WO2023118429A1

WO2023118429A1 - A method of regenerating an adsorptive medium

Info

Publication number: WO2023118429A1
Application number: PCT/EP2022/087468
Authority: WO
Inventors: Terkel C. Christensen; Michael VENDRUP; Jakob Bo Jakobsen
Original assignee: Veolia Water Solutions & Technologies Support
Priority date: 2021-12-22
Filing date: 2022-12-22
Publication date: 2023-06-29

Abstract

The present disclosure provides a method of regenerating an adsorptive medium comprising granules. The method comprises the steps of: adding, in a first step, at least one of dissolved ferrous iron and manganese(II) ions to an aqueous medium comprising the adsorptive medium, and adding, in a second step after expiry of the first step, an oxidant to the adsorptive medium. The first step and the second step are repeated as alternating steps.

Description

A METHOD OF REGENERATING AN ADSORPTIVE MEDIUM

Field of the disclosure

The present disclosure relates to a method of regenerating an adsorptive medium for use in a process of removal of dissolved metals and/or metalloids from an aqueous medium. of the disclosure

Typically, removal of metal from a metal-containing aqueous medium is carried out by chemical precipitation or by contact between the aqueous medium and a particulate adsorptive carrier material. During the adsorptive process, metal is coated onto the adsorption carrier material, and subsequently the coated carrier material particles must be separated from the aqueous medium. Since the carrier material has limited adsorption capacity, regular substitution of the carrier material is necessary. Additionally, used carrier material with the metal-containing coating must be deposited under controlled form, as the adsorbed metal may subsequently be released from the used carrier material. of the disclosure

It is an object of embodiments of the disclosure to provide a method of regenerating an adsorptive medium.

According to an aspect, the disclosure provides a method of regenerating an adsorptive medium comprising granules, the method comprising the steps of:

- adding, in a first step, at least one of dissolved ferrous iron and manganese(II) ions to an aqueous medium comprising the adsorptive medium,

- adding, in a second step after expiry of the first step, an oxidant to the adsorptive medium, and

- repeating the first step and the second step as alternating steps.

The method of regenerating the adsorptive medium may be particularly relevant for processes of removal of dissolved metals and/or metalloids from an aqueous medium, such as wastewater and raw water which may contain different types of metals and/or metalloids and other chemical compounds which can be adsorbed.

In one type of processes for the removal of dissolved metals and/or metalloid from an aqueous medium, the removal has been carried out by passing the aqueous medium though a particulate carrier material in the present of both dissolved ferrous iron or manganese(II) ions and an oxidant.

EP 0 660 804 discloses a method for the removal of metal from a metal-containing aqueous medium, where the aqueous medium is passed through a particulate carrier material in the presence of ferrous iron and an oxidant and at such velocity and in such direction that the carrier material particles are fluidised in the aqueous medium, where metal-containing coatings are formed on the surfaces of the carrier material particles, and where the particles thus coated are separated from the aqueous medium.

EP 0 938 453 discloses a process for the removal of dissolved metals and/or metalloids from an aqueous medium containing same and having a high content of salt, whereby the aqueous medium in the presence of manganese (II) ions and an oxidation agent is passed through a particulate carrier material having a more closely specified density, initial average grain size and flow rate, so as to fluidize carrier material particles in the aqueous medium, and whereby the coated carrier material particles thereby formed are separated from the aqueous medium.

WO 2005/061391 discloses a method for the removal of metals from a metal-containing aqueous medium, where said aqueous medium is contacted with a carrier material functioning as an adsorption medium for the metals. The carrier material is regenerated by contacting the carrier material with an Fe(II) solution. The Fe(II) is adsorbed onto the surface of the carrier material and oxidised as a result of the presence of oxygen in the aqueous medium.

The inventors have found that by this traditional practice, dissolved ferrous iron and manganese(II) ions compete with the dissolved metals and/or metalloid to be adsorbed, whereby the efficiency of the removal decreases.

