Separation of Ti(IV) and Fe(III) from Aqueous Sulfate solution by
Cyanex 272 [Bis(2,4,4-trimethylpentyl) phosphinic acid] in Kerosene
M.S. Rahman; R.K. Zoarder; D. A. Begum; M.F. Islam
Department of Applied Chemistry and Chemical Technology, University of Rajshahi, Rajshahi-6205,
Bangladesh
Abstract.
The extraction and separation of Ti(IV) and Fe(III) from aqueous sulfate solution by Cyanex 272
[Bis(2,4,4-trimethylpentyl) phosphinic acid] in Kerosene has been investigated as a functions of contact
time, aqueous phase acidity, concentration of extractant in the organic phase, temperature and loading
capacity of the extractant for both metal ion by using spectrophotometric technique.
Data shows Cyanex 272 can be used as a very effective extractant for Ti(IV) extraction from ilmenite
leach solution at high acidity showing large separation coefficient for Ti(IV) from [Ti(IV) and Fe(III)]
mixture. The maximum separation factor (=116.50) is obtained at moderate acidity (0.90 M H 2SO4) with
high extractant (0.20 M Cyanex 272) concentration. The experimental data also suggest that the
extraction of Ti(IV) and Fe(III) by Cyanex 272 does not follow simple extraction mechanism for all the acid
ranges. It is likely that solvation mechanism may be operative at high acidity of the aqueous phase.
Key words: Ti-Fe separation, aqueous sulfate solution, Cyanex 272, [bis(2,4,4-trimethylpentyl)
phosphinic acid] , kerosene
1
Introduction:
The extractant Cyanex 272 is a propietary but technical grade item of Cytec Canada Inc. (CYTEC). Its
active component is bis[2,4,4-trimethylpentyl) phosphinic acid. The structure of Cyanex-272 is as follows-
O
R
P
R
OH
R=
CH3
CH3
CH3
C CH2 CH CH2
CH3
This technical grade extractant has been used since 1983 and found to be very effective for the extractive
separation of Co(II) from Ni(II). [Preston, 1983; Danesi et al., 1984; Rickelton et al., 1984; Xun and
Golding 1987; Chou and Beekstead, 1990; Rickelton et al., 1991; Gandhi et al., 1993; Tait and Brain,
1993] However other metal ion pairs have been investigated for separation such
as,Co(II)/Cu(II),Cu(II)/Zn(II), Th(IV)/Fe(III)/Lu(II), Zn(II)/Cd(II), Mn(II)/Zn(II), Co(II)/Ni(II), Fe(III)/Cd(II)/Ni(II)
and Al(III)/Ni(II) [Sole and Hiskey, 1991; Cao. et al., 1992;Wang and Li, 1994; Zou et al., 1994 ; Devi et
al 1997., Reddy and Sarma 2001,. Pilar et al., 2001. Islam and Rahman, 2006 etc] There seems to be no
report on Ti(IV)/Fe(III) separation by Cyanex 272. However, the separation using carboxylic acids and di2-ethylhexyl phosphoric acid has been attempted in the past. Al(III) and Ni(II) separation has also been
tried by tolyl phosphate by using NH3 medium in presence of fluoride ions (Islam and Mostafa,1995).
The extraction and separation of titanium and iron by carboxylic acids, carbolic acid and carpic acid
(Islam et al., 1988) is very low. Though the reports on bis (2-ethylhexyl) phosphoric acid (Islam et al.,
1979) was satisfactory, the complete removed of iron was not achieved in a single operation. There are
numerous reports on the extraction, separation and study of mechanism of different metal ions by Cyanex
301, Cyanex 302 Cyanex 471 and Cyanex 923. The present work reports about the extractive behavior of
titanium and iron as well as separation from their mixture by Cyanex 272, as most of the titanium ores is
associated with iron.
Materials and Methods:
Standard solution of Ti(IV) was prepared by fusing 0.5 g of analytically pure TiO 2 with 10.0 g of KHSO4 in
a suitable platinum crucible with heating until the oxide is dissolved. It was cooled and dissolved in 15%
H2SO4 by gentle heating and diluted to 500 cm 3 by 15% H2SO4 acid. Another stock solution of Fe(III) was
prepared by dissolving exactly 0.864 g of A.R grade ferric ammonium sulfate in some distilled water and
to it 10 cm3 conc. H2SO4 was added. The resulting solution was then diluted to 1000 cm 3 and mixed
thoroughly. The solutions were standardized by methods given below.
