ISSN 1067-8212, Russian Journal of Non-Ferrous Metals, 2016, Vol. 57, No. 7, pp. 681–685. © Allerton Press, Inc., 2016. Original Russian Text © A.A. Susoyeva, A.A. Blokhin, Yu.V. Murashkin, M.A. Mikhaylenko, 2016, published in Izvestiya Vysshikh Uchebnykh Zavedenii, Tsvetnaya Metallurgiya, 2016, No. 5, pp. 35–41.
METALLURGY OF RARE AND NOBLE METALS
Sorption Recovery of Rhodium(III) from Multicomponent Chloride Solutions in the Presence of Tin(II) Chloride A. A. Susoyevaa, *, A. A. Blokhina, **, Yu. V. Murashkina, ***, and M. A. Mikhaylenkob, **** aSt.
Petersburg State Technological Institute (Technical University), St. Petersburg, 190013 Russia b Representative Office of Purolite Ltd. in Russia, Moscow, 113096 Russia *e-mail:
[email protected] **e-mail:
[email protected] ***e-mail:
[email protected] ****e-mail:
[email protected] Received April 3, 2015; in final form, May 20, 2015; accepted for publication May 25, 2015
Abstract—The influence of tin (II) chloride additives on sorption of Rh(III) on the Purolite S920 ion exchange resin with isothiouronium groups, the Purolite S985 weak base anion exchange resin, and the Purolite A500 strong base anion exchange resin is investigated. It is established that the introduction of SnCl2 leads to a substantial increase in selectivity of all tested ion exchange resins to Rh(III) and in the sorption rate of Rh(III) on S985 and S920 ion exchange resins. The optimal dosage of SnCl2 (0.01 mol/L) at which the distribution coefficients of Rh(III) during sorption for all tested ion exchange resins reach maximal values is determined. It is shown that almost quantitative recovery of Rh(III) is attained when passing the multicomponent chloride solution of the composition (g/L) 0.2 Rh(III), 72.9 HCl, 53.5 NH4Cl, 2.7 Al(III), 1.23 Fe(III) and 5.9 Sn(IV) with the SnCl2 additive through the Purolite S920 ion exchange resin with isothiouronium groups. Desorption of Rh(III) from the Purolite S920 saturated ionite with the acidified thiourea solution is incomplete, no greater than 60%. Keywords: Rh(III), tin(II) chloride, solutions, recovery, sorption, desorption, ion exchange resins, selectivity, kinetics DOI: 10.3103/S1067821216070142
INTRODUCTION Rhodium belongs to platinum group metals (PGMs), the recovery of which from solutions having a complex composition, in particular, from used refining solutions and solutions forming in the course of hydrometallurgical processing of automobile catalysts that have served their time, is especially difficult [1]. Even the application of such a generally selective recovery method of metal ions such as sorption on chelate-forming ion-exchange resins does not provide deep recovery of rhodium from chloride solutions of a complex composition [2, 3]. This is apparently caused by the kinetic inertness of aqua-chloride complexes of Rh(III), in a form of which it is present in production hydrochloric acid solutions. We can elevate the lability of Rh(III) compounds in solutions and, thereby, their reaction ability by introducing tin(II) chlorides into the solutions, during the interaction of which with the PGMs, including Rh(III), form tin halide complexes having a high lability. The internal coordination sphere of such complexes includes SnCl 3− ions [4]. This procedure (introduction of tin (II) chloride into solutions) has become
widespread in analytical chemistry of PGMs, including rhodium, for their preliminary concentration, mainly with the help of liquid extraction methods [5]. There are the publications in which the possibility of the extraction recovery of Rh(III) in a form of its complexes with tin(II) chloride is also considered for solving the process problems [6–8]. Considerably fewer publications are devoted to the investigation of the influence of SnCl2 additives on recovery of Rh(III) with the help of ion-exchange sorbents [9–11]. For example, the authors of [9, 10], by the example of sorption of Rh(III) on several strong-base and weakbase anion-exchange resins as well as modified chitosan from hydrochloric acid solutions, showed that the distribution coefficients of Rh(III) noticeably increase in the presence of SnCl2, while the authors of [11] considered the sorption mechanism of tin chloride complexes of rhodium on silica containing covalently fastened N-(2,6-dimethyl-4-methylenetriphenyl phosphonium chloride)-N'-propylthiourea groups. The objective of this study was to evaluate the possibility of increasing the recovery depth of Rh(III) from multicomponent chloride solutions by means of