The inventors have further found that by adding at least one of dissolved ferrous iron and manganese(II) ions to the adsorptive medium in a first step and subsequently adding an oxidant in a second step after expiry of the second step, it is possible to provide a method of regenerating the adsorptive medium, whereby the efficiency of the adsorption may be considerably increased, while at the same time decreasing the need for additional chemicals for the treatment of e.g., waste water or raw water.

By avoiding, or at least considerably reduce the competition between ferrous iron and/or manganese(II) ions and the dissolved metals and/or metalloid to be adsorbed, an additional effect is that the aqueous medium may be purified to a higher degree.

Thus, in the first step dissolved ferrous iron and/or manganese(II) ions are added to the aqueous medium comprising the adsorptive medium, whereby it may be assured that substantially all adsorption positions at the granules; i.e. a majority of the surface of the granules is coated by dissolved ferrous iron and/or manganese(II) ions. When adding dissolved ferrous iron and/or manganese(II) ions to the aqueous medium comprising the adsorptive medium in the first step, the aqueous medium may be located in a first container.

In the second step which is carried out after expiry of the first step, an oxidant is added to the adsorptive medium, whereby the ferrous iron and/or manganese(II) ions are oxidised to form FeOOH and MnO?, respectively. After the second step, the regeneration of the adsorptive medium may be considered complete, and dissolved metals and/or metalloid may in an adsorptions step be removed by adsorption onto the new surface of the adsorptive medium which comprises FeOOH and/or MnO?.

Subsequently, the adsorptive medium may be regenerated again by repeating the first and second step. The size of the granules of the adsorptive medium may consequently grow, as a new layer of ferrous iron and/or manganese(II) ions which is subsequently oxidised to form FeOOH and MnO?, respectively, is added to the first layer of adsorbed metals and/or metalloid.

It should be understood that the first and second step may be repeated without an adsorption step in between, as the first and second step may be repeated to re-adsorb an amount of desorbed metals/metalloids in the first step.

It should be understood, that in one embodiment, only one of dissolved ferrous iron and manganese(II) ions is added to the aqueous medium comprising the adsorptive medium in a first step, whereas both dissolved ferrous iron and manganese(II) ions in an alternative embodiment are added to the aqueous medium comprising the adsorptive medium in the first step.

Thin layers of ferrous iron and/or manganese(II) ions subsequently oxidised to form FeOOH and MnO?, respectively, and thin layers of adsorbed metals and/or metalloid may alternating be added to the granules of the adsorptive medium by carrying out an adsorption step alternating to the step of the method of regenerating the adsorptive medium.

Thus, the method of regenerating an adsorptive medium comprising granules may be carried out alternating to an adsorption step in which a substance may be at least partly adsorbed by the adsorptive medium. To facilitate adsorption of the substance, a duration of the adsorption step may be several times longer, such as 10 times longer, such as 25 times longer, such as at least 50 times longer than a duration of the first and second step. The duration may depend on the concentration of the metal/metalloids to be adsorbed.

Typically, an adsorption step may be carried out while the adsorptive medium comprising granules is kept fluidized in an aqueous medium, whereby the surface of adsorptive medium may substantially be in constant contact with the substance to be adsorbed.

The substance may as an example be dissolved metals and/or metalloid, alone or in combination, such as As, Al, Ba, B, Cd, Co, Cr, Cu, Fe, Hg, Li, Mn, Mo, P, Pb, Ra, Sb, Se, Sr, U, V, Zr, and Zn. It should however be understood that also other substance may be adsorbed in the adsorption step.

In one embodiment, the duration of the adsorption step may vary, as an example, the duration of the adsorption step may depend on a concentration of the substance to be removed. In case of high concentrations of the substance, the adsorption step may be shortened up to facilitate adsorption of a larger amount of the substance.

