Separation Of Palladium Research Articles

Separation of Palladium and Rhodium from the Spent Metal-Honeycomb Catalysts by Pulsed Discharge without Chemical Additives

Separation of Palladium and Rhodium from the Spent Metal-Honeycomb Catalysts by Pulsed Discharge without Chemical Additives

Separation of Pd from Pt and Rh by solvent extraction method from waste solution

The paper investigated the possibility of extractive separation of palladium from platinum and rhodium with ionic liquid Cyphos IL 101. A technological solution obtained by dissolving waste materials was used as the test material. Based on the experiments performed, it was found that a 10% (v/v) solution of the Cyphos IL 101 ionic liquid in toluene allows the extraction of both Pd and Pt with an efficiency of 99% from the initial solution when extraction is carried out at the pH 0.5, vorg:vaq phase ratio 1:1 and contact time of 15 min. Moreover, the research proved that it is possible to separate Pd from Pt at the stripping stage using a 0.1 mol/dm3 thiourea solution while maintaining a high selectivity coefficient.

Separation of Palladium by an Imine-Linked Cu(I)-Organic Framework.

Selective capture of palladium (Pd) is one of the important works in science due to its high application and low content in the Earth's crust. To this end, we present herein a new Cu(I)-organic framework (ECUT-MOF-1) by introducing pyridine N active sites to chelate Pd(II). ECUT-MOF-1 demonstrated that the maximal adsorption capacity of Pd(II) was 350 mg/g in pH = 3 solution. In addition, kinetic analysis, cycle performance, selectivity, and adsorption mechanisms were also investigated. All of the results suggested its superior application in the recovery of Pd(II).

Thiol-functionalized cellulose adsorbents for highly selective separation of palladium over platinum in acidic aqueous solutions

The selective separation of palladium (Pd) over platinum (Pt) remains a challenge in metal recycling, because of their similar electronic configuration and chemical properties. This study explored their selective separation using three new adsorbents by grafting sulfur-donor ligands onto cellulose, namely 2-aminothiophenol (Cell-AP), 2-mercaptopyridine (Cell-MP), and 2-mercaptobenzothiazole (Cell-MBT). These adsorbents exhibited excellent adsorption capacity for Pd(II), reaching 163.3 ± 2.5 mg/g (at pH 1), 92.5 ± 1.2 mg/g (at pH 1), and 27.5 ± 0.5 mg/g (at pH 2.5), respectively. Isotherm studies showed that the adsorption process followed Freundlich isotherm, indicating a multilayer adsorption that takes place on a heterogenous surface. Kinetic results fit best with pseudo-second-order and intra-particle diffusion model, suggesting that the rate-limiting process involves chemisorption and intra-particle diffusion. Thermodynamic studies showed that adsorption by Cell-AP and Cell-MP was a spontaneous exothermic reaction. The materials also showed superior selectivity of Pd(II) over Pt(IV) with a maximum separation factor (SFPd/Pt) of 64.50, which improves over most previous studies. The mechanism of selectivity was further investigated by XPS, FTIR, SEM and DFT calculations, which showed that PdCl42- has smaller size, shorter HOMO-LUMO gap, and lower binding energy to ligands as compared to PtCl62-. This was used to explain the higher affinity for Pd(II) over Pt(IV) of these sulfur-modified adsorbents. This work provides a practical approach for the selective separation of Pd over competing ions that could improve the efficiency for overall metal recovery or recycling processes.

Efficient capture of palladium from nuclear wastewater by the sulfide and thiol modified covalent organic framework

The effective separation of palladium isotopes from high-level radioactive waste offers significant advantages, not only in ensuring the safe management and disposal of radioactive materials but also in addressing the scarcity of noble metals. In this study, a covalent organic framework (COF-SSH) modified with thiol and thioether groups is synthesized for the purpose of palladium separation. The experimental results demonstrate that the adsorption of Pd(II) occurs rapidly, reaching equilibrium within just 10 min. The adsorption isotherm for Pd(II) aligns well with the Langmuir model, revealing a maximum adsorption capacity of 420.2 mg/g at 3 M HNO3. Through Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Photoelectron Spectroscopy (XPS), and Density Functional Theory (DFT) analyses, the interaction between Pd and S atoms as being crucial for the adsorption process is identified. Moreover, COF-SSH exhibits exceptional selectivity for Pd(II) in simulated nuclear wastewater and maintains its performance throughout six consecutive adsorption and regeneration cycles. These results suggest that COF-SSH is a promising adsorbent for palladium separation, offering both acid resistance and high selectivity, making it a valuable candidate to the field of radioactive waste management and noble metal recovery.

