85    NICKEL METAL RECOVERY FROM
METAL FINISHING INDUSTRY WASTES
Clyde S. Brooks, President
RECYCLE METALS
Glastonbury, Connecticut 06033
INTRODUCTION
A flexible separation scheme for efficient recovery of nickel from diverse metal waste systems has
been devised, using nickel oxadate precipitation augmented by ion exchange. Initial removal of the
bulk of copper, iron and zinc contaminants at low pH is conducted by solvent extraction. Removal of
the bulk of organic complexing agents and conversion of Cr3 + to Cr*+ by autocatalysis augmented by
addition of inorganic oxidants (H202, NaClOj or (NH4)2S2Og) enhances the efficiency of the nickel
separation. A final sulfidation reduces the residual metals to concentrations compatible with state and
EPA standards for water effluents.
SCOPE OF THE PROBLEM
A principal incentive for interest in nickel recycling is the need to improve the economics of
recovery by developing more efficient separation technology. Nickel is one of the principal non-
ferrous metals of economic significance, ranking 8th in demand in the United States with more than
200,000 tons/year usage. Current metal markets are lethargic but average growth rate in demand of
about four percent per year has been projected to the year 2000.'
An additional incentive for recovery is that nickel has strategic significance with only about 10% of
current demand provided by domestic U.S. production. Nickel is one of four materials designated for
the Defense Materials System with 60 to 70% of the current U.S. demand met by imports.
A further reason for wishing to improve recovery efficiency is that only about 10% is currently
recycled.2 There is a wide margin for improving recovery with about 156,000 tons per year irretrievably lost with current practice. Finally, toxic metal removal from waste streams diminishes the volume
and toxicity of waste effluents and improves the economics of hazardous waste disposal.3
The specific objective for the present work has been to develop flexible, technically feasible separation procedures for efficient recovery of nickel from diversified multimetal composition metal finishing industry wastes. Metals of primary concern are chromium, copper, nickel and zinc in the presence
of contaminant iron and low concentrations of aluminum, barium, cadmium, lead and tin. Consideration of the widely ranging available metal separation technologies4 led to the selection of a multistage
regime applicable to solid sludges and waste acids containing significant concentrations of nickel.
This regime involved an initial acid solubilization for the solid sludges. Selected separation processes
consist of non-selective solvent extraction removal of the copper and iron and the bulk of the zinc,
oxidation to convert Cr3+ to Cr*+ and to minimize the organic content with the nickel separated by
oxalate precipitation and ion exchange. A final sulfidation stage minimizes residual metal content to
meet state and EPA water discharge standards.
WASTE SYSTEMS
Five metal finishing industry wastes containing significant amounts of nickel were selected for
experimentation (Table 1). The wastes were selected on the basis of containing significant amounts of
nickel and representing a wide diversity of multimetal compositions and physical conditions. The
electrochemical machining (ECM) filter cake contained chromium, iron and diatomaceous filter aid
as contaminants. The nickel hydroxide sludge contained varying amounts of copper and iron, along
with small amounts of aluminum, barium, lead and tin as contaminants. The waste mineral acid had a
similarly diversified composition with cadmium, lead, manganese and tin contaminants. The spent
nickel hydrogenation catalyst consisted of nickel mounted on a siliceous support with appreciable oil
hydrogenation residue. The electroless nickel contained small amounts of cadmium, chromium,
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