Ind. Eng. Chem. Res. 1992,31,328-333
328
Computer Simulation of Copper Extraction-Stripping Systems Containing Different Hydroxy Oxime Extractants in Various Extraction-Stripping Loops Mariusz B. Bogacki and Jan Szymanowski* Pozmri Technical University, P1.Sklodowskiej-Curie2, 60-965 Pozmri,Poland
Extraction of copper in atypical extraction-stripping systems containing 2-hydroxy-5-nonylbenzaldehyde oxime and 2-hydroxy-5-nonylbenzophenone oxime in various extraction-stripping loops with cross-current and combined flows is discussed. The combined system containing two different loops with two extractants of various extraction strength can give better extraction results than the typical countercurrent extraction-stripping system containing only one extractant. However, appropriate sequence of extractants and appropriate extraction conditions must be applied. Hydroxy oximes are well-established extractanta for copper from acidic sulfate solutions, and they are used in several industrial installations. The extraction and stripping are carried out in mixemettlers using countercurrent flows. Two to three stages of extraction are used in a typical flow sheet to separate copper(II) from other metals, especially iron. Then, in the stripping loop of two to three mixeraettlers, copper is transferred back from the organic phase to the aqueous one and ita appropriate purity and concentration for electrowinning are obtained. As was discussed by Rod (1984)and Hughes and Parker (1985,19871,other atypical schemes of extraction-stripping flows can also be used in multistage processes. Bogacki and Szymanowski (1990,1991)demonstrated advantages of such atypical schemes for copper extraction from acidic sulfate solutions with both strong and weak extractanta, Le., 2-hydroxy-5-nonylbenzaldehydeoxime and 2hydroxy-5-nonylbenzophenoneoxime, respectively. Significantly higher extraction percentages were obtained, especially when the cross-current flows were used, Le., when extraction was followed by stripping after every extraction step. This can be explained by the reversibility of copper extraction.
+
C U ' + ~ ~2HL, = CuLzo + 2H+,,
(1)
The acidity of the aqueous phase and the copper concentration in the organic phase increase during the course of extraction, and the extraction falls off in each next step. As a result, the greatest amount of copper is extracted in the first step. The extraction can be enhanced when the stripping is carried out after each extraction step or at least after the first two steps. Thus,such atypical schemes with cross-current solvent flows seem to be very advantageous for systems with acidic and acidic-chelating extractanta in which the aqueous phase becomes more acidic during the course of extraction and, by contrast, the acid is consumed during the stripping. During the past 10 years several new extractants of LIX type were proposed. They are blends of two or three various hydroxy oximes exhibiting different strengths of copper extraction. The addition of a weaker extractant to the stronger one, i.e., 2-hydroxy-5-nonylbenzophenone oxime to 2-hydroxy-5-dodecylbenzaldehyde(LIX 865 or LIX 864 as it contains L M 65N or LIX 64N,respectively) and 2-hydroxy-5-nonylacetophenoneoxime (LIX 84) to 2-hydroxy-5-dodecylbenzaldehyde oxime (LIX 984,acta
* Author to whom correspondence should be addressed.
in the same way as alkylphenol or alcohol additives present in ACORGA reagents. However, in this case both hydroxy oximes are chemically active and they extract copper. As a result, higher transfers of copper are obtained in extraction-stripping processes. The atypical extraction-stripping schemes give the possibility of using two various extractants in separate extraction-stripping loops. Thus, the aim of this work, which is a continuation of our previous papers (Bogacki and Szymanowski,1990,1991),is to diecues such a problem using 2-hydroxy-5-nonylbenzaldehydeoxime and 2hydroxy-5-nonylbenzophenoneoxime, considered as the strong and weak extractants, respectively, in various extraction-stripping loops.
