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topic 43765

Best Metal to be used as Anodes in Electrolytic Cells

A discussion started in 2007 but continuing through 2018

(2007)

Q. I am an electrowinning in-charge of a gold processing plant and want to know what is the best metal grade available in the market for fabrication of anodes in our electrowinning circuit. Presently, our company is using the 316 stainless steel grade and it easily corroded that the life is about 2-3 months only.
The solution feed to the electrowinning circuit is a hot (80-90 oC) caustic-cyanide solution (1 - 2% caustic soda, 0.5 - 1% cyanide)containing gold,silver,copper and other base metals. Also,probably the solution contained some chlorides as a result of reaction of caustic soda with residual hydrochloric acids that adhere to the carbon during the elution process. (For info, part of our process in metal recovery from carbon is acid washing prior to stripping).
Thanks and regards,

Jose Pepino
gold mining and processing - Davao City, Philippines


(2007)

A. Planitized Titanium anodes will last a lot longer but are very expensive.

James Watts
- Navarre, Florida



Monel or Alpaca (cupronickel) wire bolted to 304 stainless plate in sodium hydroxide

January 29, 2018

Q. I want low resistance wire to connect to a stainless steel plate in an electrolytic cell, filled with a sodium hydroxide solution at no more than 120 °F. I settled on monel or alpaca (cupronickel) wire, both nickel/copper alloys, that are resistant to sodium hydroxide. The wire will be bolted or riveted to the 304 or 316 stainless steel plate. Will galvanic corrosion occur? The research I did seems to say 'not much.'

Bill Buford
- San Diego, California, USA


simultaneous January 30, 2018

A. The safe bet is to use a strip of matching stainless and make connection outside the cell.

geoff smith
Geoff Smith
Hampshire, England


January 31, 2018

I got a response in another forum. It seems as if a nickel silver alloy with zinc would not work:

Submitted by Geir Moe on Wed, 01/31/2018 - 16:53
Hi Bill

There is very little corrosion data of copper alloys in caustic service because copper contamination is objectionable. Also, alloys of brass and bronze with high zinc contents can be susceptible to dezincification.

https://www.nace.org/Corrosion-Central/Corrosion-101/Dezincification/

Though additions of nickel appear to be beneficial to corrosion resistance.
I have attached everything I have regarding corrosion resistance of copper alloys in caustic soda (sodium hydroxide)
The ASM Corrosion Data shows an acceptable performance for a 75-20-5 zinc alloy, but realize this alloy only contains 5% zinc.

I hope this helps

UPLOAD DOCUMENTATION:
PDF icon ASM Handbook of Corrosion Data.pdf
PDF icon Material Selection for the Chemical Process Industry.pdf
PDF icon MTI Material Selector or Caustic Service.pdf


Bill Buford[returning]
Questor - San Diego, California USA



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