New Approach for Highly Selective Separation and Recovery of

Sep 7, 2014 - College of Chemistry, Liaoning University, 66 Chongshan Middle Road, Shenyang 110036, People,s Republic of China. ABSTRACT: A new ...
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New Approach for Highly Selective Separation and Recovery of Osmium and Rhodium by Using a Nanoparticle Microcolumn Fang Wang, Yuejiao Wang, Yanhui Li, Qiong Wang, Xinyu Qi, and Lei Zhang* College of Chemistry, Liaoning University, 66 Chongshan Middle Road, Shenyang 110036, People’s Republic of China ABSTRACT: A new solid-phase extraction (SPE) method for recovery of osmium and rhodium was proposed with static batch and column experiments. Nano-Al2O3 exhibited high adsorption ability and selectivity for Os(IV) and Rh(III), and the adsorption depended strongly on pH. Both Os(IV) and Rh(III) could be adsorbed quantitatively on nano-Al2O3 within a pH range of 4.0−8.0, and only Os(IV) could be retained within pH 2.0−3.0 while Rh(III) could not. Selective separation could be achieved by adjusting the aqueous pH. The extraction recoveries for the mentioned noble metals were more than 95%. Good stability of nano-Al2O3 was demonstrated from regeneration investigation. Finally, selective recovery of Os(IV) and Rh(III) from simulated industrial leach liquor (SILL) was achieved by performing the extraction-stripping process. The negligible uptake of Cu, Zn, Co, Ni, Cd, Pb, and Fe in SILL solution was due to the high selectivity and extractability of nano-Al2O3 for osmium and rhodium.

1. INTRODUCTION As precious platinum group metals (PGMs), osmium and rhodium have been widely used in chemical engineering and the automobile and electronics industries1−4 owing to their specific physical and chemical properties. Millions of tons of spent electrical and electronic devices are discarded every year. Electrical and electronic wastes contain high value precious metals like osmium and rhodium, which indicates not only the loss of huge amounts of resources but also the threat of environmental pollution. Although, the portion of these metals is very low compared to the other metals like copper and iron in such wastes, their content in this form is much higher than those in their original ores. Since natural resources for these metals are limited and their demand in industry is increasing, it is important to find an effective separation process to recover these metals with high purity from diverse secondary resources. For the purpose of effective recovery of trace amounts of much more valuable metals, some highly selective processes that have no affinity for copper and other base metals are required. As the aqueous chemistry of one metal ion may resemble that of some others in the mixture, selective recovery of any desired metal from such complex mixtures is difficult. Many studies have been reported on the separation of Pt(IV), Pd (II), Au(III), and Rh(III) from chloride solution.5−7 Osmium and rhodium are PGMs located in Group VIII. The composition and chemical properties of complexes formed by Os and Rh are to a large extent similar.8,9 This makes the recovery and separation of both metals in the same solutions difficult. In this contest, it must be pointed out that great attention has been focused on the separation of platinum, palladium, iridium, and osmium along with other platinum metals,10,11 whereas Os and Rh have rarely been investigated. Several separation methods such as solvent extraction,12−17 ion exchange,18−20 sorption,21 precipitation,22,23 extraction chromatography,24−26 etc. have been reported for the separation of PGMs. Compared to these methods, SPE has achieved widespread use because of its simple procedure, higher preconcentration factor, rapid phase separation and combina© 2014 American Chemical Society

tion with different detection techniques. Various kinds of solid phase extraction agents have been investigated on metal ions separation, such as activated carbon,27 chitosan,28 multiwalled carbon nanotubes,29 microcapsules,30 persimmon residual,31 lignophenol compounds,32 etc. Nanomaterials as a solid phase extraction agent have attracted much attention due to its high adsorption capacity, simple operation, rapid adsorption process, etc. Thus, there is a growing interest in the application of separation and preconcentration of trace metal ions.33,34 However, the literature studies on using nanoparticles as adsorbents for the separation of Os(IV) and Rh(III) are very limited.35 In the present work, we developed a new method using a microcolumn packed with nano-Al2O3 for separating Os(IV) and Rh(III). Our study focused on the effectiveness of adsorption and separation. The optimized experimental conditions for the separation process were established. The proposed method was applied for separation of Os(IV) and Rh(III) in simulated industrial leach liquor.

