Functionalized and reusable polyethylene fibres for Au(III) extraction from aqueous solution with high adsorption capacity and selectivity

Abstract

A new chelating polyethylene fibre was synthesised by the radiation-induced graft copolymerisation of glycidyl methacrylate (GMA) onto ultrahigh-molecular-weight polyethylene (UHMWPE) fibres and subsequent ring-opening reaction with 4-amino-1,2,4-triazole. The chemical structure and surface morphology of the modified fibres were characterised by Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The adsorption behaviour of the fibrous sorbent for Au(III) was investigated in terms of aqueous-solution pH, contact time, initial metal concentration and competition of coexisting metal ions. Resultant fibres exhibited much higher affinity and selectivity for Au³⁺ ions than all other metal ions (Mg²⁺, Fe³⁺, Cu²⁺, Ca²⁺, Ni²⁺ and Cr⁶⁺). The affinity coefficient obtained was as high as 97.5–99.9%. The maximum adsorption amount for Au³⁺ was 429.4 mg g⁻¹. The adsorption of Au(III) followed the pseudo-second-order kinetics model controlled by chemical adsorption. The equilibrium data fitted the Langmuir isotherm model well. In particular, this fibrous adsorbent can be regenerated by treatment in 0.5 M thiourea and 0.5 M H₂SO₄ solution. The high adsorption capacity can be maintained after at least five adsorption–desorption cycles.

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1. Introduction

As a kind of precious metal, Au has been widely used in industry, agriculture and medicine because of its specific physical and chemical properties.¹ Many aqueous solutions containing Au³⁺ were produced through the metallurgical process of Au ore and other applications. Therefore, the extraction of Au from wastewater, which does not only prevent environmental pollution but also saves resources and has considerable economic benefits, is necessary. Several methods have been adopted to recover Au from aqueous solutions containing Au³⁺, such as precipitation, cyanide leaching, filtration, electrochemical treatment, reverse osmosis, ion exchange resins and evaporation. However, these techniques are costly, inefficient and even environmentally hazardous.^2,3 In recent years, great interest has been devoted to the preparation of organo-functionalized adsorbents because of their multiple uses in inspissation and separation processes.^4–9 The functional groups in the adsorbents play a vital role in the process efficiency. Adsorbents that contain subgroups with sulphur or nitrogen atoms can be used in the selective removal of precious metals.^10,11 Organo-functional groups, for example, imidazole,¹² thiourea –N(C=S)NH₂,¹³ amide (–CONH₂),^14,15 alkyl sulphide (–RSR′–)¹⁶ and Schiff bases (RC=N–),¹⁷ have been successfully applied to the collection of trace precious metals. The adsorbents for recovering precious metals should have high capacity and selectivity against interfering metal ions, such as copper, iron and zinc, and other coexisting metal ions.¹⁸

Ultrahigh-molecular-weight polyethylene (UHMWPE), a high-performance fibre with a density less than water, excellent mechanical properties and corrosion resistance,¹⁹ has a great potential application in the recovery of precious metals from wastewater. Compared with traditional granular and powder adsorbents, fibres with chelating groups have advantages, such as a preferable mechanical property, high surface area, good regeneration and recycle properties and high adsorption capacity and selectivity in treating wastewater, including precious metal ions.²⁰ However, little has been reported on the use of UHMWPE-based adsorbents for the recovery of Au(III) ions from aqueous solutions.

In this paper, a novel chelating fibre based on UHMWPE fibre was prepared through radiation-induced graft polymerisation and subsequent chemical reactions (Scheme 1). The characteristics and adsorption mechanisms were investigated through the analysis of the differences in the Fourier transform infrared (FTIR) spectra, X-ray photoelectron spectra (XPS), and scanning electron microscopy (SEM) photographs of the fibrous adsorbent before and after Au(III) adsorption. Adsorption kinetics, isotherms, the effects of initial pH value, adsorption time and coexisting anions were investigated intensively to understand the Au(III) adsorption process further.

Scheme 1 Procedure for the preparation of the UHMWPE-g-(GMA-ATZ) fibres.

2. Experimental

2.1 Materials and instruments

UHMWPE fibre (diameter: 20 μm; density: 0.97 g cm⁻³; line density: 3.61 Denier) obtained from Beijing Tongyizhong Advanced Material Company (Beijing, China) was used as a trunk polymer for grafting. Glycidyl methacrylate (GMA, Sigma-Aldrich) was used without further purification. Analytical grade chloride salts of magnesium, iron, copper, nickel, zinc and chromium were used to prepare the test solutions of the respective metal ions. Analytical grade HAuCl₄·4H₂O was used to prepare the Au solutions (Sinopharm Chemical Reagent Co., Ltd). Distilled water was used throughout the experiments. All other solvents were obtained commercially and were used without purification.

