Ion exchange recovery of palladium (II) from nitrate weak acidic solutions

doi:10.4236/ns.2009.13021

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Vol.1, No.3, 166-175 (2009)

doi:10.4236/ns.2009.13021

SciRes

Natural Science

Ion exchange recovery of palladium (II) from nitrate

weak acidic solutions

Olga N. Kononova1*, Nataliya G. Goryaeva1, Olga V. Dychko1

1Department of Chemistry, Siberian Federal University, Krasnoyarsk, Russian Federation; cm2@bk.ru

Received 12 August 2009; revised 2 September 2009; accepted 4 September 2009.

ABSTRACT

Sorption recovery of palladium (II) from nitrate

weak acidic model solutions and solutions of

spent catalysts on some ion exchangers with

different physical and chemical structure has

been investigated. The palladium concentration

in contacting solutions was 5.0 · 10-5 – 1.0 · 10-3

mol/L at nitric acid and potassium nitrate con-

centrations 0.01 and 1.0 mol/L, respectively. It

was shown that anion exchangers AV-17-8 as

well as Purolite S 985 and A 500 possess the

best sorption and kinetic properties. These

sorbents can be recommended for selective

recovery of palladium from solutions of spent

catalysts.

Keywords: Palladium; Ion Exchange; Anion

Exchangers; Nitrate Solutions

1. INTRODUCTION

As natural deposits of precious metals are being depleted,

the technologies for precious metals recovery from dif-

ferent secondary raw materials are becoming more im-

portant. The hydrometallurgical methods are success-

fully used for these purposes [1-3]. One of the most

promising methods for recovery of platinum group met-

als (in particular, of palladium) is sorption, characterized

by high efficiency and selectivity [1,3-5]. However, the

majority of investigations devoted to the sorption recov-

ery of palladium, deal with chloride or sulfate solutions

[6-14], and the studies of sorption of noble metals from

nitric acidic media are rather limited [1,15-20]. At the

same time, the recovery of palladium from some kinds

of secondary sources (e.g. electronic scrap and ex-

hausted nuclear fuel) requires its isolation from nitric

acidic and nitrate solutions [1,21].

Our previous investigations were focused on sorption

recovery of palladium from chloride model solutions

and solutions of spent catalysts by various ion ex-

changers and carbon adsorbents [9,22,23]. Apart from

this, we started the research of sorption concentration of

palladium on carbon adsorbents during its recovery from

model nitric acidic solutions [24]. We have revealed high

sorption abilities of some carbon adsorbents to palla-

dium (II) ions depending on initial concentrations of

nitric acid andPd .

)(II

The present paper is focused on sorption recovery of

palladium from nitrate weak acidic solutions (model and

of spent catalysts) by some ion exchangers with different

physical and chemical structure.

2. MATERIALS AND METHODS

2.1. Characteristics of Ion Echangers

Some ion exchangers from various manufacturers were

taken for investigation. These sorbents possess different

physical and chemical structure. Their physical-chemical

characteristics are summarized in Table 1. It should be

noted that ion exchangers produced by Purolite Com-

pany for the first time were used for recovery of plati-

num group metals. However, these ion exchangers were

successfully applied in our previous investigations on

sorption recovery of gold and silver [25].

Before sorption all the ion exchangers were prepared

according to the standard procedures and then loaded

with 1 M solution, in order to convert them to

chloride form (anion exchangers) or to

NaCl

,Na Cl



-form

(amphoteric resin).

The acid-base properties of ion exchangers investi-

gated were studied by a potentiometric titration with the

glass electrode. Based on the experimental data obtained,

we have calculated the average apparent ionization con-

stants of functional groups of ion exchangers [5]. The

calculation procedure is described below and the values

of constants are presented in Table 1.

2.2. Preparation of Palladium Ntrate

Solutions

The initial model stock solution of palladium was pre-

pared according to works [26,27]. The accurately

O. N. Kononova et al. / Natural Science 1 (2009) 166-175

167

Table 1. Physical-chemical properties of ion exchangers investigated.

