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Separation of molybdenum from tungsten by di-2-ethylhexyl phosphoric acid extractant
Hydrometallurgy, 16 (1986) 263--270 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
263
SEPARATION OF MOLYBDENUM FROM TUNGSTEN BY DI-2-ETHYLHEXYL PHOSPHORIC ACID EXTRACTANT
ZHENG QINGYUAN and FAN HUIHAO Central-South Institute of Mining and Metallurgy, Changsha, Hunan (China) (Received July 18, 1985; accepted in revised form February 15, 1986) ABSTRACT Zheng, Q. and Fan, H., 1986. Separation of molybdenum from tungsten by di-2-ethylhexyl phosphoric acid extractant. Hydrometailurgy, 16: 263--270. The efficiency of extracting molybdenum(VI) from a weakly acidic solution containing a large amount of tungsten and a small amount of molybdenum using di-2-ethylhexyl phosphoric acid (D2EHPA) is low. However, when ethylenediaminetetraacetic acid (EDTA) complexing agent is present, the efficiency of molybdenum extraction is significantly increased. In this paper the effect of various factors (including the D2EHPA and EDTA concentration, pH of the feed solution, contact time, phase ratio) on molybdenum extraction has been studied. The effect of the composition of the strip solution on stripping molybdenum from the organic phase is reported. Counter-current extraction has also been investigated. The results of multiple-stage extraction show that molybdenum can be satisfactorily separated from sodium tungstate solution obtained by leaching tungsten ore, with little loss of tungsten. A possible mechanism of the extraction of molybdenum in the presence of EDTA is discussed. The reaction for extracting molybdenum is: (MoO3)~ Edta~q) + 4 (HR~PO,)2(org) ~ 2 MoO2(R2PO4) ~ • 2HR2PO,(org ) + Edt~-q) + 2 H20
INTRODUCTION The present commercial process for removing molybdenum from sodium t u n g s t a t e s o l u t i o n involves t h e p r e c i p i t a t i o n o f m o l y b d e n u m trisulfide. This p r o c e s s is s a t i s f a c t o r y f o r r e m o v i n g m o l y b d e n u m , b u t a b o u t 1 t o 1.5% o f t u n g s t e n is lost a n d d e t r i m e n t a l h y d r o s u l f i d e is f o r m e d . T h e r e f o r e , m a n y research w o r k e r s h a v e b e e n searching f o r b e t t e r m e t h o d s in r e c e n t years. G e n e r a l l y , it is c o n s i d e r e d t h a t t h e s o l v e n t e x t r a c t i o n p r o c e s s is p r o m i s i n g f o r c o m m e r c i a l a p p l i c a t i o n , a n d s o m e s e p a r a t i o n m e t h o d s are k n o w n [ 1 - - 6 ] . In this p a p e r a s o l v e n t e x t r a c t i o n s y s t e m has b e e n studied. T h e m o l y b d e n u m is e x t r a c t e d f r o m acidified s o d i u m t u n g s t a t e s o l u t i o n c o n t a i n i n g m o l y b d e n u m a n d e t h y l e n e d i a m i n e t e t r a a c e t i c acid ( E D T A ) as c o m p l e x i n g a g e n t using an organic s o l u t i o n c o m p r i s i n g d i - 2 - e t h y l h e x y l p h o s p h o r i c acid ( D 2 E H P A ) as e x t r a c t a n t , s e c - o c t a n o l as m o d i f i e r a n d k e r o s e n e as diluent.
0304-386X/86/$03.50
© 1986 Elsevier Science Publishers B.V.
264 After extracting molybdenum, the raffinate containing tungsten, EDTA and a very small amount of m o l y b d e n u m was further treated with trialkylamine to extract tungsten. Several commercial processes for the solvent extraction of tungsten with trialkylamine are known [7, 8].