Efficient and Selective Removal of Palladium from Simulated High-Level Liquid Waste Using a Silica-Based Adsorbent NTAamide(C8)/SiO2-P.

In order to realize the effective separation of palladium from high-level liquid waste (HLLW), a ligand-supported adsorbent (NTAamide(C8)/SiO2-P) was prepared by the impregnation method in a vacuum. The SiO2-P carrier was synthesized by in situ polymerization of divinylbenzene and styrene monomers on a macroporous silica skeleton. The NTAamide(C8)/SiO2-P adsorbent was fabricated by impregnating an NTAamide(C8) ligand into the pore of a SiO2-P carrier under a vacuum condition. The adsorption performance of NTAamide(C8)/SiO2-P in nitric acid medium has been systematically studied. In a solution of 0.2 M HNO3, the distribution coefficient of Pd on NTAamide(C8)/SiO2-P was 1848 mL/g with an adsorption percentage of 90.24%. With the concentration of nitric acid increasing, the adsorption capacity of NTAamide(C8)/SiO2-P decreases. Compared to the other 10 potential interfering ions in fission products, NTAamide(C8)/SiO2-P exhibited excellent adsorption selectivity for Pd(II). The separation factor (SFPd/other metals > 77.8) is significantly higher than that of similar materials. The interference of NaNO3 had a negligible effect on the adsorption performance of NTAamide(C8)/SiO2-P, which maintained above 90%. The adsorption kinetics of Pd(II) adsorption on NTAamide(C8)/SiO2-P fits well with the pseudo-second order model. The Sips model is more suitable than the Langmuir and Freundlich model for describing the adsorption behavior. Thermodynamic analysis showed that the adsorption of Pd(II) on NTAamide(C8)/SiO2-P was a spontaneous, endothermic, and rapid process. NTAamide(C8)/SiO2-P also demonstrated good reusability and economic feasibility.

Extraction of Palladium from Spent Nuclear Fuel Reprocessing Solutions

New solvent systems for selective separation of palladium from nuclear wastes represent a prospective way to reduce the total waste volume and induce this metal’s extraction. For this purpose, the potential of modern green solvent room-temperature ionic liquid was assessed with diamide-type extractants based on N-heterocycles and S-donating thiodiglicolic acid. The N-donating heterocyclic extractants demonstrate structure-dependent high selectivity toward palladium in the presence of various impurity metals (such as Zr, Cs, Sr, Mo, Ce, Fe, and Cr) from spent nuclear fuel. Palladium is extracted into the organic phase quite selectively with a separation factor greater than a thousand for all extractants. Ionic liquid media are capable of selective palladium separation from platinum group metals and synergetically increase the selectivity of the extractants.

Ultra‐Selective and Efficient Static/Dynamic Palladium Capture from Highly Acidic Solution with Robust Macrocycle‐Based Polymers

AbstractThe capture of palladium from spent nuclear fuel is crucial for the sustainable development of nuclear energy and resource recovery. One of the most challenging issues in this direction is the survival of adsorbents under extreme reprocessing conditions such as strongly acidic media and high radiation fields while still maintaining high extraction ability and selectivity. Herein, an approach to addressing this issue is reported by incorporating macrocycle into nitrogen‐rich covalent organic polymers (COPs). Dramatically outperforming current adsorbing materials, pillar[5]arene‐based COPs with pyridyl and triazolyl functionalities display record adsorption capacity for Pd(II) at 3 M HNO3 (403 mg g−1), extraordinary stability under 500 kGy gamma irradiation, and ultra‐high selectivity toward Pd(II) over both 17 coexisting cations and six anions. In particular, the material P5COP‐m‐BPT with the best performance also shows remarkable dynamic adsorption efficiency for Pd(II). This study not only provides a strategy to enhance all‐sided adsorption performance in palladium separation with nitrogen‐rich COPs materials but also demonstrates the superiority of customizing advanced materials with macrocycles.

Separation of Palladium from Alkaline Cyanide Solutions through Microemulsion Extraction Using Imidazolium Ionic Liquids.

