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Nanorust Used To Purify Water
eldavojohn writes "How do you remove arsenic from water? Well, a research team has discovered that adding and removing nanorust works well. From the article, 'The team added nanoscale iron oxide to contaminated water, where it clumped together with the arsenic. They then magnetized the nanoparticles with an electromagnet and pulled them out. "We only needed a surprisingly weak magnetic field," says Colvin. "In fact, we could pull then out with just a hand-held magnet, making this a very practical method.' Big news for developing nations that are plagued with non-potable drinking water."
In developing nations, the key is ensuring factories and agriculture do not dump their waste into the drinking supply (one of the big problems in India), that the sewage and drinking systems are separated, and that modern filtration units are used.
The main source of arsenic poisoning is and has always been from naturally-occurring sources in soil.
I remember when the international community paid millions of dollars to supply Bangladesh with wells to give them water. The problem was, the earth in that area is naturally rich in arsenic and it caused the single largest occurrence of arsenic poisoning in the history of man. Better than dying of thirst, I guess... or not.
Latewire
It's still not a particularly wonderful idea. The best way of handling this sort of process is use of a microporous material like zeolites, ion exchange resins and so on. You still get an extremely high specific surface area - zeolites typically have areas on the order of 50 m^2 / g, which is about 10x the area claimed for the nanorust. Ion exchange resins can get up to 500 m^2 per gm (100x the nanorust). These materials because of their size can be separated using physcal processes (less capital intensive) and regenerated for reuse. In some cases they can be used in flow through systems so separation is not needed.
"All hypotheses that the well water pollution is a natural source have been discounted over the past 5-10 years,"
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/in total/ yet give rise to exceptionally large groundwater arsenic concentrations. The high solid/solution ratio in aquifers and the great toxicity of arsenic mean that the contamination of groundwaters is sensitive to an imperceptible shift in the speciation of arsenic. A change of only a few percent in the partitioning of arsenic between sediment and water is sufficient to give rise to a significant groundwater arsenic problem."
Wrong.
Unless you've got a URL that disputes what this one says:
http://www.bgs.ac.uk/arsenic/bangladesh/reports.h
"13.1.4 Source of the arsenic
There is no doubt that the source of the As is natural, i.e., derived from 'ordinary' sediments by natural geochemical processes. The quantity of As present in groundwater (and adsorbed by the sediments) is simply too large to be derived from a discrete pollution source. Also its distribution across Bangladesh and West Bengal and with depth does not tally with a pollution source. There is also no need to postulate exceptional sources such as a particular mineralised area in the upstream catchment, as some workers have done for neighbouring West Bengal (Acharyya et al., 1999), although of course such areas may exist. This is one of the lessons that needs to be learned from the Bangladesh arsenic problem.
There is more than enough arsenic in most sediments to give rise to an As problem given the appropriate geochemical conditions for release and mobilisation. If all of the arsenic in a sediment containing 1mg As kg^-1 sediment dissolves in the groundwater, then the arsenic concentration would be 6000 micrograms/L or more, way above all drinking water standards. Both the average world and typical Bangladesh sediments contain several times this amount of arsenic. In other words, Bangladesh sediments do not appear to contain an exceptional amount of arsenic
So unless you've got some sort of documentation that trumps the British Geological Survey, I suggest you take a course in "rocks for jocks" (geology 101) instead of spewing your uninformed twaddle here.
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BMO