Ind. Eng. Chem. Res. 1994,33, 1067-1075
1067
REVIEWS Extraction of Metal Salts by: Mixtures of Water-Immiscible Amines and Organic Acids (Acid-Base Couple Extractants). 1. A Review of Distribution and Spectroscopic Data and of Proposed Extraction Mechanisms Aharon M. Eyal,’ Eyal BresslerJ Raymond Bloch, and Betty Hazan Casali Institute of Applied Chemistry, School of Applied Science and Technology, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel
Distribution data and extraction mechanisms are reviewed for metal salt extraction by mixtures of water immiscible amines and organic acids in a diluent. Some new results from our laboratory were included to widen the scope of extractant components, provide more data on extraction of transition metal sulfates from concentrated solutions, and study the mutual effects of extraction and aqueous-phase acidity. An effort was made to present a matrix of the affecting parameters (extracted salt and extractant characteristics, aqueous-phase concentration and acidity, organicphase concentration, temperature, etc.) and the distribution data (capacity and extraction selectivity and stoichiometry, the shape of the distribution curve, and water coextraction). This data provides the tools required for tailoring extractants for many hydrometallurgical and waste management processes. .In addition, it provides the basis for analysis of the mechanisms involved and of the species present in the organic phase. 1. Introduction Numerous papers and many reviews describe extraction of metal ions and their salts. Three main families of extractants are we11 documented: (a) neutral solvents and chelating agents, (b) water immiscible organic acids, extracting metal ions through cation exchange (liquid cation exchangers), and (c) water immiscible bases or their salts extracting anionic complexes of transition metals through anion exchange (liquid anion exchangers). Grinstead and his co-workers (1969,1970;Davis and Grinstead, 1970) introduced a new family of extractants comprising a mixture of a liquid anion exchanger and a liquid cation exchanger in a diluent. Being of both theoretical and applicative importance, these extractants were studied by several groups including those of Watanabe and Nishimura (19761, Hanson (1974, 1975), Kholkin (1982, 1986, 1988a-c; Belova et al., 1988; Fleitlich, 19921, Sat0 (1980,19821,Kopacz and Kalembkiewicz (1986a,b, 19881, Hadjiev (1988),Schmuckler (Hare1and Schmuckler,1987; Kress et al., 1989,1990; Cohen et al., 19911,Eyal(199Oa-c; Bressler and Eyal, 1993),and others. Authors usedvarious names for these extractants, including amine salts, mixed extractants, mixed ionic solvents, binary extractants, etc. In the following the term acid-base couple (ABC) extractants will be used. ABC extractants are complex systems comprising at least three components. They are neutral and extract neutral salts rather than metal cations or their anionic complexes, although their active components are liquid ion exchangers. These active componentsare well-known and well understood as single extractants but may provide
* To whom correspondence should be addressed.
+ Present address: Department of Biological Chemistry, A. Silberman Institute of Life Science, The Hebrew University of Jerusalem.
oaaa-5aa5i94i2~33-ios7$04.50io
new properties when in a mixture. These extractants are, therefore, novel systems of theoretical interest providing for a variety of mechanisms and of organic-phase species. Studies show that ABC extractants present some attractive properties with potential advantages for application in liquid-liquid extraction processes. They are less sensitive to acidity in the aqueous feed and have relatively high efficiency in extraction of alkali and alkaliearth halides. ABC extractants are reversible, enabling regeneration of the extractant and recovery of the extracted salt at relatively high concentration by back-extraction with water (while regeneration of liquid ion exchangers consumes acids and bases and forms unwanted salts). ABC extractants can be adjusted for reversible extraction of acids (Eyal and Baniel, 1982;Eyal et al., 199Ob;Eyal, 1993) and therefore for extraction of both acids and their salt by a single extractant composition. Potential applications of ABC extractants include recovery of MgC12 from concentrated sea water (Grinstead and Davis, 1970; Hanson et al., 1974,1975; Shibata et al., 1976), extraction of Cu2+ from acidic solutions (Barrow, 19711, separation of LiCl (Hernandezand Martinez, 1981), removal of Fe3+ from AlC13 solutions (Kholkin, 1988b), separation of Cd2+from ZnCl2, recovery of H2S04 and ZnSOr from zinc electrowinning bleeds (Eyalet al., 1990a), and industrial effluent treatment. The theoretical and potential applicative interest in ABC extractants and the data generated so far justify a review of this field. This paper reviews the distribution data and summarizes the mechanisms proposed. A theoretical treatment and an analysis of the results are provided in the next paper. Some new results from our laboratory were added to widen the scope of extractant components, provide more data on extraction of transition metal sulfate from concentrated solutions, and study the mutual effects of extraction and aqueous phase acidity. 0 1994 American Chemical Society
1068 Ind. Eng. Chem. Res., Vol. 33, No. 5, 1994
2. Experimental Section
Extractant components were of technical grade. The amines used were RR’R”CNH2 (Primene JMT) and RR’R”CN(R’’’)H (Amberlite LA-2, ALA), both products of Rohm and Haas, tricaprylylamine (TCA, Alamine 336) and methyltricaprylylammonium chloride (MTCA, Aliquat 3361,both products of Henkel, and tris(Zethylhexy1)amine (TEHA, Fluka). The organic acids were dinonylnaphthalenesulfonic acid (DNNSA, King Industries), bis(2-ethylhexy1)phosphate(DEHPA, Sigma),lauric acid (LA, Fluka) and a-bromolauric acid (ABL, Miles Yeda). The diluent was a low aromatics kerosene (Parasol, Paz, Israel). Other reagents were of the best commercially available grade. The average molecular weights of the technical grade extractants were determined by titration. The ABC extractants were prepared by mixing the chosen amine and organic acid with the diluent. Unless othewise indicated the concentration of each active component was 0.5 mol/kg. The sulfonic acid containing extractants were washed to remove sulfuric acid contaminatingthe technical product. The Aliquat 336 (MTCA) containing extractants were washed to remove HC1 formed in contact with the organic acid (HA) according to
The compositions of the ABC extractants referred to in the article are given as [the amine, the organic acid, their concentration, the diluent]. On describing our results, if the concentration of the reagents in the kerosene is 0.5 mol/kg only the amine and the organic acid will be indicated. The aqueous phase was equilibrated with the chosen extractant (w/w ratio of 10/1) a t the required temperature (which, if not indicated otherwise, was the ambient temperature, about 25 “C). The phases were then separated, and the organic phase was washed with 10% HNO3 solutions (we found that two contacts were sufficient for complete washing out of the salt). The metal ion concentration in the combined wash solutions and in the separated aqueous phase was determined by titration with EDTA, using a suitable indicator (Eriochrome Black-T in the case of zinc salts). 3. Distribution Data An effort was made to present a matrix of affecting parameters and the way they determine extraction results. Affecting parameters include those of the aqueous phase: characteristics of the extracted salt (cation and anion properties), its concentration, presence of other ions, and acidity and those of the extractant: amine basicity, organic acid strength, amine to organic acid molar ratio, their concentration in the diluent, properties of the diluent, and steric effects. Temperature may alsoaffect extraction. Among the affected distribution parameters one can list extractant capacity, distribution coefficients, stoichiometry, the shape of the distribution curve, extraction selectivity, water coextraction, and changes in aqueousphase acidity on extraction. Due to the large variety in most of the above listed parameters the data availablein the literature is not always sufficient for filling in this matrix. In a few cases the information is contradictory, and in many others it is deficient, missing essential details such as the chemical nature of commercial products used as extractant components, their concentration in the extractant, equilibrium aqueous-phase concentration, or temperature.
