REMOVAL OF CHELATED NICKEL FROM WASTEWATERS
Krishna V. Mayenkar, Head
Industrial Processes Section
Environmental Engineering Department
Ashok L. Lagvankar, Head
Environmental Engineering Department
Harza Engineering Company
Chicago, Illinois 60606
INTRODUCTION
This study was undertaken to examine the adsorption process as a practical means of removing
heavy metals, in particular nickel, from boiler tube chemical cleaning wastewaters generated in steam-
electric power plants. These wastewaters are generated when boiler tubes are cleaned using chemical
solutions containing oxidizing and chelating (complexing) agents. The resulting chemical wastewaters
predominantly contain high concentrations of chelated iron and copper. Other chelated metals, such
as nickel and zinc, are also found in certain chemical cleaning wastewaters. The concentrations of iron
and copper are found to vary between ten to several hundred milligrams per liter (mg/1) while nickel
and zinc are generally less than 100 mg/1.
U.S. EPA effluent guidelines for the steam-electric power industry limit the concentrations of copper and iron in the treated chemical cleaning wastewaters to 1.0 mg/1 each, prior to their discharge to
a receiving stream. The state regulatory agencies can further impose similar limitations for other
metals which may be present in wastewaters but are not covered by federal regulations.
The adsorption process presented in this paper was developed as a result of an investigative study
conducted primarily for the removal of nickel from a chemical cleaning wastewater containing am-
moniated ethylenediamine tetracetic acid (EDTA) as a chelating agent. Conventional
physical/chemical processes could not remove nickel to the required level, and membrane processes,
such as reverse osmosis, were ruled out on the basis of cost. The applicability of the adsorption process was investigated. Laboratory screening tests were conducted, and the initial results were encouraging. Nickel concentrations were reduced by more than 60% when the wastewater was contacted
with a bed of iron filings. Because of the positive screening test results, additional bench scale testing
was conducted to investigate process feasibility.
This paper presents the findings of the bench scale studies, conclusions and recommendations
based on the study results, and a discussion of adsorption process applicability for full scale treatment. Procedures used during the laboratory testing are also described.
BACKGROUND
As a part of a project for the development of a wastewater management plant for a steam-electric
power plant, a treatment scheme for handling chemical cleaning wastewaters was required. These
wastewaters contained ammoniated EDTA and ammoniacal bromate reagents. The metals of concern
in the wastewater were iron (4200 mg/1), copper (660 mg/1) and nickel (95 mg/1). The discharge permit
required that effluent concentrations of each of these metals be 1.0 mg/1 or less.
Several treatment processes were evaluated during an initial screening of alternatives. These were:
(1) lime treatment; (2) lime treatment followed by aeration; (3) lime treatment followed by aeration
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