) is very efficient but tends to plate on the
surface then plug so there is some maintenance involved.  

Rules of electrowinning:

1.  Efficiency is always low.  Unless you are plating out a copper bath
bailout/dump, your efficiency will be low.  Plating baths plate well,
everything else doesn't.

2.  Keep is simple.  Adding a 500 ppm Cu cleaner dump to a microetch bailout
will give you the big goose egg for recovery.

3.  Do small scale experiments at first.  A hull cell will give you a good
idea of possible results.

4.  There is no magic.  Cheap solutions give you minimal results. (Sometimes
expensive solutions give you minimal results also!)

5.  The rules of electroplating are followed in electrowinning.  High
current density and low concentrations will not give your bright shiny
copper, you get copper mud (pure but yucka anyway).  Low current densities
work best.


In general each person who has bought or build an electrowinning system has
a different chemistry he is dumping into it at different concentrations.
Each individuals expectations are different so the results and general
satisfaction tend to be widely varied.  Some love it, some hate it, most use
them until the maintenance gets high and they decide to not dump any more
money in the systems and it sits in the corner for years.  

To stay happy with electrowinning.  Start with sure things like copper bath
bailout.  You can reconstitute you copper sludge by mixing it with you
microetch to kill the peroxide then use that.  As Copper concentrations drop
under 4000-5000 ppm, the results drop also.  

References:

1.  Direct electrorefining of copper scrap using a titanium anode-support
system in a monopolar cell.  Figueroa, M, et.al.  J. Appl. Electchem. 24
(1994) 206-211.

2.  Electrowinning of Copper, in EXTRACTIVE METALLURGY OF COPPER, A.K.
Biswas and  W. G. Davenport.  Pergamon Press, 1980. 324-335.

3.  Metal recovery from dilute Aqueous Solutions by various electrochemical
reactors.  Roland Kammel.  In HYDROMETALLURGICAL PROCESS FUNDAMENTALS.
Renato G. Bautista, ed.  Plenum Press. 1984 617-646 (review)

4. Improvements in Rinsewater Treatment by Electrolysis, P.M. Robertson,
et.al. Plating and Surfacing Finishing, v?(oct.) 1983. 48-52.

Regards,

Bob Mesick
Remco Engineering
Industrial Water and Wastewater Treatment Systems
San Luis Obispo, California  USA

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