Article pubs.acs.org/IECR
Ion Exchange Recovery of Palladium(II) from Acidic Solutions Using Monodisperse Lewatit SR‑7 Anna Wołowicz*,† and Zbigniew Hubicki†,‡ †
Department of Inorganic Chemistry, Faculty of Chemistry, Maria Curie-Skłodowska University, Maria Curie-Skłodowska Square 2, 20-031 Lublin, Poland ‡ Fertilizer Research Institute, 24-100 Puławy, Poland S Supporting Information *
ABSTRACT: This work focuses on the sorption recovery of palladium(II) present in chloride and chloride−nitrate(V) solutions on the commercial strongly basic anion exchanger Lewatit MonoPlus SR-7. Sorption, kinetic, and equilibrium studies were carried out using batch and dynamic methods. The basic parameters of sorption capacity, recovery degree, distribution coefficient, process rate, and half-exchange time were calculated. Effects of agitation speed, initial palladium(II) concentration, and total concentration of the chloride anions were tested. Regeneration and reuse of the resin was also investigated. The surface morphology of Lewatit MonoPlus SR-7 before and after the sorption process was described. Lewatit MonoPlus SR-7 is an efficient sorbent for Pd(II) ions (Langmuir capacity 197 mg/g), is characterized by good kinetic properties, and can be regenerated and reused repeatedly without decrease of capacity. Moreover, its capacity is high but decreases in the presence of aluminum ions and slightly increases with the temperature (313 K).
1. INTRODUCTION In the early 1980s Bayer was the first company to develop a process for producing monodispersive ion exchange resins. The production of such types of ion exchangers enjoyed great interest due to their improved chemical and physical properties which opened new perspectives for the users. Nowadays, extensive application of monodispersive ion exchange resins in many new technologies of higher standards is observed, e.g., wastewater treatment, portable water treatment, and purification of chemical solutions.1,2 Monodispersive ion exchange resins called Lewatit MonoPlus are produced as individual beads by a special process resulting in minimal deviation from a mean value. The bead size diameter for Lewatit MonoPlus lies between 0.55 and 0.75 mm, depending on the type. This type of resins is characterized by monodispersity higher than 90% (more than 90% of all beads are within 0.05 mm of the given bead diameter); therefore the uniformity coefficient of Lewatit MonoPlus resins is less than 1.1. The above-mentioned monodispersive form of resins gives high efficiency. The important advantages of Lewatit MonoPlus are presented in Figure S1 in the Supporting Information. The higher stability of the resins of Lewatit MonoPlus type and their extremely robust results in their long lifetimes are shown. In practice, this advantage leads to higher permitted differential pressures (30%) allowing greater resin bed depth and higher velocities. Moreover, their good kinetic properties cause reduction of required bed depth and ion leakage and permit shorter cycle times (contact time with water is less than 70 s). The better kinetic properties, the better exchange behavior resulting in lower regenerant and rinsewater demand. Increase of regeneration efficiency and unit capacity (total capacity is improved by about 10% compared to the heterodisperse one) as well as decreases in the amount of resin required (smaller column) and operating costs are results of their high operating © 2012 American Chemical Society