2.2 Preparation of the adsorbent

The synthesis route of UHMWPE-g-(GMA-ATZ) fibres is shown in Scheme 1. UHMWPE fibres sealed in a polyethylene bag were irradiated by the γ-ray in air at ambient temperature. The irradiated UHMWPE fibres were dispersed in a solution composed of GMA (10 vol%) and methanol. The system was degassed by bubbling with a high purity nitrogen to remove oxygen, and then the reaction mixture was stirred under a nitrogen atmosphere at a fixed temperature for 3 h. After the reaction, the grafted fibres were washed thoroughly with acetone and deionized water, successively. The fibres were dried in a vacuum oven at 60 °C. The grafting yield was calculated as follows:where W₀ and W_g are the weights of the fibres before and after grafting, respectively.

Subsequently, the resultant fibres (UHMWPE-g-GMA) were immersed in a solution containing 4-amino-1,2,4-triazole (ATZ, 10 vol%) and 1,4-dioxane. After reacting at 80 °C for 8 h, the resulting fibres were taken out and washed with deionized water, and then dried in a vacuum oven at 60 °C to a constant weight.

2.3 Characterisation

The composition and structure of the fibre samples were characterised by FTIR (AVATAR-560, America) and X-ray photoelectron spectroscopy (XPS, an Axis Ultra DLD spectrometer, Kratos, England). Also, the tensile strength and elongation at break were measured on a tensile testing machine. The concentrations of the metal ions in the aqueous solution (before and after adsorption) were determined by ICP-AES (Optima 8000, Perkin Elmer). A JSM-6360LV scanning electron microscope (SEM) was used to investigate the surface morphology of the fibre samples before and after adsorption.

2.4 Adsorption studies

Batch adsorption tests were carried out through a shaking machine (DSHZ-300A) with a rate of 120 rpm at a constant temperature. A 0.02 g UHMWPE-g-(GMA-ATZ) fibre was immersed in 100 mL of metal ions aqueous solution at the desired initial concentration, pH and constant temperature for a determined contact time. The pH was adjusted using a HCl solution (1 M). Adsorption kinetics was studied at an initial Au(III) concentration of 200 mg L⁻¹. Different initial Au(III) concentration values from 20 mg L⁻¹ to 400 mg L⁻¹ were used in the adsorption isotherm study. The adsorption amount (Q, mg g⁻¹) of metal ions on the UHMWPE-g-(GMA-ATZ) samples was measured by the subsequent formula:where C₀ is the initial concentration in the solution (mg L⁻¹), C_e is the equilibrium concentration in the solution (mg L⁻¹), V is the solution volume (L) and m is the adsorbent mass (g).

2.5 Statistical analysis

The statistical study was carried out using Microsoft Excel software. Results are expressed as the mean values of at least three independent experiments. Categorical univariable comparisons were evaluated with Student's t-test. The correlations between the parameters were assessed with Pearson's correlation coefficient. For all analyses, P < 0.05 was considered significant.

3. Results and discussion

3.1 Chemical structure analysis of the adsorbent

The FTIR spectra of the UHMWPE, UHMWPE-g-GMA, and UHMWPE-g-(GMA-ATZ) fibres are shown in Fig. 1. The characteristic peaks at 2920, 2850, 1470 and 720 cm⁻¹ were assigned to the antisymmetric and symmetric stretching, bending, and rocking vibrations of the CH₂ groups on the UHMWPE trunk polymer²¹ in Fig. 1(a). In comparison with the UHMWPE fibre, the characteristic absorption band of the –C=O group at 1740 cm⁻¹ indicated that the GMA was grafted onto the UHMWPE fibre. The band at 1669 cm⁻¹,²² belonging to –C–N– in the imidazole rings, appeared in the spectra of the UHMWPE-g-(GMA-ATZ) fibre, confirming that the reaction between the ATZ and epoxide group was complete and the ATZ ligands were anchored on the fibre.

Fig. 1 FTIR spectra of (a) trunk polymer, UHMWPE, (b) GMA-grafted polymer (sample A, 200% graft), (c) ATZ-modified GMA-grafted polymer (sample A, M_GMA = 4.5 mmol g⁻¹, M_ATZ = 4.8 mmol g⁻¹).

The scanning electron micrographs of the UHMWPE and modified UHMWPE fibres are shown in Fig. 2(a) and (b). Compared with the micrograph of the UHMWPE fibre, the surface of UHMWPE-g-(GMA-ATZ) fibres became rough and hilly because of the GMA grafting and triazole functionalisation. Many granules clearly appeared on the surface of the fibres after the adsorption of Au ions (Fig. 2(c)), and the fibre surface became more rough and compact.

