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Solvent extraction equilibrium of nickel with LIX 54
Hydrometallurgy 48 Ž1998. 291–299
Solvent extraction equilibrium of nickel with LIX 54 F.J. Alguacil ) , A. Cobo Centro Nacional de InÕestigaciones Metalurgicas (CSIC), AÕda. Gregorio del Amo 8, Ciudad UniÕersitaria, 28040 Madrid, Spain Received 13 June 1997; revised 5 December 1997; accepted 11 December 1997
Abstract Nickel extraction from ammoniacal media, containing initially 0.5 grl of nickel, by LIX 54 in an aliphatic diluent, Iberfluid, has been studied as a function of aqueous pH, equilibration time, temperature, counter anion Žsulphate. and extractant concentration. The stripping of nickel from loaded organic phases using H 2 SO4 has also been studied as a function of acid concentration, equilibration time and temperature. Nickel extraction is very sensitive to equilibrium pH and the extraction decreases beyond pH 9.0. The increase of temperature decreases nickel extraction Ž D H8 s y44.8 kJrmol.. The presence of sulphate Žas ammonium sulphate. in the aqueous solution decreases nickel extraction. The extraction equilibrium constant for nickel was determined numerically to be 4 P 10y14 and experimental data can be explained assuming the formation of NiR 2 species in the organic phase ŽR represented the extractant.. Stripping of nickel can be achieved effectively using diluted H 2 SO4 solutions and temperature has little effect on nickel stripping Ž D H8 s 10.9 kJrmol.. q 1998 Elsevier Science B.V.
1. Introduction The dissolution of nickel from nickel-bearing raw materials is often carried out either by direct ammoniacal leaching or by acidic leaching followed by treatment of solutions with ammonia. In both cases, the metal is finally found in the aqueous solution as ammine complexes. Several methods are available for the separation–purification–recovery of nickel from such solutions. One of these methods, solvent extraction, is becoming of interest )
Corresponding author.
0304-386Xr98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 0 4 - 3 8 6 X Ž 9 7 . 0 0 1 0 3 - 5
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
292
due to the attractive characteristics of the operation Že.g., it was and it is widely used in the recovery of other metals: uranium, copper, etc.. despite certain disadvantages. In the case of nickel, there is information about the use of solvent extraction for the extraction of the metal from ammoniacal solutions, although extractants are often based on oxime reagents, including the newest LIX 87QN w1–14x. There is no the same degree of information about the use of b-diketones w3x in the extraction of nickel from ammoniacal media; the main advantage of this type of extractants is that they do not extract ammonia from aqueous solutions. The present study deals with the extraction of nickel from ammoniacalrammonium sulphate solutions using the commercially available LIX 54 b-diketone dissolved in a kerosene type diluent ŽIberfluid. as detailed below.
2. Experimental LIX 54 extractant was obtained from Henkel Ireland, and was used as received by diluting it to the desired concentration in Iberfluid. LIX 54 or LIX 54-100 as recently renamed contains b-diketones as the active substance. It has been reported that its composition is based on six isomeric 1-phenyldecane-1,3-diones, heptane-8,10-dione, 1,3-diphenylpropane-1,3-dione and an unknown compound. The available extractant also contains some hydrocarbons w15x. Iberfluid is a kerosene type diluent obtained from Caliro Sotelo ŽSpain., and has the following specifications: density 785 kgrm3 Ž208C., boiling range 210–2848C, flash point 968C, aromatic components - 2%. All other chemicals were of AR grade. Extraction and stripping experiments were carried out in separatory funnels thermostatted at the required temperature and mechanically shaken. In all cases, a phase ratio OrA of 1 was used. Nickel was analyzed by atomic absorption spectrometry.