In one embodiment, the first and second step may together have a duration in the range of 1-10 hours, such as 2-8 hours, such as 3-5 hours, whereas an adsorption step may have a duration being at least 50 times longer, such as 100 times longer, or even longer. In an alternative embodiment, the first and second step may together have a duration below 2 hours, such as below 1 hour, such as below 30 minutes, such as below 15 minutes, such as below 5 minutes. An adsorption step may have a duration being at least 50 times longer, or even longer. In a further embodiment, the first and second step may together have a duration longer than 10 hours. The duration of the first and second step may as an example depend on the amount of the adsorptive medium.

To increase the efficiency of coating the surface of the granules by dissolved ferrous iron and/or manganese(II) ions, the at least one of dissolved ferrous iron and manganese(II) ions may be continuously added during the first step. In an alternative embodiment, the at least one of dissolved ferrous iron and manganese(II) ions may be stepwise added during the first step. This may as an example be carried out by dosing a first portion, pausing the dosing, dosing a second portion, pausing the dosing, etc. until the first step has expired.

The at least one of dissolved ferrous iron and manganese(II) ions may be added until the content of dissolved Fe(II) and/or Mg(II) is stable. Thus, the duration of the first step may be based on determination of a stable content hereof. In one embodiment, this may be determined based on test results.

The duration of the first step may be a fixed period. However, it should be understood, that the duration may be changed during the regeneration steps.

To increase the efficiency of oxidising the ferrous iron and/or manganese(II) ions coated on the granules, the oxidant may be continuously added during the second step. In an alternative embodiment, the oxidant may however by added during a plurality of steps.

The duration of the second step may be based on measurements to determine the content of the oxidant added. When a predetermined level of oxidant is reached, the second step may be terminated. The predetermined level may in one embodiment be set as a low level at which the oxidant is just measurable.

Alternatively, the duration of the second step may be determined based on the amount dissolved ferrous iron and manganese(II) ions added during the first step.

The duration of the second step may in a further alternative be a fixed period which, however, may be changed during the regeneration steps.

The method may further comprise an intermediate step between the first and second step. During the intermediate step neither dissolved ferrous iron, manganese(II) ions, nor the oxidant is added to the aqueous medium. During the intermediate step, the granules may be coated by the remaining dissolved ferrous iron and/or manganese(II) ions added in the first step or coated by at least a part of the remaining dissolved ferrous iron and/or manganese(II) ions added in the first step.

A duration of the first step may be at least 50% longer, such as at least 75% longer, such as 100% longer or even more, than a duration of the second step. In one embodiment, the duration of the first step may be in the range of 1 hour, whereas the duration of the second step may be in the range of 30 minutes. The corresponding intermediate step may have a duration of approximately 15 minutes. As specified above, the first and second step may together have a duration in the range of 1- 10 hours, such as 2-8 hours, such as 3-5 hours, where the duration may depend on the amount of the adsorptive medium and/or the application of either dissolved ferrous iron or manganese(II) ions and/or the concentration hereof and/or the concentration of the substance to be removed in an adsorption step.

As specified above, the aqueous medium may be in a first container during the first step. The first container may in one embodiment comprise a first outlet and a first inlet being in fluid communication by a recirculation path to allow the aqueous medium to flow out of the first container via the first outlet and into the first container via the first inlet to thereby enable recirculation of the aqueous medium. The method may comprise a step of recirculating the aqueous medium during the first step. The aqueous medium may be recirculated a plurality of times during the first step, such as twice, three times, four times, or even more.

The first step and the second step may in one embodiment both be carried out in the first container. It should however be understood that the first and second steps may be carried out in separate containers, a first and a second container. To allow the use of separate containers, the first container may additionally comprise a second outlet which may be in fluid communication of an inlet to the second container. Alternatively, the first outlet may be in fluid communication both with the first intel to allow recirculation and with the second container to allow transfer of the aqueous medium with the adsorptive medium comprising granules to the second container.