Table 1. Extraction of MgClz, NaCl, and CaCla from Synthetic Seawater (Shibatal et al. 1976) aq phase concn (M) selectivity extractant Mg Na Ca S ~ / N S. C . / ~ SC./N. MTCA, 0.374 3.88 0.0063 95 0.91 86 VA 911,”0.5 M 0.392 3.87 0.0056 50 1.56 79 MTCA, DEHPA, 0.5 M 0.447 3.89 0.0036 127 JMT, 7.69 950 VA 911,1.0M 0.424 3.81 0.0059 11 1.89 JMT, 20.4 DEHPA, 1.0M a
Versatic acid 911.
3.1. Aqueous Phase Parameters. 3.1.1 Cation/Cation Selectivity. Most of the data regarding salt extraction by ABC extractants were derived from systems comprising a single salt. Comparison of distribution curves (or coefficients)provides an indication of selectivity sequence. Conclusions based on multisalt solutions are, however, more reliable. Many articles describe the extraction of alkali and alkali earth chlorides. Grinstead et al. (1969) investigated the extraction of NaC1, KC1, MgC12, and CaC12 (single-salt systems, aqueous-phase concentrations of up to 4.5 M) by [MTCA, ethylundecanoic acid (EUD), 0.48 M, toluene]. Their distribution data showed the sequence CaClz > MgClz > NaCl> KC1. Studying extraction from MgC12 + NaCl solutions resembling X 10 concentrated seawater, Grinstead and Davis (1970) found Mg/Na selectivities of 120-160 for [MTCA, naphthenic acid E (NA), 0.5 M, toluene] and 270-290 for [Primene JMT, NA, 1.0 M, /M defined ~ as the ratio of the toluene]. Selectivity S M ~ is distribution coefficients D M J D M ~ . Shibata et al. (1976) studied the extraction of MgC12, NaC1, and CaClz from synthetic concentrated seawater comprising these salts. Their results (see Table 1)confirm the selectivity found by Grinstead. Hernandez and Martinez (1981) used [JMT, NA, 1.0 M, toluene] for extraction of MgClz and alkali chlorides from aqueous phases of up to 3 M (single- and two-salt systems). Their results confirmed those of Grinstead, Shibata, and their co-workers, showing the sequence MgC12 > LiCl > NaCl > KC1. Only a few articles describe the extraction of transition metal salts. Most of them are limited to dilute solutions. Kholkin and co-workers (Kholkin and Kuzmin, 1982; Kholkin et al., 1988) studied the extraction of nitrates by [tetraoctylamine (QOA),bis(2-ethylhexy1)dithiophosphate (DEHTP), 0.25 M, toluene]. Metal ion concentrations were 20-60 mM, and NOS- concentration reached 2 M. The sequence found in studies of single-salt systems was Cu(N03)~> Zn(NO31z> Ni(NOs12> Co(NO3)z> Ca(N03)~. Kalembkiewicz and Kopacz (1988) studied extraction of transition metal sulfates by an ABC extractant composed of a weak amine and a weak acid 10.25 M 3,4dimethylaniline, 0.5 M benzoic acid, benzene]. Metal ion concentration in the initial aqueous phase was 25 mM. For single-salt systemsthe selectivity sequence over a wide range of pH values (1-7) was Fe3+> Cu2+> Zn2+> Ni2+ > Mn2+> CoZ+. Sat0 et al. (1980,1982) extracted chlorides from singlesalt aqueous solutions with an initial metal ion concentration of 1g/L. Using [MTCA, lauric acid (LA), 0.01-0.2 M, benzene], they found HgClz >> CdClz > CuClz > ZnClz > CoClz ~ iNiClz : > MnClz for dilute extractants, changing for the more concentrated extractants to HgClz >> CuClz > ZnClz > CdClz > CoClz = NiClz > MnClZ.
Ind. Eng. Chem. Res., Vol. 33, No. 5, 1994 1069 Table 2. Distribution of Various Sulfates between Dilute Aqueous Phases and (I) Fatty Acid Mixture or (11) Fatty Acid + JMT + TBP (Hadjiev et al., 1.988) ~~
extracted salt b2Soc cuso4 CdSOi znso4 COS04
NiSO4 Fez(SOda* Pbso4
PH 4.40 3.55 4.74 5.05 5.00 5.00 2.04 2.93
init value concn (mg/L) lo00 735 670 251 549 558 140 223
PH 3.19 4.61 4.94 5.03 5.31 5.31 3.75 3.40
inequilibwith1 concn (mg/L) 41 23 314 35 424 440 2.5 174
Do 23.4 30.9 1.13 6.13 0.29 0.27 55.0 0.28
PH 3.00 2.78 3.67 3.62 3.81 3.79 1.97 2.45
in equilib with I1 concn (mg/L) 988 73 616 206 523 531 87 187
Do 0.012 9.00 0.14 0.14 0.05 0.05 0.61 0.19
OD = distribution coefficient, [Mlorg/[Mlaq. * The valency of the Fe is not specified. The high D measured, however, indicates that this
is Fea+.