In this paper, three imidazolium-based ionic liquids, viz., 1-butyl-3-undecyl imidazolium bromide ([BUIm]Br), 1-butyl-3-octyl imidazolium bromide ([BOIm]Br), and 1-butyl-3-hexadecyl imidazolium bromide ([BCIm]Br), were synthesized. Three novel microemulsions systems were constructed and then were used to recover Pd (II) from cyanide media. Key extraction parameters such as the concentration of ionic liquids (ILs), equilibration time, phase ratio (RA/O), and pH were evaluated. The [BUIm]Br/n-heptane/n-pentanol/sodium chloride microemulsion system exhibited a higher extraction percentage of Pd (II) than the [BOIm]Br/n-heptane/n-pentanol/sodium chloride and [BCIm]Br/n-heptane/n-pentanol/sodium chloride microemulsion systems. Under the optimal conditions (equilibrium time of 10 min and pH 10), the extraction percentages of these metals were all higher than 98.5% when using the [BUIm]Br/n-heptane/n-pentanol/sodium chloride microemulsion system. Pd(CN)42- was separated through a two-step stripping procedure, in which Fe (III) and Co (III) were first separated using KCl solution, then Pd(CN)42- was stripped using KSCN solution (separation factors of Pd from Fe and Co exceeded 103). After five extraction-recovery experiments, the recovery of Pd (II) through the microemulsion system remained over 90%. The Pd (II) extraction mechanism of the ionic liquid [BUIm]Br was determined to occur via anion exchange, as shown by spectral analysis (UV, FTIR), Job's method, and DFT calculations. The proposed process has potential applications for the comprehensive treatment of cyanide metallurgical wastewater.

Efficient separation of palladium from nitric acid solution by a novel silica-based ion exchanger with ultrahigh adsorption selectivity

Palladium (Pd) in high level liquid waste (HLLW) is a valuable alternative resource besides its natural reserves. On the other hand, the presence of Pd has extremely negative impacts on the vitrification process of HLLW. To separate Pd from HLLW, a novel silica-based adsorbent named HEMAP/SiO2-P was designed and prepared by using 2-hydroxyethyl-2-methyl-2-propenoate phosphate as the functional group donor, dichloromethane as the diluent and styrene–divinylbenzene modified silica particle as the carrier. The experimental results reveal that HEMAP/SiO2-P possesses excellent adsorption selectivity (SFPd/other metals > 183.2) and large adsorption capacity (393.4 mg/g) towards Pd in 1 M HNO3 solution. Moreover, column experiments show that the adsorbent can effectively separate Pd from other coexisting metal ions in simulated HLLW with the recovery yield of 99.4%. The experimental and characterization analyses as well as DFT calculations confirm that the adsorption mechanism involves ion exchange between Pd(II) and H+ (in P-OH) accompanied by the transfer of charge.

Complexation and Separation of Palladium with Tridentate 2,6-Bis-triazolyl-pyridine Ligands: Synthesis, Solvent Extraction, Spectroscopy, Crystallography, and DFT Calculations.

Selective extraction of palladium from high-level liquid waste (HLLW) is desirable for the sustainable development of nuclear energy and resource recovery. In this work, three tridentate 2,6-bis-triazolyl-pyridine ligands (L-I, L-II, and L-III) bearing different alkyl side chains were synthesized and systematically studied for the complexation and extraction of palladium. Altering the alkyl side chains of the ligands led to pronounced differences in extraction performance. Among the three ligands, L-II decorated with two n-octyl groups exhibited the highest Pd(II) extraction efficiency at acidity levels of 1-5 M HNO3 and outstanding selectivity over 13 coexisting competing metal ions. Results from UV-vis titration experiments and theoretical calculations suggested that the differentiated extraction abilities of the ligands could be because of their different hydrophilicity rather than electron-donating effects. Slope analyses and electrospray ionization-high resolution mass spectrometry (ESI-HRMS) experiments revealed the formation of both L/Pd 1:1 and 2:1 species during the extraction process. These stoichiometries were further confirmed by job plots and NMR titration experiments. The ligands were found to aggregate slightly, especially at higher concentrations, which could result from multiple intermolecular hydrogen bonds as illustrated by X-ray crystallography. The configurations of PdL and PdL2 were further elucidated by analysis of single crystal structure and density-functional theory (DFT) calculations, respectively, where the first coordination sphere of Pd(II) was surrounded by four nitrogen or oxygen atoms in a quadrangular manner. This study provides an alternative method to separate palladium from HLLW and brings a new understanding of the coordination and complexation behaviors of Pd(II) with tridentate nitrogen ligands.

