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Buffer for nickel electrowinning


(2007)

Q. Hi all, I do a experiment to test the effect of buffer on the nickel electrowinning (Nickel sulfate bath). The parameter are as below:

Electrode : lead anode & Stainless Steel cathode
Nickel concentration : 40 g/l of Ni
current : 3 Amp
Duration : 3 hours
pH : 3.5-5

I did two tests: one with 40 g/l of boric acid as buffer and the other one without buffer in order to observe their pH change and volume of ammonia aqueous used for pH adjustment. However, Ii discover that the use of the buffer did not give significant difference for maintaining the constant pH with the one without buffer. For instance, in both of the tests, their pH similarly dropped below pH 3.5 in every ten minutes that 2 ml of ammonia aq was added to rise back the pH around 4.5.

Then , is the use of buffer necessary for electrowinning? Or did I use the wrong buffer or quantity of buffer used for the electrowinning?

Hf Ang
Chemist - Malaysia


(2007)

A. You are using an insoluble anode. A lot of hydrogen is formed because of it, so the pH must drop. No buffer that I am aware of will compensate for that amount. You simply generated more acid than the buffer could accommodate.

James Watts
- Navarre, Florida


(2007)

A. I once consulted for a guy that literally had collected a million gallons of waste nickel plating solutions, mainly from the electronics industry. Most of the solutions were full strength modified watts nickel baths with a little contamination. The idea was to electrowin the nickel from the solution. The problem was that, when using inert anodes, the hydrogen ion produced from the water splitting rapidly reduces the pH. This lowers the cathode efficiency and, at some point, maybe a pH of 1 or 2, the nickel stops plating altogether.

I tried all sorts of buffer systems with no success. The problem was solved by producing nickel carbonate, from some of the solutions, and continually using it to raise the pH. This also replaced the nickel in the solution. If I remember right, we put the nickel carbonate in anode bags and hung them in the solution. The dissolution tended to stabilize itself, since it slowed down as the pH increased. We used saccharine as a grain refiner.

Chris Owen
- Nevada, Missouri


(2007)

Q. Thanks for sharing your experience. Mr Chris Owen, I know the nickel carbonate has the function to neutralize the acid of the electrolyte bath, so put nickel carbonate into the anode bad to slow down the pH drop is the good idea , however for the cost effectiveness, is it possible to use ammonia solution as the pH adjuster (raise pH) instead of using nickel carbonate?

Hf Ang [returning]
Chemist - Malaysia


(2007)

A. Just one thing about ammonia that may be important to you - it is a stress inducer and will result in tensile stress being imparted into your deposit.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


(2007)

Q. Thanks for your information, Mr. Trevor Crichton. Do you mean that ammonia is applicable but with the disadvantage that it produces tensile stress on the deposit product?
As I know, the tensile stress will cause wrinkles on the plating; however, will it affect the efficiency of nickel deposition? Because my purpose is to electroplate out the nickel for nickel recovery.

And besides resulting the tensile stress, does ammonia create other effect on the plating as well as the electrolyte bath? According to some journals and experiments that I did, the adding of ammonia do compound with nickel and easy to form crystals (even though the concentration of nickel is lower than 20 g/l of Ni). So does anyone have any ideas to the prevent the crystallization of the Nickel salt that resulted from ammonia used?

Hf Ang [returning]
Chemist - Malaysia


(2007)

A. Most modern nickel electrowinning systems use membranes to separate the anode compartment from the cathode compartment. That prevents the hydrogen ion, produced at the anode, from entering the cathode compartment, thus not lowering the pH. There are many references to this on the internet.

Chris Owen
- Nevada, Missouri


(2007)

Q. I just want to ask some questions.

1) Will your lead anode deposit small amount of lead onto the stainless Steel cathode together with your nickel?

2) What is the effect of lead if it does get deposited?

3) Does refilling the recovered nickel solution with constantly new nickel solution maintain the pH?

Thank you.

Ngo Young Yap
- Singapore


(2007)

A. Personally I would not use ammonia, as it will induce stress and continued use of it will just increase the stress and cause other problems. The simplest way to keep the pH up is to something like nickel carbonate or even sodium hydroxide. I know people claim that sodium hydroxide will also induce stress from the sodium, but I don't think I have never seen it. The idea of a divided cell also has its attractions


Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

(2007)

A. 1) Will your lead anode deposit small amount of lead onto the stainless Steel cathode together with your nickel?
From previous posts, it seems like it will slightly dissolve and co-deposit. Use carbon anodes.

2) What is the effect of lead if it does get deposited?
The deposited nickel will be less pure.