2. EXPERIMENTAL METHODS Materials and Reagents. Nano-Al2O3 was purchased from Beijing Nachen Nano-Meter Material Co., China, and its particle size was in the 10−15 nm range. (NH4)2OsCl6 (≥99.99%, Os 42.5% min) was purchased from Alfa Aesar (Tianjin) Chemical Co., Ltd. A standard stock solution of Os(IV) (1000 μg·mL−1) was prepared by dissolving 0.2308 g of (NH4)2OsCl6 in 1.2 mol·L−1 hydrochloric acid and then diluting to 100 mL with 1.2 mol·L−1 hydrochloric acid in brown glass volumetric flask. A 1000 μg·mL−1 standard stock solution of Rh(III) in 10% HCl was purchased from National Iron and Steel Research Received: Revised: Accepted: Published: 15200

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taken, and then the concentration of Os(IV)/Rh(III) was determined. The rate constants were computed according to the rate equation. Column Experiments. The column was a simple glass tube with an inner diameter of 6.0 mm and a length of 19.5 cm. A known quantity of the adsorbent (10 mg) was mixed with an optimum quality ratio of 1:10 for nano-Al2O3 to glass beads, then the mixture was dried in a muffle furnace at 473 K for 2 h. The nano-Al2O3 loaded on glass beads was packed into the column, and the column was conditioned with double-distilled water for 24 h. The solution was pumped in an up-flow mode through packed-bed column by a peristaltic pump and collected by an automatically collection at room temperature (shown in Scheme 1). Then, the microcolumn was conditioned to the desired pH values with HCl and NaOH solutions.

Institute, China. The standard stock solutions of Os(IV) and Rh(III) were diluted successively to the required concentration in the experiment by deionized water. All the other reagents including hydrochloric acid, sulfuric acid, and sodium hydroxide were of analytical reagent grade and obtained from Sinopharm Chemical Reagent Co., Ltd. without further purification. The standard stock solutions of all of the other metal ions were obtained by dissolving their chloride or nitrate salts (≥99.99%) and used to investigate the adsorption selectivity. Deionized water was used throughout the experiments. Apparatus. The morphology of nano-Al2O3 particles was determined by transmission electron microscopy (TEM JEOL Ltd., Japan). FT-IR spectrum of adsorbent was measured using FT-IR 5700 (Nicolet company, USA). The X-ray diffraction (XRD) pattern of nano-Al2O3 was recorded on Siemens D5000 Diffractometer (Germany). X Series II inductively coupled plasma-mass spectrometry (ICP-MS; Thermo Scientific) was used for the determination of Os(IV), Rh(III), and other metal ions. A pHSJ-4F pH meter Instrument (Shanghai LEICI Co. Ltd.) was used for pH measurement. HZQ-Q thermostat oscillator (HDL APPARATUS Co. Ltd.) was used in static batch experiments. A Malvern Zetasizer Nano-ZS particle analyzer (Malvern, U.K.) was used to determine the zeta potential and particle size of adsorbents. A constant flow peristaltic pump with computer displaying and fraction collector (Shanghai Huxi Analysis Instrument Factory CO., LTD) was used in separation and preconcentration process. Procedure. Static Batch Experiments. The adsorption experiments were carried out using a series of 50 mL flasks containing certain adsorbents and 10.0 mL of 5 μg·mL−1 Os(IV)/Rh(III) solution at appropriate pH. If necessary, the pH of the solution was adjusted by addition of HCl or NaOH solution before the addition of adsorbents. The solid/liquid phases were separated by centrifuging at 4000 rpm for 5 min. The solutions were immediately analyzed for the determination of Os(IV)/Rh(III) concentration. The adsorption percentage (Ads.%) was calculated based on the following equation: Ads.% =