Extractants and Equilibrium Data Pure fractions of 2-hydroxy-5-nonylbenzaldehydeoxime (I) and 2-hydroxy-5-nonylbenzophenone oxime (11)were used. Extractant syntheses were described previously (Szymanowski and Jeszka, 1985). The ratio of E to 2 isomers in 2-hydroxy-5-nonylbemphenoneoxime was 5.9; in 2-hydroxy-5-nonylbenzaldehydeoxime, 2 isomer was not found. The equilibrium extraction data for copper extraction from acidic sulfate solutions at 18-20 "C were described previously (Szymanowski and Jeszka, 1985;Piotrowicz et al., 1989)and used to discuss the extraction of copper in different extraction-stripping flow sheets in which only one extractant was used (Bogacki and Szymanowski, 1990, 1991). Extraction data were obtained for different hydroxy oxime concentrations and various initial concentrations of sulfuric acid in an aqueous phase. The oxime concentrations were equal to 5,11.3,15,and 20%) while the amount of sulfuric acid added to the aqueous phase varied from 0 to 25 g dm3.The equilibrium copper concentrations in g d~n-~ The . ionic the aqueous phase varied from 0 to strength of the aqueous phase was not adjusted. Escaid 100, ESSO,was used as a diluent. It contains 56.5% aliphatic hydrocarbons, 23.4% alicyclic hydrocarbons, and 20% aromatics. Computing Method The scheme of the considered extraction-stripping processes containing two various extractants in separate extraction-stripping loops is given in Figure 1. Seven various systems with two to three extraction stages and two to three stripping stages were considered (Table I). The only system which has typical cross-current solvent flows with the same number of extraction and stripping
08aa-5aa5/92j2631-032a$o3.00/0 0 1992 American Chemical Society
Ind. Eng. Chem. Res., Vol. 31, No. 1, 1992 329 Table I. Analyzed Extraction-Stripping Systems" type of no. of stages extr-strip. strip. system extr n k 1 m system 1 2 2 1 1 2 2 3 1 2 3 2 3 1 1 4 3 2 1 1 5 3 2 2 1 6 3 3 2 1 7 3 3 1 2
F'
F
P
I
I
I
n+k
"Symbols used are the same as in Figure 1. Table 11. Initial Data for Considered Extraction-Stripping Svstems' ratios of flow of aq phase to org phase -%,O? e dm-3 extraction. FIS StriDuine, F'IS' 1.0,1.5, 2.0 2.0,1.0,0.5,0.4,0.25,0.2,0.125,0.1 5.0 10.0 1.0,1.5, 2.0 2.0,1.0,0.5,0.4,0.25,0.2,0.125,0.1 1.0,1.5, 2.0 2.0,1.0,0.5,0.4,0.25,0.2,0.125,0.1 15.0
I l l
I n+m+' I
I n l
I
~
~~
= 1.0 g dm-3. a Initial copper concentration in stripping: Initial sulfuric acid concentration in extraction: XH,O = 5.0 g dm". Initial sulfuric acid concentration in stripping: option a, zH*+~ = 150.0 g dm-3; option b, x H * + ~ = 250.0 g dm".
steps is system no. 1. It consists of two independent extraction-stripping loops (one extraction and one stripping step) containing two various extractants. All other systems can be classified as systems with combined solvent flows having different distribution of three extraction and/or three stripping stages. These systems can be classified further taking into account the sequence of hydroxy oximes used in separate extractionatripping loops. A denotes that the strong extractant (2-hydroxy-5-dkylbenzaldehyde oxime) is used in the first loop and the weak extractant (2-hydroxy-5alkylbenzophenone oxime) in the second one while B is attributed to the opposite sequence of extractants. The meaning of n, k, 2, and m is presented in Figure 1. The initial data (Table 11)are as in our previous works (Bogacki and Szymanowski,1990,1991)with the exception of initial concentration of sulfuric acid used for stripping. Taking into account that two extractants of significantly different extraction ability are used, two initial concentrations of sulfuric acid are considered: 250 g dm-3, the same as in the work concerning oxime I (Bogacki and Szymanowski, 1990) (subtype a), and 150 g dms, the same as in the work concerning oxime I1 (Bogacki and Szymanowski, 1991) (subtype b). In this way 28 various options of the process are considered. The symbol 4Ab denotes that scheme 4 is taken under consideration. It consists of three extraction and two stripping steps: one extraction step and one stripping step in the first loop containing oxime I and two extraction steps and one stripping step in the second loop containing oxime 11. The initial concentration of sulfuric acid used for stripping is 150 g dm-3. The computing method was described previously (Bogacki et d.,1989;Bogacki and Szymanowski, 1990,1991). The mathematical model for metal extraction was presented by Rod (1984). It is assumed that extraction and stripping are quickly achieved and theoretical stages are considered. The simplified form of the model for the unsteady state was used in which the concentrations do not depend on the volumes of both phases in the stage considered. The extraction equilibrium is described by the smoothing spline functions using the boundary conditions
F Figure 1. Extraction-atripping flow sheets.
