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New technique removes even trace amounts of heavy metals from water

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December 28, 2011

A new process has been developed for removing trace amounts of heavy metals from water (Ph...

A new process has been developed for removing trace amounts of heavy metals from water (Photo: Luis nunes alberto)

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Once released into the environment from industrial sources, trace amounts of heavy metals can remain present in waterways for decades or even centuries, in concentrations that are still high enough to pose a health risk. While processes do exist for removing larger amounts of heavy metals from water, these do not work on smaller quantities. Now, however, scientists from Rhode Island's Brown University have combined two existing methods, to create a new one that removes even trace amounts of heavy metal from water.

Known as the cyclic electrowinning/precipitation (CEP) system, the process involves increasing the concentration of heavy metals in water samples, until it's high enough to be effectively removed.

Things get started when metal-tainted water is fed into a tank, and an acid or base (such as sodium hydroxide) is added to change the water's pH value. This causes the water molecules to separate from the heavy metal precipitate, which settles to the bottom of the tank. The clean water is then siphoned off, more tainted water is introduced, and its metal content joins that already lying at the bottom. The process is repeated a number of times.

Although this technique alone holds promise, the settled precipitate forms into a toxic sludge, which is difficult to safely dispose of. That's where part two of CEP comes into play.

Once the sludge in the first tank has reached a high enough heavy metal concentration, it is pumped into a second device called a spouted particulate electrode. There, it is subjected to a process called electrowinning, in which an electrical current is used to transform the metal ions into a stable, solid, and thus easily-removed state. The water left over is then returned to the first tank, where most of the remaining metal content is settled out. That water then goes to another reservoir, where other processes are employed to further remove heavy metal ions.

A diagram of the CEP system

In tests of the system, trace amounts of heavy metals such as cadmium, copper, and nickel were removed from tainted water samples, to the point that the water ended up near or below the Environmental Protection Agency's maximum contaminant levels. Project leader Prof. Joseph Calo says that CEP could also be used to remove metals including lead, mercury, and tin.

A paper on the Brown University research was recently published in the Chemical Engineering Journal.

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away.   All articles by Ben Coxworth
8 Comments

This is not new technology by any means. The settling out of metals by altering the PH and floculation of the waste water is used every day by plating and other metal finishing facilities. The Second process referred to as electrowinning has been used by precious metal platers for many years to recover gold, silver, etc. from rinse waters on plating lines. They were no more that a series of metal plates set very close together and an electrical potential placed between them to "plate" out the trace precious metals for recovery. They may have altered the anode and cathode configuration but the process is the same. The process is slow and not cost effective unless one is dealing with gold, silver, or other precious metal. Impressed....NOT.

86goldwing
29th December, 2011 @ 10:35 am PST

"...scientists from Rhode Island's Brown University have combined two existing methods..."

Combined. Two. Existing. Methods.

William H Lanteigne
29th December, 2011 @ 05:08 pm PST

"If you're not part of the solution, you're part of the precipitate." ;)

Gregg Eshelman
29th December, 2011 @ 10:09 pm PST

@Gregg Eshelman: You one funny guy! LOL!

Back to topic: Wouldn't be more effective NOT to allow such contamination? While it is a good thing, certainly, allowing companies such as BP to dump mercury into the Great Lakes mitigates all of this. This is done by BP and many others under the guidance of the EPA. All legal. Behold the power of lobbying. Crazy ain't it?

Burnerjack
30th December, 2011 @ 07:34 am PST

@Burnerjack

:) Spot on. Could not have said it better..

rrust
30th December, 2011 @ 08:23 am PST

This work was a matter of concert for them, once there was a concern for this issue, then known methods were applied, no doubt both the techniques and even the application is not new, the fact is, after so many years, there was genuine concern.

Dawar Saify
30th December, 2011 @ 01:48 pm PST

Wow, they were way off in the description of the Electrowinning process. It is more accurately described as when Charlie Sheen listens to techno.

Blixdevil
30th December, 2011 @ 06:02 pm PST

Might there be a more cost effective solution for people living in such areas as the islands of Leyte and Luzon where higher incidence of dementia (ie: Parksinson's Disease) persist due to high concentrations of heavy metals (typically 'Manganese') in erstwhile 'potable' water supplies?

Larry
21st January, 2012 @ 08:40 pm PST
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