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Removal of Zinc(II) from Spent Hydrochloric Acid Solutions from Zinc Hot Galvanizing Plants Ryszard Cierpiszewski,† Ireneusz Miesia¸ c,‡ Magdalena Regel-Rosocka,‡ Ana M. Sastre,§ and Jan Szymanowski*,‡ Faculty of Commodity Science, Poznan University of Economics, Poznan, Poland, Institute of Chemical Technology and Engineering, Poznan University of Technology, Pl. Sklodowskiej-Curie 2, 60-965 Poznan, Poland, and Departament d'Enginyeria Quimica, Universitat Politecnica de Catalunya ETSEIB, E-08028 Barcelona, Spain
The extraction of zinc(II) from spent pickling hydrochloric acid solutions obtained in zinc hotdip galvanizing plants was studied. Tributyl phosphate and its mixtures with di(2-ethylhexyl)phosphoric acid (DEHPA), HOE F 2562, ALIQUAT 336, ALAMINE 304, ALAMINE 308, ALAMINE 310, ALAMINE 336, and CYANEX 301 were used as extractants. The acidic extractants (CYANEX 301 and DEHPA) did not extract both zinc(II) and iron(III) from 10% HCl. Precipitation occurred or stable emulsions were formed when ALAMINE 304, ALAMINE 308, and ALAMINE 310 were used. Each of the other reagents coextracted both zinc(II) and iron(III). The latter had to be reduced to iron(II) prior to extraction. Tributyl phosphate and HOE F 2562 showed the best extraction performance. ALAMINE 336 and ALIQUAT 336 induced the oxidation of iron(II) to iron(III), thus enhancing the coextraction of iron. Zinc(II) could be effectively stripped from the loaded phases containing TBP and HOE F 2562 with water. A higher efficiency of stripping was observed in the second stage. Introduction Zinc layers are commonly used today to protect steel goods from corrosion. Zinc layers are deposited by immersing steel goods in molten zinc at about 450 °C. High-quality zinc layers require appropriate pretreatment of the surface to be coated, including washing, degreasing, rust removal, and fluxing. Hydrochloric acid solution (20%) is usually used for pickling carried out at room temperature. Hydrochloric acid is consumed during the process, but the concentration of chloride ions does not change. As a result, dissolved zinc and iron, present mainly in the form of iron(II), form appropriate chlorocomplexes. Zinc also accumulates in the pickling solution. In the batch process, steel goods are hung on hooks onto which zinc is also deposited. The hooks are used again, and the zinc dissolves in the hydrochloric acid. Such a solution contains only a few grams of Zn(II) per liter or even less. The spent pickling solution is processed by the Ruthner process in which the hydrochloric acid is evaporated and granules of iron oxide are formed in a fluidized bed at temperatures above 600 °C. The presence of zinc(II) in amounts higher than 0.5 g/L disturbs the process. Therefore, the spent pickling solution is often neutralized with lime and released to the environment together with the toxic zinc ions. Spent pickling solutions are also used to deplete zinc layers of insufficient quality. In such cases, the concentration of zinc(II) in the spent solution increase to a few tens of grams per liter. * Author to whom correspondence should be addressed. Fax: +48 61 665 36 49. E-mail: jan.szymanowski@ put.poznan.pl. † Poznan University of Economics. ‡ Poznan University of Technology. § Universitat Politecnica de Catalunya ETSEIB.
Solvent extraction1-7 and ion exchange7,8 can be used to remove the toxic zinc(II) from spent pickling solutions. The MeS process7 was developed by MX-Processer AB in Sweden for the recovery of zinc from spent hydrochloric acid pickling liquors, but it is not used. The use of various extractants has also been proposed, but detailed studies on their efficacies have not been published. The aim of this work was to screen various reagents and to perform more detailed studies with selected extractants. Taking into account the high concentrations of both protons and chloride ions, the studies were narrowed to selected solvating (tributyl phosphate) and basic (tri- and dialkilamines and quaternary ammonium salts) extractants. The possibility of using selected acidic extractants (DEHPA and CYANEX 301) was also investigated. The selection of reagents was constrained to include only industrial extractants that could be used in practice. Experimental Section Tributyl phosphate (TBP), various trialkylamines, trialkylmethylammonium chloride, CYANEX 301, and di(2-ethylhexyl)phosphoric acid (DEHPA) were used as extractants (Table 1). Only TBP, DEHPA, and triisooctylamine were pure reagents. The other extractants investigated were commercial reagents and were used as delivered. Only such a reagent could be used in industry. Decanol was used as a modifier, and the lowaromatic kerosene Exxsol D220/230 (Deutsche Exxon Chemical GmbH, ESSO A.G., Hamburg, Germany) as a diluent. The extraction was carried out in separatory funnels using the same volumes (10 mL) of the two phases, and the solution was allowed to stand for phase separation (usually a few minutes). The phases were mechanically shaken for 15 min. Demineralized water from reverse osmosis (10 mL) was used for stripping, which was repeated three times using fresh water samples.