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its sorption on certain ionites with various functional groups in a form of complexes with tin(II) chloride. EXPERIMENTAL We tested samples of the following industrial ionexchange resins: Purolite S920 ion-exchange resin as the representative of chelate-forming ion-exchange resins with isothiourea functional groups, which in general manifest pronounced selectivity with respect to PGMs [12]; Purolite S985 weak base anion exchange resin with secondary and primary amino groups, which showed the highest selectivity to rhodium during sorption from multicomponent chloride solutions among a series of ion-exchange resins according to the data [3]; and Purolite A500/2788 strong base anion exchange resin able to sorb chloride (and aqua-chloride) PGM complexes according to the purely anion-exchange mechanism. The head solution of tin (II) chloride with a concentration of 200 g/L was prepared by dissolving a charge of reagent grade salt in a 6 M hydrochloric acid solution. Experiments were performed in static and dynamic conditions. In all cases, after introducing SnCl2, solutions were held in a water bath at 45°C for 0.5 h to transfer Rh(III) into the form of a “red” complex, cooled, and brought into contact with ion-exchange resins. In static experiments, the charges of ion-exchange resins were placed into flasks and brought into contact with the rhodium-containing solution of the specified composition; the content of flasks was stirred using a Memmert ONE 14 shaker at room temperature for 72 h (preliminary experiments showed that this time is sufficient to establish equilibrium). Upon expiration of the noted time, solutions were separated from ionexchange resins and analyzed for the presence of Rh(III). The mass capacities of ion-exchange resins (mg rhodium/g dry ion-exchange resin) were calculated by the variation in the Rh(III) concentration allowing for the ion-exchange resin charge and solution volume; then they were recalculated to the bulk capacity (mg rhodium/mL swollen ion-exchange resin) allowing for the specific volume of ionexchange resins. The distribution coefficients of Rh(III) were determined as the ratio of the bulk ionexchange resin capacity with respect to Rh(III) to the equilibrium concentration of the latter in the solution. The sorption kinetics of Rh(III) was investigated using the confined volume method. The rhodiumcontaining solution with a volume of 50 mL was introduced into a glass. The ion-exchange resin charges 0.5 g each recalculated to the dry ion-exchange resin weight were introduced into the glass, and a stirrer was switched on. Solution specimens, which were analyzed for the presence of Rh(III), were sampled after definite time intervals. The total volume of sampled
specimens did not exceed 6% of the total solution volume. Experiments in dynamic conditions were performed in a column containing 7 mL of the ionexchange resin (S920) with the ratio of the ionexchange resin layer height to the inner column diameter of 10 : 1. The average rate of passage of the solution during sorption and desorption of the S920 ionexchange resin was ~7 mL/h (1 sp. vol./h). Solution specimens were sampled at the column output and analyzed for the presence of Rh(III). To evaluate the concentration of Rh(III), we used photocolorimetric analysis, which is based on the measurement of the optical density of solutions containing compounds forming during the interaction of Rh(III) with tin(II) chloride and iodide ion [13]. When determining Rh(III) in thiourea solutions, specimens were preliminarily treated with aqua regia to decompose thiourea. RESULTS AND DISCUSSION The completeness of transformation of metal ions into the form of certain complexes is primarily determined by the concentration of a free ligand, tin(II) chloride in our case. Indeed, if the ion-exchange resin manifests an increased selectivity to tin chloride complexes of Rh(III), it is clear that the higher the concentration of introduced SnCl2, the better Rh(III) will be sorbed, until it is completely transferred into the form of the coordination-saturated tin-chloride complex. According to [14], rhodium in chloride solutions can form not only complexes, in which rhodium is in oxidation state III, of the [Rh(SnCl3)nCl6–n]3– type with tin(II) chloride, where n can take the values from 1 to 5 depending on the amount of introduced SnCl2, among which the [Rh(SnCl3)3Cl3]3– complex is the most stable, but also a complex of Rh(I) of the composition [Rh(SnCl3)5]4–, which is formed and prevalent in solutions with molar ratio [Sn] : [Rh] ≥ 6 : 1. In connection with this fact, when performing the initial stage of this series of investigations, we studied the influence of the amount of introduced SnCl2 on sorption of Rh(III) on selected ion-exchange resins from solutions with a constant HCl concentration of 2, 4, and 6 mol/L. Our results showed that the HCl concentration in this range does not substantially affect the trend of dependences of distribution coefficients of Rh(III). Figure 1 shows the data on the influence of tin(II) chloride on distribution coefficients of Rh(III) during sorption on selected ion-exchange resins from solutions with the hydrochloric acid concentration of 4 mol/L. Their analysis shows that the distribution coefficients of Rh(III) on all studied ion-exchange resins rise more or less abruptly upon introducing SnCl2 into the solutions. This tendency manifests itself especially clearly during sorption of Rh(III) on the A500 strong base anion exchange resin as well as on the S920 ion-exchange resin with isothiourea groups.
