MEKCURY(II) REMOVAL FROM AQUEOUS SOLUTION USING
ION EXCHANGE AND CARBON ADSORPTION
Keith W. Fife, Graduate Student
Joel D. Williams, Graduate Student
H. G. Folster, Associate Professor
Chemical Engineering Department
New Mexico State University
Las Cruces, New Mexico 88003
INTRODUCTION
The protection and restoration of the environment has become a national goal in recent
years.   Legislation resulting in laws such as PL 92-500 (the Federal Water Pollution Control Act Amendment of 1972) and PL 93-523 (the National Safe Drinking Water Act)
have set forth stringent requirements for both industrial wastes and municipal treatment.
One area of concern is heavy metal contamination of waters from industrial discharges and
naturally occurring sources.
In this study mercury(II) removal from aqueous solution was evaluated using activated
carbon adsorption and ion exchange.   The results of this project are expected to contribute to a grant which is to demonstrate the application of reverse osmosis and electrodialy-
sis in the treatment of small community water supplies in New Mexico.   Two ion exchange
resins, ALM 125 and 525 (manufactured by the Nippon Soda Company) and an activated
carbon, Nuchar WV-G (which is produced by Westvaco), having a surface area of 1100
m2/g were used.   Analysis techniques used were the dithizone colorimetric method with
checks by atomic absorption for the ion exchange studies and atomic absorption for the
activated carbon studies.   All solutions were made up by dissolving mercuric nitrate into
deionized water.   A stock solution was standardized by atomic absorption and all test solutions were made by diluting the stock solution.
ACTIVATED CARBON ABSORPTION
Isotherm Tests
The first experimental work done  with activated carbon was the determination of carbon's capacity for mercury.   This was accomplished by isotherm equilibrium tests.   The
stock solution was diluted to the desired concentration with deionized water and the pH
was adjusted by the dropwise addition of concentrated nitric acid or a sodium hydroxide
solution.   A known volume of mercury solution was added to a series of nalgene containers
and identical amounts of carbon were added to all solutions.   The bottles were placed on
a shaker table at an agitation rate of 212 rpm and allowed to come to equilibrium.   Blank
solutions containing mercury but no carbon were run simultaneously to check for mercury
adsorption onto the nalgene.   All solutions were at a pH of between 2 and 3 with initial
concentrations ranging from 30 to 1776 mg/1.   The results of the first series of tests are
shown in Figure 1.   The equilibrium mercury concentrations vary from 20 to 1150 mg/1
and the adsorption capacities from 3 to 130 mg Hg per gram of carbon.   This curve doesn't
follow the Freundlich isotherm, which is generally used to describe adsorption from solution.   In fact the concave shape at the higher concentrations indicates unfavorable characteristics for mercury adsorption.
Since the chemistry of mercury(II) is pH-dependent, it was desirable to have information
about the effect of pH on capacity.   All mercury concentrations were approximately the
same for the pH-isotherm tests.   Results of these experiments are represented in Figure 2.
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