capacity. The versatility of application of Lewatit MonoPlus leads to reduction of their storage costs and tied-up capital.1,2 Among different types of monodispersive ion exchangers, cationic and anionic ones can be distinguished. This group includes, e.g., strongly acidic Lewatit MonoPlus S100, Lewatit MonoPlus S 100H (gelular, cross-linked polystyrene), Lewatit MonoPlus ASP 112 (macroporous, cross-linked polystyrene), weakly basic Lewatit MonoPlus MP 64 (macroporous, crosslinked polystyrene), and strongly basic Lewatit MonoPlus MP 500 (macroporous, cross-linked polystyrene), Lewatit MonoPlus M 500, and Lewatit MonoPlus M 600 (gelular, crosslinked polystyrene). As shown in the literature, Lewatit MonoPlus resins are widely applied in base and noble metal ion recovery, sorption, and preconcentration, dye sorption, etc. such as Cu(II), Zn(II), Co(II), Ni(II), and Fe(III) sorption on Lewatit MonoPlus M 500, Lewatit MonoPlus MP 500, and Lewatit MonoPlus M 600 resins from aqueous solutions containing iminodisuccinic acid (IDS) or (EDTA);3,4 Ni(II) ion sorption from aqueous solution by Lewatit cation exchange resin SP 112;5 sorption of Tartrazine, Allura Red, Sunset Yellow, and Indigo Carmine from aqueous solutions onto the strongly basic anion exchanger Lewatit MonoPlus M 600;6 palladium sorption on Lewatit MonoPlus MP 64,7 Lewatit MonoPlus M 500,8 and Lewatit MonoPlus 214;9 platinum recovery on Lewatit MonoPlus MP 500A;10 and many other examples. Our previous studies dealt with applicability of different types of ion exchangers in palladium sorption taking into account also monodisperse resins such as Lewatit MonoPlus M 600,7 Received: Revised: Accepted: Published: 16688
August 28, 2012 November 5, 2012 November 24, 2012 November 24, 2012 dx.doi.org/10.1021/ie302304c | Ind. Eng. Chem. Res. 2012, 51, 16688−16696
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Table 1. Lewatit MonoPlus SR-7 Characteristics
Lewatit MonoPlus MP 500 and MP 500A,8 and Lewatit MonoPlus 214.9 This paper describes the applicability of Lewatit MonoPlus SR-7 in palladium(II) removal from the acidic solutions of different compositions. Kinetic and equilibrium studies of the sorption process and regeneration and reuse of this resin were considered.
0.9), 1:4 (0.2−0.8), 1:1 (0.5−0.5), 4:1 (0.8:0.2), and 9:1 (0.9− 0.1). The concentrations and acidity as well as the composition of initial palladium(II) solutions were chosen to make the experiment closer to real industrial conditions during recycling of secondary palladium raw materials. All reagents were of analytical purification grade (POCh, Poland). 2.2. Characteristics of Ion Exchangers. In the investigation the macroporous, monodisperse, polystyrene, commercially available, and economically reasonable strongly basic anion exchange (SBA) resin Lewatit MonoPlus SR-7 produced by Lanxess (Germany) was used. The physicochemical properties and brief specifications of this resin are presented in Table 1. The resin was selected for its good sorption properties and due to its high selectivity toward nitrate ions (SBA resin has 3 times higher the selectivity for nitrates than any commercially available anion exchangers). Prior to use, the resin was washed with 1 M NaOH and 1 M HCl as well as with distilled water several times to remove organic and inorganic impurities from its synthesis and was finally air-dried.
