WO1999058243A2 - Ion exchange materials - Google Patents

Ion exchange materials Download PDF

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WO1999058243A2
WO1999058243A2 PCT/GB1999/001517 GB9901517W WO9958243A2 WO 1999058243 A2 WO1999058243 A2 WO 1999058243A2 GB 9901517 W GB9901517 W GB 9901517W WO 9958243 A2 WO9958243 A2 WO 9958243A2
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material
ion exchange
metal cation
materials
oms
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PCT/GB1999/001517
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French (fr)
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WO1999058243A3 (en
Inventor
Alan Dyer
Martyn Pillinger
Jonathan Andrew Newton
Risto Olavi Harjula
Johanna Teresia Moller
Esko Heikki Tusa
Amin Suheel
Maurice Webb
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British Nuclear Fuels Plc
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Publication of WO1999058243A2 publication Critical patent/WO1999058243A2/en
Publication of WO1999058243A3 publication Critical patent/WO1999058243A3/en

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    • GPHYSICS
    • G21NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21FPROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/04Treating liquids
    • G21F9/06Processing
    • G21F9/12Processing by absorption; by adsorption; by ion-exchange
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J39/00Cation exchange; Use of material as cation exchangers; Treatment of material for improving the cation exchange properties
    • B01J39/02Processes using inorganic exchangers
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J39/00Cation exchange; Use of material as cation exchangers; Treatment of material for improving the cation exchange properties
    • B01J39/08Use of material as cation exchangers; Treatment of material for improving the cation exchange properties
    • B01J39/10Oxides or hydroxides
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J39/00Cation exchange; Use of material as cation exchangers; Treatment of material for improving the cation exchange properties
    • B01J39/08Use of material as cation exchangers; Treatment of material for improving the cation exchange properties
    • B01J39/12Compounds containing phosphorus
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J39/00Cation exchange; Use of material as cation exchangers; Treatment of material for improving the cation exchange properties
    • B01J39/08Use of material as cation exchangers; Treatment of material for improving the cation exchange properties
    • B01J39/14Base exchange silicates, e.g. zeolites

Abstract

A method of selectively removing a target metal cation from a liquid medium containing at least one other metal cation involves the use of an ion exchange material selected from four groups: 1) crystalline materials synthesised from octahedral/tetrahedral co-ordination polyhedra; 2) layered oxide materials, including those with inorganic pillars incorporated between the layers; 3) high silica materials, including those with large mesoporosity; and 4) microporous materials with interstitial cations other than Si or Al in tetrahedral co-ordination. At least one of the pore size, the layer charge density, the interlayer cations and the doping metal cations are controlled to render the ion exchange material selective towards the target metal cation.

Description

ION EXCHANGE MATERIALS

FIELD OF THE INVENTION

The present invention relates to the removal of metal ions from solutions and relates especially to the removal of unwanted or toxic metal ions from solutions. By way of example, the present invention relates to the removal of radionuclides from solutions. However it should be understood that the present invention may also relate to the removal of non-radioactive metal ions from solutions.

BACKGROUND TO THE INVENTION

In the nuclear industry large volumes of aqueous waste streams are produced which contain radionuclides and other polluting metal species. There is a need to dispose of such waste with minimum volume for maximised capacity usage. Accordingly, it is desired to remove as far as possible actinide elements, fission products, activation products and heavy metals. Techniques such as flocculation or ion exchange have been employed to remove these species and have been generally successful. However, certain metal ions can be more problematic to remove than others and, in such instances, a combination of techniques, such as ion exchange and flocculation, has had to be used to deal with a particular waste mixture. The use of a combination of techniques adds to the overall complexity, processing time and experience of the operation.

By way of example, strontium ions are difficult to remove by known ion exchange techniques when present in acidic media. Moreover, other ions present in the solution, eg calcium, magnesium, sodium and potassium may interfere with the uptake of strontium. Commercially available materials for strontium removal include clinoptilolite (a zeolite mineral), sodium titanates (Allied Signal, USA), titanosilicate CST (UOP, USA) and titanium-oxide based SrTreat (Selion OY, Finland) which only work efficiently in alkaline media. THE PRESENT INVENTION

Ion exchange materials identified as having the potential to remove radionuclides from waste solutions may be categorised into four main groups as follows:

Group 1: Crystalline materials synthesised from octahedral/tetrahedral co- ordination polyhedra, eg 'MOS' materials built from Ti and Mo polyhedra.

Group 2: Layered oxide materials, including those with inorganic pillars incorporated between the layers. By intercalating large polymeric cations between layers of the host material and calcining the product, it is possible to prop apart the layers and thus construct a permanent open structure. The pore size obtained will depend upon a combination of the nature ofthe pillaring agent and the charge density of the host material. Ion selectivity will primarily be controlled by the pore size and hence accessibility of ions to the internal ion exchange sites.

Group 3: High silica materials, including those with large mesoporosity, eg the MCM type molecular sieves. The search for cracking catalysts with microporous domains that are accessed via mesoporous structures, to split longer hydrocarbon chains has produced this new family of robust crystalline materials designated as MCM's.

Group 4: Microporous materials with interstitial cations other than Si or A 1 in tetrahedral co-ordination, eg those based on large-pore VPI or similar frameworks. Many microporous compounds based on zeolitic frameworks, but with cations such as P, B, Fe, Co, Mg, Mn, Ti, Ga and Zn, occupying the tetrahedral framework sites, are known as well characterised crystalline solids.

The present invention provides a method of selectively removing a target metal cation from a liquid medium containing said metal cation together with at least one other metal cation, the method comprising contacting said liquid medium with an ion exchange material selected from a Group 1 to Group 4 material, as herein defined, with at least one ofthe pore size, layer charge density, interlayer cations and metal in doping being controlled to provide a material selective for said target metal cation.

Preferably, the ion exchange material is crystalline. The method may be applied to any suitable ion exchange material, preferred materials including an octahedral manganese oxide, an octahedral/tetrahedral titanosilicate and an MCM material.

Preferably, the target metal cation is one or more of caesium, strontium and cobalt, said cation being present in a hydrated or non-hydrated form.

The invention also provides the use of an ion exchange material in the selective removal of a target metal cation from a liquid medium containing said metal cation together with at least one other metal cation, the ion exchange material being selected from a Group 1 to Group 4 material, as herein defined, with at least one of the pore size, layer charge density, interlayer cations and metal ion doping being controlled to provide a material selective for said target metal cation.

In addition, the present invention provides the use of an octahedral manganese oxide, an octahedral/tetrahedral titanosilicate or an MCM material as an ion exchanger in the removal of metal cations from a liquid medium.

An ion exchange material of use in the present invention may include a mixture of ion exchange materials, for instance, two or more of an octahedral manganese oxide, an octahedral/tetrahedral titanosilicate and an MCM material.

Furthermore, the present invention provides a method of preparing an ion exchange material comprising forming an amorphous or crystalline Group 1 to Group 4 material, as herein defined, by a method designed to control at least one of the pore size, layer charge density, interlayer cations and doping of metal cations in the material so that the resultant material is capable of selective removal from a liquid medium of a target cation which is present in said liquid medium together with at least one other metal cation. FURTHER DESCRIPTION OF GROUPS 1 TO 4 MATERIALS

Group 1: These open-framework materials with octahedral/tetrahedral co-ordination include the following: 1.1 Manganese oxide octahedral molecular sieves (OMS)

The structure of the naturally occurring manganese oxide todorokite consists of MnO6 octahedra, which share edges and corners to form a 3 x 3 1 -dimensional tunnel of size 6.9 A. Charge balancing Mg2+ cations exist in the tunnel and are exchangeable. Cryptomelane has a 2 x 2 tunnel structure of size 4.6 A but with K+ as the tunnel cation. Synthetic counterparts of todorokite and cryptomelane are OMS-1 and OMS-2 respectively. Synthetic manganese oxides with 4x4 and 4x2 tunnel structures are also known.

