SYNTHETIC INORGANIC IONEXCHANGERS
Reetha Nanu Cheruvalath “Studies on some ion exchangers” Thesis. Department of Chemistry, Sree Narayana Post Graduate College, University of Calicut, 2006
CHAPTER I1
SYNTHETIC INORGANIC ION
EXCHANGERS
Many natural and synthetic substances are capable of ion exchange.
The three important groups of ion exchangers are inorganic, natural organic
bases and synthetic ion exchangers. Among the inorganic ion exchangers the
aluinino-silicates, both natural and synthetic, are suitable for technical
purposes. Zeolites are naturally occurring cation exchangers and apatite is a
naturally occurring anion exchanger. Hydrate gells of aluminium, iron(II1)
38,39 and zirconium hydroxide act as synthetic inorganic anion exchangers .
Cellulose based ion exchangers containing phosphoric- and sulphonic acid-
and diethylainine groups come under natural organic base ion exchangers.
Synthetic ion exchange resins consist of a large organic molecular network to
which active groups able to ionise are fixed. The active groups of cation
exchange resins can be phenolic hydroxyl (-OH), carboxyl (-COOH) or
phosphoric acid [-PO(OH)2]. While for anion exchange resins, the active
groups are usually primary, secondary, tertiary or quaternary basic groups.
The ion exchangers in the liquid form are known as liquid ion
exchangers. The behaviour of liquid ion exchangers are similar to that of
resin ion exchangers in both techniques, an exchange of ions of like sign
occurs between two immiscible liquids in contact with each other. Analogous
to resin ion exchangers, there are both liquid anion and cation exchangers.
The liquid anion exchangers are mainly primary, secondary, tertiary amines or
quaternary ammonium salts of high inolecular weight. The liquid cation
exchangers are usually phosphoric acid esters or carboxylic acids.
The behaviours of analogous functional groups in liquid - and in resin
ion exchange are siinilar and it is possible to predict the likely course of liquid
ion exchange extraction by comparing with similar separations using solid ion
exchangers.
The development of synthetic inorganic ion exchangers during the last
two decades has attracted the attentions of analytical chemists. This is due to
their stability towards high temperature and ionising radiation. These are
superior to cominercially available organic or natural organic exchangers and
are suitable for uses in nuclear industry, preparation of ultra pure materials,
the recovery of valuable materials from industrial waste, hydrometallurgy,
etc.
A good number of papers dealing with the synthesis and ion exchange
properties of inorganic ion exchangers have been published. The informative
book by C. B. ~ i n ~ h l e t t ~ ~ and the reviews by Churins and at er ova^^." deal
with various types of ion exchangers and their uses. These authors reviewed
the uses of various types of clay minerals as ion exchangers and their
properties, the molecular sieve properties of zeolites and their exchange
isotherms and kinetics of exchange synthesis, properties and applications of
various types of heteropolyacid salts.
A systematic classification of inorganic ion exchangers was made by
Vesely and ~ a k a r e k ' ~ as follows.
1. Hydrated oxides of metals.
2. Acidic salts of polyvalent metals
3. Insoluble salts of hetero poly acids.
4. Insoluble hydrated metal ferro- and ferri cyanides
5. Miscellaneous type
2.1. Hydrated oxides of metals
An exhaustive survey covering the preparation, properties, uses and
theory of hydrous oxides of bivalent, trivalent, quadrivalent, quinquivalent
and sexivalent metals have been made by Vesley and Paltarelc. Similar
studies on hydrated oxides of metals, such as, Al, Si, Sn, Zr, antimonic acid,
Ce and tungsten were given by De and ~ e n ' ~ . walton4' has reviewed the
studies on antimony pentoxide, tin oxide and activated carbon impregnated
with tin oxide used in chromatography.
Hydrous a l ~ i n i n a " ~ ~ samples are constantly used in analytical
separation as adsorbent and desorbent. The results of the investigation show
that ion exchange capacity of alumina is enhanced by pre-treatment with
hydrochloric acid. Among the hydrous oxides, those of antiinonic acid, both
4734 crystalline and amorphous forms have found several uses . They are used
in the mutual separation of alkali metals. The other oxides studied include
55-57 hydrous titanium dioxide , stannic oxide5*, hydrous manganese 59,60
hydrated ferric oxide and hydrous cerium(1V) oxide6'.