(C0 − Ce) × 100 C0

Scheme 1. Schematic Diagram of the Column Experiment

A solution containing 5 μg·mL−1 Os(IV) and Rh(III) was prepared, and the pH value was adjusted to 2.5 with 0.1 mol L−1 HCl and 0.1 mol L−1 NaOH. The solution was passed through the nano-Al2O3 packed microcolumn by using a peristaltic pump at a desired flow rate of 0.2 mL·min−1. Rh(III), which could not be retained by the column, passed directly through the column and the effluent solution from the nanoAl2O3 column was collected; while Os(IV) retained by the column, was eluted with 0.1 mol·L−1 HCl eluent solution. Finally, the concentrations of the separated Os(IV) and Rh(III) in the final solutions were determined by ICP-MS. Simulated Industrial Leach Liquor. SILL solution was prepared by dissolving metal salts in 1.2 mol·L−1 HCl and diluting the stock solution to the appropriate concentration of metal ions. The concentrations of the metal ions present in SILL solution consisted of 2.60 × 10−5 mol·L−1 Os(IV), 4.85 × 10−5 mol·L−1 Rh(III), and 0.02 mol·L−1 Cu (II), Zn (II), Co (II), Ni (II), Cd (II), Pb (II), and Fe (III).

(1)

where C0 and Ce are the initial and the final concentrations of the target analytes in solution phase, respectively. The adsorption capacity of adsorbents was calculated based on the following equation: q=

V (C0 − Ce) m

(2)

where q is the adsorption capacity of adsorbents (mg·g−1), V is the volume of the solution in L, and m is the mass of added adsorbent. Adsorption isotherm experiments were carried out with initial concentrations of the target analytes varying between 0.5 and 30.0 μg·mL−1, the amount of adsorbent was kept constant (10 mg), and the experimental temperatures were controlled at 298 K. Finally, ΔH0, ΔS0, and ΔG0 of the adsorption procedure were obtained, respectively. Dynamics experiments were carried out using a series of 50 mL flasks containing 10 mg of nano-Al2O3 and 10.0 mL of 5 μg·mL−1 target solution at appropriate pH in 298 K. At a certain interval of the reaction time, suitable aliquots were

3. RESULTS AND DISCUSSION Characterization of Adsorbents. Transition electron microscopy (TEM) was used to investigate the crystal structure of nano-Al2O3 (Figure 1A). TEM image revealed the nanoparticle sizes are 10−20 nm in diameter. The XRD pattern of nano-Al2O3 was investigated, the diffraction peaks of the particles matched well with the diffraction data from the JCPDS card. Figure 1C showed the FTIR spectrum of nanoAl2O3. The broad band at 3462 cm−1 is believed to be associated with the stretching vibrations of hydrogen-bonded surface water molecules and hydroxyl groups. Additionally, the bands at 1630 and 1446 cm−1 correspond to the existence of 15201

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Figure 1. (A) TEM image of nano-Al2O3. (B) FTIR spectrum of γ-nano-Al2O3. (C) XRD pattern of nano-Al2O3 powder.

Figure 2. (A) Effect of pH on the adsorption efficiency of Os(IV)/Rh(III) onto nano-Al2O3 (CRh(III) = COs(IV) = 5.0 μg·mL−1, mAl2O3 = 20.0 mg). (B) Zeta potential of nano-Al2O3 suspensions at different pH.

