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(12) United States Patent (10) Patent No.: US 8.449,756 B2 Monzyk et al. (45) Date of Patent: May 28, 2013

(54) METHOD FOR PRODUCING FERRATE (V) (52) U.S. Cl. AND/OR (VI) USPC ...... 205/543; 205/548 (58) Field of Classification Search (75) Inventors: Bruce F. Monzyk, Town Creek, AL USPC ...... 205/543, 548 (US); James K. Rose, Millersport, OH See application file for complete search history. (US); Eric C. Burckle, Dublin, OH (US); Andrew D. SmeltZ, West (56) References Cited Lafayette, IN (US); Dennis G. Rider, Baltimore, OH (US); Chad M. Cucksey, U.S. PATENT DOCUMENTS

Clark, Lancaster, OH (US) 3,904,421 A 9, 1975 Shimizu et al. (73) Assignee: Battelle Memorial Institute, Columbus, (Continued) OH (US) FOREIGN PATENT DOCUMENTS CN 1524,595 9, 2004 (*) Notice: Subject to any disclaimer, the term of this DE S53004 5, 1943 patent is extended or adjusted under 35 (Continued) U.S.C. 154(b) by 1377 days. OTHER PUBLICATIONS (21) Appl. No.: 10/597,106 Bouzek et al., Influence of Electrolyte Hydrodynamics on Current (22) PCT Filed: Jan. 18, 2005 Yield in Ferrate (VI)Production by Anodic Dissolution, Collect. 9 Czech. Chem. Commun. (vol. 65) 2000 (no month) pp. 133-140.* (86). PCT No.: PCT/US2OOS/OO1402 (Continued) S371 (c)(1), (2), (4) Date: Nov. 6, 2008 Primary Examiner — Arun SPhasge (74) Attorney, Agent, or Firm —Yimei C. Hammond; (87) PCT Pub. No.: WO2005/06.9892 Kremblas & Foster

(65) Prior Publication Data An undivided electrochemical cell. The electrochemical cell includes a housing defining an undivided chamber, the hous US 2009/0205973 A1 Aug. 20, 2009 ing having one electrolyte inlet and at least two electrolyte O O outlets; an anode in the chamber; a cathode in the chamber; Related U.S. Application Data and an electrolyte in the chamber, wherein the anode and the (60) Provisional application No. 60/537,115, filed on Jan. cathode are not gas diffusion electrodes. The invention also 16, 2004. involves a method of operating an electrochemical cell, and methods for making ferrate(VI). (51) Int. Cl. C25B I/00 (2006.01) 30 Claims, 31 Drawing Sheets

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U.S. PATENT DOCUMENTS Bouzek, K., Lipovska, M. Schmidt, M. Rousar, I., Wragg, A.A.: 4,156,613 A 5, 1979 Hund “Electrochemical Production of Ferrate(VI) Using Sinusoidal Alter 4,225,352 A 9, 1980 Makino et al. nating Current Superimposed on Direct Current: Grey and White 4,243,494. A 1/1981 Riggs, Jr. et al. Cast Iron Electrodes'. Electrochimica Acta, vol. 44 (1998) pp. 547 4,256,551 A 3, 1981 Cliff et al. 557. 4,606,843. A 8, 1986 Kaczur Bouzek, K. Rousar, I.: “The Study of Electrochemical Preparation of 4,705,726 A 11, 1987 Shindou et al. Ferrate(VI) Using Alternating Current Superimposed on the Direct 5,284.642 A 2f1994 Evrard et al. Current Frequency Dependence of Current Yields'. Electrochimica 5,416,150 A 5, 1995 Boeck Acta, vol. 38, No. 13, 1993, pp. 1717-1720. 5,607,504 A 3, 1997 Schmid et al. 6,080.288 A 6, 2000 Schwartz et al. Bouzek, K., Flower, L. Rousar, I., Wragg, A.A.: “Electrochemical 6,267,896 B1 7/2001 Patterson et al. Production of Ferrate(VI) Using Sinusoidal Alternating Current 6,471,788 B1 10/2002 Minevski et al. Superimposed on Direct Current. Pure Iron Electrode'. Journal of 6,566,574 B1 5, 2003 Tadros et al. Applied Electrochemistry, vol. 29, 1999, pp. 569-576. 6,576,346 B1 6, 2003 Ravenscroft et al. Dean, John A. “Lange's Handbook of Chemistry”. 15th edition, 6,723,890 B2 4/2004 Tucker et al. 1999, McGraw-Hill, New York, 8.104-8. 111. 6,790,429 B2 * 9/2004 Ciampi ...... 423,594.1 Delaude et al.: “A Novel Oxidizing Reagent Based on Potassium 6,837.984 B2 1/2005 Wang et al. Ferrate(VI)”. Journal of Organic Chemistry, vol. 61, 1996, pp. 6360 6,899,769 B2 5, 2005 Ravenscroft et al. 6370. 6,899,956 B2 5, 2005 Block et al. Grube, Von G., Gmelin, H.: “Effects of Superimposed Alternating 6,946,078 B2 * 9/2005 Minevski et al...... 210,695 Current on Anode Ferrate Formation'. Zeitschrift fur Electrochemie, 7,045,024 B2 5, 2006 Minevski et al. 7,045,051 B2 5, 2006 Minevski et al. vol. 26, 1920, pp. 153-161. 7,291,217 B2 11/2007 Phelps et al. He, W., Wang, J., Yang, C., and Zhang, J.: “The Rapid Electrochemi 7,347,893 B2 3/2008 Low cal Preparation of Dissolved Ferrate(VI): Effects of Various Operat 7,387,671 B2 6, 2008 Meisen et al. ing Parameters”. Electrochimica Acta, vol. 51, 2006, pp. 1067-1973. 7,387,672 B2 6, 2008 Friedrich Hirota, N.: “Anticorrosion Paints”. May 12, 1984, XP002569967, 7,410,536 B2 8, 2008 Friedrich et al. database accession No. 1972:476784. 7,422,793 B2 9/2008 Phelps et al. Hives, J., Benova, M., Bouzek, K., Sitek, J., Sharma, V.K.: “The 2002fOO98989 A1 7/2002 Heimann et al. Cyclic Voltammetric Study of Ferrate(VI) Formation in a Molten 2003/0042134 A1* 3/2003 Tremblay et al...... 204/228.1 Na/K hydroxide Mixture”. Electrochimica Acta, vol. 54, 2008, pp. 2003/00552.45 A1 3/2003 Tseng et al. 203-208. 2003. O146169 A1 8/2003 Ciampiet al. Kim, K.S., Chang, Y. Bae, S.K. and Hahn, C.S.: "Selective Oxidation 2003. O159942 A1 8, 2003 Minevski et al. of Allylic and Benzylic Alcohols Using under 2004/O104377 A1 6/2004 Phelps et al. 2004/0216637 A1 11/2004 Buchheit et al. Phase-Transfer Catalysis Condition”. Synthesis, vol. 10, Oct. 1984, 2005/002281.0 A1 2/2005 Moore et al. pp. 866-868. XP002438865. 2005.0049157 A1 3/2005 MacDonald et al. Licht, Stuart, Naschitz, Vera, Wang, Baohui: “Rapid Chemical Syn 2005.0053543 A1 3/2005 Kneip et al. thesis of the Ferrate Super-Iron Fe (VI) Compound, 2005/O123743 A1 6, 2005 MartinaZZO BaFeO4”. Journal of Power Sources Online vol. 109, Jun. 15, 2002, 2005. O152828 A1 7/2005 Aga et al. pp. 67-70, XP002569968 DOI: doi:10.1016/S0378-7753 2006/0134.339 A1 6/2006 Wang et al. (02)0004 1-1 retrieved on Feb. 23, 2010). 2006,0162613 A1 7/2006 Rosenhahn et al. Macova, Z. Bouzek, K., Hives, J., Sharma, V.K., Terryn, R.J., Baum, 2008/0305341 A1 12/2008 Pieth et al. J.C.: “Research Progress in the Electrochemical Synthesis of Fer 2009, 0216060 A1 8/2009 Monzyk et al. rate(VI)”. Electrochimica Acta, vol. 54, 2009, pp. 2673-2683. 2011 OO17209 A1 1/2011 Monzyk et al. Sharma, Virender K., “Potassium Ferrate(VI): An Environmentally FOREIGN PATENT DOCUMENTS Friendly Oxidant'. Advances in Environmental Research 6 (2002) 143-156. EP 166825 1, 2002 Yang, W., Zhou, Y. Wang, H. and Bi, D.: “Studies on Influence of FR 2805162 8, 2001 JP 591 393.14 8, 1984 Various Experimental Conditions on Electrochemical Generation of JP 61053398 3, 1986 Ferrate(VI) in NaOH-KOH mixed Electrolyte”. Russian Journal of JP 62007596 1, 1987 Electrochemistry, vol. 45, No. 7, 2009, pp. 795-799. JP 62091225 4f1987 First Report mailed May 29, 2009, from Australian Intellectual Prop JP 622924.92 12/1987 erty Office, in an Australian patent No. 2005206927. WO O121856 3, 2001 Notice of Allowance mailed Jun. 4, 2010, from Australian Intellec WO O182896 11, 2001 tual Property Office, in an Australian patent No. 2005206927. WO 2006O15756 2, 2006 The First Office Action from The State Intellectual Property Office of WO 2007075.153 7/2007 the People's Republic of China mailed on Mar. 10, 2010, in the WO 2008112657 9, 2008 Chinese patent application No. 20058002471.5. WO 20091428.23 11, 2009 The Second Office Action from The State Intellectual Property Office WO 2010.045657 4/2010 of the People's Republic of China mailed on Nov. 4, 2010, in the OTHER PUBLICATIONS Chinese patent application No. 200580002471.5. First Office action mailedon Sep. 10, 2010, in a co-pending US patent Bouzek, K., et al. “Influence of Anode Material on Current Yields application publication No. 20090216060 published on Aug. 27. During Ferrate(VI) Production by Anodic Iron Dissolution Part I: 2009. Current Efficiency During Anodic Dissolution of Grey Cast Iron to Second Office action mailed on Jan. 12, 2011, in a co-pending US Ferrate(VI) in Concentrated Alkali Hydroxide Solutions”. Journal of patent application publication No. 20090216060 published on Aug. Applied Electrochemistry, vol. 26, 1996, pp. 919-923. 27, 2009. Written Opinion of the International Searching Authority for Inter Communication from the European Patent Office mailed on Apr. 11, national Application Publication No. WO2005/06.9892 (Application 2008, in a co-pending European Patent Application No. 05858701. No. PCT/US2005/001402), published on Aug. 4, 2005. 5-1218. Audette, R.J. Quail, J.W.: “Potassium, Rubidium, Cesium, and Communication from the European Patent Office mailed on Jun. 18. Barium Ferrates(VI). Preparations, Infrared Spectra, and Magnetic 2010, in a co-pending European Patent Application No. 05858701. Susceptibilities”. Inorganic Chemistry. Online), vol. 11, No. 8, Aug. 5-1218. 1972, XP002569971 DOI: 10.1021/ic501 14a.034 retrieved on Feb. Issuance Notice mailed on Nov. 16, 2010, in a co-pending European 23, 2010. Patent Application No. 05858701.5-1218. US 8,449,756 B2 Page 3

