Energy & Fuels 1996,9, 231-239
23 1
Recovery of Metal Values from Spent Hydrodesulfurization Catalysts by Liquid-Liquid Extraction Pingwei Zhang and Katsutoshi Inoue* Department of Applied Chemistry, Saga University, Honjo-machi 1, Saga 840, Japan
Hiromi Tsuyama Catalysts & Chemicals Industries Co., Ltd., Kitaminato-machi 13-2, Wakamatsu-ku, Kitakyushu 808, Japan Received August 16, 1994@
The total dissolution of spent hydrodesulfurization catalysts in sulfuric acid yields an acidic solution containing a certain amount of rare metals like molybdenum, vanadium, cobalt, nickel, and a small amount of iron as well as an appreciable amount of aluminum. For the purpose of recovering the metallic values present in the solution, in the current work, the fundamental extraction characteristics of these metals with some typical commercial acidic organophosphorus compounds such as TR-83, PC-88A, PIA-8, and CYANEX 272 from the sulfuric acid media were investigated, and CYANEX 272 and PIA-8 were found to be suitable for selectively separating and recovering molybdenum and vanadium over the other metals from the specific solution at comparatively low pH. In addition, in order to further recover cobalt and nickel from the raffinate in the presence of a large excess of aluminum, a systematic investigation was conducted on the synergistic extraction behaviors of the mixed solvents consisting of L E 63, an aliphatic a-hydroxyoxime extractant, and a series of acidic extractants such as CYANEX 272, P I A 4 PC88A, DzEHPA, TR-83, and OPEHPA for cobalt, nickel, and aluminum. It was elucidated that all of these mixtures could exhibit a good synergistic effect for extraction of cobalt and nickel and that the lower the pKa of the acidic extractants, the greater the synergism. Contrarily, the extraction of aluminum, was considerably depressed by L M 63. Using the difference in synergistic extraction performance between these metals, the effective extraction of cobalt and nickel away from aluminum was achieved from the sulfate solution a t relatively low pH with the mixtures. In particular, the mixtures of L E 63 in combination with CYANEX 272 or PIAS appeared to be the most feasible and economic from a practical point of view yielding acceptable separatior, efficiency for cobalt and nickel over aluminum and a low acidity requirement for stripping cobalt and nickel as well as negligible degradation of LIX 63. A full recovery processing route is proposed based on the experimental results.
I. Introduction In the present day context of rapidly depleting resources, unreliable primary supply, and ever accelerating demands for energy, new resources have to be identified and utilized with the emphasis on conservation. aecovery of metal values from secondary resources has assumed great importance. Since the early 1950s, much of the world's crude oil and heavy fractions have been desulfurized by means of a catalytic process known as hydrodesulfurization (HDS). A molybdenum trioxide catalyst promoted with cobalt and nickel oxide on a carrier of y-alumina is generally used for this purpose. During the desulfurization process, such metals as nickel and vanadium present in crude oil are deposited on the catalyst together with hydrocarbons, carbon, and sulfur. After a number of recovery cycles of burning off the carbon, hydrocarbons, and sulfur, the catalytic activity is eventually reduced to the extent that the catalyst has t o be renewed. Consequently, a great amount of spent HDS catalyst is available from petroleum refiners. At present, molybdenum and vanadium @
Abstract published in Advance ACS Abstracts, February 1, 1995.
are being recovered t o a certain extent from spent HDS catalyst by leaching with hot water after roasting together with sodium carbonate at a temperature of above 650 "C, and then precipitating vanadium as ammonium vanadate by adding ammonium chloride and subsequently molybdenum as hydroxide after pH adjustment. However, all of the cobalt and nickel still remain in the alumina carrier in addition to small amount of molybdenum and vanadium not leached by this method. The waste carrier contaminated with these metals has not found any other uses and is being dumped or stored in appropriate locations until a suitable high-tech treatment is developed. The following two factors will cause a vast increase in the use of the HDS catalysts and hence the output of spent catalysts: (1)the environmental requirement to lower the sulfur contents in fuels, and (2) the increasing use of very heavy fractions with high content of sulfur caused by the exhaustion of low-sulfur petroleum resources. Moreover, it is expected that it will become very difficult t o find space for dumping such waste in heavily populated Japan. Therefore, development of efficient separation processes is urgently required t o
0 1995 American Chemical Society 0~~7-0624/9512509-023i~0~.00~0
Zhang et al.