3. Results and discussion 3.1. Effect of pH The extraction of nickel by chelating extractants, such as LIX 54, can be represented by the general equilibrium: q Ni 2q aq q 2HR org ° NiR 2 org q 2H aq
Ž 1.
where HR represents the extractant molecule and aq and org denote the aqueous and organic phases, respectively. It is shown from Eq. Ž1. that for every mol of nickel extracted into the organic phase, two protons are liberated into the aqueous phase. Thus, the acid content of the aqueous solution is one of the parameters controlling the reaction. Fig. 1 shows the variation in nickel extraction vs. pH. The extraction increases up to pH 8.5 and then decreases. This is due to the fact that at higher pH values the extractant cannot compete with the ammonium ions. Furthermore, the latter forms the nickel
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
293
Fig. 1. Effect of initial pH on nickel extraction. Organic phase: 10% vrv LIX 54 in Iberfluid. Aqueous phase: 0.5 grl Ni and 0.3 molrl ŽNH 4 . 2 SO4 . Temperature: 208C. Equilibration time: 20 min.
ammine complex with the metal ions in the aqueous solution thereby decreasing the extent of extraction. In the equilibrium of nickel with other chelating reagents Ži.e., oximes and b-diketones. it has been found that only nickel ion and not nickel ammine complex is extracted into the organic phase. Fig. 2 shows a point of inflection between pH 8.0 and 8.5. This could be explained by the fact that within this pH range, pH defined as: D pH s Ž pH init y pH eq .
Ž 2.
varies from 0.5 to 0.2 Žin the above equation, pH init is the initial pH and pH eq is the equilibrium pH. ŽFig. 2.. The phenomenon probably explains the changing nature of
Fig. 2. D pH vs. initial pH. Experimental conditions as in Fig. 1.
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
294
Fig. 3. Rate of extraction and stripping of nickel. Extraction: organic phase 10% vrv LIX 54 in Iberfluid. Stripping: organic phase as in extraction but loaded with 370 mgrl Ni. Temperature: 208C.
Ž . 2q aqueous nickel species from NiŽH 2 O. nŽNH 3 . 2q m to Ni NH 3 m . It has been shown that if . in the aqueous solution there are metal ions and ammonium ions ŽNHq 4 at a pH value where free ammonia ŽNH 3 . is produced, metal ammine complexes NiŽNH 3 . 2q to w x NiŽNH 3 . 2q m should be formed 16 . It was also shown that:
ž
E log D Ni pH
/
NH q 4
s n y m ave .
Ž 3.
where D is the metal distribution coefficient between two phases w16x. A plot of log D Ni vs. pH is parabolic due to the increase in the average number of ammonia ligands complexing the metal ion at increasing pH values. In the present extraction system, the optimum pH for nickel extraction is in the region of 8.5.
Table 1 Effect of temperature on the extraction of nickel T Ž8C.
Ni Žgrl aq .
Ni Žgrl org .
20 30 40 50 60
0.09 0.15 0.22 0.29 0.34
0.41 0.35 0.28 0.21 0.16
Aqueous phase: 0.5 grl Ni and 0.3 molrl ŽNH 4 . 2 SO4 , pH 9.0. Organic phase: 10% vrv Lix 54 in Iberfluid. Equilibration time: 10 min.
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
295
Table 2 Effect of temperature on the stripping of nickel T Ž8C.
Ni Žmgrl aq .
Ni Žmgrl org .
20 30 40 50 60
362.9 363.7 364.4 365.1 365.9
7.1 6.3 5.6 4.9 4.1
Aqueous phase: 0.1 molrl sulphuric acid. Organic phase: 10% vrv Lix 54 in Iberfluid loaded with 370 mgrl Ni. Equilibration time: 10 min.
3.2. Rate of extraction and stripping The data on the kinetics of extraction and stripping are important in the design of equipment since they affect the overall throughput and, consequently, the equipment dimensions. Fig. 3 shows the rate of extraction of nickel from 0.5 grl aqueous solution ŽpH s 8.5. by LIX 54, and the rate of stripping of the nickel from loaded organic by 0.1 molrl H 2 SO4 solution. In both cases, it can be seen that the equilibrium is reached within 10 min. Beyond this, no further improvement is found in either extraction or stripping rate. 3.3. Effect of temperature The effect of this variable on nickel extraction and stripping was studied. The results are shown in Tables 1 and 2. Table 1 shows that an increase in temperature brings about
Fig. 4. Arrhenius plot for nickel extraction. Experimental conditions as in Table 1. Dotted line shows 95% confidence interval.
