The Precious metals (Au, Ag, Pt, Pd, Rh) adsorption  

on the Silicon – organic sorbents  
 

G. Burmaa
1
, S. Alen

1
, Yu. Ganchimeg

2
, I. Sukhbaatar

2 

 
1
Institute of Chemistry and Chemical Technology, MAS 

2
Mongolian University of Science and Technology, School of Materials Technology 

 

 

Abstract: Sorption activity of two types of Silicon-organic sorbents for the previous metals has 

been studied.  A polymer – poly (3- silsesquioxanilpropylthiocarbamate) - 3- silsesquioxanilpropyl-

ammonium which was obtained by the hydrolytic poly-condensation reaction and has been 

determined its physical, chemical characteristics and its sorption activity for the Ag(I), Au(III), 

Pt(IV), Pd(II), Rh(III). It has been found out that  the sorbent shows high static sorption of Gold 

(III), Mercury (II) at acidic condition.  The second a net structured silicon-organic copolymer 

{SiO2*2[O1.5Si(CH2)3NHC5H4N}n was synthesized by hydrolytic co-poly-condensation reaction. It 

likely to react as an anionit that adsorbs chloro-complex anion of the Au (III), Pt(IV), Pd(II), 

Rh(III).  

 
Keyword: dithiocarbamate, 2-aminopyridine, sorption capacity, ion-coordination. 

 

Introduction 

nitial systemic research about the 

complexity and silicon-organic ionite 

which contain complex forming or ion 

exchange groups started since 1977, when 

discovered the poly-

mercaptomethylsilsesquioxane’s xerogel 

[1,2]. It was taken from hydrolytic poly-

condensation of the 

mercaptomethyltrialcosisilan HSCH2Si(RO)3  

(R =CH3, C2H5). Poly-mercapto-

methylsilsesquioxane’s xerogel is an 

adsorbent that has ability to adsorb Mercury 

(II) from the extremely diluted solution (0.01-

2mg/l Hg) in the high diapason of the pH, 

fully [3]. This adsorbent showed high 

selective adsorption of Mercury(II) from 

solution which contains over concentrated 

ions of the Zn(II), Fe(II), Co(II), Ni(II) at pH 

0.3-3. Now days this adsorbent is using for 

removal of Mercury from waste water of 

chlorine industry [3]. Also this sorbent has 

shown high activity (1.1mg-equa/g) in case of  

Ag(I) [4]. Then, adsorbed silver was fully 

desorbed by 0.25M ammonium hydroxide. 

When solution pH  > 3, this sorbent has full 

sorption capacity for Pb(II) and Sn(II) and 

developed a spectrometer speedy method that 

used to determine these elements in spa water 

[4].  

Therefore, silicon-organic sorbent 

(PTCA-3A) with dithiocarbamate group has 

been synthesized [5-7]. We are performing 

research evaluating of adsorption capacity of 

Hg(II), Au(III), Ag(I), Pt(IV), Rh(III) from 

aqueous solution  . 

Organic derivatives of the 

dithiocarbamate have been used widely in 

practice. Most of them have an unique 

biological activity and therefore, it is become 

raw material of the pharmacy [8]. There is a 

special trend of the practical usage of organic 

compounds with dithiocarbamate group for 

determination of heavy metals in the 

I 

29

p 29-34



industrial waste water and its purification 

[9.10]. Also, there are different types of 

adsorbent materials which contain 

dithiocarbamate group and parts [11.12].  

Silicon-organic complexities and 

ionits [13.14] have stability to high 

temperature (till 250
0
C). But study of their 

ion exchange property is scarce and never 

been studied its practical usage.  

Silicon-organic compounds with 

hetero-cycle ion has unique biological 

activeness. But poly-orginalsilsesquioxanes 

containing hetero-cycle in their organic 

radical are effective adsorbents which could 

form complex [7.17]. Therefore, we did 

research for eluvidation of precious metals 

(Au, Ag, Pt, Pd, Rh) adsorption ability of the 

silicon-organic copolymer (PAPS-2) or 

{SiO2*2[O1.5Si(CH2)3NHC5H4N}n that 

contains 2-aminopyridin which was 

synthesized by the co-poly-condensation 

reaction [18]. 

 

Experimental 

Materials. Poly(3-silsesquioxanil 

propylthiocarbamate) 3-silsesquioxanilpropyl 

ammonia (PTCA-3A) is a net constructed 

polymer with yellow color, finely dispersed 

powder. Silicon- organic copolymer PAPS-2 

is brown colored and coarse sized powder. 

