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Purple Color on Filter of Gold Cyanide Plating Bath

Q. Hello,

We operate a Gold Cyanide bath (Au 434 by Technic). The bath is kept at pH 6. Operating temperature is 150 °F. Tank size is 10 gal and we have a pump (Flow rate = 400 gal/hr) with a 10 micron polyspun filter, a PTFE heater, and platinized titanium anodes.

We have noticed that on occasion our filter will get some purple discoloration on it (see picture), and we are trying to pin point what exactly might be causing this.

We routinely replace the filter once a month, unless we note this discoloration. The discoloration will appear sporadically every ~4 months.

Tank conditions at the time are always in control. We have only noted that the Baumé is at the upper end of the allowed range (17 deg Baumé).

Has anyone experienced this before? Any suggestions?

Thank you,

Ari
- California
October 9, 2024

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