Preparation and application of 4-amino-4′-nitro azobenzene modified chitosan as a selective adsorbent for the determination of Au(III) and Pd(II)

Cross-linked chitosan as biomacromolecular adsorbents for adsorption of precious metal-chloride complexes from aqueous media

Precious metal recovery from secondary sources has received significant attention due to the reduced availability of precious metals from conventional sources. Herein, chitosan (CHT) was modified via cross-linking with glutaraldehyde (glu) to yield CHT-glu adsorbents with improved physicochemical and adsorption properties with precious metal ions (Au(III) and Pd(II)). CHT-glu adsorbents were prepared at variable glu ratios and characterized via complementary spectral (IR, 13C solids NMR, XPS) and thermogravimetry methods. The adsorbents display remarkably enhanced properties relative to CHT upon incremental cross-linking, which includes structural stability in acidic media, greater porosity and surface area with unparalleled adsorption at pH 2. The highest metal-ion uptake capacity for the CHT-glu adsorbent system was 1322 mg/g (Au(III)) and 1337 mg/g (Pd(II)). Electrostatic and chelation interactions govern the adsorption mechanism of gold and palladium species by CHT-glu, as supported by XPS results. The CHT-glu systems display superior solid phase extraction properties for the recovery of precious metals from acidic leachate, which is relevant to sustainable metal recovery from tailings or industrial wastewater effluent.

Synthesis of activated biochar from sustainable bamboo resources: An environment-friendly and low-cost solution for palladium (II) removal from wastewater

This article highlights the developing capabilities of low-cost activated biochar from bamboo waste used for Palladium (II) (Pd(II)) separation from man-made electroless plating solutions (ELP). From a novelty perspective, this article addresses the effect of coupled sonication and surfactant for the adsorptive elimination of Pd(II) on Bamboo stem activated carbon (BSAC) from ELP. The optimal activation procedure referred to an acid-to-bamboo ratio of 4:1 at sintering of 600-900 °C, which provided an activated carbon (AC) adsorbent with surface area analysis (BET) of 1014.36 m2/g, a value comparable to the commercially procured AC. Pd(II) adsorption characteristics in the solution of Pd with 50-500 mg/L concentration range were evaluated utilizing both agitation and sonication. Adsorption time, pH, dose, and adsorbate concentration were among the pertinent optimal batch adsorption parameters that were found. When utilizing ELP solutions without surfactant, the proposed adsorbent for agitation-assisted adsorption had a simultaneous improvement in metal intake of 6.68-43.2 mg/g and removal efficiency of 72.96-54.5% (cTAB). For cTAB-containing solutions, sonication and agitation-assisted adsorption were outperformed in terms of removal efficiency of 80.32-60.16% and metal uptake of 6.69-50.13 mg/g. Equilibrium, kinetic, and thermodynamic models with good fitting to the reported Pd(II) adsorption properties have been developed.

Gold(III) recovery from aqueous solutions by raw and modified chitosan: A review

Chitosan, a prestigious versatile biopolymer, has recently received considerable attention as a promising biosorbent for recovering gold ions, mainly Au(III), from aqueous solutions, particularly in modified forms. Confirming the assertion, this paper provides an up-to-date overview of Au(III) recovery from aqueous solutions by raw (unmodified) and modified chitosan. A particular emphasis is placed on the raw chitosan and its synthesis from chitin, characteristics of raw chitosan and their effects on metal sorption, modifications of raw chitosan for Au(III) sorption, and characterization of raw chitosan before and after modifications for Au(III) sorption. Comparisons of the sorption (conditions, percentage, capacity, selectivity, isotherms, thermodynamics, kinetics, and mechanisms), desorption (agents and percentage), and reusable properties between raw and modified chitosan in Au(III) recovery from aqueous solutions are also outlined and discussed. The major challenges and future prospects towards the large-scale applications of modified chitosan in Au(III) recovery from aqueous solutions are also addressed.