EXPERIMENTAL 1. Feed solution The sodium tungstate solution containing molybdenum(VI) was adjusted to the desired pH with dilute sulfuric acid or hydrochloric acid, and the desired quantity of EDTA was added. 2. Reagents The D2EHPA was purified by the method reported in the literature [9]. The sec-octanol was an industrial-grade product. The other reagents are of analytical or chemically pure grade. The commercially available kerosene was washed with concentrated H 2 S O 4 and Na2CO3 (5%). 3. Procedures The feed solution and organic phase were mechanically shaken at 243 min-1 in 125-ml separatory funnels for 10 rain (unless otherwise stated) at about 25°C. 4. Analyses The tungsten was determined with the cinchonine weight analysis method and the thiocyanate colourimetric method (spectrophotometer Type 751, made in China). The m o l y b d e n u m was determined with the thiocyanate colourimetric method (spectrophotometer Type 72, made in China). The EDTA was analysed by complexing titration. The pH was measured with a pH meter (PHS-2 type, made in China). RESULTS AND DISCUSSION When the pH values of the aqueous solution containing only m o l y b d e n u m are below 2 or 3, m o l y b d e n u m is extracted well with D2EHPA by cation exchange according to the following reaction [3]: 2+ MoO2(aq) + 2 (HR2PO4)2(org) ~ MoO2(R2PO4)2 " 2HR2PO4(org) + 2 H~aq)
where (HR2PO4)2 is the dimer of D2EHPA. However, when an aqueous solution containing both m o l y b d e n u m and tungsten is extracted with an organic phase containing D2EHPA, the effi-
265
ciency of the extraction of m o l y b d e n u m with D2EHPA is low, because of the formation of high molecular weight isopolyanions. We have discovered that when EDTA complexing agent is present in the aqueous solution, the efficiency of extraction of m o l y b d e n u m is significantly increased. The effect of various factors on m o l y b d e n u m extraction have been investigated in this case.
1. Effect of complexing agent The effect of the complexing agent on the extraction of m o l y b d e n u m with D 2 E H P A is shown in Figs. 1 and 2. Figure 1 shows that the percentage extraction of m o l y b d e n u m is small when EDTA is n o t present. However, when EDTA is present the percentage extraction of m o l y b d e n u m increases at first, b u t then decreases as the EDTA/Mo ratio increases. Figure 2 shows that equilibrium is reached after 5 min when EDTA is present {acidification with H2SO+), while w i t h o u t EDTA the extraction rate is very slow; acidification with H2SO+ gives better results than with HC1. As for the role of EDTA and the mechanism of m o l y b d e n u m extraction, we consider that the EDTA reacts with isopolyanions and forms a new complex with molybdenum such as (MoO3)2EDTA +- [I0]; the new complex then reacts with D 2 E H P A , and the E D T A is released. A possible mechanism is expressed by the following schematic equation:
(MoO3)2Edta(~q) + 4 (HR2PO+)2(org) ~ 2 (MoO=(R2PO4)2 • 2HR2PO+)(org) + Edta~aq) + 2 H 2 0 80
6O
o
40 w
2O
o
~
~
~
r o t i o of EDTA to Mo ( M ° I / o t )
Fig. 1. Effect of ratio of EDTA to Mo (mol/at) on m o l y b d e n u m extraction. Feed solution: 85 g/l WO3, 0.52 g/l Mo, pH 1.9, acidification with 5 " N H2SO+. Organic phase: 40 vol% D2EHPA, 10vo1% sec-octanol, 50 vol% kerosene. Phase ratio of 1, c o n t a c t t i m e 10 min at about 25°(3.
266
100
Cr
0
~
'0
80
60 o o
I LU 40
20
0
5
10 Contact
time
1
r
15
20
(min)
Fig. 2. Effect of contact time on molybdenum extraction. Feed solution: (o) 0.9 g/1 Mo, pH 2.4, acidification with 5 N H2SO4; (4) 80 g/l WO~, 0.47 g/l Mo, 0.0095 M EDTA, pH 2.02, acidification with 5 N H2SO,; (v) 80.4 g/l WO 3, 0.54 g/l Mo, 0.0093 M EDTA, pH 1.93, acidification with 5 N HCI; (e) 89 g/l WO3, 0.53 g/l Mo, no EDTA, pH 2.17, acidification with 5 N H2SO4. Organic phase: same as Fig. 1, phase ratio 1, about 25°C.
It follows from this reaction that a high EDTA concentration in the feed solution is advantageous for formation of the Mo--EDTA complex, but excess EDTA is undesirable for extracting further molybdenum.
2. Effect of pH of feed solution The effect of pH on m o l y b d e n u m extraction is shown in Fig. 3. The lower pH, the higher the percentage extraction of molybdenum. This effect may be considered to be due to formation of a Mo--EDTA complex at low pH values. However, the pH cannot be too low, otherwise tungstic acid will precipitate.
