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32Journal of Siberian Federal University. Chemistry 2 (2014 7) 170-184
УДК 541.183:543.426
Sorption and Separation of Platinum and Rhodium in Presence
of Transition Metals
Olga N. Kononova*, Aleksey M. Melnikov and Evgeniya V. Duba
Siberian Federal University 79 Svobodny, Krasnoyarsk, 660041, Russia
Received 05.11.2013, received in revised form 19.12.2013, accepted 14.02.2014
The present work is focused on ion exchange recovery of platinum (II, IV) and rhodium (III) from acidic chloride solutions in presence of some non-ferrous metal ions and iron (III). It was found out that 10-fold excesses of nickel (II), cobalt (II), copper (II) and zinc (II) have no interfering effect on sorption of noble metals, whereas 3-fold excesses of iron (III) can hinder this process and should be removed from the system. It was determined that platinum and rhodium can be separated and isolated from accompanying ions of non-ferrous metals and iron (III) by means of simultaneous sorption with subsequent selective elution by 2 M ammonium thiocyanate and 2 M hydrochloric acid solutions in columns.
Keywords: sorption, separation, platinum, rhodium, chloride solutions.
Introduction
The continuous growth in processing of low-grade or refractory ores containing platinum group metals (PGM) facilitates the demand for secondary PGM raw materials, such as spent automobile and chemical catalysts, electronic scrap, slag, and etc [1-6]. As the PGM content in these secondary sources is rather low, the sorption recovery appears to be quite efficient [2, 3, 6, 8-16]. Normally, the sorption extraction is carried out from solutions obtained after decomposition of noble metals containing materials (dissolution in acids, chlorination, smelting) [4-7]. Such solutions contain PGM complexes that vary in their stability and chemical inertness, and are affected by aquation and hydrolysis [2, 5, 8, 17, 18]. In this situation, the selectivity of sorbents is very important.
After processing either primary or secondary raw materials, the ready solutions contain not only noble metals, but also non-ferrous metal ions, such as nickel (II), cobalt (II), copper (II), zinc (II), and iron (III). These ions can produce an interfering effect on noble metals recovery, and should be isolated
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*
from PGM ions [2, 4, 7, 19]. This separation can be handled through their different sorption ability depending on the ionic state of metal ions in solutions.
In addition to the PGM sorption, the subsequent desorption of PGM from anion exchangers is also a matter of practical importance. As a rule, the high selectivity of ion exchangers results in a strong retention of adsorbed complexes by functional groups of resins. To extract the precious metals, the resins (being far less valuable) are simply burnt [2, 15, 20, 21]. To investigate the opportunities for regenerating the resins, we studied desorption of noble metals from the investigated resin samples.
Therefore, the focus of the present work is put on separation of noble metal ions adsorbed on anion exchangers and their isolation from some non-ferrous metal ions and iron (III) by selective elution.
Experimental
In this work, we have investigated the macroporous anion exchangers Purolite S985, Purolite A500 as well as AM-2B, which possess high sorption abilities towards chloride complexes of platinum (II, IV) and rhodium (III), as it was revealed in our previous work [22]. The physical-chemical characteristics of these anion exchangers are summarized in Table 1. Before use, the anion exchangers were prepared according to standard methods and loaded with 1 M sodium chloride, to convert them into chloride form.
The initial platinum stock solution with 9.669 mmol/L concentration in 6 M HCl was prepared by dissolution of accurately weighed H2PtCl6 quantity (analytical grade) in a small amount of concentrated HCl and subsequent diluting of the solution with distilled water to 500 mL [17, 18].
The initial rhodium stock solution with 9.709 mmol/L concentration in 6 M HCl was prepared by sintering of metallic rhodium (analytical grade) quantity (0.25 g) with 5-fold excess of BaO2 and subsequent cake dissolution in concentrated HCl [17, 18]. The content of rhodium in the prepared solution was determined by gravimetrical method using thiourea and sulfuric acid [18].
