The authoritative public forum
  for Metal Finishing since 1989
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Sludge treatment and acid problem

2005

There are large amounts of industrial sludge. I'd like to know how to recuperate aluminum sulphate from waste sludge or how to treat this sludge for a better disposal. Sludges come from bauxite and H2SO4 process. Maybe this sludge has an useful application, does somebody know it?

The other question: I'm researching about an HCl(32-35%), HF(2-3%) effluent. It requires acid neutralization using limestone, so it can be disposed. But, I've also read F ion can have a precipitation treatment with CaO.
How does it work in an HCl solution?, would it be a problem?, would it generate handle and disposal sludges or create a sludge problem?

Thanks,

María Gómez
engineering student - Buenos Aires, Argentina

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There are many industrial sludges that presently have no value because of the confluence of two factors: first, that it consumes more energy and other resources and cost to recover them than can be gained from them; second, that regulations or real hazards get in the way of reusing waste materials. This site is about metal finishing rather than mining and refining, so unfortunately most of us aren't too familiar with the aluminum process you are investigating, but alum has some uses in paper making and as a coagulant in water treatment systems.

On the second question, yes, calcium will precipitate fluoride to an extent, but calcium fluoride is not insoluble; you would need to find a solubility table as a function of pH. Chloride is for practical purposes completely soluble and would not be part of the reaction or consideration. Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005