3. Effect of D2EHPA concentration The effect of D2EHPA concentration on m o l y b d e n u m extraction was studied and the results are shown in Table 1. The higher the D2EHPA concentration, the higher the percentage extraction o f molybdenum; only a small amount o f tungsten is extracted.
267
80
70. o LU
60.
so
0
1.'5
2'.0 pH
2'.5
3'.0
Fig. 3. Effect of pH on molybdenum extraction. Feed solution: 85 g/l NO3, 0.53 g/l Mo, 0.01 M E D T A , acidification with 5 N H2SO 4. Organic phase: same as Fig. 1, phase ratio 1, contact time 10 min at about 25°C.
TABLE 1
Effect of D2EHPA concentration on molybdenum and tungsten extraction
D 2 E H P A (vol%)
10 20 30 40
Raffinate (g/l)
Extraction (%)
WO 3
Mo
WO 3
Mo
99.29 100.76 98.53 99.54
0.40 0.22 0.14 0.094
0.51
21.7 58.86 72.55 81.57
1.27 0.26
Feed solution: 99.8 g/l WO3, 0.51 g/l Mo, 0.01 M EDTA, p H 2.5, acidification with 5 N H2SO ,. Organic phase: 10 vol% sec-octanol in kerosene. Phase ratio 1, contact time 10 rain at about 25°C.
4. Effect of phase ratio The effect o f phase ratio (volumetric ratio o f organic phase to feed solution) on m o l y b d e n u m extraction was studied. The results are shown in Table 2. The higher the phase ratio, the higher the percentage extraction. The EDTA is n o t extracted into the organic phase. The results are consistent with the discussions above. MULTIPLEqSTAGE COUNTER-CURRENT EXTRACTION
Based on the results of the single-stage experiments discussed above, multiple-stage counter-current studies were conducted. Satisfactory separa-
268 TABLE 2 Effect of phase ratio on molybdenum extraction Phase ratio (O/A)
0.5 1.0 1.5 2.0 2.5 3.0
Raffinate
Extraction (%)
Mo (g/l)
EDTA(M)
0.078 0.074 0.071 0.057 0.053 0.053
0.0094 0.0095 0.0094 0.0090 0.0095 0.0094
83.4 84.3 84.9 87.9 88.7 88.7
Feed solution: 80 g/l WO3, 0.74 g/1Mo, 0.0095 M EDTA, pH 2.02, acidification with 5 N H2SO4. Organic phase: 40 vol% D2EHPA, 10 vol% sec-octanol, 50 vol% kerosene. Contact time 10 rain at about 25°C. tion of m o l y b d e n u m from tungsten was obtained. To illustrate these results, the following examples are presented. 1. A feed solution containing 109 g/1 WO3, 0.49 g/1 Mo, 0.01 M EDTA having pH 2.5 (acidification with 5 N H2SO4) was contacted with an organic phase containing (by volume) 40% of D2EHPA, 20% of sec-octanol and 40% of kerosene. The volumetric ratio of organic phase to feed solution was 1, the contact time was 10 min at about 25°C. After six-stage counter-current extraction, the raffinate contained 109.1 g/1 WO3, 0.024 g/1 Mo, and the percentage extraction of m o l y b d e n u m was 95.7%. 2. A feed solution containing 86.17 g/1 WO3, 0.51 g/1 Mo, 0.01 M EDTA, pH 2.5 (acidification with 5 N H2SO4) was contacted with an organic phase containing (by volume) 40% of D2EHPA, 10% of sec-octanol and 50% of kerosene. The volumetric ratio of organic phase to feed solution was 1.5, the contact time was 5 min at about 25°C. After ten stages of countercurrent extraction the raffinate contained 85.6 g/1 WO3, 0.011 g/1 Mo; the percentage extraction of m o l y b d e n u m was 97.8%, and that of tungsten 0.59%. 3. A feed solution containing 102.7 g/l WO3, 1.54 g/l Mo, 0.023 M EDTA, pH 3.0 (acidification with 5 N H2SO4) was contacted with an organic phase containing (by volume) 40% of D2EHPA and 60% of kerosene at a volumetric ratio of 2, and a contact time of 5 min at about 25°C. After ten-stage c o u n t e r ~ u r r e n t extraction, the raffinate contained 102.1 g/1 WO3, 0.046 g/1 Mo, and the percentage extraction of m o l y b d e n u m was 97%. STRIPPING M O L Y B D E N U M
FROM
LOADED
ORGANIC PHASE
When m o l y b d e n u m was stripped from the molybdenum-loaded organic phase with a solution containing a m m o n i u m hydroxide, an emulsion was
