The History of Ferrate

Oxo compounds of iron (Ferrates) were first synthesized in 1715 in Germany, and since that time high valence (Fe⁴⁺ through Fe⁷⁺) oxo anions of iron (Ferrates) have been studied by chemists. Commercial utilization of these unusual compounds however, has been extremely limited, primarily because of the difficulty in synthesizing them and their inherent instability. The most stable of the Ferrates is Ferrate(VI), or FeO₄^2-. Because of the high valence of iron in these compounds they are strong oxidants, and because the residual from any chemical reaction is simply ferric iron (the most common element on earth) they should be commercially useful. In fact, given these unique properties, their use for treating water and wastewater to remove contaminants would seem like an obvious avenue to explore; but it was not until the 1970s that research in the laboratories of Dr. T.D. Waite (view bio) was started on the use of ferrates for environmental applications. Ferrate(VI) research continues today world-wide generating >2,000 scientific publications per year. As anticipated, Ferrate(VI) has been repeatedly demonstrated to be a powerful oxidant of environmental contaminants, and to rapidly decompose to ferric iron which quickly precipitates from the solution. Because the residual is non-toxic ferric iron, it can be safely land-applied for disposal or recycled. This would be considered a “Green” chemical today.

The various methods for synthesizing Ferrate(VI) were described in detail over 200 years ago. Basically, ferric iron (Fe³⁺) is oxidized to a high valence (Fe⁴⁺ to Fe⁶⁺) utilizing; heat, electric power, or an oxidizing chemical. All of these oxidation reactions must take place in a caustic environment, as the synthesized Ferrate is only stable at a high pH. The end product of all of these synthesis procedures is a Ferrate material mixed either with a caustic solution, or other chemicals utilized in the oxidation process. The cost of this Ferrate product is simply the cost of the chemicals or electricity utilized for the oxidation. For example, the unit cost of Ferrate(VI) in these mixtures is inexpensive if commercial feedstocks are utilized (currently around $5.00 per lb. of Ferrate(VI) produced, which translates to approximately $50.00 per million gallons treated at a dose of 1 mg/L FeO₄^2-). If a highly purified Ferrate(VI) product is desired however, the mix must be further processed to separate the Ferrate(VI) from the synthesis solution. This is a tedious (and therefore expensive) process increasing the unit cost of the Ferrate(VI) product by >15X. In summary, if a pure Ferrate(VI) product is required, the cost of it will be prohibitive for large scale environmental use, and cannot compete with other water and wastewater treatment chemicals for similar treatment. In addition, a pure Ferrate(VI) product (powder) is impossible to stabilize, handle, ship, store and apply as a commodity chemical. Essentially all of the research utilizing Ferrate(VI) to date has been done with small quantities of a laboratory-synthesized, pure Ferrate(VI) compound.

It became clear to Dr. Waite many years ago that a pure Ferrate(VI) powder could never be generated at a competitive cost for use in large-scale environmental applications. However, it was possible that the inexpensive Ferrate(VI) solution generated without further purification could be utilized and would be competitive in price, thereby providing a commercial supply of Ferrate(VI) to the environmental market. However, because of the instability of any Ferrate product, it would need to be produced near-by or central to the site of its application. After years of research and development Dr. Waite perfected Ferrate(VI) blends, produced with inexpensive chemical feedstocks, along with support unit operations that could utilize liquid Ferrate(VI) products. For the past eight years Dr. Waite has worked on treating all types of water and wastewater using these unique Ferrate(VI) solutions.