The extractant Cyanex 272 having 85% purity was used without further purification. All other chemicals
were of reagent grade and used without further purification. The diluent, kerosene, was purchased from
the local market and distilled to collect the colorless fraction obtained in the range of 200-260°C.
A stock solution of Cyanex 272 (1 M) was prepared by weighing out exactly 290 g of Cyanex 272 in a 1 L
volumetric flask and diluting by distilled kerosene. Extractant solutions of different concentrations were
prepared by proper dilution of these stock solutions by distilled Kerosene.
A definite aliquot of an aqueous phase 20 ml was taken in a 125 ml reagent bottle and to it same aliquot
of organic phase 20 ml was added. The bottle was stoppered and shaken vigorously for a definite time
period in a thermostatic water bath at 30°C (otherwise stated in the phase contact study). After attainment
of equilibrium, the phases were allowed to settle and disengaged. The aqueous phase was used to
measure the metal ion content. The equilibrium organic phase metal ion concentrations were estimated
by the method of difference. The distribution ratio (D) of a metal ion was calculated as the ratio of metal
ion concentration in the organic phase to that in the aqueous phase at equilibrium. In the case of loading
test, the organic phase was repeatedly contacted with fresh equal volume of aqueous solutions until the
saturation of the organic phase with the metal was attained. Metal contents [Ti(IV) and Fe(III)] in the
2
aqueous phase was estimated by the hydrogen peroxide colorimetric method at λ=410 nm for Ti(IV)
(Vogel, 1989) and the thiocyanate method at λ=480 nm for Fe(III) (Vogel, 1989) using spectrophotometer
ANA-75 (Tokyo Photoeletric Company, Japan).
Results and Discussion:
1. Effect of phase–contact time.
The Fig-1, represents contact time in minutes and the distribution ratio. It is evident from the figure that
the extraction ratio of Ti(IV) and Fe(III) increases continuously with the contact time. Near the equilibrium
point the increase of extraction ratio with respect to time is much slower. No appreciable extraction of
Ti(IV) and Fe(III) takes places after 35 and 18 minutes respectively. Therefore, it is concluded that the
equilibrium is reached at 40 minutes for Ti(IV) and at 20 minutes for Fe(III) and after that the curves
leveled off for 0.10 M Cyanex 272 concentration.. Thus in subsequent experiments, 40 minutes mixing
have been used to ensure equilibrium for both aqueous [Ti(IV) and Fe(III)] mixture.
2.0
logD Ti(IV)/Fe(III)
1.6
1.2
0.8
0.4
0.0
0
10
20
30
40
50
60
Contact time (minutes)
Fig.-1: Effect of contact time to reach equilibrium Ti(IV) and Fe(III)
 Initial [Ti(IV)] = 1.1 gm dm-3, Acidity = 0.60 mol dm-3 H2SO4, 0.1 M Cyanex 272
, Initial [Fe(III)] = 1.1 gm dm-3, Acidity = 0.005 mol dm-3 H2SO4, 0.1 M Cyanex 272
2. Effect of extraction of Ti(IV) and Fe(III) from [ Ti(IV) and Fe(III)] mixture on
aqueous phase acidity.
The data are plotted as log D vs. log [H2SO4] in Fig.-2 & 3. This figure represents the variation of
distribution ratio on its aqueous phase acidity. The plot shows that the extraction is decreased with
increasing aqueous phase acidity both for Ti(IV) and Fe(III) extraction within the range of 0.25 to 0.90 M
H2SO4.The extraction of Ti(IV) is higher than that of Fe(III).About 95% Ti(IV) is extracted at 0.25 M H2SO4
with 0.20 M Cyanex 272 and about 24% of Fe(III) is extracted with the same condition which indicates
that comparatively larger separation of the metal ions [Ti(IV)and Fe(III)] is possible at higher acidity under
this investigation. The extraction of Ti(IV) and Fe(III) is more with 0.20 M Cyanex 272 than with 0.05 M
Cyanex 272 extractant. At 0.90 M, the extraction rate of Fe(III) is very poor which is about 1.82 % and
almost similar with different extractant concentration (0.05, 0.10, 0.15 and 0.20 M Cyanex 272) and for