232 Energy & Fuels, Vol. 9, No. 2, 1995 remove all of the molybdenum, vanadium, cobalt, and nickel from spent HDS catalysts leaving high-purity aluminum oxide free from metal contamination. To date, research activities on the recovery of metal values from spent HDS catalysts have been focused on selective and effective leaching of these metals keeping the dissolution of alumina carriers into the leach liquor as low as possible. Unfortunately, these methods do not solve the problem of the waste aluminum oxide carriers because an unacceptable amount of the metals always remain in the carrier. The alternative treatment to avoid the problem of solid waste disposal is total leaching of metals from the spent catalysts with sulfuric acid. According to this treatment process, the crushed sample powder, with a metal composition (%) of 12.26 MOOS,4.04Vz05, 3.52COO,0.75NiO, and 64.17A1203 obtained after burning the spent catalysts to remove sulfur, hydrocarbons, and carbon deposited on them, was roasted for 2 h at a temperature of 300 "C and then it was suspended in 62.7% sulfuric acid solution and heated a t 120-200 "C for 3 h for vaporization to dryness. Subsequently, it was dissolved in water and heated at 100 "C for 1h. The final solution was filtered to eliminate a small amount of solid silica and the filtrate was further diluted with water. A typical solution yielded by this total dissolution process consisted of (ppm) 2600 Mo, 810 V, 1000 Co, 210 Ni, 40 Fe, 12410 Al, and pH 1.2,from which metal values had to be selectively and nearly completely separated and recovered leaving aluminum free from metal contamination in the solution. The high degree of separation and recovery of each metal by means of liquid-liquid extraction andlor ion exchange is the key feature of this treatment process. The present research program was directed toward seeking a basic extraction process route and providing the equilibrium data necessary for recovering the metal values such as molybdenum, vanadium, cobalt, and nickel from the specific solution. A literature survey revealed little information with respect to the separation and recovery of metallic values from HDS catalysts by liquid-liquid extraction. From the solution yielded by the alkaline leaching of spent alumina-based catalysts, molybdenum, and vanadium were isolated and recovered by quantitatively extracting molybdenum a t pH < 1 with 0.1M Alamine 336 or by selectively extracting vanadium a t 8 < pH < 9 with 0.1 M Aliquat 336 after a small amount of aluminum was eliminated a t pH 7-8 with 0.3% LIX 26.1,2Cobalt and nickel were further recovered from the acidic sulfate solution with CYANEX 272 after the removal of a small of aluminum with the same e ~ t r a c t a n t .In ~ addition, it was also reported that vanadium and molybdenum were recovered from the ammoniacal leach liquor of spent HDS catalysts a t pH 7.3 and pH 3.6,respectively by using dialkylmonothiophosphoric acid (MSP-8) after nickel was extracted from the solution at pH 9.1 with the same e ~ t r a c t a n t . ~ However, no work has ever been conducted on the separation and recovery of molybdenum, vanadium, cobalt, and nickel from a solution containing an ap(1)Olazabal, M. A,; Fernandez L. A.; Madariaga J. M. Solvent Extr. Ion Exch. 1991,9 (51, 735-748. (2) Olaxabal, M. A,; Oriver, M. M.; Fernandez, L. A.; Madariaga, J. M. Solvent Extr. Ion Exch. 1992,10 (41, 623-635. (3) Orive, M. M.; Olazabal, M. A.; Fernandez, L. A.; Madariaga, J. M. Solvent Extr. Ion Exch. 1992,10 (51, 787-797.
preciable amount of aluminum, resulting from total dissolution of spent HDS catalysts in sulfuric acid as outlined above by means of a liquid-liquid extraction technique.
11. Experimental Section 1. Chemical Reagents and Preparation of Solutions. The commercial extractants employed in the present work were purchased or kindly donated from the following manufacturers: CYANEX 272, containing bis(2,4,44rimethylpenty1)phosphinic acid as the active components, from Cyanamid Canada Inc.; PIA-8, PC-88A, DzEHPA, TR-83, and OPEHPA, containing active component bis(2-ethylhexy1)phosphinicacid, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, bis(2ethylhexy1)phosphoric acid, and di[2-(1,3'-trimethylbutyl)5,7,7-trimethyloctyllphosphoricacid, 4-(1,1,3,3-tetramethylbutyl)phenyl-2-ethylhexylphosphoric acid, respectively, from Daihachi Chemical Co. Ltd.; and L E 63, the active constituent, 5,8-diethyl-7-hydroxy-6-dodecanone oxime, from Henkel Corp. The structural formulas and the values of pKa of these extractants are shown in Figure 1. The determination of the values of pKa of the acidic organophosphorus reagents was carried out at 298 K by potentiometric titration described by P r e ~ t o n . All ~ of these reagents were utilized as supplied without further purification after diluting in EXXSOL D80, an aliphatic commercial diluent. The concentration of the extractant in solvent is expressed by percentage of volume (v/ v, %). Cobalt, nickel, aluminum, ferric, and vanadyl sulfates as well as sodium molybdate were of analytical grade. The aqueous feed solutions of known composition were made up and pH was adjusted to the desired values by addition of sulfuric acid or ammonia in the usual manner. The actual leach liquor of the total dissolution of spent HDS catalysts by sulfuric acid was obtained according to the method described in the Introduction. The synthetic aqueous solution containing the similar composition t o the actual sulfate leach liquor was prepared as necessary. 2. Experimental Procedure. Solvent extraction tests were carried out batchwise by shaking equal volumes of the aqueous and organic phases in a series of 50 mL flasks immersed in a thermostated water or air bath maintained at 313 K t o attain equilibrium, unless otherwise specified. The time to reach equilibrium was within 40 h for all the cases except for those shake-out tests concerning the extraction and strip of nickel with mixtures of L M 63 and acidic organophosphorus reagents, which was 72 h. After the two phases were allowed to settle for phase separation, pH and the concentrations of metals in the aqueous phase were measured. 3. Analysis. The metal contents in both feed solutions and equilibrium aqueous phases were determined after suitable dilution with water using a Seiko Model SAS7500 atomic absorption spectrophotometer for the individual element system with the exception of molybdenum and vanadium or using a Shimadzu Model ICP-1000 I11 sequential plasma spectrometer for the multielement system as well as those of molybdenum and vanadium in the single element extraction system. The concentrations of metals in the organic phases were calculated in accordance with mass balance, unless otherwise noted.
111. Results and Discussion 1. Recovery of Molybdenum and Vanadium. Bis(2-ethylhexy1)phosphoric acid (D2EHPA) has been employed to study the extraction and recovery of (4) Tsuboi, I.; Hashimoto, T.; Komasawa, I. Proc. 10th Annu. Meet. Solvent Extraction, Osaka 1991,pp 81-86. (5) Preston, J. S . Hydrometallurgy 1983,11, 105. (6) Castresana, J. M.; Elizalde, M. P.; Aguilar, M.; Cox, M. Solvent Extr. Ion Elcch. 1988,6 (21, 265-274.
