Chemical Engineering August 2023 - 15

New adsorbent removes radioactive
cesium ions from nuclear wastewater
O
ne of the major byproducts
of the nuclear fission process
used for power generation is
137Cs, a radioactive isotope
of Cs that has a half-life of 30 years
and is often removed from nuclearpower-plant
wastewater
via
selective
adsorption using ion exchangers.
However, this process is severely
hindered in acidic wastewater where
excess protons impair the adsorption
ability and damage the lattice structure
of the adsorbent.
Now, researchers from Pusan National
University (Busan, South Korea,
www.pusan.ac.kr) found a way to turn
this adversity into an advantage. In
their work, to be published in the August
issue of the Journal of Hazardous
Materials, they introduce potassium
calcium thiostannate (KCaSnS), a new
layered Ca2+-doped chalcogenide ion
exchanger. It utilizes the typically problematic
H+ ions in acidic wastewater
to enhance the adsorption of Cs+. Essentially,
the Ca2+ ions from KCaSnS
are leached out by H+ and Cs+ ions,
making way for Cs+ ions.
" Through a transformative approach,
the troublesome proton was converted
into a functional agent by incorporating
Ca2+ into the Sn-S matrix, resulting in a
metastable structure. Moreover, Ca2+ is
a harder Lewis acid than Cs+ and can
thus leave the lattice easily because of
its weaker affinity to the Lewis soft base
S2- under acidic conditions. This provides
a large enough space for Cs+ to
reside after its release from the lattice
structure, " explains Kuk Cho, professor
at the Department of Civil and Environmental
Engineering.
In the study, the team used a hydrothermal
process to synthesize the
KCaSnS ion-exchange material, which
was then used to investigate the adsorption
of a non-radioactive isotope of
Cs+ (to avoid radioactivity exposure) in
different solutions with pH values ranging
from 1 to 13. The team found that
at pH 5.5, the Cs+ ion-adsorption capacity
was 370 mg/g, whereas at pH 2,
the capacity increased by 68% to 620
mg/g. Remarkably, this trend was completely
opposite to what previous studies
had established.
A biomimetic process to make
soft fibers for smart textiles
F
or intelligent textiles to function
effectively, they need to be
strong, stretchable and electrically
conductive. However, fabricating
fibers that possess these three
properties has been challenging.
Drawing inspiration from how spiders
spin silk to make webs, an international
team of researchers has developed a
method of producing soft fibers that
possess these three key properties. The
study - led by assistant professor Tan
Swee Ching from the Dept. of Materials
Science and Engineering under the
National University of Singapore (NUS;
www.nus.sg) College of Design and Engineering
- was reported in a recent
issue of Nature Electronics.
Conventional spinning methods to
fabricate synthetic fibers require high
pressure, high energy input, large volumes
of chemicals, and specialized
equipment. Moreover, the resulting fibers
typically have limited functions. In
contrast, the spider-silk-spinning process
forms strong and versatile fibers
at room temperature and pressure.
Two unique steps in spider-silk formation
were identified that the team could
mimic. The first is the change of a highly
concentrated protein solution (silk dope)
into a strand of fiber. The second step
identified was that the arrangement of
proteins within the dope changes when
triggered by external factors to help
separate the liquid portion from the silk
dope, leaving the solid silk fibers. The
team recreated the two steps and developed
a new spinning process known
as the phase separation-enabled ambient
(PSEA) spinning approach.
The soft fibers were spun from a viscous
gel solution comprised of polyacrylonitrile
(PAN) and silver ions (PANSion)
dissolved in dimethylformamide.
When the gel is pulled and spun under
ambient conditions, the soft fiber forms.
When exposed to air, water molecules
in the air cause the liquid portion of the
gel to separate from the solid portion of
the gel - a phenomenon known as the
nonsolvent vapor-induced phase-separation
effect. The droplets are simply
removed by gravity.
n
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
AUGUST 2023
solar process heat beyond 1,500°C,
enabling the decarbonization of industrial
processes and the production
of sustainable fuels. For this project,
Synhelion and UF will jointly develop
a solar reactor powered by high-temperature
solar-thermal energy to produce
H2 gas from water and sunlight.
The H2 produced can then be stored,
transported, and utilized on demand,
for example in transportation sectors
that are focused on decarbonizing
their industries. The project team will
work to improve the efficiency and
cost of solar thermochemical H2 production
by taking advantage of new
redox materials that enable the chemical
reactions in the reactor.
CARNOT BATTERIES
Carnot batteries, which temporarily
store electricity as heat, are a promising
technology for storing electricity
generated by the sun and wind, without
having to rely on the increasingly
" precious " supplies of lithium used
in Li-ion batteries. A Carnot battery
consists of three components connected
in series: a high-temperature
heat pump, a heat-storage unit and
a heat engine. The heat pump converts
the electricity generated by
sun and wind (but not immediately
required) into heat, which is used to
charge the storage unit. When the
electricity demand increases, the
heat engine discharges the storage
unit, thereby converting the heat
back into electricity.
Last month, a new project was
launched to optimize working fluids
used by Carnot batteries. The
three-year, €298,000 project is being
funded as part of the DFG Priority Program,
and led by the Chair of Technical
Thermodynamics and Transport
Processes (LTTT) in the Center of
Energy Technology (ZET) at the University
of Bayreuth (Germany; www.
uni-bayreuth.de).
" Initial demonstration plants show
that high round-trip efficiency can be
achieved with Carnot batteries: Up
to 70% of the excess electricity fed
into the grid from renewable energy
sources can ultimately be recovered, "
explains Florian Heberle, research associate
at the LTTT research group and
managing director of the ZET. " The
storage costs per kilowatt hour are in
the range of pumped-storage power
plants or electrochemical batteries. "
The investigations will focus on
special mixtures of natural hydrocarbons
and unsaturated partially
halogenated refrigerants. The aim is
to precisely identify thermochemical
properties, but also to test the fluids
in practice.
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Chemical Engineering August 2023

Table of Contents for the Digital Edition of Chemical Engineering August 2023
