Section 14. PLATING WASTES
NICKEL REMOVAL FROM NICKEL PLATING WASTEWATER
USING IRON, CARBONATE, AND POLYMERS FOR PRECIPITATION
AND COPRECIPITATION
Frank McFadden, Water Quality Engineer
Alabama Department of Environmental Management
Montgomery, AL 36130
Larry Benefield, Associate Professor
Department of Civil Engineering
Russell B. Reed, Research Associate
Research Data Analysis
Auburn University, AL 36849
INTRODUCTION
The toxicity of metal finishing wastewaters has prompted numerous guidelines to be promulgated
by the Environmental Protection Agency (EPA) and the States. As a result of these guidelines, it has
become important to the metal plating industry to optimize the treatment of their wastewater to
prevent toxicity problems in the receiving stream or local treatment plant [1]. By optimizing the
treatment process, considerable savings can be realized in the operational cost of a plant.
Several methods have been used to treat the wastewater from electroplating operations. These
include reverse osmosis, evaporation, ion exchange, and precipitation. While all of these methods
are technically feasible, the most economical approach seems to be hydroxide precipitation.
There have been several modifications of the precipitation process to achieve a higher degree of
treatment and enhance settleability. These modifications include carbonate precipitation and copre-
cipitation using other metals. This paper investigates the effect of iron as a coprecipitator as well as
carbonate addition, pH adjustment and polymer addition, on nickel removal from wastewater.
LITERATURE REVIEW
Chemical Precipitation
Chemical precipitation has proven to be one of the most effective ways of removing heavy metals
from industrial wastewaters [2,3,4]. The most common form of chemical precipitation is hydroxide
precipitation where the pH of the waste solution is raised to an optimum point with lime or NaOH.
At the optimum pH, metal hydroxides are formed which, when they settle, produce a supernatant
with a low metal concentration. Following sedimentation, filtration of the supernatant by sand or
pressure filters may be desirable.
Patterson et al. [3] have observed that hydroxide precipitation, although very effective, has some
inherent problems. These include poor dewaterability of the sludge due to the gelatinous nature of
the sludge, large volumes of sludge formed, and in the case of nickel and other cations which have
an optimum pH above 10, continuous pH adjustment which increases the overall treatment costs.
A theoretical metal solubility curve can be constructed by applying solubility equations relating
the metal hydroxide solid species in equilibrium with soluble free metal ions or metal hydroxide
species. Figure 1 shows an equilibrium diagram for the nickel-hydroxide system. The corresponding
equations used to construct this diagram are listed in Table I [3,5,6].
Theoretically the optimum pH for minimum nickel solubility is approximately 10.5. This is slightly
lower than the pH observed by Patterson et al. [3] for minimum solubility of nickel (pH 11). However, their results were based on a four-hour mixing time without considering sedimentation.
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