296
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
Fig. 5. Arrhenius plot for nickel stripping. Experimental conditions as in Table 2. Dotted line shows 95% confidence interval.
a decrease in nickel extraction, whereas Table 2 shows a slight increase in nickel stripping with increase in temperature. The values of log D Ni Žfor extraction. or log 1rD Ni Žfor stripping. vs. 1000rT have been plotted for nickel extraction and stripping in Figs. 4 and 5. As stated in w1x, the linear relationship of log D Ni vs. 1000rT plots for complex formation should be an indication that only a single species is involved. This indirectly supports the assumption ŽEq. Ž1. and further data presented in this work. that only Ni 2q is extracted.
Fig. 6. The effect of ammonium sulphate concentration on nickel extraction. Organic phase: 10% vrv LIX 54 in Iberfluid. Aqueous phase: 0.5 grl Ni. Temperature: 208C. Equilibration time: 20 min.
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
297
Table 3 Effect of H 2 SO4 concentration on nickel stripping H 2 SO4 Žmolrl.
Ni Žmgrl aq .
Ni Žmgrl org .
% Ni stripping
0.025 0.050 0.075 0.1 0.2
363.0 362.9 364.0 362.9 362.8
7.0 7.1 6.0 7.1 7.2
98.10 98.08 98.38 98.08 98.05
Organic phase: 10% vrv Lix 54 in Iberfluid loaded with 370 mgrl Ni. Temperature: 208C. Equilibration time: 10 min.
Fig. 4 shows D H8 s y44.8 kJrmol indicating an exothermic reaction of extraction, whereas Fig. 5 shows D H8 s 10.9 kJrmol indicating the slightly endothermic character of the reaction. 3.4. Effect of ammonium sulphate The presence of various concentrations of this salt on nickel extraction by LIX 54 was also studied. Ammonium sulphate concentration was varied from 0.1 molrl to 1 molrl at a constant pH value of 8.5. Results obtained are shown in Fig. 6. The effect of increasing the concentration of ammonium sulphate in the aqueous solution is to decrease the percentage of nickel extraction. 3.5. Effect of H2 SO4 concentration on stripping Table 3 shows the effect of sulphuric acid concentration on stripping. Almost complete stripping is obtained within all the range of H 2 SO4 concentrations used showing the ease of nickel recovery from loaded organic phases. 3.6. Effect of extractant concentration The variation in nickel extraction with various LIX 54 concentrations has also been studied. Table 4 shows some of the results obtained. As expected, the nickel extraction increased with the increase in the extractant concentration. A plot of log D Ni vs. Žlog wHRx q pH.eq ŽFig. 7. shows that the slope is near 2, which demonstrates that the
Table 4 Effect of LIX 54 concentration on nickel extraction LIX 54 Ž% vrv.
Ni Žgrl org .
Ni Žgrl aq .
pH eq
2.5 5 10
0.11 0.32 0.41
0.39 0.18 0.09
8.15 8.23 8.27
Organic diluent: Iberfluid. Aqueous phase: 0.5 grl Ni and 0.3 molrl ŽNH 4 . 2 SO4 , pH: 8.50. Temperature: 208C. Equilibration time: 20 min.
298
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
Fig. 7. Variation in log D Ni vs. Žlog wHRxqpH.eq for nickel extraction by LIX 54. Aqueous phase: 0.5 grl Ni and 0.3 molrl ammonium sulphate. Organic phases: 2.5–10% vrv LIX 54 in Iberfluid. Temperature: 208C. Equilibration time: 10 min. Dotted line shows 95% confidence interval.
stoichiometry of the extracted species is represented by NiR 2 as shown in Eq. Ž1.. These experimental data were also treated numerically using the program LETAGROP-DISTR w17x. The best fit which was obtained confirmed the stoichiom-etry described in Eq. Ž1.; the value of log K ext s y13.295 " 0.072 Ž s Žlog K ext s 0.024.. and U s 0.111 Ž s s 0.08.. From this value is obtained DG8 s 74.2 kJrmol, and hence D S8 s y406 Jrmol K. The large positive value of DG8 is an indication of the high pH values necessary to allow Ni extraction to proceed, whereas the negative D S8 indicates that nickel is being transferred from a highly disordered state to one of a greater order.