I
nr'
F'
described previously (Bogacki and Szymanowski, 1990). The Adams-Moulton method (Bogacki et al., 1989) was used for computing.
Results and Discussion System Dynamics. The dynamics of the extractionstripping systems containing only one extractant was presented in previous papers (Bogacki and Szymanowski, 1990,1991). The systems now discussed show dynamic characteristic similar to systems previously considered. The attainment time of steady state is similar to that determined previously and is equal to l e 1 2 units. During this time, constant values of copper concentrations are achieved, in both the organic and aqueous phases. The changes in the mass balance calculated as the difference between outlet and inlet values for each stage or for the whole system converge quickly to zero. The maximal error of the total balance of the extractionatripping system doea not exceed 5 X lo-" g dm-3. Hence, solution driftii is not observed. Effect of Extractant Sequence. Figures 2 and 3 demonstrate the percentage of copper extracted from the aqueous phase in the selected systems with two extraction and two stripping stages for various initial copper concentrations, while Tables I11 and IV present the observed results for various systems considered for the same starting ~ g dm-3, F / S = 1.5, F'/S' = 0.2). conditions ( x ~ =, 10 The obtained results show an important effect of the hydroxy oxime sequence in extraction systems. Generally, much better results are obtained when the weak extractant I1 is used in the first loop and the strong extractant I in the second loop. In the first loop the sulfuric acid concentration in the aqueous phase is low and copper can be
3
1
I
@%
a-4
2 4 6 b e'4p Figure 2. Percentage of copper extracted in extraction-stripping systems with two extraction and two stripping stages: x ~ , , + ~= 150.0 g dm-3 (1,2, and 3 correspond to F / S = 1.0,1.5, and 2.0, respectively; top and bottom row8 correspond to extraction-stripping systems of type A and B, respectively).
2
4
t
a
4
Table 111. Comparison of Various Extraction-Stripping Systems for F / S = 1.5, F'/S' = 0.2, X M , =~ 10 g dm-*,XM,,,+, 1.0 g dm-s, x ~= 150 . ~g dm-3
1 2
3 4 5 6 7 1
2 3 4 5 6 7
5.7932 5.7149 5.5237 5.5781 5.7451 5.4471 5.4760
Type A 32.5513 33.1381 34.5724 34.1641 32.9128 35.1468 34.9299
11.4931 11.6138 11.9090 11.8250 11.5672 12.0272 11.9826
101.3021 100.3964 98.1827 98.8129 100.7457 97.2961 97.6309
4.8308 4.2849 4.6938 4.6967 4.6009 4.4333 4.0310
Type B 39.7689 43.8630 40.7963 40.7748 41.4933 42.7499 45.7672
12.9784 13.8209 13.1898 13.1854 13.3333 13.5919 14.2128
90.1622 83.8432 88.5764 88.6096 87.5006 85.5611 80.9041
extracted with the weak extractant. In the second loop the aqueous phase contains additional sulfuric acid formed in the first loop according to reaction 1. Thus, due to the reversibility of this reaction the use of a stronger extrantant must give a positive effect and higher extraction is obtained in comparison both to the opposite system containing a strong extractant in the fmt loop and a weak extractant in the second loop and the countercurrent system containing only a weak extractant. A similar effect can be obtained as the aqueous phase is neutralized after each extraction stage. However, the use of two various extractants seems to be more advantageous
6
4
Table IV. Comparison of Various Extraction-Stripping Systems for F / S 1.5, FYS' = 0.2, x M , ~ = 10 g dm-3, x ~ , ~=+ , 1.0 g dm-s, x A = 250 g dm-3 xM,n,
xH.n,
XH,n+k?