The method may comprise a step of recirculating the aqueous medium during the second step. The recirculation may be carried out in the first container or in the second container.

The first and second steps may be alternating repeated 2-7 times, such as 2-5 times. After a first and a second step, an adsorption step may be carried out before a first step and a second step are repeated. However, it should be understood that a first step and a second step may be repeated after previous first and second steps without an adsorption step in between. The latter may be particularly relevant when first and second steps have been repeated together with an adsorption step a plurality of times, as repeating the first and second steps, e.g., 2-4 times without an adsorption step in between may seal the adsorbed substance and thereby provide a used adsorption medium which can be deposited under less strict conditions.

The method may further comprise a step of determining a particle size of the granules. In one embodiment, the first step and the second step may be alternatingly repeated until the determined particle size exceeds a predetermined threshold value. In one embodiment, the particle size may be determined manually by visual inspection, e.g., by assessment of the total volume of the granules. Thus, the particle size may be a measure for the total volume.

In an alternative embodiment, the particle size may be determined based on a sample extracted from the aqueous medium. Thus, the method may comprise a step of extracting the sample and a subsequent step of determining the particle size. The particle size may as an example be determined either directly by microscopic measurement or indirectly by sieving, e.g., determined by a standard particle size distribution method based on a D50 median particle size.

In one embodiment, the predetermined threshold value may be at least 3 times an initial particle size, where the initial particle size may be determined prior to the first step in a first cycle of alternating first and second steps. In an embodiment, where the particle size is determined by visual inspection to assess the total volume of the granules, the first step and the second step may consequently be alternatingly repeated until the total volume is three times the initial volume.

In one embodiment, the first step and the second step may be carried out in separate containers. This may be achieved by adding at least one of dissolved ferrous iron and manganese(II) ions to the adsorptive medium comprising granules in a first container in the first step. After termination of a first time-period, the adsorptive medium comprising granules may be transferred to a second container, where an oxidant to the adsorptive medium comprising granules in the second step. In an embodiment, where the method comprises an intermediate step between the first and second step, the intermediate step may be carried out in the first container, before transferring the adsorptive medium comprising granules to the second container. It should be understood, that the intermediate step may alternatively be carried out in the second container.

When repeating the first step and the second step, the adsorptive medium may be transferred to the first container prior to the first step, and subsequently transferred to the second container prior to the second step.

In an alternative embodiment, the first step and the second step are carried out in the same container.

It should be understood, that the first step and the second step may be carried out in the same container in which an adsorption step is also carried out. However, an adsorption step may alternatively be carried out in a separate adsorption container. In one embodiment, the adsorptive medium comprising granules may be drained before the second step. If the second step is carried out in a second container, the adsorptive medium comprising granules may be drained before transferring the adsorptive medium to the second container. In an alternative embodiment, the adsorptive medium may be drained after the second step. The adsorptive medium may as an example be drained to remove chemicals and/or sludge and/or suspension. Draining may be carried out on a regular basis, such as one time for each regeneration cycle. Alternatively, draining may be carried out in dependency on the amount of material to be removed.

The granules may have a density below 3.5 g/cm³, where the density may depend on the type of material selected. In an embodiment in which the density of the granules is below 1.0 g/cm³, a flow direction of the aqueous medium may advantageous be down flow during an adsorption step. In an embodiment in which the density of the granules is above 1.0 g/cm³, a flow direction of the aqueous medium may be down flow or up flow. The flow direction may depend on the type of reactor and/or the type of plant.

The adsorptive medium may comprise granules in the form of sand, fly ash, slag, granite, quartz, chalk, clay, activated carbon, gneiss, artificial manufactured granules, and combinations hereof.

The oxidant is selected from a group consisting of oxygen, ozone, chlorine, hypoclorite, chloride, hydrogen peroxide, potassium - or sodium - permanganate, chromates, and dichromates. The type of oxidant may be selected dependent on the pH-value of adsorptive medium comprising granules and/or whether dissolved ferrous iron and/or manganese(II) ions is used in the first step.