Trade

name

Exchanger

type

Copoly-

mer

Physical

structure

Functional

groups

Exchange

capacity to Cl-

ion (mmol/g)

Swelling

grade

(%)

K Manufacturer

Purolite

A 500

Strong base

anion ex-

changer

St – DVB MP QAB 1.2 15 2.31 Purolite, UK

Purolite

A 530

Strong base

anion ex-

changer

St – DVB MP QAB 0.60 12 1.15 Purolite, UK

Purolite

S 985

Weak base

anion ex-

changer

Ac – DVB MP PA 2.3 42 0.74 Purolite, UK

AV-17-

Strong base

anion ex-

changer

St – DVB G QAB 3.6 23 0.99 TOKEM, Russia

AN-25

Weak base

anion ex-

changer

VP – DVB MP TAG, PN 5.3 10 1.78 Chercassy,

Ukraine

ANKF-

Amphoteric

ion exchanger VP – DVB P PAG, TAG,

3.8

(2.6 to Na+) 22

1.42

K=1

1.83)

Chercassy,

Ukraine

St-styrene; DVB-divinylbenzene; Ac-acryl; VP-vinylpyridine; MP-macroporous; G-gel; P-porous; QAB-quaternary ammonium base;

PA-polyamine; TAG-tertiary aminogroups; PAG-phosphorylic acid groups; PN-pyridine nitrogen.

weighed metallic palladium (0.50 g) was dissolved under

heating in concentrated 3 (analytical grade) ac-

cording to the following reaction:

HNO

332

383()2 4PdHNOPdNONOH O 

(1)

The palladium concentration in initial stock solution

was 0.01 mol/L. The working solutions with palladium

concentrations 5.0 · 10-5 – 1.0 · 10-3 mol/L were prepared

from the stock solution. The nitric acid concentration in

these solutions was 0.01 mol/L and the constant ionic

strengths was made by means of 1.0 M 3

NO . Before

the preparation of working solutions, the palladium con-

centration in initial stock solution was controlled by gra-

vimetric method with dimethylglyoxime as a reagent

[26]. The palladium (II) concentration in working solu-

tions and in solutions after sorption was determined by

spectrophotometrical with nitroso-R-salt [27,28].

We chose the range of palladium and nitric acid con-

centrations for our experiment, aiming to make it closer

to real industrial conditions.

Apart from the model nitrate solutions of palladium,

we also used the solutions of spent palladium-containing

catalysts. These solutions were prepared as follows:

the catalyst quantities (0.20 g) were dissolved under

heating in concentrated nitric acid, similar to prepara-

tion of model solution. The working solutions of spent

catalysts with palladium concentrations 5.0 10-5–5.0

10-4 mol/L were prepared from the initial solution.

Before dissolution of spent catalysts samples in nitric

acid, we have determined their average composition by

X-ray-fluorescence method. The results are repre-

sented in Table 2.

2.3. Batch Studies

The sorption of palladium was studied under batch ex-

perimental conditions: resin mass–0.20 g, volume of

contacting solution–20.0 mL, stirring in a thermostat at

(20 ± 1) ºС. The equilibrium time determined by special

tests was about 24 h.

Sorption ability of ion exchangers investigated was

estimated by means of the recovery degree () and

distribution coefficient (, which were calcu-

lated from:

,%R

,/)DL g

()

100%





(2)

 (3)

where and are the initial and equilibrium mo-

lar concentrations of palladium solution; is the

exchange capacity of the resin for palladium, mmol/g.

Ceq

The kinetics of sorption of palladium from weak

acidic nitrate solutions on ion exchangers investigated

was studied by the “limited bath” method [29,30] and

diffusion coefficients of (

()Pd II2

cms ) were

calculated. The kinetic experiment procedure is de-

scribed below.

The desorption of palladium was carried out by 1 M

thiourea solution in 0.01 M or in 1 M .

The mechanism of palladium sorption recovery by ion

exchangers from nitrate systems was studied by means

of IR-spectroscopy and diffuse reflectance spectroscopy.

The preparation procedures of samples are present be

HNO NaOH

low.

O. N. Kononova et al. / Natural Science 1 (2009) 166-175

168

Table 2. Average composition of initial sample of palla-

dium-containing spent catalyst.

All the results were statistically processed by standard

methods [31,32]. The average experimental error for 3-4

parallel runs was below 6 %.