Written Opinion of the International Searching Authority for Inter Written Opinion of the International Searching Authority for Inter national Application Publication No. WO2007/075153 (Application national Application Publication No. WO2010/045657 (Application No. PCT/US2005/04714), published on Jul. 5, 2007. No. PCT/US2009/061204), published on Apr. 22, 2010. International Search Report for International Application Publication No. WO2007/075153 (Application No. PCT/US2005/04714), pub Written Opinion of the International Searching Authority for Inter lished on Jul. 5, 2007. national Application Publication No. WO2009/142823 (Application Written Opinion of the International Searching Authority for Inter No. PCT/US2009/038472), published on Nov. 26, 2009. national Application Publication No. WO2008/112657 (Application No. PCT/US2008/056446), published on Sep. 18, 2008. * cited by examiner U.S. Patent May 28, 2013 Sheet 1 of 31 US 8.449,756 B2

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| US 8,449,756 B2 1. 2 METHOD FOR PRODUCING FERRATE (V) Minevski describes a process that includes continuous fil AND/OR (VI) tration using methods including magnetic means. It describes the “ferrate' as being attracted to a magnetic Surface, i.e., a The present invention relates generally to electrochemical ferromagnetic material. However, ferrate(VI) is a paramag cells and more particularly to undivided electrochemical netic material (containing unpaired electrons) but not a fer cells, methods of operating undivided electrochemical cells, romagnetic material. Paramagnetic materials are not suffi and methods for making ferrate(VI) and for making certain ciently attracted to magnetic Surfaces to allow simple ferrate(VI) products. magnetic separations. Ferromagnetic particles (aligned mag Ferrate(VI) is a strong oxidizer and produces a water impu netic moments) are required for Such separation and they rity coagulant and precipitant in water. These properties make 10 exhibit an external ordered magnetic field that is attracted to ferrate(VI) useful for water decontamination and purification or repulsed by external magnetics depending on relative Such as industrial waste waters, farming process waters, sew direction of magnetic field alignment. Ferrate(VI) does not age treatment plants, and in the production of potable water have ferromagnetic particles and is not attracted to magnetic Supplies. It is also useful as battery materials, in chemicals 15 Surfaces. However, ferrate(VI) can contain loose ferromag production, for metal Surface corrosion control, Surface netic impurities (such as magnetite FesO4) which are mag decontamination and cleaning and many other industrial netic but are not strong oxidants or sufficiently water Soluble, applications. and are therefore of no value to the uses of ferrate(VI). Hiros The two basic methods of making ferrate(VI) in aqueous towski et al., “The Magnetic Susceptibility of Potassium Fer Solution are chemical and electrochemical. To date, only rate.” Journal of Chemical Physics, Vol. 18, No. 1, 105-107, chlorination chemical methods have shown utility in prepar 1950; Shinjo et al., Internal Magnetic Field at Fe in Hexava ing isolated useful solid forms of ferrate(VI), producing only lent States, J. Phys. Soc. Japan 26 (1969) 1547: Oosterhuis et a few grams at a time. Chemical methods involve contacting al., “Paramagnetic Hyperfine Interactions in an el Configu a ferric iron compound with an oxidizing material, usually ration of Fe,” Journal of Chemical Physics, Vol. 57, No. 10, hypochlorite, in an aqueous alkaline environment (wet route), 25 4304-4307, 1972; and Hoy et al., “Critical Slowing Down of or at high temperature (dry route). However, the use of Spin Fluctuations in K-FeCa. Journal of Magnetism and hypochlorites is undesirable because of difficulty in opera Magnetic Materials 15-18 (1980) 627-628, are incorporated tion, nonscaleability of the process, contamination of the herein by reference for the description of the paramagnetic product, large waste streams, production of chlorine gas character of ferrate(VI) and the existence of ferromagnetic byproducts and expensive raw materials. 30 impurities in ferrate(VI). Note that these magnetic impurities Electrochemical methods for producing reactive products are as particles that are physically separate from the ferrate or separations have typically utilized divided cells. In divided (VI) crystals, and these do not agglomerate together and cells, an ion-transfer polymer’s or ceramic frit membrane hence do not offer a means to recover both ferrate(VI) and the separates the liquids in the cell into anode and cathode cham magnetic particles together magnetically. Minevski's bers. For ferrate(VI) solution preparation, there is a sacrificial 35 description of magnetic separation Suggests that its process anode made of an iron containing material. The cathode can primarily produced magnetic iron compounds, such as mag be made of various materials including iron, carbon, nickel, netites rather than ferrate(VI) compounds. The authors of the carbon Steel, stainless steel, nickel plated iron, or combina invention described herein for ferrate(VI) compounds are tions thereof. Concentrated aqueous sodium hydroxide is nor also aware of the conditions for operating the electrochemical mally introduced into the bottom of the anode chamber and 40 cell to produce magnetic iron oxide products of the type removed from the top. Similarly, sodium hydroxide is intro described by Minevski, and these inventors also have duced into the bottom of the cathode chamber and removed invented means to avoid Such unwanted byproducts, and from the top. Electrical current, or just "current is applied these means are described herein. across the cell causing the anode to oxidize to water soluble The prior art teaches that while electrochemical processes ferrate(VI), which is carried off with the anolyte. 