The initial stock solutions of nickel, cobalt, copper, zinc and iron with concentrations of 0.1 mol/L were prepared by dissolution of accurately weighed NiCl2 ■ 6H2O, CoCl2 ■ 6H2O, CuCl2 • 2H2O, ZnCl2 and FeCl2 ■ 6H2O quantities (analytical grade) in distilled water.
The working solutions of noble and non-ferrous metals as well as of iron (III) with concentrations of 0.05 - 5.0 mmol/L were prepared from their stock solutions. The concentration of hydrochloric acid
Table 1. Physical-chemical characteristics of anion exchangers investigated
Trade name Exchanger type Copolymer Functional group Exchange capacity in the Cl--form (mmol/g) Swelling grade (g/cm3)
Purolite S985 Weak base PAc - DVB PA 2.1 1.3
Purolite A500 Strong base St - DVB QAB 1.1 1.6
AM-2B Intermediate base St - DVB QAB (~ 25 %) TAG (~ 75 %) 3.2 2.1
PAc - polyacrylic; DVB - divinylbenzene; St - styrene; PA - polyamine; QAB - quaternary ammonia base; TAG - tertiary aminogroups
in chloride solutions was 0.01 and 2.0 mol/L. The initial concentrations, acidity and composition of solutions were chosen with an intention to make the experiment closer to industrial conditions after breakdown of secondary raw materials.
The content of noble metal ions in working solutions and eluates was determined by a spectrophotometrical method with SnCl2 ■ 2H2O [17, 18]. The content of iron (III) and non-ferrous metals was determined in individual solutions also by spectrophotometrical method using sulfosalicylic acid (Fe3+), dimethylglyoxime (M2+), nitroso-R-salt (Co2+), rubeanic acid )Cm2+) and PAN (Zn2+) [17, 18, 23]. The contents of noble and non-ferrous metals as well as of iron (HI) in mixed solutions were determined by atomic emissaon menaod.
The sorption of noble metals was carried out undei dynamic condiiions in glass columns with diameter ~1rm and height ~)20 cm. Tie dry bed height was 3 cm. The chloriae solution containing platinum and rhodium with concentrations on 0.25 mmolen (for each oh noble metals) and with acidity 0.01 or 2.0 mol/L wos passed through the column. The flow rate was 1.5 mL/min. The outlet solution portions were 220.0 mL. The concentraiio ns of nob le metal io ns wete detenminedia each )nartio n of the eluate.
Then the recovery degree iR, %) and dynamic exaCanga capacity (DEC, mmol/g) were calculated as follows:
Ch - C
R = C-2L-lhh%, (1)
C
V ■ M
DEC = LV^. (2)
VR
r R
where C0 and Ceq are initial and equilibrium molat concentrations of plat)num (nl(oaium) in solut((tii, respectively; Visthe solulion volume (in L); Mis molar solutionconcentration (in mmol/L); VRin resin volume (in L).
The content of noble metals )n sorbent phane was calculated ftom the difference beiween initial and equilibrium concentrations in solution phase, taking into acrount resin mass and vnlume of the contacting solution. We have plotted the distribution curves against the coordinatea a, / at = /(V), where a, and aœ are the amounts (inmmoa of adsorbed mrtal ions afteo pass(ngof portion i and at equilibrium, respectively; Vis the solutionvolume (in mL).
Desorption of (he adsoibed metal ions was studied unden batch and dyonmic condrtions. In (he batch experiments, the resin quantities (0.1 - 0.2 gi were (t(raed wit) 10.0-20.0 mL erf" conCactinn solution, to saturate the resins wiih matal ions. The stirring continued for 24h (equilibrium time). After that, the resins and nolutions wene separated and the equilibrium concentrationr of metal ions were determined in solutions. Then tine; resins were washed with distilled water and contacCed widh 10.0-20.0 mL of eluent solunions (2M HCl as well as 2M NHiSCN), again over a ptriod of 24 h. Theae eluents were taken btcause they possess high affinity to the ad sorted metal ions, especially to noble metal ions [19, 24n26]. Aitet (hat, the col(d and liquid phcnes were separated and (hie concentrations of desorbed metal ions were deteamined in solutions.