1.2 Octahedral/tetrahedral titanosilicates ETS-10 has a framework consisting of "TiO2" rods, which run in two orthogonal directions, surrounded by tetrahedral silicate units. The pore structure consists of 12- rings, 7-rings, 5-rings, and three-rings and has a 3-dimensional channel system whose minimum diameter is defined by the 12-ring apertures. Both aluminium and gallium can be isomorphously substituted exclusively at silicon sites such that aluminium or gallium avoids neighbouring silicon. The structure of ETS-4 has been discussed and models have been developed based on the structure of zorite but containing either extensive defects or intergrowths with other titanosilicate phases such as nenadkevichite. Zorite has a highly disordered framework with ostensibly a two-dimensional channel system. The two orthogonal sets of channels are defined by 12-Si/Ti atom and 8-Si atom rings, with silicon in tetrahedral co-ordination and titanium in octahedral and semi-octahedral co-ordination. The structure of the titanium-niobium-silicate nenadkevichite consists of square rings of silica tetrahedra Si4O12 in the (100) plane joined together by chains of NbO6 octahedra in the [100] direction. The structure of the titanium-silicate analog of the mineral pharmacosiderite KFe4(OH)4(AsO4) ~6H2O, is built up from octahedral TiO6 units sharing faces, to form a cube-like Ti4O4 unit, which in turn share vertices with tetrahederal silicon atoms (SiO4 groups), forming an open framework enclosing spherical cavities, interconnected in three dimensions by 8-ring windows.

Group 2: These pillared layered oxide materials include materials having the ability to swell and incorporate large polynuclear hydroxycations such as

[Al πO4(OH)24+p(H2O)12.p](7"p )+ and [Zr4(OH)n(H2O)24-n]16 These include smectite clays such as montmorillonites, layered titanates and niobates, manganates and molybdates, α-tin and α-zirconium phosphates, and hydrous layered sodium silicates, e.g. magadiite, Na2Si 14O29.l lH2O.

Group3: These materials are ordered mesoporous oxides and high silica materials. They include a new family of mesoporous silicates and aluminosilicates designated M41S which may be prepared by a surfactant-controlled process. Hexagonal MCM-41, cubic MCM-48 and lamellar MCM-50 are three members of this family. The incorporation of metal cations into the silicate framework was of particular interest from the point of view of obtaining materials with ion exchange capacity. Isomorphous substitution has been achieved with elements such as Al, Ti, V, B, Mn, Fe, Sn and Ga. MCM-22 is a high silica molecular sieve that is synthesised as aluminosilicate or borosilicate, with hexamethyleneimine as the directing agent. The framework topology contains two independent pore systems, both of which are accessed through 10-membered rings (lOMRs). Group 4: These materials, which possess a tetrahedral framework structure include: 4.1 Zincosilicates

The zincosilicates Na-VPI-7 (structure type code VSV), (Na, K)-RUB-17 (structure type code RSN), VPI-8 (structure type code VET), (K-Rb)-VPI-9 (structure type code VNI) and VPI-10 (structure not yet determined) were chosen for investigation. The framework structures of VPI-7 and RUB-17 have intersecting 3-dimensional channel systems of 8- and 9-membered rings. Layer like building units stack in such a way that in VPI-7 there are strings of 5 membered rings between the layers, whereas in RUB- 17 there are 4-/6-rings and 5-rings. "Spiro-5" units exist within the layers which consist of two interconnected 3 membered rings with zinc completely ordered in each 3 membered ring. VPI-8 is a high-silica molecular sieve with a pore system that consists of 1 -dimensional channels containing 12 membered ring that run down the c-axis. VPI-9 has a complex framework topology that can be described in terms of two types of layers joined via isolated tetrahedra. There is a 2-dimensional 8-ring channel system.

4.2 Zincophosphates A number of hydrated open-framework sodium zinc phosphates were selected that included Na6[CoxZn,.xPO4]6.yH2O (x = 0 to 0.3), NaZnPO4.H2O (structure type code CZP) and Na3Zn4O(PO4)3.6H2O. In the first material, an infinite helix built up of sodium cations and water molecules exists inside 1 -dimensional 6-ring channels. The Na3Zn4O(PO4)3,6H2O. In the first material, an infinite helix built up of sodium cations and water molecules exists inside 1 -dimensional 6-ring channels. The Na3Zn4O(PO4)36H2O network encloses roughly spherical cavities connected by a 3- dimensional network of 8-ring channels propagating in the orthogonal [100], [010] and [001] directions. The extra-framework species in NaZnPO4.H2O are located in pear-shaped cavities (12-ring diameter), interconnected through 8-rings and 6-rings.

The present invention will now be further described with reference to various ion exchange materials and by way of examples only.

MANGANESE OXIDE OCTAHEDRAL MOLECULAR SIEVES M ^-OMS-l

Mg(MnO4)2.nH2O (n « 6) was prepared by disproportionation of barium manganate in water according to equation (1).

3BaMnO4 + MgO + 3H2SO4 > Mg(MnO4)2 + MnO2 + 3BaSO4 + 3H2O (1) Thus, 20.561g BaMnO4 (72.2 mmol) were added to a solution of 0.97g MgO (24.1 mmol) in 7.08 lg concentrated H2SO4 (72.2 mmol) diluted to about 50ml with deionised H2O. Vigorous stirring was continued for 45 mins. The crude product was obtained by filtration through celite and evaporation of the deep purple filtrate. Purification was carried out by redissolving in deionised H2O (25ml total), filtering to remove some insoluble brown precipitate, and evaporation at room temperature (5.45g).

50ml 5.0 M NaOH were added dropwise into 40ml 0.5 M MgCl2.4H2O at room temperature under vigorous stirring, to prepare a Mn(OH)2 suspension. The

Mn(OH)2 suspension was then added dropwise to 40ml 0.1 M Mg(MnO4)2.6H2O at room temperature under vigorous stirring, to prepare Na+-birnessite (layered manganese oxide) suspension (pH 13.7). This was aged at room temperature for 4 days and then filtered and washed with deionised H2O until no Cl" was detected. Mg2+-buserite suspension was obtained by ion exchanging Na+-birnessite with 500ml

1 M MgCl2.6H2O while stirring at room temperature overnight. The exchanged product was filtered and washed several times with deionised H2O, and finally reslurried in water to a total volume of about 130ml. This suspension was distributed evenly between three 50ml capacity synthesis bombs and each was placed in an oven at 166°C for 49 hours. The dark brown-black solids were collected by filtration, washed with deionised H2O, and air dried at room temperature (total yield 2.64g).

K+-OMS-2 (sol-gel synthesis)

0.387g maleic acid was added to a solution of 1.5804g KMnO4 (10 mmol) in 100ml deionised H2O and the mixture was stirred for 60 mins. The resultant H2O-gel product was 40% H2O by volume on top of the dark brown gel. The H2O was decanted and the gel washed 4 times with 100ml portions of deionised H2O and the wash water was decanted. The gel was then transferred to a filter funnel under vacuum (water aspirator) for 20 mins at room temperature. It was then heated at 100°C for 12 hours, and then calcined in air at 450°C for 4 hours (0.90g). K+-OMS-2 (hydrothermal synthesis)

A solution of 5.89g KMnO4 (37.3 mmol) in 100ml H2O was added to a solution of 8.8g MnSO4. H2O (52.1 mmol) in 30m H2O and 3ml concentrated HNO3. The mixture was either refluxed or autoclaved (distributed between four 50ml capacity synthesis bombs) at 100°C for 24 hours. The products were filtered, washed with deionised H2O, and air dried at 120°C (8.3-8.4g).