0.60 M H2SO4, the extraction rate of Fe(III) are also same with extractant concentration ( 0.10, 0.15 and
0.20 M Cyanex 272).
3
0.0
1.2
-0.4
logD Fe(III)
logD Ti(IV)
1.6
0.8
0.4
0.0
-1.2
-1.6
-0.4
-0.8
-0.7
-0.8
-0.5
-0.3
-0.1
0.1
-2.0
-0.7
-0.5
-0.3
-0.1
0.1
log [H2SO4]
log [H2SO4]
Fig.-2: Effect of extraction of Ti(IV) from Ti(IV) and
Fe(III) mixture on aqueous phase acidity.
Fig.-3: Effect of extraction of Fe(III) from Ti(IV) and
Fe(III) mixture on aqueous phase acidity.
[Ti(IV)]: [Fe(III)] = 1:1; initial [Ti(IV)] = 1.1 gm dm -3, Temperature =
(301)C; Contact time = 40 minutes; Phase ratio, A/O = 1:1;  
0.05 M Cyanex 272; Slope = 1.24;   0.10 M Cyanex 272; Slope =
1.58;  0.15 M Cyanex 272; Slope = 1.50;  0.20 M Cyanex
272; Slope = 1.57
[Ti(IV)]: [Fe(III)] = 1:1; initial [Ti(IV)] = 1.1 gm dm-3, Temperature =
(301)C; Contact time = 40 minutes; Phase ratio, A/O = 1:1;  
0.05 M Cyanex 272; Slope = 1.29;   0.10 M Cyanex 272; Slope =
1.72;   0.15 M Cyanex 272; Slope = 1.94;  0.20 M Cyanex
272; Slope = 2.15
In the case of low aqueous acidity the extractant molecule ionize in the aqueous phase boundary
liberating hydrogen ion or its ionizing tendency becomes predominant, forming a neutral extractable
species in which the polar phosphoryl oxygen atom may satisfy the co-ordination number of the metal
cation. Lower is the aqueous acidity, higher is the ionization or metal cation replacement; and thus more
is the extraction. In a highly acidic solution the above tendency is suppressed due to common ion effect,
as a result the exchange of metal cation with hydrogen ion of the extractant becomes difficult and
extraction is decreased. At a very high acidic solution no ionization of the extractant occurs at all and it
behaves like a neutral phosphate ester. In such a case, if any extraction occurs, the solvation by the
extractant becomes the principal governing factor. The distribution ratio is decreased with the increase of
hydrogen ion concentration in the aqueous phase (peppard et al. 1962). It is observed that the distribution
ratio of both Ti(IV) and Fe(III) increases with the increase of extractant concentration. In the case of Ti(IV)
extraction, the slopes of acid dependence curved are 1.24, 1.58, 1.50,and 1.57 with the extractant
concentration (0.05, 0.10, 0.15 and 0.20 M Cyanex 272) respectively and in case of Fe(III) extraction the
acid dependence slopes are 1.29, 1.72, 1.94,and 2.15 with the extractant concentration (0.05, 0.10, 0.15
and 0.20 M Cyanex 272) respectively. These are much lower than theoretical 3 as discussed below.
3. Effect of extraction of Ti(IV) and Fe(III) from [ Ti(IV) and Fe(III)] mixture on
extractant concentration.