Recovery of Metal Values from Spent HDS Catalysts
Energy & Fuels, Vol. 9,No. 2, 1995 233 0
RO,
,
11
Rq::
P-OH
R/p-
CYANEX 212
pKa = 5.22
RO
0
\ 11 ,P-OH
PIA4
OH
PC-MA
pKa = 5.20
DzEHPA
pKa = 3.01
pKa = 4.21
RO
R-CH-C4?
TRd3
I1
I
OH
R'O
RO
RO
N,
OH
LIX 63
OPEHPA
pKa = 176
pKa = 4.02 pKa = 2.58 Figure 1. Chemical structures and pKa values of the commercial extractants.
0
2
4 Equilibrium pH
Equilihrium pH
8
6
Figure 2. Percentage of extraction of metals from sulfate
Figure 3. Percentage of extraction of metals from sulfate
solutions as a function of equilibrium pH with 20% CYANEX 272 dissolved in EXXSOL DSO.
solutions as a function of equilibrium pH with 20% PIA-8 dissolved in EXXSOL D80.
molybdenum7y8and vanadiumgJOfrom their individual sulfate solutions in the past. Nevertheless, this extractant is not suitable for separating the two metals from their coexisting solutions owing to its poor selectivity, particularly in the case of the presence of a large amount of aluminum since it can strongly extract aluminum even a t low pH. Accordingly, in order to selectively separate and recover molybdenum and vanadium from the acidic sulfate solutions containing cobalt, nickel, aluminum, and iron in addition to molybdenum and vanadium, other extractants suitable for this purpose must be screened. In the present study, the commercial acidic organophosphorus reagents TR-83,PC-88A, CYANEX 272, and PIA-8 were chosen as the candidate extractants to examine their extraction behaviors for each of the metal ions concerned here. The experimental results are shown as a plot of percentage extraction of each metal against equilibrium pH in Figures 2, 3, 4, and 5, respectively, together with the experimental conditions. (7)'Esnault, F.; Robaglia, M.; Latard, J. M.; Demarthe, J. M. Proc. ISEC'74~1974,3, 2765-2785. (8) Zheng, Q.; Fan, H. Hydrometallurgy 1986, 16, 263. (9) Ottertun, H.; Strandell, E. Proc. ISEC'77 1977, 501-508. (10)Ritcey, G. M.; Lucas, B. H. Proc. ISEC'77 1977, 520-531.
100
80
c e
8
40
20
0
2
4
6
Equilibrium pH
Figure 4. Percentage of extraction of metals from sulfate solutions as a function of equilibrium pH with 20% PC-88A dissolved in EXXSOL D80.
It is clear that the usual S-shaped extraction curves are obtained for all of the systems studied and it can be seen from the comparison of these figures that molybdenum is nearly completely extracted even at low pH with all of the extractants employed. In particular it can be highly selectively extracted away from other metals at pH = 0 with CYANEX 272 or PIA-8. Vanadium is also favored over aluminum with CYANEX 272 or PIA4 but not with the other two extractants. Thus
234 Energy & Fuels, Vol. 9, No. 2, 1995
Zhang et al. Table 1. Extraction of Mo and V from the Sulfate Leach Liquor of Spent HDS Catalysts with 40%PIA-8in EXXSOL D 8 P
XO b?
2 2
h"
10
2
4
h
8
Equilibrium pH
+
+
+ 2(H2R2)(org)= Mo02R,.2HR(org)
+ 2H+(aq) (1)
where H2R2 represents the dimeric form of the phosphinic acids and labels aq and org are related t o the phases. Vanadium, iron, and a small amount of aluminum coextracted together with molybdenum into the solvent phase should be removed by scrubbing before molybdenum is recovered. Table 2 gives the results for the scrub tests from the loaded CYANEX 272 solvent with different concentrations of sulfuric acid solutions. The data show how effective in removing these impurities sulfuric acid is as a scrub reagent. Stripping of molybdenum from the loaded solvent is a key problem in the recovery of molybdenum by extraction with acidic organophosphorus compounds. Because molybdenum gives rise to anionic species unextractable with acidic extractants in alkaline solui l l ) Cao,
Y.; Nakashio, F. Mo Kerue Yu Jushu 1989,9 (41, 6-12.
Mo
V
65.5 82.4 91.1 96.1
92.0 91.1 80.5 71.7
Co 0.2 0.0 0.0 5.1b
Ni
Al
0.4 0.0 0.0 4.0b
2.2 100 0.9 100 0.7 97.7 0.2 94.9
Fe
The composition of feed was (ppm): 2741 Mo, 859.2V,1066 Co, 226 Ni, 12990 Al,38.4Fe for tests 1, 3,and 4, and 2752 Mo, 867 V,945 Co, 194.9Ni, 11385Al,38 Fe for test 2. This may be the result of analytical errors.
