The invention relates to a method for manufacturing ferrate and a ferrate(VI) manufacturing device.

Ferrate, especially ferrate(VI) is a compound that can be used in a wide variety of industrial activities, including water treatment, metal extraction, metal production, elimination of radioactive corrosion products and/or reduction of radioactive particles. The use of ferrate(VI) often is preferable over other methods or compounds for those particular uses.

One of the main challenges however is to manufacture ferrate(VI) in an effective, cost- efficient manner. In practice, ferrate(VI) is mostly produced using an electrochemical cell with an iron anode and a highly alkaline solution or electrolyte. Such a method comprises applying an electric potential to the anode and cathode, which leads to a reaction producing ferrate(VI).

One of the disadvantages of the known methods is that the ferrate(VI) is highly unstable and has a limited shelf life, which is measured in several hours. As a result, the production needs to be located in the direct vicinity of the location of use.

The invention is aimed at obviating or at least reducing the abovementioned disadvantages. More specifically, the invention is aimed for providing a method for manufacturing ferrate(VI) that provides ferrate(VI) with a longer shelf life.

To that end, the invention provides a method for manufacturing ferrate, the method comprising the steps of:

- providing an electrochemical cell having an anode containing iron, and a cathode that is placed at a distance from the anode;

- inserting an alkaline solution into the electrochemical cell;

- applying, by a power supply, an electric potential between the iron containing anode and the cathode; characterized by the step of:

- inducing a current density on one or more surfaces of the anode in the range of 1 A/cm ² to 500 A/cm ² .

It is noted that the application in multiple places refers to ferrate, which in the invention means ferrate(VI), which is also synonym for iron(VI). These terms are used interchangeable and are all considered to refer to the same subject in this application.

It is further noted that the terms alkaline solution, electrolyte and electrolyte solution are all used interchangeably in this application and refer to the same subject. An advantage of the method according to the invention is that it provides ferrate(VI) with a shelf life of up to two months. This allows the product to be manufactured in a central location or plant and subsequently shipped to (end) users. In the known methods, ferrate(VI) is manufactured on-site, that is at the location of use, because it loses its stability after a short period of time (up to a few hours).

The ferrate(VI) can be provided in powdered form, which makes it easily transportable. This is also due to the fact that the ferrate(VI) is more stable than ferrate(VI) that is manufactured using the known methods.

In addition, due to the stability of the ferrate(VI) that is manufactured using the method according to the invention, the need for localized plant is obviated and high investments in local manufacturing plants is obviated.

Another advantage of the method according to the invention is that the production costs of the ferrate(VI) is significantly lower than with the known methods of production. More specifically, the production cost of ferrate(VI) according to the invention have been found to be about 50% of the production costs of the known methods, and may even be lower in some embodiments of the method.

The method according to the invention therewith allows ferrate(VI) to be produced in a highly efficient, cost-effective way.

Yet another advantage is that a high purity of the produced ferrate(VI) is achieved with the method according to the invention.

A further advantage of the method according to the invention is that, due to the high current densities at the anode surface, passivation of the anode is substantially prevented. As a result, no barrier layer is formed. Such a barrier layer, for example a layer comprising oxides, prevents further dissolution of the anode material. By preventing the barrier formation (i.e. preventing passivation) allows a more efficient and effective method.

In an embodiment of the method according to the invention, the distance between the anode and the cathode can be in the range of 1 to 10 cm, preferably 2 to 6 cm and more preferably about 3 cm.

In an embodiment of the method according to the invention, the method may additionally comprise the step of, during the step of applying the electric potential, adding an additional amount of alkaline solution.

By adding, for example by injecting, an additional amount of alkaline solution to the electrochemical cell, the production rate of ferrate can be increased. This in turn leads to a reduction in production costs (per manufactured unit of product, such a weight). In an embodiment of the method according to the invention, the alkaline solution may comprise concentrated aqueous sodium hydroxide, concentrated aqueous potassium hydroxide, concentrated calcium hydroxide, concentrated magnesium hydroxide, or a mixture thereof.