2. EXPERIMENTAL SECTION 2.1. Reagents and Solutions. Palladium(II) chloride solid was used to prepare palladium(II) stock solutions. The accurately weighed sample of this salt was dissolved in 1.0 M hydrochloric acid solutions at the temperature 333 K and subjected to microwaves (Inter Sonic, Type IS-1 with a thermoregulator; digestion time 1 h). After that, from the stock palladium(II) solution of 10 000 mg/L concentration palladium(II) working solutions were prepared. Concentrated hydrochloric acid and nitric acid were used to obtain their proper concentrations in Pd(II) working solutions. The concentrations of these acids were 0.1−6.0 and 0.1−0.9 M, respectively, under the molar ratios of HCl:HNO3 = 1:9 (0.1− 16689
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2.3. Apparatus and Analytical Procedure. The palladium(II) concentration in solution after the sorption or desorption process was determined by the spectrophotometric iodide and atomic absorption spectroscopy (AAS) methods; see details in Table S1 in the Supporting Information. Scanning electron BS:301 (Tesla) and atomic force NanoScope V (Veeco, USA) microscopes were used in order to obtain information about Lewatit MonoPlus SR-7 surface morphology. The content of C, H, and N elements in the SBA resin under discussion was obtained by means of the PerkinElmer CHN 2400 analyzer and the Sartorius M2P microbalance. 2.4. Methods for Sorption/Desorption Investigation. Kinetics and equilibrium studies of palladium(II) were carried out using the batch method. During the kinetic studies the experimental conditions were following: resin mass, 0.5 ± 0.0005 g; volume of contacting solution, 50 mL; temperature 298 ± 2 K; initial palladium(II) concentration, 50−300 mg/L; agitation speed, 120, 150, and 180 rpm; amplitude = 8. The SBA resin quantities were stirred with 50 mL of palladium(II) solution at 298 ± 2 K over a time period from 1 min to 24 h. The mixing times were 1 min, 3 min, 5 min, 10 min, 15 min, 30 min, 1 h, 2 h, 3 h, 4 h, 6 h, and 24 h. After a certain time period, the SBA resins and Pd(II) solutions were separated by filtration and concentration of Pd(II) ions was determined in the solutions by the AAS method. In the case of equilibrium studies the initial palladium(II) concentrations were in the range from 100 to 2800 mg/L, the agitation speed was 180 rpm, amplitude = 8, and other parameters were the same as in the kinetic studies. The efficiency of the ion exchange recovery of palladium by the SBA resin under discussion was estimated by means of the recovery degree (R, %):11,12 R = (Co − Ce/Co) ·100%
% D = accomplished metal weight (mg) /initially sorbed metal weight (mg) ·100%
The above-described procedure was repeated five times (five cycles of sorption/desorption) in order to obtain important information about Lewatit MonoPlus SR-7 reuse. 2.5. Column Studies. Fixed bed sorption was done in glass columns of 1.0 cm diameter and 25 cm height, packed with 10 mL of swollen SBA resin. For single palladium sorption, 100 mg/L Pd(II) solution was flowed through the Lewatit MonoPlus SR-7-packed column, at a flow rate of 4 mL/min. The effluent was collected manually in fractions of different volumes depending on the stage of the sorption (near the breakthrough point the fractions were of 100 mL volume). Each fraction containing unknown palladium(II) content was analyzed for residual Pd by the iodide and AAS methods. The solution was continued to pass through until the attainment of inlet−outlet Pd concentration equilibrium, which indicated no further palladium sorption was occurring. 2.6. Effect of Interfering Aluminum Ions and Temperature on Pd(II) Sorption. Palladium(II) sorption on Lewatit MonoPlus SR-7 was also examined in the presence of aluminum ions and with increasing temperature (batch method). The solution composition and sorption parameters of the batch method were the following: 10% HCl−5% AlCl3− 100 mg/L Pd(II); temperature, ambient and 313 K. The other parameters such as ion exchange resin dose (0.5 g), agitation speed (180 rpm), amplitude (A = 8), volume of the solution (50 mL), and phase contact time (from 1 min to 24 h) were the same as in the kinetic studies.