Fig. 8. Loading capacity of LIX 54 in Iberfluid.
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
299
Further experiments were carried out to obtain information on the maximum loading of a LIX 54 solution. These experiments were carried out by contacting for 20 min a 10% vrv LIX 54 solution with fresh aqueous phases containing 1 grl Ni and 0.3 molrl ŽNH 4 . 2 SO4 at a pH of 8.6 at an organic:aqueous phase ratio of 1. A maximum loading of near 2.75 grl Ni was reached after six extraction stages ŽFig. 8.. 4. Conclusions The extraction of nickel with LIX 54 increases with pH value, reaching a maximum in the zone of pH 8.5 and subsequently decreases. The decrease in extraction is attributable to the formation of non-extractable nickel ammine complexes at higher aqueous pH. There is a decrease in nickel extraction with temperature Žexothermic reaction.. Numerical treatment of experimental data showed that nickel extraction can be explained by the formation of NiR 2 species in the organic phase Ž K ext s 4 P 10y1 4 .. Nickel stripping from loaded organic solutions of LIX 54 in Iberfluid can be readily achieved with H 2 SO4 solutions; the extent of stripping is almost independent of the acid concentration Ž0.025–0.2 molrl.. There is a slight increase in nickel stripping with increasing temperature. Acknowledgements To the CSIC ŽSpain. for support to carry out this work. References w1x N.M. Rice, M. Nedved, G.M. Ritcey, Hydrometallurgy 3 Ž1978. 35–54. w2x G.M. Ritcey, A.W. Ashbrook, Solvent Extraction. Principles and Applications to Process Metallurgy. Part II. Elsevier, Amsterdam, 1979, pp. 279–361. w3x S. Przeszlakowski, H. Wydra, Hydrometallurgy 8 Ž1982. 49–64. w4x G.M. Ritcey, in: T.C. Lo, M.H.I. Baird, C. Hanson ŽEds.., Handbook of Solvent Extraction, Wiley, New York, 1983, pp. 673–687. w5x W.C. Cooper, Y.F. Mak, Solvent Extr. Ion Exch. 2 Ž7–8. Ž1984. 959–984. w6x K. Inoue, H. Tsunomachi, Hydrometallurgy 13 Ž1984. 73–87. w7x L.R. Penner, J.H. Rusell, Solvent Extr. Ion Exch. 9 Ž3. Ž1991. 403–422. w8x C. Pazos, J.P.S. Curieses, J. Coca, Solvent Extr. Ion Exch. 9 Ž4. Ž1991. 569–592. w9x M. Cox, in: J. Rydberg, C. Musikas, G.R. Choppin ŽEds.., Principles and Practices of Solvent Extraction, Marcel Dekker, New York, 1992, pp. 357–412. w10x K.C. Nathsarma, P.V.R. Bhaskara Sarma, Hydrometallurgy 33 Ž1993. 197–210. w11x J. Szymanowski, Hydroxyoximes and Copper Hydrometallurgy, Chap. IV, CRC Press, Boca Raton, FL, 1993. w12x M.J. Price, J.G. Reid, in: D.H. Logsdail, M.J. Slater ŽEds.., Solvent Extraction in the Process Industries, Vol. 1, Elsevier, London Ž1993. pp. 159–166. w13x P.V.R. Bhaskara Sarma, K.C. Nathsarma, Hydrometallurgy 42 Ž1996. 83–91. w14x A. Sandhibigraha, P.V.R. Bhaskara Sarma, Hydrometallurgy 45 Ž1997. 211–226. w15x E. Dziwinski, J. Szymanowski, Solvent Extr. Ion Exch. 14 Ž2. Ž1996. 219–226. w16x K.S. Rao, P.V.R.B. Sarma, P.K. Jena, Erzmetall 43 Ž1990. 366–369. w17x D.H. Liem, Acta Chem. Scand. 25 Ž1971. 1521–1534.