10.1021/ie0103207 CCC: $22.00 © 2002 American Chemical Society Published on Web 01/10/2002
Ind. Eng. Chem. Res., Vol. 41, No. 3, 2002 599 Table 1. Extractants Used for Zinc(II) Recovery extractant
active substance
producer
purity
TBP DEHPA HOE F 2562 CYANEX 301 ALAMINE 304 ALAMINE 308 ALAMINE 310 ALAMINE 336 ALIQUAT 336 TIOA
tributyl phosphate di(2-ethylhexyl)phosphoric acid diisotridecylamine di(2,4,4-trimethylpentyl)dithiophosphinic acid tridodecylamine triisooctylamine triisododecylamine trialkylamine, C8/C10 ) 2:1 trialkylmethylammonium chloride, C8/C10 ) 2:1 triisooctylamine
Hoechst, Germany Fluka, Germany Hoechst, Germany American Cyanamid Company, U.S. Cognis, Germany Cognis, Germany Cognis, Germany Cognis, Germany Cognis, Germany Windsor Laboratories Limited, U.K.
pure pure technical technical technical technical technical technical technical pure
Table 2. Screening of the Abilities of Various Reagents for the Extraction of Zinc(II) and Iron(III) from 10% HCl feeda
metal extracted (%)
reagent
Zn(II) (g/L)
Fe(III) (g/L)
Cl- (M)
Zn(II)
Fe(III)
TBP 1:1 (v/v) TBP/DEHPA 2:1 (v/v) TBP/DEHPA 3:1 (v/v) TBP/DEHPA HOE F 2562 ALAMINE 304
0.485 0.485 0.485 0.485 0.495 0.495
35.52 35.52 35.52 35.52 35.04 35.04
5.37 5.37 5.37 5.37 5.29 5.29
63.0 33.5 33.8 44.3 68.1 -
60.9 4.3 5.1 5.6 34.2 -
ALAMINE 308
0.496
35.04
5.29
-
-
ALAMINE 310
0.496
34.86
5.31
-
-
ALAMINE 336 ALIQUAT 336
0.496 0.496
34.86 34.86
5.31 5.31
72.2 67.3
61.1 65.4
remarks
strong emulsion in stripping brown precipitate in extraction brown precipitate in extraction hazy phases, emulsions
a
Columns 2-4 give the composition of aqueous feed in 10% HCl. The organic phase contains 30% reagent, 15% decanol, and 55% kerosene. Decanol and kerosene were not used for TBP and its mixtures.