Several alkaline solutions may be used to perform the method according to the invention. An advantage of the abovementioned alkaline solutions is that a relatively high amount of ferrate(VI) can be manufactured using these solutions.

In addition, these alkaline solutions provide a good balance between the quantity and quality of the manufactured ferrate(VI) and the costs of the solution.

In an embodiment of the method according to the invention, the alkaline solution may comprise a solution with a concentration of 17 M to 20 M.

It is noted that 17 M to 20 M refers to 17 molar to 20 molar or 17 moll per litre to 20 moll per litre.

An advantage of providing the abovementioned concentration in the alkaline solution is that it provides an effective and efficient production rate for ferrate(VI). This is mainly due to the low amount of (free) water in the solution, which has an adverse effect on the production rate. Therewith, the degeneration of the manufactured ferrate(VI) to divalent and trivalent iron nuclei by decomposition of the ferrate(VI) is substantially prevented.

In an embodiment of the method according to the invention, the method may comprise the step of mixing the solution, preferably by using a mixing system.

An advantage of mixing the solution, preferably during the step of applying an electric potential, is that the uniformity of the chemical composition in the solution is improved, therewith increasing the production rate.

Another advantage of mixing the solution is that it provides an improved heat exchange within the electrochemical cell, which leads to an increased production rate of ferrate (IV).

In an embodiment of the method according to the invention, the method may comprise the step of, during the steps of applying of the electric potential and/or inducing the current density, maintaining the solution at a temperature below 60 °C by cooling the solution, preferably using a cooling system, preferably maintaining the solution at a temperature below 50 °C, more preferably maintaining the solution at a temperature below 45 °C, and most preferably maintaining the solution at a temperature of around 35 °C.

An advantage of cooling the solution to a temperature below 60 °C is that degeneration of the manufactured ferrate(VI) to divalent and trivalent iron nuclei by decomposition of the ferrate(VI) is substantially prevented or at least significantly reduced. This increases the production rate per time unit. In addition, it allows a high purity ferrate(VI) to be manufactured using the method according to the invention. For example, the cooling of the solution to a temperature below 60 °C may be performed using a cold water jacket around (different parts off) the electrochemical cell.

As a result, different temperature zones in the electrochemical cell may be achieved in the manufacturing of ferrate.

In an embodiment of the method according to the invention, the step of applying a current density on one or more surfaces of the anode may comprise applying a current density in the range of 1 A/cm ² to 500 A/cm ² , preferably in the range of 10 A/cm ² to 250 A/cm ² , more preferably in the range of 120 A/cm ² to 150 A/cm ² .

It was found that the range of 120 A/cm ² to 150 A/cm ² provides an efficient and effective method for manufacturing ferrate.

In an alternative embodiment of the method according to the invention, the step of applying a current density on one or more surfaces of the anode may comprise applying a current density in the range of 10 A/cm ² to 500 A/cm ² , preferably in the range of 120 A/cm ² to 500 A/cm ² , more preferably in the range of 150 A/cm ² to 500 A/cm ² , even more preferably in the range of 300 A/cm ² to 450 A/cm ² .

It has been found that an advantage of providing a current density in the abovementioned ranges is that it provides a high production rate and simultaneously provides a high purity product.

In an embodiment of the method according to the invention, the method further comprises the step of processing the ferrate (VI) to form a ferrate (VI) powder, for example using evaporation, centrifuging and/or other suitable techniques, wherein the step of processing preferably may provide ferrate powder with a purity of at least 95% at a rate of at least 160 grams per hour, and preferably may provide a purity of at least 98% at a rate of at least 160 grams per hour.

An advantage of the method according to the invention is that the ferrate(VI) manufactured therewith has a high purity combined with a high production rate. This combination exceeds both purity and production rate of known methods and is therefore more (cost-)efficient.

In a preferred embodiment, the method according to the invention may have a different, preferably higher, temperature at the anode to enable a higher conversion rate as more hydroxide ions are available at said concentration. Furthermore, cooling the solution in the electrochemical cell to a temperature below 60 °C, preferably maintaining the solution at a temperature below 50 °C, more preferably maintaining the solution at a temperature below 45 °C, and most preferably maintaining the solution at a temperature of around 35 °C, enables an efficient and effective manufacturing of ferrate.