OCTAHEDRAL/TETRAHEDRAL TITANOSILICATES Pharmacosiderite analog

HK3Ti4O4(SiO4)3.H2O, a structural analog of the mineral pharmacosiderite, was prepared by hydro lysing titanium isopropoxide (8.26g, 29.1 mmol) in a mixture of fumed silica (3.47g Cab-O-Sil M5, 57.7 mmol) and deionised water (45ml). After stirring overnight, the slurry was centrifuged and the solids washed twice with water. The mass of the gel after finally centrifuging and discarding the supernatant was 24.4g. Deionised water (10.3ml) and 5.06 M KOH (19.65g) were added and a milky suspension was obtained after shaking vigorously. This was autoclaved at 200°C for 63 hours to afford the product as a white microcrystalline powder (5.96g).

ETS-10

Solid TiO2 (TitanOxid P25, Degussa, 76% anatase and 24% rutile was used as the source of titanium. TiO2 (3.5g) was dispersed, by stirring, into deionised water (43ml) to which 10 M NaOH (13.125ml) and KF (1.88g) were added. After 5 mins of stirring, colloidal silica (32.8 lg Ludox HS-40, 40% silica) was poured into the mixture while stirring vigorously, and the stirring was continued for 5 hours. The slurry was then autoclaved at 200°C for 64 hours. The product was isolated by centrifugation, washed twice by redispersing it into deionised water, and dried in air at 50-60°C (15.15g).

ETS-4 A similar procedure to that of ETS-10 was employed for the synthesis of ETS-4 where the initial mixture contains TiO2 (3.5g P25), deionised water (35ml), 10 M NaOH (21.875ml) and NaF (0.875g). The crystallisation was again carried out statically at 200°C for 64h.

Zorite analog

Titanium isobutoxide (2.33g, 6.8 mmol) was hydro lysed slowly in 7 M NaOH (17.5ml, 122.1 mmol). H2O2 (100 VOL, 13.0G, 114.6 mmol) was then added, forming a clear yellow solution, to which tetrapropylammonium bromide (2.54g, 9.5 mmol) was added, followed by fumed silica (3.80g Cab-O-Sil M5, 63.2 mmol) and deionised water (3ml). The reaction mixture was autoclaved at 180°C for 92 hours. The product, a zorite analogue, was centrifuged, washed with deionised water, and dried in air at room temperature (1.59g).

Nenadkevichite analog (Ti:Nb « 4.1)

Sodium silicate solution (14% NaOH, 27% SiO2, 10 M NaOH (5.75ml), Nb2O5 (0.144g, 0.54 mmol), NaCl (0.461g, 7.9 mmol), KC1 (0.38g, 5.1 mmol), KF (0.96g, 16.5 mmol) and deionised water (8ml) were combined and homogenised for 15min. 1.9 M TiCl3 in 2 M HCl (2.96g) was then added dropwise over a few minutes followed by 2.4 M HCl (3.25ml). This gel was autoclaved under autogeneous pressure for 183 hours at 230°C. The resulting product, a nenadkevichite analogue, was cooled to room temperature, centrifuged and washed with deionised water and dried in air at 50-60°C (1.71g).

RESULTS

Distribution Coefficients

Distribution coefficients were determined in five test solutions: Deionised water, 0.1 M NaNO3, 0.1 M NaNO3/0.1 M NaOH, 0.1 M HNO3 and 4 M HNO3. Appropriate quantities of carrier-free tracers (1 7Cs or 89Sr) were present in these solutions such that the count rate (liquid scintillation, 0-2000 KeV) was about 20000cpm/ml. In general 0.50g of exchanger was equilibrated (rolling) with 5ml of solution in a 20ml capacity polyethylene liquid scintillation vial for 24 hours at room temperature. The slurries were then centrifuged in the vials (4000 rpm, 15-20 mins). For deionised water, an accurate 1ml aliquot was taken and mixed with 9ml scintillation cocktail. For 4 M HNO3, slightly greater than 2ml were taken and filtered through 0.22 μ PVDF filters attached to 5 or 10ml plastic disposable syringes. An accurate 2ml were then taken for counting (no cocktail). For the remaining solutions, slightly greater than 1ml was taken and filtered through a 0.22μm PVDF filter. An accurate lml aliquot was then taken and mixed with 9ml scintillation cocktail.

Table 1 gives the results obtained for Distribution Coefficients (KD). KD is calculated according to the equation:

KD = (Ai-A).V/Ai.m Where Ai is the initial cation concentration, A is the cation concentration after contact with the ion exchanger, V is the volume of solution and m is the mass of the ion exchanger material.

All of the materials were effective in removing both Cs-137 and Sr-89 from deionised water (KD greater than 1000 mL/g). OMS-1 and OMS-2 display somewhat similar behaviour, with OMS-1 showing the best performance for both Cs- 137 and Sr-89. OMS-1 is selective for Cs-137 in 0.1 M HNO3 (20700 mL/g) and even in 4 M HNO3 (250 mL/g), but the uptake is very low in neutral to mildly alkaline sodium salt solutions. Conversely, the material appears to be very effective in removing Sr-89 from the latter. All of the titanosilicates are very selective for both Sr-89 and Cs-137 in neutral to mildly alkaline sodium salt solutions, with the exception of Cs-137 on nenadkevichite (KD <50 mL/g) and so some extent Cs-137 on ETS-10 (KD <320 mL/g). The zorite sample and K-pharmacosiderite showed high capacities of 1.75 x 105 mL/g and 420 mL/g respectively for Cs-137 in 0.1 M HNO3. The exceptionally high distribution coefficients observed for the zorite sample may be due to some extent on an amorphous sodium titanate impurity. Table 1 Distribution coefficients (mLg" )

Material Nuclide Deionised 0.1 M 0.1 M 0.1 M 4 M HNO3

H2O NaNO3 NaNOJ HNO3 0.1 M NaOH

Mg2+-OMS-l 137Cs 50350 38 5 20720 251

89Sr > 100000 11090 > 100000 1 3

C cOz K+-OMS-2 137Cs 7415 185 45 127 8

03

— 1 89Sr > 100000 149 >100000 2 0

5 rπ £ ^ NA+-ETS-4 137Cs 25475 1587 780 51 3 c roe 89Sr 6693 27165 9962 1 0

(Na+, K+)- 137Cs 8423 312 179 20 1

ETS-10 89Sr 30451 37755 > 100000 0.3 0 to

Zorite analog 137Cs 31990 >100000 83085 174800 47

89Sr 2038 > 100000 > 100000 13 0

K+-Pharmaco- 137Cs 37825 1165 268 423 59 siderite analog 89Sr 64370 > 100000 16000000 0 0

Ion exchange experiments

Distribution of coefficients of tracer quantities of strontium or caesium ions were determined by equilibrating 0.5g sample of exchanger with 5ml of solution for 1 day (rolling). The solid phase was separated from the solution by centrifugation followed by filtration through 0.2 μm PVDF membrane. The specific 137Cs and 89Sr activities were measured using liquid scintillation. Figure 1 shows the pH before and after equilibration for each of the six exchangers in each of the nine 0.1 M NaNO3/xM HNO3 solutions used to measure KΌS as a function of pH.

Discussion

The results of caesium and strontium distribution coefficients determined for each of the six exchangers as a function of sodium, potassium, magnesium and calcium concentration are given in Table 2.