The Fig.-4 & 5 represents the variation of distributions ratio of Ti(IV) and Fe(III) on extractant
concentration. It is seen that the extraction of Ti(IV) increases linearly with the increase of extractant
concentration. The slopes of the lines in this figure are 1.50, 1.31, 1.30 and 1.20 for the aqueous phase
acidities 0.25, 0.46, 0.60 and 0.90 M H2SO4 respectively. In the case of Fe(III) at low acidities 0.25,
0.46,and 0.60 M H2SO4 the extraction of Fe(III) increases linearly with the increase of extractant
concentration. The slopes of the lines in this figure are 0.73, 0.42 and 0.15 for the aqueous phase
acidities 0.25, 0.46 and 0.60 M H2SO4 respectively. On the contrary, at 0.90 M H2SO4, the extraction of
Fe(III) is constant with different extractant concentrations and distribution ratio is very low or constant for
0.10, 0.15 and 0.20 M Cyanex 272 concentration, in other words the extraction does not increase with
the extractant concentration but with 0.50 M Cyanex 272 is much lower than with extractant concentration
of 0.20 M Cyanex 272. The extraction of Fe(III) by Cyanex 272 is also interesting. The slope decreases
with increasing acidity. The maximum slope obtained in the acidity range studied is 0.72, which is much
less than the theoretical value as given by the general equationFe+3+3[HA] = Fe+3[HA]3 +3H+....................................................(I)
(HA= Monomer of Cyanex 272)
Where extractant dependence of 3 and inverse hydrogen ion dependency of 3 is suggested. The
experimental low values of extractant and hydrogen ion dependency suggests that the TiO 2+ extraction,
4
1.6
0.0
1.2
-0.4
0.8
logD Fe(III)
logD Ti(IV)
The Fe(III) does not follow the simple extraction mechanism for all the acid ranges. It is likely that
solvation mechanism may be operative at high acidity of the aqueous phase.
0.4
0.0
-1.2
-1.6
-0.4
-0.8
-1.4
-1.2
-1
-0.8
-2.0
-1.5
-0.6
log [Cyanex 272]
Fig.-4:
-0.8
Effect of extraction of Ti(IV) from Ti(IV)
and Fe(III) mixture on extractant
concentration.
[Ti(IV)] : [Fe(III)] = 1:1; Initial aqueous phase, [Ti(IV) = 1.1 gm dm-3;
Contact time = 40 minutes; Phase ratio, A/O = 1:1; Temperature = (30
 1) C;   0.25 mol dm-3 H2SO4; Slope = 1.50;   0.46 mol dm-3
H2SO4; Slope = 1.31; 0.60 mol dm-3 H2SO4; Slope = 1.30;  
0.90 mol dm-3 H2SO4; Slope = 1.20
-1.25
-1
-0.75
-0.5
log [Cyanex 272]
Fig.-5:
Effect of extraction of Fe(III) from Ti(IV)
and Fe(III) mixture on extractant
concentration.
[Ti(IV)] : [Fe(III)] = 1:1; Initial aqueous phase, [Ti(IV) = 1.1 gm dm -3;
Contact time = 40 minutes; Phase ratio, A/O = 1:1; Temperature = (30
 1) C;  0.25 mol dm-3 H2SO4; Slope = 0.73;   0.46 mol dm3
H2SO4; Slope = 0.42;  0.60 mol dm-3 H2SO4; Slope = 0.15;
0.90 mol dm-3 H2SO4; Slope = 0.00
4. Effect of extraction of Ti(IV) and Fe(III) from [ Ti(IV) and Fe(III)] mixture on
temperature.
The Fig.-6 & 7 represent log D vs. inverse of absolute temperature, showing the variation of distribution
ratio on temperature. It is seen that the extraction of Ti(IV) increases linearly with the increase of
temperature at all acidities. On the contrary, the extraction of Fe(III) at different acidities show different
extraction behavior. At acidity 0.46 M H2SO4, the extraction rate increases with the increase of
temperature up to 400C and then decreased with the increase of temperature. At acidities 0.60 and 0.90
M H2SO4 concentration, the extraction of Fe(III) increases with the increase of temperature and at 50 0C it
is maximum for these two acidities and then the extraction is decreased with the increase of temperature.
The extraction becomes equal at 600C for all three acidities. The lower extraction above 500C at acidities
0.60 and 0.90 M H2SO4 may be explained on the basis of the formation inextractable hydrolyzed Fe(III)
with the increase of temperature. The slope of the lines has been calculated by Vant-Hoff equation giving
the average enthalpy change (H) as 5.34 k cal mol-1 for Ti(IV) and 20.14 k cal mol-1 for Fe(III) for the
portion at which the distribution ratio increases with the increase of temperature. The extraction of Ti(IV)
is endothermic up to 600C and Fe(III) extraction is also endothermic process up to 500C by 0.10 M
Cyanex 272.Thus extraction of Ti(IV) and Fe(III) by 0.10 Cyanex 272 in kerosene system is strongly
influenced by temperature.
