Disposal of Waste Pickling Liquors
Thomas F. Reed, Chemical Engineer
United States Steel Corporation of Delaware
Pittsburgh, Pennsylvania
The problem of the disposal of waste pickling liquors has been
a perennial headache to the metallurgical industries for a great many
years. Many, many solutions have been suggested, a few with some
merit and many without, but no practical general solution has emerged.
In fact, as will be developed in this paper, it is quite possible that
a general solution which will yield a profit may be difficult to find,
so that the best general answer may not lead to a profit at all, but
may lead to the cheapest net cost.
The failure to obtain a general solution to this knotty disposal
problem certainly does not result from any lack of diligence on the part
of those who face it. A great deal of time, money, and effort has been
spent to seek out the answer. Many are undoubtedly familiar with
some of these efforts. The Ferron development was an attempt to con¬
vert the sludge resulting from the neutralization of pickle liquor with
lime into a usable synthetic aggregate. The production of ferrous
sulphate from waste pickling liquor is mentioned both with and with¬
out return of the mother liquor to the pickling operations. In one
case, a large-scale attempt was made to use the recovered ferrous sul¬
phate for conversion to sulphuric acid. At present there are a number
of plants where the waste liquor is fully neutralized with lime, ad¬
mittedly only as an expedient, and there are some plants producing
copperas.
The present lack of a suitable answer to the disposal problem is
not the result of indifference or lack of diligence. Many processes which
have been proposed or which are now in use do not in themselves
provide a suitable answer. The first thing to do is to establish and
define the problem so that its metes and bounds may be determined.
Attention should be focused primarily on the disposition of the
waste pickle liquor from installations using sulphuric acid because in
discussing this type of waste sulphuric acid accounts for most of the
problem. Sulphuric acid pickle liquor waste may be defined as that
solution of ferrous sulphate and sulphuric acid which results when
sulphuric acid is used to remove surface oxides from steel.   It contains
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