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Metal recovery from pickling liquor


I am a research student. There are major pickling waste (acidic) generate from cold still rolling sector. I am trying to recycle & reuse it again. Metal loss is also identified in pickling waste. That are Cr, Zn, Ni, Fe, Mn etc. The pickling waste is acidic. They are use H2SO4, HNO3 and HF for their pickling process. Pickling process is done after every annealing process. The annealing process done at 1000°C, so the burnt metal (corrosive metal) found on the surface of the SS sheet which is then go for pickling. The process done as under:

1. After annealing the sheet deep in H2SO4(98%)
2. Then after second annealing they send to HNO3(60%) & HF(30-40%)
3. After final pickling the waste pickling liquor sent for neutralization, so lots of solid waste is generate & they are send it to solid waste dumping site. For that they have to pay also.

1. Can we recovered that metals from the pickling waste?
2. Can we recycle the spent acid & reuse it again?
3. Can we recover the metals from the solid waste?

Kindly give your nice & useful suggestion that will help me as well as all the still toiling sector which are generate that type of wastes. Please Reply early as soon as possible

- Ahmedabad, Gujarat, India


The answer to all three of your questions is yes. But the problem lies in doing any of them economically compared to present methods. They only become attractive when landfilling is more expensive than recovery, and most of the world is not at that point.

Many books and thousands of government funded reports have been written on these subjects, and nobody is going to be able to summarize them all for you. Forget trying to locate the universal solution to all pollution problems, and pick one of these two pickling solutions to study, and one of the three recovery methods, and one or two of the contaminating metals--and do some detailed study of the dozens of previous reports you will find on that far more limited universe.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Dear inquirer,

I want to tell you some thing you might be interested in. I had done my thesis on topic of removal of hexavalent chromium by using. Pickling waste. The thesis involved extensive laboratory research. hexavalent Cr is mainly encountered in electroplating waste. It is carcinogenic and can not be removed by precipitation. To precipitate it it is converted in CR+3 which can be removed by precipitation with Ca(OH)2 or NaOH.To do this reduction FeSO4 is generally used in acidic media. Now pickling is done by immersing big iron rings or whatever item in huge tanks of H2SO4. It is done to clean the surface of different kind of impurities like Mn, Mg, Ni etc.While precipitating these impurities, Base metal also reacts with acid thus forming FeSO4, thereby preparing a compound that can be used for treatment of CR+6. This way two wastes can be symbiotically reacted to each other to nullify the effect of both. Any takers Go ahead!

Ajay Kumar
- New Delhi, Delhi, India

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