Environmental separation and enrichment of gold and palladium ions by amino-modified three-dimensional graphene

The excellent adsorption properties of three-dimensional graphene (3DG) can be further enhanced by triethylenetetramine modification to increase its adsorption capacity for precious metal ions. Herein, we successfully synthesized an amino-modified 3DG (N-3DG) adsorbent with improved adsorption conditions with regards to pH value, dosage, and adsorption time. Adsorption equilibrium was reached at pH 3 over 120 min. In addition, the theoretical basis for the adsorption of N-3DG is provided by fitting the adsorption isotherm model. The synthesized material was tested in seawater and lake water samples for the adsorption of precious metals, namely Au(iii) and Pd(ii), achieving a recovery rate of 87% to 106% as assessed by inductively coupled plasma mass spectrometry. Thus, N-3DG showed good adsorptivity. The present results indicate that N-3DG materials could have a viable application in environmental and sewage treatment in the near future.

Role of EDTA on the Pd(II) adsorption characteristics of chitosan cross-linked 3-amino-1,2,4-triazole-5-thiol derivative from synthetic electroless plating solutions

This article targets the efficacy of chitosan cross-linked 3-Amino-1,2,4-triazole-5-thiol derivative for the recovery of Pd from synthetic electroless plating solutions (ELP) whose solution chemistry complexity is brought forward with ethylenediaminetetraacetic acid (EDTA), ammonium hydroxide (NH₄OH), and surfactant (cetyl trimethyl ammonium bromide (CTAB)). Batch adsorption characteristics of the resin were investigated in the parametric range of 2-10 pH, 0.2-2 g L^-1 adsorbent dosage, 5-1080 min contact time, 50-300 mg L^-1 Pd concentration and 25-60 °C operating temperature. Equilibrium, kinetic and thermodynamic model fitness studies were also considered. Pd(II) adsorption characteristics were determined using NaOH, KOH and HCl solutions with variant eluent concentrations (0.1-2 N). The solution chemistry complexity has been evaluated to have profound impact in detrimentally influencing Pd sorption characteristics of the CH-AZ resin. The resin has been characterized to be highly effective for Pd removal from synthetic ELP solutions but with moderate efficacy towards the noble metal recovery and reuse.

A New Ion-Imprinted Chitosan-Based Membrane with an Azo-Derivative Ligand for the Efficient Removal of Pd(II)

Herein, we described the synthesis of a novel ion-imprinted membrane for the detection of palladium(II) prepared through the glutaraldehyde crosslinking of chitosan with a 4-[(4-Hydroxy)phenylazo]benzenesulfonic acid ligand trapped into the membrane. The imprinting technology was used to improve adsorption capacity and adsorption selectivity, and was combined with some advantages of the developed membrane, such as low cost and ease of preparation, water-friendly synthesis, and high biocompatible chitosan material. The membranes were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectrometry (EDS). The results obtained showed a high swelling ratio with a maximum value of 16.4 (1640%) at pH 4 with a strong pH dependence. Batch rebinding experiments gave a maximum adsorption capacity of 101.6 mg of Pd(II) per gram of imprinted membrane. The Pd(II) adsorption behavior was well-described by a Langmuir model with a theoretical maximum adsorption capacity of 93.48 mg g^-1, similar to the experimental one. Finally, a selectivity study versus Ag(I), Pb(II), and Fe(III) ions demonstrated a good selectivity of chitosan-imprinted membrane towards Pd(II).