Fig. 2 SEM images of (a) UHMWPE; (b) UHMWPE-g-(GMA-ATZ) and (c) UHMWPE-g-(GMA-ATZ)–Au(III) complex.

The elemental surface compositions and chemical changes occurred on the trunk polymer were investigated by XPS analysis. As shown in Fig. 3(a), a strong peak attributed to C 1s (283.4 eV) is observed on the XPS spectrum of the pristine UHMWPE. The GMA grafted UHMWPE exhibited two characteristic peaks corresponding to C 1s (285 eV) and O 1s (532.5 eV). The O 1s spectrum (Fig. 3(b)) can be fitted into two peak components, including C–O (533.4 eV) and C=O (532.04 eV). After ring-opening reaction, a new peak due to N 1s appears in the spectrum of UHMWPE-g-(GMA-ATZ), owning to the incorporation of ATZ groups to GMA units. Those results reveal that UHMWPE-g-(GMA-ATZ) fibres are successfully synthesized, which might provide available binding sites for Au(III) adsorption.

Fig. 3 The XPS survey scan spectra of UHMWPE, UHMWPE-g-GMA, UHMWPE-g-(GMA-ATZ) and UHMWPE-g-(GMA-ATZ)–Au(III) fibres (a) overall spectrum, (b) O 1s, (c) Au 4f, (d) and (e) N 1s. (Adsorption conditions: adsorbent 0.02 g, initial Au(III) concentration = 200 ppm, T = 298 K, 120 rpm, initial pH = 2.0, 48 h).

In addition, the spectrum (Fig. 3(a)) shows that a huge amount of chlorine is present on the UHMWPE-g-(GMA-ATZ) after the adsorption of Au(III), suggesting the direct sorption of some Au(III) as HAuC1₄. In order to further understand the adsorption mechanism of Au(III) on the surfaces of UHMWPE-g-(GMA-ATZ), (Fig. 3(c)) the high resolution XPS spectra of N 1s spectra were investigated. The N 1s binding energy located at 400.6 eV before Au adsorption was composed of a signal, which belongs to the nitrogen in the –N–H, N–C and =N– groups of triazole in the fibres. The N 1s band was shifted to 401.6 eV (Fig. 3(d)) when Au ions were adsorbed on the UHMWPE-g-(GMA-ATZ) adsorbents. This can be attributed to the coordination of nitrogen atoms in the triazole groups with the Au ions. Because of the appreciable uptake of Au(III) in the acidic media (HCl), the protonated auric species (HAuCl₄) may compete with HCl for interaction with the fibre as follows:²³

Polymeric matrix-N + HCl = polymeric matrix-NH + Cl⁻ (3)

Polymeric matrix-N + HAuCl₄ = polymeric matrix-NH + AuCl₄⁻ (4)

Therefore, the basicity of the donor atoms (N) plays a significant role in the formation of the salt above. The signals caused by Au 4f can be clearly observed in Fig. 3(a). The magnified spectrum shows that the Au 4f signal consists of two adjacent peaks assigned to Au 4f_7/2 (BE = 85.39 eV) and Au 4f_5/2 (BE = 88.3 eV) (Fig. 3(c)).²⁴ The peaks corresponding to Au 4d are located at BE = 353.2 eV,²⁵ indicating that Au(III) ions were adsorbed onto the UHMWPE-g-(GMA-ATZ) through the ion exchange mechanism.

The mechanical properties of the fabric adsorbents is a main factor affecting its service life and should be carefully examined. Tensile characterization was carried out on a tensile tester (LLY-06E, Laizhou Electron Instrument Co. Ltd. China) according to GB/T14337-2008, at a crosshead speed of 10 mm min⁻¹, and a span length of 20 mm. The maximum breaking force of 118.6 cN and the elongation at break of about 6.8% for the pristine UHMWPE fibre is achieved from the test results. A decrease in tensile properties of UHMWPE-g-(GMA-ATZ) fibre was observed where the breaking force decreased to 86.7 cN while the elongation-at-break increased to 21.3%. The reason behind this statistical decrease in the breaking force at break of the UHMWPE-g-(GMA-ATZ) compared with that of the UHMWPE fibre was likely to be explained by the irradiation and grafting GMA onto the UHMWPE backbone, resulting in a reduced flexibility of the fiber. However, UHMWPE-g-(GMA-ATZ) fibre still maintains a high enough tensile strength to adsorb Au(III) from aqueous solution.