The concentrations of the metal ions were always determined in the aqueous phase before and after extraction and after stripping. Different analytical techniques were used. High concentrations of iron(III) and zinc(II) present alone in the aqueous solution were determined by titration with EDTA. When zinc(II) was present together with iron(II) and/or iron(III), the content of zinc(II) and the total concentration of iron ions were determined by atomic absorption spectroscopy using a SPECTR AA800 instrument made by Varian. The measurements were carried out at 213.4 and 248.3 nm for zinc(II) and iron ions, respectively. Potentiometric titration was also used to determine the content of zinc(II) in the presence of iron(II) and iron(III), as well as the content of iron(III) in the aqueous phase after extraction and stripping. A Titrino 702 SM titrator (Metrohm, Switzerland) was used. An ion-selective Cu electrode with a Ag/AgCl/KNO3 reference electrode was used to determine the content of zinc in the presence of iron ions.9 For such determinations, a 0.5-2-mL sample [0.5-20 mg Zn(II)] was treated with 0.5 mL of H2O2 for 3 min when the sample contained iron(II) and then with 3 mL of NH3 solution (pH above 10.7) to precipitate iron(III); the solution was then stored for 3 min until the gas bubbles disappeared. Then, 5 mL of water was added, and HCl solution was added dropwise to achieve a pH of 10 ( 0.1. The solution was diluted with water to 20 mL and stored for 5 min for sedimentation. Exactly 10 mL of separated supernatant was placed in a 30-mL vessel with a magnetic stirrer, 1 mL of CuEDTA was added, and the mixture was titrated with 0.05 M EDTA. An equivalence point was obtained in the potential range 170-230 mV. A Pt massive electrode with a Ag/AgCl/KNO3 reference electrode was used to determine the content of iron(III). Ten milliliters of 20% HCl was added to an acidic
sample (0.1-20 mg of Fe). Then, 1 mL of tin solution (5% in 3% HCl) was introduced in excess into a 30-mL vessel with a magnetic stirrer to reduce iron(III) to iron(II), and the mixture was titrated with 0.1 M K2Cr2O7. Two equivalence points at 210 mV for Sn(II) and at 620 mV for Fe(II) were obtained.10,11 The relative errors of the analytical methods were as follows: titration with EDTA, ∼1%; AAS analysis of zinc(II) and total iron, less than 3%, potentiometric titration, ∼1%. The concentration of chloride ions was determined using the Volhard method.11,12 The analytical error was less than 1%. The concentrations of hydrochloric acid were determined by titration with 0.1 M NaOH in the presence of methyl orange. Results and Discussion Table 2 shows the results of the screening tests for aqueous feed containing Zn(II) and Fe(III) simultaneously. The tests showed that some reagents, such as ALAMINE 304, ALAMINE 308, and ALAMINE 310, were not useful because precipitation occurred or strong emulsions were formed. This was also true for ALIQUAT 336, although high extractions of both Zn(II) and Fe(II) were observed. TBP and ALAMINE 336 extracted iron(III) very strongly [over 60% of the Fe(III) was extracted]. As a result, zinc(II), although present in small quantities (0.5 g/L), was not completely removed from the aqueous feed. Dialkylamine (HOE F 2562) extracted less iron(III) than trialkylamine and tributyl phosphate. The acidic extractants (CYANEX 301 and DEHPA) did not extract both zinc(II) and iron(III) simultaneously from 10% HCl. This failure was caused by the high concentration of chloride ions and the high acidity of the aqueous phase. However, the presence of the acidic extractant affected
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organic phase at appropriately high concentrations of H+ and Cl-, i.e., 1-2 M HCl14
B‚HClo + H+w + Cl-w ) BHCl‚HClo
(4)
Each of these four reactions was shifted to the right by an increase of the aqueous-phase acidity and chloride concentration. When at least one of these concentrations decreased, then other reactions became more important, namely and
Figure 1. Isotherms of iron(III) extraction from 10% HCl with (b) undiluted TBP, (O) 1.44 M triisooctylamine, (2) 1.44 M HOE F 2562, and (9) 1.44 M TBP in kerosene.