Figure 5. Percentage of extraction of metals from sulfate solutions as a function of equilibrium pH with 20% TR-83 dissolved in EXXSOL D80.
it can be concluded that CYANEX 272 and PIA-8 are likely to be suitable extractants for the selective separation and recovery of molybdenum and vanadium from aluminum, cobalt, and nickel from sulfuric acid media at low pH. A confirmatory experiment was carried out from the typical sulfate leach liquor of spent catalysts mentioned earlier by using 40% PIA-8 in EXXSOL D80 as the solvent. The results are given as extraction efficiency of each metal a t varying pH in Table 1. I t is apparent, as expected, that aluminum is poorly extracted into PIA-8 organic solvent and cobalt and nickel are completely left in the raffinate. The percentage extraction of vanadium and iron decreased whereas that of molybdenum increased with a decrease of pH under the given test conditions. Thus, by controlling pH to an appropriate low range, molybdenum, vanadium, and iron can be preferentially separated from a substantial quantity of aluminum and a moderate amount of cobalt and nickel by extraction with PIA-8. Additionally, similar test results were also obtained with 40%CYANEX 272 dissolved in EXXSOL D80. The increase of molybdenum extraction with decreasing pH is attributed to through the formation of Mo0z2+ in the aqueous solution a t low pH according to the equation' M004~- 4H+ = M002~+ 2H20, which is a species extractable by PIA-8 and by CYANEX 272 in terms of the general cation exchange mechanism expressed as followsll
5% extraction
1.44 1.36 1.20 1.00
2 3 4
I1
MoO;+(aq)
equilibrium PH
no. 1
Table 2. Scrub of V, Fe, and Al from the Loaded Solventa
5% scrub of metals V Fe 68.3 100 62.1 100 54.5 74.3
scrub reagent
M)
Mo
2.75 2.15 1.45
0.1 0.07 0.0
Al
100 100 100
The organic solvent was 40% CYANEX 272 and the metal loading was (ppm): 2870 Mo, 760 V,35 Fe, 40 Al.
Table 3. Strip of Mo from the Scrubbed Solventa
NH~OH (viv. 8) 2.0 4.0 5.0 5.5 6.0
7.0 8.0 10.0 15.0 20.0 a
strip solution (ppm) DH Mo V -
8.21 8.27 8.30 8.43 -
2590 2580 2590 2640 -
80 86 94 110 -
8 strip ofMo -
90.2 89.9 90.2 92.0 -
ohase seDaration aq white turbid aq white turbid clear, good clear, good clear, good clear, good third phase, viscous third phase, viscous third phase, viscous third phase, viscous
Solvent loading (ppm): Mo = 2870,V = 240.
tions and it is a requirement to recover it as ammonium molybdate for its reuse,12J3 aqueous ammonia was chosen as the strip reagent and its optimum concentration for stripping was determined. Table 3 shows that the strip performance of molybdenum is largely dependent upon the content of ammonia. A white turbidity appeared in the aqueous strip solutions during stripping from the loaded CYANEX 272 organic phase when the content of the ammonia solutions were less than 5%. The same phenomenon has been observed in the stripping of molybdenum from the loaded DzEHPA with ammoniacs On the other hand, when the content of ammonia solutions was greater than 7%, the formation of a second organic phase was observed and the viscosity in both phases was much increased, making phase separation difficult. This phenomenon has also been reported for the Mo-DzEHPA extraction system by Esnault et aL7 The increase in visco.Ay of the CYANEX 272 organic phase at high pH has been explained as micelle f0rmati0n.l~In contrast, however, good phase separation was observed in the range of 5-7% ammonia and more than 90% stripping of molybdenum could be (12) MacInnis M. B.; Kim, T. K. In Handbook of Solvent Extraction; Lo, T. C., Baird, M. H., Hanson, C., Eds.; John Wiley & Sons: New York, 1983;p 694. (13)Huggins, D.K.; Queneau, P. B.; Ziegler, R. C.; Nauta, H. H. K. Hydrometallurgy 1980,6,63-73. (14)Inoue, K.; Nakayama, D.; Watanabe, Y. Hydrometallurgy 1986, 16, 41-53.
Energy & Fuels, Vol. 9, No. 2, 1995 236
Recovery of Metal Values from Spent HDS Catalysts Table 4. Extraction of Vanadium from the Scrub Solution' 40% CYANEX 272 in EXXSOL D80 solvent equilibrium pH 1.52 Mo 100, V 92.8, Fe 100b extraction, 8 The composition of the feed solution was (ppm): 2.0 Mo, 430 V, 29 Fe, 32 Al,and pH 1.56. Aluminum in the organic phase was not detected by analyzing the strip solution obtained after stripping the loaded solvent by HzS04 solution. a
100
xo gcio
$v
92
40 20
Table 5. Strip of Vanadium from the Loaded SolvenP strip agent 2.75MHzSOi 6% NH40H Q
strip solution (ppm) Mo V Fe 0 330 24 0 2.0 384
0
Vstrip,% 82.7 96.2
Solvent loading (ppm): 2.0 Mo, 399 V, 29 Fe.
achieved by one batch operation under these experimental conditions. After the recovery of molybdenum, vanadium can be further recovered from the scrub solution containing a small amount of iron and aluminum with PIA-8 or CYANEX 272 as extractant. In order to make the vanadium-bearing scrub solution fit for the favorable extraction of vanadium, the pH was adjusted to around 1.5 by adding calcium hydroxide powder. The results given in Table 4 indicate that higher than 92% of vanadium and nearly 100% of iron were extracted into the 40% CYANEX 272 solvent while the aluminum in the aqueous solution was not extracted at all under the selected conditions. Stripping of vanadium from the loaded solvent can be accomplished by the use of either aqueous ammonia or sulfuric acid solutions. Table 5 shows that stripping with 2.75 M HzS04 solution recovered only 82.7% of the vanadium and most of the coextracted iron. However, 96.2% stripping of vanadium could be achieved with 6.0% aqueous ammonia solution and, in addition, the small amount of coextracted iron was not stripped at all. Such results suggest that by using ammonia solution as the strip agent, not only can a suitably high strip of vanadium be obtained but also a complete separation of vanadium from iron can be easily accomplished. In addition, similar phase separation behavior to that observed in the stripping of molybdenum with ammonia solution was also encountered in the case of vanadium. Vanadium in the strip solution, like molybdenum, can be recovered as ammonium vanadate.15 2. Recovery of Cobalt and Nickel. Although much work with respect to CoNi separation by solvent extraction has been already carried out as reported in the literature,16-18 none of this research has been concerned with the simultaneous presence of an appreciable amount of aluminum. A mixed solvent phase consisting of L E 63 in combination with dinonylnaphthalenesulfonic acid (DNNSA)19,20 provided a possibility of preferentially extracting cobalt and nickel from aluminum a t low pH since the selectivity series for (15)Rice, N. M. In Handbook of Solvent Extraction; Lo, T. C . , Baird, M. H., Hanson, C., Eds.; John Wiley & Sons: New York, 1983; p 698. (16) Ritcey, G. M. In Handbook of Solvent Extraction; Wiley-Interscience: New York, 1983; pp 673-687. (17) Preston, J. S. Hydrometallurgy 1982, 9, 115. (18)Danesi, P. R.; Reichley-Yinger, C.; Mason, G.; Kaplan, L.; Honvitz, E. P.; Diamond, H. Solvent Extr. Ion Ezch. 1985, 3, 435.
