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Author: Subject: Million dollar chemistry question!
Pommie
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shocked.gif posted on 14-2-2005 at 20:36
Million dollar chemistry question!


A million dollars is on offer for anyone who can develop a cheap, easy-to-use and sustainable way to remove arsenic from drinking water in developing countries. Arsenic contamination has affected millions of people, largely in Bangladesh, after wells dug to provide clean water turned out to have tapped water laden with arsenic from deep mineral deposits.

From New Scientist Article

Anyone any ideas?

Mike.
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BromicAcid
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[*] posted on 14-2-2005 at 20:52


I heard on television a few months ago that there was a new procedure to do this, that was cheap and effecitve, apparently not cheap or effective enough though. They took iron turnings and added them to water, stirred for a few minutes, then filtered though sand. Supposedly it make the water clean enough to pass acceptible arsenic levels in the states.

After looking up some information it appears that iron oxide and sand work together to remove nearly all the arsenic but also remove dissolved phosphate. How much cheaper do they want then rust and sand? There is one hangup though, the arsenic absorbed by the sand and iron oxide can be leeched out again if left in contact with the enviorment for long periods of time, so unless it is removed from the site it is only a temporary solution.




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chloric1
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smile.gif posted on 15-2-2005 at 03:48
Hmmm


Thats really cool Bromic, its sounds very simular to clarifying water with alum. THe iron oxide snad maybe a cool filtering trick to try on other contaminants. Especially those lower on the electromotive force than iron.



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Mr. Wizard
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[*] posted on 15-2-2005 at 07:42


Maybe hydrogen generated by electrolysis, or Zn, or active metal couples to make Arsine which is then burned to test for an arsenic mirror. This would be an version of the "Marsh Test"
http://www.encyclopedia.com/html/M/Marshtes.asp




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chloric1
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[*] posted on 15-2-2005 at 15:51


Quote:
Originally posted by Mr. Wizard
Maybe hydrogen generated by electrolysis, or Zn, or active metal couples to make Arsine which is then burned to test for an arsenic mirror. This would be an version of the "Marsh Test"
http://www.encyclopedia.com/html/M/Marshtes.asp


Nope sorry! That is way too dangerous on a large scale! You could bet some worker would inadvertantly cause a leak in the arsine line and kill hundreds of civilians much like the release of methyl isocyanate in India in 1984




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Mr. Wizard
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[*] posted on 24-2-2005 at 09:01


"Nope sorry! That is way too dangerous on a large scale! You could bet some worker would inadvertantly cause a leak in the arsine line and kill hundreds of civilians much like the release of methyl isocyanate in India in 1984 "

Oh well, let them just keep drinking the water then. If they are in danger of a 'leaking arsine line' maybe chemistry is just too complicated for them. We should shut off electricity in the region too, as someone might get a shock. Let's stop fuel sales too, as they might burn themselves or suffer carbon monoxide poisoning.

It might be too expensive, but it is certainly not too dangerous.:P




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uber luminal
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[*] posted on 25-2-2005 at 00:03


ok, so we build a giant Liver...


... since our bodies are pretty good at filtering out arsenic and other nasty things.
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darkflame89
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[*] posted on 25-2-2005 at 03:53


No, the liver ain't that good at filtering toxic stuff. At tiny levels of such stuff, the liver puts up with it, but too much such stuff, no matter how big your liver is, is not going to save you.

Take for example, alcohol. Too much alcohol is bad for our liver. So don't drink too much...:D




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JohnWW
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[*] posted on 25-2-2005 at 20:41


It depends on the form in which the arsenic is present. It would have to be in some water-soluble form, which suggests alkali metal arsenates or arsenites. In that case, passing it through a column packed with beads of some sort of ion-exchange resin may be appropriate.
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sparkgap
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[*] posted on 26-2-2005 at 00:24


Look at this:

http://www.bayer-ls.com/ls/lswebcms.nsf/id/637124CB0B5DB7614...

Apparently, there's more to iron oxides than thermite making...

sparky (^_^)

P.S. I guess every criterion mentioned by Pommie is satisfied, except "cheap". :D Then again, Bayer, IMHO, would have no use for the $1M award, as they earn much more than that.




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JohnWW
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[*] posted on 26-2-2005 at 01:40


If it is present as Na/K arsenate or arsenite, another possible treatment (ion exchange resin being fairly expensive for the volume of water required to be treated) would be precipitation as an insoluble arsenate or arsenite, such as by adding a calcium or magnesium salt. If the water is also highly acid, which is sometimes the case with groundwater especially if it is from areas where are sulfide minerals, the chemicals to use to both precipitate the arsenic and increase the pH would be either Ca(OH)2 or Mg(OH)2.

It would be better to precipitate the arsenic as Ca or Mg arsenate, which should be less soluble than the arsenites. Any arsenite present could be oxidized to arsenate by pre-treatment with chlorine, which is usual to disinfect water to be used for drinking; or, instead of Ca(OH)2 or Mg(OH)2 being used to precipitate the arsenate, "chloride of lime", mostly Ca(OCl)2, could be used to perform all three functions of disinfection, arsenate removal, and pH adjustment at once.
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