2.4. Calculation of Apparent Constants of

Acid-Base Ionization of Ion

Exchangers

The constants values were calculated using potentiomet-

ric titration data. For each point of the titration curve, the

functional groups content was determined and the ap-

parent ionization degree (



) of the resin was calculated:

[]





 (4)

where []

 is the equilibrium concentration of



ions in the ion exchanger phase, mmol/mL; is the

initial concentration of the titrant solution (0.1 M

Cl ).

Then a curve was plotted on the coordinates

(log )

pH f



 and at 0.5



, the apparent

acid-base ionization constants of functional groups of

the ion exchangers (a

pK ) were calculated from Hen-

derson’s equation:

log( )

pKpH m



  (5)

where is the slope angle tangent of the curve. m

2.5. “Limited Bath” Method for Sorption

Kinetics of Palladium (Ii)

The quantities of preswollen resin (0.10 g) were stirred

with 25.0 mL of palladium nitrate solutions at (20 ± 1)ºС

over a period of 30 s to 24 h. The suspensions were in-

tensively stirred (more than 800 rev/min). After a certain

time period, the resins and solutions were quickly sepa-

rated and the concentration of was determined

in the solutions. Then the exchange degree (

()Pd II

)

was

calculated from



 (6)

where and

Q Q



are the amounts (in mmol) of the

palladium sorbed to the time (s) and to the equilib-

rium time.

According to the Boyd’s method [29,30,33], the ki-

netic coefficient was calculated from

(1.08)



 (7)

The data obtained were plotted as a function()Btf t



If the process is controlled by gel diffusion [29,30,33],

this function should be linear. After that, the diffusion

coefficients (

D) were calculated according to the equa-

tion:



 (8)

where

is the radius of the resin grain (cm).

The half-exchange time of the kinetic process () was

calculated as follows:

1/ 2

1/2 2



 (9)

2.6. Preparation of Sample for

FT-IR-Spectroscopy

IR–spectra of ion exchangers investigated were recorded

by means of FT-IR- spectrometer Vector 22 (Bruker).

Before that, ion exchanger samples were dried during 4

h at 40ºС in convection drier. Then the samples were

held in a vacuum-desiccator over freshly calcinated cal-

cium chloride. The specimens were ground in a me-

chanical mill without air access and after that were

pressed with spectrally pure

Br to discs. The quanti-

ties of resin samples and potassium bromide were con-

stant (200 mg each of resin and

Br ).

2.7. Preparation of Samples for Diffuse

Reflectance Spectroscopy

The diffuse reflectance spectra were recorded by means

of spectrometer PULSAR (Russia). The resin quantities

(0.20 g) were preliminary saturated with palladium (II)

ions with concentration 5.0· 10-4 mol/L during 24 h. Af-

ter that, the resins were filtered and wet samples were

placed into cell. Then the diffuse reflectance spectra

Component Content (%)

Palladium 0.79

Sodium 0.41

Aluminum oxide ~ 84

Silicon 0.03

Sulfur 0.12

Chlorine 0.80

Iron 0.19

Nickel < 0.02

Zinc < 0.02

Gallium < 0.02

O. N. Kononova et al. / Natural Science 1 (2009) 166-175

169

were recorded.

3. RESULTS AND DISCUSSIONS

3.1. Ionic State of Palladium in Contacting

Solutions

It is known from [26,27,34,35] that the ionic state of

platinum group metals in solutions depends on acidity

of contacting solution as well as on concentration of

chloride or nitrate ions (for chloride and nitrate systems,

respectively). It is determined at present that 32

()Pd NO



is formed after the dissolution of metallic palla-

dium in concentrated nitric acid according to reaction (1)

and subsequent diluting of the solution obtained [36,37].

It is also determined [38] that the hydrated palladium (II)

ions and their mononitrate complexes

[ are present in solution at mol/L.

With the increase in nitric acid con- centration, the

amount of different nitrate cationic and anionic com-

plexes as well as of neutral species is growing [19,20]:

()HO

3]PdNO

[(

[( )]PdH O



23 3

) ]

HNO

C1

dHONO , ,

22 32

[()( )]PdHONO233

)()]O NO[(PdH



. When the nitric acid concentration dimin-

ishes from 1 mol/L to 0.01 – 0.001 mol/L, the formation

of hydroxocomplexes with the general formula

is observed in solution [36,38]. That

occurs due to the so-called “aging” of solutions, which

takes place in weak acidic media, and especially after

keeping of such solutions for longer than 24 h. This

phenomenon is typical for solutions of platinum group

metals [27,34,38]. At mol/L, the solution

does not contain aquatic ions and its nitrate

complexes, and only hydroxocomplexes of different

composition exist in this media [38].