1
2
3
4
5
Equilibrium pH
Figure 6. Extraction of nickel from sulfate solutions with mixtures of 20% L E 63 and 7% various acidic organophosphorus reagents: (bold 0) L E 63/CYANEX 272; (v)L E 631 PIA-8; (A) LM 63PC-88A; (0) L E 63PTR-83; (0)L E 63/ DzEHPA, (0) LM 63/OPEHPA, (U) 20% DzEHPA alone; ( 0 ) 20% OPEHPA alone.
nickel, cobalt, and aluminum was reversed when LIX 63 was added to the acidic extractant. However, poor stripping of nickel and degradation of L E 63 in the presence of DNNSA as well as emulsification problems were the major obstacles encountered with this mixture.21 Although the extraction processes for separation and recovery of cobalt and nickel with the mixture of LIX 63 in combination with bis(2-ethylhexy1)phosphoric acid have been reported and ~ a t e n t e d , it~ also ~ - ~suffers ~ from some serious defects, e.g., the high concentration of sulfuric acid required for stripping nickel and the degradation of L M 63 in some degree as will be seen later. Consequently, to identify improved synergistic mixtures capable of effectively extracting cobalt and nickel away from aluminum in sulfuric acid medium at relatively low pH, batch solvent extraction tests were conducted to characterize the extraction and stripping of cobalt, nickel, and aluminum with mixed solvents consisting of LIX 63 and the commercially available acidic reagents such as CYANEX 272, PIA-8, PC-88A, TR-83, and OPEHPA as well as D2EHPA for comparison. Special interest was paid to the recovery of cobalt and nickel from the raffinate obtained previously after recovering molybdenum and vanadium from the sulfate leach liquor of spent HDS catalysts. (A) Effect of p H on Extraction of Metals. The effect of pH on extraction was separately examined for each metal ion with various acidic organophosphorus reagents (HR) such as CYANEX 272, PIA-8, PC-88A, TR83, DzEHPA, and OPEHPA alone and in admixture with L E 63. Typical experimental results for extraction of nickel, cobalt, and aluminum with each of these mixtures are shown as plots of percentage extraction of metals against equilibrium pH in Figures 6, 7, and 8, respectively (see Figures 2-5 for the extraction of cobalt, nickel, and aluminum with CYANEX 272, PIA-8, PC88A, and TR-83 alone). (19) Fekete, S. 0.;Meyer, G . A. US.Patent 4,193,969 (1980). (20)Amax Inc.; Japan Kokai Patent 7,886,621 (1978). (21) Osseo-Asare, It;Renninger, D. R. Hydrometallurgy 1984, 13, 45-62. (22)Joe, E. G.;Ritcey, M. G.; Ashbrook, A. W. J.Metals, N.Y. 1966, 18, 18-21. (23) Schepper,A. De; Coussement,M.; Peteghem A. Van Prepr. Int. Conf. Adu. Chem. Metall. 1979,1, pp 8-25. (24)Ashbrook, A. W.; Ritcey, G . M.; Joe, E. G. US.Patent 3,455,680 (1969). (25) Schepper, A. De; Peteghem A. Van Br. Patent 1,470,046(1977).
Zhang et al.
236 Energy & Fuels, Vol. 9, No. 2, 1995
Table 6. pb.6 Values and Synergistic Coefficients (SC) for the Extraction of Cobalt and Nickel by the Mixtures Containing 20%L E 63 and 7%Organophosphorus Acids in EXXSOL DSO at 40 "C"
0
I
#
'
I
1 7 ,
1
2
1
I
1
1
4
3
,
I
5
Equilibrium pH
Figure 7. Extraction of cobalt from sulfate solutions with mixtures of 20% LM 63 and 7% various acidic organophosphorus reagents: (bold 0)LM 63/CYANEX 272; (V)L E 631
CYANEX272LM63 PIA-8LM 63 PC-88MLM 63 TR-83LM 63 D2EHPMLM 63 OPEHPMLM 63
1.03 1.00 0.80 0.72 0.35 0.24
1.23 1.31 0.69 0.65 0.44 0.37
4.78 4.87 5.24 5.40 6.14 6.36
5.34 5.18 6.42 6.50 6.92 7.06
a The values of pH0.5 with L E 63 alone were 3.90 for Co and 3.42 for Ni.