The method may comprise a step of adding an acid or a base in the first step to maintain a pH-value in the range of 4-11, such as in the range of 6-9. The method may likewise comprise a step of maintaining the pH-value in the range of 4-11 in the second step, such as in the range of 6-9. In one embodiment, the pH-value may be maintained in a first pH-range in the first step and maintained in a second pH-range in the second step. Furthermore, the required pH-value may be set dependent on the substance, such as metals and/or metalloid, which are to be adsorbed by the adsorptive medium in an adsorption step.

In one embodiment, the method may further comprise an initial step of coating the adsorptive material before the first step. When coating the adsorptive material, the adsorptive capability hereof may be enhanced. This may as an example be achieved by adding ferrous iron and/or manganese(II) ions to the adsorptive material during recirculation, e.g., 2-3 times, and subsequently adding an oxidant. The adsorptive medium may be substituted by a substitute adsorptive medium after a plurality of alternating steps; i.e. after a plurality of first and second steps. The substitution may in one embodiment be carried out, when the determined particle size exceeds the predetermined threshold value. In an alternative embodiment, the substitution may be carried out after a predetermined number alternating first and second step. It should be understood that the substitution may in a further alternative be carried out in dependency of both a predetermined threshold value for the determined particle size and predetermined number of alternating step; e.g. by substituting the adsorptive medium when first reaching either the predetermined threshold value of the predetermined number of alternating steps.

Removal of the used adsorptive medium may as an example be carried out by separating the adsorptive medium comprising granules from an aqueous medium by decantation, centrifugation, or other separation processes.

Brief description of the drawings

Embodiments of the disclosure will now be further described with reference to the drawings, in which:

Fig. 1 illustrates an embodiment of a set-up for test of adsorption capacity,

Fig. 2 illustrates an alternative set-up for regeneration,

Fig. 3 illustrates a bed reactor,

Fig. 4 illustrates a moving bed filter,

Fig. 5 illustrates a system for regeneration of an adsorptive medium,

Figs. 6a and 6b illustrate two different systems for regeneration of an adsorptive medium, and

Fig. 7 illustrates a system 1 for regeneration of an adsorptive medium. Detailed description of the drawinqs

It should be understood that the detailed description and specific examples, while indicating embodiments of the disclosure, are given by way of illustration only, since various changes and modifications within the scope of the disclosure will become apparent to those skilled in the art from this detailed description.

Fig. 1 illustrates an embodiment of a set-up for test of adsorption capacity. The system 1 comprises an adsorptive medium 2 comprising granules arranged in the column 12. For the tests, the column 12 is approximately 30 cm heigh with a diameter of 20 mm. During the tests, an amount of 100 g granules is used. Test are carried out in which the adsorptive medium comprising granules is precoated with FeOOH and other in which the adsorptive medium comprising granules is precoated with MnO?. The precoating is selected in dependency of the metals and/or metalloid being used for the tests.

The water comprising dissolved metals and/or metalloids to be removed may enter the column 12 via an aqueous inlet 6. After removal of dissolved metals and/or metalloids, the water may leave the column 12 via an aqueous outlet 8.

A recirculation flow path 10 is arranged to enable recirculation of water containing dissolved metals and/or metalloids to be removed over the adsorptive medium comprising granules.

During the tests, Fe⁺⁺ or Mn⁺⁺ in an amount of 50 mg per 100 g granules is added to the adsorptive medium 2 in a first step via an inlet 4. Samples of 5 ml were extracted 2, 5, 10, 15, 20, and 30 minutes after supply of Fe⁺⁺ or Mn⁺⁺. pH is regulated under adding of Fe⁺⁺ or Mn⁺⁺.

In a second step, an oxidant, depending on the adding of Fe⁺⁺ or Mn⁺⁺, is added to the adsorptive medium via the inlet 4 to form FeOOH or MnO?. pH is regulated under adding of an oxidation agent. An alternative inlet 4' is provided in a lower part of the column 12.