the selectivity of zinc(II) extraction with TBP. The best rejection of iron(III) was observed when mixtures of TBP and di(2-ethylhexyl)phosphoric acid (DEHPA) were used. Only a few percent of iron(III) was extracted in this case. However, the extraction of zinc was also suppressed and amounted to only 33-44%. The mixture containing TBP and DEHPA in a 3:1 ratio (wt/wt) seemed the most advantageous. High extraction of iron(III) with the considered reagents was also demonstrated in the extraction isotherms (Figure 1) presented for undiluted TBP and 1.44 M solutions of triisooctylamine (TIOA), TBP, and HOE F 2562 in kerosene. The loaded TBP phase could contain about 45 g of Fe(III) per liter, whereas the 1.44 M solutions of HOE F 2562, TIOA, and TBP were loaded up to 30, 34, and 17 g of Fe(III) per liter), respectively. Effective extraction of iron was induced by a significant content of neutral (FeCl3) chlorocomplex and a high concentration of hydrochloric acid. The mole fractions of iron(III) chlorocomplexes were estimated using the MEDUSA program13 for an ion strength of 5 and a chloride concentration of 5 M, i.e., for conditions corresponding to actual pickling solutions. They amounted to approximately 0.18, 0.49, 0.26, and 0.08 for FeCl3, FeCl2+, FeCl2+, and Fe3+, respectively. Iron(II) formed only the first chlorocomplex, and the mole fractions amounted to 0.58 and 0.42 for Fe2+ and FeCl+, respectively. These cationic species could not both be extracted with the solvating and basic reagents. Zinc(II) was present almost completely in the anionic forms, e.g., ZnCl42- and ZnCl3-. Their mole fractions were estimated to be 0.92 and 0.07, respectively. At a high acidity of the aqueous feed, the chlorocomplexes of zinc(II) were extracted according to the following equations5
2H+w + ZnCl42-w + 2So ) H2ZnCl4‚2So
(1)
at HCl concentrations above 2.7 M and
ZnCl42-w + 2B‚HClo ) (BH)2ZnCl4o + 2Cl-w (2) where S and B denoted solvating and basic reagent, respectively. Amine reagent was protonated prior to extraction
Bo + H+w + Cl-w ) B‚HClo
(3)
Amines could even transfer two molecules of HCl to the
H+w + ZnCl3-w + 3So ) HZnCl3‚3So
(5)
ZnCl2w + 2So ) ZnCl2‚2So
(6)
Reaction 5 becomes important for concentrations of hydrochloric acid in the range 0.8-2.7 M,5 and it is shifted to the right with increasing concentration of protons. Reaction 6 is dominant for concentrations of HCl and Cl- below 0.8 and 1 M, respectively.5 The neutral iron(III) chlorocomplex could be extracted with the solvating reagent according to the reaction analogues of eq 6 with the basic reagent donating the lacking chloride ion
FeCl3w + B‚HClo ) (BH)FeCl4o
(7)
The considered system differed significantly from the zinc(II)-DEHPA-sulfate systems discussed broadly in the literature.15,16 Solvating or basic reagents were used in our work as extractants, and proton ions were not liberated during extraction. Thus, the effect of the hydrochloric acid concentration was significantly less important in comparison to the effect of acidity observed in the sulfate system. It was impossible to reverse the process by changing the acid concentration. This means that the driving force for the extraction-stripping process was not the difference in the aqueous-phase acidity but rather the difference in the chloride equilibrium concentration between the aqueous feed and the aqueous strip solution. Appropriately high concentrations of hydrochloric acid were, however, needed to preprotonate the basic reagents (eqs 2-4) and to form the ion pair (weak acid H2ZnCl4) extracted by the solvating reagent according to eq 1. The concentration of 10% HCl (3.16 M) was so high that both of these requirements were fulfilled. It is necessary to explain that the compositions of the extracted zinc(II) complexes were determined for model dilute solutions. Thus, eqs 1-7 provide only general trends because it is impossible to transfer the data, including the regions of complex existence, from dilute to actual industrial solutions. The actual spent pickling solutions contained over 90% of their iron in the form of Fe(II). When needed, iron(III) could be reduced to iron(II) with iron scrap or, better, with recycled hooks covered with a zinc layer and/or goods with a zinc layer of bad quality. The oxidation of iron(II) to iron(III) occurred slowly and was reduced by high concentrations of HCl and Cl-.17 Figures 2 and 3 present the concentrations of Zn(II) in the aqueous phases before and after extraction with TBP and HOE F 2562 and after stripping with water. Good agreement between the amounts of zinc(II) introduced and determined in aqueous solutions (i.e., [Zn2+]ow
Ind. Eng. Chem. Res., Vol. 41, No. 3, 2002 601 Table 4. Stripping of Zinc(II) (% S) with Water from the Loaded Organic Phasea reagent TBPb 3:1 (v/v) TBP/DEHPAb HOE F 2562 ALAMINE 336 ALIQUAT 336
Figure 2. Comparison of zinc(II) content in the aqueous phase in extraction-stripping process with undiluted TBP. Aqueous feed containing 10% HCl, 0-60 g/L of Zn(II), 60 g/L of Fe(II), deionized water used for stripping; 1/[, aqueous phase after extraction; 2/9, 3/2, and 4/b, aqueous phase after first, second, and third strippings, respectively; ×/5, total amount of zinc(II) determined.
