A. Clearfield

New crystalline phases of zirconium phosphate possessing ion-exchange properties☆

Abstract The preparation of two new crystalline zirconium phosphates, Zr(HPO4)2 and Zr(HPO4)2 · 2H2O, is reported. The compounds are characterized and formulated on the basis of their X-ray diffraction powder patterns, chemical analysis, thermal dehydration behaviour, and ion-exchange properties. Model structures for the new compounds are proposed on the basis of the previously known structure of Zr(HPO4)2·H20.

The preparation and crystal structure of a basic zirconium molybdate and its relationship to ion exchange gels

Abstract ZrMo 2 O 7 (OH) 2 (H 2 O) 2 was prepared in microcrystalline form by refluxing precipitated zirconium molybdate gels in 1–4M HCl. Macroscopic single crystals have been grown under hydrothermal conditions. In their amorphous, precipitated-gel form the gels are known to function as cation-exchangers. The crystal structure of zirconium molybdate was determined from integrated precession photographs using MoKα radiation. Crystal data: tetragonal space group 14 1 cd (No. 110); a = 11·45±0·01 A c = 12·49±0·01 A (25°C); ϱ obs = 4·0±0·1, ϱ calc = 3·774 g . cm −3 . The structure, refined by block diagonal least squares to (conventional) R = 0·037, is a three-dimensional network of cross-linked chains built-up of quite regular [ZrO 3 eq (OH 2 eq O 2 ax ]-pentagonal bipyramids and distorted cis -MoO 4 (OH)(H 2 O-octahedra. The structure is held together primarily by [Zr-O (and OH)-Mo]-bridges; chains of hydrogen bonds involving the oxo-, hydroxo-, and aquo- groups play a secondary role. Intermatomic distances and angles are normal, however, one oxygen atom has unusual coordination geometry; it forms a three-way bridge in a (symmetry-required) planar [ZrOMo 2 ]-moiety. The structure provides a rationale for the thus far observed physical and chemical properties.

Factors determining ion exchange selectivity—I high temperature phases formed by α-zirconium phosphate and its sodium and potassium exchanged forms☆

Abstract The phases formed at elevated temperatures by α-zirconium phosphate (α-ZrP) and its partially exchanged sodium and potassium ion phases have been determined by a combination of thermal and X-ray methods. α-ZrP converts to ζ-ZrP without water loss at 105–115°C. At somewhat higher temperatures one mole of water is lost followed by conversion of ζ-ZrP to ν-ZrP at ca . 230°C. Starting at 400–450° phosphate groups condense by split out of another mole of water. In the process a largely amorphous solid results. This in turn is converted to α-ZrP 2 O 7 at still higher temperatures. Two new partially sodium and potassium exchanged phases were discovered to form at elevated temperatures. The phases have the approximate compositions ZrNa 0·20 H 1·80 (PO 4 ) 2 and ZrNa 0·80 H 1·20 (PO 4 ) 2 and ZrK 0·16 H 1·84 (PO 4 ) 2 and ZrK 0·64 H 1·36 (PO 4 ) 2 in the sodium and potassium ion systems, respectively. The spontaneous disproportionation at room temperature of partially exchanged sodium and potassium ion phases into phases of lower and higher Na + or K + content indicates that ions can diffuse very readily throughout the crystal lattice. In the same context a new phase, λ-ZrP, was prepared by reaction of gaseous HCl with the cation exchanged zirconium phosphate phases.

On the mechanism of ion exchange in zirconium phosphates—XIII: Exchange of some divalent transition metal ions on α-zirconium phosphate

Abstract The exchange of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) on crystalline zirconium phosphate has been examined. High loadings may be achieved by using dilute acetate solutions of the cations at elevated temperatures. The exchange does not represent a true equilibrium since “site binding” traps the ions within the crystal lattice. This is reflected in the essentially complete removal of ions from solution up to high loadings. Nickel ion represents an exception as it is only loaded to a modest extent. Possible explanations for the observed behavior are presented.

On the mechanism of ion exchange in crystalline zirconium phosphates - IV potassium ion exchange of α-zirconium phosphate

Abstract The ion exchange behavior of α-zirconium phosphate crystals titrated with potassium ion and the behavior of the potassium-exchanged forms titrated with HCl has been examined. The replacement of protons by potassium ion takes place in two stages. In the first stage, the α-ZrP crystals are converted to Zr(KPO4)(HPO4)·H2O and this reaction is followed by replacement of the second proton to yield Zr(KPO4)2·3H2O. The reactions are not reversible as solid solutions of hydrogen ion in the potassium phases are formed on addition of dilute hydrochloric acid to the potassium-exchanged phases. The dehydration behavior of the exchanged forms was also determined. It is also shown that the approach to equilibrium is very slow and explanations for this behavior are presented.