Table 3. Distribution of Fd+, Znz+, and Cu’+ Sulfates equilib extractant dist coef x lo00 loading (mmol/kg) extractantcompn Fes+ Zn2+ Cu2+ FeS+ Zn2+ Cu2+ TCA+DEHPA 124 86 3.5 42.8 34.4 2.0 JMT + DEHPA 81 7 32.4 4.0 MTCA+DEHPA 170 122 50 58.6 48.8 28.6 170 46 34 58.6 18.4 19.4 JMT + ABL MTCA + ABL 88 54 14 30.3 21.6 8.0 JMT + LA 184 111 88 63.4 44.4 50.3 174 88 37 60.0 35.2 21.1 MTCA + LA
Table 4. Extraction of Sodium Salts by ABC Extractants (Grinstead et al.. 1969) ~
extractant compn MTCA, EUD, 0.48 M, toluene DHOA,”EUD, 0.5 M, toluene
0
Hadjiev et al. (1988) studied the extraction of various sulfates from single-salt aqueous solutions by (I) 10% v/v Cl4-Cls fatty acid mixture and (11)10% v/v C14-ClS fatty acid mixture + 5 % v/v JMT (acid/amine molar ratio > 2) 2% v/v tributyl phosphate (TBP). Their results are summarized in Table 2. Some marked differences exist in the selectivity sequence between the amine-containing system: Fe3+> Cu2+> Ag+ > Zn2+> Cd2+> Co2+E Pb2+ E Ni and the amine-free system: Cu2+ > Fe3+ > Pb2+> Cd2+ ic: Zn2+ > CoZ+ = Ni2+ > Ag+. We have studied distribution of Fe3+, Zn2+,and Cu2+ sulfates between their saturated single-salt solutions and severalABC extractants. The results summarized in Table 3 show the sequence Fez(SO4)s > ZnSO4 > CuSO4. Kholkin et al. claim selective Fe3+ extraction from aqueous FeCl3 + AlC13 HCl solutions (1988b; Fleitlich et al., 1990)and selective extraction of CdC12 from aqueous CdClz ZnSO4 + HC1 solutions (1988~).Selectivitieswere not reported. For the recovery of Zn2+valuesfrom zinc electrowinning bleeds (Eyal et al., 1990) we studied the extraction selectivity in ZnSO4 + MnSO4 + MgSO4 systems. High selectivity to Zn was found for all the studied ABC extractants. Thus, in equilibrium with an aqueous solution of 0.69 mol/kg ZnSO4 + 0.45 mol/kg MgS04 0.07 mol/kg MnS04, [MTCA, DEHPA] contained 140mM ZnSOcO.3 mM MgSO4, and 0.5 mM MnSO4 (selectivity sequence of Zn2+ > MnZ+ > Mgz+). Contacting this extractant with an aqueous solution containing 1.94 mol/kg ZnSO4 + 0.34 mol/kg MgS04 + 0.08 mol/kg MnS04 (organic to aqueous w/w ratio of lO/l, temperature of 40 OC) resulted in extraction of 80% of the ZnSO4 with ZnSO4/(MgS04 + MnSO4) selectivity > 100. 3.1.2. Anion/Anion Selectivity, Grinstead et al. (1969) studied the effect of the anion on extraction of sodium salts (single-salt systems). They found that the selectivity depends on aqueous-phase concentration (see Table 4). Preference to nitrate decreases with concentration elevation. Hernandez and Martinez (1981) studied extraction of lithium and magnesium salts by [JMT, NA, 1M, toluene]. In their single-salt systems the sequence > C1- >>
+
+
+
+
~~~~~
aq phase concn (MI B r > C1- >> 504%
>1.75 NOS-> C1- >> sod”NOS- > B r > C1-
1-4 >4
Br > NOS- > C1B r > C1- > NOS-
DHOA = 2 , 2 - d i h e x y l - l - a m i n ~ e .
Table 5. Extraction from CaClr + Ca(NO& Solutions equilib aq phase concn (edkg) selectivity extractant compn NOSc1SNOStCIMTCA, DNNSA, 0.8 M, xylene 2.69 3.33 8.6 3.69 3.53 4.8 MTCA, DEHPA, 0.8 M, xylene 2.69 3.21 12.0 3.13 3.53 6.8 TCA, DNNSA, 0.8 M, xylene 2.69 3.21 6.3 3.69 3.47 3.5 TCA, DEHPA, 0.8 M, xylene 2.95 3.20 11.5 3.30 3.50 6.2 5 0 4 % was maintained through the whole concentration range studied (up to 1.5 M for Mg salts and up to 3 M for Li salts). Several ABC extractants were studied in extraction from aqueous phases containing CaCl2 + Ca(NO& (Kogan and Eyal, 1993). The results (Table 5 ) show that the selectivity to Ca(NO3)2decreases with the elevation of aqueous-phase concentration. Kholkin and Kuzmin (1982) studied the extraction of nickel salts by [QOA, DEHTP, 0.25 M, toluene]. The sequence for single-salt aqueous-phase concentrations of UP to 1 M was I- > No3- > C1- >> SOr2-. We studied ZnCln and ZnSO4 extraction by eight compositions of ABC extractants (composed of tris(2ethylhexy1)amine (TEHA), TCA, JMT, or MTCA as the amine and LA or DEHPA as the acid, 0.5 M, kerosene). For single-salt aqueous phases of up to 2.5 M the sequence for all the extractants is ZnCl2 > ZnSO4. 3.1.3. Effect of Aqueous-PhasepH. Extraction of LiCl by [JMT, NA, 1 M, toluene] was not sensitive to aqueous-phase pH changes in the range of 3-11 (Hernandez and Martinez, 1981). A similar pH independence (range 2-8.5) was found for MgClz extraction by [MTCA, Acid 810, 0.5 M, toluene] (Hanson et al., 1975). Sat0 et al. (1980) reported enhancement of NiClz extraction with pH elevation up to -3 after which it stays unchanged (initialNiZ+concentration in the aqueous phase was 7.8 mM and extractant composition was [MTCA, LA,
1070 Ind. Eng. Chem. Res., Vol. 33, No. 5, 1994
1-““ m
Y
H2W4in solvent (mmol/Kg)
Figure 1. Effect of HzSO, presence on ZnSOd extraction by 0.5 mol/kg TCA + 1.0 mol/kg DEHPA in kerosene.
