Ferrates

[JamesW]

Has anyone heard about using ferrates for water treatment? This company seems to have some interesting technology. The patent claims that it can be used for treating swimming pool water.

The device of the present invention can be fitted to any swimming pool or Jacuzzi such that the ferrate produced by the device is mixed with the water in a mixing chamber, whereby all the organic waste is oxidized to innocuous products, the iron salts are filtered away, and the clean water is re-introduced into the pool. This represents a highly effective and cost-efficient method of cleaning the pool water, since ferrate produced by the methods of the present invention is less costly in the long run than purchasing the numerous oxidants and anti-fungal chemicals necessary to treat a pool.
http://patft.uspto.gov/netacgi/nph-Pars ... e+AND+daly

 

[JasonLion]

I can't imagine that it is as easy as they imply to filter out the ferrates. They are also greatly exaggerating the problems associated with "the numerous" chemicals currently required. It also suffers from the problem that it only treats the water passing through the pump and not the bulk pool water.

Overall, it looks like they only mentioned the pool applications as a "just in case" broadening of the patent, not because they had a practical system in mind. The focus of the patent is in other areas.

 

[teapot]

Generally the higher the state of reactivity the shorter the life span of the compound so ozone as we know has a very short lifespan so you don't alleviate the bulk water primary sanitiser problem.

"The regulatory fecal coliform limit of 200 CFU/100mL was easily achieved with a Ferrate dose of 2 ppm". So does chlorine and usually at a lower ppm!

"It disinfects and stabilizes biosolids to inhibit putrefaction, destroys odors, and adds iron as a vital micronutrient. Ferrate also helps bind phosphorus and nitrogen to the organic matter to create a “slow-release” fertilizer, which prolongs its availability, increases uptake in the root zone". So you've killed the bacteria but feed the algae. We already know that the algae part of what we do is the hardest part to conquer and responsible for the levels of chlorine we use.

There is no mention of the potential staining issue, probably not an issue in the ionised state but afterwards?

 

[JamesW]

I think that the iron would probably be a problem for many applications. I think that for a swimming pool, it would be a bad choice. Staining would probably be a problem.

Something about the way they are presenting the technology seems exaggerated and too-good-to-be-true. I think that they are downplaying the potential problems and limitations.

This is something I saw in Forbes yesterday. I had not previously heard about ferrates and I haven't had time to research it too much. It will be interesting to see if anyone begins selling swimming pool treatment or products based on this technology.

Reference 1 Reference 2 Reference 3

 

[chem geek]

Note the following from the patent:

In the absence of a more suitable reductant, ferrate will react with water to form ferric ion and molecular oxygen according to the following equation (J. Gump, W. Wagner, and E. Hart, Anal. Chem., Vol. 24., p. 1497-1498 (1952)). 4FeO₄^2- + 10H₂O --> 4Fe³⁺ + 20OH^- + 3O₂

This reaction is of particular interest to water treatment because it provides a suitable mechanism for self-removal of ferrate from solution. In all oxidation reactions, the final iron product is the non-toxic ferric ion which forms hydroxide oligomers. Eventually flocculation and settling occur which remove suspended particulate matter.

This makes it impractical in pools as the ferric ion that results can stain pool surfaces (as James noted). Note that the EPA Secondary Drinking Water Regulation standard for iron is 0.3 mg/L. It is unclear whether flocculation and settling would easily reduce ferric ion levels this low.