3.2 Effect of pH on Au adsorption

The effect of initial pH on the uptake of Au(III) was studied and the results are presented in Fig. 4. Solution pH has a signification effect on the chemical morphology of chlorogold complexes. Au(III) was strongly adsorbed in acidic media and the distribution coefficient decreased with the increasing acidity.^26,27 The predominant complex of Au is evidently AuCl₄⁻ at pH < 3. Increasing the solution pH causes the hydrolysis of AuCl₄⁻ to proceed, and thus hydrolysed chlorogold, such as AuCl₃(OH)⁻, appears in the aqueous chloride solution.²⁸ The equilibrium constants are as follows:

Au(OH)₄⁻ + H⁺ + Cl⁻ ⇌ AuCl(OH)₃⁻ + H₂O, K₁ = 10^8.51 (5)

AuCl(OH)₃⁻ + H⁺ + Cl⁻ ⇌ AuCl₂(OH)₂⁻ + H₂O, K₂ = 10^8.06 (6)

AuCl(OH)₂⁻ + H⁺ + Cl⁻ ⇌ AuCl₃(OH)⁻ + H₂O, K₃ = 10^7.00 (7)

AuCl₃(OH)⁻ + H⁺ + Cl⁻ ⇌ AuCl₄⁻ + H₂O, K₄ = 10^6.07 (8)

Fig. 4 Effect of initial pH on the uptake of Au(III).

Au(III) was reported to be negatively charged anions in the presence of hydrochloric acid. Although triazole groups may contribute to metal chelation, their protonation significantly reduces their ability to react with Au and most of the metal sorptions can be explained by the electrostatic attraction of anion metal complexes by the protonated triazole groups. Based on the findings above, the adsorption mechanism of Au(III) on UHMWPE-g-(GMA-ATZ) in acidic solutions is assumed an electrostatic attraction and ion exchange. The decreased adsorption of precious metals observed at higher pH may be because of the electrostatic repulsion between the surface of the adsorbent and metals ions. Several studies in the literature²⁹ also reported that the higher adsorption of Au(III) was obtained at pH 2.0–3.0.

In the case of the solution pH range 1.0–3.0, the adsorption capacity of the Au(III) ions on UHMWPE-g-(GMA-ATZ) reached the maximum value of 349.8 mg g⁻¹ when the pH was 2. Fig. 5 illustrates the maximum adsorption capacities for Au³⁺ ion adsorption on three different types of modified adsorbents which are developed under various conditions as reported in the literature.^30–52 It can be seen that UHMWPE-g-(GMA-ATZ) fibres have the advantages of high adsorption capacity under the conditions of this research. Accordingly, the present adsorbent is expected to be applied to the wastewater treatment in this area because the pH of Au wastewater from the electroplating industry is usually in the range 1.0–3.0.^53,54

Fig. 5 Comparison of adsorption capacity of UHMWPE-g-(GMA-ATZ) for Au(III) with various adsorbents reported in the literature.

3.3 Adsorption kinetics

Fig. 6 shows that the adsorption capacity of Au(III) on the adsorbents decreased with the increasing temperature. The maximum sorption capacity was achieved at 288 K. A higher adsorption capacity at a lower temperature suggests that the mass transfer resistance was greatly reduced by the highly active adsorbent sites, resulting in the easy access of Au³⁺ to the imidazole group.⁵⁵

Fig. 6 Pseudo-second-order adsorption kinetics (a) and capacity Q (b) of Au(III) onto UHMWPE-g-(GMA-ATZ) fibres at different times and temperatures (weight of the adsorbent = 0.02 g, the initial Au(III) concentration = 200 ppm, the initial pH = 2.0).

The experimental date was analysed by the Lagergren first-order and pseudo-second-order models,^56,57 which are as expressed in the following equations, to investigate the mechanism and the rate-controlling step of the Au(III) adsorption process further.

where Q_e and Q_t are the adsorption capacities at equilibrium and various time (mg g⁻¹), respectively; Q₁ and Q₂ are the calculated adsorption capacities of the Lagergren first-order model and pseudo-second-order model (mg g⁻¹), respectively; and k₁ and k₂ are the rate constants of the Lagergren first-order model (h⁻¹) and the pseudo-second-order model (g mg⁻¹ h⁻¹). Table 1 shows that the correlation coefficients (R₂²) in the pseudo-second-order model were larger than 0.99. The Lagergren pseudo-second-order was better than the Lagergren first-order model in terms of the fitting of the Au(III) adsorption process. In other words, the adsorption process of Au(III) on the UHMWPE-g-(GMA-ATZ) fibre is controlled by chemisorption.^58,59

Table 1 Kinetics model constants for the adsorption of Au(III) by the UHMWPE-g-(GMA-ATZ) fibre