)]



(2 )

)]

naq





[(Pd NO

[(Pd OH

30.001

HNO

C

()Pd II

The above discussion concerns only the ()Pd II3

HNO



systems, i.e. without adding background electrolytes.

Our previous investigation [24] was focused on palla-

dium (II) recovery from strong acidic solutions

()

was 1, 2 and 5 mol/L) in the system sorbent

–3

dIIHNO. However, the sorption of palladium

from weak acidic solutions in the presence of salt back-

ground is also of practical interest, since such media are

formed in number of technological schemes [1,3].

Therefore, we have also studied the following system:

ion exchanger –()

dII 0.01 M 1 M

HNO 3

NO . It

should be noted that data on ionic state of palladium in

such systems are not available at present and this prob-

lem requires a special study. However, we have at-

tempted to make some conclusions on this matter in the

present paper, as discussed below.

Before studying the palladium sorption recovery, we

have obtained electron absorption spectra of freshly

prepared palladium solutions in 1 M 3

NO and at

pH=2, presented in Figure 1. It should be noted that

palladium sorption was carried out from freshly prepared

solutions to minimize their “aging”. It can be seen from

Figure 1 that absorption maximum in spectrum 1 (Pd

1 M

NO is located at 390 nm and indicates the

presence of complexes [( as a pre-

vailing form [36-38]. However, the absorption maxima

in spectra 2 and 3 ( in 0.01 M in the pres-

ence of 1 M

)

)(PdH ONO

)]



NO ) are also located at 390 nm and

show presence of the same ()

dII complexes in solu-

tion. Probably, the formation of anionic nitrate com-

plexes of palla dium (II) is promoted by the high con-

centration of nitrate ions, despite the weak acidity of

solution (pH=2). Later, during our experiments on

sorption, we have not observed any precipita-

tion of metal specimens on a surface of resins, unlike

authors [20]. It means that there was no hydrolysis in the

investigated systems under chosen conditions (fresh

prepared weak acidic solutions and presence of 1 M

(PdII)

(NO

). However, the precipitation effect was clearly

observed when palladium sorption was carried out from

solutions kept more than 8 h or from freshly prepared

solutions with pH=4. This proves the formation of dif-

ferent hydroxocomplexes. Therefore, we can conclude

from the absorption spectra that complexes

[(H)OPd

)]



prevail in contacting freshly prepared solutions

under the chosen conditions.

3.2. Sorption Recovery of Palladium from

Model Nitrate Solutions

The sorption properties of ion exchangers investigated to

palladium (II) are presented in Table 3. It can be seen

from these data that in general all the resins reveal high

sorption ability, since they recover on the level ~70

Figure 1. Absorption spectra of palladium (II) working solutions

in 1 M (1) and in the system 0.01 M + 1.0 M

(2,3), mol/L (1,2) and

mol/L (3).

HNO

KNO

KNO -3

(Pd)= 2.0×10-3

1.0×10

O. N. Kononova et al. / Natural Science 1 (2009) 166-175

170

% (ANKF-5) and more than 90 % (Purolite S 985). The

studied sorbents can be arranged by their affinity grade

to palladium in the following order: Purolite S 985 >

Purolite A 530 > Purolite A 500 ~ AV-17-8 > AN-251 >

АNKF-5.

It is interesting to note, that all ion exchangers except

Purolite S 985 possess approximately equal affinity to

, despite of their different physical and chemical

structure. The nature of functional groups of the ion ex-

changers investigated allows to form the following types

of chemical bonds during their contact with noble metal

ions [5,6,19,20]:

 ionic, i.e. ion – ion interaction, which takes place

on strong basic anion exchangers;

 coordination, forming as a result of conservation of

electron pair between ligand (electron-pair donor),

which is the nitrogen atom of resin functional

groups, and the metal (electron-pair acceptor); this

bond takes place on weak basic anion exchangers.