Thus, the increased temperature at the anode is locally and limited to the surrounding of the anode. Preferably, the surrounding is at most 0.5 cm around the anode. In addition, the method according to the invention may during the steps of applying of the electric potential and/or inducing the current density, maintaining the solution at a temperature below 60 °C by cooling the solution, preferably using a cooling system, preferably maintaining the solution at a temperature below 50 °C, more preferably maintaining the solution at a temperature below 45 °C, and most preferably maintaining the solution at a temperature of around 35 °C, wherein the alkaline solution comprises a solution with a concentration of 17 M to 20 M, and wherein the current density is a current density on one or more surfaces of the anode in the range of 1 A/cm ² to 500 A/cm ² , preferably comprises a current density in the range of 1 A/cm ² to 500 A/cm ² , preferably in the range of 10 A/cm ² to 250 A/cm ² , more preferably in the range of 120 A/cm ² to 150 A/cm ² .

It was found that said method provides an efficient and effective method for manufacturing ferrate.

The invention also relates to a ferrate(VI) manufacturing device comprising:

- an electrochemical cell configured to be filled with an alkaline solution, the electrochemical cell comprising:

- an anode containing iron; and

- a cathode that is placed at a distance from the anode;

- a power supply configured to provide a electric potential between the anode and the cathode; characterized in that:

- the power supply is configured to, during operation, induce a current density at one or more surfaces of the anode in the range of 1 A/cm ² to 500 A/cm ² .

The ferrate(VI) manufacturing device according to the invention provides similar effects and advantages as described for the method according to the invention. It is noted that the embodiments mentioned above in respect to the method may also freely be applied and/or incorporated in various combinations in the ferrate(VI) manufacturing device according to the invention.

An advantage of the device according to the invention is that it allows a high production rate of ferrate(VI), such as about 160 grams/hour, leading to an efficient and cost-effective production.

Another advantage of the device according to the invention is that it allows the production of a stable ferrate(VI) that has a shelf-life in excess of a day. More specifically, the shelf-life of the manufactured ferrate may have a shelf-life up to several months, which allows central production and transportation around the globe.

In an embodiment of the ferrate(VI) manufacturing device according to the invention, the electrochemical cell comprises an supply opening that is connectable to a source of alkaline solution, wherein the supply opening, in use of the device, is used to add additional alkaline solution into the electrochemical cell. An advantage of providing an supply opening is that additional solution can be added, preferably injected, during operation of the device. To that end, the opening is configured to be connectable, for example via a tube, hose, channel or conduit, to a source of alkaline solution. The alkaline solution is provided to the electrochemical cell, which leads to an increased production rate and/or efficiency.

It is preferred that the alkaline solution that is added, or injected, into the electrochemical cell is similar in composition as the electrolyte (i.e. the alkaline solution) that is already provided to the device.

In an embodiment of the ferrate(VI) manufacturing device according to the invention, the power supply is a direct current power supply.

It has been found that a direct current power supply provides the most effective results with regard to production rate and/or composition and/or purity of the ferrate(VI) that is manufactured using the device according to the invention.

In an embodiment of the device according to the invention, the ferrate manufacturing device may further comprise a cooling system configured to control the temperature of the solution, wherein the cooling system is preferably configured to maintain the alkaline solution at a temperature below 60 °C and more preferably below a temperature of 40 °C.

An advantage of cooling the alkaline solution in the electrochemical cell to a temperature below the abovementioned values is that it prevents degeneration or even disassociation of the ferrate(VI) that is produced during operation. As a result, the amount of ferrate produced, in terms of production rate, are increased compared to the known devices. It is preferred that the cooling system is configured to, during operation, maintain the alkaline solution at a temperature between 30 °C and 40 °C, preferably around 35 °C, because it has been found that this value provides an excellent balance between the energy required for cooling and the increased production rate of ferrate(VI).

In an embodiment of the device according to the invention, the device may be configured to be filled with an alkaline solution that comprises concentrated aqueous sodium hydroxide, concentrated aqueous potassium hydroxide, concentrated calcium hydroxide, concentrated magnesium hydroxide, or a mixture thereof.