0.02-0.2 M, benzene]). Note that the pH reported is the
initial one rather than the equilibrium pH and that the extractant used is very efficient in acid extraction. Fleitlich et al. (1990) studied FeC13 extraction at 80 OC from AlC13 FeCl3 solutions (initial concentration: Al, 54 g/L; Fe, 10G/L). The extractant composition was [ C r Cs-trialkylamine, a-branched carboxylic acids (VIC)]. Aqueous phases were modified by HC1addition. The Fe3+ distribution coefficient decreased with increasing free HC1 level up to -25 g/L and then increased (highest HC1 level studied was 100 g/L). Belova et al. (1988) reported enhancement of [PtCl#and [PdCl.#- extraction with pH reduction (pH range studied, 0-5). The extractants contained trioctylamine (TOA) and p-tert-butylphenolate, caprylic acid, DEHPA, or alkylsulfonic acid. We studied the effect of H2S04 presence on ZnSO4 extraction by [0.5 mol& TCA, 1.0mol DEHPA, kerosene]. The results (Figure 1) show that acidity has a strong negative effect on the extraction. Similarly, on equilibrating [MTCA, DNI, [TCA, ABLI, or [TCA, DEHPA] with saturated solutions of Fe2(S04)3, FeS04, or MnS04, eachone also containing 0.5 M H2S04, metal ion extraction was negligible. In our process for the recovery of sulfuric acid and zinc sulfate values from zinc electrowinning bleeds, this phenomenon enabled, through internal recycling, concentration of the zinc in the product solution to about 3 times its concentration in the bleed (Eyal et al., 1990). Hadjiev et al., (1988) studied the effect of pH (in the range 2-5) on the selectivity of extraction from aqueous solutions containing initially 0.65 g/L Zn + 0.60 g/L Cu + 1.15 g/L Mn. The extractant was 10% v/v DEHPA + 2% v/v TCA (aminelacid molar ratio 1/51 + 2% v/v TBP. Mn/Cu selectivity decreased with pH elevation, Cu/Zn increased, and Mn/Zn showed a maxima at pH =
+
-
4.
3.1.4. Common-Ion Effect. Grinstead et al. (1969) show that the presence of NaCl in the aqueous phase markedly enhances MgCl2 extraction by [MTCA, EUD, 0.48 MI. In the presence of 4.0 M NaC1, distribution coefficients at about 0.2 M MgC12 are about 4 times larger than those in the absence of NaCl. The effect decreases at higher MgC12 concentrations. Grinstead and Davis (19701, Hanson et al. (19751, and Shibata et al. (1976) studied MgC12 extraction from seawater by various ABC extractants. Distribution coefficients were higher than those in extraction from solutions containing MgCl2 as a single solute. Hernandez and Martinez (1981) found that the presence of KC1 and NaCl
enhances LiCl extraction by [JMT, NA, 1 M, toluene]. Sat0 et al. (1980) show that NiCl2 extraction by [MTCA, LA] is enhanced by LiCl presence. We studied ZnSO4 extraction by [TCA, DNNSAI and by [TCA, DEHPA] from aqueoussolutions also containing MgS04and MnSO4 (Eyal et al., 1990a). The results show that the presence of Mg2+ and Mn2+ at relatively high concentrations provides a strong driving force for ZnSO4 extraction. 3.2. Organic-Phase Parameters. The organic-phase parameters are the characteristics of the amine, organic acid, and diluent and their proportion in the extractant. They may affect the degree of extraction and its dependence on aqueous-phase acidity, the selectivity, and the pH changes in the aqueous-phase during extraction. 3.2.1. Amine Characteristics. Grinstead et al. (1969) studied the extraction of NaCl and MgClz by ABC extractants containing EUD and various amines. The degree of extraction followed the sequence trioctylamine (TOA) < N-dodecyl-(2-ethylhexyl)amine < JMT C 2,2dihexyl-1-aminooctane [MTCA, cup-dialkyl monocarboxylic acid] > [MTCA, DEHPA] > [MTCA, DEHTP] . We studied the distribution of ZnSO4 and ZnCl2 between aqueous solutions (equilibrium concentrations ranging from 0.2 to 2.2 mol/kg) and ABC extractants composed of lauric acid (LA) or DEHPA and one of the following amines: TEHA, TCA, JMT, or MTCA. For both salts the LA-containing extractants were more sensitive to the aqueous-phase concentration while the DEHPA-based ones reached a plateau at relatively low concentrations. For both salts [amine, DEHPAI are more efficient than [amine, LA] up to high aqueous-phase concentrations except for JMT-containing ones in ZnClz extraction. Shibata et al. (1976) showed that on extraction from synthetic seawater higher Mg/Na, Ca/Mg, and Ca/Na selectivities were reached for JMT-based ABC extractants comprising VA 911 compared with those comprising DEHPA (Table 1). For MTCA-containing extractants there was no clear trend. We studied acidity changes in the aqueous phase during equilibration of ZnSO4 and ZnClz with LA, DEHPA, and ABC extractants comprising them. pH lowering was stronger for DEHPA and for DEHPA comprising ABC extractants. 3.2.3. Amine/Organic Acid Molar Ratio. Kholkin et al. (1988~)studied the extraction of CdC12 from ZnSO4 solution by 10.6 M trialkylamine, 0.3-1.2 M VIC-2 (abranched carboxylic acids), 10% isooctanoll, the diluent was not indicated. They reported the effect of the acid proportion in the extractant on back-extraction of the CdClz by NaOH (alongwith coextracted HC1). Compared on the same pH basis, higher amine proportions led to preferred distribution into the organic phase (Figure 4). A similar effect was found by Deptula (1967) extracting HzPtCb from HzS04 solutions by [TOA, di-n-butyl phosphate].