Table 2 Distribution coefficients of caesium and strontium as a function of sodium, potassium, magnesium and calcium ion concentration

Initial concentration of MN03 or M(N03),(mol dm"3) 2 1 0.3 0. Ϊ 0.003 0.01 0.001

Distribution coefficients of caesium (mLg )

OMS- Na 38 186 1679

K 1 10 61

OMS-2 Na 9 21 185 792 2253

K 3 2 9 64 548

ETS-4 Na 15 45 118 1587 12093 25392

K 9 17 269 5704 26510

ETS-10 Na 12 31 312 2089 6797

K 3 3 39 513 5421

Zonte Na 1228 4225 13324 5212675 15227 7027

K 24 47 652 18164 33563

Pharm Na 216 391 557 1 166 24697 54925

K 12- 252 2630 20298 51893

OMS- 1 Mg 40 163 1050 1905 5527

Ca 3 1 12 56 425

OMS- Mg 44 126 610 715 1151

Ca 7 8 169 448 740

ETS-4 Mg 2668 7425 18710 24435 25482

Ca 1610 4584 14547 23726 34024

ETS10 Mg 2 13 86 344 4217

Ca 7 24 119 399 4305

Zonte Mg 62734 287053 1786579 16870212 6821064

Ca 2799 8402 115583 5430963 144977

Pharm Mg 2096 3254 6783 11404 51129

Ca 530 994 2700 7236 47123

Distribution coefficients of strontiujmm ((mmLLgg""1 '))

OMS-1 Na 41 118 293 1 1090 30181 76356

K 37 70 501 3456 13340

OMS-2 Na 9 19 149 1786 10119

K 1 4 16 105 982

ETS-4 Na 172 973 27165 7909 6310

K 673 2059 57744 1 19267 28488 18181 7660

ETS-10 Na 119 445 1387 37755 30679 13987

K 923 2122 63777 44465 10452 41578 15628

Zorite Na 438 1921 8005 300000 9464 5841

K 23050 48885 8664 529602 129938 4188 4804

Pharm Na 2830 8115 21460 300000 35512 16657

K 22685 48246 165019 540039 140986 32830 12617

OMS-1 Mg 7 31 517 4078 22653

Ca 2 1 16 184 2676

OMS-2 Mg 2 6 61 268 1097

Mg 6 5 * 24 152

ETS-4 Mg 1 8 132 3790 1430828

Ca 0 1 1 11 13256

ETS-10 Mg 16 50 947 13012 40265

Ca 1 1 3 108 29148

Zorite Mg 30 209 28808 1384489 3767752

Ca 1 1 12 118 64806

Pharm Mg 137 555 9169 114582 41382

Ca 8 17 209 8604 132301 Referring to the various materials :-

Manganese oxides Mg2+-OMS-l and K+-OMS-2

Distribution coefficients of caesium as a function ofNa+, K+, Mg?+ and Ca^+ ion concentration, and as a function ofpH in 0.1 MNaNOj

OMS-2 was found to be more effective than OMS-1 at removing trace caesium from solutions between 0.001 M and 4 M in potassium or sodium (Fig 2). Both ions interfere strongly (potassium more so) and only in 0.001 M NaNO3 were distribution coefficients greater than 1000 mLg"1 measured (1679 mLg"1 for OMS-1 and 2253 mLg"1 for OMS-2). However, in 0.1 M NaNO3, KΌ for OMS-1 increases with decrease in pH (Fig 4), reaching a maximum at about pH 1 (6670 mLg"1, initial [HNO3] = 0.1264 M). The performance is still good even in 0.948 M HNO3 (KΌ = I960 mLg-1). The reason for this behaviour is that protons exchange for magnesium ions as the pH is lowered and exchange of strontium on the hydrogen form is more favourable. In contrast KD for OMS-2 is low in the pH range 0.5-3. In the presence of magnesium ions, OMS-1 performs better than OMS-2, although the distribution coefficients merge at high concentrations (Fig 3). Calcium ions interfere more strongly than magnesium ions, so much so in the case of OMS-1 that the trace caesium uptake becomes a great deal lower than that on OMS-2. Distribution coefficients of strontium as a function ofNa+> K+, Mg^+ and Ca + ion concentration, and as a function ofpH in 0.1 MNaNOβ

In contrast to the sorption behaviour of caesium, Figures 6 and 7 show that OMS-1 rather than OMS-2 is the best material for removal of trace strontium in the presence of Na+, K+ or Ca2+ (pH > 7). In the sodium ion concentration range 0.001 to O.lmol dm"3, the KΌ decreases from 76360 to 11090 mLg"1 FOR OMS-2. The situation is even less favourable once the pH is lowered in 0.1 M NaNO3 and the KΌ falls below 1000 at pH 6 (Fig 5). Again, both potassium or calcium ions interfere more strongly than sodium or magnesium ions respectively. Titanosilicates (Na\ K+)-ETS-10 and Na+-ETS-4 Distribution coefficients of caesium as a function ofNa+, K+, Mg + and Ca^+ ion concentration, and as a function ofpliin 0.1 MNaNO

In the sodium ion concentration range 0.001 to lmol dm"3, KΌ for ETS-10 was lower by a factor 3.7-5.8 compared with ETS-4 (Fig 8). ETS-4 is only effective however (KD > 1000 mLg"1) for sodium ion concentrations less than about 0.2mol dm"3 or potassium ion concentrations less than about 0.02mol dm"3. Also, KΌ falls below 1000 mLg"1 in 0.1 M NaNO3 at pH < 5 (Fig 10). There appears to be little difference between calcium or magnesium ions concerning their effect on the caesium KΌ of the titanosilicates (Fig 9). ETS-4 experiences relatively minor interference from these two ions compared to ETS- 10.

Distribution coefficients of strontium as a function ofNa, K+, Mg2+ and Ca + ion concentration, and as a function ofpH in 0.1 MNaNOs

On the whole ETS-10 is slightly more selective for strontium than ETS-4, especially in magnesium or calcium nitrate solutions (Fig 13). The sorption behaviour on both materials in the presence of sodium or potassium ion is unusual and similar to that observed for the titanosilicate analogs of zorite and pharmacosiderite (Fig 12). For example, up to a sodium concentration of about O.lmol dm"3 KΌ increases from 6310 to greater than 27000 mLg"1 of ETS-4. A possible explanation lies in the fact that hydrolysis of the exchanger could be significant, ie an equilibrium exists between ETS-4 in the sodium form and ETS-4 in the hydrogen form. As the sodium concentration increases in the solution there will be an essential shift in this equilibrium, resulting in a decrease in the proportion of the hydrogen form. To an extent Na+-ETS-4 prefers hydrogen ions to sodium ions, and therefore absorption of strontium on the sodium form is more favourable (see Fig 11). Beyond a sodium ion concentration of about 0. lmol dm"3 the KΌ decreases approximately linearly. Titanosilicate analogs of the minerals zorite and pharmacosiderite Distribution coefficients of caesium as a function of sodium, potassium, magnesium and calcium ion concentration, and as a function ofpH in 0.1 MNaNOβ The zorite sample was very selective for caesium versus sodium over a wide pH range (Figs 14 and 16). Thus, the KD was 1228 mLg"' even in 4 M NaNO3, about 2000 mLg"1 at pH 1 in 0.1 M NaNO3 and above 105 mLg"1 from pH 4.6 to pH 10 in O.lmol dm"3 NaNO3. The pharmacosiderite sample was considerably less effective in these conditions.

Distribution coefficients of strontium as a function of sodium, potassium, magnesium and calcium ion concentration, and as a function ofpH in 0.1 MNaNO^ In the presence of sodium (pH > 10) the pharmacosiderite sample was slightly more effective than the zorite sample for the removal of strontium (Fig 18). The KΌ remained favourable even up to 4 M NaNO3. There was little difference though between the two materials once the pH was less than 7 in 0.1 M NaNO3 (Fig 17). The distribution coefficients decreased approximately linearly as the pH was lowered, passing through 1000 mLg"1 at about pH 5.5. Sorption of strontium on the zorite sample was poor with calcium ion concentrations greater than 0.01 M (Fig 19).