The fact that amphoteric ion exchanger ANKF-5 re-

covers ions from nitrate solutions on the same

level (and even less) than anion exchanger AN-251 (both

resins were synthesized on the basis of vinylpyridine),

unambiguously points out to ionic state of in

contacting solution. If cationic hydroxocomplexes or

hydrated ions were present in this solu-

tion, the degree of palladium (II) recovery would proba-

bly be above 69% due to the activity of phosphorylic

acid and pyridine nitrogen functional groups in weak

acidic media.

()Pd II

[( )]PdHO

Moreover, it is noteworthy that strong basic anion ex-

changers recover to a greater extent (Table 3),

although the additional complex formation of palladium

ions with functional groups of quaternary ammonium

base is impossible (unlike the weak basic anion ex-

changers). Therefore, we consider highly probable that

anionic palladium complexes

()Pd II

[()()]PdH ONO



exist in the systems investigated in the

presence of 1 M

[( )]Pd NO

NO .

Table 3. Sorption of palladium from nitrate model solutions

on ion exchangers investigated Initial concentration

is 5.0 · 10-4 mol/L, pH = 2.

Pd(II)

Trade

name

log

D (%)R Trade

name log D (%)

Purolite A

500 2.79 86 AV-17-8 2.77 85

Purolite A

530 2.87 88 AN-251 2.54 78

Purolite S

985 3.23 94 ANKF-5 2.34 69

As for sorption recovery of palladium (II) on anion

exchanger Purolite S 985, which reaches 94%, there is

little doubt that this recovery proceeds according not

only to anion exchange, but also to complexation proc-

ess, taking into account the presence of polyamine

groups in the structure of this sorbent.

3.3. FT-IR Study of Palladium Sorption

To study the palladium recovery from nitrate solutions in

more detail, we have carried out IR-spectroscopic inves-

tigation. We have obtained IR-spectra of anion exchang-

ers Purolite S 985, AV-17-8 and AN-251, the fragments

of which are shown in Figure 2. IR-spectra of initial

samples of these resins in chloride form are presented

for comparison.

It can be seen from IR-spectra that appearance of in-

tensive peaks in the range of 1400–1300 cm-1 (1384,

1352 and 1300 cm-1) is observed for all the ion exchang-

ers, independently of their basicity and structure of

polymeric matrix. These peaks are assigned to vibrations

of N–O bonds of nitrate ion: peak at 1384 cm-1 corre-

sponds with stretching vibrations of free 3



[20,39],

whereas peaks at 1352 and 1300 cm-1 can be assigned to

the N–O stretching vibrations in palladium complex [39].

It should be noted that the greatest intensity of these

peaks is revealed in IR-spectrum of strong basic anion

exchanger AV-17-8 (Figure 2, spectrum 5). It was men-

tioned above that the functional groups of this resin

(quaternary ammonium base) cannot react with palla-

dium through additional coordination. Therefore, it can

be concluded that the anion exchange takes place in this

case:

233 233

[()( )][()( )]RClPdHONOR PdHONOCl



 

(10)

Since the similar but less intensive peaks are re-

vealed in IR-spectra of weak basic anion exchangers

Purolite S 985 and AN-251 (Figure 2, spectra 1 and 3),

it can be concluded that the reaction (10) is to some ex-

tent attributable to these resins too.

However, in case of recovery on weak ba-

sic anion exchanger AN-251, the redistribution of the

intensities in the range of 1700 – 1400 cm-1, corre-

sponding to symmetric and asymmetric stretching vi-

brations of pyridine ring, is observed in IR-spectrum

of this resin (Figure 2, spectrum 3). The absorption

bands at 1600, 1558, 1494 and 1417 cm-1 are assigned

to С = С and C = N stretching in pyridine ring

[20,39,40]. The reduction of peak intensity at 1510

cm-1 and depression of that one at 1492 cm-1 points out

to the probable complexation between palladium and

pyridine nitrogen [5,40].

()Pd II

O. N. Kononova et al. / Natural Science 1 (2009) 166-175

171

Figure 2. IR-spectra fragments of anion ex-

changer samples Purolite S 985 (1), AN-251 (3),

AV-17-8 (5) saturated from nitrate solutions of

palladium (II) mol/ L;

mol/L; mol/L

Spectra (2), (4) and (6) correspond respectively to

initial samples of Purolite S 985, AN-251 and

AV-17-8 in chloride form.