269
generated. The emulsion disappeared when ammonium chloride was added to the stripping solution and the separation of the phases was more rapid. The object of these experiments was to determine a suitable concentration of ammonium hydroxide and ammonium chloride. The results shown in Table 3 indicate that a suitable composition for stripping is 3 M NH4OH and 0.2 M NH4CI. In two stages the stripping efficiency of molybdenum was 98%, using this stripping solution at a phase ratio (O/A) of 2.0. TABLE 3 Effect of composition of stripping solution on m o l y b d e n u m stripping Composition (M)
Stripping
Composition (M)
Stripping
NH4CI
NH,,OH
(%)
NH,OH
NH4C1
(%)
0.4 0.4 0.4 0.4 0.4
0.5 1.0 1.5 2.5 3.0
45.8 58.3 66.7 83.3 84.2
3.0 3.0 3.0 3.0
0.1 0.2 0.4 0.6
85.4 86.5 85.8 86.9
Molybdenum-loaded organic phase: 40 vol% D2EHPA, 10 vol% sec-octanol, 50 vol% kerosene, 0.3 g/1 Mo, phase ratio (O/A) 2, contact time 10 rain at about 25°C. EXTRACTION OF TUNGSTEN
After extracting molybdenum from tungsten solution by D2EHPA, the raffinate containing tungsten, EDTA and small amounts of molybdenum was further contacted with trialkylamine. Tungsten was quantitatively extracted, while the EDTA and some of the molybdenum remained in the aqueous solution. To illustrate these results, the following examples are presented. 1. A solution obtained after extracting molybdenum was adjusted to a pH of 3.5 with NaOH. Then the solution, containing 95.6 g/l WOa, 0.014 g/l Mo, was contacted with an organic phase containing (by volume) 10% trialkylamine, 10% sec-octanol and 80% kerosene; the phase ratio of organic phase to aqueous solution was 1, and the contact time was 3 rain at about 25°C. After four stages of counter-current extraction the raffinate contained 0.66 g/1 WO3 and 0.008 g/l Mo; the extraction of tungsten was 99.3%, and that of molybdenum 43%. 2. A solution obtained after extracting molybdenum was brought to a pH of 4.0 with NaOH. Then the solution, containing 96.9 g/1 WO3, 0.036 g/l Mo, was contacted with an organic phase containing (by volume) 10% trialkylamine, 10% sec-octanol and 80% kerosene. The phase ratio was 1. The contact time was 3 rain at about 25°C. After four stages of counter-
270
current extraction the raffinate contained 0.28 g/1 WO3, 0.022 g/l Mo, and the extraction o f tungsten and molybdenum was 99.7% and 39%, respectively. These two examples show that the tungsten can be extracted completely, while the extraction of molybdenum was less than 50%. It shows that molybdenum can be separated further from tungsten when extracting tungsten with trialkylamine.
REFERENCES 1 Zelikman, A.N., Voldman, G.M., Ranyantsev, V.K., Ziberov, G.N. and Kagermanian, V.S., U.S. Patent 3,969,478, 1976. 2 MacInnis, M.B. and Kirn, T.K., U.S. Patent 4,276,42, 1981. 3 Esnault, F., Robaglia, M., Latazd, J.M. and Demarthe, J.M., in: Proc. Int. Solvent Extraction Conf. ISEC'74, Vol. 3, Soc. Chem. Ind., London, 1974, pp. 2765--2786. 4 Kim, T.K. and Bradford, P., U.S. Patent 4,255,396, 1981. 5 Chiola, V., Dodds, P.R., Kim, T.K. and Powers, J.A., U.S. Patent 3,607,008, 1971. 6 Chiola, V., Dodds, P.R. and Kim, T.K., U.S. Patent 3,607,007, 1971. 7 Lo, T.C., Baird, M.H.I. and Hanson, C. (Eds), Handbook of Solvent Extraction, Wiley, N e w York, NY, 1983, pp. 689--693. 8 Sohn, H.Y., Carlson, O.N. and Smith, J.T., Extractive Metallurgy of Refractory Metals, Metallurgical Society of AIME, 1980, pp. 33--44. 9 Smirnov, K.E., Cherniak, A.S. and Kostromina, O.N., Russ. J. Inorg. Chem., XXII (9) (1977) 2527. 10 Stability Constants of Metal-ion Complexes, Chemical Society, Special Publication No. 25, Supplement 1, London, 1971, 627.