FURTHER OCTAHEDRAL MANGANESE OXIDES

Na+-birnessites

Three preparative methods were used. In each case the products were isolated by filtration, washed with deionised water and dried in air at room temperature.

Method 1 SLMl. A Mn(OH)2 sol was prepared by treating 80ml 0.5mol/L MnCl2 with 100ml 5.0mol/L NaOH at room temperature under vigorous stirring. It was then added dropwise to 80ml 0.093mol/L Mg (MnO4)2.6H2O at room temperature with vigorous stirring (MnO47Mn2+ = 0.372). The resulting layered manganese oxide Na+- birnessite suspension (pH 13.7) was aged at room temperature for 4 days. Half of the material was isolated as described above and the remaining half was used to prepare Mg2+-todorokite (SMO1RR). Four other samples were prepared similarly but with initial MnO47Mn2+ ratios of 0.297, 0.334, 0.37 and 0.40, and an ageing time of 1 week (SLM26).

Method 2 SLM27. This procedure avoids the use of Mg(MnO4)2.6H2O. 100ml 5.0mol/L NaOH were added dropwise to 80ml 0.5mol/L MnCl2.4H2O containing MgCl2 such that Mg2+/Mn2+ = 0, 0.4, 0.7 and 1.0. 80ml 0.2mol/L KMnO4 were then added dropwise and the suspension aged at room temperature for 3 days.

Method 3

SLM28. 125ml 0.3mol/L Mn(NO3)2 were treated with 250ml 3% H2O2 containing NaOH such that Na7Mn2+ = 3.33, 4.0, 5.0 and 6.0. The resulting suspension was stirred at room temperature for 1 hour.

Mg2+ -OMS-1 and (H+, Mg2+)-OMS-l

SMOIRR. Mg2+-buserite (layered manganese oxide) was obtained by ion exchanging Na+-birnessite (SLMl) with 1 L lmol/L Mg(NO3)2 while stirring at room temperature overnight. The exchanged product was filtered and washed several times with deionised water, and finally redispersed in water to a total volume of about 70ml. The suspension was autoclaved in a 100ml capacity synthesis bomb at 170°C for 2 days. The dark brown-black product was collected by filtration, washed with deionised water and air dried at room temperature (2.64g). Two other samples of Mg2+-todorokite were prepared from Na+-birnessite precursors with initial MnO4 " /Mn2+ = 0.358 (SMO1, scale: 20 mmol Mn2+) and 0.346 (SMO1R, scale: 40 mmol

Mn2+).

The exchangeable magnesium ions in the tunnel of OMS-1 (3x3 tunnel structure) were extracted by repeated treatments in lmol/L nitric acid. The acid treatment was repeated up to 7 times to obtain an acid-treated sample, (H+, Mg2+)-OMS-l. Three samples were prepared: SMOR (from SMOIRR, V:m = 200, seven exchanges of 1 day each), SMO2R (from SMOIRR, V:m = 100, five exchanges of 1 day each) and SMO2RR (from SMOlr, V:m = 100, three exchanges of 2 days each).

FURTHER OCTAHEDRAL/TETRAHEDRAL CRYSTALLINE TITANOSILICATES

Na+ -ETS-4 and (Na+, K+)-ETS-10 (Na+,K+)-ETS-10 (SMS11) and Na+-ETS-4 (SMS12) were synthesised by hydrothermal treatment at 200°C for 64 hours of mixtures with the initial compositions TiO2 : 5SiO2 : 3NaOH : 0.74KF : 4.1H2O and TiO2 : 5SiO2 : 5NaOH : 0.48NaF : 4.1H2O respectively. Titanium dioxide (Degussa TitanOxid P25) and Ludox HS-40 colloidal silica were the raw materials used.

Attempts were made to synthesise pure sodium ETS-10 by substituting NaF for KF in the above gel composition. It was found that hydrothermal treatment for 5 days resulted in a mixture of ETS-10 and ETS-4. Seeding the gel with ETS-4 resulted in only ETS-4. However, no peaks due to either ETS-4 or ETS-10 were evident in the powder X-ray diffraction pattern of the microcrystalline product obtained from the unseeded reaction mixture autoclaved for 10 days. In fact the pattern matches closely that of the synthetic analog of the mineral penkvilksite (orthorhombic polytype). Penkvilksite has an ideal formula Na4Ti2Si8O22.5H2O. The mineral occurs in two polytypic modifications, orthorhombic (penkvilksite-20), and monoclinic (penkvilksite- \M) W The structure consists of TiO6 octahedral and SiO4 tetrahedral connected to each other to form a three-dimensional network.

Analogs of pharmacosiderite, zorite and nenadkevichite Titanosilicate analogs of the minerals zorite, pharmacosiderite and nenadkevichite were obtained from gels with the initial compositions SiO2 : 1.92NaOH : 0.15TBABr : 25 H2O : 1.8 H2O2 : 0.1TiO2 (raw materials: titanium isobutoxide, Cab-O-Sil M5 fumed silica), 0.076KOH : 0.029TiO2 : 0.058SiO2 : 2.5H2O (raw materials: titanium isopropoxide, Cab-O-Sil M5 fumed silica) and 0.0927NaOH : 0.0079NaCl : 0.0165KF : 0.0051KC1 : 0.0452SiO2 : 0.0045TiO2 : 0.00055Nb2O5 [raw materials: sodium silicate solution (14% NaOH, 27% SiO2), l,9mol/L TiCl3 in 2.0mol/L HCl]13 respectively. The zorite samples were crystallised at 180°C for 92 hours (SMS9, SMS9R and SMS9RR), the pharmacosiderite samples at 200°C for 64 hours (SMS8 and SMS8R) and the nenadkevichite sample at 230°C for 183 hours (SMS10). The X-ray powder diffraction pattern of SMS9R was a close match with that ofthe mineral zorite. RESULTS

Octahedral manganese oxides

Distribution coefficients on Na+-birnessites

Screening Tests

Very high degrees of sorption were obtained for the first row transition metal radionuclides on SLMl (Table 3, Fig. 20). Hydrolysis of the exchanger is significant, as evidenced by the high equilibrium pH of 10.81 in deionised water which decreases to 9.08 in 0.1 mol/L NaNO3. The material is particularly effective for cobalt and ion in the pH range 1-11. This was not a surprising result since it is well known that cobalt and other trace elements are often strongly associated with manganese minerals in soils and in the marine environment. In the case of 59Fe the dominant process is probably oxidation of Fe2+ to Fe + either on the surface of the manganese oxide or in the interlayer, with concomitant liberation of Mn2+. Except possibly at pH < 2, ion oxide will precipitate. The material was not effective in removing trace cobalt from 0.1 mol/L NaOH/0.1 mol/L NaNO3. The decrease of sorption at alkaline pH is due to hydrolysis to CoOH+ and soluble Co(OH)2.

Table 3 Distribution coefficients ( mL/g) on Na+-birnessite, SLMl (equilibrium pH in parenthesis for V:m = 200)

V:m Distilled 0.1 mol/L 0.1 mol/L 0.1 mol/L 4 mol/L water NaNO3 NaNO3/NaOH HNO3 HNO3

(10.81) (9.08) (12.98) (1.18)

57Co 200 46910 445500 0 2531 0.3

65Zn 200 384000 ! 69930 55 0.9

54Mn 200 !a 364000 4048 55 _b

236pu 100 27740 39720 1620 49 0.3 a activity below detection limit b not measured Distribution coefficients of 137Cs and 89Sr as a function of pH and sodium ion concentration

The distribution coefficient of 137Cs is SLM23 (initial MnO47Mn2+= 0.334) in 0.1 mol/L NaNO3 increases from about 10 mL/g at pH 10 to just over 1000 mL/g at pH 1-2 (Fig. 21). The reason for this behaviour is that protons exchange for sodium ions as the pH is decreased and exchange of caesium on the hydrogen form is more favourable. Below pH 1 uptake of caesium begins to decrease. Consistent with these results, sodium ion interferes very strongly in the sorption of caesium at high pH (Fig. 5). On a logarithmic scale and between initial sodium ion concentrations of 0.01 and 1.0 mol/L, the distribution coefficient decreases linearly from 76 to 1.6 mL/g. The slope is -0.83, close to the theoretical value of -1 for univalent-univalent exchange. Uptake of 89Sr on SLM26 is good only at pH > 7 and [Na+] , 0.1 mol/L (Figs. 22 and 24).