Figure 3. Comparison of zinc(II) content in the aqueous phase in extraction-stripping process with 1.44 M HOE F 2562 in kerosene Exxsol D220/230. Aqueous feed containing 10% HCl, 0-60 g/L of Zn(II), 60 g/L of Fe(II), deionized water used for stripping; 1/[, aqueous phase after extraction; 2/9, 3/2, and 4/b, aqueous phase after first, second, and third strippings, respectively; ×/5, total amount of zinc(II) determined. Table 3. Extraction of Zinc(II) (% E) from 10% HCl in the Presence of 110 g/L of Fe(II)a reagent
%E
remarksb
TBPc 3:1 (v/v) TBP/DEHPAc HOE F 2562d ALAMINE 336d ALIQUAT 336d
96.3 84.0 93.9 99.2 99.2
GS GS GS GS emulsion
a Initial concentration of zinc(II), 5 g/L; chloride concentration, 6.98 M. b GS ) good separation of phases. c Without kerosene. d Reagent/decanol/kerosene volume ratio ) 30:15:55.
) [Zn 2+]w) was observed. The average deviations were 4.5 and 6.3% for TBP and HOE F 2562, respectively. Each reagent used alone permitted almost total recovery of zinc(II) from 10% HCl containing an enormous amount of iron(II) (Table 3). Thus, a negative effect of iron(II) on zinc(II) extraction was not observed. Emulsions were formed when the quaternary ammonium salt (ALIQUAT 336) was used. The addition
Zn(II) in organic feed (g/L)
No. of stages
%S
0.286 0.132 0.051 0.207 0.076 0.028 0.337 0.133 0.081 0.358 0.254 0.115 0.334 0.319 0.291
1 2 3 1 2 3 1 2 3 1 2 3 1 2 3
53.9 82.2 99.8 63.2 86.5 87.3 60.5 76.1 99.8 29.0 68.0 89.3 4.5 12.9 62.4
a The concentrations of the aqueous feed used to load the organic phase are given in Table 2. The organic phase contained 30% reagent, 15% decanol, and 55% kerosene. b Without kerosene.
of decanol (15%) did not solve this emulsion problem. Thus, this reagent is not appropriate for the considered system. The addition of the acidic extractant di(2-ethylhexyl)phosphoric acid to tributyl phosphate did not decrease the extraction as drastically (Table 3) as it did in the presence of iron(III) (Table 2). The best stripping of zinc(II) was observed for TBP and HOE F 2562 (Table 4). The phases separated completely. However, the costripping of zinc(II) and hydrochloric acid was observed. Simultaneously, the composition of the complex remaining in the organic phase was shifted from H2ZnCl4‚2S toward ZnCl2‚2S. Thus, high concentrations of HCl in the stripping solution decrease the stripping of zinc(II). This hypothesis was confirmed by the mass balance of chloride (Table 5) carried out for the extraction of zinc(II) from 10% HCl containing 56 g/L of Zn(II). TBP saturated with water was used, and extraction was followed by three-step stripping. The volume ratio of the phases was 1:1. Each aqueous phase was analyzed, and the contents of Cl-, H+, and Zn(II) were determined. The concentrations of H+ and Zn(II) were recalculated into Cl- concentrations and compared with the initial concentration of Cl-. Satisfactory agreement between experimental and approximated Cl- concentrations was observed for each considered phase. The deviations did not exceed 2.5% and had a mean of 1.6%. The mass balances of Cl-, H+. and Zn2+ determined in the aqueous phases after extraction and stripping agreed with the contents of these species in the aqueous feed to within an error of 2.1-3.9%. The Zn(II)/Cl-/H+ mole ratios in the aqueous phases were 1:3.23:1.29; 1:2.47:0.44, and 1:2.36:0.41 after the first, second, and third strippings, respectively, clearly indicating the high stripping of hydrochloric acid in the first step. A high efficiency of stripping could be obtained, already in the first stage, by using an ammoniacal solution. However, this could provoke the precipitation of iron hydroxides, if carried out inappropriately. Acceptable stripping (near 90%) was also obtained for the mixtures of TBP with DEHPA and ALAMINE 336. The favorable results in the latter case can be attributed to the presence of modifier (15% decanol) because, in its absence, the stripping was rather poor. Some oxidation of iron(II) to iron(III) occurred during extraction, and some transfer of iron was observed, even
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Table 5. Mass Balance (g/L) of Chloride Ions Directly Determined [Cl-]exp and Recalculated from Concentrations of Protons ([Cl-]H+) and Zinc(II) ([Cl-]Zn(II))a parameter [Cl-]exp [Cl-]H+ [Cl-]Zn(II) totalc a
aqueous feed
aqueous phase after extraction
156.0 96.9 60.9 157.8
105.3 81.5 25.2 106.7
aqueous phase after stripping stage 1 stage 2 stage 3 35.5 14.0 22.1 36.1
15.5 2.7 12.6 15.3
4.0 0.7 3.4 4.1
totalb (g/L) 160.3 98.9 63.3 162.2
TBP presaturated with water was used. b Sum of concentrations from columns 3-6. c Sum of concentrations from rows 3 and 4.