Solvent extraction equilibrium of nickel with LIX 54 F.J. Alguacil ) , A. Cobo Centro Nacional de InÕestigaciones Metalurgicas (CSIC), AÕda. Gregorio del Amo 8, Ciudad UniÕersitaria, 28040 Madrid, Spain Received 13 June 1997; revised 5 December 1997; accepted 11 December 1997
Abstract Nickel extraction from ammoniacal media, containing initially 0.5 grl of nickel, by LIX 54 in an aliphatic diluent, Iberfluid, has been studied as a function of aqueous pH, equilibration time, temperature, counter anion Žsulphate. and extractant concentration. The stripping of nickel from loaded organic phases using H 2 SO4 has also been studied as a function of acid concentration, equilibration time and temperature. Nickel extraction is very sensitive to equilibrium pH and the extraction decreases beyond pH 9.0. The increase of temperature decreases nickel extraction Ž D H8 s y44.8 kJrmol.. The presence of sulphate Žas ammonium sulphate. in the aqueous solution decreases nickel extraction. The extraction equilibrium constant for nickel was determined numerically to be 4 P 10y14 and experimental data can be explained assuming the formation of NiR 2 species in the organic phase ŽR represented the extractant.. Stripping of nickel can be achieved effectively using diluted H 2 SO4 solutions and temperature has little effect on nickel stripping Ž D H8 s 10.9 kJrmol.. q 1998 Elsevier Science B.V.
1. Introduction The dissolution of nickel from nickel-bearing raw materials is often carried out either by direct ammoniacal leaching or by acidic leaching followed by treatment of solutions with ammonia. In both cases, the metal is finally found in the aqueous solution as ammine complexes. Several methods are available for the separation–purification–recovery of nickel from such solutions. One of these methods, solvent extraction, is becoming of interest )
Corresponding author.
0304-386Xr98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 0 4 - 3 8 6 X Ž 9 7 . 0 0 1 0 3 - 5
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
292
due to the attractive characteristics of the operation Že.g., it was and it is widely used in the recovery of other metals: uranium, copper, etc.. despite certain disadvantages. In the case of nickel, there is information about the use of solvent extraction for the extraction of the metal from ammoniacal solutions, although extractants are often based on oxime reagents, including the newest LIX 87QN w1–14x. There is no the same degree of information about the use of b-diketones w3x in the extraction of nickel from ammoniacal media; the main advantage of this type of extractants is that they do not extract ammonia from aqueous solutions. The present study deals with the extraction of nickel from ammoniacalrammonium sulphate solutions using the commercially available LIX 54 b-diketone dissolved in a kerosene type diluent ŽIberfluid. as detailed below.
2. Experimental LIX 54 extractant was obtained from Henkel Ireland, and was used as received by diluting it to the desired concentration in Iberfluid. LIX 54 or LIX 54-100 as recently renamed contains b-diketones as the active substance. It has been reported that its composition is based on six isomeric 1-phenyldecane-1,3-diones, heptane-8,10-dione, 1,3-diphenylpropane-1,3-dione and an unknown compound. The available extractant also contains some hydrocarbons w15x. Iberfluid is a kerosene type diluent obtained from Caliro Sotelo ŽSpain., and has the following specifications: density 785 kgrm3 Ž208C., boiling range 210–2848C, flash point 968C, aromatic components - 2%. All other chemicals were of AR grade. Extraction and stripping experiments were carried out in separatory funnels thermostatted at the required temperature and mechanically shaken. In all cases, a phase ratio OrA of 1 was used. Nickel was analyzed by atomic absorption spectrometry.