3. RESULTS AND DISCUSSION 3.1. Behavior of Sorption Column: Effect of Acid Concentration. The palladium(II) sorption capacities of Lewatit MonoPlus SR-7 under column conditions (see the Experimental Section) for solutions of different compositions were obtained. The results are presented in the form of breakthrough curves which present the correlation between the total volume of effluents collected (V (mL) is the volume of the effluent collected from the column) and the normalized concentration C/Co, which means the ratio of Pd(II) concentration determined by the AAS method at the outlet to the initial palladium(II) concentrations in the feeding solutions. These breakthrough curves for the chloride (Figure 1) and chloride−nitrate(V) solutions (not presented) show an S-shape. These curves are much more steep for the chloride solutions than for the chloride−nitrate ones. Additionally, the palladium(II) concentrations obtained by means of the AAS and iodide methods are really close; therefore, the curve courses are similar and they are negligibly dependent on the detection technique. Based on these breakthrough curves, the volumes of the effluent at C/Co equal to 0.5 and 0.159, respectively, were read from the plot of C/Co vs V [mL] and the working ion exchange capacities as well as the distribution coefficients and the number of theoretical plates were calculated from the following equations:
(1)
and the equilibrium sorption capacity is expressed as13 qe = (Co − Ce)V /W
(2)
where Co and Ce are the initial and equilibrium concentrations of Pd(II), respectively (in mg/L); V (in L) is the volume of Pd(II) contacting solution; W (in g) is the SBA resin mass. Additionally, the saturation degree (F) was calculated from eq 3:
F = qt /qe
(4)
(3)
where qt and qe are the amounts of Pd(II) sorbed (in mg/g) at time t and equilibrium, respectively. The kinetic curves were obtained (plot of F versus t), and the half-exchange times, t1/2 (in s) were determined from these curves at F = 0.5.11,12 The desorption experiments were conducted for the SBA resin Lewatit MonoPlus SR-7 to determine the palladium(II) recovery of the exhausted sorbents. The Pd-loaded sorbent was resuspended with 50 mL of various concentrations of eluting solutions, e.g., hydrochloric acid (0.1−6.0 M HCl), nitric acid (0.1−4.0 M HNO3), and ammonia (0.5−2.0 M NH4OH). The suspension was shaken at 180 rpm for 4 h to allow Pd(II) to release from the SBA resin. After filtration in order to separate the liquid and solid, the Pd(II) concentration in the supernatant portion was measured. The percentage of palladium(II) desorbed from the SBA resin was calculated from eq 4: 16690
Cw = (VpCo)/Vj
(5)
Dw = (U − Uo − Vv)/mj
(6)
Dv = Dw dz
(7)
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the void (interparticle) anion exchanger bed volume, mj is the dry anion exchanger mass [g], and dz is the anion exchanger density. As Table 3 shows, the highest sorption parameters were obtained for the 0.1 M HCl and 0.9 M HCl−0.1 M HNO3 solutions. Varying HCl concentrations may affect palladium(II) sorption through the effect of both chloride and hydrogen ions. Depending on the pH and their total concentrations in solutions, the speciation of palladium(II) can be different (see Figure S2 in the Supporting Information) and, in turn, it can control the affinity of palladium(II) for the binding sites.14 In the case of solutions under consideration, palladium(II) in the chloride solutions forms the chloride complexes of negative charge PdCl42−. On the other hand, hydrogen ions control the protonation of amine groups, which, in turns, allows binding of anionic complexes on Lewatit MonoPlus SR-7 according to eq 9:
Figure 1. Breakthrough curves for Pd(II) sorption on Lewatit MonoPlus SR-7.
N = (U ′ − Uo)(U − Uo)/(U − U ′)2
Moreover, the solution of higher hydrochloric acid concentration leads to the presence of an excess of counteranions (chloride anion) which compete with the anionic metal species of the Lewatit MonoPlus SR-7 binding sites, resulting in reduction of its capacity by about 96% (0.1−6.0 M HCl).15 In the solution of high hydrochloric acid concentration, the
(8)
where Vp is the effluent volume to the breakthrough point [mL], Vj is the bed volume [mL], 10 mL, U is the effluent volume at C/Co = 0.5 [mL], U′ is the effluent volume at C/Co = 0.159 [mL], Uo is the dead volume in the column [mL], Vv is
Table 2. Recovery Degree (% R), Sorption Capacity (qe), and Half-Exchange Time (t1/2) Values in Pd(II) Sorption under Different Experimental Conditions
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Table 3. Palladium(II) Sorption Parameters on Lewatit MonoPlus SR-7 Obtained by the Column Method hydrochloric acid concentration [M]
a
hydrochloric/nitric acid concentration [M]
sorption parametera
symbol
0.1
1.0
3.0
6.0
0.1/0.9
0.2/0.8
0.5/0.5
0.8/0.2
0.9/0.1
working ion exchange capacity weight distribution coeff bed distribution coeff no. of theoretical plates
Cwb
0.0490 2062.4 548.4 1497.4
0.0230 1084.6 288.4 109.6
0.0070 379.1 100.8 21.5
0.0015 88.4 23.5 14.5
0.0030 698.0 185.6 2.1
0.0050 540.8 143.8 2.0
0.0030 418.2 111.2 2.9
0.0080 646.1 171.8 13.7
0.0150 823.6 219.0 3.5
Dw Db N
Parameters obtained by the iodide method. bIn g/mL.