263
SEPARATION OF MOLYBDENUM FROM TUNGSTEN BY DI-2-ETHYLHEXYL PHOSPHORIC ACID EXTRACTANT
ZHENG QINGYUAN and FAN HUIHAO Central-South Institute of Mining and Metallurgy, Changsha, Hunan (China) (Received July 18, 1985; accepted in revised form February 15, 1986) ABSTRACT Zheng, Q. and Fan, H., 1986. Separation of molybdenum from tungsten by di-2-ethylhexyl phosphoric acid extractant. Hydrometailurgy, 16: 263--270. The efficiency of extracting molybdenum(VI) from a weakly acidic solution containing a large amount of tungsten and a small amount of molybdenum using di-2-ethylhexyl phosphoric acid (D2EHPA) is low. However, when ethylenediaminetetraacetic acid (EDTA) complexing agent is present, the efficiency of molybdenum extraction is significantly increased. In this paper the effect of various factors (including the D2EHPA and EDTA concentration, pH of the feed solution, contact time, phase ratio) on molybdenum extraction has been studied. The effect of the composition of the strip solution on stripping molybdenum from the organic phase is reported. Counter-current extraction has also been investigated. The results of multiple-stage extraction show that molybdenum can be satisfactorily separated from sodium tungstate solution obtained by leaching tungsten ore, with little loss of tungsten. A possible mechanism of the extraction of molybdenum in the presence of EDTA is discussed. The reaction for extracting molybdenum is: (MoO3)~ Edta~q) + 4 (HR~PO,)2(org) ~ 2 MoO2(R2PO4) ~ • 2HR2PO,(org ) + Edt~-q) + 2 H20
INTRODUCTION The present commercial process for removing molybdenum from sodium t u n g s t a t e s o l u t i o n involves t h e p r e c i p i t a t i o n o f m o l y b d e n u m trisulfide. This p r o c e s s is s a t i s f a c t o r y f o r r e m o v i n g m o l y b d e n u m , b u t a b o u t 1 t o 1.5% o f t u n g s t e n is lost a n d d e t r i m e n t a l h y d r o s u l f i d e is f o r m e d . T h e r e f o r e , m a n y research w o r k e r s h a v e b e e n searching f o r b e t t e r m e t h o d s in r e c e n t years. G e n e r a l l y , it is c o n s i d e r e d t h a t t h e s o l v e n t e x t r a c t i o n p r o c e s s is p r o m i s i n g f o r c o m m e r c i a l a p p l i c a t i o n , a n d s o m e s e p a r a t i o n m e t h o d s are k n o w n [ 1 - - 6 ] . In this p a p e r a s o l v e n t e x t r a c t i o n s y s t e m has b e e n studied. T h e m o l y b d e n u m is e x t r a c t e d f r o m acidified s o d i u m t u n g s t a t e s o l u t i o n c o n t a i n i n g m o l y b d e n u m a n d e t h y l e n e d i a m i n e t e t r a a c e t i c acid ( E D T A ) as c o m p l e x i n g a g e n t using an organic s o l u t i o n c o m p r i s i n g d i - 2 - e t h y l h e x y l p h o s p h o r i c acid ( D 2 E H P A ) as e x t r a c t a n t , s e c - o c t a n o l as m o d i f i e r a n d k e r o s e n e as diluent.
0304-386X/86/$03.50
© 1986 Elsevier Science Publishers B.V.
264 After extracting molybdenum, the raffinate containing tungsten, EDTA and a very small amount of m o l y b d e n u m was further treated with trialkylamine to extract tungsten. Several commercial processes for the solvent extraction of tungsten with trialkylamine are known [7, 8].