g dm-3
g dm-3
5.0084 4.9817 4.5470 4.7793 4.9249 4.4230 4.7433
12.7043 12.7454 13.4164 13.0579 12.8331 13.6078 13.1135
192.2186 191.9093 189.8771 189.5655 191.2515 185.4420 189.1491
3.9175 2.9691 3.8593 3.6429 3.6356 3.5579 2.6987
Type B 46.6186 53.7317 47.0554 48.6785 48.7331 49.3156 55.7599
14.3880 15.8518 14.4779 14.8119 14.8231 41.9430 16.2692
179.5900 168.6113 178.9159 176.4107 176.3264 175.4274 165.4809
g dm-3
1 2
3 4
5 6 7 1 2
3 4 5 6 7
xM,n+k,
g dm-3 Type A 38.4372 38.6369 41.8973 40.1555 39.0631 42.8271 40.4253
system
than additional neutralization, from both the economical and technological points of view. The difference in the percentage of extraction depends upon other extraction conditions and it can even achieve 15% (in absolute value). The same concerns the concentration of copper in the outlet aqueous stream. Due to the different extraction strengths of the considered extractants, their sequence in the extraction-stripping scheme affects significantly the extraction of copper. It is obvious that after extraction the concentration of copper in the organic phase containing extractant II is significantly lower when this weak extractant is present in the second
Ind. Eng. Chem. Res., Vol. 31, No. 1,1992 331
1
4
2 3
2
Figure 3. Percentage of copper extracted in extractionatripping systems with two extraction and two stripping stages: xHJI+l= 250.0 g dm-3 (1,2,and 3 correspond to F / S = 1.0,1.5,and 2.0,respectively; top and bottom row8 correspond to extractionatripping systems of type A and B, respectively).
loop. Much better extraction results are obtained as this weak extractant I1 is present in the first loop. Effect of Sulfuric Acid Concentration. The effect of sulfuric acid concentration is very important. The high percentage of copper extraction and the low copper concentration in the aqueous phase on the outlet are obtained when the high concentration of sulfuric acid is used for stripping. Due to the reaction reversibility the organic phase after stripping contains lower amounts of copper if more concentrated sulfuric solution is used for stripping, and it can extract copper more efficientlyfrom the aqueous stream. The amount of sulfuric acid present in the aqueous phase significantly decreases during the stripping, especially when a large excess of the organic phase, which is typical for stripping, is used. As a result, the percentage of copper extraction in the whole system significantly decreases when the flow ratio of the organic and aqueous phases used for stripping increases. In this case the effect is weaker than in systems containing only the strong extractant I but stronger than in systems containing the weak extractant 11. All this demonstrates that Ba systems are more advantageous than systems Ab. However, it is necessary to take into account that the increase of sulfuric acid concentration can be limited because of the technological problems connected with electrowinning and copper production of appropriate purity. Results given in Table IV confirm it, showing that the outlet sulfuric acid concentration decreases only to 165-170 g dm-3 when its initial concentration is 250 g dm-3. Effect of Other Parameters. The comparison of the considered systems containingtwo various extractants with
Table V. Comparison of Extraction-Stripping Systems Containing Extraction (E) and Two Stripping (S) Stages (xrc = 150 g dmJ. F / S = 1.0, and F f / S f= 0.2) copper extracted, 0'9 system xwn,gdm-3 A B ~~
-ffagTR
5 15
83.39 86.00 44.72 58.45
+ a T m
5 15
85.31 46.81
81.44 56.90
those typical countercurrent systems containing only extractant I or 11may give different results depending upon other extraction parameters. Systems B are always better than countercurrent processes with the use of oxime 11. However, they are better than countercurrent processes containing extractant I only for subtypes a when the flow ratio of the organic phase to the aqueous one in the stripping is above 5; the countercurrent process gives higher extraction of copper for S'IF' < 4. Systems A are better than the countercurrent processes using oxime I1 when S'IF'C 2 but worse when S i / F i > 2. The distribution of extraction and/or stripping steps between the first and the second loop has relatively small
332 Ind. Eng. Chem. Res., Vol. 31, No. 1, 1992
t
Figum 4. McCabe-Thiele diagram. System type 5Ab. (1,2-hydroxy-5-nonylbeddehyde oxime; 11,2-hydroxy-5-nonylbenzophenone oxime; a, extraction; b, stripping; LO, operating line; s, stripping, e, extraction, 1, first loop; 2, second loop.)