Highly selective separation of palladium from spent catalysts by ozonation with ultrasonic enhancement in a low-acid medium

It is of great significance to consider the recovery of palladium from spent catalyst in terms of resource reserve and environmental protection. However, the leaching percentage of palladium is limited by high oxidation potential and cladding layer. In order to solve this process problem, externalfield enhancementmethod with ultrasonic-assisted ozone is proposed for the recycling of palladium in this study. Mechanical and cavitation effects of ultrasonic can destroy cladding layer and promote solid–liquid interface reaction. The highly oxidizing free radicals generated by ultrasonic excitation of ozone can improve the oxidation of the reaction system and accelerate the oxidation rate of palladium. The leaching percentage of palladium is 93.7% under ultrasonic/ozone condition, which is 23.7% higher than that under conventional conditions. The leaching reaction kinetics shows that the reaction barrier is reduced and the apparent activation energy is reduced by 35.25 kJ/mol after introducing ultrasound and ozone. Additionally, mineralogical analysis is carried out to analyze the enhanced leaching mechanism of palladium. This work demonstrates the value of advanced oxidation process with ultrasonic-assisted ozone in efficient and green recovery of precious metals from secondary resources.

Selective capture of palladium by protonation-armed pyridine nitrogen in extreme water environments

Due to the hostile environment in which it is recovered, selective separation of palladium from the leachate of spent catalysts containing palladium is of considerable utility but faces substantial obstacles. This work designed and synthesized a bipyridine-based porous organic polymer (POP-BPy) via free radical polymerization. Meanwhile, its adsorption characteristics and the mechanism of adsorption in extreme environments were examined. In hostile conditions, the resultant POP-BPy display exceptional mechanical stability and environmental resistance. Impressively, POP-BPy has an excellent adsorption capacity of Pd(II) (248 mg/g) in harsh environments (aqua regia: AR; half-diluted aqua regia: AR“1 + 1”), and also had superior selectivity and rapid kinetics. The selectivity of POP-BPy for Pd(II) was verified in combination with relevant experiments (βPd(II)/Pt(II) = 36.19, βPd(II)/Pt(II) = 23.90). Furthermore, combining density functional theory (DFT) and molecular dynamics (MD) simulations, the mechanism of selectivity of POP-BPy for Pd(II) was revealed from static adsorption sites to dynamic adsorption processes in a holistic manner, which attributed to the strong attraction of protonated pyridine nitrogen to PdCl42- and site suitability. Furthermore, the application of POP-BPy to spent catalyst recovery resulted in up to 100% removal of Pd(II) from the actual leaching solution, and fixed bed column experiments can effectively treat 2688 bed volumes (L) of feed streams (10 mg/L) before reaching the breakthrough point (<1 mg/L). Overall, this work has opened up new avenues for the selective recycling of valuable metals in harsh environments.

Efficient separation of palladium from high-level liquid waste with novel adsorbents prepared by sulfhydryl organic ligands containing imidazole, thiazole and oxazole composited with XAD7HP

Separation of palladium from high level liquid waste (HLLW) not only manages the dispose of HLLW, but could also aid in overcoming the shortage of palladium resources. Herein, three novel adsorbents, namely, 2-mercaptobenzimidazole (MBI)/XAD7HP, 2-mercaptobenzothiazole (MBT)/XAD7HP, 2-mercaptobenzoxazole (MBO)/XAD7HP were prepared by vacuum impregnation method using Amberlite XAD7HP resin (XAD7HP) as the carrier for the selective separation of Pd(II) from simulated HLLW. SEM-EDS (Scanning Electron Microscopy), BET (Brunauer-Emmett-Teller) and PXRD (Powder X-ray diffraction) analysis showed that the ligands were successfully impregnated into the carrier. The saturated adsorption capacities of MBI/XAD7HP, MBT/XAD7HP, MBO/XAD7HP in 0.5 M HNO3 were 126.2 mg Pd/g, 137.6 mg Pd/g, 98.4 mg Pd/g, respectively, and excellent adsorption and separation performance towards Pd(II) (SFPd/other metals > 500 and Kd > 104 mL/g from 0.1 to 4 M HNO3) were also achieved. The adsorption kinetics and adsorption isotherms for Pd(II) matched well with pseudo-second-order kinetic model and Langmuir model, indicating that the adsorption for Pd(II) by three adsorbents were monolayer chemical adsorption. The adsorption mechanism was analyzed by FT-IR, XPS combined with DFT calculation. The extremely high selectivity of three adsorbents towards Pd(II) among 15 metal ions is due to the soft N and S donor atoms at ligands which have good affinity for Pd(II) in HNO3 solution. As MBT/XAD7HP exhibited the best adsorption and separation properties, it is supposed to have more application potential for the separation of Pd(II) from HLLW.