45 may be useful for laboratory scale production of ferrate(VI), Prior work on electrochemical cells Suggested that undi they are unsuitable for commercial scale production for sev vided cells were undesirable for making ferrate(VI) because eral reasons: 1). First, they can only be run for short periods of the electrolytic efficiency dropped off rapidly with operation time (a few hours) before the cell must be shut down and time, the ferrate(VI) is decomposed (chemically reduced) at cleaned 2) During ferrate(VI) production, some Fe(VI) the cathode, the ferrate so produced, decomposed quickly and 50 degrades to Fe(III), which is insoluble in hydroxide solutions. only dilute ferrate solutions could be prepared. A recent pub 3) The Fe(III) precipitates out of solution, coating the cell lished application, US 2003/0159942 A1 (Minevski), walls and, individed cells, plugs the pores of the membraneas describes a single chamber electrochemical cell that is said to well. 4) This fouling results in decreased current efficiency be useful for the production of ferrate salts for short periods. and ferrate production. In Such instances, the ferrate produc The cell has one electrolyte inlet and one electrolyte outleton 55 tion will decrease until it is less than ferrate decomposition. opposite ends of the chamber. The electrolyte is an aqueous Moreover, the use of membranes individed cells increases the hydroxide solution comprising one or more alkali metal cost dramatically for materials, labor, and more than triples hydroxides, one or more alkaline earth metal hydroxides, or the required electrical power. combinations. The hydroxide concentration is between about As a result of these problems, there is currently no regular 1 molar and about 30 molar. The molar ratio of KOH to NaOH 60 commercial Supply of even Small laboratory quantities of is up to about 5, and is preferably between about 1 and about compounds of ferrate(VI) using any synthetic or production 3. The cell can include an optional porous frit between the process method. anode and cathode. However, porous frits are brittle and sub Therefore, there is a need for a commercially feasible ject to dissolving in caustic, cracking, pluggage with iron method and apparatus for making ferrate(VI), and for an oxide Solids, and are thick which raises operational Voltages, 65 electrochemical cell which is simple, inexpensive, forms thereby increasing heat, power consumption, slowing pro insignificant amount of by-products, and is easy to operate, duction rates, and increasing cost. even at a large scale of production. US 8,449,756 B2 3 4 The present invention meets this need by providing an Another aspect of the invention is a method for making undivided electrochemical cell which is designed and oper ferrate(VI) which includes providing a housing defining an ated in a manner which avoids by-products, is highly energy undivided chamber, the housing having an electrolyte inlet, at efficient, Scaleable, and operates continuously. The undivided least one electrolyte outlets, an iron-containing anode in the electrochemical cell includes a housing defining an undivided 5 chamber, and a cathode in the chamber; introducing an elec chamber, the housing having one electrolyte inlet and at least trolyte solution into the chamber through the electrolyte inlet, one outlet, one located to gather electrolyte from the cathode the electrolyte solution comprising at least NaOH, wherein a side and one which gathers electrolyte from the anode side; an molar concentration of NaOH is greater than about 5; flowing anode in the chamber; a cathode in the chamber; and an electrolyte out the of outlet; applying a variable DC voltage electrolyte in the chamber, wherein the anode and the cathode 10 are not gas diffusion electrodes. The invention includes one, between the anode and the cathode of sufficient amplitude to or preferably a "stack', of such cells. form the ferrate(VI), the variable direct current voltage vary The electrochemical cell of the invention preferentially ing between a maximum Voltage and a minimum Voltage, the includes a fluid controller in fluid communication with the minimum applied Voltage, being 0 or greater. Typically the electrolyte outlets. Suitable fluid controllers include, but are 15 method may include the step of applying the variable DC not limited to flow restrictions, valves, bends in fluid flow voltage obtain a voltage level where ferrate active film direction, weirs having different heights, or constrictions in removal exceeds or equals net active film formation rate for a one or more of the exit lines. selected time period, said time period selected to substantially The electrochemical cell of the invention most preferably prevent excessive film growth. In other aspect of the invention includes a screen between the anode and the cathode. It can the minimum applied Voltage is greater than 0. not include a membrane. Membranes are cell inserts which In another aspect of the invention there is disclosed an physically separates the fluid around the cathode from the apparatus for an undivided electrochemical cell made up of a fluid around the anode, and adds significantly to the Voltage housing defining an undivided chamber, the housing having drop across the cell when compared with the same cell dimen one electrolyte inlet and at least two outlets; an anode in the sions and design without the membrane, for example by sev 25 chamber; a cathode in the chamber; and an electrolyte in the eral tenths of a volt, and even several volts, where the elec chamber, wherein the anode and the cathode are not gas trochemictry only requires at most a few (<4) volts. On the diffusion electrodes. other hand, screens provide an undivided cell in that they Still another aspect of this invention is the provision of a allow intermixing of anolyte and catholyte and do not show new, electrochemically active oxide of iron. this costly Voltage drop. Screens also allow the gassing and 30 FIG. 1A is a representative waveform for ferrate(VI) pro fluid mixing hydrodynamics to be different on each side of the duction. Applied waveform is a square wave at about 1 HZ SCC. with Vmax seet at 320 msec. and Vmin adjusted to 80 msec. Another aspect of the invention is a method of operating an using power control circuit of FIG.2. At these cell conditions, undivided electrochemical cell. The method includes provid Vmax is 2.32 V and Vmin is 1.2 V. Illustrates relationship ing a housing defining an undivided chamber, the housing 35 between power signal control parameters and electrochemi having at least one electrolyte inlet, and preferably at least cal reactions. two outlets, an anode in the chamber, and a cathode in the FIG. 1B is an oscilloscope meter display of waveforms chamber; introducing an electrolyte into the chamber through according to the present invention. the electrolyte inlet; and controlling an amount of electrolyte FIG. 2 is a schematic diagram of a controller, actually used and/or gas flowing out of the outlets so that Substantially more 40 in the examples herein, for controlling a power Supply for electrolyte flows past one electrode than the other. Preferably, providing appropriate varying DC for the invention. the chamber also contains the above-mentioned screen. Most FIG. 3 is a schematic diagram of a proposed version of a preferred is that the chamber also contains the screen and exit controller for controlling a power Supply for providing appro fluid controller. priate varying DC according to the invention. Another aspect of the invention is a method for making 45 FIG. 4 is a schematic diagram of one version of a controller ferrate(VI). The method includes providing an undivided (that uses a microprocessor) for controlling a power Supply electrochemical cell comprising an iron-containing anode, or for providing appropriate varying DC to the apparatus of the an inert anode with an iron containing electrolyte particulate invention. slurry, a cathode, and an electrolyte Solution, the electrolyte FIG. 5 is one embodiment of an electrochemical cell Solution comprising an aqueous solution of NaOH, or a mix 50 according to the present invention which illustrates electro ture of KOH and NaOH, wherein a molar concentration of lyte flow pattern around the electrodes, and replenishment NaOH is greater than about 5 and a molar ratio of KOH to pattern of electrolyte through the screen to the cathode. NaOH of less than 0.4, preferably less than 0.25, and most FIGS. 6A and 6B are perspective views of electrolyte over preferably less than 0.12; and applying a Voltage between the flows using weirs for an anode/spacer/cathode assembly. anode and the cathode to form the ferrate(VI) solutions and 55 FIG. 7 is a cutaway view of one embodiment of an elec compounds. trochemical cell according to the invention showing a typical Still another aspect of the invention is a method for making face