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Letter 13011
Sludge removal from Zinc Cyanide
tank
We have a problem with the level of sludge in our cyanide zinc
plating tank (sodium cyanide/zinc/brighteners etc).
None of the local waste removal companies will touch the stuff,
and I am wondering a) what it is (greyish sludge which I believe I've
heard comes from the caustic soda in the solution) and b) how can we
neutralise it or reduce it's toxicity to a level where we can have it
dumped.
Also suggestions on easiest removal would be best. Only our acid
tank is the same size as the plating tank, and for obvious reasons
that will not be used. Filtration is also unlikely to be an option,
as we're talking at least a foot of depth here :-( The only filter we
have is on the acid zinc barrel line - unusable for the same reasons
as the pickle tank.
Many thanks in advance for any help.
David Chord
plating shop - Lower Hutt, New Zealand
David, you have a major problem. This sludge contains breakdown
byproducts from plating, it is normal. It contains sodium carbonates,
ferrocyanate (from cyanide, virtually insoluable in hot water),
metallics i.e. iron, copper, chrome, etc. Probably have undissolved
cyanide and caustic from additions. You cannot successfully filter
this mess. When I was plating cyanide zinc, we had waste treatment
tanks specifically for this sludge. We would slowly add small amounts
to warm water, stong mechanical mixers, added copius amounts sodium
hypochlorite, acids (toxic fumes), many tanks. Then bleed small
amounts into our main reactor. It took months and much money. Perhaps
someone on this site can help you. In the USA, only a small number of
licensed haulers that can neutralize this stuff are around. It was
still cheaper to have it hauled than process it ourselves.
Good luck,
Bill Hemp
tech svc. w/ chemical supplier -
Grand Rapids, Michigan
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