2.2. Acidic salts of polyvalent metals
Details of various acidic salts of polyvalent metals having different
anionic parts such as phosphate, arsenate, antimonite, selenate, ferrocyanides,
molybdate, tungstate were given by Vesley and ~ a k a r e k ~ ~ , De and ~ e n ' ~ and
~ a l t o n ' ~ . Other exchangers of special uses reported4' are hafnium- and
thoriuin phosphate, cerium oxalate, zirconium tungstate and -1nolybdate.
Molecular sieves of aluminium silicate were used to separate glucose and
fructose45.
Crystalline phosphates of zirconium and titanium as ion exchangers
were reviewed by ~ o b a ~ a s h i ~ ' . Industrial applications of ion exchangers
include, ways of increasing the efficiency of ion exchange method for
separation of mixtures, substance purification and preparation.
Characteristics and properties of group (IV) acid salts as ion exchanges had
62-65 been studied . The catalytic properties and applications of ion exchangers,
and super ionic conductivity in cubic potassium antimonite(V) zirconium
phosphate and exchange of alkali metals, thermal, redox and catalytic
characterisation of inorganic ion exchangers were discussed by Ruvarac,
66-73 Howe, Clearfield, Besse, Garicia Laginestra, Alberti and Abe .
Alberti et al.74 studied the synthesis and preliminary characterisation of
ion exchange behaviour of zirconiuin phosphate and -phosphite with layered
structures of a-type. Tetramineplatinum(I1)-H ion exchange on a-zirconium
75,76 phosphate . The conduction, the preparation and ion exchange properties of
77,78 y-NH4Zr H(PO4)2 and Y - Z ~ ( H O P ~ ) ~ were reported .
Synthesis, ion exchange characteristics and application of zirconium
79,80 antiinonate , zirconium molybdate8' and zirconium t ~ n ~ s t a t e ~ ~ were
studied. Anion exchange characteristics of zirconium tellurite were
thoroughly studied by Srivastava et aL8' Thorium tellurite acted as a cation
exchanger in alkaline medium and as an anion exchanger in acidic medium83.
The exchanger is useful in the separation of NO3 from NO2 and Moo4 from
PO4. The reaction mechanism involved and the stabilities of a- and y-
titanium phosphates have been investigated8" The complex ion exchanger,
titanium phosphate aininoniuin inolybdophosphate was used for the recovery
of 1 3 7 ~ s from power reactor fuels85 and H+/N~'+ ion exchange in a-
86,87 Ti(HP04)2H20 at 5°C and 25OC was determined .
Chroinatographic and photon conduction behaviour of 44 metal ions in
DMSO-HN03 and DMSO-H20 systems on thin layers of stannic phosphate
55,56 have been described . Also the stability of composition during the sorption
of traces of I< from 2-7 M K1 solution was noted8'. Similar studies based on
stannic arsenates9 and stannic pyrophosphate was also c o n d u ~ t e d ~ ~ ~ ~ ' .
A new inorganic ion exchanger prepared by mixing solutions of
cerium(1V) aininonium sulphate and tellurous acid at different concentrations
and different pH, namely cerium(1V) telluriteg2 were studied. Ceric phosphate
was used as ion exchanger in the separation of carrier free bismutch-2 10 from
lead-210, yttrium-90 from ~r-gog3. Cerium(1V) selenite was synthesised and
93,94 its ion exchange properties were studied by Hussain et al. A preliminary
study on the selectivity of ceric antimonite as ion exchange material for
various metal ions other than alkali metal ions has been reportedg5.
Cation exchange study, effect of y-irradiation on ion exchange
behaviour, separations of cadmium(I1) from Zn(I1) and Mn(II), Mg(I1) from
Ba(II), Cu(I1) and Sr(I1) were achieved on a crystalline thermally stable phase
of antimony(II1) silicateg6. Separation of cd2+ from pd2+ and from cu2+
and ~ i ~ ' were carried out on a column of amorphous lanthanum tungstateg7.