Although various alkaline solution can be used in the device according to the invention, it has been found that the abovementioned alkaline solutions or electrolytes provide excellent results in terms of production rate and purity of the ferrate(VI) that is produced.

In an embodiment of the device according to the invention, the device may be configured to be filled with an alkaline solution comprising a solution with a concentration of 17 M to 20 M. It is noted that 17 M to 20 M refers to 17 molar to 20 molar or 17 moll per litre to 20 moll per litre.

An advantage of providing the abovementioned concentration in the alkaline solution is that it provides an effective and efficient production rate for ferrate(VI). This is mainly due to the low amount of (free) water in the solution, which has an adverse effect on the production rate. Therewith, the degeneration of the manufactured ferrate(VI) to divalent and trivalent iron nuclei by decomposition of the ferrate(VI) is substantially prevented.

In an embodiment of the device according to the invention, the device may comprise an alkaline solution, wherein the alkaline solution comprises concentrated aqueous sodium hydroxide, concentrated aqueous potassium hydroxide, concentrated calcium hydroxide, concentrated magnesium hydroxide, or a mixture thereof.

Although various alkaline solution can be used in the device according to the invention, it has been found that the abovementioned alkaline solutions or electrolytes provide excellent results in terms of production rate and purity of the ferrate(VI) that is produced.

In an embodiment of the device according to the invention, the device may comprise an alkaline solution with a concentration of 17 M to 20 M.

It is noted that 17 M to 20 M refers to 17 molar to 20 molar or 17 moll per litre to 20 moll per litre.

An advantage of providing the abovementioned concentration in the alkaline solution is that it provides an effective and efficient production rate for ferrate(VI). This is mainly due to the low amount of (free) water in the solution, which has an adverse effect on the production rate. Therewith, the degeneration of the manufactured ferrate(VI) to divalent and trivalent iron nuclei by decomposition of the ferrate(VI) is substantially prevented.

In an embodiment of the device according to the invention, the device may further comprise a mixing system configured to homogenize the alkaline solution.

An advantage of providing a mixing system is that, by mixing the solution, the uniformity of the chemical composition in the solution is improved, which in turn increases the production rate.

Another advantage of a mixing system is that, by mixing the solution, the heat exchange within the electrochemical cell is improved, which leads to an increased production rate of ferrate (IV).

In an embodiment of the device according to the invention, the cooling system may comprise fluid cooling, and preferably may comprise a liquid tank in which the electrochemical cell is positioned.

An advantage of providing a fluid cooling system, especially a liquid tank, is that it provides a high cooling capacity with a relatively low volume. Therewith, it provides an effective cooling to the electrochemical cell. The liquid cooling system may be provided with a circulation system, which circulates the cooling fluid through the fluid cooling system to increase the heat exchange even further. Such a circulation system may comprise conduits that are directly adjacent or contiguous with the electrochemical cell, or may be a circulation system that is connected to the liquid tank.

In an embodiment of the device according to the invention, the device comprises a second supply opening that is configured to supply additional iron and/or an iron containing solution and that preferably is connectable to a supply of additional iron and/or an iron containing solution.

An advantage of providing additional iron and/or iron containing solution to the electrochemical cell during operation allows the production rate to be increased and/or allows a (semi-)continuous production process. This in turn results in lower production costs and/or a higher production rate.

For example, the iron may be provided to the electrochemical cell during operation as a suspension.

Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, in which:

Figure 1 shows an example of the method according to the invention;

Figure 2 shows a second example of the method according to the invention;

Figure 3 shows a schematic view of an example of a device according to the invention; and Figure 4 shows a schematic view of a second example of a device according to the invention. In an example of the method according to the invention (see figure 1), the method comprises the step of providing 1002 an electrochemical cell having an anode containing iron, and a cathode that is placed at a distance from the anode. The electrochemical cell is filled by inserting 1004 an alkaline solution into the electrochemical cell, which solution preferably is a highly alkaline solution (17M to 20M). Inserting the alkaline solution can for example be done using a alkaline supply opening or input opening. The method further comprises applying 1006, by a power supply, an electric potential between the iron containing anode and the cathode and inducing 1008 a current density on one or more surfaces of the anode in the range of 1 A/cm ² to 500 A/cm ² .