1072 Ind. Eng. Chem. Res., Vol. 33, No. 5, 1994 Table 6. Effect of TCA/DEHPA Molar Ratio on ZnSO4 and CuClz Extraction extractant compn TCA/DEHPA equilib org phase TCAD DEHPA" molar ratio ZnSOdn CuClf 0.009 0.5 0.1 5/ 1 0.5 0.5 l/l 0.098 0.070 0.5 1.0 112 0.147 0.25 0.5 1/2 0.018 0.5 1.5 113 0.188 0.167 0.5 113 0.011 Concentration (mol/kg).
Watanabe (1970) used 1-5 mM JMT, 0--60 mM DEHPA, CC41 for the extraction of In3+, Fe3+,Th(IV), and Ce3+ from their dilute sulfate solutions (0.01-8 mM). The effect of increasing the organic acid proportion was studied. For all the studied cations a minimum was observed at amine to organic acid molar ratio of -1. Liu et al. (1990) studied the extraction of Fe(II1) from its sulfate solutions (3-5 g/L) using t0-0.6 M N1923 (RR'CHNHz), 0.18 M DEHPA, octane]. Extraction decreases with increasing amine concentration up to -0.1 M and than increases. We tested the effect of amine to organic acid molar ratio on the extraction of ZnSO4 (40 "C, equilibrium aqueousphase concentration 2.5 mol/kg) and on the extraction of CuClz (ambient temperature, equilibrium aqueous-phase concentration 2.0 mol/kg). The extractant in both cases was composed of TCA and DEHPA in Parasol, and the organic- to aqueous-phase ratio was small. As shown in Table 6, ZnSO4 extraction increases with DEHPA concentration in the extractant, while CuClz extraction shows a maximum at an amine to acid molar ratio of 1/1. 3.2.4. Extractant Concentration. Grinstead et al. (1969) and Hernandez and Martinez (1981) studied the effect of extractant concentration on the extraction of alkali and alkali earth chlorides. On the extraction of NaCl (equilibrium aqueous-phase concentrations 0.1-5.0 M) and MgC12 (0.1-1.4 M) by [MTCA, EUD 0.1-0.5 M, toluene] (high distribution coefficients,convex distribution curves) the distribution coefficient(D) increasesslightly more than the extractant concentration. On the extraction of NaCl (equilibrium aqueous-phase concentrations of 0.1-5.0 M) EUD, 0.1-0.5 M toluene] by [2,2-dihexyl-l-aminooctane, (lowdistribution coefficients,concave distribution curves), D increases at a much higher rate than the extractant concentration. In equilibrium with concentrated aqueous phases, a 5-time increase in extractant concentration increased D by a factor of 35. Extraction of LiCl(O.05-1.0 M) by [JMT, NA, 0.2-1.0 M, toluene] shows an intermediate behavior. Sat0 and Yamamoto (1982) extracted chlorides of Mn, Cd, Ni, Co, Cu, and Zn (initial aqueous-phase concentration of 1 g/L) by [MTCA, LA, 0.01-0.2 M, benzene]. D dependence on extractant composition was nearly linear for most chlorides, while for CuClz extraction, D increases by a factor of 200 on increasing extractant concentration 20 times. 3.2.5. Diluent Effect. NaCl and MgClz were extracted by [MTCA, EUD, 0.48 M, diluentl. Extraction dependence on the diluent showed the sequence: amyl acetate > chloroform = toluene for NaCl and toluene 2 amyl acetate > chloroform for MgC12 (Grinstead et al., 1969). Extraction of MgClz by [MTCA, Acid 810, 0.5 M, diluentl showed the sequence toluene > nitrobenzene > n-hexane >> CC4 > chloroform (Hanson et al., 1975). 3.3. Temperature Effect. Grinstead et al. (1969) studied the effect of temperature on NaCl and MgClz
-
ZnS04 aqueous ( mol 1 Kg 1 Figure 5. ZnSO4 distribution into [MTCA, DEHPA] at 70 "C and 24 'C.
extraction by [JMT, NA, 1 M, toluenel and by [MTCA, EUD, 0.48 M, toluene]. Temperature elevation from 23 to 60 "C led to a decrease in extraction. This effect is stronger for NaCl than for MgC12 and more pronounced for the quaternary amine-containing extractant. Hernandez and Martinez (1981) found similar behavior for LiCl and LiN03 extraction by [JMT, NA, 1 M, toluene] at 5, 30, and 60 "C. The effect was stronger for LiN03. Small temperature effects were observed by Sato et al. (1980) on the extraction of transition metal chlorides (initial aqueous-phase concentrationsof 1g/L) by [MTCA, LA, 0.02 M, benzene] at 10-50 "C. Extraction of CuC12 and MnClz slightly decreases on temperature elevation while that of ZnClz and CoCl2 increases. NiC12 extraction shows no temperature effect in this range. We studied the effect of temperature on ZnSO4 extraction by [MTCA, DEHPA]. In equilibrium with aqueousphase solutions of up to saturation, higher distribution coefficients were found at 70 "C than at 24 "C (Figure 5). Fleitlich et al. (1990) studied Fe3+ extraction from aqueous solutions initially composed of 54 g/L AP+, 9.5 g/L Fe3+,and 40 g/L HC1. The extractants were trialkylamine carboxylates in VIC or in caprylic acid. Both show an almost linear increase in the Fe3+distribution curve on temperature elevation from 20 to 80 "C after which D starts to decrease. 3.4. Water Coextraction. Water coextracts with the salts into the ABC extractants. Water content of [JMT, NA, 1.0 M, toluene] in equilibrium with 3 M aqueous solutions of NaCland MgC12 was 0.7and 0.6 M, respectively (water to ABC molar ratio of -0.6). Higher water coextraction is observed in extraction by quaternary amine based extractants [MTCA, EUD, 0.48 M, toluene]. Water content of the NaCl- and MgClaloaded ABC extractants was 3.9 and 3.5 M, respectively, water to ABC molar ratio of about 7.5 (Grinstead et al., 1969). We found similar water coextraction on ZnSO4 extraction by [MTCA, DEHPA]. Liu et al. (1990) studied Fe3+ extraction from HzS04 solutions by [5% RR'CHNH2,5 % DEHPA, octane]. They found that for a constant HzS04 concentration of 0.27 M in the aqueous phase, water extraction decreases with increasing Fe3+concentration in the organic phase. They conclude that one atom of Fe3+displacesone H2O molecule. Kress et al. (1990)studied water coextractionwith CuClz, Cu(NO&, ZnClz, and Zn(NO312. The extractant was [TOA, 2-ethylhexanoic acid, 0.5 M, toluene]. A linear relationship was found between the copper salt extraction and the water coextraction. The H20/Cu molar ratio in the organic phase was 1.3for CuClz and 0.33 for Cu(N03)2. For the zinc salts, water coextraction with the nitrate was higher than with the chloride and there was no linear relationship.