Electro chroinatographic studies of several metal ions were carried out on
98-99 paper impregnated with lanthanum antiinonate . Mukherjee et al."'
described the synthesis, physicochemical properties and applications of
lanthanum arsenate. Samples of iron(I11) molybdatelo1 were prepared by
mixing 0.05M aqueous solution of Fe(N03)3 and ammonium inolybdate at
various pH. Distribution coefficients for many metal ions were determined on
this material, and its structure was proposed tentatively on the basis of pH
titration, cheinical and thermal analysis, and IR and Mossbauer spectra.
Thind et a1.'O1 described the properties, application and the separation of
thoriuin on iron(II1) selenite exchanger. Composition and ion exchange
properties of K and Zn selective tantalum tungstate and basic tantalum
sulphate were reported by Qureshi et a1.1°2 A new inorganic ion exchanger,
tantalum selenite 103y104 was used for paper chromatographic separation of
different phenols. Ion exchange characteristics of lithium niobate crystals
were studied by Ganshin et al. 105,106
2.3. Insoluble salts of hetero poly acid salts
42,43 Vesely and Sen have reviewed various types of heteropoly acid
salts containing phosphorous, arsenic, silicon, germanium, boron,
molybdenum, tungsten, vanadium, etc, as hetero elements. CS selective
aininoniuin phosphomolybdate continues to be used as ion exchanger,
especially in the isolation of CS froin sea water. Using this, the separation of
Th, In, U and Se was also reported.
Synthesis, structure determination, chemical and thermal stability and
y-radiation stability of zirconium(1V) arsenophosphate and -arsenosilicate had
been reported lo7-11'. These exchangers are used for the separation of A1 and
Mg in some antacid drugs1l2. Other exchangers based on zirconiuin are
zirconium inolybdophosphate, zirconium tungstoarsenate, zirconiuin
iodophosphate, zirconium selenophosphate and zirconium(1V)
iodoinolybdate 113-117
A new mercury selective ion exchanger, thorium(1V) phosphosilicate
was synthesised and the effect of y-irradiation on its ion exchange property
was reported118. The results showed that the material was unaffected by doses
of 2 X 10' rad. Synthesis of titanium(1V) arsenophosphate, its ion exchange
property and utility in the analysis of certain alloys and rocks had been
107,109 published . Similarly, ion exchange behaviour of titanium(1V)
tungstoarsenate had been studied1I9. It is stable towards acids, salt solutions
and can be used up to 8-10 cycles without loss in efficiency. Titanium
inolybdoarsenate had been used for the separation of Pb(I1) and Hg(I1) from
La and cei20. Effect of y-irradiation on ion exchange characteristics of
titanium vanadophgsphate had also been reported12'. Study of stannic
selenophosphate with other heteropoly acid alts like stannic selenoarsenate
had been made 122,123 . Quantitative separation of binary mixtures of
manganese(I1) and Mg(I1); Ba(I1) and Cd(I1); and nickel(I1) and copper(I1) on
stannic arsenoantimonate column was reported12'. Preparation, properties,
analytical applications and comparative study on tin(1V) tungstoselenate,
tin(1V) boratomolybdate, tin(1V) iodophosphate, stannic vanadotungstate and
tin(1V) inolybdosilicate had been studied 115,125-129
Distribution and pH titration studies of alkali metal ions on amorphous
tin(1V) a r s e n ~ ~ h o s ~ h a t e ' ~ ~ has been reported. Tin(1V) tungstovanado-
phosphate'3' had been used for the separation of the following mixtures:
Mg(I1)-Cd(II), Cd(11)-Zn(II), Cd(11)-Pb(II), Mn(I1)-Hg(II), Ba(I1)-Ca(II),
Hg(I1)-P b(II), Ce(1V)-Th(1V) , Y (1V)-Th(1V)-Zr(1V) and Cd(I1)-Y (1V)-Zr(1V) .
Gupta et all3' reported the properties of stannic tungstophosphate towards
bivalent metal ions. Crystalline tin(1V) antimonophosphate was prepared and
its application in binary separation of metal ions were studied'32. Likewise,
synthesis and ion exchange characteristics of thermally stable tin(1V)
molybdophosphate had been reported by Qureshi et
Varshney et al.'" prepared cerium(1V) phosphosilicate and
chromium(II1) arsenophosphate exchangers and converted to H+ form. Their
ion exchange behaviours towards L?, ~ d , K' and NH; were investigatedI3O.