Figure 2, it is clear that nano-Al2O3 was not capable of adsorption of Rh(III) at pH 2.0−3.0 while it is perfectly capable of adsorption of Os(IV). This meant that it was possible to separate Rh(III) and Os(IV) with nano-Al2O3 at pH 2.0−3.0. Therefore, the best pH for separating Rh(III) from Os(IV) was pH 2.5 in the experiment. In this study, knowledge of pH was important because the pH of the solution influenced not only the distribution of active sites on the surface of nano-Al2O3 but also influenced the target analyte species. To find the surface electric charge of nanoAl2O3 suspensions, the zeta potential (ξ) was measured in the medium of 0.001 mol·L−1 NaCl solution. The point of zero charge (pzc) of nano-Al2O3 obtained was 9.0. At pH < pHpzc, the nano-Al2O3 surface carried positive charges, while at pH > pHpzc the nano-Al2O3 surface was negatively charged. The electrostatic attraction may play an important role on the adsorption of Os(IV) /Rh(III) onto nano-Al2O3. In hydrochloric acid media, Os(IV)/Rh(III) ions mainly exist as [OsCl6]2−/[RhCl6]3−,36,37 the nano-Al2O3 surface is positively charged (at pH < pHpzc = 9.0), which will enhance its electrostatic attraction with [OsCl6]2−/[RhCl6]3− (≡Al− OH2+(surf)•[OsCl6]aq2−/ ≡ Al−OH2+(surf)•[RhCl6]aq3−). For this reason, the adsorption progressed more easily, so the adsorption of [OsCl6]2−/[RhCl6]3− was more efficient. But in the strong acidic media, there is an equilibrium reaction: 2H+ + [OsCl6]2− ⇔ H2[OsCl6] or 3H+ + [RhCl6]3− ⇔ H3[RhCl6]. The main chemical species of Os(IV) and Rh(III) are H2[OsCl6] and H3[RhCl6], so the adsorption ratio of Os(IV)/Rh(III) was slightly low. Effect of Eluent Concentration and Reusability. In order to check the recovery efficiency of Os(IV)/Rh(III), desorption

large numbers of residual hydroxyl groups, which implys the O−H vibrating mode of traces of adsorbed water. The band located at 950−480 cm−1 can be ascribed to the Al−O−Al vibrations of Al2O3 nanoparticles. Static Batch Procedures. Optimized Conditions of Os(IV)/Rh(III) Adsorption on Nano-Al2O3. Conditions for maximum removal of Os(IV)/Rh(III) from aqueous solution were initially optimized. A detailed study of the adsorption process was performed by varying adsorbent amount and adsorption time. Ten mL of 5 μg·mL−1 Os(IV)/Rh(III) solution was applied to test the adsorption behavior at different conditions. It was found that the adsorption percentage increased with the increasing amount of nano-Al2O3, and when the amount exceeded 20.0 mg for Os(IV)/Rh(III), the adsorption percentage (Ads.%) reached 98.5% with no obvious change at pH 5.0. Os(IV)/Rh(III) adsorption system reached equilibrium around 5.0 min. Henceforth the optimum amount of adsorbent was 20.0 mg, and the best adsorption time was restricted up to 5.0 min. Effect of pH. In order to evaluate the effect of pH, the pH values of sample solutions were adjusted to a range of 1.0−8.0 with HCl or NaOH. To attain enough sensitivity, standard solutions containing 5.0 μg·mL−1 of Os(IV)/Rh(III) at different pH values were used. The nano-Al2O3 was employed to separate Os(IV) and Rh(III). The effect of pH on the adsorption of Os(IV) and Rh(III) is shown in Figure 2. It is clear from Figure 2 that the Rh(III) could be adsorbed quantitatively (Ads.% is more than 95%) by nano-Al2O3 in the pH range of 4.0−8.0, while Rh(III) could not be retained on nano-Al2O3 at pH 1.0−3.0. On the contrary, nano-Al2O3 could quantitatively adsorb Os(IV) at pH 2.0−8.0. According to 15202

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where qm is the maximum monolayer adsorption (mg·g−1), Ce is the equilibrium concentration of Os(IV)/Rh(III), qe is the amount of the target analytes adsorbed per unit weight of nanoAl2O3 at equilibrium concentration (mg·g−1), and b is the Langmuir constant related to the affinity of binding sites (L· mg−1). The Langmuir isothermal constants were calculated from the plots of Ce/qe against Ce, at 298 K. It was found that the adsorption of Os(IV)/Rh(III) on adsorbents correlated well (r > 0.99) with the Langmuir equation under the studied concentration range (Figure 4A). The maximum adsorption capacity of Os(IV) and Rh(III) ions on the nano-Al2O3 were 21.71 and 5.52 mg·g−1 at room temperature, respectively. Thermodynamic Studies. The adsorption behaviors of different concentrations of Os(IV) and Rh(III) onto nanoAl2O3 were critically investigated at various temperatures. Thermodynamic parameters were calculated using the following formula:

experiments were carried-out. Different kinds and concentrations of eluent, such as HCl and H2SO4 solutions (0.1−0.5 mol·L−1), were tested for recovery of Os(IV)/Rh(III) (shown in Figure 3). The best elution efficiency of Os(IV) (desorption