Figure 5. McCabe-Thiele diagram. System type 5Bb. (I, 2-hydroxy-5-nonylbeddehyde oxime; 11,2-hydroxy-5-nonylbenzophenone oxime; a, extraction;b, stripping; LO, operating line; 8 , stripping, e, extraction; 1, first loop; 2, second loop.)
effects, especially in comparison to those observed in systems containing single extractants (Bogacki and Szymanowski, 1990, 1991). When the total number of extraction and stripping stages increases from four to six,extraction of copper increases relatively weakly but not in each case. For six stages the effect of their distribution is negligible. For system with the total number of stages equal to five, two options with three extraction stages and two stripping stages or two extraction stages and three stripping stages are possible. In the first case two extraction stages should be in the loop containing the weak extractant 11, while in the second case two stripping stages should be in the loop containing the strong extractant I. These small effects of the number of extraction and stripping stages upon the copper extraction in systems now
considered are clearly demonstrated in exemplary Figures 4 and 5. They demonstrate the very small transfer of copper in the first stage of extraction and stripping, respectively. The effectivenessof these stage is specially low for systems A having two extraction stages in the loop containing the strong extractant I or two stripping stages in the loop containing the weak extractant 11. This means that the effect of the change of extraction-tripping system from the typical countercurrent system to the combined one containingtwo different loops with various extractants is more signifcant than the increase of the stage numbers. Conclusions The combined system containing two different loops with two extractants of various extraction strengths can give better extraction results than the typical counter-
Znd. Eng. Chem. Res. 1992,31,333-339 current extraction-stripping system containing only one extractant. However, appropriate sequence of extractants and appropriate extraction conditions must be applied. Better results are obtained if the strong extractant is in the second loop and the weak one is in the first loop (Table V). The use of one extraction stage and one stripping stage in each loop is sufficient. In the case of more stages used two extraction stages should be in the loop containing the weak extractant or two stripping stages in the loop containing the strong extractant. The increase of sulfuric acid concentration used for stripping yields the increase of the total transfer of copper. The excessive sulfuric acid concentration can be compensated for by the use of appropriate excess of the organic phase in the stripping. Acknowledgment The work was supported by Grant DNS-T/09/144/90-2. Nomenclature F = flow rate of the aqueous phase (extraction) F’ = flow rate of the aqueous phase (stripping) k = total number of stripping stages 1 = number of extraction stages in the first processing loop m = number of stripping stag- in the second processing loop n = total number of extraction stages o = organic phase (subscript) S = flow rate of the organic phase (extraction) S’ = flow rate of the organic phase (stripping) x H , ~= feed sulfuric acid concentration x H , ~ +=~equilibrium sulfuric acid concetration x ~= feed , ~ copper concentration in the aqueous phase
333
x ~ , = ~ equilibrium + ~
copper concentration in the aqueous phase Registry No. I, 50849-47-3; 11, 37339-32-5; Cu, 7440-50-8.