Table 1 shows physical and IR spectrum data 

of used polymers. 

 
Table 1. Polymer (PTCA-3А) and PAPS-2 

F
o

rm
u

la
 

Physical data 

Т
0
С

 

IR spectrum 

(, cm
-1

) 

Р
б
 (

g
/c

m
3
) 

Р
п
 (

g
/c

m
3
) 

Р
т
 (

g
/c

m
3
) 

Р
А
 (

%
) 

V
(c

m
3
/g

) 

S
 (

m
2
/g

) 

 

S
i 2

C
7
H

1
6
N

2
S

2
O

3
 (

P
C

K
A

-

3
А

) 

 
1

.2
4
 

0
.5

8
 

0
.5

5
 

5
6

.0
 

1
.0

1
 

- 

2
2

0
 

3400, 2930, 

1540,1020 (NH), 

2570(S-H), 1340 

(C=S), 1100(Si-O-

Si) 

C
1

6
H

2
2
N

4
O

5
S

i 3
 

(P
A

P
S

-2
) 

- - - - 

1
.3

9
 

5
1

5
 

2
8

0
 

3400, 3300 (NH), 

1615, 1595, 1480, 

1440 ( circle of the  

Pyridine C=C, 

C=N), 1120-

1000(Si-O-Si), 

1560 [(NH)] 

Рб – density, Рп – pour density, Рт – apparent density, 

РА – porosity , V – total pore volume, S – surface area 

 

IR spectrum of polymers before and after 

sorption of the precious and rare metal ions 

were obtained by using high purity KBr with 

Specord IR 75 and Specord M 80. Physical 

data were determined according to previous 

method [19]. 

Colour of polymer (PTCA-3A) is changing to 

yellow after adsorption of Hg(II) while with 

Au(III) – orange, Pt(IV) – yellowish, Pd(II) – 

brown, Rh(III) – pink, Ag(I) – amber.  

Sorption method of the precious metals 

Sorption of Hg(II), Au(III), Pt(IV), Pd(II), 

Rh(III) was studied in hydrochloric acid with 

concentration of 0.1-5.0 mol/l while Ag(I) 

sorption was studied in nitric acid with same 

concentration.   

Polymers (PTCA-3A, PAPS-2) were taken 

0.05g of and mixed and shaked with solution 

of precious metal’s chloro-complex in 0.1-

5.0mol/l concentrated hydrochloric and nitric 

acids by shaker HY-4. Content of the metals 

in the solution was 0.05-0.8mg/ml. After a 

certain time polymer was separated from 

solution and washed thoroughly and 

concentration of metal ions left in the solution 

was determined by spectrophotometer method 

(HITACHI U-1000 and KFK-2) with  tin 

chloride [20,21].  

Precious metals absorption capacity of the of 

polymers was calculated by maximum 

content of the metal per gram of polymers at 

the equilibrium condition. .  

Standard solutions of precious metals were 

prepared by dissolving of AgNO3; 

H[AuCl]4H2O; H2[PtCl6]6H2O; PdCl2 and 

RhCl34H2O in distilled water.  

 

Result and D   iscussion     

Sorption study of PTCA-3A polymer 

Adsorption Ag(I) and Pd(II) is correlated with 

acid concentration, while other ions have no 

direct correlation. However, Ag(I) and Pd(II) 

correlation shows reverse behaviour (Figs 1 

and 2). Figures 1 and 2 indicate when Ag(I) is 

adsorbed from nitric acid, proton 

concentration is increased because of H
 +

 is 

interacting with sulfur atom of the thiolyate 

that caused decreasing Ag(I) adsorption. 

Sorption of [PdCl4]
2 

and [RhCl6] improved in 

30



result of increasing of chloride ions 

concentration in solution. Influence 

hydrochloric acid concentration on the 

Au(III) and Hg(II) sorption was much weaker 

than other ions. 

It can be suggested that in acid solution 

thiocarbamate group of polymer (PTCA-3A) 

is interacting with acid molecule (HA) and 

reaching to equilibrium condition (equation 

1.1). 

 
IR spectroscopy result indicated (not shown) 

peak at 1500cm
-1

 is related in asymmetric 

fluctuation of NH3
+ 

group of the polymer 

(PTCA-3A) which showed in the equation 

1.1. After sorption in nitric acid there 

appeared a new peak at 1380cm
-1

. It proves 

that nitrate ion was entered into structure of 

the polymer.  