of a hanging anode/cathode. ferrate(VI) which includes providing an electrochemical cell FIG. 8 is a cutaway side view of one embodiment of an comprising an iron-containing anode, a cathode, and an elec electrochemical cell showing a typical screen framed in the trolyte Solution, the electrolyte solution comprising at least 60 spacer. In some embodiments the Screen is not present, only one hydroxide; and applying a variable direct current Voltage its Support spacer. between the anode and the cathode to form the ferrate(VI), the FIG. 9 is a top view of a typical layout for anode/spacer/ variable direct current Voltage varying between a maximum cathode combinations. Spacer optionally holds a screen (not Voltage (Vmax) and a minimum Voltage (Vmin), the mini shown). mum Voltage being greater than 0, and the maximum Voltage 65 FIG. 10 is a face view of a typical anode/spacer/cathode being in the range 0.7-4.0 Volts, with current densities varying arrangement showing their relative sizes and positioning, between Vmax and Vmin in the range of 0.1-200 mA/cm. according to one aspect of the invention. US 8,449,756 B2 5 6 FIG. 11 is a side view of a typical anode, cathode, and application across the anode and cathode. The direct current screen layout according to yet another aspect of the invention. Voltage is typically applied so as to have a peak Voltage, It illustrates an end view of anodes slightly shorter than cath Vmax, and a minimum Voltage, Vimin. Vmin is above 0 Volts, odes to achieve better electrical field distribution. and is that Voltage required to Substantially avoid passivation FIG. 12A is a side view of a typical anode, cathode, and of the anode surface (as described in the detailed description screen layout according to another embodiment of the inven section). tion. Active Ferrate(VI) Producing Oxide Film: FIG.12B illustrates a centercutaway view of the apparatus While not wishing to be bound by theory, it is believed that of FIG. 12A the following anode Surface iron oxide reaction mechanism FIG. 12C illustrates the catholyte exit cell end panel with 10 ports for catholyte over flow. applies to understanding the invention of achieving continu FIG. 12D illustrates the anolyte exit cell end panel with ous and efficient electrochemical production of ferrate(VI) ports for anolyte over flow. compounds. Under conditions of the invention, an iron anode FIG. 13 is a side view of an “L” shaped flow deflector typically forms a uniformly red-orange colored, Smooth tex Spacers. 15 tured, non-flaking, non-crumbly, thin, “active' iron oxide FIG. 14A is a side view of the tank showing a typical surface layer as an intermediate in the formation of ferrate electrode stack for one embodiment. (VI). Formation and control of this active, unpassivated oxide FIG. 14B is a tip view of the bottom of the tank showing surface layer is unexpected and is believed to be formed by electrolyte feed to the tank. the reaction of Fe(0) to form certain FeC), “oxides of iron'. FIG. 15 is schematic showing electrode side and button Passivating oxide films of iron typically have formulas such Spacers. as Fe0OH,FeO, Fe(OH), and FeO. Color of such oxides FIG. 16 is a schematic diagram of a laboratory apparatus varies with particle and grain size, and/or degree of hydration typical of the invention. and wetness. The red-orange oxide film, indicative of an FIG.17 is a graph depicting the production offerrate where active ferrate(VI) producing Surface, appears to be a single or the ferrate (VI) concentration is on the left vertical scale in 25 combination of these oxides, or an entirely different formula. mM and the time in minutes is on the horizontal scale. Open The red-orange film is reactive as it only persists for a few squares represent measurements at the 785 nm peak and pone hours once isolated in room air, whereupon it changes to more triangles represent measurements at the 505 nm peak. conventional yellow-orange, black, and brown colors. Such FIG. 18 is a graph showing the results from the production Surface colors are also associated with iron anodes which do of ferrate(VI). The weight of the potassium ferrate produced 30 not produce ferrate(VI). An appropriate reactive composition is shown on the left vertical scale in grams; the time interval for the red-orange oxide film of the invention might reason in minutes is shown on the horizontal scale. Ferrate (VI) was ably containablend of hydrated Fe(III) and Fe(IV) oxides. It harvested at four intervals shown on the graph starting at is believed that the active film is not Fe(III) oxides alone, about) minutes, 1100 minutes, 2300 minutes and 3900 min especially FeOs, as such oxides are kinetically very inert and utes. The graph shows that harvesting greatly increased the 35 so slow to react (passivating), and not expected to make an rate of production of potassium ferrate. That is each time the effective reactive intermediate for efficient ferrate(VI) prepa product was removed by filtration or centrifugation, the pro ration. In fact, the red-orange active oxide film may be pri duction rate (increased slope of line) increased over that of the marily Fe(IV)-based (e.g. hydrated Fe'O(OH), or the average slope that is depicted by the long straight line. equivalent, thereby by-passing well-known and sluggish FIG. 19 is a schematic drawing of one typical embodiment 40 reacting Fe(III)-oxide films (see below for more detailed of the invention having three cathodes and two anodes. description). FIG. 20 is a schematic diagram of one embodiment of an Passivating Iron Oxide Film Barrier To Ferrate(Vi) Produc overall apparatus for production of ferrates. tion: Application of a filtered, very low ripple, (non variable) FIG. 21 is a graph depicting ferrate (VI) concentration, and DC voltage to an iron anode-based electrochemical cell with the production rate of ferrate(VI) versus time. 45 strong caustic soda electrolyte produces dilute ferrate(VI) FIG.22 is a graph depicting ferrate(VI) concentration, and coloration of the electrolyte in the first minutes, and then the production rate of ferrate(VI) versus time. ceases ferrate(VI) production. In this event, a orange-brown, FIG. 23 is a graph depicting the ferrate(VI) concentration, yellow and sometimes black Splotchy colored anode Surface Versus time for a continuous production run. is produced. The iron oxide formed in this case does not form FIG. 24 is a graph of ferrate(VI) visible absorption spec 50 ferrate(VI) and thickens with time. This iron oxide may be trum. The Y axis is Absorbance in absorbance units and the X referred to as a passivating layer, and appears to be composed axis is Wavelength in nanometers. of the Fe(III) oxides of the type or similar to FeCOH, Fe2O, FIG. 25 is a graph of total iron UV/visible absorption Fe(OH), and FeO). Sufficiently thick iron oxide passivat spectrum. The Yaxis is Absorbance in absorbance units. And ing layers can form in a few minutes and then always result in the X axis is Wavelength in nanometers. 