3) Does refilling the recovered nickel solution with constantly new nickel solution maintain the pH?
Without the additions of nickel carbonate, I don't think you'll ever be able to keep up with lowering of the pH. You'll never get all of the nickel out. Use a membrane and you won't have to worry about all these problems.

Chris Owen
- Nevada, Missouri


(2007)

Q. Mr. Crichton, I had used the sodium hydroxide for pH adjustment before, the NaOH will first compound with the nickel ions in the nickel sulfate solution, coagulate into greenish precipitate before it raised up the pH. what should I do when I use the NaOH for the pH issue?

Besides, the lead anode do contaminate a bit of deposited metal on cathode. In my experiment,there was 0.2% of Pb in the electroplated nickel.

HF Ang [returning]
Chemist - Malaysia


simultaneous (2007)

A. You absolutely will have nickel precipitation by adding concentrated NaOH to a nickel tank. You can make a dilute solution by using some of your tank solution in a pH adjusting tank that overflows back into the main tank. You put the caustic into the adjusting tank with extreme agitation and dropwise! Consider a metering pump.

James Watts
- Navarre, Florida


(2007)

A. Sodium hydroxide reacts with dissolved nickel salts to form insoluble nickel hydroxide, which is a green gelatinous substance. However, the excess acid in the bath will dissolve the nickel hydroxide to form the nickel salt of the acid and water. The nickel hydroxide may take some agitation to dissolve it, but it will go back into solution. Obviously do not have your filter pump on when you do this, or the nickel hydroxide will be filtered out.


Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

(2007)

Q. I met a few problems when I used the diluted NaOH (24%) as pH adjuster:
- dropwise of NaOH is time taken to adjust pH.
- The diluted NaOH (24%) still able to precipitate the Nickel hydroxide out and manually strong agitation/stirring was required to dissolve the substance, but some can not be dissolved.
- more volume of the diluted NaOH used to raise the pH (compared to ammonia) ,that cause the dilution of the nickel concentration in the nickel sulfate bath and will affect my calculation of the nickel plating efficiency.

Do you all have any ideas to the problems?

Besides, May I know more regarding to the membrane used in the modern electrowinning? I found that there are different kind of membrane, e.g.: nafion membrane ,polymer electrolyte membrane... which kind is more suitable? and also can the membrane act as the anode bag ,so that the hydrogen ions can be trapped in the bag?

HF Ang [returning]
Chemist - Malaysia


(2007)

A. By using a pH adjusting tank that overflows into the nickel tank, you can use air agitation or mechanical agitation very well or a combination of both.
Ammonia forms a nickel complex, so it will affect your plating in a negative manner.
Membrane technology is probably the better way to go. This is way beyond analytical chemistry, so you need to find a company that will sell you the correct product and not try to go the cheap route by designing your own.

James Watts
- Navarre, Florida


February 24, 2009

A. About the membrane, alternatively you can use a flow through diaphragm (fine mesh cloth that slowly allows solution to pass). You then need to setup your cell so that the cathode chamber solution is higher than your anode chamber solution. This will minimize acid generated at the anode from getting to the cathode. You will need to pump solution out of the anode chamber.

James Vaughan
- Brisbane, QLD Australia



January 30, 2017

Q. Dear sir, I tried to electrodeposit nickel from its sulfate solution and bath condition was 27 gpl Ni; 110 gpl sodium sulfate ; pH 3; using nickel carbonate as adjusting pH agent and current density of 180 a/m2, after addition of 10 gpl boric acid the deposited cathode became very brittle! What is the problem?

M. Taghizadeh
- Tehran, Iran


January 2017

A. Hi M. I am a bit confused that you are worried about the cathode material being brittle because you don't seem to be describing ideal conditions for electrowinning nickel.

Are you using membranes as suggested by Chris Owen? Please take a moment to introduce yourself and explain why you are trying to electrodeposit from this solution so we have some more clues. Thanks!

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


simultaneous January 30, 2017

Q. Dear Mr. Mooney
Thank you for your attention to my problem, I separate nickel from waste material by solvent extraction and after purification, solution of sodium carbonate is added to the final solution to precipitate nickel carbonate, this compound is added to electrowinning cell to provide nickel and adjust pH. By enough circulation, without membrane electrolysis is possible like that electro metal company is done.

M. Taghizadeg
- Tehran, Iran


January 30, 2017

A. Three things that you should consider.
1- plate will be brittle for several hours after adding nickel carbonate; and
2- 10 g/L of boric acid is a low concentration compared to a typical plating bath; and
3- Heating is also usually required to > 120 °F

Lyle Kirman
Consultant - Cleveland Heights, Ohio

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