acidic solutions and also implied that the resin could possibly be used in continuous flow systems. The pseudo-first-order (PFO), pseudo-second-order (PSO), and intraparticle diffusion kinetic equations can be expressed as follows:
formation of other Pd(II) chloro complexes starts such as PdCl53− and PdCl64−. Making a comparison between the amounts of PdCl42− and other anionic chloro complexes presented above, it can be stated that the PdCl42− form is still dominant in the solutions of high hydrochloric acid concentration and the contribution of other Pd(II) complexes is small and can be neglected. A similar trend is observed for other monodispersive anion exchangers examined previously; e.g., the reduction of capacity is equal to 78.6% (MP 500A, 0.1−2.0 M HCl−1.0 M NaCl),7 70.58% (M-600, 0.1−2.0 M HCl−1.0 M NaCl), 64.3% (MP 500, 0.1−2.0 M HCl−1.0 M NaCl),9 and 57.2% (TP-214, 0.1−3.0 M HCl), respectively. Other sorption parameters also decrease with the hydrochloric acid increase. The effectiveness of the sorption process was also confirmed by the studies of the resin surface after the Pd(II) sorption process. 3.2. Pd(II) Sorption and Kinetics. Sorption studies of Pd(II) ions were selected with regard to potential application of the adsorbents in the hydrometallurgical separation procedure and recovery processes. The sorption ability of the investigated sorbents belonging to the SBA resins, type 3, was investigated in acidic solution. Initial palladium(II) concentrations, phase contact time, and agitation speed effect were considered. The obtained results are collected in Table 2. As shown by the data in the batch experimental conditions, Lewatit MonoPlus SR-7 removed palladium(II), but the removal is not quantitative. Based on different initial Pd(II) concentrations, the equilibrium capacities should be near 5, 10, 20, or 30 mg of Pd(II)/g. In this case these capacities are lower and the recovery factor is in the range from 92.8 to 99.92%. Values of sorption capacities increase with the initial palladium(II) concentration increase. Moreover, the half-exchange time values, t1/2, indicate that the rate of the sorption process is affected by the initial palladium(II) concentration resulting in slower kinetics in the solution with higher Pd(II) concentration, but the differences of t1/2 values are not significant. A much stronger effect on the rate of the sorption process is exerted by the agitation speed, which was in this study in the range from 120 to 180 rpm, particularly at the beginning of the sorption process. The halfexchange time values drop significantly with the increase of agitation speed, but the equilibrium capacities reached the same values (9.99 mg/g) or higher with the higher agitation speed. Increase of the total concentration of the chloride anions leads to the slowest kinetics of the system due to the competitive effect which is stronger in the solution of higher hydrochloric acid concentration (increase of the half-exchange times is observed). The kinetic curve showed that the Pd(II) sorption was rapid, with high Pd(II) removal efficiency, and equilibrium was reached rapidly but depending on the experimental conditions. The rapid kinetic rate exhibited the significant advantage of Lewatit MonoPlus SR-7 for application in Pd(II) removal from
pseudo-first-order kinetic equation: log(qe − qt ) = log qe − k1/2.303t
(10)
pseudo-second-order kinetic equation: t /qt = (1/k 2qe 2 + 1/qe)t
(11)
intraparticle diffusion equation: qt = k intt 1/2 + C
(12)
Equations 10−12 were applied in the analysis of the experimental data. In these equations, qe and qt are the amounts of Pd(II) sorbed at equilibrium and at any time t (mg/ g), k1 and k2 are the pseudo-first-order and pseudo-secondorder rate constants (in L/min and g/mg min, respectively), and kint is the rate parameter for the intraparticle diffusion (mg/ g min1/2). C is the intercept obtained by extrapolation of the linear portion of the plot of qt versus t0.5 back to the axis and is taken to be proportional to the extent of the boundary layer thickness. In the case of the pseudo-second-order kinetic equation, the initial sorption rate, h (mg/g min), was obtained using the following equation: h = k 2qe 2
(13)
The average percentage error, ε (%), between the experimental and predicted values was calculated using the following equation: N