55 no, or just a low concentration of ferrate(VI) production not FIG. 26 shows a typical embodiment for a bipolar electro useful for even lab-scale preparations. This passive layer chemical cell arrangement. appears to interfere with the desired ferrate(VI) reaction Broadly, the invention provides for apparatus for produc allowing these other oxides to form, which are unreactive, and ing oXometal ions e.g., ferrate(VI)) using an undivided elec hence become the final iron product. By increasing the volt trochemical cell. Typically, the electrochemical cell includes 60 age required to operate the cell only results in undesirable side a housing defining an undivided chamber, the housing having reactions to occur, Such as further buildup of passive oxide at least one electrolyte inlet and at least one outlet for gas layer thickness or gas generation, and then ferrate(VI) and/or electrolyte, or one gas and one liquid electrolyte out production ceases to occur. Accordingly, this need to clean lets; an anode in the chamber, a cathode in the chamber, and and restart such conventionally powered cells result in exor an electrolyte in the chamber, wherein the anode and the 65 bitant production delays, and increases ferrate(VI) produc cathode are not gas diffusion electrodes. There is a power tion inefficiencies enormously due to the need for many more Supply for generating a variable direct current and Voltage for cells to be operating, the large amount of labor required for US 8,449,756 B2 7 8 refurbishing pacified cells, and the lower average efficiency follows. The fast reactions, R1,R2, and R3 proceed rapidly at of conversion to Fe(VI) product. Voltages near Vmax via one and two electron transfers, to Electrochemical Equations Leading to Ferrate(VI) Forma produce an red-orange oxide film buildup on the anode Sur tion from Iron Metal Anode: face composed of Fe(III) and Fe(IV), a mixture of the two, While not wishing to be bound by theory, it is believed that and perhaps mostly Fe(IV), as insoluble oxides. The conver the following electrochemical reaction mechanism applies to sion of this insoluble film, containing Fe(III) and Fe(IV) understanding the invention of achieving continuous and effi oxides, into Fe(V) and Fe(VI) soluble oxoionic species is also cient electrochemical production of ferrate(VI) solutions and believed to occur continuously but at a slower rate than red compounds. The electrochemical and other related ferrate orange oxide film build-up. This slower rate is believed to be (VI) formation chemical reactions are typified and described 10 due to the molecular geometry change that is required to by the following. In a first reaction, associated with holding convert from octahedral complexes to tetrahedral complexes. the electrochemical cell, or just “cell” Voltage, Vcell, at a high To prevent the oxide film from thickening too much, and value, Vmax, iron anodes, Fe(0) is converted to several higher thereby eventually forming a passivating oxide film of e.g. oxidation species, including ferrate(VI), Fe(VI), by electro kinetically and thermodynamically inert, insoluble, Fe(III) lytic one and two “electron transfer reactions depicted as: oxides, soluble Fespecies must be allowed to form at a rate

Fe(0) -> Fe(II) -> Fe(III) -> Fe(IV) Fe(V) -> Fe(VI) fast fast fast slow fast

Reaction No.: R1 R2 R3 RS No. of electrons 2 1 1 1 1 TOTAL: 6 transferred: No. of 4s + 3d 8 6 4 3 2 electrons for the electronic configuration:

Vcell is the measured Voltage across a single electrochemi similar to Fe(0) dissolution so that the net effect is to maintain cal cell of the invention, at a particular point in time, and 30 a thin, active iron oxide film. This balance in chemical reac influenced by the applied Voltage, the electrochemical poten tion rates is accomplished in the invention in two steps; first tial of the cell, and any internal voltage drops. For example, at by adjusting the cell voltage, Vcell, to a value lower than high applied Voltages, Vcell is Vmax at low applied Voltages Vmax which is selected low enough to slow Fe(0) dissolution like 0.0, then Vcell varies from Vmax Vmin (curves C and D to a much slower rate, for example <5%, and preferably <2% of FIG. 1A). 35 of the dissolution rate of Fe(0) at Vmax (as measured by Fe(I) is not shown as it is believed not to exist to a signifi current density and current efficiency with respect to anode cant degree based on conventional iron chemistry in aqueous, weight loss rate), but which is selected still too positive to oxidizing environments. In addition, Fe(IV) may be produced allow large amounts of Fe(I) to form via reaction R1, as Fe(II) in a fast reaction from Fe(II) thereby bypassing possibly would react quickly with Fe(IV), Fe(V) and Fe(VI) species to slow reacting Fe(III) species, by a two-electron transfer, (see 40 form a passivating layer consisting of Fe(III) oxides, ferric below). From conventional coordination chemistry theory, colloids in the electrolyte, and the like. Hence, Vmin is con the molecular geometries of these iron chemical species are trolled positive enough to continue conversion of any Fe(II) expected to be as follows: Fe(0) metallic crystal; Fe(II), into Fe(III) and Fe(IV) oxide, but not the oxidation of Fe(0) to Fe(III) and Fe(IV) all six coordinate (octahedral, geometry or Fe(II) at a significant rate. Hence, when Vcell=Vmin, the cell Oh); Fe(V) and Fe(VI) four coordinate (tetrahedral geometry 45 current, Icell, is very nearly Zero, i.e. preferable <5% of Icell Td). By definition, all of these reactions are electrochemical, at Vmax, and preferably <2% of Icell at Vmax, and most i.e. electrolytic, oxidation/reduction or “redox', and dispro preferably <1% of Icell at Vmax. portionation in nature (see below for further illustration and The beneficial chemical reactions which occur during the description of these chemical reactions and how they apply to Vmin portion of the power supply cycle, believed to involve ferrate(VI) formation). The overall driving force for the con 50 disproportionation redox reactions, are key to the continuous version of iron metal to ferrate(VI) ions is the cell voltage production of ferrate(VI) as these reactions allow continuous applied externally across the anode and cathode, forming the ferrate(VI) production cell operation by thinning the iron final production, designated Fe(VI). FeC), or ferrate(VI). oxide film which thickens during the Vmax phase of the Based on ligand field theory, such reactions (R1 to R5) would power signal. This discovery extends the limit of cell opera be expected to occurat different rates as the electronic struc 55 tion of the prior art from at most a few hours, to at least several tures of the ions involved differ substantially from each other, weeks. Although these disproportionation reactions also and also since each reaction would vary with cell operating occur during the Vmax portion of the power cycle, they are conditions; especially the hydroxide concentration, the total believed to be in addition to Fe(V) and Fe(VI) direct produc iron concentration, the residence time at the anode surface, tion at the anode. At Vimin, the disproportionate chemical the temperature (which affects both chemical reaction rates 60 reactions convert the insoluble active red-orange iron oxide and diffusion rates in the fairly viscous medium), Voltage film into soluble oxo iron species, and thereby thin the oxide (Vmin and Vmax), variable DC voltage and current fre layer. This disproportionation reaction is believed to be one or quency, electrolyte flow rate, thickness of anode diffusion both of the following chemical reactions. As one dispropor boundry layers internal-cell mixing, and nature of counter tionation reaction, it is believed that two ions of Fe(IV), ion(s) present. 