Desorption of metal ions under the dynamic conditions waa carrird out as follows. The solution (50.0 mL) containing platinum, rhodium and tice oiher cons was passed through (he column with anion
exchanger, for the purpose of saturation. The flow rate was 1.5 mL/min. After that, the metal contents in resin phase were calculated. Then the eluent solutions were passed through the column under the same flow rate. The outlet solution portions were 20.0 mL. The concentrations of eluted metal ions were determined in each portion.
All the obtained results were statistically processed by standard methods [23]: the average from 5 parallel tests was measured, and then the variance, standard deviation and confidence interval were calculated using Student's t at a confidence level of 0.95. The average experimental error is less than 6 %.
Results and Discussion
Ionic state of platinum and rhodium as well as of non-ferrous metal ions and iron (III) in chloride solutions. It is known [2, 5, 8, 17, 18] that the equilibrium ionic state of PGM in solutions depends on the medium acidity, metal ion concentrations and on temperature. These systems are characterized by different transformations of complexes, such as their hydrolysis, hydration, and isomerization. It was shown that the hexachloro-platinate (IV) complex [PtCl6]2- prevails in strong acidic media (C HCt > 3 mol/L), whereas the hexachloro-rhodiate (III) complex [RhCl6]3- predominates in solutions at HCl concentration above 6 mol/L. With the diluting of platinum solutions and increase in pH value, complexes of platinum (II) appear in the system and co-exist in different proportions with chloride complexes of platinum (IV). With the dilution of rhodium solutions, the formation of aqua chloro-complexes as well as of the cis- and trans-isomers [Rh(H2O)2Cl4] and [Rh(H2O)4Cl2]+ takes place. Moreover, both noble metals form binuclear complexes [Pt2(H2O)2(OH)7Cl]2- and [Rh2Cl9]3- [2, 17, 18, 24-26].
The neutral aqueous nickel (II) solutions contain hexa-aqua complexes [№(H2O)6]2+. The tetra-chloro-nickelate (II) [№Cl4]2- is formed in strong acidic HCl solutions, whereas weak acidic solutions contain the complexes [№Cl]+ and [MCl2]°, characterized by low stability [27].
The neutral and weak acidic aqueous cobalt (II) solutions contain hexa-aqua complexes [Co(H2O)6 ]2+, whereas the tetrachloro-cobaltate (II) [CoCl4 ]2- is formed in strong hydrochloric acid solutions. These complexes are labile and possess low stability [28].
Copper (II) is present in solution with HCl concentration 1-4 mol/L in the form of complexes [CuCl4]2- and [CuCl3]-, but in strong acidic solutions (5-10 M HCl) its polymeric species [Cu2Cl6]2- are formed [29]. With the dilution and decrease in acidity, the cationic complexes [Cu(H2O)6]2+ and [CuCl]+ as well as neutral complexes [CuCl2]0 appear in the system.
The ionic state of zinc also depends on medium acidity [30]. For instance, anionic complexes [ZnCl4]2- are present in strong acidic solutions (1-6 M HCl). With the decrease in acidity (0.01-0.001 M HCl), the formation of cationic and neutral species [ZnCl]+and [ZnCl2]0takes place. These species co-exist with anionic complexes [ZnCl4 (H2O)2]2-.
The strong acidic iron (III) solutions contain the tetrachloro-ferrate (III) [FeCl4]-. With the diluting of iron (III) solutions as well as with the decrease in medium acidity, the complexes [Fe(H2O)6]3+ appear in the system [31, 32].
It should be noted that the so-called "ageing" (i.e., formation of kinetically inert complexes) is observed during storage of weak acidic solutions of noble metals over 24 h and more [2, 5, 17, 18, 2426], but such processes do not occur in non-ferrous metal ions solutions as well as in solutions of iron
(III). We have used in our present work only freshly prepared platinum and rhodium solutions. It can be, therefore, concluded that the initial solutions of the investigated systems are characterized by a diversity of complexes.