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Fig. 1. Dependence of distribution coefficients of Rh(III) during sorption on ion-exchange resins A500 (1), S985 (2), and S920 (3) on the SnCl2 concentration from 4 M hydrochloric acid. Concentration of Rh(III) in the initial solution is 1.4 mmol/L.
Fig. 2. Dependence of distribution coefficients of Rh(III) during sorption on ion-exchange resins A500 (1), S985 (2), and S920 (3) on the concentration of tin(IV) chloride from 4 M hydrochloric acid in the presence of 0.02 mmol/L tin(II) chloride. Concentration of Rh(III) in the initial solution is 1.4 mmol/L.
The distribution coefficients of Rh(III) for all approved ion-exchange resins reach maximal values at the SnCl2 concentration of 0.01 mol/L, i.e., at molar ratio Rh : SnCl2 = ~1 : 7.1. The ability of A500 and S985 ion-exchange resins to sorb Rh(III) starts to decrease with the further increase in the concentration of introduced tin(II) chloride, and that of the A500 strong base anion exchange resin decreases more abruptly, while that of the S920 chelate-forming ionexchange resin remains at the same level. It seems likely that the appearance of Rh(III) chloride in solutions, mainly due to the partial oxidation of tin(II) chloride with dissolved oxygen in the course of contact of solutions with ion-exchange resins under intense stirring, which is accompanied by aeration of solutions as well as possibly oxidation of tin(II) chloride during the formation of the [Rh(SnCl5)]4– tin chloride complex [14], can be the cause of reduction of the ability of ion-exchange resins to sorb Rh(III). It is natural that the concentration of tin (IV) chloride should increase with an increase in amount of introduced tin(II) chloride. Tin(IV) chloride is present in hydrochloric acid solutions in the form of the SnCl 62 − anion complex having high affinity to anion-exchange resins [15] and, thereby, is able to compete for anionexchange sorption with tin chloride complex anions of Rh(III). It follows from Fig. 2 that the presence of tin(IV) chloride largely affects sorption of anion complexes of Rh(III) with tin(II) chloride on the A500 strong base anion exchange resin, sorption of ions on which can be performed exclusively according to the ion-exchange mechanism, and to a lower extent, on the S985 ion-exchange resin, which, in our opinion,
sorbs rhodium at least partially owing to the formation of coordination bonds between Rh(III) and amino groups of the anion-exchange resin. The absence of the influence of tin(IV) chloride on sorption of Rh(III) on the S920 ion-exchange resin allows us to assume that this ion-exchange resin sorbs Rh(III) found in the solution in the form of complexes with tin(II) chloride mainly according to the complex formation mechanism apparently with the formation of mixed ligand complexes, the composition of which simultaneously includes SnCl 3− ions and isothiourea groups of the ion-exchange resin [11]. The introduction of tin(II) chloride into solutions affects not only the equilibrium but also the sorption kinetics of Rh(III). We performed comparative experiments on studying the sorption kinetics of Rh(III) on ion-exchange resins S985 and S920 in the presence of SnCl2 and in its absence. The sorption kinetics of Rh(III) was investigated from the 4 M hydrochloric acid solution with the rhodium concentration of 1.4 mmol/L at t = 25°C. One solution was with the additive of tin(II) chloride (0.02 mol/L), and another one was without it. Our data are presented in Fig. 3. It is seen that the introduction of tin(II) chloride into the solution leads not only to an increase in selectivity of ion-exchange resins S985 and S920 with respect to Rh(III) but also to an increase in its sorption rate. For example, Rh(III) initially sorbs with a high rate on the S985 ion-exchange resin in the absence of SnCl2, but the process rate noticeably decreases upon reaching the degree of equilibrium of ~0.8. This fact is apparently associated with differences in sorption rates of hexachloride and aqua-chloride complexes of