After the second step, the first and second steps are repeated, and the regeneration of the adsorptive medium 2 comprising granules may be considered complete. Subsequently, water comprising dissolved metals and/or metalloid to be removed is supplied via the inlet 4. The supplied metals and/or metalloid are removed from the water by adsorption onto the new surface of the adsorptive medium comprising granules which comprises FeOOH or MnO?.

After adding of the oxidation agent, samples of 5 ml were extracted after 2, 5, 10, 15, 20, and 30 minutes. Samples are extracted at the sample point 8'. During testing of the system 1, the pH-value may be measured and adjusted by supply of NaOH at the measurement point 4'. A further flow path 16 is arranged for providing the ability of rinsing the column 12 during testing of the system. Water may be used to rinsing.

In the illustrated testing system, a steering element 18 is arranged in the column 12. This steering element is under normal conditions unnecessary.

In the below table 1, test results from the system 1 illustrated in Fig. 1 is provided. Tests have been carried out using either FeOOH or MnO?. In column 1, the adsorbed metal which is to be removed is specified. The use of either FeOOH or MnO? depends on the metal to be adsorbed. Only, for PO4-P tests have been carried out using both FeOOH and MnO?.

Table 1 - Adsorption of metal from an aqueous medium by use of FeOOH and Mn02, respectively.

Fig. 2 illustrates a system 1 for test of regeneration of an adsorptive medium comprising granules prior to application of the adsorptive medium comprising granules for removal of dissolved metals and/or metalloid in an adsorptions step. The system 1 for coating the adsorptive medium 2 comprising granules comprises a column 12 with a steering element 18. In the illustrated embodiment, FeS04 is added to the adsorptive material 2 during mixing in a first regeneration step. It should be understood, that in an alternative embodiment, FeSO4 may be substituted by MnSO4.

Tests were performed by in a first step supplying Fe(II) and Mn(II), respectively to a precoated adsorptive medium comprising granules. After 30 minutes an oxidant in the form of H2O2 or CIO was added in a second step. After repeating step 1 and step 2, an aqueous medium containing dissolved metals and/or metalloid to be removed was supplied to the reactor 1. This procedure was repeated 3-4 times. As an alternative to H2O2 other oxidants, such as e.g., O2, O3, NaCIO, KMnC , NaMnO4, and CrO4" may be used. During testing of the system 1, the pH-value may be measured and adjusted by supply of NaOH.

Fig. 3 illustrates a fluidized bed reactor 1 for regeneration of an adsorptive medium comprising granules and for adsorption of metals/metalloids. The system 1 has been used to test 1000 g of an adsorptive medium comprising granules with a through flow of an aqueous medium in the form of water from a quarry, the water containing Zn, Ni, Co, and Cd.

The system 1 comprises an adsorptive medium 2 comprising granules arranged in the column 12. Test have been carried out in which the adsorptive medium comprising granules is precoated with Mn(II).

The aqueous medium comprising metals/metalloids to be removed may enter the column 12 via an aqueous inlet 6. After removal of dissolved metals and/or metalloid, the aqueous medium may leave the column 12 via an aqueous outlet 8.

A recirculation flow path 10 is arranged to enable recirculation of the aqueous medium. An additional flow path 14 is provided for sampling and for measurements of the pH-value.

Tests were performed by in a first step supplying Mn(II) to a precoated adsorptive medium comprising granules. After 30 minutes an oxidant was added in a second step. After repeating step 1 and step 2, the aqueous medium containing Zn, Ni, Co, and Cd was supplied to the column 12. This procedure was subsequently repeated.

Test samples were extracted via a sampling mini tank 15.

In the below table 2, test results from the system 1 illustrated in Fig. 3 is provided. The aqueous medium used, is polluted water form a quarry in Belgium.