Sorption of noble metals and their separation. In our previous work [22] we have determined that anion exchangers Purolite S985 and Purolite A500 as well as AM-2B possess good sorption and kinetic properties and reveal high selectivity towards chloride complexes of platinum (II, IV) and rhodium (III). The results were obtained through batch experiments. The present investigation is devoted to PGM sorption under the dynamic conditions, where the exchange capacity of resins is better employed and the sorption process is shortened [33-38].
We began with investigation of the effects of solution flow rate and bed height on sorption and separation ability of a column. For this purpose, we took the flow rates 1.5; 3.0 and 4.5 mL/min and bed heights 1.0; 3.0 and 5.0 cm. It was revealed that the optimal values for sorption process and components separation are the flow rate 1.5 mL/min and bed height 3.0 cm. The further investigation was carried out with these parameters.
Fig. 1 contains the fragments of distribution curves obtained for simultaneous sorption of noble metals from chloride solutions with different acidity on anion exchanger Purolite S985. It should be noted that similar dependences were obtained for the other anion exchangers investigated.
Fig. 1 shows that with the increase in HCl concentration, the recovery of noble metal complexes is decreased. Such a behavior of Purolite S985 can be explained by improvement in compl-exation ability that occurs with the increase in media pH resulting from deprotonation of nitrogen atoms of functional groups [39, 40]. The similar dependence observed for anion exchanger AM-2B has the same explanation. Although the strong basic anion exchanger Purolite A500 does not possess the complex-forming properties, its behavior is similar to that of Purolite S985. This can be explained by the decrease in competing effect of chloride ions with the increase in pH of the contacting solution.
It should be noted that the high selectivity of investigated anion exchangers to noble metals makes it impossible to separate platinum and rhodium during their simultaneous sorption in columns. However, the successful application of sorbents for PGM separation implies their quantitative desorption
0.80
0 50 ! 00 150 200 250 300
V. ml
Fig. 1. Fragments of distribution curves during simultaneous sorption of platinum (1, 3) and rhodium (2, 4) from chloride solutions with different acidity on anion exchanger Purolite S985. 1, 2 - C0(HCl) = 0.01 mol/L; 3, 4 -C(i(HCl) = 2.0 mol/L; C((Pt) = C((Rh) = 0.25 mmol/L
Table 2. Separation of platinum and rhodium after their sorption recovery from chloride solutions with different acidity C0(Pt) = C0(Rh) = 0.25 mmol/L)
Trade name C„(HCl)a Volumes of elution agents for total recovery of PGM (mL)
(mol/L) Pt elution with 2 M nh4scn Rh elution with 2 M HCl
Purolite S985 2.„ 150 160
„.„1 160 17„
Purolite A500 2.„ 12„ 14„
„.„1 14„ 150
AM-2B 2.„ 14„ 150
„.„1 145 160
a Initial concentration during simultaneous sorption of platinum (II, IV) and rhodium (III)
from resins and their subsequent regeneration [41]. That is why we have studied the selective elution of noble metal ions from investigated anion exchangers.
As mentioned above, we have used several elution agents in our work. The most effective eluents for platinum desorption are 2 M HCl and 2 M NH4SCN, with recovery degrees 95-99 % and 94-99 %, respectively. As for rhodium desorption, it is not feasible to use the ammonium thiocyanate solution, probably due to the ability of rhodium to form the kinetically inert complexes. For rhodium, the most effective elution agent is hydrochloric acid, where the recovery degree exceeds 88 %. Therefore, the combination of elution agents, in particular, NH4SCN and HCl, facilitates the separation of platinum and rhodium, which is demonstrated in Table 2. It can be seen that eluent volumes are 120-160 mL. The differences in required elution volumes for noble metals comply with the selectivity of investigated anion exchangers. The more selective anion exchanger is towards platinum or rhodium, the higher volume of elution agent is required for their recovery.