T (K)	Qe (mg g^−1)	Pseudo-first-order model			Pseudo-second-order model
		K1 (min^−1)	Q1 (mg g^−1)	R1^2	K2 (g mg^−1 min^−1) × 10^−5	Q2 (mg g^−1)	R2^2
288	429.4	0.00129	310.678	0.954	1.571	414.937	0.993
298	381.8	0.000975	137.756	0.781	4.818	381.679	0.999
308	372.6	0.00125	287.719	0.579	3.321	366.300	0.998

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3.4 Adsorption selectivity

Other metal ions, such as Ni²⁺, Cu²⁺, Fe³⁺ and Ca²⁺, often coexist with Au³⁺ in aqueous solutions. Therefore, estimating the selectivity of the UHMWPE-g-(GMA-ATZ) fibre for Au(III) ions is necessary in the solution with high concentrations of other metal ions. The fixation rate (R_F) was calculated according to the comparison of the affinity of the UHMWPE-g-(GMA-ATZ) fibre to each metal ion, which is expressed as follows:⁶⁰where the fixation rate, R_F, is the ratio of the equivalent number of each cation fixed on the fibres, n_equiv.(cation), to the total equivalent number in the fibres sample, n_equiv.(fibres).

The affinity coefficient α_(A–B) (or separation factor) was the quotient of the equivalent ionic fraction ratios, X_i, of two cations, A and B, in the fibres and the solution.⁶¹ It was calculated from the following equation:

Fig. 7 exhibits the adsorption results of Au(III) in a series of typical binary metal ions systems. Table 2 shows that the UHMWPE-g-(GMA-ATZ) fibres have much higher affinity for Au(III) than for other metals, such as Mg(II), Fe(III), Cu(II), Ca(II), Ni(II), Zn(II) and Cr(VI), under the operating condition when the concentration ratio of M (coexisting metal ion) and Au(III) is 1.0. The decreasing order of the adsorption capacities of the UHMWPE-g-(GMA-ATZ) fibre for the tested metal ions at pH 2 is Au(III) ≫ Cu(II) > Ca(II) > Mg(II) > Cr(VI) > Fe(III) > Ni(II) > Zn(II). The comparison of the adsorption capacities of the UHMWPE-g-(GMA-ATZ) fibre and noble metals for two days shows that the introduction of nitrogen atom (a base) noticeably increased the affinity for the precious metal ions, which are the soft acids according to the concept of hard and soft bases and acids defined by Pearson.⁶² As a result, no effect on the uptake of Au(III) ions was found in the evaluation of the adsorption selectivity at pH 2.0 using a Multi-ionic aqueous system. Therefore, the proposed method can be applied in practical use, for example, in mining Au ore. The UHMWPE-g-(GMA-ATZ) fibre is more efficient, environmental and convenient in extracting Au that several traditional technologies and methods that commonly utilise toxic mercury and cyanidation in Au(III) extraction.

Fig. 7 Adsorption capacity of the UHMWPE-g-(GMA-ATZ) fibres for Au(III) and another metal ion in the binary metal ions system (the initial concentration Au(III) and another metal ion both was 200 ppm; pH = 2.0; T = 25 °C).

Table 2 Adsorption selectivity of the UHMWPE-g-(GMA-ATZ) fibre for Au(III) in binary metal ions system

System	Fixation rate (%)		Affinity coefficient (α)
	Au(III)	Mixed ions
Au(III)–Cu(II)	97.7	2.3	42.5
Au(III)–Ca(II)	97.9	2.1	46.6
Au(III)–Mg(II)	97.5	2.5	39.0
Au(III)–Cr(VI)	97.9	2.1	46.6
Au(III)–Fe(III)	99.3	0.7	141.9
Au(III)–Ni(II)	99.5	0.5	199
Au(III)–Zn(II)	99.9	0.1	999

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3.5 Adsorption isotherms

Adsorption isotherm model is employed to describe the interaction between the adsorbate and adsorbent. Freundlich isothermal model is generally applied to describe the adsorption process on a heterogeneous surface,⁶³ while the Langmuir isothermal model is established on the assumption of adsorption on a homogeneous monolayer surface with identical adsorption sites and no lateral interaction between the adsorbed sites.⁶⁶ The expressions of the Langmuir and Freundlich models^64–66 are presented in eqn (14) and (13), respectively:where Q_e, C_e, Q_m, b, n and K_f are the equilibrium adsorption capacity, equilibrium concentration, maximum adsorption capacity of Langmuir, Langmuir constant, Freundlich constant associated to the adsorption intensity and indicator of the adsorption capacity, respectively. The Langmuir and Freundlich isotherm constants are computed and listed in Fig. 8 and Table 3. The Langmuir isotherm model has a better correlation (R² > 0.99) than the Freundlich isotherm model at the same temperature, indicating that the monolayer adsorption of Au(III) ions occurs on the adsorbent surface.