Ind. Eng. Chem. Res., Vol. 33, No. 5,1994 1073 4. Extraction Mechanisms
Grinstead and co-workers (1969,1970; Davis and Grinstead, 19701, Hanson and Murthy (19741, Hernandez and Martinez (19811, and Kholkin et al. (1982,1988a) suggest mnRp"kpA(org)
+ Mnrn+Xmn-(aa =
m(Rp"kp)nX(org)
+ nMm(org) (1)
where A- and X" are the anions of the organic acid in the ABC extractant and of the mineral salt to be extracted, respectively, R,NHkp+ and Mm+are the corresponding cations and (aq) and (org) denote aqueous phase and organic phase, respectively. Grinstead and Hanson and their co-workers and Hernandez and Martinez studied extraction of alkali and alkali earth salts (mainly chlorides) while Kholkin et al. extracted transition metal salts. According to Grinstead, on equilibrating highly concentrated aqueous MgC12 solutions with ABC extractants composed of quaternary amine carboxylates MgClA(,,) may form. Hanson et al. (1975) refer the above stoichiometric extraction of MgClz to the participation of hydrolyzed species in the extracted complex and to the effect of water dissolved in the organic phase. Kholkin and co-workers (1988b,c; Belova et al., 1988) explain extraction of transition metal chlorides by the formation of anionic complexes [MCljIm-jthat bind to the amine. H(m-j)[MCljl(aq)+ (m -J')RP"kpNA(,,) = (Rp"kp)(mj)[MCljl (org) + (m - J')HA,org)(2) The [MClj]"+jstudied by Kholkin were [FeCbl-, [CdCbP, [PdC14I2-, and [PtCl6l2-. According to Sato and co-workers (1980,1982)extraction of Zn2+,Mn2+,Co2+,Ni2+,and Cu2+from chloride solutions by quaternary amine carboxylates follows 3R4NA(org)
+ Mc12(aq)
= R4N[MA3](org)
+ 2R4NC1(0rg)
(3)
For CdCl2 extraction, however, they suggest 2R4NA(,,,) + CdCl,(aq) = (R4N)2[CdC12AJ (erg)
(4)
amine and monoalkyl phosphate. They explain the extraction by the formation of RNH&K!4-(RNH3C1)4 with no participation of the organic acid. They claim, however, that the species formed contain more RNH3C1 molecules than the species formed in the absence of the organic acid. Davis and Grinstead (1970) conclude that RpNHkpC1 and MgA2, formed on MgCl2 extraction, are monomeric and not associated with one another. Hernandez and Martinez (1981) claim, however, that on the extraction of NaCl and KC1by [JMT, NAI, KA and NA form the trimers (NaA)3and (KA)3while on the extraction of LiCl dimers (LiA)2 are formed. Hare1 and Schmuckler (1987) studied aggregation in the organic phase obtained on CaCl2 extraction by ABC extractants comprising tricaprylylamine and 2-ethylhexanoic acid. Based on fluorescence excitation spectra of CaCl2-loaded organic phases, to which Rhodamine B hydrochloride was added, they describe water-containing mixed reverse micelles of low aggregation number (11-22 amphiphilic groups) comprising both functional groups. The salt is claimed to be dissolved in the polar core of the reverse micelle. Based on the distribution data they propose the empirical formula (R3NH+R'C00)2.2CaCl~3H20.For CuClz extraction by the same extractant Schmuckler and co-workers claim that the extracted salt forms complexes with the extractant components and these complexes form reverse micelles with unused extractant molecules at low extractant loading. The aggregation number according to vapor pressure osmometry is low (Kress et al. 1990). Liu et al. (1990) studied Fe3+ extraction from sulfate solutions by primary amine DEHPA mixtures. They describe the formation of [Fe(S04)Al [(RNH&where S04ln[HAlm-1 or [Fe(S04)0Hl[R"3)&%1n[HAIrn, m and n increase with the initial acidity of the aqueous phase. On the basis of laser light scattering they calculated the mean hydrodynamic radius of the reverse micelles formed to be about 30 A. In summary, various metal ion containing species were proposed, including MA,, [MAm+ili-,[MXkAJ m-(k+h) and [MXjIm-j with or without aggregation or interaction with unused extractant molecules. In certain cases there is no agreement between the authors as to the species formed, the degree of aggregation, and the interaction with the species comprising the anion of the extracted salt. This unclear picture is mainly due to the complexity of the system, to insufficient data, and to the large variety in the components comprising the ABC extractants in the various studies.