EXPERIMENTAL 1. Feed solution The sodium tungstate solution containing molybdenum(VI) was adjusted to the desired pH with dilute sulfuric acid or hydrochloric acid, and the desired quantity of EDTA was added. 2. Reagents The D2EHPA was purified by the method reported in the literature [9]. The sec-octanol was an industrial-grade product. The other reagents are of analytical or chemically pure grade. The commercially available kerosene was washed with concentrated H 2 S O 4 and Na2CO3 (5%). 3. Procedures The feed solution and organic phase were mechanically shaken at 243 min-1 in 125-ml separatory funnels for 10 rain (unless otherwise stated) at about 25°C. 4. Analyses The tungsten was determined with the cinchonine weight analysis method and the thiocyanate colourimetric method (spectrophotometer Type 751, made in China). The m o l y b d e n u m was determined with the thiocyanate colourimetric method (spectrophotometer Type 72, made in China). The EDTA was analysed by complexing titration. The pH was measured with a pH meter (PHS-2 type, made in China). RESULTS AND DISCUSSION When the pH values of the aqueous solution containing only m o l y b d e n u m are below 2 or 3, m o l y b d e n u m is extracted well with D2EHPA by cation exchange according to the following reaction [3]: 2+ MoO2(aq) + 2 (HR2PO4)2(org) ~ MoO2(R2PO4)2 " 2HR2PO4(org) + 2 H~aq)
where (HR2PO4)2 is the dimer of D2EHPA. However, when an aqueous solution containing both m o l y b d e n u m and tungsten is extracted with an organic phase containing D2EHPA, the effi-
265
ciency of the extraction of m o l y b d e n u m with D2EHPA is low, because of the formation of high molecular weight isopolyanions. We have discovered that when EDTA complexing agent is present in the aqueous solution, the efficiency of extraction of m o l y b d e n u m is significantly increased. The effect of various factors on m o l y b d e n u m extraction have been investigated in this case.
1. Effect of complexing agent The effect of the complexing agent on the extraction of m o l y b d e n u m with D 2 E H P A is shown in Figs. 1 and 2. Figure 1 shows that the percentage extraction of m o l y b d e n u m is small when EDTA is n o t present. However, when EDTA is present the percentage extraction of m o l y b d e n u m increases at first, b u t then decreases as the EDTA/Mo ratio increases. Figure 2 shows that equilibrium is reached after 5 min when EDTA is present {acidification with H2SO+), while w i t h o u t EDTA the extraction rate is very slow; acidification with H2SO+ gives better results than with HC1. As for the role of EDTA and the mechanism of m o l y b d e n u m extraction, we consider that the EDTA reacts with isopolyanions and forms a new complex with molybdenum such as (MoO3)2EDTA +- [I0]; the new complex then reacts with D 2 E H P A , and the E D T A is released. A possible mechanism is expressed by the following schematic equation:
(MoO3)2Edta(~q) + 4 (HR2PO+)2(org) ~ 2 (MoO=(R2PO4)2 • 2HR2PO+)(org) + Edta~aq) + 2 H 2 0 80
6O
o
40 w
2O
o
~
~
~
r o t i o of EDTA to Mo ( M ° I / o t )
Fig. 1. Effect of ratio of EDTA to Mo (mol/at) on m o l y b d e n u m extraction. Feed solution: 85 g/l WO3, 0.52 g/l Mo, pH 1.9, acidification with 5 " N H2SO+. Organic phase: 40 vol% D2EHPA, 10vo1% sec-octanol, 50 vol% kerosene. Phase ratio of 1, c o n t a c t t i m e 10 min at about 25°(3.
266
100
Cr
0
~
'0
80
60 o o
I LU 40
20
0
5
10 Contact
time
1
r
15
20
(min)
Fig. 2. Effect of contact time on molybdenum extraction. Feed solution: (o) 0.9 g/1 Mo, pH 2.4, acidification with 5 N H2SO4; (4) 80 g/l WO~, 0.47 g/l Mo, 0.0095 M EDTA, pH 2.02, acidification with 5 N H2SO,; (v) 80.4 g/l WO 3, 0.54 g/l Mo, 0.0093 M EDTA, pH 1.93, acidification with 5 N HCI; (e) 89 g/l WO3, 0.53 g/l Mo, no EDTA, pH 2.17, acidification with 5 N H2SO4. Organic phase: same as Fig. 1, phase ratio 1, about 25°C.
It follows from this reaction that a high EDTA concentration in the feed solution is advantageous for formation of the Mo--EDTA complex, but excess EDTA is undesirable for extracting further molybdenum.
2. Effect of pH of feed solution The effect of pH on m o l y b d e n u m extraction is shown in Fig. 3. The lower pH, the higher the percentage extraction of molybdenum. This effect may be considered to be due to formation of a Mo--EDTA complex at low pH values. However, the pH cannot be too low, otherwise tungstic acid will precipitate.
3. Effect of D2EHPA concentration The effect of D2EHPA concentration on m o l y b d e n u m extraction was studied and the results are shown in Table 1. The higher the D2EHPA concentration, the higher the percentage extraction o f molybdenum; only a small amount o f tungsten is extracted.