After that we examined the proposed Pt / Rh separation method by applying different initial amounts of noble metals. The results are presented in Table 3. It can be seen from these data that with the increase in initial platinum amount to 1.000 mg (concentration is 100 mg/L in this case), the relative error increases up to 36 - 41 %. The acidity of initial solutions has no substantial effect on platinum recovery. In case of rhodium, the relative error does not exceed 16 % even with the increase in initial amount of Rh to 1.000 mg. Therefore, it can be concluded that the most effective separation of platinum and rhodium can be achieved at their initial amounts 0.100 - 0.500 mg (10 - 50 mg/L).
Separation of noble metals from accompanying non-ferrous metal ions and iron (III). It was mentioned above that, as a rule, iron (III) and non-ferrous metal ions are present in PGM-containing solutions after processing of primary and secondary raw materials. Their presence has an interfering effect on recovery of noble metals and, therefore, it is necessary to separate PGM from these accompanying ions.
We studied the sorption recovery of non-ferrous metal ions and of iron (III) from their individual chloride solutions first, and then investigated the simultaneous sorption of these ions and noble metal ions. The results on individual sorption of nickel (II), cobalt (II), copper (II), zinc (II), and iron (III) are summarized in Table 4.
Table 3. Recovery of Pt by means of 2 M NH4SCN and of Rh by means of 2 M HCl after their simultaneous sorption from chloride solutions with different acidity (resin mass - 0.1 g; volume of contacting solution - 10.0 mL) NM - noble metal; s - relative error
NM amount at sorption (mg) C0(HCl) (mol/L) Platinum recovery Rhodium recovery
Amount after sorption (mg) Amount after elution (mg) Amount after sorption (mg) Amount after elution (mg)
Purolite S 985
0.100 2.0 0.099±0.001 0.098±0.001 -1 0.099±0.001 0.098±0.001 -1
0.01 0.099±0.001 0.097±0.001 -2 0.099±0.001 0.098±0.001 -1
0.250 2.0 0.246±0.002 0.242±0.002 -2 0.228±0.003 0.210±0.002 -8
0.01 0.248±0.003 0.244±0.002 -2 0.234±0.003 0.208±0.002 -11
0.500 2.0 0.472±0.003 0.446±0.004 -6 0.384±0.004 0.337±0.003 -12
0.01 0.484±0.004 0.456±0.004 -6 0.406±0.005 0.347±0.003 -15
1.000 2.0 0.907±0.007 0.548±0.005 -40 0.397±0.004 0.338±0.003 -15
0.01 0.951±0.008 0.562±0.005 -41 0.416±0.006 0.350±0.004 -16
Purolite A 500
0.100 2.0 0.099±0.001 0.098±0.001 -1 0.099±0.001 0.098±0.001 -1
0.01 0.099±0.001 0.098±0.001 -1 0.099±0.001 0.097±0.001 -2
0.250 2.0 0.244±0.002 0.238±0.002 -2 0.168±0.002 0.156±0.002 -7
0.01 0.247±0.003 0.241±0.002 -2 0.188±0.003 0.179±0.002 -5
0.500 2.0 0.453±0.003 0.444±0.003 -2 0.184±0.003 0.166±0.002 -10
0.01 0.491±0.004 0.486±0.005 -1 0.201±0.003 0.183±0.002 -9
1.000 2.0 0.896±0.007 0.573±0.005 -36 0.188±0.002 0.170±0.002 -10
0.01 0.961±0.008 0.588±0.006 -39 0.205±0.003 0.185±0.002 -10
AM-2B
0.100 2.0 0.099±0.001 0.097±0.001 -2 0.099±0.001 0.098±0.001 -1
0.01 0.099±0.001 0.097±0.001 -2 0.099±0.001 0.097±0.001 -2
0.250 2.0 0.244±0.002 0.238±0.002 -2 0.159±0.002 0.151±0.002 -5
0.01 0.246±0.003 0.240±0.003 -2 0.204±0.003 0.195±0.002 -4
0.500 2.0 0.448±0.004 0.440±0.004 -2 0.174±0.002 0.161±0.002 -7
0.01 0.491±0.004 0.483±0.005 -2 0.215±0.003 0.198±0.002 -8