Table 6. Percent of Total Iron Extracted from 10% HCla reagent
% Eeb
% Esb
TBPc 3:1 (v/v) TBP/DEHPAc HOE F 2562d ALAMINE 336d ALIQUAT 336d
-7.6 0.8 -5.0 5.6 3.9
4.9 3.9 7.1 12.1 16.5
a Concentrations are the same as in Table 3. b % E and % E e s denote the extraction percentages calculated from extraction and stripping data, respectively. c Without kerosene. d Reagent/decanol/kerosene volume ratio ) 30:15:55.
Figure 5. Isotherms of zinc(II) stripping from loaded TBP. The aqueous feed used for the loading of the organic phase contained 60 g/L of Zn(II) and 60 g/L of Fe(II) dissolved as chloride salts in 10% HCl. Number of stripping stages: 9, 1; b, 2; and O, 3.
Figure 4. Isotherms of zinc(II) extraction with (9) undiluted TBP and (b) 1.44 M HOE F 2562 in kerosene. Solid points correspond to the aqueous feed containing 0-60 g/L Zn(II) and 1.07 M ) 60 g/L Fe(II), added as FeCl2 and 10% HCl; open points correspond to 1.07 M Fe(II) + Zn(II) and 10% HCl.
when only iron(II) was present in the aqueous feed (Table 6). The total iron content (110 g/L) was determined with some error. As a result, the percent of iron extracted calculated from the extraction data fluctuated near 0%. Even negative values were obtained for two reagents. As a result, the stripping data were used to avoid the error of subtracting high iron contents. These data (% Es) indicated that, in fact, small quantities of iron were transferred to the organic phase. They changed in the order 3:1 TBP/DEHPA e TBP < HOE F 2562 < ALAMINE 336 < ALIQUAT 336. The difference between TBP used alone and its mixture with DEHPA was small and almost negligible. Again, trialkylamine and its ammonium salt showed the worst performance. The selectivity of the extraction with dialkylamine was better. It is known that traces of various metals, e.g., Co and Cu, can induce the oxidation of iron(II) to iron(III).17 These contaminants could be introduced to the extraction system with the organic reagent, e.g., alkylamine and its derivatives. This possibility was quite likely because the hydrogenation of alkylnitriles to alky-
Figure 6. Isotherms of zinc(II) stripping from loaded 1.44 M HOE F 2562 in kerosene Exxsol D220/230. The aqueous feed used for the loading of the organic phase contained 60 g/L of Zn(II) and 60 g/L of Fe(II) dissolved as chloride salts in 10% HCl. Number of stripping stages: 9, 1 and b, 2).