267
80
70. o LU
60.
so
0
1.'5
2'.0 pH
2'.5
3'.0
Fig. 3. Effect of pH on molybdenum extraction. Feed solution: 85 g/l NO3, 0.53 g/l Mo, 0.01 M E D T A , acidification with 5 N H2SO 4. Organic phase: same as Fig. 1, phase ratio 1, contact time 10 min at about 25°C.
TABLE 1
Effect of D2EHPA concentration on molybdenum and tungsten extraction
D 2 E H P A (vol%)
10 20 30 40
Raffinate (g/l)
Extraction (%)
WO 3
Mo
WO 3
Mo
99.29 100.76 98.53 99.54
0.40 0.22 0.14 0.094
0.51
21.7 58.86 72.55 81.57
1.27 0.26
Feed solution: 99.8 g/l WO3, 0.51 g/l Mo, 0.01 M EDTA, p H 2.5, acidification with 5 N H2SO ,. Organic phase: 10 vol% sec-octanol in kerosene. Phase ratio 1, contact time 10 rain at about 25°C.
4. Effect of phase ratio The effect o f phase ratio (volumetric ratio o f organic phase to feed solution) on m o l y b d e n u m extraction was studied. The results are shown in Table 2. The higher the phase ratio, the higher the percentage extraction. The EDTA is n o t extracted into the organic phase. The results are consistent with the discussions above. MULTIPLEqSTAGE COUNTER-CURRENT EXTRACTION
Based on the results of the single-stage experiments discussed above, multiple-stage counter-current studies were conducted. Satisfactory separa-
268 TABLE 2 Effect of phase ratio on molybdenum extraction Phase ratio (O/A)
0.5 1.0 1.5 2.0 2.5 3.0
Raffinate
Extraction (%)
Mo (g/l)
EDTA(M)
0.078 0.074 0.071 0.057 0.053 0.053
0.0094 0.0095 0.0094 0.0090 0.0095 0.0094
83.4 84.3 84.9 87.9 88.7 88.7
Feed solution: 80 g/l WO3, 0.74 g/1Mo, 0.0095 M EDTA, pH 2.02, acidification with 5 N H2SO4. Organic phase: 40 vol% D2EHPA, 10 vol% sec-octanol, 50 vol% kerosene. Contact time 10 rain at about 25°C. tion of m o l y b d e n u m from tungsten was obtained. To illustrate these results, the following examples are presented. 1. A feed solution containing 109 g/1 WO3, 0.49 g/1 Mo, 0.01 M EDTA having pH 2.5 (acidification with 5 N H2SO4) was contacted with an organic phase containing (by volume) 40% of D2EHPA, 20% of sec-octanol and 40% of kerosene. The volumetric ratio of organic phase to feed solution was 1, the contact time was 10 min at about 25°C. After six-stage counter-current extraction, the raffinate contained 109.1 g/1 WO3, 0.024 g/1 Mo, and the percentage extraction of m o l y b d e n u m was 95.7%. 2. A feed solution containing 86.17 g/1 WO3, 0.51 g/1 Mo, 0.01 M EDTA, pH 2.5 (acidification with 5 N H2SO4) was contacted with an organic phase containing (by volume) 40% of D2EHPA, 10% of sec-octanol and 50% of kerosene. The volumetric ratio of organic phase to feed solution was 1.5, the contact time was 5 min at about 25°C. After ten stages of countercurrent extraction the raffinate contained 85.6 g/1 WO3, 0.011 g/1 Mo; the percentage extraction of m o l y b d e n u m was 97.8%, and that of tungsten 0.59%. 3. A feed solution containing 102.7 g/l WO3, 1.54 g/l Mo, 0.023 M EDTA, pH 3.0 (acidification with 5 N H2SO4) was contacted with an organic phase containing (by volume) 40% of D2EHPA and 60% of kerosene at a volumetric ratio of 2, and a contact time of 5 min at about 25°C. After ten-stage c o u n t e r ~ u r r e n t extraction, the raffinate contained 102.1 g/1 WO3, 0.046 g/1 Mo, and the percentage extraction of m o l y b d e n u m was 97%. STRIPPING M O L Y B D E N U M
FROM
LOADED
ORGANIC PHASE
When m o l y b d e n u m was stripped from the molybdenum-loaded organic phase with a solution containing a m m o n i u m hydroxide, an emulsion was