ΔG 0 = −RT ln Kc

Figure 3. Elution efficiency of Os(IV)/Rh(III) in different concentrations of HCl or H2SO4.

where T is temperature (K) and Kc is the distribution coefficient. Gibbs free energy change of adsorption (ΔG0) was calculated using ln Kc values for different temperatures. The Kc value was calculated using the following equation: q Kc = e Ce (5)

% > 98%) was obtained with 2.0 mL of 0.1 mol·L−1 HCl solution, and 95% Rh(III) was recovered with 2.0 mL of 0.3 mol·L−1 H2SO4 solution. After desorption, the regenerated nano-Al2O3 was washed with deionized water to nearly neutral. The recycled adsorbent was reused, and it was found that the regenerated nano-Al2O3 still maintained a high adsorption efficiency for Os(IV)/ Rh(III) (Ads.% > 90%) after four adsorption-regeneration cycles. Therefore, nano-Al2O3 had good reutilization and could be used in the recovery of Os(IV) and Rh(III). Adsorption Isotherms of Os(IV) and Rh(III). Adsorption isotherms describe how solutes interact with adsorbents. In Figure 4A, the equilibrium adsorption amount of Os(IV)/ Rh(III) on adsorbents as a function of the equilibrium concentration of Os(IV)/Rh(III) was depicted. An increased adsorption was observed for Os(IV)/Rh(III) until saturation was attained. Equilibrium adsorption isotherms are often described by the Langmuir model:38 Ce C 1 = e + qe qm bqm

(4)

where Ce is the equilibrium concentration of Os(IV)/Rh(III) and qe is the amount of Os(IV)/Rh(III) adsorbed per unit weight of nano-Al2O3 at equilibrium concentration (mg·g−1). The enthalpy change (ΔH0) and entropy change (ΔS0) of adsorption were estimated from the following equation: ln Kc =

ΔS 0 ΔH 0 − R RT

(6)

According to eq 6, ΔH0 and ΔS0 parameters can be calculated from the slope and intercept of the plot of ln Kc versus 1/T, respectively. The thermodynamic parameters were summarized in Table 1. The negative values of ΔG0 showed the spontaneous nature of adsorption process, and the endothermic nature of adsorption process due to the positive value of ΔH0. Kinetic Behavior of Os(IV) and Rh(III) Adsorption onto Adsorbents. In batch experiments, the Os(IV)/Rh(III) ions

(3)

Figure 4. (A) Isotherms of Os(IV)/Rh(III) adsorption on nano-Al2O3 at 298 K (10 mg of nano-Al2O3; the initial concentration range was 0.5−30.0 μg·mL−1; pHRh(III) = pHOs(IV) = 5.0). (B) Adsorption capacity of Os(IV) and Rh(III) on adsorbents versus time. 15203

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Table 1. Thermodynamic Parameters for the Adsorption of Os(IV)/Rh(III) onto Nano-Al2O3 ΔH0

C0 −1

ΔG0 (kJ·mol−1)

ΔS0

−1

−1

−1

(mg·L )

(kJ·mol )

(kJ·mol ·K )

273 K

298 K

323 K

5 5

24.1580 10.300

0.0951 0.035

−1.804 −0.043

−4.182 −0.131

−6.559 −3.152

Os(IV) Rh(III)

Figure 5. (A) Breakthrough profiles for Os(IV) and Rh(III) with a column packed with the nano-Al2O3. Conditions: CRh(III) = COs(IV) = 5 μg·mL−1, pHRh(III) = pHOs(IV) = 5.0, flow rate = 0.2 mL·min−1, weight of adsorbent = 10 mg. (B) Elution profiles for Os(IV)/ Rh(III) with 0.1 mol·L−1 HCl or 0.3 mol·L−1 H2SO4 (flow rate = 0.5 mL·min−1). (C) Breakthrough profiles for Os(IV) and Rh(III) mixture in the condition of CRh(III) = COs(IV) = 5 μg·mL−1, pH 2.5, flow rate = 0.2 mL·min−1, weight of adsorbent = 10 mg.