Optionally, the method may also comprise the step of adding 1010 an additional amount of alkaline solution, which is executed during step 1006 and/or step 1008.

In a second example of the method according to the invention (see figure 2), the method comprises the step of providing 2002 an electrochemical cell having an anode containing iron, and a cathode that is placed at a distance from the anode. The electrochemical cell is filled by inserting 2004 an alkaline solution into the electrochemical cell, which solution preferably is a highly alkaline solution (17M to 20M). Inserting the alkaline solution can for example be done using a alkaline supply opening or input opening. The method further comprises applying 2006, by a power supply, an electric potential between the iron containing anode and the cathode and inducing 2008 a current density on one or more surfaces of the anode in the range of 1 A/cm ² to 500 A/cm ² . In this example, the method also comprises the step of mixing 2014 the solution to homogenize the electrolyte. In addition, the method in this example also comprises the step of maintaining 2016 the solution at a temperature below 60 °C by cooling the alkaline solution.

In addition to increasing the production rate, the steps 2014 and/or 2016 also may (further) increase the effect of the optional steps 2010 as described below.

The optional step of adding 2010 an additional amount of alkaline solution, which is executed during step 2006 and/or step 2008. It is noted that the steps of mixing 2016 and maintaining 2016 the solution at a temperature below 60 °C may be combined, but can also be applied separately from each other in the method according to the invention. Similarly, any combination of these steps with the optional steps as described above is possible.

In an example of ferrate manufacturing device 2 according to the invention (see figure 3), device 2 comprises electrochemical cell 4 that is provided with anode 6 and cathode 8, each of which partially extends into an inner space 10 of electrochemical cell 4. Device 2 further comprises power supply 12, which is connected to anode 6 and cathode 8 and is configured to, during operation, induce a current density at one or more surfaces of the anode in the range of 1 A/m ² to 500 A/m ² .

In a second example of ferrate manufacturing device 102 according to the invention (see figure 4), device 102 comprises electrochemical cell 104 that is provided with anode 106 and cathode 108, each of which extends into an inner space 110 of electrochemical cell 104. In this example, inner space 110 is partially filled with electrolyte 112 or alkaline solution 114. Although anode 106 and cathode 108 in this example extend only partially into electrolyte 114, it is noted that inner space 110 of electrochemical cell 104 may also be filled substantially completely. In that case, the parts of anode 106 and cathode 108 that extend in inner space 110 is completely submerged in electrolyte 114. Device 102 further comprises power supply 112, which is connected to anode 106 and cathode 108 and is configured to, during operation, induce a current density at one or more surfaces of the anode in the range of 1 A/cm ² to 500 A/cm ² .

Electrochemical cell 104 is in this example further provided with supply opening 116 in side wall 104a of electrochemical cell 104. In this case, side wall 104a is top wall 104a. Supply opening 116 is connected to schematically drawn electrolyte supply 118 from which additional electrolyte can be supplied to electrochemical cell 104 during operation.

Device 102 in this example also comprises mixing system 124 or mixing unit 124, which (at least partially) extends into inner space 110 and which is configured to mix the electrolyte during operation. Although mixing system 124 is in this example shown as vertically oriented, it is clear that other orientations and/or other suitable mixing systems 124 can be applied within the device according to the application.

In this example, ferrate(VI) manufacturing device 102 also comprises cooling system 126, which in this example is embodied as cooling tank 128 having supply opening 130 and discharge opening 132, which allow cooling fluid to be replaced and/or circulated to discharge heat from electrochemical cell 104. Supply opening 130 and discharge opening 132 are optional.

It is noted that supply opening 116, second supply opening 120, mixing system 124 and cooling system 126 are all optional and can be applied in any combination in device 102. As such, this example is not limited to the combination as shown in figure 4. The present invention is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following claims within the scope of which many modifications can be envisaged.