3. Results and discussion 3.1. Effect of pH The extraction of nickel by chelating extractants, such as LIX 54, can be represented by the general equilibrium: q Ni 2q aq q 2HR org ° NiR 2 org q 2H aq
Ž 1.
where HR represents the extractant molecule and aq and org denote the aqueous and organic phases, respectively. It is shown from Eq. Ž1. that for every mol of nickel extracted into the organic phase, two protons are liberated into the aqueous phase. Thus, the acid content of the aqueous solution is one of the parameters controlling the reaction. Fig. 1 shows the variation in nickel extraction vs. pH. The extraction increases up to pH 8.5 and then decreases. This is due to the fact that at higher pH values the extractant cannot compete with the ammonium ions. Furthermore, the latter forms the nickel
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
293
Fig. 1. Effect of initial pH on nickel extraction. Organic phase: 10% vrv LIX 54 in Iberfluid. Aqueous phase: 0.5 grl Ni and 0.3 molrl ŽNH 4 . 2 SO4 . Temperature: 208C. Equilibration time: 20 min.
ammine complex with the metal ions in the aqueous solution thereby decreasing the extent of extraction. In the equilibrium of nickel with other chelating reagents Ži.e., oximes and b-diketones. it has been found that only nickel ion and not nickel ammine complex is extracted into the organic phase. Fig. 2 shows a point of inflection between pH 8.0 and 8.5. This could be explained by the fact that within this pH range, pH defined as: D pH s Ž pH init y pH eq .
Ž 2.
varies from 0.5 to 0.2 Žin the above equation, pH init is the initial pH and pH eq is the equilibrium pH. ŽFig. 2.. The phenomenon probably explains the changing nature of
Fig. 2. D pH vs. initial pH. Experimental conditions as in Fig. 1.
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
294
Fig. 3. Rate of extraction and stripping of nickel. Extraction: organic phase 10% vrv LIX 54 in Iberfluid. Stripping: organic phase as in extraction but loaded with 370 mgrl Ni. Temperature: 208C.
Ž . 2q aqueous nickel species from NiŽH 2 O. nŽNH 3 . 2q m to Ni NH 3 m . It has been shown that if . in the aqueous solution there are metal ions and ammonium ions ŽNHq 4 at a pH value where free ammonia ŽNH 3 . is produced, metal ammine complexes NiŽNH 3 . 2q to w x NiŽNH 3 . 2q m should be formed 16 . It was also shown that:
ž
E log D Ni pH
/
NH q 4
s n y m ave .
Ž 3.
where D is the metal distribution coefficient between two phases w16x. A plot of log D Ni vs. pH is parabolic due to the increase in the average number of ammonia ligands complexing the metal ion at increasing pH values. In the present extraction system, the optimum pH for nickel extraction is in the region of 8.5.
Table 1 Effect of temperature on the extraction of nickel T Ž8C.
Ni Žgrl aq .
Ni Žgrl org .
20 30 40 50 60
0.09 0.15 0.22 0.29 0.34
0.41 0.35 0.28 0.21 0.16
Aqueous phase: 0.5 grl Ni and 0.3 molrl ŽNH 4 . 2 SO4 , pH 9.0. Organic phase: 10% vrv Lix 54 in Iberfluid. Equilibration time: 10 min.
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
295
Table 2 Effect of temperature on the stripping of nickel T Ž8C.
Ni Žmgrl aq .
Ni Žmgrl org .
20 30 40 50 60
362.9 363.7 364.4 365.1 365.9
7.1 6.3 5.6 4.9 4.1
Aqueous phase: 0.1 molrl sulphuric acid. Organic phase: 10% vrv Lix 54 in Iberfluid loaded with 370 mgrl Ni. Equilibration time: 10 min.
3.2. Rate of extraction and stripping The data on the kinetics of extraction and stripping are important in the design of equipment since they affect the overall throughput and, consequently, the equipment dimensions. Fig. 3 shows the rate of extraction of nickel from 0.5 grl aqueous solution ŽpH s 8.5. by LIX 54, and the rate of stripping of the nickel from loaded organic by 0.1 molrl H 2 SO4 solution. In both cases, it can be seen that the equilibrium is reached within 10 min. Beyond this, no further improvement is found in either extraction or stripping rate. 3.3. Effect of temperature The effect of this variable on nickel extraction and stripping was studied. The results are shown in Tables 1 and 2. Table 1 shows that an increase in temperature brings about
Fig. 4. Arrhenius plot for nickel extraction. Experimental conditions as in Table 1. Dotted line shows 95% confidence interval.