adsorption onto nano-Al2O3 adsorbents at 298 K was quite fast and the equilibrium was attained in about 5 min (Figure 4B). For this reason 5 min was selected in all subsequent studies. In order to investigate the adsorption processes of Os(IV) and Rh(III) on the adsorbents, pseudo-first-order and pseudosecond-order kinetic models were used. Pseudo-first-order39 lg(qe − qt) = lgqe −

k1t 2.303

(pH 5.0) was passed through the loaded nano-Al2O3 adsorbent at a rate of 0.2 mL·min−1. As shown in Figure 5A, it is clear that the breakthrough of Os(IV) took place after 145 min (513 bed volume), whereas it took about 45 min (159 bed volumes) for Rh(III). From the area of the breakthrough curve, the maximum loading capacities of the nano-Al2O3 for Os(IV) and Rh(III) were evaluated as 20.97 and 5.84 mg·g−1, respectively. The breakthrough curve showed a fast adsorption kinetic which was in agreement with the result obtained in batch operations. Figure 5B showed the elution profiles of the loaded Os(IV)/Rh(III) ions with 0.1 mol·L−1 HCl/0.3 mol·L−1 H2SO4 solution at the eluent flow rate of 0.5 mL·min−1. It revealed that all the metal ions were eluted with high concentration factors of 91.0 for Os(IV) and 38.6 for Rh(III). According to the area of the curves, 95.12% Os(IV) and 99.91% Rh(III) were eluted and recovered. It is clear that the recovery of precious metals in this study was quite high, and it is probably due to the optimal affinity of nano-Al2O3 for precious metal ions. Column Selective Separation. Since nano-Al2O3 had shown high selectivity for Rh(III) and Os(IV) (as seen in Figure 2) at pH 2.0−3.0, a continuous-mode column experiment was performed to obtain a breakthrough profile where a binary mixture of osmium and rhodium solution was fed through the column. It is clear from Figure 5C that the breakthrough for Os(IV) has occurred at 513 bed volumes while Rh(III) has passed through the column almost with no adsorption, suggesting very easy mutual separation between these metal ions by adjusting the pH of solution, and then the collecting effluent liquid was passed through the column packed with nano-Al2O3 for recovering Rh(III). Four consecutive adsorption−elution cycle tests using a column packed with the nano-Al2O3 for recovering Os(IV) and Rh(III) were also conducted, and results are shown in Figure 6. It was found that nano-Al2O3 could be efficiently reused without any damage. Comparison of the amount of Os(IV) and Rh(III) adsorbed and eluted in each cycle verified that they could be quantitatively recovered under continuous flow

(7)

Pseudo-second-order39 t 1 t = + 2 qt qe k 2qe

(8)

where qe and qt are the amounts (mg·g−1) of solute bound at the interface at the equilibrium and after time t (min), respectively, k1 is the rate constant of the pseudo-first-order adsorption (min−1), and k2 is the rate constant of the pseudosecond-order adsorption (g·mg−1·min−1). The parameters of the kinetic models can be extracted from the batch kinetic data of this study. The straight-line plots of lg(q − qt) or t/qt versus t have been tested to obtain rate parameters, respectively. Based on the correlation coefficients, the adsorptions of Os(IV) and Rh(III) were better described by the pseudo-second-order model (r2 > 0.99, insert into Figure 4B) than pseudo-first-order (r1 < 0.95). The rate constant k2 for Os (IV) and Rh (III) were 0.16 and 2.714 g·mg−1·min−1, respectively. The activation energy (Ea) could also be calculated based on the obtained rate constants k2 presented using the Arrhenius formula.40 A values of Ea for Os(IV) and Rh(III) adsorption onto nano-Al2O3 were obtained to be 16.98 and 3.32 kJ·mol−1, respectively. Column Studies. Column Experiment and Elution. Column experiments were carried out in a glass column connected to a peristaltic pump for controlling the flow rate. Feed solution with Os(IV)/Rh(III) concentration of 5 μg·mL−1 15204

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preconcentration of osmium and rhodium ions. The extraction equilibrium was achieved in less than 5 min. The packed column was reused many times (n = 4) without loss in column performance. The data obtained would prove useful in designing an effluent treatment plant for Os and Rh rich effluents in batch as well as in column systems.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86 24 62207809. Fax: +86 24 62202380. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

Figure 6. Four consecutive adsorption−elution cycles for recovering Os(IV) and Rh(III) using a column packed with the nano-Al2O3.