 

 
Figure 1. Influence of the acid concentration on 

sorption of Au(III), Pt(IV) and Rh(III) 

 

 
Figure 2. Influence of the acid concentration on 

sorption Ag(I), Hg(II) 

 

A solution pH increased a little due to 

protonation of functional group of polymer 

(PTCA-3A). This behaviour of the polymer 

(PTCA-3A) in acid solution shows its 

functional group has ion-coordination 

property. Also determines influence of acid 

concentration on metal ions sorption 

(Figure1and 2). In the matter sorption of the 

Hg(II) and Ag(I) ions occurred by ion- 

coordination mechanism and possibly was 

interacted with both 2 atoms of the sulfur 

(equation 1.2): 

 
 

In the IR spectra of polymer (PTCA -3A) 

saturated by Hg(II) and Ag(I) ions, 

disappeared peaks at 1340 (C=S) and 2570 

(S-H) cm
-1

 an indication of mechanism shown 

in equation 1.2 takes place. There weren't 

shown any changes in amine (1540cm
-1

) and 

amino (1500cm
-1

) groups fluctation.  

Desorption of the Hg
2+

 and Ag
1+

 cations by 

6M solution of nitric acid indicates that they 

were adsorbed by ion exchange mechanism.  

Functional groups of the polymers could be 

interacted with AuCl4
-
, PtCl6

2-
, PdCl4

2-
 and 

RhCl6
2-

 via atoms of the nitrogen and sulfur. 

In the IR spectra of polymers saturated with 

these ions disappeared peak at 1500cm
-1

 

(NH3
2+

). Also there were not appeared any 

peaks associated with the other forms of 

precious metals in the polymer matrix. 

Elemental analysis indicated that polymer 

(PTCA-3A) in acid solution contains Au and 

Pd as AuCl and PdCl0.5. This shows these 

element atoms are connected with no less 

than 3 atoms of functional groups 

(coordination number 4). In the spectrum of 

polymer saturated with ions Au(III), Pt(IV), 

Pd(II) and Rh(III) disappeared peak at 

1340cm
-1

 (C=S) and peaks of the amine group 

at 3400 and 1540cm
-1

 were shifted to high 

wave numbers region. These results and low 

desorption values (not more than 5-10%) of 

gold, platinum, palladium, rhodium by 

hydrochloric and nitric acid solutions (6-9 

0

10

20

30

40

50

60

70

80

90

0 2 4 6

С (mol/l) 

R (%) 

Au (III) 
Pd (II) 

 Pt (IV) 

Rh (III) 

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6
С (mol/l) 

R (%) 

Hg (II) 

Ag (I) 

31



mol/l) showed that acido-complexes of these 

metals interacting via ion-coordination 

mechanism with sulfur atom of thion group 

and nitrogen atoms of ammonium and amine 

group. There is chance of ammonium group 

participation decrease in adsorption of 

precious metals with increase of hydrochloric 

acid concentration. Gold and palladium in 

hydrochloric acid with concentration of 5 

mol/l exist as AuCl2 and PdCl2.  

Static sorption capacity (SSC)  was 

determined in 3 mol/l acid solution. 

Connection degree of active group of the 

polymer (PTCA-3A) was determined by 

comparison of static sorption capacity value 

with theoretical sorption capacity value 

(SSC∙100/TSC) and showed in  

Table 2. 

 
Table 2. SSC, TSC and ratio to connect with chemical 

active group of PTCA-3A sorbent 

Volume 
Rh(I

II) 
Pt(IV) Pd(II) Au(III) Ag(I) Hg(II) 

SSC, mg/g 26 86 122 300 160 400 

TSC, mg/g 340 660 350 650 370 658 

SSC·100/TSC  

(%) 
9.0 14.0 33.0 45.0 46.0 59.0 

 

Connection degree of active group of polymer 

was increased as:  

Rh(III)<Pt(IV)<Pd(II)<Au(III)<Ag(I)<Hg(II). 

This result is in agreement with the previous 

published reference [22]. It also shows direct 

dependence with the metal sulfides solubility. 

Adsorption equilibrium time in hydrochloric 

and nitric acids with 3 mol/l were for Pd(II)-

1.5h, Au(III)-2h, Hg(II)-2h, Ag(I)- 3h, Pt(IV)-

3h and Rh(III)-3h, respectively. Poly (3-

silsesquioxanilpropylthiocarbamate)3-

silsesquioxanilpropylammonium has high 

adsorption capacity to gold and mercury from 

acid solution and its static sorption capacity 

SSC is not less than silicon-organic and 

organic sorbents which studied previously [5-

7,22].  