-4

C(Pd)= 5.0×10

C(KNO)=1

C (HNO)= 0.01.0

Figure 3. IR-spectra fragments of samples of anion

exchanger Purolite S 985 saturated from nitrate pal-

ladium (II) solution (1) and of initial resin in chlo-

ride form (2) mol/L;

mol/L; mol/L.

-4

C (Pd)= 5.0×10

C(KNO)= 1.0

C (HNO)= 0.01

The IR-spectrum of weak basic anion exchanger Puro-

lite S 985 saturated with palladium shows the greatest

changes compared to the spectrum of its initial sample in

chloride form (Figure 2, spectra 1 and 2). The peaks at

1384, 1352 and 1304 cm-1, which correspond to nitrate

ion and are characteristic for anion exchange in accor-

dance with reaction (10), also appear in the spectrum 1.

In the range of stretching vibrations of aminogroups

(1550 – 1530 cm-1), the reduction of peak intensities

takes place, and in the range of 1450–1420 cm-1, the

peak disappears, corresponding to vibrations of methyl-

ene groups [5,40]. Such changes indicate that complexa-

tion processes in the sorbent’s phase take place [5].

In case of Purolite S 985, special attention should be

paid to the short-wavelength fragments of IR-spectra,

shown in Figure 3. It contains an increase in peak inten-

sity at 771 cm-1 and appearance of bands at 822 and 711

cm-1. These changes correspond to deformation vibra-

tions of bond, which is characteristic for co-

ordination compounds [5,40,41].

NPd

Therefore, it can be concluded that palladium sorption

from nitrate weak acidic solutions on weak basic anion

exchangers proceeds not only according to anion ex-

change mechanism (reaction (10)), but also is accompa-

nied by coordination:

[][ ]

RN PdLRNPdLL







(11)

where 23

;;2LHONOn





.

3.4. Sorption Isotherm Studies

The isotherms of palladium sorption from nitrate solu-

tions on anion exchangers Purolite S 985, A 500 and A

530 are represented in Figure 4. It is known [29,33] that

the shape of these curves is an evidence of sorption se-

lectivity. It can be seen from Figure 4 that all the iso-

therms are convex curves and they are classified to

Langmuir isotherms, which are described as follows:

eq eq

EC EC







 (12)

where EC



is the maximal equilibrium exchange ca-

pacity of the resin to palladium, mmol/g; eq

is the

apparent constant of ion exchange equilibrium, L/mmol.

By transforming the Eq. (12) to the linear form, we

calculated ion exchange equilibrium constants and de-

termination coefficients (r2), which are presented in Ta-

ble 4. It can be seen from these data that coefficients r2

are close to 1. This fact supports our hypothesis about

Langmuir-type isotherms for palladium sorption.

3.5. Kinetics Studies

The successful application of ion exchangers in indus-

trial conditions requires their good kinetic properties.

That is why the research on kinetics of ()Pd II sorp-

tion on Purolite ion exchangers in the investigated sys-

tems is both of theoretical and practical interest. The

10001200140016001800

transmission

-1

670700730760790820850

transmission

cm-1

O. N. Kononova et al. / Natural Science 1 (2009) 166-175

172

Figure 4. Isotherms of palladium sorption on anion exchangers

Purolite A 530 (1), A 500 (2) and S 985 (3)

mol/L; mol/L.

C (HNO)= 0.01

C(KNO)= 1.0

Table 4. Apparent constants of ion exchange equilibrium

(eq

) and determination coefficients (r2) during recovery

of palladium (II) from nitrate model solutions.

Trade name eq

Purolite A 500 135 0.894

Purolite A 530 34.4 0.991

Purolite S 985 588 0.975

Figure 5. Kinetic dependencies of function on time for

anion exchangers Purolite A 530 (1), S 985 (2) and A 500 (3).

Bt t

Table 5. Kinetic parameters of palladium (II) sorption

from nitrate model solutions mol/L;

-4

C (Pd)= 5.0×10

C (HNO)= 0.01 mol/L; mol/L.