Distribution coefficient of 57Co on Na+-birnessite as a function of pH, sodium, citrate and borate ion concentrations

SLM26 compares very favourably with the activated carbon Norit ROW Supra. For example, at pH 9.8 and [Na+] = 1 mol/L the distribution coefficient of 57Co on SLM26 is 582000 mL/g compared with 79400 mL/g on Norit ROW Supra (Fig. 25). Sodium ion does not interfere in the sorption efficiency of 57Co on SLM26 at least in the pH range 9.8-10.5, in fact the distribution coefficient tends to increase up to [Na+] = 1 mol/L. At neutral pH and in deionised water Norit ROW Supra does not perform well (KΌ = 200 mL/g) whereas SLM26 is still very effective (K_ = 400000 mL/g). Even at pH 2, 98% of trace cobalt is removed (Fig. 26). In 0. lmol/L NaNO3 sorption is seen to decrease significantly only in the pH range 5-9 (Fig 27).

The effects of complexing agents, sodium tetraborate (Na2B4O7) and sodium citrate (Na3O7C6H5) on the distribution coefficient of 57Co were studied in the concentration range 10"6 to 10"3 mol/L (Fig 28). Citrate ions (L) form monocomplexes with Co2+, the logK (stability constant) for the reaction Co2+ + L = CoL being 5.00.1 Boric acid [L = B(OH)4 "] forms a tetracomplex with the logK for CoL4 being 10.03. Citrate concentration did not have a very strong effect on the uptake of cobalt. At the highest concentration the distribution coefficient was nearly 100000 mL/g, which is about half that determined in the absence of citrate in 0.003mol/L NaNO3 (pH 10.4). The distribution coefficient on SLM26 is at least one order of magnitude greater than that on Norit ROW Supra in the concentration range studied. In contrast borate concentration had a much stronger effect on the sorption efficiency of trace cobalt on SLM26. Thus, the distribution coefficient decreases by greater than one order of magnitude in the concentration range studied. This is surprising since the citrate complex is stronger than that of borate. At the highest borate concentration SLM26 sorbs trace cobalt only slightly more efficiently than Norit ROW Supra.

Distribution coefficient of 57Co on Na+-birnessites prepared by different methods

SLM26 was prepared by reacting magnesium permanganate with a manganese(II) hydroxide sol (method 1). The initial MnO47Mn2+ ratio was varied in the range 0.30- 0.40 as the first step to optimise the performance ofthe material. This parameter has a strong effect on the sorption efficiency (Fig. 29). Thus, the distribution coefficient of 57Co on SLM26 with MnO47Mn2+ = 0.40 is up to one order of magnitude greater than that on SLM26 with MnO47Mn2+ = 0.30, in 0.1 mol/L NaNO3. pH 2-6.

A slight variation on the above reaction is to react potassium permanganate with a mixed magnesium manganese(II) hydroxide sol (method 2, SLM27). The materials formed perform similarly to SLM26 (Fig. 35). The optimum Mg2+/Mn2+ ratio is not clear as yet since the incorporation of magnesium strongly influences the acidity of the material and the initial three-point plots (KΌ VS pH in 0.1 mol/L NaNO3) for each ratio do not overlap due to differences in equilibrium pH. However it seems that incorporation of magnesium does not have a strong effect on the sorption deficiency. An alternative method for the synthesis of Na+-birnessite is to use hydrogen peroxide instead of permanganate (method 3, SLM28). The materials formed are again very promising for the removal of trace cobalt (Fig. 31).

Distribution coefficients on OMS-1 and OMS-2 Screening tests

Todorokite-type manganese oxides with a 3x3 tunnel configuration were very effective in removing a wide range of radionuclides, in some cases over a wide pH range (Table 5 and 6). Mg2+-OMS-l (SMO1) was selective for 137Cs in 0. lmol/L HNO3 (20700 mL/g) and even in 4 mol/L HNO3 (250 mL/g), but the uptake was very low in neutral to mildly alkaline 0.1 mol/L NaNO3 (Table 5). Acid extraction of SMOIRR produced SMO2 that gave an improved caesium distribution coefficient of nearly 40000 mL/g in 0.1 mol/L HNO3 (Table 6). The benefits of this treatment are shown even more clearly for SMO2RR, produced from SMOIR. Acid treatment resulted in an increase in the distribution coefficient of 59Fe in 0.1 mol/L HNO3 from 24300 to 38840 mL/g.

Distribution coefficient of 57Co on Na+-birnessite, Mg2+-OMS-l and (Mg2+, H OMS-1

Distribution coefficients of 57Co were about 1000 mL/g on Na+-birnessite and Mg2+- OMS-1 at pH 1 in 0.1 mol/L NaNO3, rising to about 7000 mL/g at pH2 in the case of Na+-birnessite (Fig 32). The acid-treated OMS-1 performs worse than the untreated sample of pH <2, but the situation is unclear above pH2.

Distribution coefficient of 137Cs as a function of sodium, potassium, magnesium and calcium ion concentration, and as a function of pH in 0.1 mol L NaNO3 OMS-2 was found to be more effective than OMS-1 at removing trace caesium from solutions between 0.001 mol/L and 4 mol/L in potassium or sodium (Fig. 33). Both ions interfere strongly (potassium more so) and only in 0.001 mol/L NaNO3 were distribution coefficients greater than 1000 mL/g measured (1679 mL/g for OMS-1 and 2253 mL/g for OMS-2). However, in 0.1 mol/L NaNO3, uptake of trace caesium on OMS-1 increases with decrease in pH (Fig. 21), reaching a maximum at about pH 1 (6670 mL/g, initial [HNO3] = 0.1264 M). The performance is still good even in 0.948 mol/L HNO3( D = 1960 mL/g). This behaviour is similar to that observed for Na+-birnessite. In contrast, the sorption efficiency of 137Cs on OMS-2 is poor in the pH range 0.5-3. In the presence of magnesium ions, OMS-1 performs better than OMS-2, although the distribution coefficients merge at high concentrations (Fig. 34). Calcium ions interfere more strongly than magnesium ions, so much so in the case of OMS-1 that the trace caesium uptake becomes a great deal lower than on OMS-2.

Distribution coefficients of 89Sr as a function of sodium, potassium, magnesium and calcium ion concentration, and as a function of pH in 0.1 mol/L NaNO3

In contrast to the sorption behaviour of caesium, OMS-1 rather than OMS-2 is the best material for removal of trace strontium in the presence of Na+, K+ or Ca2+ and pH > 7 (Figs. 35 and 36). In the sodium ion concentration range 0.001 to 0.1 mol/L, the distribution coefficient on OMS-1 decreases from 76360 to 11090 mL/g, compared with 13340 to 501 mL/g of OMS-2. The situation is even less favourable once the pH is lowered in 0.1 mol/L NaNO3 and the sorption falls below 90% at pH 6 (Fig. 22). Again, both potassium or calcium ions interfere more strongly than sodium or magnesium ions respectively.

