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Cadmium Cyanide Plating Bath Maintenance & Analysis

Q. Dear sir,
We have yellowish problem in cadmium plating with olive drab passivation please give any suggestions.

Narasimha CH
- Bangalore, Karnataka
April 13, 2024

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⇩ Related postings, oldest first ⇩

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Q. We are currently running a cyanide bath cad plating line, and have been having trouble keeping our solution parameters in spec. We recently started precipitating out sodium carbonates (as they were creeping above 60 g/L) by cooling buckets of the solution to around 1 - 2° C. Once we began doing this, we found that it became very difficult to maintain our cadmium oxide levels (getting down around 19 or 20 g/L). Presently, we do not agitate or filter the solution (we stir it thoroughly prior to plating or taking bath samples), but will be purchasing a pump in the near future to perform both of these functions.

I was told by a reputable source that cadmium oxide shouldn't be added to the tank unless making up a new solution, and that the anodes should provide the supply of cadmium ions necessary to balance the tank. I have since seen several other specs (as well as postings here) that recommend adding cadmium oxide when the levels get low.

Is the fix as easy as adding the cadmium oxide? Is this what we need to do to maintain our solution parameters on a regular basis? So far, when the cad levels drop, we have been plating sheet stock until our levels come back, then beginning production again. We recently changed out our anodes, with the concern that the older ones had become passive.

Our solution specifications are:
Cadmium Oxide = 21 - 42 g/L
Sodium Cyanide = 87 - 150 g/L
Sodium Carbonate = 15 - 59 g/L
NaCN / Cd = 2.8 - 6.0

Our tank temperature sits around 75° F (24° C). Should we operate it at a higher temp? ASM seems to recommend 80 - 85° F. Should we also measure sodium hydroxide?

Any other pieces of advice for improved operation of this process would also be greatly appreciated.

Thanks in advance,

Nathan Sanz
Manufacturing Engineer - Sidney, BC, Canada
June 14, 2011

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Multiple threads merged: please forgive chronology errors :-)

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Q. Hello,

We have a cadmium cyanide plating bath and I was hoping someone could help clarify my understanding of the solution analysis for cadmium metal.

Our process:

We take an aliquot and add the following:
pH buffer 10 consisting of ammonium hydroxide, ammonium chloride, and water (~ 10 mL)
10% formaldehyde (~ 15 mL)
and Erichromte Black T
We then titrate with EDTA.

I have three questions:

1) What is the purpose of the pH buffer (or really the addition of the ammonium hydroxide)? Is it to help drive a reaction?
2) Can someone confirm that the formaldehyde is there to liberate the cadmium-cyanide complexes freeing the cadmium for the titration?
3) In the books I have been reading, some recommend adding a few drops of 25% HCl prior to adding the ammonium hydroxide, is this step necessary and if so, what is its purpose if the next step is to add a few mL of a alkaline liquid?

Thank you all in advance.

Kendyl Gibbons
- Denver, Colorado, USA
February 29, 2012

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Q. I'm having trouble with the sodium hydroxide level (too high) and sodium carbonate level (too high) in my cyanide cadmium plating tanks (barrel and tank). The specification for NaOH is 1.6 - 4.0 oz/gal for both (result is 5.1 for tank and 6.6 for barrel). The specification for Na2CO3 is <8.0 oz/gal result is 11.0 oz/gal for tank and 10.9 oz/gal for barrel) I've tried chemical removal using calcium hydrated lime which did nothing but increase NaOH. Freezing is not an option.Tank sizes are about 2500 gallons for tank and 175 gallons for drum.
Please help if you can.

Michael Blair
- Birmingham, Alabama, USA
June 13, 2013

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Q. I have an aerospace plating spec that lists as a makeup for our cyanide cadmium plating bath the following:

Chemical   Cadmium cyanide Cadmium metal Sodium cyanide Free Cyanide Total Cyanide Sodium carbonate Caustic Soda

Initial conc.     oz/gal 4.27 2.94 8.41 5.94 11.02 0 1.34

Oper. range     oz/gal not given 2.67 to 4.00 not given 4.00 to 10.28 8.70 to 16.69 0 to 8.68 1.07 to 2.00

As for the "Cyanide tests" our prod. mfr lab and most labs are only testing for: "total Sodium Cyanide" and "Free sodium Cyanide" and "Cyanide Metal"
Is just "Sodium Cyanide" the same as "Total Sodium Cyanide""?
and is "total Sodium Cyanide" the same as just "Total Cyanide"? Our cust. spec seems to differentiate as shown in the list above but I can't seem to get answers from labs whether I can test for all that's listed. Your help would be greatly appreciated.

Thanks

Sherrill Connell
- Monroe, North Carolina, USA
July 29, 2013

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Q. Hello, I am quite new to the electroplating industry and have been hired on as my company's chemist. Unfortunately there was no one in the position before I entered the scene and I am woefully uninformed on nearly all the analyses which need completed to ensure proper functioning of our process tanks. My current headache is my Cadmium metal content in our Cad / Cyanide plating tank. The only procedures which I have to follow or go on are several older metal finishing books and what I can glean from sites online such as this. That being said the current procedure I am attempting to follow is that spelled out in the metal finishing guidebook for Cad metal content analysis.