On the mechanism of ion exchange in crystalline zirconium phosphates—III: The dehydration behavior of sodium ion exchanged phases of α-zirconium phosphate

Abstract The dehydration characteristics of two sodium ion exchanged phases of crystalline α-zirconium phosphate have been determined. The half-exchanged phase, Zr(NaPO 4 (HPO 4 · 5H 2 O, was found to form two lower hydrates and an anhydrous phase. At a temperature of 390° or higher sodium or dizirconium triphosphate, NaZr 2 (PO 4 ) 3 , was obtained. The fully exchanged phae, Zr(NaPO 4 ) 2 · 3H 2 O, forms one lower hydrate and three anhydrous phases. The sodium ion may be eluted from all of these phases to recover the original α-zirconium phosphate crystals except for the fully exchanged phase heated to 800°C which yields a new form of zirconium phosphate.

THE CRYSTAL AND MOLECULAR STRUCTURE OF AN OCTACOORDINATED IRON(II) COMPOUND—TETRAKIS(1,8-NAPHTHYRIDINE)Fe(II) PERCHLORATE

Abstract Recently, Hendricker and Bodner reported the synthesis of a series of first-row transition metal complexes of the type M(L)4(C1O4)2, where M is a metal of the 3d transition series and L = 1,8-naphthyridine. Preliminary space group determination indicates that all the perchlorates of the 3d-transition series from M = Mn2 + to M = Zn2 + are isomorphic. Single crystals suitable for X-ray diffraction studies were grown from methanol solutions of the perchlorate salts. Red, prismatic, crystals of the Fe(II) salt were found to be triclinic with the following cell dimensions: a = 9.163(3), b = 9.315(3), c = 20.116(8) A, α = 99.66(8), β = 77.37(8) and γ = 91.70(8)°; Z = 2 molecules/unit cell. V(obs) = 1651.62(A)3 D(exp) = 1.57; D(calc) = 1.56 gms/cc. It was assumed that the space group is PΓ, which was verified by structure solution and refinement. The intensity data were collected with MoKα radiation (λ = 0.71069 A) using a manually-operated Picker four-circle goniometer. In all 1969 non-zero, independe...

More on crystalline zirconium phosphates

Abstract Heating α-zirconium phosphate (α-ZrP) for long periods of time leads to the formation of two new phases ζ-ZrP and η-ZrP. The former phase is similar in structure to the phase obtained from solid-solid ion exchange reactions at low metal ion loadings. Refluxing α-ZrP in 15·7 M H 3 PO 4 results in the formation of δ-ZrP which is converted to e-ZrP on longer refluxing. Neither of these phases is a good ion exchanger. Several additional zirconium phosphate phases prepared in a variety of ways are also reported.

ON THE MECHANISM OF ION EXCHANGE IN ZIRCONIUM PHOSPHATES. XXIII. EXCHANGE OF FIRST ROW DIVALENT TRANSITION ELEMENTS ON Γ‐ZIRCONIUM PHOSPHATE

Abstract The exchange of transition metal (M 2+ ) ions from manganese to zinc with γ-zirconium phosphate was examined. By using acetate salts the hydrogen ion concentration is kept low enough to achieve high loadings. The fully loaded solids have the composition ZrM(PO 4 ) 2 ·4H 2 O. Near quantitative uptakes are achieved at 100°C. The interlayer spacings change very little with loading indicating that γ-zirconium phosphate is able to accomodate cations and water molecules without appreciable increase in volume. The copper exchanged phase readily forms an acetylacetonate when shaken with 2,4-pentanedione.

On the mechanism of ion exchange in zirconium phosphates—XVII: Dehydration behavior of lithium ion exchanged phases☆

Abstract The phases formed by the dehydration of lithium exchanged α-zirconium phosphate, Zr(HPO 4 )·H 2 O, were determined by a combination of X-ray, TGA and DTA studies. Samples containing 10, 20, 30 … 100% of theoretical lithium ion capacity were examined. The data are summarized in a phase diagram which however is not an equilibrium diagram because of the slowness of approach to equilibrium. The numerous phases obtained and the ease with which they rearrange indicates a high mobility for the incorporated cations. This suggested that α-zirconium phosphate may behave as a solid electrolyte and indeed this was demonstrated by having it serve in that capacity in a small sodium sulfur battery.