C(KNO)= 1.0

Trade name





(mmol/g·s)

D

(cm2/s)

1/ 2

(s)

Purolite A 500 11.70 8.26 1558

Purolite A 530 2.06 0.58 23164

Purolite S 985 9.26 5.94 2390

calculated main kinetic parameters are summarized in

Table 5 and Figure 5 contains the dependencies

. ()Btf t

It can be seen from Figure 5 that dependen-

cies ()Btf t



are the straight lines for all the resins

Purolite investigated and comply with criterion of gel

kinetics, i.e. the whole sorption process is controlled by

interdiffusion of the ions exchanged in a resin grain

[29,30,33]. As for the main kinetic parameters, it should

be noted that average rate of ion exchange process is

higher on strong basic anion exchanger Purolite A 500

(Table 5). Consequently, the value of average diffusion

coefficient for this resin exceeds such values for the

other sorbents and the half-exchange time is lesser. A

comparison of kinetic process between anion exchangers

Purolite S 985 and A 500 shows that such behavior of

these sorbents is in good consistence with our above-

mentioned assumptions about sorption mechanism.

Since the palladium sorption on Purolite A 500 is not

complicated by additional complexation (in contrast to

Purolite S 985), the rate of this process is higher and

diffusion coefficient values are also bigger, whereas the

half-exchange times are lesser for this resin. However, it

is interesting to note that the strong basic anion ex-

changer Purolite A 530, which is not practically distin-

guished from A 500 in its sorption properties (Table 3),

compares much unfavorably with A 500 in its kinetic

properties (Table 5). The average rate of ion exchange

process on Purolite A 530 is about 5 times lower than on

Purolite A 500. Also the average diffusion coefficient

values for A 530 are by one order smaller and the

half-exchange time is by one order greater (Table 5).

Such behavior of anion exchanger Purolite A 530 in

comparison with also strong basic resin A 500 can be

probably explained by its exchange capacity, which is

less by half than this value for A 500, and by its lesser

swelling as well (Table 1). Moreover, it can be assumed

that the sorbed complex ions of palladium (II), which

possess a square spatial configuration [42], have not

enough time to reach the active centers of the sorbent A

530, where the anion exchange occurs, because of its

small exchange capacity (there are few available ex-

change centers on a resin surface). Certainly this phe-

nomenon requires a special study, but from the practical

point of view the anion exchanger Purolite A 500 is

preferable than sorbent Purolite A 530 for recovery of

palladium (II) from nitrate solutions.

3.6. Sorption of Palladium from Nitrate

Solutions of Spent Catalysts

Further we have studied the sorption recovery of palla-

dium (II) from solutions of spent catalysts on some an-

ion exchangers chosen on the basis of their good sorp-

tion and kinetic properties. The results are summarized

in Table 6.

It can be seen from these data that the anion exchang-

ers in general possess good sorption ability to

ions, but this characteristic is slightly lower in compari-

()Pd II

0 102030405060708090100

EC·10-3,

mmol/g

CPd·10-6, mol/L

0,1

0,2

0,3

0,4

0,5

0,6

0,7

010002000 3000 4000 5000 60007000

t, s

O. N. Kononova et al. / Natural Science 1 (2009) 166-175

173

son with the data obtained for model solutions, exclud-

ing anion exchanger AV-17-8 (Table 3). Partly the de-

crease in recovery from real solutions can be

explained by complex composition of initial solution of

spent catalyst (Table 2), where a number of ions produce

a competing effect on palladium sorption process.

