1738 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
distribution coefficients of Nb and Ta change from
81 and 493 to 288 and 380 respectively. The variation in
extraction efficiency for both metals above pH 1.2 is less
pronounced and is less than 2%. The highest distribution
coefficient of Nb (D=576) was observed when the pH of
the aqueous phase was maintained at 2.2, while the one
for Ta (493) was observed at pH of 1.1. On the other
hand, decreasing the pH below 1.1 seems less significant
since it leads to decrease in both the extraction efficiencies
and the distribution coefficients of both metals. To avoid
pH adjustments during solvent extraction, a pH range of
1.1–2.2 is recommended. However, to prevent the forma-
tion of emulsions that would result from the hydrolysis and
polymerization of the Ta and Nb complexes in a slightly
acidic medium, we maintain the starting pH of 1.1.
Effect of Extraction Temperature
The temperature of the aqueous phases may change signifi-
cantly during solvent extraction. It is therefore important
to study the extraction of Ta and Nb under different tem-
perature conditions. Its effect was studied in the range of
293–318 K using Aliquat ® concentration of 14%, an O/A
ratio of 2, and a contact time of 4 min. The results from the
trials in this direction are illustrated in Figure 8.
The enthalpy change (∆Ho) of Nb and Ta extraction
was determined based on the slope of the plot of log DM
(M=Ta, Nb) versus 1000/T (K–1) using the derived Van’t
Hoff equation (Sun et al., 2021):
,logDM RT
H C 2 303 =-+° (3)
where R is the universal gas constant and C is the integra-
tion constant. The integration constant was assumed to be
constant at a given temperature and under the same experi-
mental conditions.
Figure 9 evidenced a linear relationship between log
DM and 1000/T, from which the ∆Ho of the extraction
reaction was estimated to be –6.7 kJ/mol (Nb) and –4.4
kJ/mol (Ta), suggesting a slightly exothermic nature of the
extraction reaction in the range 293.15–318.15 K. Thus, a
low temperature seems preferable during solvent extraction
of niobium and tantalum, without significant decreas-
ing the distribution coefficients.
Effect of O/A Ratio
Figure 10 shows the results from the effect of the O/A ratio
(0.2:1 to 2.5:1) on extraction efficiency under the most
appropriate conditions: temperature of 20°C, concentra-
tion of Aliquat ® 336 of 14%, pH of the aqueous phase 1.1,
and a contact time of 4 minutes.
20 25 30 35 40 45
40
50
60
70
80
90
100
E
Nb
E
Ta
D
Nb
D
Ta
Temperature (°C)
50
100
150ti
200
250nt
300
350
Figure 8. Effect of temperature on the extraction efficiency of
Ta and Nb
3.10 3.15 3.20 3.25 3.30 3.35 3.40 3.45
1.4
1.6
1.8
2.0
2.2
2.4
2.6
log D Nb =0.35/T+0.52
log DTa=0.23/T+1.71
1000/T (K-1)
Figure 9. Relationship between log DM vs 1/T for the
extraction of Ta and Nb
0.0 0.5 1.0 1.5 2.0 2.5
20
40
60
80
100
E
Nb
E
Ta
D
Nb
D
Ta
O/A
0
100
200
300
400
500
600
Figure 10. Effect of O/A ratio on Ta and Nb extraction
Extracti
,
%
Distribu
cefficie
(
l
D
Extracti
,
%
Distributi
cefficien(
distribution coefficients of Nb and Ta change from
81 and 493 to 288 and 380 respectively. The variation in
extraction efficiency for both metals above pH 1.2 is less
pronounced and is less than 2%. The highest distribution
coefficient of Nb (D=576) was observed when the pH of
the aqueous phase was maintained at 2.2, while the one
for Ta (493) was observed at pH of 1.1. On the other
hand, decreasing the pH below 1.1 seems less significant
since it leads to decrease in both the extraction efficiencies
and the distribution coefficients of both metals. To avoid
pH adjustments during solvent extraction, a pH range of
1.1–2.2 is recommended. However, to prevent the forma-
tion of emulsions that would result from the hydrolysis and
polymerization of the Ta and Nb complexes in a slightly
acidic medium, we maintain the starting pH of 1.1.
Effect of Extraction Temperature
The temperature of the aqueous phases may change signifi-
cantly during solvent extraction. It is therefore important
to study the extraction of Ta and Nb under different tem-
perature conditions. Its effect was studied in the range of
293–318 K using Aliquat ® concentration of 14%, an O/A
ratio of 2, and a contact time of 4 min. The results from the
trials in this direction are illustrated in Figure 8.
The enthalpy change (∆Ho) of Nb and Ta extraction
was determined based on the slope of the plot of log DM
(M=Ta, Nb) versus 1000/T (K–1) using the derived Van’t
Hoff equation (Sun et al., 2021):
,logDM RT
H C 2 303 =-+° (3)
where R is the universal gas constant and C is the integra-
tion constant. The integration constant was assumed to be
constant at a given temperature and under the same experi-
mental conditions.
Figure 9 evidenced a linear relationship between log
DM and 1000/T, from which the ∆Ho of the extraction
reaction was estimated to be –6.7 kJ/mol (Nb) and –4.4
kJ/mol (Ta), suggesting a slightly exothermic nature of the
extraction reaction in the range 293.15–318.15 K. Thus, a
low temperature seems preferable during solvent extraction
of niobium and tantalum, without significant decreas-
ing the distribution coefficients.
Effect of O/A Ratio
Figure 10 shows the results from the effect of the O/A ratio
(0.2:1 to 2.5:1) on extraction efficiency under the most
appropriate conditions: temperature of 20°C, concentra-
tion of Aliquat ® 336 of 14%, pH of the aqueous phase 1.1,
and a contact time of 4 minutes.
20 25 30 35 40 45
40
50
60
70
80
90
100
E
Nb
E
Ta
D
Nb
D
Ta
Temperature (°C)
50
100
150ti
200
250nt
300
350
Figure 8. Effect of temperature on the extraction efficiency of
Ta and Nb
3.10 3.15 3.20 3.25 3.30 3.35 3.40 3.45
1.4
1.6
1.8
2.0
2.2
2.4
2.6
log D Nb =0.35/T+0.52
log DTa=0.23/T+1.71
1000/T (K-1)
Figure 9. Relationship between log DM vs 1/T for the
extraction of Ta and Nb
0.0 0.5 1.0 1.5 2.0 2.5
20
40
60
80
100
E
Nb
E
Ta
D
Nb
D
Ta
O/A
0
100
200
300
400
500
600
Figure 10. Effect of O/A ratio on Ta and Nb extraction
Extracti
,
%
Distribu
cefficie
(
l
D
Extracti
,
%
Distributi
cefficien(