1.000 2.0 0.890±0.006 0.570±0.005 -36 0.176±0.002 0.162±0.002 -8
0.01 0.960±0.008 0.580±0.006 -40 0.218±0.003 0.200±0.003 -8
Table 4. Sorption recovery of non-ferrous metal and iron (III) ions from individual chloride solutions (C0(Ni) = 0.85 mmol/L; C0(Cu) = 0.78 mmol/L; C0(Co) = 0.85 mmol/L; C0(Z«) = 0.77 mmol/L; C0(Fe) = 0.89 mmol/L)
Trade name Co(HCl) (mol/L) Sorption parameters a Metal ions
Ni (II) Cu (II) Co (II) Zn (II) Fe (III)
Purolite S985 2.0 R ( %) 26±1 95±2 68±2 77±4 99±1
D 35±2 1984±82 203±10 333±17 8233±410
0.01 R ( %) 96±3 33±2 54±2 62±3 99±1
D 2532±127 50±2 117±6 160±8 8520±426
Purolite A500 2.0 R ( %) 86±3 95±3 93±4 78±4 99±1
D 2464±123 1780±80 1366±68 364±17 8750±430
0.01 R ( %) 99±1 13±2 58±2 71±4 99±1
D 8520±426 15±1 138±7 254±12 9245±462
AM-2B 2.0 R ( %) 83±3 85±4 91±3 71±4 99±1
D 488±24 572±26 1020±51 246±12 8450±420
0.01 R ( %) 99±1 3±1 54±2 71±4 99±1
D 8234±412 4±1 118±7 242±13 8994±455
■ D - distribution ratio (mmol of Me sorbed per g of resin/mmol of Me in mL of solution)
It can be seen from the data presented in Table 4 that anion exchangers investigated possess high sorption ability towards the isolated ions. The recovery of nickel (II) is increased with the decrease in hydrochloric acid concentration. Such behavior of anion exchangers can be explained by the decrease in the competing effect of chloride ions. Moreover, the behavior of Purolite S985 and AM-2B can be explained by their complexation ability, which increases with the increase in pH of the contacting solution due to deprotonation of nitrogen atoms of their functional groups [42].
The data presented in Table 4 show that the sorption ability of anion exchangers investigated towards cobalt (II), copper (II) and zinc (II) ions is higher in strong hydrochloric acid solutions in comparison with weak acidic media. Probably the presence of neutral and cationic complexes of these ions in weak acidic solutions has an effect on their sorption recovery. As for sorption of iron (III) ions, it does not practically depend on the acidity of the contacting solution.
Then we have investigated the effect of foreign ions on sorption recovery of platinum and rhodium. The results are presented in Table 5. It can be seen from these data that 10-fold excesses of non-ferrous metal ions do not practically affect the sorption of platinum and rhodium, whereas the presence of 3-fold excess of iron (III) has a substantial effect on sorption of noble metals. The relative errors are low in the first case and account for 16-17 % in the second case. Such a behavior of anion exchangers to Ni(I), Co(I), Cu(I) and Zn(I) ions can be explained by greater selectivity of the investigated resins to platinum and rhodium. Moreover, an acid effect takes place, causing changes in the anion exchanger phase and facilitating the sorption of components, which form stable anionic chloride complexes [43]. Since the stability of above-mentioned chloride complexes of non-ferrous metal ions is much less than that of noble metals, they are substituted with well-sorbed platinum and rhodium complexes that occupy the sorption centers of anion exchanger. As for the iron (III), its interfering effect should be suppressed by removal of Fe(III) before the elution of noble metal complexes.