PIA-8; (A) L E 63/PC-88A, (0) LM 63PTR-83; ( 0 ) L E 631 DsEHPA (0) LIX 63/OPEHPA, (m) 20% DzEHPA alone; (0) 20% OPEHPA alone. 1001
I
I
+ o
2
3
4
Relative ratio of LIX 63 lo CYANEX 272
0
I
I
1
2
Figure 9. Dependence of L E 63 on extraction of Ni, Co, and Al. Solvent: 8% CYANEX 272 in EXXSOL D80 plus LM 63 as shown. Equilibrium pH: 1.94 f 0.06. 3
Equilibrium pH
Figure 8. Extraction of aluminum from sulfate solutions with mixtures of 20% L E 63 and 7% various acidic organophosphorus reagents: (bold 0) L E 63/CYANEX 272; (v)LIX 631 PIA-8; (A) LM 63PC-88A ( 0 )LM 63/TR-83; ( 0 ) LIX 631 DzEHPA (0) L E 63/OPEHPA, (m) 20% DzEHPA alone; ( 0 ) 20% OPEHPA alone.
It can be clearly seen that the values of pHo.5 (defined as the pH at which 50% extraction occurs) for both cobalt and nickel are markedly shifted to lower pH by adding L M 63 to these organophosphorus acids, demonstrating the remarkable synergistic effect for cobalt and nickel of the mixed systems. Conversely, the extraction of aluminum is significantly suppressed by adding L M 63. Such results suggest that all of the synergistic systems exhibit good selectivity for cobalt and nickel over aluminum, making it possible to extract cobalt and nickel away from aluminum using these synergistic extraction mixtures from sulfate solutions at low pH. In addition, if a synergistic coefficient (SC) is defined, in accordance with ref 6, as SC = nApHo.5 (where n is the oxidation state of the metal and ApHo.5 is the difference in pHo.5 for the LIX 63 systems with and without the organophosphorus acids, e.g., ApHo.5 = p H 0 . 5 -~ p~ H~ 0~. 5 ~ " ~ ~the + ~ relative ~) values of the synergistic coefficients for cobalt and nickel in the systems studied can be calculated as given in Table 6. These results show clearly that the degree of the synergism resulting from the addition of the organophosphorus acids to L E 63 decreases in the following order: OPEHPA > DZEHPA > TR-83 > PC-88A > PIA-8 CYANEX 272
-
c 4
$ U
B
3
0
1 2 3 Relativc ratio of LIX 63 to PC-88A
4
Figure 10. Dependence of LIX 63 on extraction of Ni, Co, and Al. Solvent: 7% PC-88A in EXXSOL D80 plus LIX 63 as shown. Equilibrium pH: 1.77 f 0.04.
This is consistent with the order of pKa of these acidic extractants as shown previously, i.e., the lower the pKa, the greater the synergism. (B)Dependence of LIX 63 Concentration on Extraction of Metals. The dependence of the distributions of cobalt, nickel, and aluminum on the concentration of LIX 63 was examined by varying the LM 63 content in organic mixtures while holding the concentration of the acidic organophosphorus reagents (HR) constant. The results of the extraction with the mixtures of LIX63 in combination with CYANEX 272, PC-88A, and OPEHPA are shown as a function of the relative proportion of LM 63 to HR in Figures 9, 10, and 11,respectively, together with the experimental conditions. These results show that the synergistic effects for cobalt and nickel rapidly increase at first as the ratio of LIX 63 to HR increases. A greater degree of synergism is observed for nickel than for cobalt at relatively low ratios. Then nickel extraction approaches a constant or somewhat decreases while cobalt still maintains a tendency t o increase over a wide range of higher ratios.
Recovery of Metal Values from Spent HDS Catalysts
Energy & Fuels, Vol. 9, No. 2, 1995 237 100
80 &3
w 6 0 6 Y
s40
3
20 5
1 2 3 4 Relative ratio of LIX 63 to OPEHPA
0
I
,
I
I
I
I
P
,
"-1
1
2
3
4
5
Relative ratio of PC-88A to LIX 03
Figure 11. Dependence of LM 63 on extraction of Ni, Co, and Al. Solvent: 10% OPEHPA in EXXSOL D80 plus L E 63 as shown. Equilibrium pH: 1.0 f 0.05. 100
0
Figure 13. Influence of PC-88A on extraction of Ni, Co, and Al. Solvent: 6.5% L E 63 in EXXSOL D80 plus PC-88A as shown. Equilibrium pH: 1.75 f 0.05.
I
100
80
80
60
$60
$ 40
g40
3 20
0
20 1 2 3 4 Relative ratio of CYANEX 272 to LIX 63
5
0
1 2 3 4 Relative ratio of DzEHPA to LIX 63
5
Influence of CYANEX 272 on extraction of Ni. C< and Al. Solvent: 6.5% L E 63 in EXXSOL D80 plus CYANEX 272 as shown. Equilibrium pH: 2.05 & 0.05.
Figure 14. Influence of DzEHPA on extraction of Ni, Co, and Al. Solvent 6.5% LIX 63 in EXXSOL D80 plus DzEHPA as shown. Equilibrium pH: 1.40 f 0.03.