ε (%) = (∑ |(qexp , i − qcal, i)/qexp , i| /N )·100% i
(14)
In eq 14, N is the number of measurements and qexp and qcal represent the experimental and calculated Pd uptake values (mg/g), respectively. The rate constants, calculated Pd(II) equilibrium uptakes, and corresponding correlation coefficients were calculated and collected in Table S2 in the Supporting Information. In the case of the pseudo-first-order kinetic equation, the calculated sorption capacity values significantly deviated from the experimental ones and also the correlation coefficient was very low with a very high percentage error value in the range from 37.6 to 46.5%. The pseudo-second-order kinetic equation predicted the sorption behavior throughout the entire study, and the predicted Pd(II) uptake was consistent with the experimental ones. Additionally, the correlation coefficient for the pseudo-second-order kinetic equation was much higher than in the case of the PFO in all presented cases 16692
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Figure 2. Langmuir isotherm (a) fitting to the experimental data, (b) curve, and (c) comparison of the maximum sorption capacities for ion exchangers.
3.3. Pd(II) Sorption Isotherms. The palladium(II) equilibrium studies were carried out by means of the batch method due to their importance for the design of the sorption system. The experimental Pd(II) isotherm and maximum Lewatit MonoPlus SR-7 resin uptake were obtained and compared to those of the other sorbents. The best known and frequently applied isothermthe Langmuir isothermwas used. It describes the physisorption of neutral particles (molecules, atoms) on the surface of a sorbent which possesses energetically homogeneous sorption sites. Additionally, only a monolayer adsorbate coverage of the adsorbent surface is assumed and the desorption rate is independent of the neighboring sorption sites occupancy. The Langmuir isotherm can be represented using the following equation:14,18
(>0.99(9)) with an average percentage error much lower than before (lower than 7.6%), indicating the applicability of this kinetic equation and the pseudo-second-order nature of the palladium(II) sorption process on the Lewatit MonoPlus SR-7. According to the intraparticle diffusion, the uptake varies almost proportionately with the half-power of time, t0.5, and if the rate-limiting step is intraparticle diffusion, a plot of solute sorbed against the square root of the contact time should yield a straight line passing through the origin.16 This type of plots may present a multilinearity indicating that two or more stages are involved in the sorption process. The first stage (sharper) can be attributed to the sorbate diffusion through the solution to the external surface of the sorbent or the boundary layer of ions or sorbate molecule diffusion. The second one describes the gradual sorption, where intraparticle diffusion is a ratelimiting step and the third stage is attributed to the final equilibrium for which the intraparticle diffusion starts to slow down due to extremely low sorbate concentration left in solution.17 In the case of palladium(II) complex sorption onto the ion exchanger Lewatit MonoPlus SR-7 a multilinearity of the intraparticle diffusion plot is observed (Table S2 in the Supporting Information). Moreover, this plot is not linear over the whole time range. This fact may indicate that the palladium(II) sorption process occurs by surface sorption as well as by intraparticle diffusion (meso- and micropores); that means that more than one process affects the palladium(II) sorption. The multiple nature of intraparticle diffusion plots can be explained by boundary layer diffusion which gives the first portion and the intraparticle diffusion that gives further two linear portions. It can be deduced from the multilinear plots that there is more than one process that controls the rate of sorption. As presented in Table S2 (intraparticle diffusion plots) in the Supporting Information, the external surface adsorption (stage 1) is present and completed up to 5 min, and then the stage of intraparticle diffusion control (stage 2) is attained and continues from 5 to 60 min. Finally, final equilibrium adsorption (stage 3) starts after 60 min.
