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POLLUTION : PICKLING OF STAINLESS STEEL

Ours is a unit manufacturing Stainless Steel Sheets. We are facing a problem of pollution in our process which is as follows :

In steel rolling, the hardness of the sheet increases due to cold working. To soften the steel, we have to anneal the sheets in a furnace. Due to annealing, an oxide scale deposits on the sheet which is removed by pickling with following acids : Nitric Acid, Hydrofluoric Acid & hydrochloric Acid. Now we are facing the following problems pertaining to pollution:

1) The scale which is removed chokes the drain and is also a health hazard. How to minimize this scale?

2) The used acid after pickling is thrown into drains which is still acidic. This mixes with ground water and also pollutes the drains & river water. How can this be neutralized practically?

Please send your replies as soon as possible

Anand Vaid
- Pitampura - New Delhi
2000

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You're doing the pickling right, but maybe you could do the annealing process in an inert atmosphere to inhibit some of the oxide. Also if you look around a little you may be able to find someone reasonably close that will take your spent pickling liquor for use in their process, waste exchanges are gaining popularity here because they frequently are the best option for everyone involved. If you need to neutralize the waste stream, use NaOH, (Sodium Hydroxide), it will yield the least harmful set of reaction products.

Jeff Watson
- Pearland, Texas
2000

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2006

We are currently carrying out pickling of Stainless Steel Wire Rods in grades like 304/304L,316/316L & 303. The pickling is done with Hydrochloric, Nitric & Hydrofluoric Acid.

The quality seems to be really great, but over period of time the surface goes Red in color. For e.g. if the material is drawn into bars then there are no problems, but if the same material is sent for export and unprocessed for about 6 weeks,it goes red.

Is there someone who would guide us, please Should you need any further information, please do ask us.

Bhavin Shah
- Mumbai, India