For aluminum extraction, a greater depression effect took place with the mixture of OPEHPAILIX 63 (Figure 11)than with that of PC-88NLM 63 (Figure lo), which indicates that the stronger the acidities of organophosphorus compounds, the higher the suppression effect for aluminum. However, an interesting fact is noticed from Figure 9 that aluminum extraction by the mixture of LIX 63lCYANEX 272 becomes negligible under the given conditions even though CYANEX 272 is the weakest acid and thus gives rise to the smallest synergistic effect among all organophosphorus reagents examined here. The following two reasons are considered to be responsible for this result: the weak extractability of aluminum by CYANEX 272 itself and the negative synergism caused to a certain degree by addition of LIX 63 to CYANEX 272. (C) Influence of H R Concentration on Extraction of Metals. The influence of variation in the HR concentration on the extraction behavior of metal ions was also examined by fixing the LIX 63 content while changing HR concentration in the mixed extractants. The test data are presented as a function of relative ratio of HR to LIX 63 in Figures 12, 13, and 14 for the mixtures of L E 63 in combination with CYANEX 272, PC-88A, and DBEHPA,respectively. Very similar extraction curves were observed for other synergistic extraction systems examined. With increasing HR concentration, extraction of cobalt and nickel abruptly increases and reaches a maximum and is then followed by a slight decrease within the range of the test conditions. It appears that the tendency to decrease is greater for cobalt than for nickel with the same organic acid. Aluminum extraction is gradually increased with increasing HR concentration and it is even preferred to cobalt and nickel at high HR concentrations because, after all, the organo-
phosphorus acids alone can extract only aluminum to some extent but not cobalt and nickel within the range of pH examined. (D)Separation and Recovery of Cobalt and Nickel from Acidic Sulfate Solutions in the Presence of a Large Amount ofAluminum by the Synergistic Mixtures of LIX 63lHR. In order t o obtain more accurate information on the separation of cobalt and nickel from aluminum with such synergistic mixtures, a series of shake-out tests were carried out using a synthetic aqueous solution except for the test with the mixture of PIA-BfLIX 63, which was carried out using the actual sulfate leach liquor. The choices of composition of organic solvents and feed pH were based on the results obtained from the individual metal extraction tests. The data shown in Table 7 indicate that cobalt and nickel are extracted in preference to aluminum for all synergistic systems under the present experimental conditions. Table 8 illustrates that the complete removal of a small amount of aluminum coextracted with cobalt and nickel into the organic phase can be accomplished by contacting the loaded solvent with dilute sulfuric acid solutions. At the same time, about 10% of cobalt is scrubbed off whereas nickel is not scrubbed at all in this case. Cobalt and nickel in the scrubbed solvent are successfully stripped by moderate concentrations of sulfuric acid solutions. Table 9 indicates that more than 80% stripping of cobalt can be achieved by a single batch operation for all the synergistic systems under the selected conditions and strip solutions with a high proportion of cobalt to nickel are obtained, which enables recovery of pure cobalt and nickel separately with such synergistic mixtures by preferentially strip-
Zhang et al.
238 Energy & Fuels, Vol. 9, No. 2, 1995
Table 7. Extraction of Metal Ions with the Mixed Extractants from the Multicomponent Sulfate Solutionsa composition of feed (g/L) extracted (%) synergetic system PH [All [COI [Nil Al co Ni 0.85 92.75 62.90 1.118 0.221 10% CYANEX 272 30% L E 63 2.38 13.136 1.15 96.67 73.54 0.963 0.192 10% PIA-8 30% LM 63 2.40 11.117 0.221 3.40 94.90 79.64 1.78 13.136 1.118 10% PC-88A 30% L M 63 1.48 14.153 1.142 0.232 0.25 99.10 100.0 10%TR-83 + 30% L E 63 2.66 98.03 94.12 1.118 0.221 10% DzEHPA 30% L M 63 1.38 13.136 1.118 0.221 1.68 98.34 93.53 10% OPEHPA 30% L E 63 1.09 13.136
+
+
+ + +
The feed solution used in the extraction test with the 10% PIA-8130% L E 63 mixture was the raffinate obtained after completely recovering molybdenum and vanadium from the actual sulfate leach liquor of spent HDS catalysts as stated earlier.
Table 8. Scrub of Aluminum from the Loaded Solvent by HzS04 Solutions synergetic system 10% CYANEX 272 + 30% LIX 63 10% PIA-8 30% LIX 63 10% PC-88A 30% L E 63 10% DzEHPA + 30% LM 63 10% OPEHPA 30% L E 63
+
+
+
composition of loaded solvent (g/L) [All [COI [Nil 0.112 0.128 0.447 0.350 0.221
1.037 0.931 1.061 1.096 1.099
Table 9. Strip of Cobalt from the Scrubbed Solvent by HzS04 Solutionsa synergetic system
+
10% CYANEX 272 30% LM 63 10%PIA-8 30% LIX 63 10% PC-88A 30% LIX 63 10% TR-83 30% L E 63 10% DzEHPA 30% LM 63 10% OPEHPA 30% LM 63
+ + + + +
strip reagents (HzS04,M) 0.25 0.25 0.74 1.40 2.53 3.60
89.45 82.90 86.16 82.13 84.70 93.37
0.0 0.0 0.0 1.71 0.98 4.69
Table 10. Strip of Nickel from the Organic Phase Previously Stripped of Cobalt"
+ + +
strip reagents (HzS04,M) 1.03 1.04 3.54 4.45 4.59 4.74
0.038 0.035 0.125 0.375 0.503
stripped (Ni, 9%) 67.26 68.70 61.63 70.38 71.08 74.11
"The concentration of nickel in the organic phase was approximately 0.14-0.2 g L
ping of cobalt from nickel. Unlike cobalt, the nickel strip appears to be comparatively difficult and high concentrations of sulfuric acid have to be used to increase the strip ratio of nickel, with the exception of the mixtures consisting of LIX 63 and CYANEX 272 or PIA-8 for which only relatively low acidities were required for stripping nickel (Table 10). In addition, it can also be seen, by comparing Table 9 with Table 10, that the acidities necessary for stripping cobalt and nickel are obviously related to the pKa of the organophosphorus acids in the mixtures, namely, the lower the pKa, the higher the acidity necessary for stripping. (E)Degradation of LIX 63. As mentioned earlier, LM 63, an aliphatic hydroxyoxime, is expected to be gradually degraded and thus lose its extraction activity from attack by the coexisting acidic extractants in the solvent. Consequently, comparative tests were conducted to determine the stability of LM 63 in the mixed extractant systems that had been aged for a long time at
scrubbed (%) Al co 100.0 11.76 97.49 5.76 100.0 10.84 99.43 14.32 97.93 10.92
Ni 0.0 0.0 0.0 0.0 0.0
Table 11. Comparison of the Extraction of Co and Ni with Aged HWLM 63 Mixturesa distribution coefficients, D
stripped (%) Co Ni
The concentrations of cobalt and nickd in the scrubbed solvent were approximately: [Col = 0.8-1.0 giL, [Nil = 0.14-0.2 g/L, respectively.
