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PH adjustment in a Nickel electro bath

Hi ¿ I have to adjust the pH in an industrial 60 liters nickel bath (NiSO4 + NiCl2 + H3BO3). pH is for now at 5.7 which is quite high. Constructor says to decrease the pH to 4.8 using a 20% sulfuric acid solution (20% in volume I guess). My question: how many milliliters of a 20% sulfuric acid solution should I add to decrease the pH from 5.7 to 4.8 in a 60L bath. Thanks to detail the calculations for a better understanding. Thanks in advance ;)

François Pignon
Plating shop employee - France
February 5, 2009

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First of three simultaneous responses --

The best answer is: as much as it takes. You're dealing with a complex, buffered system where pH 'calculations' are liable to be wildly off. Might be a good topic for a pHD thesis.

Try seeing how much it takes to get the required adjustment in a 1 l sample of bath, at operating temperature, then scaling up. Still, be cautious in doing the actual addition.

You can always add more.

Dave Wichern
Consultant - The Bronx, New York
February 7, 2009

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Second of three simultaneous responses --

Due to the small size of the bath, I would add the sulfuric acid solution slowly while agitating the solution continuously(mixing). As the pH nears 4.3 wait and let the agitation continue. Now very slowly add what is necessary to adjust the pH to 4.0. If you are a little low i.e. 3.9 or a little high i.e. 4.1 do not worry.

Before you perform the above make sure that you have a pH meter calibrated using the correct range buffer (4.0 or as needed for the meter). If your meter is not self adjusting for temperature make sure to adjust the temperature for the temperature of the buffer and then the temperature of the solution. pH paper is not as accurate and may be off by up to 0.5 units.

Gene Packman
process supplier - Great Neck, New York
February 7, 2009

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Third of three simultaneous responses --

The amount of boric acid in the solution will not allow you to directly calculate the amount.
You will find that adding say 10 mL at a time will seem to take forever and then magically the pH will drop like a rock. This is because the boric is a great buffer and will resist the pH change until it has reached the point that it no longer can stop the pH change. Notice that it has 3 acid hydrogens, so it will buffer at 3 considerably different pH ranges.
From experience, try adding 10 mL, stir well and recheck the pH . Continue this until it gets to the high end of your range.

Also do not be shocked if the pH drops further overnight.

It is best to make minor adjustments to keep the solution in the center of the range. This will always be an acid add unless your nickel anodes are passivated or you are using an insoluble anode.

James Watts
- Navarre, Florida
February 7, 2009

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February 17, 2009

Hi Franco..

Need not to worry at all.. Its just a matter of monitoring the pH while adding small quantity of H2SO4 into the bath. Also check boric acid concentration if the pH raises regularly.

Regards,

Jose George
- Cochin, Kerala, India

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First of two simultaneous responses --

With proper anode corrosion, the pH must rise, with or without boric acid. for better tank control and better looking parts, use the boric acid at the recommended amount.

James Watts
- Navarre, Florida
February 18, 2009

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Second of two simultaneous responses --

It would help to dilute the sulfuric first, or you WILL overshoot your target.

George Brackett III
- Maine
February 19, 2009

He is using 20% which is not too bad, but 10% might be a little bit better if the tank can stand the volume. It is not a big tank and the pH should be taken with the tank at the proper level and very well stirred so that he gets a representative sample. I used a home made colwissa.

James Watts
- Navarre, Florida
February 20, 2009

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