Separation of Palladium, Platinum and Rhodium from Metallic Mixture by Selective Dissolution with Hydrochloric Acid Solutions Containing Oxidizing Agents

ABSTRACT Platinum group metals are widely used in the manufacture of advanced materials due to their excellent physical and chemical properties. Especially, palladium (Pd), platinum(Pt), and rhodium(Rh) are used as catalysts for automobiles. In general, combination of pyrometallurgical and hydrometallurgical process is necessary to recover PGMs. In this work, the separation of Pd, Pt, and Rh from the metallic mixture was investigated by selective dissolution using HCl solutions containing oxidizing agents such as H2O2 and NaClO3. As a diluent for the leaching medium, either water or ethylene glycol (EG) was employed and the dissolution behavior of the three metals was compared. Selective dissolution of 99.9% Pd from the metallic mixture was achieved by using 1 M HCl and 1.225 M M H2O2 (H2O medium, 40°C, 30 min), while that of 99.9% Pt was possible by using 5 M HCl and 0.5 M NaClO3 (H2O medium, 60°C,120 min). By these two-step dissolution, Rh metal remained in the residue. A simple process was proposed to separate Pd, Pt, and Rh from their metallic mixture by selective dissolution.

Preparation of metal-organic framework composite beads for selective adsorption and separation of palladium: Properties, mechanism and practical application

Separation and recovery of palladium from industrial waste is an environmental way to utilize the valuable secondary resources. Metal-organic framework (MOF) has a great potential for the adsorption of Pd(Ⅱ) from aqueous solutions, but the tiny powder form of MOF restricts its practical applications. In this work, a feasible and green method is developed to prepare novel MOF composite beads (B-MOF) with a stable cross-linked network. The adsorption performance of B-MOF for Pd(Ⅱ) was evaluated in acidic solutions. Comprehensive characterization results show that the structure of B-MOF is stable throughout the adsorption process. At pH 3.0, the adsorption capacity of Pd(Ⅱ) on B-MOF was high up to 334.68 mg.g−1, exhibiting superiority to most of the other congeneric adsorbents. The adsorption behavior accorded with the pseudo-second-order kinetic model and the Langmuir adsorption isotherm, which was a spontaneous and endothermic chemisorption process. Moreover, the adsorption performance of B-MOF persisted almost unchanged even after 12 regeneration cycles. B-MOF also demonstrated high selectivity to Pd(Ⅱ) in the presence of interfering ions, including Na(Ⅰ), K(Ⅰ), Ni(Ⅱ), Mg(Ⅱ), Cu(Ⅱ), Zn(Ⅱ), Co(Ⅱ), Ca(Ⅱ) and Al(III). Mechanism studies reveal that Pd(Ⅱ) can be adsorbed on B-MOF by the inner-sphere complexation to Zr-nodes and the electrostatic attraction with protonated amine groups. The recovery of Pd from a real industrial waste was successfully achieved with a recovery rate of 92.5 %. This study provides an effective method to improve the practicability of MOF-based materials and may open a new way for the disposal of industrial waste containing palladium.