Fig. 8 Isotherm adsorption curve fitted by the Langmuir equation (a) and the Freundlich equation (b).

Table 3 Coefficient of the Langmuir and Freundlich isotherm adsorptions of Au(III) ions on the UHMWPE-g-(GMA-ATZ) fibre at 298 K

T (K)	Langmuir			Freundlich
	Qm (mg g^−1)	b (L mg^−1)	R^2	1/n	Kf ((mg g^−1) (mg^−1 mL^−1)^−1/n)	R^2
298	303.952	0.924	0.999	0.776	8.749	0.939

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3.6 Regeneration of adsorbents

The desorption efficiency of Au(III) ions from the modified UHMWPE was investigated by various concentrations of HCl, H₂SO₄, thiourea, thiourea–HCl and thiourea–H₂SO₄ solutions. Compared with other eluent solutions (Table 4), 0.5 M thiourea–0.5 M H₂SO₄ can more effectively elute the Au(III) ions adsorbed by UHMWPE-g-(GMA-ATZ) fibres. This can be explained by the interaction between the metal ions and charged species in the elution based on electrochemical theory.⁶⁷ Thiourea can be oxidized to formamidine disulfide in acidic solutions that enhances the Au(III) extraction.⁶⁸ The obtained results demonstrate that 0.5 M thiourea mixed in 0.5 M H₂SO₄ solution is an effective elution because of the high affinity of S atom of thiourea to Au(III). Hence, 0.5 M thiourea–0.5 M H₂SO₄ is adopted to conduct adsorption–desorption cycles. Fig. 9 shows the relationship of the Au(III) adsorption and the corresponding regeneration cycle number. It is indicated that the adsorption capacity decreased slightly from 280 mg g⁻¹ to 200 mg g⁻¹ and remained at a high level after five adsorption–desorption cycles. UHMWPE-g-(GMA-ATZ) fibres with great adsorption capacity, high selectivity and recyclability are excellent adsorbents for the efficient recovery of Au from industrial wastewater containing Au(III) ions.

Table 4 Desorption data of Au(III) from adsorbents

Eluent	Desorption efficiency (%)
0.3 M HCl	7.2
0.5 M HCl	12.4
0.3 M H2SO4	11.9
0.5 M H2SO4	28.3
0.3 M thiourea	62.4
0.5 M thiourea	73.2
0.5 M thiourea–0.3 M HCl	89.7
0.5 M thiourea–0.5 M HCl	91.6
0.5 thiourea–0.3 M H2SO4	95.1
0.5 M thiourea–0.5 M H2SO4	98.2

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Fig. 9 Regeneration study of 5 cycles (adsorbent dose, 0.02 g; volume of the medium, 100 mL; initial Au(III) concentration, 200 ppm; pH = 2.0; T = 298 K).

4. Conclusions

The modified UHMWPE fibres with imidazole group were prepared by the radiation-induced graft polymerisation of GMA and subsequent modification via the reaction with ATZ. The adsorption properties of UHMWPE-g-(GMA-ATZ) fibres for Au(III) were studied in detail by fitting with Lagergren first-order and pseudo-second-order models, as well as the Freundlich and Langmuir isothermal adsorption models. FTIR and SEM tests confirmed the modification of GMA and ATZ on the UHMWPE fibre. XPS analysis strongly indicated that Au chloride was adsorbed on the UHMWPE-g-(GMA-ATZ) fibre via complexation and ion exchange. The optimal initial pH value for the adsorption of Au(III) ion is 2.0. The adsorption process complied with the Lagergren pseudo-second-order and Langmuir adsorption isotherm models. Au ions can be effectively eluted from fibrous adsorbents with the use of 0.5 M thiourea–0.5 M H₂SO₄. Furthermore, UHMWPE-g-(GMA-ATZ) fibre has a better adsorption selectivity for Au(III) than any other coexistent metal ions. The fibre also maintained a high adsorption capacity even after five adsorption–desorption cycles. This new type of fibrous adsorbent has promising applications in the recovery of Au from industrial wastewater, including Au(III) ion.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (11275252, 11605275 and 11305243).