It goes as such:
Add 2 ml sample from Cad tank
Add 100 ml DI water
Add 10 ml pH 10 buffer
Add EBT powder
Add 15 ml 10% Formaldehyde
Titrate with 0.1M EDTA
Color change of Red to Blue

I am having significant problems. The first being recognizing the endpoint. From what I have researched online the color of EBT in an alkaline solution complexed with "metal" ions should be somewhat of a "wine red." After following the above outlined procedure and adding the EBT I am NOT getting any sort of red color, more of a purple that seems to be what I have seen as the color of the EBT as it nears an endpoint. In an effort to determine the endpoint more exactly I took a flask of tap water, added a small amount of of EBT / NaCl mixture (1/100) and a small amount of my pH 10 buffer and to my delight began to see the red color I was supposed to. I wanted it a bit darker and proceeded to add a bit more EBT mix and splashed in a significant amount of pH 10 buffer and to my dismay the solution turned a deep purple blue. This confounded me. The pH 10 buffer I have is 0.38% Sodium tetraborate, 0.05% NaOH, and 99.57% water.

I am now here asking for any help that anyone may be able to offer. I have no other resources available, no procedures to follow, no one to ask. We do not run our Cad with brighteners, and I have very little information on the bath other than its current pH. (13.2) If I can determine Cad metal, I can determine total CN- and then free.

Again any help would be more than appreciated, or any resources anyone could point me towards would be fantastic.

Thank you in advance.

Jordan Egnatoff
plating shop - Huntington, West Virginia USA
November 21, 2017

Q. Geoff, thanks for the response. I will attempt to answer your queries in the order which you dispensed them.

I do not have a fume hood, however the area is fairly well ventilated as is the shop. I am aware of the dangers of cyanide, the quickest routes of exposure, warning signs and slight first aid, though there are two large hospitals less than 2 miles from the shop.That being said, I appreciate the concern.

I have a copy of The Chemical Analysis of Electroplating Solutions ⇦[this on Amazon or eBay or AbeBooks affil links] by T.H. Irvine although it is somewhat dated and preaches a sulfide method for metal determination.

I will have to look into an Atomic Absorption Kit.

As far as contacting my chemical supplier I would say that is an excellent idea, however, our Cad tank is run without brighteners, off a metal finishing handbook "recipe" which I have inherited and as such has no technical data associated with it. I guess there is nothing to lose in asking, although I have run into some issues with companies being wary of cyanide baths.

I will look into your additional links and hopefully they may give me some additional direction.

If I may place another question, what is the use of the 10% formaldehyde in the titration and would a different buffer solution provide better results? As I mentioned, I have yet to achieve the "wine red" color associated with complexed EBT in an alkaline solution and am attempting to fully understand the mechanisms by which everything is taking place.

Again, thank you for your quick reply and sources, glad to hear I am not the only person that experiences issues with compleximetric titrations.

Regards

Jordan Egnatoff [returning]
plating shop - Huntington, West Virginia USA

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Q. I do not see an answer to the situation addressing how to reduce a high NaOH concentration exceeding the control limits. I have inherited a new LHE Cadmium solution make up that did not fully take into consideration of the increase from the cadmium Oxide. This is an Aerospace company with Boeing and Safron specification requirements. Besides decant, is there a treatment to reduce the NaOH concentration in an LHE cadmium solution.
Thank you.

Tim Aish
Landing Gear Overhaul - Longwon, China
March 22, 2018

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Q. Can I know what is the reference document for cadmium plating (titration method)?

Nor Elly
- JOHOR, MALAYSIA
December 14, 2018

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Q. Hi,
Currently I have troubles with the conductivity for my cadmium cyanide tanks, we established optimal parameters but it was in February. In February the weather is too cold here in Nogales, and we started to get troubles when we notice that the tank temperatures started to get high and we do not have currently chiller equipment.

I've tried to go High with different parameters like Sodium Cyanide, Sodium Hydroxide, brightener, Cad oxide and wetting agents, but we cannot get good results yet.

These are our parameters before the temperature getting up.
Cad metal (Oz/Gal)= 3.0
NaCN (Oz/Gal)= 15.0
NaOH (Oz/Gal)= 3.0
Ratio (NaCN/Cd)= 5.0
Temperature= 75 °F (70 °F-82 °F)

And our current temperature is 95 °F-115°F. I hope that you can advise us.

Rodrigo Ornelas
- Nogales, Mexico
June 7, 2021

Thank you Robert H Probert!!

Yes, actually I've cooled down the cad from 105 °F to 87-91 ° F and with cyanide additions (from 15 Oz/gal moved to 17-18 oz/gal) I got good results.

Rodrigo Ornelas [returning]
- Nogales, Sonora