5
-0.4
0.6
-0.6
-0.8
logD Fe(III)
logD Ti(IV)
0.8
0.4
0.2
0.0
-1.0
-1.2
-1.4
-0.2
-1.6
-0.4
-1.8
2.9
3
3.1
3.2
3.3
3.4
2.9
3
3
3.2
3.3
3.4
3
1/T °A × 10
Fig.-6:
3.1
1/T °A × 10
Effect of extraction of Ti(IV) from Ti(IV)
and Fe(III) mixture on temperature.
[Ti(IV)] : [Fe(III)] = 1:1; Initial aqueous phase, [Ti(IV) = 1.1 gm dm-3;
Extractant = 0.1 mol dm-3 Cyanex 272 in kerosene; Contact time = 40
minutes; Phase ratio, A/O = 1:1; Temperature = (30  1) C;   0.46
mol dm-3 H2SO4; Slope = -1.03;   0.60 mol dm-3 H2SO4; Slope = 0.85;   0.90 mol dm-3 H2SO4; Slope = -1.62
Fig.-7:
Effect of extraction of Fe(III) from Ti(IV)
and Fe(III) mixture on temperature.
[Ti(IV)] : [Fe(III)] = 1:1; Initial aqueous phase, [Ti(IV) = 1.1 gm dm-3;
Extractant = 0.1 M Cyanex 272 in kerosene; Contact time = 40
minutes; Phase ratio, A/O = 1:1; Temperature = (30  1) C; 0.46
mol dm-3 H2SO4;   0.60 mol dm-3 H2SO4; Slope = -3.4;  0.90
mol dm-3 H2SO4; Slope = -5.4
5. Loading capacity of Cyanex 272 for Ti(IV) and Fe(III).
Total cumulative Ti(IV)/Fe(II I) gmdm -3
The loading capacity is defined as the amount of metal content in grams extracted per 100 g of pure
extractant. It is an important factor for the study of mechanism of extraction and also for the industrial
evaluation of the extractant. High values of loading capacity are desirable for any particular extractant metal
system for industrial applications.
20.0
15.0
10.0
5.0
0.0
0
2.5
5
7.5
10
12.5
15
Contact number
Fig.-8:
Effect of loading of organic phase in the extraction
of Ti(IV)/Fe(III).
Contact time = 40 minutes; Temperature = (301)C; Acidity = 0.32 mol dm-3
H2SO4 Ti(IV):  0.40 M Cyanex 272;   0.20 M Cyanex 272;
Fe(III):  0.40 M Cyanex 272;   0.20 M Cyanex 272
The organic phases 20 ml was repeatedly contacted for 40 min at 300C with the fresh equal volume of
aqueous solution containing fixed concentration of metal ions [3.50 gm dm-3 Ti(IV) and 2.0 gm dm -3 Fe(III)
mixture with 0.32 M H2SO4]. After equilibration, the phases were disengaged and the aqueous phases
were analyzed for Ti(IV) and Fe(III) contents. The amount of metal ions [Ti(IV) and Fe(III)] transferred into
the organic phase for each contact was then determined by difference from initial aqueous concentration
6
and the cumulative concentration of Ti(IV) and Fe(III) in the organic phase after each stage of contact
was estimated. The cumulative [(Ti(IV)/Fe(III)] g dm-3 vs. contact number plot is given in Fig- 8. In this
figure, it is seen that the organic phase is saturated with Ti(IV) after 9 th contact. The organic phase is
saturated with Fe(III) after 13th contact for the experimental condition stated [3.50 gm dm -3 Ti(IV),0.32 M
H2SO4 and 0.40 M Cyanex 272]. The loading capacity for Ti(IV) is 18 g dm-3 and 3.65 g dm-3 for Fe(III) at
0.32 M H2SO4 and 0.40 M Cyanex 272 concentration and about 7.70 g dm-3 of Ti(IV) and 3.64 g dm-3 of
Fe(III) for 0.32 mol dm-3 H2SO4 and 0.20 M Cyanex 272 concentration. It is observed that the maximum
loading of Cyanex 272 for Fe(III) is almost same for both 0.40 and 0.20 M Cyanex 272.Therefore, 0.20 M
Cyanex 272 is satisfactory for Fe(III) loading of Cyanex 272. Loading data indicates Ti(IV) : Cyanex-272
ratio is 1:1.25 and Fe(III) : Cyanex 272 ratio is 1:2.86 at 0.20 M Cyanex 272, indicating almost 1:1 metal
complexes in the organic phase.