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generated. The emulsion disappeared when ammonium chloride was added to the stripping solution and the separation of the phases was more rapid. The object of these experiments was to determine a suitable concentration of ammonium hydroxide and ammonium chloride. The results shown in Table 3 indicate that a suitable composition for stripping is 3 M NH4OH and 0.2 M NH4CI. In two stages the stripping efficiency of molybdenum was 98%, using this stripping solution at a phase ratio (O/A) of 2.0. TABLE 3 Effect of composition of stripping solution on m o l y b d e n u m stripping Composition (M)
Stripping
Composition (M)
Stripping
NH4CI
NH,,OH
(%)
NH,OH
NH4C1
(%)
0.4 0.4 0.4 0.4 0.4
0.5 1.0 1.5 2.5 3.0
45.8 58.3 66.7 83.3 84.2
3.0 3.0 3.0 3.0
0.1 0.2 0.4 0.6
85.4 86.5 85.8 86.9
Molybdenum-loaded organic phase: 40 vol% D2EHPA, 10 vol% sec-octanol, 50 vol% kerosene, 0.3 g/1 Mo, phase ratio (O/A) 2, contact time 10 rain at about 25°C. EXTRACTION OF TUNGSTEN
After extracting molybdenum from tungsten solution by D2EHPA, the raffinate containing tungsten, EDTA and small amounts of molybdenum was further contacted with trialkylamine. Tungsten was quantitatively extracted, while the EDTA and some of the molybdenum remained in the aqueous solution. To illustrate these results, the following examples are presented. 1. A solution obtained after extracting molybdenum was adjusted to a pH of 3.5 with NaOH. Then the solution, containing 95.6 g/l WOa, 0.014 g/l Mo, was contacted with an organic phase containing (by volume) 10% trialkylamine, 10% sec-octanol and 80% kerosene; the phase ratio of organic phase to aqueous solution was 1, and the contact time was 3 rain at about 25°C. After four stages of counter-current extraction the raffinate contained 0.66 g/1 WO3 and 0.008 g/l Mo; the extraction of tungsten was 99.3%, and that of molybdenum 43%. 2. A solution obtained after extracting molybdenum was brought to a pH of 4.0 with NaOH. Then the solution, containing 96.9 g/1 WO3, 0.036 g/l Mo, was contacted with an organic phase containing (by volume) 10% trialkylamine, 10% sec-octanol and 80% kerosene. The phase ratio was 1. The contact time was 3 rain at about 25°C. After four stages of counter-
270
current extraction the raffinate contained 0.28 g/1 WO3, 0.022 g/l Mo, and the extraction o f tungsten and molybdenum was 99.7% and 39%, respectively. These two examples show that the tungsten can be extracted completely, while the extraction of molybdenum was less than 50%. It shows that molybdenum can be separated further from tungsten when extracting tungsten with trialkylamine.
REFERENCES 1 Zelikman, A.N., Voldman, G.M., Ranyantsev, V.K., Ziberov, G.N. and Kagermanian, V.S., U.S. Patent 3,969,478, 1976. 2 MacInnis, M.B. and Kirn, T.K., U.S. Patent 4,276,42, 1981. 3 Esnault, F., Robaglia, M., Latazd, J.M. and Demarthe, J.M., in: Proc. Int. Solvent Extraction Conf. ISEC'74, Vol. 3, Soc. Chem. Ind., London, 1974, pp. 2765--2786. 4 Kim, T.K. and Bradford, P., U.S. Patent 4,255,396, 1981. 5 Chiola, V., Dodds, P.R., Kim, T.K. and Powers, J.A., U.S. Patent 3,607,008, 1971. 6 Chiola, V., Dodds, P.R. and Kim, T.K., U.S. Patent 3,607,007, 1971. 7 Lo, T.C., Baird, M.H.I. and Hanson, C. (Eds), Handbook of Solvent Extraction, Wiley, N e w York, NY, 1983, pp. 689--693. 8 Sohn, H.Y., Carlson, O.N. and Smith, J.T., Extractive Metallurgy of Refractory Metals, Metallurgical Society of AIME, 1980, pp. 33--44. 9 Smirnov, K.E., Cherniak, A.S. and Kostromina, O.N., Russ. J. Inorg. Chem., XXII (9) (1977) 2527. 10 Stability Constants of Metal-ion Complexes, Chemical Society, Special Publication No. 25, Supplement 1, London, 1971, 627.