+
Schmuckler and co-workers (Kress et al., 1989, 1990) conclude that CuC12 is extracted by an ABC extractant composed of trioctylamine and 2-ethylhexanoic acid through the formation of (R3NH)dCuC12A21(erg) (as suggested by Sat0 for CdC12, but in conflict with Sato's finding for CuCl2). In a recent article (Cohen et al., 1991) they proposed [ ( R ~ N H + A - . H ~ O ) ~ C U C ~ ~ ~ R ~ N I ( ~ ~ ) . Many of the articles describe the formation of aggregates 5. Conclusions on the extraction of metal saltsby ABC extractants. Thus, The large variety of commercially available amines, according to Davis and Grinstead (1970) on extraction of organic acids, and diluents (many of which are well-known MgC12 from dilute solutions by quaternary amine carin metal ion extraction as single components) provide a boxylates, species comprising extracted ion are solvated new family of extractants with a wide range of properties by 2-3 unused extractant molecules. Kopacz and Kalewithout resorting to synthesis of new extractants. These mbkevich (1986a,b) studied extraction of transition metals multicomponent extractants are unique in being neutral from sulfate solutions by an extractant comprising a weak on one hand and forming a variety of complexes and ion amine, 3,4-dimethylaniline, and a carboxylic acid, benzoic pairs on the other. They combine high efficiency and or o-toluic acid in benzene. The complexes they identified selectivity in extraction of salts with reversibility that in the organic phase were ZnArHA-RNH2, CoA2.(HA)y provides for recovery of the extracted salt and for (RNH2)2, and [CuArRNHzIz. Geogia et al. (1984) conextractant regeneration by back-extraction with water. cluded that on the extraction of Zn2+and Cd2+by aliphatic The consumption of acids and bases and the formation of amine containing ABC extractants MAr3HA*R4NHgp unwanted salts are avoided. Understanding the effects of forms. For the heterocyclic amine (B) containing system the various parameters on the competing mechanisms they propose MAr2HA-2B. enables tailoring of acid-base couple extractants for many Gao and co-workers (1988) studied the extraction of hydrometallurgical and waste management processes. gold from chloride solutions by a mixture of a primary
1074 Ind. Eng. Chem. Res., Vol. 33, No. 5, 1994
The systems formed on equilibrating water-soluble cations (Mm+), water-soluble anions (X”), water, waterimmiscible amine (RpNHsp), organic acid (HA), and diluent are complex. The chemical properties of the system components, the acidity of the aqueous phase, common-ion effects, the amine to organic acid molar ratio, their concentration in the diluent, and the extraction temperature were all found to affect extraction mechanisms and thereby its efficiency and selectivity. A theoretical treatment of this complex system and an analysis of the results summarized above are provided in the next paper.
Nomenclature ABC: acid-base couple ABL: a-bromolauric acid Acid 810 a mixture of isooctanoic, isononanoic, and isodecanoic acid ALA: Amberlite LA-2 DEHPA bis(2-ethylhexyl) phosphate DEHPT: bis(2-ethylhexyl) dithiophosphate DHOA: 2,2-dihexyl-l-aminooctane DNNSA dinonylnaphthalenesulfonic acid EDTA: (ethylenedinitri1o)tetraacetic acid EUD ethylundecanoic acid JMT: Primene JMT, RR’R’’CNH2 LA: lauric acid MTCA methyltricaprylylammonium chloride N-1923: RR’CHNH2 NA: naphthenic acid, a mixture of bicyclic, 5-membered ring, and aliphatic acids QOA tetraoctylamine TBP: tributyl phosphate TCA: tricaprylylamine TEHA: tris(2-ethylhexy1)amine TOA trioctylamine VA 911: versatic acid, a mixture of Cs-C11 secondary and tertiary aliphatic acid VIC: a-branched carboxylic acids
Literature Cited Belova, V. V.; Kholkin, A. I.; Muhl, P.; Gloe, K.; Kholkina, V. N.; Khomchuk, T. V. A Study on Extracting Hexachloroplatinum and Tetrachloropalladium Acids with Salts of Tri-n-Octylamine and Organic Acids. Proc. Znt. Solvent Extr. Conf. 1988,ZZZ, 191194. Bressler, E.; Eyal, A. M. Extraction of ZnSOd by Acid Base Couple Extractants. Proc. Znt. Solvent Extr. Conf. 1993,1,549. Cohen, 0.;Arad, D.; Schmuckler, G. Extraction of Copper Salts with a Mixed Extractant (111): Aggregation and Molecular Structure. Solvent Extr. Zon Exch. 1992,9,703-716. Davis, J. C.; Grinstead, R. R. Mixed Ionic Solvent Systems. 111. Mechanism of the Extraction. J. Phys. Chem. 1970,74,147-151. Deptula, C. The Synergisticand AntagonisticEffect in the Extraction of Inorganic Compounds with a Mixture of Amines and Organophosphoric Acids. J. Znorg. Nucl. Chem. 1967,29,1097-1102. Eyal, A. M. Reversible Extractants for Acids and Processes Based on Them. Proc. Znt. Solv. Extr. Conf. 1993,3,1633. Eyal, A. M.; Baniel, A. Extraction of Strong Mineral Acids by Organic Acid-Base Couples. Znd. Eng. Chem. Process Des. Dev. 1982,21, 334-337. Eyal, A. M.; Baniel, A. M.; Hajdu, K. New Process for Recovery of Zinc Sulfate and Sulfuric Acid from Zinc Electrowinning Bleed Solutions. Solvent Extr. Zon Exch. 1990a,8, 209-222. Eyal, A. M.; Baniel, A. M.; Mizrahi, J. A New Approach to Treatment of Acid-Containing Waste Streams. In Emerging Technologies in Hazardous Waste Management; Tedder, D. W., Pohland, F. G., Eds.; American Chemical Society: Washington, DC, 1990b;pp 214-233. Eyal, A. M.; Arbel-Haddad,M.; Bressler,E. New Aspecta in Extraction by Acid-Base Couple Extractants. Proc. Znt. Solvent Ertr. Conf. 1990~, Part A, 333-337.