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Rh(III), in a form of which it is found in the melt in the absence of tin(II) chloride. Rh(III) almost completely sorbs on this ion-exchange resin in the presence of SnCl2 in 1 h. The addition of tin(II) chloride leads to a considerably larger increase in the sorption rate of Rh(III) on the S920 ion-exchange resin with isothiourea groups. We performed experiments on the sorption recovery of Rh(III) on the S920 isothiourea ion-exchange resin at the final stage of the research in dynamic conditions from the model solution of the composition (g/L): 0.2 Rh(III), 72.9 HCl, 53.5 NH4Cl, 2.7 Al(III), 1.23 Fe(III), and 5.9 Sn(IV), into which, allowing for
the consumption for reduction of Fe(III), tin(II) chloride was introduced in the amount of 0.04 mol/L. Desorption of Rh(III) was performed, as it was recommended in [12], by the solution of the composition 50 g/L thiourea and 1 mol/L HCl at t = 60°C. The output sorption curve of Rh(III) on the S920 ion-exchange resin in the presence of tin(II) chloride is shown in Fig. 4; its output desorption curve is also shown there. It was established that, even using a miniature column with the ion-exchange resin load of only 7 mL, deep recovery of Rh(III) is observed, and its content in the sorbate does not exceed the value corresponding to
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its detection limit by the used method of analysis (0.5 mg/L). Thus, the degree of recovery of Rh(III) was no lower than 99%. We recall that it was previously revealed [3] that the degree of recovery of Rh(III) from the solution of close composition in dynamic conditions on the S985 ion-exchange resin in the absence of tin(II) chloride does not exceed 90%. The breakthrough of Rh(III) took place only after passing 130 specific volumes of the solution. The output sorption curve of Rh(III) has a very steep trend, and the total dynamic exchange capacity of the ion-exchange resin with respect to rhodium turned out to be 33.4 mg Rh(III)/mL of the swollen ion-exchange resin. The capacity before the breakthrough is 30.2 mg Rh(III)/mL of the swollen ion-exchange resin, which is ~90% of the total dynamic exchange capacity. The ion-exchange resin saturated with rhodium acquired a reddish brown color. When desorbing Rh(III) with the acidified thiourea solution, its substantial concentration in desorbate is observed. The maximum concentration of Rh(III) in the desorbate reaches ~5.2 g/L, which exceeds its content in the working solution supplied for sorption by a factor of 26. However, desorption of Rh(III) with the acidified thiourea solution proceeds incompletely, and the total amount of desorbed Rh(III) (20.3 mg/mL ion-exchange resin) does not exceed 60% of the amount of sorbed Rh(III). The ionexchange resin became noticeably lighter after treatment with the thiourea solution but did not decolorize completely and remained light brown. From here, it follows that it is necessary to find another more efficient composition of the desorbing solution and other desorption conditions. CONCLUSIONS (1) By the example of the Purolite S920 ionexchange resin with isothiourea functional groups, the Purolite S985 weak base anion exchange resin, and the Purolite A500 strong base anion exchange resin, it is established that the introduction of tin(II) chloride