()Pd II

HNO

In order to determine the form of palladium in con-

tacting solution of spent catalyst as well as in the phase

of strong basic anion exchanger, we have obtained the

diffuse reflectance spectra presented in Figure 6. It can

be seen from these data that the maximum in diffuse

reflectance spectra is located at 410 nm. It corresponds

with the maximum in absorption spectrum at 390 nm

(Figure 1), since the bathochromic shift of maximum in

diffuse reflectance spectra is observed during sorption

concentration of noble metal ions in view of matrix ef-

fect of solid phase [43,44]. Therefore, the prevailing

form of existence in nitrate weak acidic solu-

tions of spent catalysts is its complex

[( )PdH O

()]NO 

It is known [2-5,15] that the desorption of noble

metals from highly selective ion exchangers is hardly

achievable process because of strong retention of ad-

sorbed metal ions by functional groups of resins. Due

to that, for the successful regeneration of these sor-

bents it is necessary to use the elution agents which

form more stable complexes with the recovered metal

ions than the complexes of these metals existing in the

resin phase. From this point of view, the acidic or ba-

sic thiourea solutions are widely applied as eluting

agent [1,15,19,22-24,27]. We have also used in the

present work the thiourea solutions for palladium de-

sorption after its sorption recovery. The results are

shown in Table 7. It can be seen from the presented

data that the palladium (II) elution degrees after its

recovery from model solutions reach the level of

78-82% – the result which is considered quite satis-

factory. However, the palladium desorption after its

recovery from solutions of spent catalysts proceeds on

the level of 22–25%. When carrying out this process,

we have changed thiourea concentration and used its

solutions in or , but the best result we

could reach was ~ 25% by palladium elution with 1 M

thiourea solution in 1 M

3NaOH

aOH. It should be noted

that the recovery of noble metals from industrial solu-

tions after their sorption on highly selective ion ex-

changers is often carried out by burning of such resins,

since the value of noble metals exceeds the costs of ion

exchange materials, even selective ones [2,4,24,45].

Therefore, it is necessary to continue the research for

improving the palladium recovery after its sorption on

selective ion exchangers from solutions of spent cata-

-lysts.

Figure 6. Diffuse reflectance spectra of anion exchangers’

samples AV-17-8 (1) and Purolite A 500 (2) saturated with

palladium (II) from nitrate solutions of spent catalysts.

mol/L; mol/L;

mol/L F(R) – diffuse reflectance coefficient.

-4

C(Pd)= 5.0×10

C(KNO)= 1.0

C(HNO)= 0.01

Table 6. Sorption recovery of palladium (II) from nitrate

solutions of spent catalysts mol/L;

mol/L; mol/L.

-4

C(Pd)= 5.0×10

(KNO)= 1.0

C(HNO)= 0.01C

Trade name log

D(%)R

Purolite A 500 2.31 65

Purolite S 985 2.86 88

AV-17-8 2.72 84

Table 7. Elution of palladium from anion exchangers in-

vestigated by thiourea solution (1.0 mol/L) in 0.01 M

after palladium sorption from nitrate weak acidic

model solutions.

HNO

Trade name Desorption degree (%)

Purolite S 985 78

Purolite A 500 82

4. CONCLUSIONS

Sorption recovery of palladium (II) from nitrate weak

acidic model solutions and solutions of spent catalysts

on some ion exchangers with different physical and

chemical structure was investigated. Based on electron

absorption spectra, it was determined that complexes

233

[()()]PdH ONO



prevail in contacting solutions. It

was shown that ion exchangers investigated possess

good sorption and kinetic properties.

The mechanism of palladium sorption recovery on

strong and weak basic anion exchangers from nitrate

weak acidic solution was outlined by means of

FT-IR-spectroscopy. It was shown that strong basic an-

ion exchangers sorb palladium according to anion ex-

change, whereas weak basic resins recover

()Pd II

380 400 420440 460480 500 520 540 560



, nm

F(R)

O. N. Kononova et al. / Natural Science 1 (2009) 166-175

174

complexes not only by anion exchange, but also by

means of additional coordination with nitrogen atoms of

functional groups.

The palladium (II) desorption after its recovery on se-

lective ion exchangers from model solutions and solu-

tions of spent catalysts was carried out using thiourea

solutions. It was shown that the degree of palladium

elution by 1 M thiourea solution in 0.01 M 3

NO after

its sorption from model solutions is on the level of 78 –

82 %, whereas this value does not exceed 25% after

sorption from solutions of spent catalysts. The

improvement of this process should be a subject for fur-

ther research.

()Pd II

Based on results of present investigation, the anion

exchangers AV-17-8 as well as Purolite S 985 and A 500

can be recommended for selective recovery of palladium

(II) from nitrate weak acidic solutions.

5. ACKNOWLEDGEMENT

The authors would like to express profound gratitude to

the team of Moscow office of Purolite International Ltd,

who kindly provided us with ion exchanger samples.

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