The Economist (2022-02-26) Riva

The Economist February 26th 2022 Science & technology 77

An American firm called EnergyX,
plans, however, to change that. Using a po-
lymer membrane developed by Benny
Freeman of the University of Texas at Aus-
tin the company intends, beginning later
this year, to filter lithium directly from
brine. Dr Freeman says the company’s pilot
plant, which will be able to fit into a stan-
dard shipping container, should be able to
handle millions of litres of brine a day.
Once the process is perfected, he reckons it
will be able to extract at least 90% of the
lithium within a brine.
Speaking at the aaasmeeting, Dr Free-
man explained that his inspiration was the
protein channels which control the flow of
metal ions in and out of biological cells. A
potassium channel, for example, is 10,000
times more permeable to potassium ions
than to those of sodium. Modern imaging
tools and supercomputers have revealed
the structure of these channels, permitting
them to be mimicked.
The upshot is a membrane pierced by
nanometre-sized pores made from rings of
carbon and oxygen atoms precisely ar-
ranged to let lithium ions through while
slowing the passage of others, such as so-
dium. To start with, these membranes will
enrich a brine’s lithium levels before it en-
ters the ponds. Eventually, they could re-
place the ponds by generating a pure and
concentrated solution of lithium hydrox-
ide suitable for immediate industrial use.
Another way to improve the efficiency
of ponds was also proposed at the meeting,
by Seth Darling of Argonne National Lab-
oratory, in Illinois. The actual evaporating
is done mainly by heat delivered as sun-
light. But much of this is wasted. Either it
warms water below a pond’s surface—
which, not being in contact with the air, is
thus unavailable for evaporation—or it is
re-radiated before it has had a chance to
liberate any water molecules.
Dr Darling worked out that covering a
pond with a material that converts light to
heat quickly would stop these unfortunate
losses by concentrating the warming effect
at the pond’s surface, thus promoting
evaporation. As long as that material was
also porous, it would then let the resulting
water vapour through and out into the air,
to be blown away. His first try was Chinese
calligraphy ink which, being viscous and a
light-absorbing black, worked well—ex-
cept that eventually (as ink does) it dis-
solved in the water. Now, though, he pref-
ers charcoal, which also has the green bo-
nus of being made from farm waste.
Dr Darling says the result is a process
that can convert incident sunlight into
heat at the water’s surface with near 100%
efficiency. Besides improving lithium ex-
traction, that could also help industries,
such as fracking and mining, that tend to
accumulate large ponds of waste water as a
by-product of their activities. It could be

usedaswellasalow-costwaytoturnsea-

waterintofresh,bycapturingthewaterva-

pourasitevaporated.

Moreover,ifDrFreeman’sandDrDar-

ling’sideascangetridoftheneedtouse

vastevaporationponds,thatwouldopen

upnewsourcesoflithium.TheSaltonSea,

a lakeinsouthernCalifornia,contains

hugequantitiesofthestuff,andinTexasa

lotofgroundwaterreleasedasaside-effect

ofoilproductionisrichinit.Unfortunate-

ly,neitheroftheseplaceshasthevastacre-

agesofotherwisevaluelesslandrequired

for thesortsofinefficientevaporation

pondsusedinSouthAmerica.Shrinking

thesizesofthoseponds,orevengettingrid

ofthemaltogether,wouldchangethat.

Tomorrow’sbatteriestoday

Thepsychologyofjustice

First impressions

T

he “satanic panic” that swept

through America in the 1980s and 1990s

held that thousands of ordinary people up

and down the country were secretly mem-

bers of devil-worshipping cults which

were abusing, raping and murdering chil-

dren on an industrial scale. Alleged victims

made detailed allegations, often after ther-

apy designed to “recover” memories that

had supposedly been buried in the after-

math of trauma. Many people went to pri-

son. None of it was true.

One after-effect of the panic was to ce-

ment in the minds of both the public and

the justice system the idea that eyewitness

testimony is unreliable. That fitted with

experiments by psychologists such as Eliz-

abeth Loftus, which demonstrated just

how malleable memories can be. The Inno-

cence Project, an American charity, exam-

ined 375 cases of wrongful conviction for

all sorts of crimes, and found misidentifi-

cation of suspects by witnesses was a fac-

tor in around 70% of them.

But at the annual meeting of the Amer-

ican Association for the Advancement of

Science, John Wixted, a psychologist at the

University of California, San Diego, argued

that this institutional distrust has gone too

far. Eyewitness memories, he said, can in

fact be very reliable—if they are tested in

the right circumstances.

The key to reliability, said Dr Wixted, is

the confidence of witnesses in their as-

sessments. Experiments suggest that

when witnesses to a simulated crime are

confident of having identified the suspect

in a later photo line-up, they are almost al-

ways correct. Similarly, if they are sure the

suspect is not present, that is likely to be

right too. Only when a witness is unsure

does a risk of misidentification arise. A

field study conducted in 2016 by Houston’s

police came to similar conclusions.

The problem is that this confidence is

trustworthy only the first time the ques-

tion is asked. One of the unavoidable frus-

trations of quantum mechanics is that

measuring a particle’s position or energy

irretrievably alters it. Something similar,

said Dr Wixted, happens with memories.

The very act of testing them contaminates

every other test that comes after. Assessing

people’s faces for a possible match, for ex-

ample, lodges them in a witness’s memory.

Once that has happened, anything from

police encouragement to the high-pres-

sure environment of a courtroom can twist

subsequent attempts at recollection.

Dr Wixted drew a comparison with evi-

dence such as dnasamples. Improper han-

dling can contaminate these. That does not

mean dnatests are inherently unreliable,

but it does mean the technology must be

used carefully. The same, he says, is true of

witnesses. The answer, as he and Dr Loftus

argue in a recently published paper, is to

test a witness’s memory as fairly as possi-

ble, and—crucially—to do so only once.

Decades after the Satanic panic, the

matter remains important. Dr Wixted cited

the case of Charles Don Flores, a prisoner

awaiting execution for a murder commit-

ted in 1998. Initially, when shown a line-up

that included Mr Flores, a crucial witness

said none of the people matched her recol-

lection. (She had recalled a white man with

long hair. Mr Flores is of Latin American

extraction, and had short hair then.) By the

time the case came to trial a year later, she

had changed her mind, and Mr Flores was

convicted. His appeal on the basis of the

witness’s change of mind has been denied.

Dr Wixted, however,suggests she was like-

ly to have beenrightthe first time and

wrong the second.

Eyewitness evidence can be more

reliable than thought