Table 2 - Results of adsorption test on polluted water from a quarry in Belgium

Fig. 4 illustrates a moving bed filter 30 for continuous regeneration of an adsorptive medium 2 comprising granules arranged in the moving bed filter and for adsorption. An aqueous medium comprising metals/metalloids to be removed enters the filter via an aqueous inlet 6 and flows upward towards an aqueous outlet 8 arranged at a top portion of the filter.

An inner tube 20 is arranged substantially centrally in the filter 30. A part of the adsorptive medium 2 comprising granules is moved upwardly in the inner tube 20 together with air, water, and an oxidant. The adsorptive medium 2 comprising granules is subsequently moved downwards outside the inner tube 20.

Fe(II) and/or Mn(II) is supplied via the inlet 4 in a lower part of the filter in the downwards moving adsorptive medium 2.

The oxidant is supplied via the inlet 4'.

A minor amount of sludge is moved upwardly in the inner tube 20 together with the adsorptive medium 2. In the upper part 32 of the filter, the sludge and the adsorptive medium 2 are separated. The sludge is removed via a sludge outlet 22, while the adsorptive medium 2 comprising granules is moved downwards outside the inner tube 20.

Fig. 5 illustrates a system 1 for regeneration of an adsorptive medium 2 comprising granules.

The upper part of the figure (the upper ellipse) illustrates regeneration of the adsorptive medium 2 comprising granules and removal of sludge in a hydrocyclone via the sludge outlet 22.

Fe(II) and/or Mn(II) is supplied via the inlet 4 to the reactor for adsorption of Fe(II)/Mn(II). From this reactor the aqueous medium is transferred to oxidation reactor. The oxidant is supplied via the inlet 4'. After regenerating the adsorptive medium 2 comprising granules, the adsorptive medium 2 is moved to a tank 24. The lower circle to the left illustrates adsorption of dissolved metals and/or metalloid in an aqueous medium in the tank 24. An aqueous medium comprising metals/metalloids to be removed is supplied via the aqueous inlet 6 or the alternative aqueous inlet 6'.

The lower ellipse to the right illustrates clarification of the aqueous comprising the adsorptive medium 2 comprising granules. In the illustrated embodiment, FeCI_3 is supplied via inlet 32 for flocculation. A polymer is supplied via inlet 34 for dewatering in the tank 26. In the last tank 28, a scraper 36 is arranged for removal of sludge.

Figs. 6A and 6B illustrate two different systems 1 for regeneration of an adsorptive medium comprising granules and adsorption of metals/metalloids. The system 1 schematically illustrated in Fig. 6a is a fixed bed filter 1A, whereas Fig. 6b schematically illustrates a fluidized column IB.

The fixed bed filter 1A and the fluidized column IB, respectively, comprises an adsorptive medium 2 comprising granules. The method of regenerating the adsorptive medium 2 is carried out by, in a first step, adding dissolved ferrous iron and/or manganese(II) ions to the adsorptive medium 2 comprising granules. The dissolved ferrous iron and/or manganese(II) ions are added via an inlet 4, whereby it may be assured that substantially all adsorption positions; i.e. a majority of the surface of the adsorptive medium comprising granules is coated by dissolved ferrous iron and/or manganese(II) ions.

In a second step, an oxidant is added to the adsorptive medium comprising granules via the inlet 4, whereby the ferrous iron and/or manganese(II) ions are oxidised to form FeOOH and MnO2, respectively.

After the second step, the regeneration of the adsorptive medium 2 may be considered complete, and dissolved metals and/or metalloid may in a subsequent adsorptions step be removed from an aqueous medium by adsorption onto the new surface of the adsorptive medium which comprises FeOOH and/or MnO?.

The aqueous medium comprising metals/metalloids to be removed may enter the fixed bed filter 1A and the fluidized column IB, respectively, via an aqueous inlet 6. After removal of dissolved metals and/or metalloid, the aqueous medium may leave the fixed bed filter 1A and the fluidized column IB, respectively, via an aqueous outlet 8.