Table 5. Inhibitory effect of foreign ions on sorption recovery of platinum (II, IV) and rhodium (III) from chloride solutions with different acidity (initial contents of Pt - 0.488 mg and of Rh - 0.257 mg)
Me Excess C0(HCl) (mol/L) Pt recovery without foreign ions (mg) Pt recovery in the presence of foreign ions (mg) e (%) Rh recovery without foreign ions (mg) Rh recovery in the presence of foreign ions (mg) e (%)
Purolite S 985
Ni 10 2.0 0.458±0.003 0.448±0.004 -2 0.230±0.005 0.228±0.005 -1
0.01 0.476±0.005 0.472±0.006 -1 0.240±0.004 0.235±0.004 -2
Co 10 2.0 0.458±0.003 0.452±0.007 -1 0.230±0.005 0.227±0.007 -1
0.01 0.476±0.005 0.472±0.007 -1 0.240±0.004 0.240±0.002 0
Cu 10 2.0 0.458±0.003 0.451±0.006 -2 0.230±0.005 0.229±0.004 0
0.01 0.476±0.005 0.475±0.006 0 0.240±0.004 0.240±0.004 0
Zn 10 2.0 0.458±0.003 0.453±0.004 -1 0.230±0.005 0.227±0.003 -1
0.01 0.476±0.005 0.470±0.003 -1 0.240±0.004 0.239±0.003 0
Fe 3 2.0 0.458±0.003 0.380±0.005 -17 0.230±0.005 0.193±0.002 -16
0.01 0.476±0.005 0.396±0.004 Purolite A 500 -17 0.240±0.004 0.205±0.005 -15
Ni 10 2.0 0.441±0.004 0.438±0.004 -1 0.159±0.004 0.157±0.003 -1
0.01 0.480±0.005 0.472±0.006 -2 0.191±0.004 0.187±0.004 -2
Co 10 2.0 0.441±0.004 0.435±0.008 -1 0.159±0.004 0.156±0.002 -2
0.01 0.480±0.005 0.474±0.003 -1 0.191±0.004 0.187±0.003 -2
Cu 10 2.0 0.441±0.004 0.438±0.007 -1 0.159±0.004 0.158±0.004 -1
0.01 0.480±0.005 0.479±0.004 0 0.191±0.004 0.190±0.003 -1
Zn 10 2.0 0.441±0.004 0.437±0.006 -1 0.159±0.004 0.157±0.005 -1
0.01 0.480±0.005 0.475±0.005 -1 0.191±0.004 0.186±0.006 -3
Fe 3 2.0 0.441±0.004 0.365±0.004 -17 0.159±0.004 0.129±0.003 -19
0.01 0.480±0.005 0.400±0.004 AM-2B -17 0.191±0.004 0.156±0.003 -18
Continuation Table 5
Me Excess C0(HCl) (mol/L) Ptrecovery without foreign ions (mg) Pt recovery in the presence of foreign ions (mg) e (%) Rh recovery without foreign ions (mg) Rh recovery in the presence of foreign ions (mg) e (%)
Ni 10 2.0 0.444±0.004 0.441±0.008 -1 0.155±0.003 0.153±0.002 -1
0.01 0.480±0.003 0.474±0.005 -1 0.205±0.004 0.200±0.003 -2
Co 10 2.0 0.444±0.004 0.443±0.004 0 0.155±0.003 0.153±0.002 -1
0.01 0.480±0.003 0.473±0.007 -1 0.205±0.004 0.203±0.004 -1
Cu 10 2.0 0.444±0.004 0.441±0.005 -1 0.155±0.003 0.155±0.003 0
0.01 0.480±0.003 0.477±0.004 -1 0.205±0.004 0.204±0.004 0
Zn 10 2.0 0.444±0.004 0.443±0.006 0 0.155±0.003 0.154±0.002 -1
0.01 0.480±0.003 0.473±0.004 -1 0.205±0.004 0.203±0.003 -1
Fe 3 2.0 0.444±0.004 0.371±0.004 -16 0.155±0.003 0.124±0.003 -20
0.01 0.480±0.003 0.398±0.006 -17 0.205±0.004 0.170±0.005 -17
0 30 60 90 120 0 30 60 90 120 150
V, ml
Fig. 2. Graphical elution profiles for platinum by 2 M NH4SCN (1) and rhodium by 2 M HCl (2) from anion exchanger Purolite A500. C((HCl) = 2.0 mol/L; C((Pt) = C((Rh) = 0.25 mmol/L
Then we have developed the separation method for Pt and Rh in the presence of accompanying ions under the dynamic conditions. An initial chloride acidic solution (50.0 mL) containing noble and non-ferrous metal ions as well as iron (III), was passed through the column with anion exchanger. The flow rate was 1.5 mL/min. It was revealed that non-ferrous metal ions were practically not sorbed on anion exchanger in the presence of noble metal ions. Therefore, they were collected in the first portion of eluate after passing through the resin column, almost without any change in concentrations.