296
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
Fig. 5. Arrhenius plot for nickel stripping. Experimental conditions as in Table 2. Dotted line shows 95% confidence interval.
a decrease in nickel extraction, whereas Table 2 shows a slight increase in nickel stripping with increase in temperature. The values of log D Ni Žfor extraction. or log 1rD Ni Žfor stripping. vs. 1000rT have been plotted for nickel extraction and stripping in Figs. 4 and 5. As stated in w1x, the linear relationship of log D Ni vs. 1000rT plots for complex formation should be an indication that only a single species is involved. This indirectly supports the assumption ŽEq. Ž1. and further data presented in this work. that only Ni 2q is extracted.
Fig. 6. The effect of ammonium sulphate concentration on nickel extraction. Organic phase: 10% vrv LIX 54 in Iberfluid. Aqueous phase: 0.5 grl Ni. Temperature: 208C. Equilibration time: 20 min.
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
297
Table 3 Effect of H 2 SO4 concentration on nickel stripping H 2 SO4 Žmolrl.
Ni Žmgrl aq .
Ni Žmgrl org .
% Ni stripping
0.025 0.050 0.075 0.1 0.2
363.0 362.9 364.0 362.9 362.8
7.0 7.1 6.0 7.1 7.2
98.10 98.08 98.38 98.08 98.05
Organic phase: 10% vrv Lix 54 in Iberfluid loaded with 370 mgrl Ni. Temperature: 208C. Equilibration time: 10 min.
Fig. 4 shows D H8 s y44.8 kJrmol indicating an exothermic reaction of extraction, whereas Fig. 5 shows D H8 s 10.9 kJrmol indicating the slightly endothermic character of the reaction. 3.4. Effect of ammonium sulphate The presence of various concentrations of this salt on nickel extraction by LIX 54 was also studied. Ammonium sulphate concentration was varied from 0.1 molrl to 1 molrl at a constant pH value of 8.5. Results obtained are shown in Fig. 6. The effect of increasing the concentration of ammonium sulphate in the aqueous solution is to decrease the percentage of nickel extraction. 3.5. Effect of H2 SO4 concentration on stripping Table 3 shows the effect of sulphuric acid concentration on stripping. Almost complete stripping is obtained within all the range of H 2 SO4 concentrations used showing the ease of nickel recovery from loaded organic phases. 3.6. Effect of extractant concentration The variation in nickel extraction with various LIX 54 concentrations has also been studied. Table 4 shows some of the results obtained. As expected, the nickel extraction increased with the increase in the extractant concentration. A plot of log D Ni vs. Žlog wHRx q pH.eq ŽFig. 7. shows that the slope is near 2, which demonstrates that the
Table 4 Effect of LIX 54 concentration on nickel extraction LIX 54 Ž% vrv.
Ni Žgrl org .
Ni Žgrl aq .
pH eq
2.5 5 10
0.11 0.32 0.41
0.39 0.18 0.09
8.15 8.23 8.27
Organic diluent: Iberfluid. Aqueous phase: 0.5 grl Ni and 0.3 molrl ŽNH 4 . 2 SO4 , pH: 8.50. Temperature: 208C. Equilibration time: 20 min.
298
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
Fig. 7. Variation in log D Ni vs. Žlog wHRxqpH.eq for nickel extraction by LIX 54. Aqueous phase: 0.5 grl Ni and 0.3 molrl ammonium sulphate. Organic phases: 2.5–10% vrv LIX 54 in Iberfluid. Temperature: 208C. Equilibration time: 10 min. Dotted line shows 95% confidence interval.
stoichiometry of the extracted species is represented by NiR 2 as shown in Eq. Ž1.. These experimental data were also treated numerically using the program LETAGROP-DISTR w17x. The best fit which was obtained confirmed the stoichiom-etry described in Eq. Ž1.; the value of log K ext s y13.295 " 0.072 Ž s Žlog K ext s 0.024.. and U s 0.111 Ž s s 0.08.. From this value is obtained DG8 s 74.2 kJrmol, and hence D S8 s y406 Jrmol K. The large positive value of DG8 is an indication of the high pH values necessary to allow Ni extraction to proceed, whereas the negative D S8 indicates that nickel is being transferred from a highly disordered state to one of a greater order.