Fleitlich, I. Yu.; Luboshnikova, K. S.; Kholkin, A. I.; Pashkov, G. L.; Serbeev, V. V.; Kulmuchamedov, G. K.; Muhl, P.; Galontseva, T. V.; Zelenstova, L. V. Extraction of Iron from Chloride Solutions with Binary Extractants (Carboxylatesof Tertiary Amines). Proc. Znt. Solvent Extr. Conf. 1990,Part B, 1187. Gao, Z.; Sun, S.; Gai, H.; Yang, M.; Shen, J. Extraction Equilibria of Gold(II1) with a Mixture of Primary Amine N1923 and MonoalkylphosphoricAcid P538 in Kerosene. Proc. Znt. Solvent Extr. Conf. 1988,ZZZ, 210-211. Gogia, S . K.; Singh, D.; Singh, 0. V.; Tandon, S. N. Synergism in the Extraction of Zinc(I1) and Cadmium(I1) with Some Lower Fatty Acids in the Presence of Amines and their Separation. Solvent Extr. Zon Exch. 1984,2,899-992. Grinstead, R. R. Base Strength of Amines in Liquid-LiquidExtraction Systems. Solvent Extr. Chem., Proc. Znt. Conf. 1966,425-432. Grinstead, R. R.; Davis, J. C. Base Strength of Amine-Amine HydrochlorideSystemsinToluene. J. Phys. Chem. 1968,72,16301638. Grinstead, R. R.; Davis, J. C. Extraction by Phase Separation with Mixed Ionic Solvents. Recovery of Magnesium Chloride from Sea Water Concentrates. Znd. Eng. Chem. Prod. Res. Dev. 1970,9, 66-72. Grinstead, R. R.; Davis,J. C.; Lynn, S.; Charlesworth, R. K. Extraction by Phase Separation with Mixed Ionic Solvents. Descriptive Chemistry. Znd. Eng. Chem. Prod. Res. Dev. 1969,8,218-227. Hadjiev, D.; Galabova, C. Some Possibilities for Improvement of the Extraction Properties in Mixed Extraction Systems. Proc. Znt. Solvent Extr. Conf. 1988,Z, 301-304. Hanson, C.; Murthy, S. L. N. Recovery of Magnesium Chloride from Sea Water Concentrates. Proc. Znt. Solvent Extr. Conf. 1974,1, 779-790. Hanson, C.; Hughes,M. A.; Murthy, S. L. N. Extraction of Magnesium Chloride from Brines Using Mixed Ionic Extractants. J. Znorg. Nucl. Chem. 1975,37,191-198. Harel, G.; Schmuckler, G. Ion-Pair Extraction of Salts by Mixed Liquid Ion Exchangers. React. Polym. 1987,5,203-208. Harel, G.; Kress, N.; Schmuckler, G. Extraction of Copper Salts with a Mixed Extractant. Proc. Znt. Solvent Extr. Conf. 1988,Z , 224225. Hernandez, R. A.; Martinez, J. M. Extraction of Lithium and Magnesium Salta with Mixed Ionic Extractants. Znd.Eng. Chem. Process Des. Dev. 1981,20,698-704. Kalembkiewicz, J.; Kopacz, S. Synergistic Effects in Extraction of Mn(II),Fe(III),Co(II),Ni(II),Cu(II),andZn(II) IonswithMixtures of Aromatic Carboxylic Acids with Amines into Benzene. Proc. Znt. Solvent Extr. Conf. 1988,ZZZ, 291-293. Kalembkiewicz, J.; Kopacz, S. Extraction and Separation of Some Metala in Complex Extraction Systems with Carboxylic Acids. Rudy Met. Niezelaz. 1990,35,100-103. Kholkin, A. I.; Kuzmin, V. I. Binary Extraction. Russ. J. Znorg. Chem. 1982,27,1169-1171. Kholkin, A. I.; Kuzmin, V. I.; Protasova,N. V. The Binary Extraction of Acids. Russ. J . Znorg. Chem. 1986,31,708-710. Kholkin, A. I.; Kuzmin, V. I.; Protasova, N. V.; Logutenko, 0. A.; Pashkov, G. L.; Belova, V. V. Major Regularities of Binary Extraction. Proc. Znt. Solvent Extr. Conf. 1988a,Z, 170-175. Kholkin, A. I.; Fleitlich, I. Yu; Luboshnikova, K. S.; Poshkov, G. L.; Kulmukchamedov, G. K.; Zelentsova, L. V.; Muhl, P.; Gloe, K. Extraction Purification of Aluminium Solutions from Iron. Proc. Znt. Solvent Extr. Conf. 198813, ZZZ, 262-265. Kholkin, A. I.; Poshkov, G. L.; Dokuchayev, V. N.; Kuzmin, V. I.; Sergeyeva, V. V.; Protasova, N.V.; Luboshnikova, K.S.; Fleitlich, I. Yu; Norikov, L. K. The Extraction of Cadmium Chloride with Binary Extractants. Proc. Int. Solvent Extr. Conf. 19880,ZV, 299-301. Kogan, L.; Eyal, A. M. Unpublished results, 1993. Kress, N.; Harel, G.; Schmuckler, G. Extraction of Copper Salts with a Mixed Extractant. Solvent Extr. Zon Exch. 1989, 7,47-56. Kress, N.;Cohen, 0.; Schmuckler, G. Extraction of Copper Salts with a Mixed Extractant (11): Water Uptake and Osmometric Measurements. Solvent Extr. Zon Exch. 1990,8,477-490. Liu, H.; Yu, S.; Chen, J. Studies on Mechanism of Extraction of Iron (111)from Sulfate Solutions and Stripping with Sulfuric Acid by FT-IR and Laser Light Scattering Spectrometry. I1HDEHP and RNH2 as Extractant with Octane as Diluent. Proc. Znt. Solvent Extr. Conf. 1990,A, 853-858. Nishimura, S.; Watanabe, M. Jpn. Patent 76,134,390,1976. Sato, T.; Yamamoto, M. The Extraction ofBivaIentTransition Metals from Aqueous ChlorideSolutions by Long-chain Alkyl Quaternary Ammonium Carboxylates,Bull. Chem. SOC.Jpn. 1982,55,90-94.
Ind. Eng. Chem. Res., Vol. 33, No. 5, 1994 1075 Sato, T.; Yamamoto,M.; Watanabe, H. The Extraction of Divalent Manganese, Cobalt, Nickel, Copper, Zinc, Cadmium and Mercury from Aqueous solutions by Long-chain Alkylammoniw Carboxylates. Znt. Solvent Extr. Conf., [ R o c . ] 1980,paper 80-178. Shibata, J.; Kawabata, H.; Nishimura, S. Extraction of Magnesium Chloride from Sea Water with Mixed Ionic Extractants. Nippon Kinzoku Gakkaishi 1976,40,412-418. Watanabe, H.The Solvent Extraction of Metal Ions from Sulfuric Acid Solutions with a Mixed Extractant - Long-chain Primary Amineand Di-2-ethylhexylphosphoric Acid. Bull. Chem. SOC. Jpn. 1970,43,100-104.
Zhang, T.; Jiazan, N. Extraction of Copper (11) by Primary Amine N1923. Youse Jimhu 1982,40,73-77.
Received for review June 23, 1993 Revised manuscript received December 6 , 1993 Accepted January 4, 1994. Abstract published in Advance ACS Abstracts, March 15, 1994.