65 present in the active but insoluble oxide film, react with each It is believed the ferrate(VI) production electrochemistry other by inter-metal ion electron transfer to disproportionate of the invention proceeds as, or is similar to, that described as into one Fe(V), a soluble oxoanion, and Fe(III), an insoluble US 8,449,756 B2 9 10 oxide, thereby reducing the amount of iron ions in the film by critical ferrate(VI) production factors will be described more a large amount, theoretically 50% if the film is mostly Fe(IV) fully below. These factors allow the industrial viability of the based. As a second disproportionation reaction, it is believed ferrate(VI) chemical manufacturing process of the invention that two Fe(V) ions, either present from the reactions at in quantities intended to service all scales of needs for ferrate Vmax, or from the Fe(IV) disproportionation reaction just (VI), including laboratory quantities, specialty chemicals mentioned, disproportionate into one Fe(VI) ion, which, uses, and large-scale commodity production markets, such as being water soluble, diffuses into Solution as final product, water purification, where millions of pounds/year production and into one Fe(IV) species which stays within the solid oxide rates are needed for each ferrate(VI) manufacturing plant. By film to react further in the first disproportionation reaction, operating a process where the process components of the thereby reducing the extent of film thinning somewhat by the 10 invention are incorporated, and more or less continuously first disproportionation (theoretically by 25% on a contained operated, provides the continuous or semi-continuous ferrate iron ion weight basis). However, this Fe(IV) so formed, then (VI) production process of the invention. This invention per feeds into the first disproportionation reaction mentioned, mits efficient large-scale continuous production of ferrate thereby forming more Fe(V) and Fe(III) species, which then (VI) products, as well as a means to obtain Sufficiently high forms more Fe(VI) ions, as described, which diffuse out of the 15 electrical current efficiency needed for industrially viable, oxide film into the electrolyte as product, again reducing the large-scale ferrate(VI) production oxide film thickness further. This cyclic nature of dispropor Summary of Key Process Parameters for Ferrate(Vi) Pro tionation redox reactions, occurs due to the presence of two duction Using the Invention: Such reactions in the same system. As per the invention, continuous ferrate(VI) production at Impact of Above Described Ferrate(VI) Electrochemistry scaleable, low-cost conditions is made possible through the on Viable Production of Ferrate(VI) Compounds at the Indus use of certain process unit operations and process control trial Scale: conditions. The first of these are limitation of the anode sur Fe(III) oxide films are not highly electrically conducting face oxide film thickness and accumulation rate to that and are very insoluble in water or alkaline solutions used in required for high current efficiency and continuous operation the electrochemical generation of ferrate. Hence, as is dem 25 using a certain variable direct Voltage, VDC, resulting in vari onstrated in the prior art, conventional electrochemcial con able direct current, VDI. The second of these key operating ditions result in short-lived cells, which is believed to be due factors is continuous or semi-continuous harvesting of Solid to the accumulation of a non reactive iron-based oxide film product, e.g. crystals ferrate(VI) with counter ion cations of (“passivating layer') on the anode which interferes with elec Sodium, potassium, lithium, strontium, alkali metal ions, trical current and mass flow to and from the surface of the 30 alkaline earth metal ion, Zinc, calcium, magnesium, alumi anode. This passive film, which develops quickly, in a few num, barium, cesium, and the like including blends thereof. In minutes to 2-3 hours, slows the formation rate, and even stops contrast, prior art methods have used alternating currents the formation of ferrate(VI). Therefore prior art methods (AC) and direct currents (DC), and AC superimposed onto require that production be stopped after only minutes or just DC, that do not provide for appropriate reduction of the oxide a few, normally about three hours, to remove the highly dis 35 film that readily forms on the iron anode and passivates it, colored (black, brown, orange and yellow, with minimal red resulting in very short (minutes to a few (<4) hours cell life. coloration) film mechanically by wire brushing, using Sulfu Continuous harvesting of ferrate(VI) product enables the ric acid or hydrochloric acid pickling, or by reverse cell electrolyte to be recirculated through the production cell(s) polarity to discharge the oxide film Solid using hydrogen with little or no ferrate(VI) ion content, which thereby pre gassing from beneath the oxide Surface (electro-cleaning). 40 vents ferrate(VI) electrochemical reduction at the cathode, Sandblasting was found ineffective in cleaning Such surfaces and hence allows the use of a membrane-free cell design. adequately. These refurbishing operations generate waste Sol Removing the membrane reduces the power consumption ids, waste contaminated pickling acid, waste electrolyte, and/ substantially, over 60%, reduces the cost of cell fabrication or consume electricity. No practical process for ferrate(VI) materials by >50%, and decreases the frequency of cell shut preparation can be written or produced using the methods of 45 down for cleaning maintenance from hours to months, which the prior art. then almost entirely eliminates total wastes amounts from cell The present invention provides a practical and economical cleaning. Means for achieving continuous harvesting was not method Suitable for large-scale, continuous, low-cost ferrate obvious as the ferrate(VI) is produced as a highly water (VI) production. This new and useful capability, described in soluble ion at the anode, and, should a precipitating agent be detail below, is a process with several critical features that can 50 added, then precipitation would normally occur where the be combined and operated in a number of ways. The chem ferrate(VI) ion concentration is greatest, at the anode. How istry basis and means of control for the systematic prevention ever, precipitation at the anode fouls the anode and eventually of the buildup of a passivating film on the anode allows the fills the anodic compartment of the cell with solids that then continuous production of ferrate(VI) by the cell, and so requires the cell to be shut down for maintenance. Hence, as avoids the wastes of electricity, raw materials, labor, the loss 55 part of this invention, the conditions required for ferrate(VI) of iron to non-ferrate(VI) byproducts, and the loss of produc solid products to form via a controlled crystallization rate is tion time, and nonscaleability associated with technology of provided, such that the ferrate(VI) solid product forms from the prior art. A second critical feature is the design of a the surface of the anode and after the electrolyte exits the cell, membraneless cell or undivided cell, which reduces power and before the electrolyte is re-circulated back to the cell consumption by at least two thirds, and greatly extends cell 60 while maintaining low electrolyte Volume to anode Surface operation life by more than 10 fold by avoiding issues regard area ratios. Key to this discovery is that large electrolyte ing pluggage of the membrane by Fe(III) oxide Solids. A third holdup times external to the cell are undesirable as substantial critical feature is the continuous formation of ferrate(VI) product decomposition then occurs. Hence the product crys crystalline product that can be removed from the electrolyte tallization conditions need to provide sufficiently fast crys by continuous, nonmagnetic, Solids/liquid separation opera 65 tallization so that the electrolyte can be recirculated back to tions, which thereby also allows continuous operation and the cell quickly, to finish oxidation of highly reactive iron critical recycle of the highly concentrated electrolyte. These intermediates believed to be Fe(V) species, yet a high yield US 8,449,756 B2 11 12 of ferrate(VI) recovery is needed to prevent circulation of tions, so that only Fe(III) or higher oxidation states of Fe can ferrate(VI) past the cathode and causing it to be reduced to be formed from Fe(0) and Fe(I). However, as the voltage is magnetic by-product crystals, similar, or identical to, magne just barely sufficient to drive these reactions, very little reac tite, FeO. It was determined that a novel blend of potassium tion occurs in the frequency cycle of Viminas is measured by ions, Sodium ions and hydroxide ions provide this needed the current density at this time (see above). During this time balance of stable product crystallization without fouling the chemical reactions other than electrolytic reactions can occur anode or leaving too high a residual of ferrate(VI). Note that (see below), allowing the oxide film to thin as desirable fer the prior art (minevski) teaches away from the KOH:NaOH rate product is formed. use ratio range of this invention as being useful. This electro At the Vmin conditions described above, important spon lyte blend, in combination with the variable DC power signal, 10 taneous (thermodynamically allowed) intra-film electro the temperature control profile, and electrolyte internal cell chemical conversions continue, especially disproportion flow characteristics are key to high production rates of ferrate ation reactions. It is believed that the invention uses such (VI) as measured by electrical current efficiencies, percent chemical reactions to maintain a thin, non-passivating, red conversion of iron anode into ferrate(VI) product and actual orange, active, iron oxide film on the Surface of the anode. weight of ferrate(VI) per unit area of anode. 