Literature Cited Bogacki, M. B.; Szymanowski,J. Modeling of Extraction Equilibrium and Computer Simulation of Extraction Stripping Systems for Copper Extraction by 2-Hydroxy-5-nonylbenzaldehydeOxime. Znd. Eng. Chem. Res. 1990,29,601+06. Bogacki, M. B.; Szymanowski, J. Computer Simulation of Copper Multistage Extraction-Stripping System with 2-Hydroxy-5nonylbenzophenone Oxime. Inz. Chem. Proc. 1991, in press. Bogacki, M. B.; Alejski, K.; Szymanowski, J. The Fast Method of the Solution of a Reacting Distillation Problem. J. Comput. Chem. Eng. 1989,13, 1081-1085. Hughes, M. A.; Parker, N. A. Computer Study of Liquid-Liquid Stage-Wise Calculation in Typical and New Counter Current Contacting. J. Chem. Technol. Biotechnol. 1985, S a , 255-262. Hughes, M. A.; Parker, N. A Practical Proof of New Contacting Schemes for Copper Extraction. In Separation Processes in Hydrometallurgy; Davies, G. A., Ed.; Wiley: London, 1987; Part 2, Chapter 16. Piotrowicz, J.; Bogacki, M. B.; Wasylkiewicz, S.; Szymanowski, J. Chemical Model for Copper Extraction from Acidic Sulfate Solutions by Hydroxy Oximes. Ind. Eng. Chem. Res. 1989, 28, 284-288. Rod, V. Unconventional Extraction-stripping Flows Sheeta for the Separation of Metal by Liquid-Liquid-Extiaction. Chem. Eng. J. 1984,29. 77-83. Szymanowski, J.; Jeszka, P. Modeling of Simple Multistage and Counter Current Multistage Copper Extraction by Hydroxyoximes. Znd. Eng. Chem. Process Des. Dev. 1985,24, 244-250.
Received for review March 8, 1991 Revised manuscript received September 3, 1991 Accepted September 19,1991
Supercritical Extraction of Hexachlorobenzene from Soil Aydin Akgerman,* Can Erkey, a n d Seyyed M.Ghoreishi Chemical Engineering Department, Texas A&M University, College Station, Texas 77843
Feasibility of supercritical extraction of hexachlorobenzene from soil by COz is investigated. A dynamic tracer response technique is employed to measure the adsorption equilibrium and rate at the temperature range 298-323 K and pressure range 1200-4000 psia at C02flow rates of 120-160 mL/ h. Thermodynamic consistency of the adsorption equilibrium constants is verified through isochoric temperature dependency and isothermal density dependency of the equilibrium constants. Overall mass transfer coefficients and axial dispersion coefficients are also determined at the experimental conditions. Introduction Supercritical extraction has been demonstrated in the literature at the bench scale for extraction of organic contaminants from a variety of solid matrices. Capriel et al. (1986) used supercritical methanol to extract bound pesticide residues from soil and plant residues. Hawthrone and Miller (1986) extracted polycyclic aromatic hydrocarbons (PAH) from diesel soot and Tenax packing for gas chromatographic columns by supercriticalcarbon dioxide. Schantz and Cheder (1986), similarly, used supercritical COP to extract polychlorinated biphenyls (PCB) from sediment and PAHs from urban particulate matter. Methanol/N20 mixtures are also used to extract PAHs from river sediments and urban particulate matter (Hawthrone and Miller, 1987). Supercritical COPis used to remove hexachlorocyclohexane, parathion, PCBs, and
* Author to whom correspondence should be addressed.
PAHs from Tenax packing (Raymer and Pellizari, 1987) and polyimide-based adsorbents (Raymer et al., 1987). SupercriticalCOPis also the solvent of choice for extraction of PAHs from various adsorbents selectively by varying the operating conditions (Wright et al., 1987a,b). The results of these studies have demonstrated at the bench scale that it is possible to extract compounds with molecular weight as high as 400 at mild conditions and selectively if desired. This conclusion constitutesthe basis of supercritical chromatography. Recently we have reported on the application of chromatography theory to supercritical extraction from solid matrices (Erkey and Akgerman, 1990). Concerning environmental applications, Kingsley (1985) applied subcritical and supercritical COPfor extraction of oil from metal fiies (mill scale) and bleaching clay in the pilot scale. The process operated on a semibatch mode, and the results indicated that the recovery of extractable material depended on the solvent flow rate. It was also
0888-5885/92/2631-0333$03.00/00 1992 American Chemical Society