References

1. K. Fujiwara, A. Ramesh, T. Maki, H. Hasegawa and K. Ueda, J. Hazard. Mater., 2007, 146, 39–50.
2. H. Xin, Y. P. Wang, X. P. Liao and B. Shi, J. Hazard. Mater., 2010, 183, 793–798.
3. Y. Göksungur, S. Üren and U. Güvenc, Bioresour. Technol., 2005, 96, 103–109.
4. E. M. Moyers and J. S. Fritz, Anal. Chem., 1976, 48, 1117–1120.
5. D. Chen, X. L. Xiao and K. Yang, RSC Adv., 2016, 6, 35332–35339.
6. G. Reza Mahdavinia, S. Hasanpour, L. Behrouzi and H. Sheykhloie, Starch-Stärke, 2016, 68, 188–199.
7. M. Chen, L. L. Shao, J. J. Li, W. J. Pei, M. K. Chen and X. H. Xie, RSC Adv., 2016, 6, 35228–35238.
8. M. Monier and D. A. Abdel-Latif, J. Hazard. Mater., 2013, 250, 122–130.
9. R. Li, X. Z. He, Q. H. Gao, L. J. Pang, H. L. Wang, J. T. Hu, Z. Xing and G. Z. Wu, Nucl. Sci. Tech., 2016 DOI:10.1007/S41365-016-0075-9.
10. F. E. Beamish, Talanta, 1967, 14, 991–1009.
11. E. M. Moyers and J. S. Fritz, Anal. Chem., 1976, 48, 1117–1120.
12. C. X. Li, J. T. Dou, J. J. Cao, Z. Q. Li, W. K. Chen, Q. Z. Zhu and C. F. Zhu, J. Organomet. Chem., 2013, 727, 37–43.
13. A. M. Donia, A. A. Atia and K. Z. Elwakeel, Sep. Purif. Technol., 2005, 42, 111–116.
14. L. Gao, C. Z. Wang and Y. M. Wei, RSC Adv., 2016, 6, 28470–28476.
15. S. A. Ansari, N. Kumari, D. R. Raut, P. Kandwal and P. K. Mohapatra, Sep. Purif. Technol., 2016, 159, 161–168.
16. L. Dominguez, Z. R. Yue, J. Economy and C. L. Mangun, React. Funct. Polym., 2002, 53, 205–215.
17. A. M. Atta, S. I. El-Sherbiny, A. M. Salah and A. R. A. E. Ahmed, J. Dispersion Sci. Technol., 2013, 34, 1113–1123.
18. J. R. Cui and L. F. Zhang, J. Hazard. Mater., 2008, 158, 228–256.
19. P. Smith, P. J. Lemstra and H. C. Booij, J. Polym. Sci., Part B: Polym. Phys., 1981, 19, 877–888.
20. S. B. Deng, R. B. Bai and J. P. Chen, J. Colloid Interface Sci., 2003, 260, 265–272.
21. H. L. Wang, L. Xu, J. T. Hu, M. H. Wang and G. Z. Wu, Radiat. Phys. Chem., 2015, 115, 88–96.
22. R. M. Silverstein and G. C. Bassler, J. Chem. Educ., 1962, 39, 546.
23. A. Ramesh, H. Hasegawa, W. Sugimoto, T. Maki and K. Ueda, Bioresour. Technol., 2008, 99, 3801–3809.
24. H. Kitagawa, N. Kojima and T. Nakajima, J. Chem. Soc., Dalton Trans., 1991, 11, 3121–3125.
25. A. N. Mansour, Surf. Sci. Spectra, 1994, 3, 197.
26. A. M. Donia, A. A. Atia and K. Z. Elwakeel, Sep. Purif. Technol., 2005, 42, 111–116.
27. F. E. Beamish, Talanta, 1967, 14, 991–1009.
28. T. Ogata and Y. Nakano, Water Res., 2005, 39, 4281–4286.
29. M. Sathishkumar, A. Mahadevan, K. Vijayaraghavan, S. Pavagadhi and R. Balasubramanian, Ind. Eng. Chem. Res., 2010, 49, 7129–7135.
30. M. Behbahani, T. Gorji, M. Mahyari, M. Salarian, A. Bagheri and A. Shaabani, Food Anal. Method., 2014, 7, 957–966.
31. H. Zheng, X. J. Chang, N. Lian, J. Mao, S. Wang and Y. M. Dong, Microchim. Acta, 2005, 149, 259–266.
32. M. Monier, M. A. Akl and W. Ali, J. Appl. Polym. Sci., 2014, 131, 9277–9287.
33. C. M. Sun, G. H. Zhang, C. H. Wang, R. J. Qu, Y. Zhang and Q. Y. Gu, Chem. Eng. J., 2011, 172, 713–720.
34. X. J. Chang, Y. M. Wang and R. Zhao, Anal. Bioanal. Chem., 2003, 377, 757–762.