During the regeneration steps; i.e. the first and the second step, the aqueous medium may be recirculated via a recirculation flow path 10. Subsequently, the first step and the second step are repeated as alternating steps.

Fig. 7 illustrates a system 1 for regeneration of an adsorptive medium 2 comprising granules and adsorption of metals/metalloids.

The method of regenerating the adsorptive medium 2 comprising granules is carried out by, in a first step, adding dissolved ferrous iron and/or manganese(II) ions to the adsorptive medium 2 comprising granules via the dosing unit 40.

In a second step, an oxidant is added to the adsorptive medium comprising granules via the dosing unit 42, whereby the ferrous iron and/or manganese(II) ions are oxidised to form FeOOH and MnO?, respectively.

The aqueous medium comprising metals/metalloids to be removed enters the container 12 via an aqueous inlet 6. After removal of dissolved metals and/or metalloid, the aqueous medium leaves container 12 via an aqueous outlet 8.

The pH value may be measured at two different measurement positions 44, Additionally, the pH-value may be adjusted by supply of e.g., NaOH via the dosing unit 46.

Test samples may be extracted at sample point 48.

Claims

1. A method of regenerating an adsorptive medium comprising granules, the method comprising the steps of:

- repeating the first step and the second step as alternating steps.

2. A method according to claim 1, wherein the at least one of dissolved ferrous iron and manganese(II) ions is continuously added during the first step.

3. A method according to any of claims 1-2, wherein the oxidant is continuously added during the second step.

4. A method according to any of the preceding claims, further comprising an intermediate step between the first and second step during which intermediate step neither dissolved ferrous iron, manganese(II) ions, nor the oxidant is added to the aqueous medium.

5. A method according to any of the preceding claims, wherein a duration of the first step is at least 50% longer than a duration of the second step.

6. A method according to any or the preceding claims, further comprising a step of recirculating the aqueous medium during the first step.

7. A method according to any of the preceding claims, further comprising a step of recirculating the aqueous medium during the second step.

8. A method according to any of the preceding claims, wherein the first and second steps are alternatingly repeated 2-7 times, such as 2-5 times.

9. A method according to any of the preceding claims, further comprising a step of determining a particle size of the granules, and wherein the first step and the second step are alternatingly repeated until the determined particle size exceeds a predetermined threshold value.

10. A method according to claim 9, wherein the particle size is determined based on a sample extracted from the aqueous medium.

11. A method according to any of claims 9-10, wherein the predetermined threshold value is at least 3 times an initial particle size, the initial particle size being determined prior to the first step in a first cycle of alternating first and second steps.

12. A method according to any of the preceding claims, wherein the first step and the second step are carried out in separate containers.

13. A method according to any of the preceding claims, wherein the adsorptive medium is drained before the second step.

14. A method according to any of the preceding claims, wherein the granules have a density below 3.5 g/cm³.

15. A method according to any of the preceding claims, wherein the granules are selected from a group consisting of sand, fly ash, slag, granite, quartz, chalk, clay, activated carbon, gneiss, artificial manufactured granules, and combinations hereof.

16. A method according to any of the preceding claims, wherein the oxidant is selected from a group consisting of oxygen, ozone, chlorine, hypoclorite, chloride, hydrogen peroxide, potassium - or sodium - permanganate, chromates, and dichromates.

17. A method according to any of the preceding claims, further comprising a step of adding an acid or a base in the first step to maintain a pH-value in the range of 4-11 in the first step.

18. A method according to any of the preceding claims, further comprising a step of adding an acid or a base in the first step to maintain a pH-value in a first pH-range in the first step and a step of adding an acid or a base in the second step to maintain a pH-value in a second pH-range in the second step.

19. A method according to any of the preceding claims, further comprising an initial step of coating the adsorptive material before the first step.