Application of chitosan and its N-heterocyclic derivatives for preconcentration of noble metal ions and their determination using atomic absorption spectrometry

Chitosan and its N-heterocyclic derivatives N-2-(2-pyridyl)ethylchitosan (2-PEC), N-2-(4-pyridyl) ethylchitosan (4-PEC), and N-(5-methyl-4-imidazolyl) methylchitosan (IMC) have been applied in group preconcentration of gold, platinum, and palladium for subsequent determination by atomic absorption spectroscopy (AAS) in solutions with high background concentrations of iron and sodium ions. It has been shown that the sorption mechanism, which was elucidated by XPS, significantly influences the sorption capacity of materials, the efficiency of metal ions elution after preconcentration, and, as a result, the accuracy of metal determination by AAS. We have shown that native chitosan was not suitable for preconcentration of Au(III), if the elution step was used as a part of the analysis scheme. The group preconcentration of Au(III), Pd(II), and Pt(IV) with subsequent quantitative elution using 0.1M HCl/1M thiourea solution was possible only on IMC and 4-PEC. Application of IMC for analysis of the national standard quartz ore sample proved that gold could be accurately determined after preconcentration/elution with the recovery above 80%.

ESI(+)-MS and GC-MS study of the hydrolysis of N-azobenzyl derivatives of chitosan

New N-p-chloro-, N-p-bromo-, and N-p-nitrophenylazobenzylchitosan derivatives, as well as the corresponding azophenyl and azophenyl-p-sulfonic acids, were synthesized by coupling N-benzylvchitosan with aryl diazonium salts. The synthesized molecules were analyzed by UV-Vis, FT-IR, ¹H-NMR and ¹⁵N-NMR spectroscopy. The capacity of copper chelation by these materials was studied by AAS. Chitosan and the derivatives were subjected to hydrolysis and the products were analyzed by ESI(+)-MS and GC-MS, confirming the formation of N-benzyl chitosan. Furthermore, the MS results indicate that a nucleophilic aromatic substitution (S_nAr) reaction occurs under hydrolysis conditions, yielding chloroaniline from N-p-bromo-, and N-p-nitrophenylazo-benzylchitosan as well as bromoaniline from N-p-chloro-, and N-p-nitrophenylazobenzyl-chitosan.

Separation of trace amounts palladium by SiO2/TiO2/Ce nanoparticles prior to flame atomic absorption spectrometry determination in anodic slime and wastewater samples

In the present work, a new SiO2/TiO2/Ce, nanoparticle was synthesed using sol-gel method and evaluated as an adsorbent for preconcentration trace amounts of Pd(II) ions. The characterization of the nanoparticles has been studied by transmission electron microscope and X-ray diffraction. The preconcentration method is based on palladium adsorption onto the surface of nanoparticle at pH 8.5. The main factors affecting Pd(II) adsorption, such as pH of sample solution, concentration and volume of eluent, sample volume, interfering of the coexisting ions and flow rate of sample and eluent were investigated and optimized. At optimum conditions, linearity was maintained between 4.0 to 1000.0 ng mL−1. Detection limit based on 3Sb/m was 2.3 ng mL−1. Seven replicate determinations of a solution containing of 12.5 µg palladium gave a relative standard deviation ±1.7%. According to the Langmuir linear model, the maximum adsorption capacity of palladium was found to be 34.5 mg g−1. Finally, the feasibility of the proposed method for Pd(II) determination was assessed by analysis of certified reference materials, anodic slime and wastewater samples and satisfactory results were obtained.

Precious metal recovery by selective adsorption using biosorbents

Silk sericin and chitosan biosorbents are low cost and highly efficient biosorbents derived from waste biomass. Both biosorbents displayed good capacity and excellent selectivity for gold adsorption. Silk sericin and chitosan adsorbed respectively 1 and 3.3mmolg(-1) of gold and have K(d) values of 450 and 34,000, respectively. Experimental evidence showed that gold adsorbed on the amide groups of the silk sericin, while gold and copper adsorbed on the amino groups of chitosan via charge-interactions and complexation. Binary (Au-Cu), five (Au-Co-Ni-Cu-Zn) and six (Au-Pd-Co-Ni-Cu-Zn) component separations consistently showed that silk sericin has better selectivity (Sel(Au)>2.4) than chitosan. It is possible to recover gold at 99.5% purity by silk sericin and 90% if the solution contained palladium.