35. Ü. C. Erim, M. Gülfen and A. O. Aydın, Hydrometallurgy, 2013, 134, 87–95.
36. J. Ran, N. Wang, X. You, C. M. Wu, Q. H. Li, M. Gong and T. W. Xu, J. Hazard. Mater., 2012, 241, 63–72.
37. X. J. Chang, Q. Q. Su, D. Y. Liang, X. J. Wei and B. T. Wang, Talanta, 2002, 57, 253–261.
38. W. Wei, D. H. K. Reddy, J. K. Bediako and Y. S. Yun, Chem. Eng. J., 2016, 289, 413–422.
39. A. V. Pethkar and K. M. Paknikar, J. Biotechnol., 1998, 63, 121–136.
40. A. Ramesh, H. Hasegawa, W. Sugimoto, T. Maki and K. Ueda, Bioresour. Technol., 2008, 99, 3801–3809.
41. D. Jermakowicz-Bartkowiak, B. N. Kolarz and A. Serwin, React. Funct. Polym., 2005, 65, 135–142.
42. D. Jermakowicz-Bartkowiak and B. N. Kolarz, Eur. Polym. J., 2002, 38, 2239–2246.
43. J. M. Wasikiewicz, N. Nagasawa, M. Tamada, H. Mitomo and F. Yoshii, 6th International Symposium on Ionizing Radiation and Polymers (IRaP 2004), Houffalize, Belgium, July, 2005.
44. M. Iglesias, E. Anticó and V. Salvadó, Anal. Chim. Acta, 1999, 381, 61–67.
45. R. J. Qu, C. M. Sun, C. H. Wang, C. N. Ji, Y. Z. Sun, L. X. Guan, M. Y. Yu and G. X. Cheng, Eur. Polym. J., 2005, 41, 1525–1530.
46. H. Ebrahimzadeh, N. Tavassoli, M. M. Amini, Y. Fazaeli and H. Abedi, Talanta, 2010, 81, 1183–1188.
47. K. F. Lam, K. L. Yeung and G. McKay, J. Phys. Chem. B, 2006, 110, 2187–2194.
48. G. Gentscheva, P. Tzvetkova, P. Vassileva, L. Lakov, O. Peshev and E. Ivanova, Microchim. Acta, 2006, 156, 303–306.
49. Y. C. Chang and D. H. Chen, Gold Bull., 2006, 39, 98–102.
50. W. Nakbanpote, P. Thiravetyan and C. Kalambaheti, Miner. Eng., 2002, 15, 549–552.
51. P. Liu, Q. S. Pu and Z. X. Su, Analyst, 2000, 125, 147–150.
52. S. M. Zhang, Q. S. Pu, P. Liu, Q. Y. Sun and Z. X. Su, Anal. Chim. Acta, 2002, 452, 223–230.
53. S. Ishikawa, K. Suyama, K. Arihara and M. Itoh, Bioresour. Technol., 2002, 81, 201–206.
54. M. Soleimani and T. Kaghazchi, Bioresour. Technol., 2008, 99, 5374–5383.
55. X. Huang, Y. P. Wang, X. P. Liao and B. Shi, J. Hazard. Mater., 2010, 183, 793–798.
56. S. Sharma, C. M. Wu, R. T. Koodali and N. Rajesh, RSC Adv., 2016, 6, 26668–26678.
57. Y. S. Ho and G. McKay, Process Biochem., 1999, 34, 451–465.
58. C. H. Xiong, S. G. Zhou, X. Z. Liu, Q. Jia, C. A. Ma and X. M. Zheng, Ind. Eng. Chem. Res., 2014, 53, 2441–2448.
59. Z. W. He, L. H. He, J. Yang and Q. F. Lü, Ind. Eng. Chem. Res., 2013, 52, 4103–4108.
60. A. Smara, R. Delimi, E. Chainet and J. Sandeaux, Sep. Purif. Technol., 2007, 57, 103–110.
61. F. G. Helfferich, Ion Exchange, McGraw-Hill book Company, New York, 1962.
62. R. G. Pearson, J. Chem. Educ., 1987, 64, 561–567.
63. M. Monier and D. A. Abdel-Latif, J. Hazard. Mater., 2013, 250, 122–130.
64. I. Langmuir, J. Am. Chem. Soc., 1916, 38, 2221–2295.
65. M. Martín, J. M. D. Tascón, J. L. G. Fierro and J. A. Pajares, J. Catal., 1981, 71, 201–204.
66. S. Tas, O. Kaynan, E. Ozden-Yenigun and K. Nijmeijer, RSC Adv., 2016, 6, 3608–3616.
67. J. Li and J. D. Miller, Hydrometallurgy, 2002, 63, 215–223.
68. X. Yang, M. S. Moats and J. D. Miller, Miner. Eng., 2010, 23, 698–704.

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