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ACKNOWLEDGMENTS This project was supported by the National Nature Science Foundation of China (NSFC51178212), Liaoning Provincial Department of education innovation team projects (LT2012001), the Shenyang Science and Technology Plan (F12-277-1-69) and the Foundation of 211 project for Innovative Talent Training, Liaoning University. The authors also thank their colleagues and other students who participated in this work.

systems. Such preliminary experiments demonstrated that nano-Al2O3 was compatible with column operation. Recovery of Precious Metals from Simulated Industrial Leach Liquor. Based on the results of the adsorption tests, the applicability of nano-Al2O3 was examined for the recovery of precious metals from simulated industrial waste. The flow experiment was conducted using a column for the separation of Os(IV) and Rh(III) from some base metals ions. Waste effluent was synthesized; the mixture solution consists of 2.60 × 10−5 mol·L−1 Os(IV), 4.85 × 10−5 mol·L−1 Rh(III), and 0.02 mol·L−1 Cu(II), Zn(II), Co(II), Ni(II), Cd(II), Pb(II), and Fe(III). As shown in Figure 7, the results showed that almost all of the Os(IV) and Rh(III) were recovered according to the area of the breakthrough and elution curves, while the adsorption of copper, zinc, cobalt, nickel, cadmium, lead, and iron as observed was negligible. It could be calculated from Figure 7B that 95.1% Os(IV) and 99.9% Rh(III) were eluted and recovered, respectively. Thus, the adsorbent was quite efficient for the separation of multimixture into individual components of Os(IV) and Rh(III).

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REFERENCES

(1) Barakat, M.; El-Mahdy, G.; Hegazy, M.; Zahran, F. Hydrometallurgical Recovery of Nano-Palladium from Spent Catalyst. Open Miner. Process. J. 2009, 2, 31. (2) Barakat, M. A.; Mahmoud, M. H. H.; Mahrous, Y. S. Recovery and Separation of Palladium from Spent Catalyst. Appl. Catal. A: Gen. 2006, 301, 182. (3) Gromov, O.; Kunshina, G.; Kuz’min, A.; Seitenova, E.; Lokshin, E.; Kalinnikov, V. Recovery of Platinum and Palladium from Deactivated Catalysts. Russ. J. Appl. Chem. 1999, 72, 1865. (4) Moawed, E. A.; Ishaq, I.; Abdul-Rahman, A.; El-Shahat, M. F. Synthesis, Characterization of Carbon Polyurethane Powder and Its Application for Separation and Spectrophotometric Determination of Platinum in Pharmaceutical and Ore Samples. Talanta 2014, 121, 113. (5) Fontàsa, C.; Hidalgoa, M.; Salvadóa, V. Adsorption and Preconcentration of Pd(II), Pt(IV), and Rh(III) Using AnionExchange Solid-Phase Extraction Cartridges (SPE). Solvent Extr. Ion Exc. 2009, 27, 83. (6) Shen, Y. F.; Xue, W. Y. Recovery Palladium, Gold and Platinum from Hydrochloric Acid Solution Using 2-Hydroxy-4-Sec-Octanoyl Diphenyl-Ketoxime. Sep. Purif. Technol. 2007, 56, 278.

4. CONCLUSION In this study, a highly selective sample cleanup procedure combined with nano-Al2O3 was developed for the separation and recovery of osmium and rhodium from aqueous solution. This SPE technique was successfully applied for separation and preconcentration of osmium and rhodium from simulated industrial leach liquor samples. Furthermore, external Cu, Zn, Co, Fe, Cd, Ni, and Pb ions had no significant effects on

Figure 7. (A) and (B) Breakthrough curves and the elution curves for selective adsorption and separation Os(IV) and Rh(III) from some base metals ions. 15205

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dx.doi.org/10.1021/ie502501g | Ind. Eng. Chem. Res. 2014, 53, 15200−15206