15 Vmax:Vmax, as used herein, is the Voltage across each anode Variable Dc (Vdc) Power Signal Description For The Inven and cathode of the invention that is at or above the voltage and tion, And Determination Of Acceptable Vmax And Vmin current density where the iron anode dissolves electrolyti Settings For A Particular Cell Design: As used herein, DC, cally at a fast rate, and where the lower oxidation states of stands for direct current and has the meaning usually associ iron, Fe(O) through Pe(V), are converted to Fe(VI) quickly. ated therewith in the art. For VDC, the voltage will typically Vmax is determined and set for the cells of the invention as Swing between minimum (Vimin) and maximum (Vmax) val that Voltage determined for the particular cell design and set ues with the absolute values dependent on cell design and of operating conditions, manifested as a “flattening out of a operating settings, especially the temperature, anode-to-cath VDC or AC electrical power Supply signal wave, e.g., a sine ode gap, the concentration of caustic, the caustic cation used (normally potassium ion, Sodium ion, lithium ion, and the like wave, saw-toothed wave, or other Voltage vs time wave pat and/or blends thereof, see above) precise morphological 25 tern, placed across the cell at otherwise operating conditions. structure of the iron anode, the cathode material, and the In actual practice of maximizing ferrate(VI) production by cathodic reaction normally exhibits hydrogen gas formation the invention, a square wave power Supply signal is preferred since it maximizes the time spent at Vmax, where most of the from water, and so on. ferrate(VI) production is occurring and minimizes it else 30 where. However, a simple rectified AC single at the frequency However, for the invention, once set for a particular cell of the utility supply, without filtration, is a preferred source design, power signal frequency, and operating conditions, the of v)C due to its ready availability, low cost, and simplicity VDC voltage does not swing substantially below Vmin or of use. above Vmax. An intermediate simplicity and cost power signal of vLC to Vmin is controlled just low enough to slow or stop the 35 generate Vmax and Vmin settings to practice this invention dissolution of iron metal anode, to Suppress the formation of can also be prepared by Superimposing a high current DC Fe(III)/Fe(IV) oxide layer thickness, but high enough to (offset) voltage (from a DC power source of any kind) onto a maintain oxidizing conditions at the anode Surface to prevent high current AC wave provided, most preferably in a ratio side reactions taking place, especially the reactions between where the resultant VDC voltage never drops to below zero in the product, ferrate(VI) ions with reduced forms of iron, i.e. 40 the Voltage vs time plot. As is well known in the art, Such metallic iron and/or divalent Fe, Fe(II) which would quickly Voltage with frequency profile plots are readily measured, result in formation of a passivity layer of Fe(III) oxide on the characterized, adjusted and monitored using an oscilloscope. surface of the anode. Therefore, Vmin is controlled low enough to prevent the oxidation of more Fe(0) from the The oscilloscope trace then is also useful in screening candi anodes surface, and this is indicated by the overall cell cur date power Supplies and power Voltage wave signals for those rent, Icell, dropping to, or near to, Zero, or about 1% of the 45 that meet the criteria of this invention, for determining, set value of Icell at Vamx, or at most about 5% of this value. Vmin ting and measuring Vmax and Vmin values, and for determin set in this manner prevents significant additional thickening ing the optimal VDC frequency. of the oxide film during the Vmin cycle of the power signal. Electrochemistry Of Ferrate(Vi) Production. In Relation To Therefore, Vmin is the voltage across the anode and cathode Variable Dc Power Signal: Referring to oscilloscope tracings above which the conversion of Fe(0) to Fe(III) and Fe(VI) 50 in FIGS. 1A and 1B, the present invention uses a power oxides is thermodynamically favored, but is very slow kineti Supply to an electrolytic cell consisting of a variable Voltage cally, so that oxide film formation is Substantially depressed. wave of any type (G) of direct current (DC), symbolized as As current density, this setting of Vmin corresponds to about VDC in this application, that varies at a certain controlled 0.01 to 1.0 mA/cm. In chemical reaction form, Vmin is the regular or irregular frequency between a maximum Voltage, cell voltage needed to substantially prevent the following 55 Vmax (B), at which the iron anode dissolves and ferrate(VI) spontaneous redox reactions from occurring: is produced along with intermediate oxidation States of iron, and a minimum Voltage, Vmin (F), set at Zero or, preferably, above Zero but at a voltage where Vmin is sVmax, and Fe(VI) + Fe(0) - 2Fe(III) (2) passivating film preferably at a value of Vmin in which iron anode dissolution 60 is essentially stopped, or slowed substantially, relative to its and/or dissolution rate at Vmax, and where the oxide film, formed on the anode during the period the cell voltage (Vcell (G)) is at Fe(VI) + 3Fe(II) – 4Fe(III) (3) Vmax, is allowed to thin down by disproportionation. Ferrate (VI) production is observed to occur mostly during the time These reactions are prevented by passivating film having just 65 periods when Vcell=Vmax (B) by direct electrolytic oxida barely sufficient Voltage present Such that if any reactions tion of Fe(0) to Fe(VI), where it is believed the Fe oxidations involving Fe(0) or Fe(II) occur, that they are oxidizing reac states of Fe(II), Fe(III), Fe(IV) and Fe(V) are involved (Reac US 8,449,756 B2 13 14 tions R1 through R5). An insoluble solid oxide film also anode Surface), thereby, stabilizing the Voltage which appears forms during this time that is believed to be mostly comprised as a flat-topped wave (B) in the oscilloscope trace. of insoluble oxides of Fe(III) and Fe(IV) (see below). If Vcell Specifically, referring to FIG. 1A, in a preferred case, the (G) is maintained constant, for example at about Vmax (B), applied Voltage, Vcell (G), is increased in roughly square then this oxide film will thicken to the point of causing anode 5 waveform (A), and becomes constant as the Voltage increases passivation whereat ferrate(VI) production is substantially to Vcell=Vmax, (B). During this voltage sweep ferrate(VI) reduced and can cease formation altogether. Such low levels production commences at Voltage level Q, and is believed to of ferrate(VI) production are nonviable for industrial-scale be fastest when Vmax is reached. The Vmax voltage is main production of even specialty quantities of ferrate(VI) salts, tained for a selected time (t), set by the wave form frequency, much less commodity