Chemical Engineering January 2023 - 6

This hydrovoltaic effect occurs
at the interface of water
and polarizable materials,
due to the presence of an
electric double layer at the
solid-liquid interface.
In an effort to capitalize on
this phenomenon, scientists
at KTH Royal Institute
of Technology (Stockholm,
Sweden; www.kth.se) have
refined wood samples to
increase the amount of
bioelectricity sufficiently to
be " harvested " into useful
power. As described in a
recent issue of Advanced
Functional Materials, the
scientists used a one-step
chemical process to nanoengineer
the wood. This was
done by immersing wood
into an aqueous sodium hydroxide
solution for several
days at -6°C. The treated
wood was shown to have a
microporous structure with
nanoporous cellulosic networks
within the lumen.
" We have compared the
porous structure in regular
wood with the material
we have improved with
regard to surface, porosity,
surface charge and
water transportation. We
have measured electricity
generation that's ten
times higher than natural
wood, " says Yuanyuan Li,
associate professor at the
KTH Division of Biocomposites.
She adds that further
tuning the pH difference
between wood and water,
due to an ion concentration
gradient, achieves a
potential of up to 1 V and a
power output of 1.35 µW/
cm2 - enough to run an
LED or calculator. To power
a laptop computer would
require about 1 m2 of wood
(1-cm2 thick) and about
2 L of water, she says.
TOUGH ALLOY
Scientists have measured
the highest toughness ever
recorded - of any material
- while investigating a
metallic alloy made of chromium,
cobalt and nickel (CrCoNi).
Not only is the metal
extremely ductile (highly
malleable) and strong (resists
permanent deformation),
its strength and ductil(Continues
on p. 9)
6
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
JANUARY 2023
Hydrogen-enabled recovery of raw materials
from 'red mud' and other metallurgical waste
B
auxite residue (red mud) is a byproduct
from the smelting of aluminum.
Like other waste slags
from
the
metallurgy
industry,
bauxite residue is traditionally put into hazardous-waste
landfills, although it contains
a mixture of valuable raw materials in low
concentrations. A new process is being
developed in a four-year, European project,
called HARARE (Hydrogen As the Reducing
Agent in the REcovery of metals and
minerals from metallurgical waste), which
began in June 2021.
Led by Sintef (Trondheim, Norway; www.
sintef.no), with nine industry and research
partners from four European countries, the
four-year HARARE project aims to recover
copper and aluminum, as well as iron, cobalt,
scandium and other critical metals
from copper slag and bauxite residue (diagram),
without generating CO2 emissions
in doing so.
Conventional aluminum smelting processes
generate about twice as much
red mud as Al metal, and copper smelting
generates about 2.2 metric tons of slag for
every kilogram of Cu metal produced. Although
metallurgical slags contain mineral
and metal residues, these have only low
concentrations of the metals and minerals
of interest, which makes them difficult to recover
economically. For example, slag that
contains less than 1% copper will normally
be regarded as waste and dumped. Other
rare and valuable metals and minerals occur
in even smaller concentrations.
Iron oxide is the main component in both
the slag from flash smelting of copper and
the bauxite residue from alumina production
in the Bayer process. In the Harare
concept, the iron oxide is reduced with hydrogen
(instead of carbon) at high temperatures,
thus avoiding the release of CO2.
Once the iron is recovered, the copper, alumina
and other metals can be recovered
by metallurgical treatment. After metals are
recovered, the remaining residue could be
suitable for building materials.
SINTEF
Solvent-based regeneration of
granular activated carbon
G
ranular activated carbon (GAC)
can be used to remove polyfluoroalkyl
substances (PFAS) from
groundwater and drinking water,
but current methods to regenerate spent
GAC are costly and require high temperatures
of greater than 1,000°C. A team of
scientists at Battelle Memorial Institute
(Columbus, Ohio; www.battelle.org) has
developed a solvent-based method for
restoring PFAS-laden GAC that requires
much less energy and time than the conventional
method.
The Battelle researchers identified two
organic-alcohol solvents that were effective
for the GAC regeneration process
and developed a product, known as GAC
Renew, based on those solvents. To regenerate
the GAC at a water-treatment facility,
one treatment tank is taken offline while a
second tank allows GAC treatment to continue.
The regenerant solution is stored on
site and is cycled through the tank for the
number of bed volumes that best regenerate
the GAC, according to Battelle. The
number of bed volumes is determined during
laboratory column studies. After the
solution has regenerated the spent GAC,
potable water is passed through that tank
to rinse the GAC before putting it back online,
Battelle explains.
The GAC Renew process can reactivate
GAC at lower cost than heating the GAC,
and the PFAS-removal performance of the
solvent-regenerated GAC is better than virgin
GAC, even after four solvent-regeneration
cycles, Battelle says.
The spent regeneration solution can be
distilled for recycling and the concentrated
distillate treated on site with Battelle's
PFAS Annihilator Destruction Technology
(see Chem. Eng., March 2022, p. 8).
https://www.kth.se https://www.sintef.no https://www.battelle.org http://WWW.CHEMENGONLINE.COM
Chemical Engineering January 2023

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