80 TREATMENT AND METAL RECOVERY FOR ELECTROLESS
METAL PLATING WASTES
Clyde S. Brooks, President
RECYCLE METALS
Glastonbury, Connecticut 06033
INTRODUCTION
An examination has been conducted of the effectiveness of homogeneous oxidation catalysis of
metal organic complexes, notably the carboxylate salts of nickel and copper, to facilitate metal
recovery from industrial waste effluents. Metal finishing industry electroplating solutions contain
various organic complexes such as nickel with citric acid and copper with ethylene diamine tetraacetic
acid (EDTA).
The principal wastewater treatment routes used for electroless plating solutions consist of chemical
or electrolytic reduction to metallic state, precipitation as insoluble compounds (carbonates, hydroxides or sulfides) or removal by adsorption/ion-exchange processes. In this study the objective has
been to use mild aeration oxidation of the organometallic complexes, possible in the presence of an
oxidation agent like H202 which would not add any additional solids to the treated aqueous effluents.
Efficient oxidation destruction of the organic component of the organometallic complex would
facilitate metal separation for either disposal or recovery.
It has been known for some time that metal organic complexes such as the carboxylate salts of Co,
Cu, Ni, Mn, etc. are effective homogeneous oxidation catalysts.1-3 The objective in this study was to
determine if homogeneous oxidation catalysis under mild conditions (temperatures < 100°C) of the
organometallic complexes, nickel citrate or copper EDTA, would produce efficient self destruction by
auto catalysis making the nickel or copper readily available for separation by the common routes of
electrodeposition, precipitation or adsorption/ion-exchange. Synthetic solutions of cobalt and nickel
with citric acid and of copper with EDTA and a waste solution of a commercial electroless plating
solution were evaluated by bench scale experimentation.
EXPERIMENTAL PROCEDURES
Organometallic Systems
The organometallic systems studied consisted of the citric acid complexes of cobalt and nickel and
of EDTA complexes of copper. The solution compositions used were selected to be typical for
commercial electroless metal plating solutions4 without secondary components such as hypophosphite
reducing agents. Additional solutions used consisted of nickel-acetate mixtures to provide models of
postulated intermediate stage oxidation products.
Oxidation Tests
Aeration oxidation tests were conducted with 50-100 Cm3 of solution aerated with a 100-200 Cm3/
min air flow at 1 atmosphere in a cylindrical glass column (5 cm x 45 cm) equipped with a fine
dispersion frit. Aeration exposures were conducted for periods from 2-8 hr at 25 and 75°C in the pH
range 2-6. Hydrogen peroxide (concentration to 30,000 mg/L) were used in some tests. Carboxylic
acids (ascorbic and lauric acids) in concentrations of 500 to 1000 mg/L were used in some tests. The
rationale for addition of these latter compounds was to insure the presence of metal carboxylate
compounds known to be homogeneous oxidation catalysts.
Solution Analysis
The extent of the oxidation destruction of the organic component of the aerated test solutions was
established by determination of the total organic carbon (TOC) content. Additional characterization
of the nature of the residual organic compounds contributing to the post aeration TOC values
43rd Purdue Industrial Waste Conference Proceedings, © 1989 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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