Sludge Characteristics of Lime
Neutralized Pickling Liquor*
RICHARD Y.   LEVINE
Research Engineer Industrial Division
Association of Casualty and Surety Companies
New York, N. Y.
WILLIAM   RUDOLFS
Chairman Department of Sanitation
Rutgers  University
New   Brunswick,  N. J.
Before applying the final finish to steel products, the steel fabricator must remove dirt, grease, and especially the iron oxide scale
(or film) which accumulates on the metal during fabrication. This is
generally accomplished by immersing the steel in dilute sulfuric acid
(15-25 per cent by weight). The process is known as pickling and
produces a waste known as pickling liquor, composed largely of unused
acid and the iron salts of the acid  (ferric and ferrous oxide).
The acid reacts with the iron salts forming ferrous sulfate. As
the acid is consumed, it becomes correspondingly more dilute and
must be replenished. In time the ferrous sulfate content of the
pickling solution increases to such a point that it inhibits the action
of even a high concentration of acid. The pickle liquor must be
discarded and a new, fresh acid solution prepared. Generally, waste
pickle liquors from batch processes contain 0.5-2 per cent sulfuric
acid and 15-22 per cent ferrous sulfate. Some plants employ a continuous pickling operation. Since this process is predicated on speed,
the discharge of the waste pickle liquor is more frequent. As a result,
the wastes are higher in acid content and lower in ferrous sulfate
than the batch process  (acid content ranges from 4-7 per cent).
QUANTITY AND  CHARACTERISTICS  OF  WASTE
The total volume of waste pickle liquor produced is estimated
at one billion gallons per year. The amount of pickle waste produced per ton of steel product depends on the size and type of
plant. Since the steel products must be rinsed in water after removal
from the pickling tank to remove all traces of acid, the rinse water
*Paper of the Journal Series, New Jersey Agricultural Experiment Station,
Rutgers University, the State University of New Jersey, Department of Sanitation.
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