synergetic system 10% CYANEX 272 + 30% L M 63 10% PIA-8 30% L E 63 10% PC-88A 30% L E 63 10% TR-83 30% L E 63 10% DzEHPA + 30% L E 63 10% OPEHPA + 30% L E 63
0.139 0.141 0.176 0.204 0.207
scrub reagent M)
co
Nib
mixture system
0'
6'
0"
6'
10%CYANEX 272/30% L E 63 10%PC-88A/30% L E 63 10% DzEHPA/30% L E 63 10% OPEHPN30% L E 63
11.8 23.6 110 207
12.3 23.0 78.0 99.5
1.5 3.7 64.0 70.0
1.5 3.5 49.0 41.0
a The composition of feed solution was (ppm) 12000 Al, 1105 Co, 214 Ni, and the values of pH were 2.2 for CYANEX 272/LE 63, 1.8 for PC-88ALM 63, 1.4 for D z E H P f i M 63, and 1.1for OPEHPALM 63. No obvious change for the distribution ratios of aluminum was observed after the mixtures were aged for 6 months and thus these are not listed in Table 11. Aged time in months. The 0 and 6 months represent that the mixtures were utilized at once and aged for 6 months, respectively, after they were prepared.
ambient temperature. The results, given in Table 11, indicated that extraction abilities for cobalt and nickel decreased to a greater or lesser extent with the mixtures comprising LIX 63 and the relatively strongly acidic extractants like D2EHPA or OPEHPA after the mixtures had been aged for 6 months, whereas no obvious change in distribution ratios of cobalt and nickel was observed with those mixtures consisting of LIX 63 and the relatively weakly acidic extractants such as CYANEX 272 and PC-88A, in particular the mixture of CYANEX 272LIX 63. Additional inspection of the color of the mixed solvents revealed that the samples containing D2EHPA or OPEHPA had gradually changed from light to heavy yellow with increasing aging time whilst those containing PC-88A and CYANEX 272 did not essentially change in color. Such results reflect that LIX 63 is degraded to varying degrees by the strongly acidic extractants while on the other hand, the degradation caused by the weakly acidic extractants seems to be negligible. The degradation of LIX 63 is considered to be via the nitrogen in LM 63 which forms an ammonium ion (NHd+) and the C=N group is transformed into a C=O group as in the HC1-DZEHPAEHO(2-ethylhexanal oxime) system as reported by Groves and Redden.26 3. Process Recommended. Based upon the investigations described here, an elemental schematic flowsheet for separation and recovery of metallic values such
-
Energy & Fuels, Vol. 9,No. 2, 1995 239
Recovery of Metal Values from Spent HDS Catalysts
LEACH LIQUOR
CYANEX 272 or PIA-8
f
Raffinate AI, Co. Ni
LIX 6UCYANEX 272 or PIA-8
NaOH
4
s strip of
v
LTl
I
Adjustment of pH to 2.4
I
Raf -
t H2s049-l
I
c o product
Aq.sol n. (Fe)
Mo product
i
v product
Nt product
Figure 16. Flow sheet for recovery of metallic values from the sulfate leach liquor of spent HDS catalyst by solvent extraction.
as molybdenum, vanadium, cobalt, and nickel from the sulfate leach liquor of spent HDS catalysts by liquidliquid extraction techniques is suggested as shown in Figure 15.
IV. Conclusions A n effort has been made to develop a recovery process for molybdenum, vanadium, cobalt, and nickel from the acidic sulfate leaching liquor of spent HDS catalysts by means of liquid-liquid extraction. The extraction process presented is composed of the recovery of molybdenum and vanadium by employing CYANEX 272 or PIA-8 as the extractant, and that of cobalt and nickel by a mixture of L E 63 in combination with CYANEX 272 or PIA-8. The attractive features of the process mainly lie in the following: 1. The selected extractants CYANEX 272 or PIA-8 exhibit an excellent selectivity for molybdenum and vanadium over aluminum, cobalt, and nickel at relatively low pH and provide high recovery yields for both molybdenum and vanadium. (26) Groves, R. D.; Redden, L. D. Hydrometallurgy 1990,24, 271290.
2. Although the mixtures consisting of L E 63 and CYANEX 272 or PIA-8 produce the weakest synergistic effect for cobalt and nickel among all the mixtures studied in the present work, both of these systems exhibit excellent selectivity for cobalt and nickel over aluminum at appropriately low pH. The acidities necessary for stripping cobalt and nickel from these loaded mixed solvents are relatively mild and, also, no marked degradation of LIX 63 is observed. Therefore, from the viewpoint of industrial application, the mixtures of L E 63 and CYANEX 272 or PIA-8 are considered to be the most suitable for separating and recovering cobalt and nickel from the sulfuric acid solutions in the presence of an appreciable amount of aluminum a t low pH, for example, from the acidic sulfate leach liquor of spent hydrodesulfurization catalyst.
Acknowledgment. This work was financially supported in part by a Grant-in-Aid for Scientific Research No. 06271251 from the Ministry of Education, Science and Culture of Japan. Thanks are due to the Industrial Technology Center of Saga for providing ICP analysis equipment. EF9401637