Fig. 8. Loading capacity of LIX 54 in Iberfluid.
F.J. Alguacil, A. Cobo r Hydrometallurgy 48 (1998) 291–299
299
Further experiments were carried out to obtain information on the maximum loading of a LIX 54 solution. These experiments were carried out by contacting for 20 min a 10% vrv LIX 54 solution with fresh aqueous phases containing 1 grl Ni and 0.3 molrl ŽNH 4 . 2 SO4 at a pH of 8.6 at an organic:aqueous phase ratio of 1. A maximum loading of near 2.75 grl Ni was reached after six extraction stages ŽFig. 8.. 4. Conclusions The extraction of nickel with LIX 54 increases with pH value, reaching a maximum in the zone of pH 8.5 and subsequently decreases. The decrease in extraction is attributable to the formation of non-extractable nickel ammine complexes at higher aqueous pH. There is a decrease in nickel extraction with temperature Žexothermic reaction.. Numerical treatment of experimental data showed that nickel extraction can be explained by the formation of NiR 2 species in the organic phase Ž K ext s 4 P 10y1 4 .. Nickel stripping from loaded organic solutions of LIX 54 in Iberfluid can be readily achieved with H 2 SO4 solutions; the extent of stripping is almost independent of the acid concentration Ž0.025–0.2 molrl.. There is a slight increase in nickel stripping with increasing temperature. Acknowledgements To the CSIC ŽSpain. for support to carry out this work. References w1x N.M. Rice, M. Nedved, G.M. Ritcey, Hydrometallurgy 3 Ž1978. 35–54. w2x G.M. Ritcey, A.W. Ashbrook, Solvent Extraction. Principles and Applications to Process Metallurgy. Part II. Elsevier, Amsterdam, 1979, pp. 279–361. w3x S. Przeszlakowski, H. Wydra, Hydrometallurgy 8 Ž1982. 49–64. w4x G.M. Ritcey, in: T.C. Lo, M.H.I. Baird, C. Hanson ŽEds.., Handbook of Solvent Extraction, Wiley, New York, 1983, pp. 673–687. w5x W.C. Cooper, Y.F. Mak, Solvent Extr. Ion Exch. 2 Ž7–8. Ž1984. 959–984. w6x K. Inoue, H. Tsunomachi, Hydrometallurgy 13 Ž1984. 73–87. w7x L.R. Penner, J.H. Rusell, Solvent Extr. Ion Exch. 9 Ž3. Ž1991. 403–422. w8x C. Pazos, J.P.S. Curieses, J. Coca, Solvent Extr. Ion Exch. 9 Ž4. Ž1991. 569–592. w9x M. Cox, in: J. Rydberg, C. Musikas, G.R. Choppin ŽEds.., Principles and Practices of Solvent Extraction, Marcel Dekker, New York, 1992, pp. 357–412. w10x K.C. Nathsarma, P.V.R. Bhaskara Sarma, Hydrometallurgy 33 Ž1993. 197–210. w11x J. Szymanowski, Hydroxyoximes and Copper Hydrometallurgy, Chap. IV, CRC Press, Boca Raton, FL, 1993. w12x M.J. Price, J.G. Reid, in: D.H. Logsdail, M.J. Slater ŽEds.., Solvent Extraction in the Process Industries, Vol. 1, Elsevier, London Ž1993. pp. 159–166. w13x P.V.R. Bhaskara Sarma, K.C. Nathsarma, Hydrometallurgy 42 Ž1996. 83–91. w14x A. Sandhibigraha, P.V.R. Bhaskara Sarma, Hydrometallurgy 45 Ž1997. 211–226. w15x E. Dziwinski, J. Szymanowski, Solvent Extr. Ion Exch. 14 Ž2. Ž1996. 219–226. w16x K.S. Rao, P.V.R.B. Sarma, P.K. Jena, Erzmetall 43 Ž1990. 366–369. w17x D.H. Liem, Acta Chem. Scand. 25 Ž1971. 1521–1534.