Ce C 1 = + e qe qmax b qmax
(15)
In eq 15, qe is the amount of Pd(II) sorbed on Lewatit MonoPlus SR-7 (mg/g), Ce is the equilibrium concentration of the Pd(II) in the solution (mg/L), qmax is the maximum sorption capacity (mg/g), and b is the Langmuir equilibrium constant (L/mg) that is related to the free energy of the Pd(II) sorption. Figure 2 presents the fitting of the experimental data with the Langmuir and Freundlich isotherms and the Langmuir isotherm with the calculated parameters obtained by the regression method. Also a comparison of the maximum Pd(II) uptake by different types of resins is presented. The correlated coefficients of determination (R2) were over 0.989, indicating that the sorption of Pd on Lewatit MonoPlus SR-7 was consistent with the Langmuir model. High qmax values and a steep initial isotherm slope (high b) were desirable for favorable sorption. In this case, the maximum uptake and the Langmuir equilibrium constant of Pd(II) were approximately 197 mg/g and 0.037 L/mg, respectively. Moreover, the dimensionless constant, RL ((RL = 1/(1 + bCo); RL > 1, unfavorable isotherm; RL = 1, linear isotherm; RL = 0, irreversible isotherm), which is equal to 0.21 and contained in the range from 0 to 1, confirmed favorable sorption. The Lewatit MonoPlus SR-7 monodisper16693
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Figure 3. Regeneration and reuse possibility of Lewatit MonoPlus SR-7 by (a−d) acid and (e) base solutions.
data, the desorption efficiency of palladium(II) from Lewatit MonoPlus SR-7 is different depending on the eluting agents used. Sulfuric acid is not a suitable agent in Pd(II) removal from loaded resins. In this case desorption efficiency is nearly null. More efficient are acids such as hydrochloric and nitric or their mixture, but the desorption yield is higher in the case of hydrochloric and nitric acid mixture (e.g., 1.0 M HCl−1.0 M HNO3, 39.58%, D1; 1.0 M HCl, 1.59%, D1; 1.0 M HNO3, 10.52%, D1). Moreover, ammonia solutions at different concentrations of 0.5−3 M have been also tested and the above half amount of Pd(II) sorbed was desorbed from the resin (55−61%). A much lower, less than 10%, desorption yield of palladium(II) from N-(2-(2-pyridyl)ethyl)chitosan (PEC) by means of ammonia solutions (0.5−3 M) was obtained by
sive resin is very promising and interesting from the application point of view due to the fact, that as shown in Figure 2, its maximum capacity is much higher than that of many other ion exchangers. 3.4. Sorption/Desorption Cycles: Lewatit MonoPlus SR-7 Reuse. The reversibility of palladium(II) sorption was tested as a key parameter for evaluating the potential of Lewatit MonoPlus SR-7 for large scale application. The costs of Lewatit MonoPlus SR-7 make polymer recycling necessary; therefore, its reuse was also presented. Several eluents were tested: acidic (0.1−6.0 M HCl, 0.1−4.0 M HNO3, 0.1−1.0 M HCl−0.1−1.0 M HNO3, 0.1−2 M H2SO4) and basic (0.5−2.0 M NH4OH) solutions. Figure 3 presents the results obtained from five cycles of sorption/desorption. As can be seen from the presented 16694
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Santos Sopena et al.14 Also, a lower Pd(II) desorption yield (