Titanosilicates and Zincosilicates

Some promising results were obtained for the removal of δ5Zn, 54Mn and 236Pu from neutral to mildly alkaline (pH 13) sodium salt solutions (Fig. 4). In common with all of the materials examined, none of the metallosilicates were effective in removing trace 57Co from 0.1 M NaOH/0.1 M NaNO3. The decrease of sorption at alkaline pH could be due to hydrolysis to CoOH+, which competes to a lesser extent than co2+ for occupying the exchange sites.

Octahedral Manganese Oxides

Both the layered sodium birnessite and todorokite-type manganese oxides were very effective in removing a wide range of radionuclides, in some cases over a wide pH range (Table 4 to 6, Fig. 37). The 57Co KO's were about 1000 ml/g for Na-birnessite and Mg-OMS-1 at pH 1 in 0.1 M NaNO3, rising to bout 7000 ml/g at pH 2 in the case of Na-birnessite. At neutral pH the K^ s are at or above 100000 ml/g. The results for 59Fe are complicated by the fact that the dominant process is oxidation of Fe2+ to Fe3+ either on the surface of the manganese oxide or in the interlayer, with concomitant liberation of Mn2+, except possibly at pH < 2 when iron oxide will precipitate.

Manganese Oxides Optimisation

Figure 3a shows a process for the optimisation of the manganese oxides. Sorption studies with trace cobalt are used to screen the improvements or otherwise in the performance of the materials. Factors affecting performance include layer charge densities, interlayer cations and doping of metal atoms into the framework.

Table 4 Distribution coefficients (mL/g) on K+-OMS-2, SM04 (equilibrium pH in parenthesis for V:m = 200)

V:m Distilled 0.01 mol/L 0.1 mol/L 0.1 mol/L 4 mol/L water NaN03 NaN03/NaOH HN03 HNO3

(4.07) (3.43) (12.95) (1.08) l37Cs 100 7415 185 45 127 8

89Sr 100 > 1000000 149 > 1000000 2 0

"Co 100 43320 32000 50 24 0

65Zn 200 30850 657 22790 0 0.5

"°Ag 100 - 286230 1609 71950 -

236pu 100 7124 447 80.3 0.3 0

Table 5 Distribution coefficients (mL/g) on Mg2+-OMS-l (equilibrium pH in parenthesis for SMOl , V:m = 200)

Code V:m Distilled 0.01 mol/L 0.1 mol/L 0.1 mol/L 4 mol/L water NaN03 NaN03/NaOH HNO3 HNO3

(7.20) (7.00) (12.96) (1.20)

137Cs SMOl 100 50350 38 5 20720 251

8 Sr SMOl 100 1 1 1090 ! 1 3

"Co SMOl 100 83500 295600 11 1973 9

65Zn SMOl 200 ! 716200 29600 9.4 0.3

54Mn SMOl 200 45890 366500 12540 290 -

59Fe SMOIR 200 2819 ! 1 24300 -

1 ,0Ag SMOl 100 593 1554 5566 58420 -

236pu SMOl 100 1 ! 14560 0 0.5

Table 6 Distribution coefficients (mL/g) on (Mg2+, H+)-OMS-l (equilibrium pH in parenthesis for SMOIR, V:m = 200)

Code V:m Distilled 0.01 mol/L 0.1 mol/L 0.1 mol/L 4 mol/L water NaN03 NaN03/NaOH HN03 HN03

(4.16) (2.86) (12.90) (1.08)

,37Cs SM02 100 122000 18790 0 39540 204

S9Sr SM02 100 5022 45 7707 5.7 0

"Co SM02R 200 434700 235800 0 943 10

65Zn SM02R 200 568500 2970 865400 18 1.0

54Mn SM02R 200 ! 51490 1807 632 -

59Fe SM02RR 200 I 1 1 38840 - MCM MATERIALS

There is a wide range of synthesis gels that can be used to produce MCM-type materials. In this case synthesis involved just the basic ingredients, ie silica source, surfactant and water. The gels were optimised in order to prepare the desired materials which could then be further treated to substitute hetero-atoms such as boron, zinc and aluminium.

For the synthesis of MCM-41, sodium metasilicate and the bromide form of the quaternary ammonium surfactant were chosen with a view to an industrial scale up, ie cost, abundance and simplicity. The advantage of using sodium metasilicate is that no other phase can be formed ie MCM-48/50, and so no inter-phase contamination can occur. The reason for this may be due to the fact that the hydrolysis reaction is very fast and so thicker, inflexible (amorphous) walls are formed and so cannot accommodate the more curvaceous MCM-48 structure.

MCM-41 was synthesised using a static bomb and autoclave at 100°C for 48 hours using the bromide surfactant. After this time the product was filtered and washed with hot water (50°C) and air dried (30°C). The product was then calcined under a nitrogen atmosphere to 560°C and then in air for a further 6 hours at this temperature. This calcination step removes the surfactant to leave the hollow siliceous tube structure.

Synthesis of MCM-48 is very similar except that TEOS is used as the surfactant and sodium hydroxide needs to be added in order to induce hydrolysis.

Summary of the MCM-41 and MCM-48 results

A series of experiments were conducted in order to determine the quality of the product (as determined by XRD). Various parameters were varied such as silica concentration, surfactant concentration, water content and finally the pH of the gel system. It was found that:- • Increasing surfactant concentration improves the overall quality of the material and increases (slightly) the unit cell dimension.

• Lowering the water content improves the quality ofthe material.

• Quality of the product is unaffected in the pH range 10-11, but long range ordering ofthe product is affected at around pH 9.

• Quality ofthe product is massively improved by autoclaving.

• Quality ofthe product is massively improved by calcination.

• XRD patterns gave a very broad peak in the 20-30 20 range which has been attributed to the amorphous nature ofthe wall structure (ie a definite shape on the macro-scale but amorphous on the molecular scale).

The next series of experiments looked at this gel formulation using different alkyl chain length surfactants (C8, C12, C14 and C]6). Decreasing the alkyl chain length of the surfactant decreases the unit cell size of the material, but coupled with this decrease, there is a decrease in the ordering of the material, ie the XRD peaks get broader and less intense.

Aluminium and boron were incorporated into the MCM-41 framework. XRD analysis showed that there was a slight reduction in peak intensity and very little loss or order reflected in the higher order peaks. When aluminium was added to the gel and then aged, small platelets were seen. These platelets were not seen for the pure siliceous material. This may mean that the structure may require aluminium to reduce strain.

The aluminium source used caused a problem with the synthesis of the highest substituted material, due to its acidic nature. Sodium hydroxide was added to overcome the acidity ofthe aluminium source. There was no change in the d-spacing for the [100] reflection ~4θA. The XRD pattern showed that the addition of sodium hydroxide caused a disruption in the long range ordering ofthe material. For boron incorporated materials, unlike aluminium materials, there seems to be no loss of crystallinity ofthe materials even for the highest substituted products.

Results have shown that good quality pure siliceous MCM-41 type can be produced with varying pore sizes and good quality MCM-41 materials templated with C16TMABr have been produced with varying levels of incorporated aluminium and boron.

The MCM-41 materials which were synthesised are summarised in Table 7. Table 7

Figure imgf000030_0001

The abbreviation "(Cs, Sr)-(A1, B, Zn)" indicates that the synthesis gels were doped with CsCl and SrCl2.6H2O (SiO2:Dopant Oxide = 25). These were produced to see if any ion exchange specificity arises towards caesium and strontium. Also an (Al, B)-MCM-41 material were produced.

Screening Tests

Distribution coefficients for various heteratom substituted MCM-41 materials of varying pore sizes. The batch factors for all measurements was kept at 200, unless otherwise stated. The tests were carried out with the following solutions: i) Trace caesium, cobalt and strontium uptake from H2O, 0.1M NaNO3,

0.1M NaNO3 and 0.1M NaOH, and 0.1M HNO3 ii) Trace caesium and strontium uptake from 1M, 10"'M, 10"2M, lO^M, 10"5M solutions of caesium nitrate and strontium nitrate respectively iii) Trace cobalt uptake 10"3M, lO^M, 10"5M, 10"6M sodium tetraborate and tri- sodium citrate.