Extractive Recovery and Separation of Palladium(II) and Platinum(IV) from Chloride Solutions

Extractive Recovery and Separation of Palladium(II) and Platinum(IV) from Chloride Solutions

Preparation of a novel silica-based N-donor ligand functional adsorbent for efficient separation of palladium from high level liquid waste

In this work, a novel silica-based N-donor ligand functional adsorbent (SiVpC) is prepared by in situ polymerization for the efficient separation of palladium from high level liquid waste (HLLW). The as-prepared SiVpC adsorbent is characterized by SEM-EDS, TGA, and BET. The effects of nitric acidity, SiVpC adsorbent dosage, time, temperature, and palladium ion concentration on the adsorption are investigated. Among the 12 typical fission product metal ions (Ru, Rh, La, Y, Pr, Ce, Sm, Nd, Gd, Eu, Zr, Mo) existing in HLLW, SiVpC adsorbent can selectively adsorb palladium (SFPd/other metals = 137.6) in 0.5 M HNO3 solution. The adsorptio kinetics of Pd(II) are consistent with the pseudo-second-order model, reaching equilibrium within 120 min. The maximum adsorption capacity is 38.4 mg/g in 0.5 M HNO3, and the adsorption process is consistent with the Langmuir model. The adsorbed palladium can be completely desorbed with 0.5 M HNO3-0.5 M Thiourea. Furthermore, SiVpC adsorbent remains good performance after five adsorption–desorption cycles, which indicates good reusability. The adsorption mechanism of SiVpC adsorbent on palladium is analyzed by FT-IR and XPS that N-containing functional groups on the ligand are coordinated with palladium, which is also further verified by DFT calculations. In addition, through the column chromatography separation system, SiVpC adsorbent can efficiently adsorb palladium from HLLW and the adsorbed palladium can be desorbed with 0.5 M HNO3-0.5 M thiourea solution, which has great application potential.

High-efficiency separation of palladium from nitric acid solution using a silica-polymer-based adsorbent isoPentyl-BTBP/SiO2-P

A silica-polymer-based adsorbent (isoPentyl-BTBP/SiO2-P) was prepared via a vacuum impregnation method for efficient and continuous separation of palladium from complex systems. The results revealed that the distribution coefficient (Kd) value of isoPentyl-BTBP/SiO2-P toward Pd in 3 M HNO3 solution was 5226 mL/g, with a maximum adsorption capacity of 31.7 mg/g. Besides, isoPentyl-BTBP/SiO2-P exhibited a superior adsorption selectivity toward Pd to the other 14 coexisting interfering fission product ions, with the separation factor SFPd/M value over 433 in 0.1–6 M HNO3 solution. Moreover, column experiments results demonstrated that isoPentyl-BTBP/SiO2-P can efficiently separate Pd with approximately 100% recovery, from simulated high level liquid waste (HLLW) solutions with multiple competing ions. Finally, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analysis results revealed strong interactions between nitrogen-containing functional groups (C-NC) and Pd throughout the adsorption process, wherein the NO3− acting as the counterions to balance the charge. In conclusion, isoPentyl-BTBP/SiO2-P has shown promising applications for effectively separating Pd from multi-component and highly acidic environments.

Separation of palladium and silver from E-waste leachate: effect of nitric acid concentration on adsorption to Thiol scavenger

The development of recovery techniques for metals present in low concentrations in E-waste, such as silver and palladium, is important from the aspect of the circular economy. Adsorption of palladium and silver was studied in detail in a batch process with silica-based Thiol scavenger from nitric acid leachate of waste printed circuit boards (PCBs). High adsorption efficiencies of Pd(II) and Ag(I), >97%, were reached in nitric acid concentrations below 3 mol L−1. At higher acid concentrations, adsorption efficiency of Ag(I) decreased drastically which enables the separation of Ag(I) and Pd(II) based on nitric acid concentration in sample solution. Pd(II) and Ag(I) followed pseudo 2nd order kinetical model with fast adsorption with contact times of 60 and 30 min, respectively, in all studied acid concentrations. Adsorption followed Langmuir isotherm reaching highest loading capacities of 199 mg g−1 for Ag(I) and 105 mg g−1 for Pd(II) in 1 mol L−1 nitric acid media, after which loading capacities decreased while nitric acid concentration increased. Thiourea-based desorption agents were most effective for desorption with >80% desorption efficiencies for Ag(I) and 55 - 88% efficiencies for Pd(II) in a one-step desorption. However, separation of Pd(II) and Ag(I) is not entirely possible in desorption step, hence the highest separation between Pd(II) and Ag(I) was found with two-step adsorption in which Pd(II) and Ag(I) were separated initially at adsorption step based on nitric acid concentration, followed by desorption step with acidic thiourea solution.