lamines in the process of extractant synthesis was carried out in the presence of nickel or cobalt. The obtained results permitted tributyl phosphate and HOE F 2562 to be selected as the most suitable extractants for the recovery of zinc(II) from spent pickling solutions. The isotherms of extraction given in Figure 4 indicated that undiluted TBP could be loaded with up to 35 g/L of Zn(II), whereas 1.44 M HOE F 2562 could only be loaded with up to 15 g/L of Zn(II). Higher concentrations of the active substance could be used in the latter case. However, such solutions became more viscous, and a slow disengagement of the phases was observed. In fact, the phases did not even separate completely in
Ind. Eng. Chem. Res., Vol. 41, No. 3, 2002 603
some cases. The presence of iron(II) (open points in Figure 4) did not affect the extraction of zinc(II). The stripping isotherms presented in Figures 5 and 6 confirm that zinc(II) can be effectively stripped from the organic phase with water. The efficiency of stripping from loaded TBP increased significantly in the second stage. An approximately linear isotherm with a slope near 1 was obtained for the first stage of stripping. However, very steep isotherms were demonstrated for the second and third stages of stripping, i.e., after removal of the main quantities of hydrochloric acid in the first stage. As a result, the stripping was more effective in the second step. The volume ratio of the phases could be near 1, and only two steps were needed to strip 90-95% of zinc(II) and to decrease the concentration in the organic phase to 2-3 g/L. The stripping isotherm obtained for HOE F 2562 had a similar character, but the improvement of the stripping in the second step was not as significant as in the case of TBP. Moreover, the stripping was not as effective as in the case of TBP. Acknowledgment This work was supported by NATO Grant Science for Peace SfP 972398 Hydrochloric Acid. Literature Cited (1) Alguacil, F. J.; Cobo, A.; Caravaca, C. Study of the extraction of zinc(II) in aqueous chloride media by Cyanex 302. Hydrometallurgy 1992, 31, 163. (2) Forrest, V. M. P.; Scargill, D.; Spichernell, D. R. Extraction of zinc and cadmium by tributyl phosphate from aqueous chloride solutions. J. Inorg. Nucl. Chem. 1969, 31, 187. (3) Sato, T. Extraction of some mineral acids by tri-n-octylamine. J. Appl. Chem. 1965, 15, 10. (4) Schu¨gerl, K.; Larm, A.; Gudorf, M. Recovery of zinc from zinc mordant solutions of dovetail plants. In Proceedings of the
International Solvent Extraction Conference 96 (ISEC’96); University of Melbourne: Melbourne, Australia, 1996; Vol. 2, p 1543. (5) Morris, D. C. F.; Short, E. L. Zinc chloride and zinc bromide complexes. Part II. Solvent-extraction studies with zinc-65 as tracer. J. Chem. Soc. 1962, 2662. (6) Schulz, W. W.; Navratil, J. D.; Bess, T. Science and Technology of Tributyl Phosphate; CRC Press Inc.: Boca Raton: FL, 1987; Vol. 2. (7) Anderson, S. O. S.; Reinhardt, H. Recovery of Metals from Liquid Effluents. In Handbook of Solvent Extraction; Lo, T. C., Hanson, C., Baird, M. H., Eds.; John Wiley & Sons: New York, 1983; Chapter 25.10. (8) Klein, K.; Prade, H. Recovery of zinc from rinsing water of a strip galvanizing line. Stahl Eisen 1996, 116, 45. (9) Metrohm Application Bulletin No. 101; Metrohm: Herisau, Switzerland. (10) Metrohm Ion Analysis, 702SM Titrino Applications; Metrohm: Herisau, Switzerland, 1997. (11) Minczewski, J.; Marczenko, Z. Analytical Chemistry; PWN: Warsaw, Poland, 1985 (in Polish). (12) Vogel A. I. A Textbook of Quantitative Inorganic Analysis. Theory And Practice; Longman: London, 1961. (13) Puigdomench, I. Program MEDUSA, www.inorg.kth.se (accessed Aug 2000). (14) Kyuchoukov, G.; Miskonov, I. On the extraction of copper and zinc from chloride media with mixed extractant. Solvent Extr. Res. Dev. Jpn. 1999, 6, 1. (15) Bart, H. J. Reactive Extraction; Springer-Verlag: Berlin, 2001. (16) Mo¨rters, M.; Bart, H. J. Extraction equilibria of zinc with di(2-ethylhexyl)phosphoric acid. J. Chem. Eng. Data 2000, 45, 82. (17) Stumm, W.; Morgan, J. J. Aquatic ChemistrysAn Introduction Emphasizing Chemical Equilibria in Natural Waters, 2nd ed.; John Wiley & Sons: New York, 1981; Chapter 7.6.
Received for review April 11, 2001 Revised manuscript received August 30, 2001 Accepted October 21, 2001 IE0103207