additives leads to an abrupt increase in selectivity and rate of sorption of Rh(III). (2) It is shown that almost quantitative recovery of Rh(III) is attained in the process of passage of a multicomponent chloride solution with the additive of tin(II) chloride through the Purolite S920 ionexchange resin with isothiourea groups. (3) Desorption of Rh(III) from the saturated Purolite S920 ion-exchange resin with the acidified thiourea solution proceeds incompletely. REFERENCES 1. Веnguerel, E., Demopoulos, G., and Harris, G., Speciation and separation of Rh(III) from chloride solutions: a critical review, Hydrometallurgy, 1996, vol. 40, nos. 1–2, pp. 135–152. RUSSIAN JOURNAL OF NON-FERROUS METALS
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2. Blokhin, A.A., Gelman, G.E., Kleandrov, V.T., and Murashkin, Yu.V., Sorption recovery of platinum metals from the used electrolyte of gold electrolytic refining, Dragots. Kamni. Dragots. Met., 2008, no. 11, pp. 170–173. 3. Blokhin, A.A., Voronina, S.N., Murashkin, Yu.V., Mikhailenko, M.A., and Medvedskii, N.L., Sorption recovery of rhodium from multicomponent hydrochloric acid solutions, Khim. Tekh., 2012, no. 9, pp. 543–547. 4. Antonov, P.G., Kukushkin, Yu.N., Anufriev, V.I., Vasil’ev, L.N., and Konovalov, L.V., Complexes of Rh(III) with tin trihalides (II), Zh. Neorg. Khim., 1979, vol. 21, no. 2, pp. 419–425. 5. Petrukhin, O.M., Myasoedova, G.V., and Malofeeva, G.I., Chemical methods of separation and concentration, in: Analiticheskaya khimiya metallov platinovoi gruppy: Cbornik obzornykh statei (Analytical Chemistry of Platinum Group Metals: Collected Review Articles), Zolotov, Yu.A., Varshal, G.M., and Ivanov, V.M., Moscow: Editoroal URSS, 2003, ch. 5, pp. 140–195. 6. Demopoulos, G.P., Benguerel, E., and Harris, G., US Patent 5 201 942, 1993. 7. Alam, M. and Inoue, K., Extraction of rhodium from other platinum group metals with Kelex 100 from chloride media containing tin, Hydrometallurgy, 1997, vol. 46, no. 3, pp. 373–382. 8. Sun, P. and Li, M., Separation of Ir(IV) and Rh(III) from chloride solutions by solvent extraction, Hydrometallurgy, 2011, vol. 105, nos. 3–4, pp. 334–340. 9. Alam, M., Inoue, K., and Yoshizuka, K., Adsorptive separation of Rh(III) using Fe(III)-templated oxine type of chemically modified chitosane, Sep. Sci. Technol., 1998, vol. 33, no. 5, pp. 655–666. 10. Alam, M., Inoue, K., and Yoshizuka, K., Ion exchange adsorption of Rh(III) from chloride media on some anion exchangers, Hydrometallurgy, 1998, vol. 49, nos. 2–3, pp. 213–217. 11. Losev, V.N., Kudrina, Yu.V., and Trofimchuk, A.K., Reactions of rhodium and iridium chloride and chlorostannate complexes with N-(2,6-dimethyl-4-methylenetriphenylphosphonium chloride)phenyl-N'-propylthiourea groups covalently grafted to the silica surface, Russ. J. Inorg. Chem., 2005, vol. 50, no. 6, pp. 882–887. 12. Warshawsky, A., Fieberg, M.B., Michalik, P., Murphy, T.C., and Ras, Y.B., The separation of platinum group metals (PGM) in chloride media by isothioronium resins, Separ. Purific. Methods, 1980, vol. 9, no. 2, pp. 209–265. 13. Marchenko, Z. and Bal’tsezhak, M., Metody spektrofotometrii v UF i vidimoi oblastyakh v neorganicheskom analize (Spectrophotometry Methods in UV and Visible Regions in the Inorganic Analysis), Moscow: Binom. Laboratoriya Znanii, 2009. 14. Moriyama, H., Aoki, T., Shinoda, S., and Saito, Y., Tin-119 Fourier-transform nuclear magnetic resonance study of rhodium–tin complexes formed in aqueous hydrochloric acid solutions of RhC13 and SnCl2, J. Chem. Soc. Dalton Trans., 1981, no. 2, pp. 639–644. 15. Marhol, M., Ion Exchangers in Analytical Chemistry, Prague: Academia, 1982.
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