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Determination of nitric acid content in acid bath

Q. Hi,

I would like to enquire about how to calculate the Nitric concentration in the acid bright dip bath in Aluminium finishing? As I have been given two different methods.
1. 50 ml H3PO4 + 5 ml Bright dip sample and titrate it with ferrous sulfate ⇦this on eBay or Amazon [affil links] until clear %HNO3=no of mls * titration factor * 2.1225 / 5
2.Measure 5.0 ml bright dip solution into a 250 ml clean dry beaker [beakers on eBay or Amazon [affil links] and add 100 ml of H3PO4 and heat it up to 40-45 °c. Titrate it with ferrous sulfate ⇦this on eBay or Amazon [affil links] until the first golden brown colour appears.

Let "b" ml be the volume of ferrous sulfate ⇦this on eBay or Amazon [affil links] used. and "a" ml is the titration factor of ferrous sulfate ⇦this on eBay or Amazon [affil links] against the standard % by volume of 70% nitric acid in the "phospol" = (b/a)*5

From my opinion, I think the 2nd method is the correct one. Can anyone please get back to me?

Another problem, we have a client that orders their aluminium from China then being send to Melbourne. Their aluminium has to be washed in caustic first before being dipped in the acid bath to obtain good finishing. Why is that?

Another problem, we have another client that complains that they are using too much caustic to neutralize their treatment tank. Is there any cheaper way to neutralize their tank? They probably go through about 8 tons of caustic every month. Please advise.

Any advice would be very much appreciated.

Regards,

Joe Yefrey
- Melbourne, Australia
2002

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2002

Q. Hi,

I would like to further specified the problem above. About the method of determination of Nitric acid concentration in the acid bright dip bath in Aluminium finishing? As I have been given two different methods.

1. 50 ml H3PO4 + 5 ml Bright dip sample and titrate it with ferrous sulfate ⇦this on eBay or Amazon [affil links] until clear %HNO3=no of mls * titration factor * 2.1225 / 5

2. Measure 5.0 ml bright dip solution into a 250 ml clean dry beaker and add 100 ml of H3PO4 and heat it up to 40-45 °C. Titrate it with ferrous sulfate ⇦this on eBay or Amazon [affil links] until the first golden brown colour appears. Let "b" ml be the volume of ferrous sulfate ⇦this on eBay or Amazon [affil links] used. and 'a' ml is the titration factor of ferrous sulfate ⇦this on eBay or Amazon [affil links] against the standard % by volume of 70% nitric acid in the "phospol" = (b/a)*5.br I still think the 2nd method is the correct one. Can anyone please get back to me?

Problem 2: we have a client that orders their aluminium from china then being send to Melbourne. their aluminium has to be washed in caustic first before being dip in the acid bath to obtain good finishing. why is that? It is not the case if the aluminium is bought from a Melbourne supplier. Yes All the aluminium has to go thru a cleaner stage called 'borax' but for the aluminium that is bought from China , they have to go thru caustic bath before being dipped into the bright dip, they need an extra step and that is taking too much time, why is that?

Problem 3: we have another client that complains that they are using too much caustic to neutralize their treatment tank. Is there any cheaper way to neutralize their tank? They probably go through about 8 tons of caustic every month. The caustic is used to treat the waste water and overflow from the aluminium anodising plant. it is merely acid bath, sulfuric acid, caustic bath and etc. Is caustic the best way to treat the waste water? Is there another efficient method to reduce the amount of caustic being used to treat the waste water? Please advise.

Any advice would be very much appreciated.

Regards,

Joe Yefrey [returning]
- Melbourne, Australia

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A. Hi, Joe. Problem 2 probably relates to "etching" rather than cleaning. It is possible, I suppose, that the local company is etching before shipping the product to your client. Then again, who knows if it's even the same alloy. Problem 3: Caustic is the most commonly used neutralizing agent. There are cheaper alternatives like hydrated lime, as I mentioned. But everything has advantages and disadvantages and a qualified wastewater treatment engineer can help them decide the economics of this fairly complex issue which also involves sludge disposal costs, scavenging ability of the neutralizing agent, possible savings on coprecipitant if lime is used, but repiping of the reagents to handle lime, issues of how the lime slurry will be made up, etc. I'm sure you can find articles and chapters of books that will help a well qualified engineer decide which reagent to use in this specific case. Good luck. Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey 2002 Q. Hi, Geoff Whitelaw, Thank you for your advice. However, do you know how often I have to standardise the ferrous sulfate ⇦this on eBay or Amazon [affil links] solution. Usually I only make up about a litre of ferrous sulfate ⇦this on eBay or Amazon [affil links] and I standardise it once to get a factor and it last me for about a month. I am also curious why ferrous sulfate ⇦this on eBay or Amazon [affil links] is not stable and why the titration has to be heated first? Can you please advise? Regards, Joe Yefrey [returning] - Melbourne, Australia 2002 A. I use 5 mls of the bath to 95 mls of DI. Add 5-10 drops of phenolphthalein ⇦this on eBay & Amazon [affil links] into the beaker, put on a stirrer. Titrate with 1.0N sodium hydroxide solution and wait for a solid red color. Calc. is: 1.34*vol. titrant= Nitric concentration (%) Bob Forrest - Port, Maine 2002

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