Then, ~100 mL of 0.01 M HCl was passed through the column, in order to remove iron (III). After that, 2M solution of NH4SCN (150 mL) was passed, aiming to recover the platinum. The breakthrough of Pt was observed after passing of 20.0 mL of this solution. The elution of platinum as a function of eluate volume is graphically shown at Fig. 2. It can be seen that the maximum of Pt desorption (~0.85 mg) is observed after breakthrough of ~60 mL. The complete Pt elution can be achieved after breakthrough of 125 mL. The total average platinum concentration in eluate was 19.51 mg/L. Rhodium was retained in the resin phase.
Then the column was washed with distilled water (~40 mL), to remove the excess of ammonium thiocyanate. After that, rhodium was eluted by 2 M HCl. The breakthrough of Rh to eluate was observed in the first portion (20.0 mL). The dependence of Rh elution on eluate volume is shown at Fig. 2. As follows from the Fig. 2, the maximal desorption of rhodium (~0.4 mg) can be achieved after breakthrough of ~80 mL and about 145 mL are needed for its complete elution. The total average Rh concentration in the eluate was 8.87 mg/L.
The results on sorption recovery, elution and separation of PGM and non-ferrous metal ions as well as iron (III) are schematically presented at Fig. 3. It should be noted that the regeneration of resin is not necessary after desorption, as since the sorbent is converted into the chloride form after rhodium elution with 2 M HCl.
Conclusions
The simultaneous sorption recovery of platinum (II, IV) and rhodium (III) from acidic chloride solutions on anion exchangers was investigated in the presence of some non-ferrous metal ions and iron (III). It was determined that 10-fold excesses of nickel (II), cobalt (II), copper (II) and zinc (II) have no interfering effect on noble metals sorption, whereas 3-fold excess of iron (III) deteriorates the recovery
Fig. 3. Process of sorption recovery, elution and separation of platinum, rhodium, non-ferrous metal and iron (III) ions on the investigated anion exchangers C0(Pt) = C0(Rh) = 0.25 mmol/L
of Pt and Rh. The developed method for sorption recovery and separation of platinum and rhodium is based on removal of accompanying non-ferrous metal ions, subsequent desorption of iron (III) with 0.01 M HCl and on selective elution of platinum by 2 M NH4SCN and rhodium with 2 M HCl. It was found out that anion exchangers Purolite S985, Purolite A500 and AM-2B can be recommended for sorption recovery of chloride complexes of platinum and rhodium in the presence of some non-ferrous metal ions and iron (III). The subsequent selective elution of noble metals, based on the combination of elution agents, allows obtaining individual solutions of platinum and rhodium.
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Сорбция и разделение платины и родия в присутствии переходных металлов
О.Н. Кононова, А.М. Мельников, Е.В. Дуба
Сибирский федеральный университет Россия, 660041, Красноярск, пр. Свободный, 79
Данная статья посвящена ионообменному извлечению платины (II, IV) и родия (III) из кислых хлоридных растворов в присутствии ионов некоторых цветных металлов и железа (III). Установлено, что на сорбцию благородных металлов не влияют 10-кратные избытки никеля (II), кобальта (II), меди (II) и цинка (II), однако 3-кратный избыток ионов железа (III) мешает этому процессу и потому эти ионы должны быть удалены из системы. Установлено, что платина и родий могут быть разделены и отделены от сопутствующих ионов цветных металлов и железа (III) путем совместной сорбции в колонках с последующим селективным элюированием посредством 2 М растворов тиоцианата аммония и соляной кислоты.
Ключевые слова: сорбция, разделение, платина, родий, хлоридные растворы.