Iron(II1) iodophosphate was synthesised and compared with tin(IV), Zr(1V)
iodophosphatel 15. A column packed with thalliuin tungstophosphate was used
for the separation of Sr(II), Co(II), Ce(II1) and Cs(1). Talati et1 all3' studied
uranyl zinc molybdophosphate as an ion exchanger.
2.4. Insoluble hydrated metal ferro- and ferri cyanides
A new type of inorganic ion exchanger aminetin(1V)-
hexa~~anoferrate(11)'~~ with seven different ainines was prepared. Based on
pH titration, elution curves, IR and therinograviinetric studies, a tentative
formula of the compound was proposed.
Copper ferricyanide ion exchanger was used for the separation of
caesi~rnl'~. Badik et aLn8 reported the ion exchange properties of mixed
uranyl - and alkaline earth ferrocyanides. A thermodynamic model for the ion
exchange of K, NH4 and CS on the exchanger was proposed138. Preparation,
properties and selectivity of rubidium on titanium(1V) ferrocyanide gel was
studied 139-141
2.5. Miscellaneous types
Recently, a variety of inorganic chelating ion exchangers were
prepared. A chelating ion exchanger prepared from SnC14 and
diethanolamine14* was used for the separation of various metal ions by
chromatography. Similarly, titanium diethanolamine and aluminium
triethanolamineI4' were prepared by modification of hydrated aluminium
oxide. Singh et synthesised iron(II1) diethanolainine and studied its ion
exchange behaviour.
Ion exchange and dehydration of layer of titanates, Na3T1307 and
K2T1409 had been reported14s. Studies on preparation and properties of
ineta aininophosphoinolybdate and molybdosilicophosphate had been
reported 146-147 . Poly acrylamide-zirconium phosphate148 shows a high affinity
137 for CS at given conditions offering a possible way for radioactive liquid
waste treatinent.
Distribution studies and selective ion exchange separation of inetal ion
on polytungstoantiinonate14g and sorption behaviour of collodinum
i n ~ l ~ b d o a r s e n a t e ~ ~ ~ had been made. Tin(1V) EDTA ion ex~hanger '~ ' had
been synthesised and cation exchange properties of activated carbon by
treatment with HN03 had been reportedls2. Liquid ion exchange
chroinatography and recovery of some inetal ions on PAN-sorbed tin(1V)
silicate had also been reportedls3.
New ion exchanging materials - organic and inorganic, continue to be
reported, but less frequently than before. A nuinber of ion exchangers, both
in amorphous and crystalline forins were synthesised. After preparation, they
were subjected to different physico-chemical investigations for elucidation of
structure, composition and nature. For selective sorption, the distribution
coefficient (Kd) of different cations and anions were measured. It has been
found that inorganic ion exchangers are selective for a particular inetal ions.
Inorganic ion exchangers impregnated on papers have been used for
chroinatography, electro chromatography and thin layer chroinatography.
2.6. Significance and scope of the investigation
The nuinber of materials which may be understood as inorganic ion
exchanging substances have grown enormously during the period. However,
because of the ion exchange processess in many substances are accompanied
by other phenomena, such as, physical adsorption, surface adsorption,
precipitation and CO-precipitation processes, lattice defects, etc. It is difficult
to find an exactly limited scope for the term "inorganic ion exchanger."
There appears to have been a marked trend towards providing a inore
exact explanation of ion exchange rectors rather than studying purely practical
separation applications. The basic studies of ion exchange mechanism have
been carried out on defined crystalline materials, the detailed structure of
which, along with the location of the exchanging ions in the crystal lattice, are
of great interest. This knowledge, accompanied by the determination of the
main therlnodynainic functions have permitted a full explanation of the ion
exchange process. It is interesting that the exchange processes in many
substances are connected with the formation of insoluble compounds of the
ingoing ion with the "matrix", and that the forination of two distinct solid
phases has been detected in some cases. These facts together with the other
observed phenonlena mentioned above suggest that the ion exchange process
in the case of inorganic ion exchangers are of colnplex character and that the
traditional treatment of these processes in terms of pure ion exchange does not
fully describe all aspects of the processes. In view of the above facts,
different types of exchangers have been prepared and their specificity towards
several metal ion have been studied.