quantities. However, in the current 10 and then dropped to Vmin (Curve C and D of FIG. 1A) over invention, it was found that, by frequently adjusting Vcell (G) periods t and t, which essentially results in a Zero electro to Vmin (F), e.g. by using VDC at about 0.001 to 240 Hz, and lytic current, i.e. <5% and normally <1% of the total current preferably 0.01-120 Hz, and most preferably 0.1-60 Hz, then flow at Vmax. Note however, that it has been discovered that disproportionation (self electron exchange) chemical reac the voltage does not drop off in the form of the wave that is tion (s) occur alone, and/or in combination with other elec- 15 applied (Curve C, C' and A'). This is true regardless of the trochemcial reactions, thereby forming water soluble oxoan shape of the applied signal, which can be a square wave, sine ions of Fe(VI) and Fe(V), (i.e. FeC), and Fe0. wave, rectified AC, or saw-toothed wave, combinations respectively), which diffuse away causing the iron oxide film thereof, and the like. Rather the drop off is delayed as shown on the anode to thin down preventing it from reaching passi by the Curve D after time t, essentially an exponential decay Vating thickness, which would cause stoppage of ferrate(VI) 20 in Vcell with time t (Curve D, starting with point Q and production. It is believed that the electrochemical reactions ending at point F). This observation is interpreted as indicat which occur during the Vmin period (t, and t of FIG. 1A) ing that electrochemical (not electrolytic) reactions continue thins the oxide film on the anode by forming these water when the applied DC voltage is reduced by the power supply soluble Fe(V) and Fe(VI) ferrates which then can diffuse (Curve C) at the selected frequency and waveform as VDC. away from the anode and into the electrolyte, where the 25 Thus, instead of following the applied voltage (Curve C plus ferrate(VI) can be induced to crystallize into a solid that can C"), instead the measured Voltage drops exponentially to one be harvested. While Vcell=Vmin, dissolving significantly level (Curve C) during period t, then asymptotically to the more iron metal from the anode is prevented, which thereby still lower voltage (Curve D) during period t to Vmin point avoids formation of more iron oxide film, which would give (F) and then remains essentially constant at A' (observed but rise to eventual passivation thickness. Therefore the second- 30 not shown in FIG. 1A). The Voltage then increases again as ary ferrate production chemistry (disproportionation) results shown by curve A' during the next Voltage pulse giving the in maintaining a thin and conductive “active oxide film, and voltage sweep A then B. Note that no, or at most a small hence offering the continuous production of ferrate(VI) capa amount, of ferrate(VI) is made if nonvariable (filtered) DC is bility, representing the breakthrough that is a significant part employed at Vmax value B for t. It is important that the of the invention (along with continuous product harvesting 35 voltage be allowed to fall lower than point Q in order to process technique). achieve thinning of the iron oxide film to prevent passivation, While not wishing to be held to the specific colors of oxide which also produces more ferrate(VI) (see below for pro Surface films on Steels as being significant, experimentally it posed mechanism). Note that at certain cell operating condi was invariably observed that the desirable non-flaking film tions, e.g. FIG. 1B, Curves C and D can blend together some appears as a uniform red-orange color, and not black, brown, 40 what. FIG. 1B illustrates a square wave type used fir an yellow or rust orange in color, nor are there heavy deposits of electrochemical cell where the change at the Q point is not so precipitate solids present on this desirable red-orange film. apparent (see FIG.1A). However, an approximate decrease in Therefore, it appears that this red-orange coloration of the voltage to a value of 1.08V from Vmax of 2.3 over about 500 anode indicates a viable surface for ferrate (VI) production. is still very pronounced, and found to be markedly different Therefore, it is believed that the chemical reactions which 45 than the cell-free reference case wherea 1 ohm resistoris used occur during the Vminportion of the power cycle (tandt) do in place of the cell. Vmin is still determined and set in the not require electrolytic reactions at the anode as the observed same manner as for FIG.1A. The appearance of critical Curve cell current during this part of the cycle is minor, i.e. <5%, and D can normally be adequately deconvoluted from Curve C" by normally, <2%, and often <1%, of the total current flow at collecting a reference oscilloscope trace in which a resistor, Vmax. Therefore, it is presently concluded that the anode 50 e.g. of approximately one ohm or less, and rated to carry the oxide film reactions during the period of transition from expected current of the power Supply, and then comparing this Vmax to Vmin (curves C and D of FIG. 1A) involves iron trace to the Curves obtained with the cell inline in place of the molecular species produced during the electrolytic oxidation resistor. of the anode while the cell was at Vmax (FIG. 1A, curve B). To determine Vimin, using the power Supply of the inven As FIG. 1A, regions (A) and (B) indicate, if one attempts to 55 tion, FIG. 2, Vcell (G) can be reduced from Vmax such that provide a DC voltage higher than Vmax, i.e., that at which current flow is less than about 10% of the current at Vmax, ferrate(VI) production occurs, the observed and measured preferably <5%, and most preferably Fe(OH) +2e. fast to very fast (4) Fe(OH) + 2 OH - Fe(OH)2- very fast (5) tion of Ferrate(VI) Using the Invention: 45 Fe(OH)2--> FelicOH) + e - OH- fast (6) Although not wishing to be limited in this invention by FelicOH) + OH - Fe (O)(OH), + slow to rapid (7)a theory, it is useful to have a theoretical basis of understanding e E HO of chemical processes to understand the importance of certain Fe'(OH)2 -> Fe'(O)(OH) +2e + HO fast (8a) parameters and process behaviors. In this vein, a theoretical {and/or Fe"(OH), + HO -e fast (8b)} Fe(O)(OH), +2e. basis is provided here for important roles for certain highly 50 Fe (O)(OH), 4OH- Fe O-4 e- 3HO slow (RDS)” (9) reactive chemical intermediates that affect ferrate(VI) pro duction using the method of this invention. Such species, Rate determined by applied current density most likely consisting of insoluble Fe(IV) hydrated oxide and RDS = rate determining step due to geometry change soluble Fe(V) oxoanionic species, are believed to be involved This may be a slow reaction depending on degree of hydration, oxide film thickness, etc., of as highly reactive intermediates in the production of Fe(VI) 55 the anode surface iron oxide film (see text) product, though they are always present at very low levels at inderscore indicates solid oxide film phase component on surface of anode any particular time. Such reactive intermediate chemistry behavior is well known in the Science of chemistry, being a Followed by, factor in most chemical reactions. Fe(V) and Fe(IV) axe Reaction Set 2: Disproportionation and Dissolution of believed to be involved in the production of Fe(VI) product 60 Active Red-Orange Iron Oxide Layer on the Anode That using the invention in a manner similar to the following Occurs During Vmax and Vcell.

PATENT NO. : 8,449,756 B2 Page 1 of 1 APPLICATION NO. : 10/5971.06 DATED : May 28, 2013 INVENTOR(S) : Monzyk et al.

It is certified that error appears in the above-identified patent and that said Letters Patent is hereby corrected as shown below:

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Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 2047 days.

Signed and Sealed this Eighth Day of September, 2015 74-4-04- 2% 4 Michelle K. Lee Director of the United States Patent and Trademark Office