TWO-PHASE METAL REMOVAL USING
GRANULAR
ACTIVATED CARBON AND
5-METHYLBENZOTRIAZOLE
Cheryl Horn
Advisors:
Muna Abu-Dalo, Mark
Hernandez
University of Colorado,
Boulder
Research Experience for
Undergraduates, Summer 2002
Abstract
Project
Proposal
Final
Presentation
Thanks and
Acknowledgements
Abstract
Recent USGS surveys have
reported that at least 1300 miles of streams in
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Research
Proposal
Introduction
Recent USGS surveys have
reported that at least 1300 miles of streams in Colorado are impacted by acid
mine drainage (AMD). The generation of acid mine drainage occurs due to the
exposure of sulfide containing minerals to oxygen and water, which can result in
acidic conditions. Additionally, this runoff is characterized by high metal
loadings according to local geology. Remediation attempts using natural and
engineering methods have been relatively successful, but are often costly. The
most common remediation approach involves the addition of carbonate alkalinity
(lime) to adjust pH and promote metal precipitation; however this method is
expensive and generates large volumes of sludge, which require handling and
disposal.
Preliminary research has indicated that benzotriazole derivatives, which are commonly used both as
corrosion inhibitors and in aircraft deicing fluids, may be useful in removing
metals from solution. Because benzotriazoles can bind
metal ions while maintaining a strong surface sorption character, they may be
useful for removing metals from AMD without pH adjustment or sludge production.
Such a process would be more economical than lime addition, and would allow for
eventual metal recovery. Further research is needed to determine the specific
adsorption characteristics for benzotriazoles, as well
as the effectiveness of removal for various metals.
Background
Minimal occupational and epidemiological studies
have been conducted for benzotriazole derivatives;
further, literature concerning the metal immobilization capabilities of benzotriazoles is very limited. Recent research of
aircraft deicing fluids has shown that 4- and 5- methylbenzotriazole (4- and
5-MeBT) strongly adsorb to biomass surfaces, and that this sorption may be
accurately predicted using a standard Freundlich
isotherm. Research has also shown that under aerobic conditions, 5-MeBT is
biodegradable, while 4-MeBT is not (Cornell, 2002).
Problem
Statement
In acidic pH ranges, most transition metal ions do not sorb to activated carbon surfaces; thus carbon is not used
for metals removal in acidic aqueous systems. However, benzotriazoles do sorb strongly to
some carbon surfaces. Further, benzotriazoles strongly coordinate with some toxic
transition metals. Preliminary research observations suggest that sorption of
MeBT onto granular activate carbon (GAC) can be modeled by a Freundlich isotherm (Abu-Dalo, 2002). It is unknown whether
MeBT adsorbs to activated carbon, or if the activated carbon-MeBT compound could
be engineered as a cost-effective metal scavenger. The primary focus of this
project will be to observe the sorption characteristics of MeBT and the metals
copper, zinc, and cobalt using various types of activated carbon. The ultimate
goal of this research will be the optimization of this two-phase process through
the development of a better understanding of these sorption mechanisms.
Hypotheses
In order to gain a better understanding of the
sorption and metal immobilizing capabilities of benzotriazoles, the following hypotheses will be tested:
1. Benzotriazole derivatives exhibit a sorption behavior with
activated carbon that can be accurately predicted by a Freundlich isotherm.
2. Given
economical doses of GAC used in wastewater treatment processes, benzotriazoles will effectively bind Cu and Co ions in
acidic water.
Methods and Materials
Three types of activated
carbon will be used in order to develop a better understanding of the sorption
process for MeBT-metal complexes with GAC. Batch experiments using five known
concentrations of MeBT in the range of 10 – 2000 mg/l will be allowed to reach
equilibrium (approximately 4 hours) after the addition of activated carbon.
Controls containing only water and GAC will also be tested. Adsorption models
for each type of GAC will then be built and tested.
After the MeBT
adsorption models have been built, microcosms containing constant concentrations
of MeBT and GAC will be prepared. Varying metals concentrations will be added in
the range of 1-10 mg/l (1, 5, and 10 mg/l). After these experiments reach
equilibrium, final concentrations will be measured and removal efficiencies will
be calculated for both MeBT and metals. Controls containing only a metal and
activated carbon will be used, so that adsorption of metals onto GAC can be
compared both with and without MeBT present. All assays will be executed in
triplicate.
MeBT determination will be accomplished using high
performance liquid chromatography (HPLC), and polarography will be used to
confirm results. Measurements will be taken using an HPLC fitted with a UV
detector (l = 254 nm). Separation of isomers will be performed isocratically using two Zorbax Rx-C8 4.6 x 250 mm columns in series. The HPLC
elluent will be composed of a phosphate buffer to
HPLC-grade acetylnitrile ratio of 70:30 at a flow rate
of 1.5 ml/min with a sample injection volume of 200 ml. Prior to injection, all samples will be centrifuged at 10,000
rpm for 5 minutes. Metal concentrations will be determined using DPP and
confirmed using ICP/AES in the
Anticipated Results
It is expected that benzotriazole
derivatives will exhibit a sorption behavior with GAC that can be accurately
modeled by a Freundlich isotherm. Further, these
derivatives will bind with GAC surfaces when transition metals are present.
Finally, it is expected that using MeBT and some economical dose of GAC similar
to that used in wastewater treatment will effectively remove transition metals
that form strong complexes with MeBT from acidic waters to below EPA drinking
water standards.
Bibliography
1. Abu-Dalo, M. (2002). Personal
Communication.
2. Abu-Dalo, M. (2002). Electrochemical Characterization of Benzotriazole Derivatives and Their Behavior in Industrial
Waste Treatment.
Dissertation Proposal, Department of Civil, Environmental,
and Architectural Engineering, The University of
3. Cornell, J. (2002). The Environmental Chemistry of Aircraft Deicing Fluid Component
Chemicals. Department of Civil, Environmental and
Architectural Engineering, The
4. Hernandez, M.
(2001). Coupling Granular Activated Carbon with Common
Metal Chelating Corrosion Inhibitors for Two Phase Transition
Metal Immobilization. Project
Proposal, Department of Civil, Environmental, and Architectural Engineering,
The University of
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Thanks and Acknowledgements
I am
deeply indebted to many people for making my research experience a remarkable
one. I will mention only a few, but there are many more...
Muna Abu-Dalo
Mark
Hernandez
JoAnn Silverstein
Jenny Baeseman
Thank you!
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