Science and Technology Water purification Any old iron?
科技 水的净化 有废铁吗？
A little-known chemical may provide a new way to clean water
IRON in water is normally regarded a pollutant.
Luke Daly, the boss of Ferrate Treatment Technologies of Orlando, Florida, however, plans to turn that thought on its head.
He intends to use a chemically unusual form of iron to clean water up, not make it dirty.
Iron is found in the part of the periodic table known as the transition metals.
Like all metals, these react with other elements by giving up electrons to form positively charged ions.
Transition metals, though, give up different numbers of electrons in different circumstances, and thus have ions of various charges.
Usually, iron loses two or three electrons. But in ferrates, which are compounds of iron and oxygen with non-transition metals like sodium and calcium, it loses six.
That makes ferrates extremely reactive, and it is this reactivity which Mr Daly hopes to exploit.
First, ferrates are strong oxidising agents.
That means they destroy bacteria and viruses, and break up organic molecules with alacrity.
Second, they are coagulants and flocculating agents. They attract other chemicals in the water, including dissolved metals, and precipitate them for easy removal.
Moreover, once it has done its job, the iron in ferrates precipitates too, as iron oxide, leaving pure water behind.
The reason these wonder materials have not been used as water purifiers before is that their reactivity makes them unstable and thus difficult to store.
Thomas Waite of the Florida Institute of Technology, an academic scientist on whose work the company has drawn, jokes that in the early days of his research he kept the whole world's supply of ferrates in a cabinet in his laboratory.
Ferrate Treatment Technologies' trick is to make ferrates on site, for instant use, rather than attempting to transport them to where they are needed.
The firm's "Ferrator" uses three cheap raw materials—bleach, ferric chloride and caustic soda—to produce sodium and calcium ferrate at a price competitive, in terms of oxidising power, with more familiar water-cleaners like chlorine and ozone.
A machine small enough to be carried around in a pickup truck, Mr Daly claims, could generate enough ferrates to purify 75m litres (20m American gallons) of water a day.
The system is now being tested at two plants in Florida.
If all goes well, the first commercial Ferrators will be up and running later this year.