METAL RECOVERY FROM WASTE ACIDS
Clyde S. Brooks, President
Recycle Metals
Glastonbury, Connecticut 06033
INTRODUCTION
Bench scale evaluation tests of the feasibility of achieving promising separation of metals, such
as nickel, copper and zinc, in the presence of chromium and iron from industrial waste pickling acids
have been conducted. Precipitation, solvent extraction, cation exchange and flotation separation
technologies were evaluated. The separation concept which was evaluated consisted of adjusting the
pH of the waste acids with alkalis to a moderately acid range of 2 to 5 to precipitate the bulk of the
iron, followed by separation of the nickel, copper and zinc, using solvent extraction with lauric acid/
xylene, cation exchange with a hydrogen resin and precipitate flotation with lauric acid and sodium
lauryl sulfate. All three separation alternatives were found to provide promising recovery (>67%),
dependent upon the waste acid composition.
Selection of two separation procedures, dependent upon the particular waste acid composition,
should permit useful separation of single or binary combinations of nickel, copper or zinc in the
presence of iron and/or chromium.
SIGNIFICANCE OF THE PROBLEM
Proper management of industrial hazardous wastes persists as a major national problem area. A
recent national survey conducted by Westat [1) estimates the total volume of industrial wastes generated from sources subject to regulation to amount to 264 million metric tons. A significant fraction,
approximately 22(7o, of these wastes has been identified as consisting of metallic wastes (SIC codes
33-37), among them many metals of economic and strategic significance. However, only about 4%
of the total hazardous wastes are recycled.
A more recent survey conducted in the relatively small industrial state of Connecticut indicates a
total industrial hazardous waste volume, generated by regulated sources, to be of the order of 190,000
metric tons annually. About 60% of this waste contains metals such as nickel, copper, zinc, cobalt,
tin, molybdenum, manganese, titanium, cadmium, chromium, and lead [2]. The waste generated in
Connecticut in 1983 approximates the volume for the entire New England region estimated in a survey
conducted a few years earlier in 1979 [3].
The management priorities arrived at by many state planning agencies consist of waste reduction,
waste recycling, physical/chemical/biological treatment, incineration, solidification/stabilization, and
landfill. Development of efficient metal recovery technologies would forward several of these objectives by reduction of waste volume, detoxification and reduction of waste treatment costs by obtaining a byproduct credit for the recovered metal.
The technologies that are recognized to have potential application for soluble metal recovery from
industrial waste streams consist of electrowinning, electrodialysis, reverse osmosis, ion exchange,
solvent extraction, evaporation and precipitation. Flotation, solvent partition, density segregation,
magnetic segregation, flocculation and filtration are technologies applicable to metals in insoluble
form.
The concept for the present study was that favorable conditions for separation and concentration
of nickel, copper or zinc, metals commonly present in significant amounts in waste pickling acids,
could be created by a combination of pH adjustment to precipitate the bulk of the iron, followed
by more selective separation of the desired metals. Separation technologies selected for evaluation
consist of solvent extraction, cation exchange, and flotation. These separation technologies are considered to provide potential economies if proven applicable to metal recovery from waste acids.
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