2 research outputs found
Kinetic Modeling of the Anodic Degradation of Ni-EDTA Complexes: Insights into the Reaction Mechanism and Products
In this study, an electrochemical
advanced oxidation process (EAOP)
was employed to effectively degrade complexes of nickel and ethylenediaminetetraacetic
acid (EDTA) present in electroless nickel plating wastewaters. Our
results show that Ni-EDTA complexes can be effectively degraded by
an EAOP with degradation of the complexes occurring at/near the anode
surface via interaction with hydroxyl radicals generated on water
splitting. Our results further show that the rate of Ni-EDTA degradation
is not a function of the rate of any particular chemical reaction
but, rather, is controlled by the rate of transport of Ni-EDTA to
the anode surface. The oxidation of EDTA to smaller noncomplexing
entities releases Ni2+, which is subsequently
deposited onto the cathode as Ni0. While complete Ni-EDTA
removal and Ni recovery are achieved within 2 h, the overall TOC removal
by EAOP is limited, with only 50% TOC removal achieved after 2 h of
treatment. The low affinity of small molecular weight EDTA degradation
products (such as formic acid, glycine, oxamic acid, and acetic acid)
for the anode surface limits oxidation of these compounds and overall
TOC removal by the anodic oxidation process. We have developed a mathematical
kinetic model that satisfactorily describes Ni-EDTA removal, Ni recovery,
and TOC removal over a range of Ni and EDTA concentrations and provides
a good description of the oxidation of various EDTA degradation intermediates.
The mathematical model developed here, when coupled with the hydrodynamics
of the electrochemical cell using a computational fluid dynamics tool,
can assist in both cell design and the selection of operating parameters
such that the performance of the EAOP process for Ni-EDTA degradation
and TOC removal is optimized
Removal of Trace Uranium from Groundwaters Using Membrane Capacitive Deionization Desalination for Potable Supply in Remote Communities: Bench, Pilot, and Field Scale Investigations
The performance of membrane capacitive deionization (MCDI)
desalination
was investigated at bench, pilot, and field scales for the removal
of uranium from groundwater. It was found that up to 98.9% of the
uranium can be removed using MCDI from a groundwater source containing
50 μg/L uranium, with the majority (94.5%) being retained on
the anode. Uranium was found to physiochemically adsorb to the electrode
without the application of a potential by displacing chloride ions,
with 16.6% uranium removal at the bench scale via this non-electrochemical
process. This displacement of chloride did not occur during the MCDI
adsorption phase with the adsorption of all ions remaining constant
during a time series analysis on the pilot unit. For the scenarios
tested on the pilot unit, the flowrate of the product water ranged
from 0.15 to 0.23 m3/h, electrode energy consumption from
0.28 to 0.51 kW h/m3, and water recovery from 69 to 86%.
A portion (13–53% on the pilot unit) of the uranium was found
to remain on the electrodes after the brine discharge phase with conventional
cleaning techniques unable to release this retained uranium. MCDI
was found to be a suitable means to remove uranium from groundwater
systems though with the need to manage the accumulation of uranium
on the electrodes over time