The MCM-41 framework is labile to hydrolysis. This is more pronounced when the materials have been equilibrated with a solution of high alkalinity or solutions of low ionic strength (i.e. water will practically dissolve the pure siliceous materials, but will hardly affect an aluminium substituted material). Also pore size is another factor involved in stability, the smaller pore size materials are more prone to hydrolysis due to their more disordered, less condensed framework structure (due to steric factors arising from highly curved pore wall structure). There has been no in depth study of this, these observations have only been deduced by noting how much of the material remains after centrifugation and on how easily the PVDF 0.2μm filters blocked with colloidal siliceous material.

Sorption of trace caesium

Results are presented in Figure 40. Generally all materials sorb caesium poorly in the presence of 0.1M NaNO3, 0.1M NaNO3 and 0.1M NaOH, and 0.1M HNO3. It seems that aluminium substituted MCM-41 materials perform the best of all materials tested. For aluminium substituted materials the higher the level of aluminium substitution the greater the sorption of caesium, the exception is A 1(8)- MCM-41 where this level of substitution compromises the framework order. The smaller pore size materials perform better than the larger pore materials with the same level of heteroatom substitution. Similar trends are seen with the zinc substituted materials but the level of sorption is orders of magnitude lower than that of the aluminium materials. The pure siliceous materials perform similarly and sometimes show higher sorption than some ofthe zinc containing materials of similar pore size.

Sorption of trace strontium Results are presented in Figure 41. Like with caesium strontium uptake in the presence of 0.1M NaNO3 and 0.1M HNO3 is almost negligible. However, by studying the uptake performance trends in 0.1M NaOH combined matrix it can be seen that Zn substituted materials have far superior sorption properties than all of the other materials. Generally, smaller pore size and higher zinc substitution leads to greater sorption of strontium. Here the sorption of strontium is likely to be as SrOH+, this will be supported from evidence obtained from the uptake of strontium as a function of increasing concentration ofthe nitrates of sodium, potassium, magnesium and calcium. Such strong sorption behaviour indicates that these materials may have a small number of very specific sorption sites. These sites could result from having a mix of tetrahedral zinc framework sites and fully ionised silanol groups whose presence is due to the partially condensed nature ofthe framework.

Sorption of strontium from pure water is, as expected, generally high. The highest sorption is seen from the aluminium containing samples. There are a few exceptions to this including the large pore zinc containing materials and the smaller pore boron substituted materials.

Another unusual sorption trend can be seen from the pure siliceous materials as these show unusually high sorption. This could be explained by the extent of framework damage resulting from equilibration with a dilute electrolyte, which will give rise to SiOH groups which may, at best, only be partially ionised at the solution equilibrium pH(pH~5.5-6.0).

Uptake of caesium as a function of caesium nitrate concentration Results are presented in Figure 42. A range of concentrations from 1M to 10"5M caesium nitrate are used. From a quick glance at graph three there are a few simple trends that can be seen. These are: the percentage of caesium removed from solution increases as the concentration of caesium in solution decreases; aluminium substituted materials have the greatest capacity which is especially seen at low concentrations; and increasing heteroatom means increasing sorption properties as does smaller pore size. As the concentration of caesium increases the materials reach their saturation capacity and so proportionally the amount of radioactive caesium taken up is lower, thus the Kd value is lower. It should be noted that all the trends exhibit a decrease in Kd value with increasing caesium nitrate concentration, unlike some materials where framework hydrolysis plays a part in the sorption mechanism, e.g. the titano-silicates. Having framework aluminium present in the material means that, large and relatively unhydrated ions are preferentially removed from solution, e.g. caesium. As can be seen from the graph these aluminium containing materials have a large capacity for sorption of caesium despite the presence of trace competing ions, e.g. hydronium (from the material and the ionic product of the solvent) and sodium (from the material).

Having more framework aluminium, a greater sorption capacity is expected. As can be seen from the graph there is a marked increase in sorption as the molar ratio SiO2Al2O3 increases from > (pure siliceous) to 25. When the ratio is 8 there is a massive decrease in caesium removal. This is probably due to compromised framework order as the ratio increases to beyond the framework capacity (see later to inferences drawn from ion exchange capacity experiments). As the pore size decreases there is correspondingly more sodium in the MCM-41 materials and by default less charge balancing hydrogen ions. Therefore it is expected that lower sorption is expected if the pore solution composition was more acidic (i.e. if the ratio of H+:Na+ was higher, as with the larger pore materials).

Reasonably similar trends are seen with the zinc substituted materials, except that the sorption properties are orders of magnitude lower. Again the pure siliceous materials seem to show higher sorption capacity for caesium than the boron substituted samples. Whereas the pure siliceous materials show similar capacity for differing pore size, the boron substituted samples show regularly increasing sorption trends as the pore size decreases. Table 8 - Distribution coefficients for MCM Materials

CZ2 w

H H

H a 00

r

Figure imgf000034_0001

Table 8 (Cont) - Distribution coefficients for MCM Materials

J *

J

Figure imgf000035_0001

Claims

1. A method of selectively removing a target metal cation from a liquid medium containing said metal cation together with at least one other metal cation, the method comprising contacting said liquid medium with an ion exchange material selected from a Group 1 to Group 4 material, as herein defined, with at least one of the pore size, layer charge density, interlayer cations and metal in doping being controlled to provide a material selective for said target metal cation.
2. A method according to claim 1 wherein the ion exchange material is crystalline.
3. A method according to claim 1 or claim 2 wherein the ion exchange method is an octahedral manganese oxide, an octahedral/tetrahedral titano silicate or an
MCM material.
4. A method according to any of the preceding claims wherein the target metal cation is one or more of caesium, strontium and cobalt, said cation being present in a hydrated or non-hydrated form.
5. A method according to any of the preceding claims wherein the ion exchange material is an aluminium-substituted MCM material.
6. A method according to any of claims 1 to 5 where the ion exchange material is a zorite titanosilicate containing niobium and/or aluminium.
7. The use of an ion exchange material in the selective removal of a target metal cation from a liquid medium containing said metal cation together with at least one other metal cation, the ion exchange material being selected from a Group 1 to Group
4 material, as herein defined, with at least one of the pore size, layer charge density, interlayer cations and metal ion doping being controlled to provide a material selective for said target metal cation.
8. A method of preparing an ion exchange material comprising forming an amorphous or crystalline Group 1 to Group 4 material, is herein defined, by a method designed to control at least one of the pore size, layer charge density, interlayer cations and doping of metal cations in the material so that the resultant material is capable of selective removal from a liquid medium of a target cation which is present in said liquid medium together with at least one other metal cation.
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US8759597B2 (en) 2012-04-18 2014-06-24 Uop Llc Methods for producing zeolite catalysts and methods for producing alkylated aromatic compounds using the zeolite catalysts
WO2015059445A1 (en) * 2013-10-03 2015-04-30 University Of Central Lancashire Chromatographic separation of nuclear waste
US20160107140A1 (en) * 2014-03-27 2016-04-21 Nippon Chemical Industrial Co., Ltd. Adsorbent material and method for producing crystalline silicotitanate
CN106062885A (en) * 2014-03-27 2016-10-26 日本化学工业株式会社 Adsorbent and method for manufacturing crystalline silicotitanate
US9486776B2 (en) * 2014-03-27 2016-11-08 Nippon Chemical Industrial Co., Ltd. Adsorbent material and method for producing crystalline silicotitanate
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