Sorption study of copolymer(PAPS-2) 

This silicon-organic copolymer’s Au(III), 

Pt(IV), Pd(II), Rh(III) sorption activity was 

determined in the hydrochloric acid solution 

with concentration of 0.1-0.5 mol/l. Their 

sorption activity was the highest in 

hydrochloric acid solution with concentration 

of less than 1mol/l. When acid concentration 

is more than 1mol/l, the precious metals 

sorption (R%) was decreased considerably 

(Figure 3a,b). When temperature of solution 

increased from 20
O
C to 40

O
C there wasn’t 

any change in sorption behaviour of metals 

(Figure 3a,b) as well as in equilibrium time. 

Equilibrium time in 0.5M HC at 20
o
C and 

40
o
C was similar i.e 20-40 min.  Static 

sorption capacity and coefficient of interphase 

distribution (D, cm
3
/g) were calculated based 

on isotherm curves of sorption and showed in 

Table 3. 

 

 
Figure 3. Influence of the hydrochloric acid 

concentration on metal sorption. 

 

Figure 4. Influence of equilibrium time on the metals 

sorption. 

Table 3. Static sorption capacity (SSC, mg/g) and 

coefficient of interphase distribution (D,cm
3
/g) of the 

copolymer (PAPS-2) 

Data Au(III) Pt(IV) Pd(II) Rh(III) 

SSC, mg/g 134.0 141.0 124.0 110.0 

D·10
3
cm

3
/g 4.3 5.4 2.8 1.3 

 

The result shown in Table 3 indicated that it’s 

possible to separate precious metals with a 

micro content  in solution by polymer (PAPS-

32



2). Metals adsorbed on the polymer (PAPS-2) 

can be desorbed by 6 mol/l hydrochloric acid 

solution. When desorption is done at room 

temperature, 1ml desorbent was capable to 

desorb 120 ppm Au, 190 ppm Pt, 90 ppm Pd 

and 35 ppm Rh, respectively.  

 

Sorption mechanism 

Precious metals are adsorbed on the polymer 

(PAPS-2) according to the anion exchange 

mechanism. Elemental analysis of the 

polymer saturated with the precious  metals 

showed adsorption occurs in form of [MCln]
n-

k 
where M-metal, n-4,6, k- oxidation degree 

of metal. Adsorption occurred according to 

ion exchange mechanism and it has been 

supported by decrease of adsorption activity 

with increasing of acid concentration. This 

polymer didn’t show any capacity to adsorb 

silver and copper in acid solution.  In acid 

solution Ag(I) and Cu(II) are presented in 

cation type and it’s one more evidence that 

PAPS-2 acts as an anionit in acid solution. 

Sorption activity of the PAPS-2 is similar 

with pyridine based organic sorbents [23].  

In order to find out either nitrogen atom of 

pyridine circle or amine group is participating 

in anion exchange process were taken 

comparative IR spectrums of the pure and 

saturated with precious metals polymer. In the 

pure polymer (PAPS-2) IR spectrum were 

found peaks at 1615, 1600, 1485, 1440 cm
-1 

due to –C=C- and –C=N- groups of pyridine 

and also peak at 1560cm
-1

 due to deformation 

fluctuation of the NH group. In the spectrum 

of polymer (PAPS-2) saturated with metal 

ions was disappeared NH group peak and a 

clear change in –C=C- and –C=N- groups 

(peaks at 1600 and 1495cm
-1

were widened). 

Such clear changes in IR spectrum indicated 

in anion exchange were participated both 

nitrogen atom of pyridine and amine group 

and it can be showed according to equation 

1.3. 

 
Simultaneously with anion exchange occurred 

substitution of 2 chlorine atoms with the 

polymer functional group and formation of 

the coordination bond with nitrogen atoms 

(example: Palladium acido-complex [PdCl4]
2-

).    

Conclusions 

The application of PTCA-3A and PAPS-2 

polymers for sorption of precious metals was 

studied. Based on the experimental results 

following conclusion can be drawn:  

* Sorption of Au(III), Ag(I), Pt(IV), Pd(II) 

and Rh(III) by silicon-organic polymers 

depend on the concentration of acids. The 

best result was obtained for concentration of 

0.1 and 1 mol/l. Sorption efficiency decreases 

with the increase of acid concentration. 

* Silicon-organic polymers can be used 

efficiently for removal of a large amount of 

precious metals from aqueous solutions. 

 

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