Separations study:
1. Effect of aqueous phase acidity and extractant concentration on separation
factor.
The separation factor () for [Ti(IV) and Fe(III)] system has been calculated for each extractant
concentration for 0.05, 0.10, 0.15 and 0.20 M Cyanex 272.It is seen from the plots (Fig.9) that the
separation factor increases with the increase of aqueous phase acidities at all concentration of Cyanex
272. As the acidity increases the separation factor differs for different extractant concentration in the
following sequences: 0.20 M 0.15 M  0.10 M 0.05 M Cyanex 272.The maximum separation factor is
noted for extraction with 0.20 M Cyanex 272 from highly acidic (0.90 M H2SO4 ) [Ti(IV) and Fe(III)] mixed
(1:1) solution.
Separation factor(Ti/Fe)
It is concluded that the maximum separation factor for [Ti(IV) - Fe(III)] system is achieved at high aqueous
acidity with high extractant concentration (0.20 M Cyanex 272).
120
100
80
60
40
20
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
[H2SO4] mol dm-3
Fig. 9:
Effect of aqueous phase acidity on separation.
[Ti(IV)] : [Fe(III)] = 1:1; Initial aqueous phase=1.1 g, dm-3,
[Ti(IV) and 1.1 gm dm-3 Fe(III); Extractant = 0.1 M Cyanex 272
in kerosene; phase ration, A/O = 1:1 Contact time = 40 minutes;
Temperature = (291)C; 0.05M Cyanex 272;   0.10 M
Cyanex 272;   0.15 M Cyanex 272; 0.20 M Cyanex 272
2. Effect of temperature of extraction separation factor.
The separation factor () at acidities 0.46, 0.60 and 0.90 M is graphically represented as function of
temperature (Fig.10). In all the cases the separation factor decreases with the increase of temperature
7
then it is increased again with the increase of temperature. Maximum separation factor is obtained at
lower aqueous acidity and higher temperature. The separation factor increases in the following order:
0.46 M 0.60 M 0.90 M H2SO4 at 0.01 M Cyanex 272.Thus the separation factor () is markedly
temperature dependent. From the plots we may conclude that, a) Ti(IV) can be separated from Fe(III) at
all (0.46, 0.60 and 0.90 M H2SO4 ) acidities. b). The maximum separation of Ti(IV) from Fe(III) is possible at
Separation factor, (Ti/Fe)
600C with 0.46 M Cyanex 272 concentration.
60
50
40
30
20
10
0
25
30
35
40
45
50
[H2SO4] mol dm
55
60
65
-3
Fig. 10:
Effect of temperature on separation factor ()
[Ti(IV)] : [Fe(III)] = 1:1; Initial aqueous phase = 1.1 gm dm -3
Ti(IV) and 1.1 gm dm-3 Fe(III); Phase ratio, A/O = 1:1; Contact
time = 40 minutes;   0.46 mol dm-3 H2SO4; 0.60 mol dm-3
H2SO4; 0.90 mol dm-3 H2SO4
Conclusions:
Cyanex 272 is a very effective extractant for the extraction and separation of Ti(IV) and Fe(III) from an
aqueous sulfate solution containing [Ti(IV) and Fe(III)]. The equilibrium is reached within 40 min for Ti(IV)
and 20 min for Fe(III).The loading capacity of Ti(IV) and Fe(III) are 18 gm/L and 3.65 gm/L respectively for
0.40 M Cyanex 272 and 0.32 M H2SO4 concentration. Separation factor () of Fe(III) with respect to Ti(IV)
is 116.50 at the experimental conditions [temperature = (30  1)C, extractant concentration = 0.20 M
Cyanex-272 in kerosene, phase ratio = 1:1, 0.90 M H2SO4], suggesting good separation from titanium.
The positive H value suggests that the extraction process is endothermic in nature and the average
enthalpy change (H) values are 5.34 and 20.14 k cal mol-1 for Ti(IV) and Fe(III) respectively for 0.10 M
Cyanex 272. From the temperature dependence mechanism it is shown that Ti(IV)/Fe(III) is strongly
influenced by temperature of extraction.
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