Ecofriendly Upcycling of Poly(vinyl chloride) Waste Plastics into Precious Metal Adsorbents

Abstract

Global interest in the recycling of precious metals (PMs) in various industrial sectors has spurred the exploration of high-performance PM adsorbents. Unfortunately, many adsorbents exhibit unsatisfactory PM adsorption performance and require complex fabrication protocols and toxic chemicals. Hence, further development of simple, efficient, and eco-friendly adsorbents is necessary. Herein, poly(vinyl chloride) (PVC) waste plastics are simply transformed into high-performance PM adsorbents via benign solvent treatment and hydrazination. The resultant hydrazine-functionalized PVC (h-PVC) plastic can effectively recover gold, palladium, and platinum from real-world leachates owing to its combined reduction and chemisorption mechanisms. The PM-adsorbed h-PVC plastic can be regenerated, calcined into high-purity PMs, or directly employed as a catalyst, demonstrating its practical feasibility. Techno-economic and life-cycle assessments reveal that the h-PVC plastic-utilizing industrial-scale recovery of gold from electronic waste is cost-competitive and environmentally advantageous. The strategy supports environmental and sustainable technologies by enabling the sustainable maintenance of carbon and PM resources and provides an efficient and sustainable method for fabricating advanced adsorbent materials.

Keywords: eco‐friendly upcycling; hydrazine functionalization; poly(vinyl chloride); precious metal adsorbent; waste plastic upcycling.

Figure 1

a) Schematic of the synthesis of the h‐PVC polymer via hydrazination. b) Photographs of the PVC and h‐PVC polymer aqueous solutions. c) Zeta potentials of the h‐PVC polymer as a function of the solution pH. d) Photographs of PM (Au, Pd, and Pt, 200 mg L⁻¹) aqueous solutions (pH = 2) before (top) and after (bottom) the introduction of the h‐PVC polymer (0.2 g L⁻¹). e–g) High‐resolution TEM images of the PM@h‐PVC precipitates: e) Au, f) Pd, and g) Pt. h–j) Deconvoluted h) Au4f, i) N1s, and j) C1s XPS peaks of the Au@h‐PVC precipitate. The PM@h‐PVC precipitates were collected by PSU membrane filtration after PM (200 mg L⁻¹) aqueous solutions (pH = 2) containing the h‐PVC polymer (0.2 g L⁻¹) were shaken for 3 h. k–m) Proposed PM adsorption mechanism of the h‐PVC polymer. Data represents the mean ± standard deviation (n = 3).

Figure 2

a) PM adsorption kinetics (PM adsorption capacity (q _t) as a function of the contact time (t)) of the h‐PVC polymer and their fits to established kinetics models (h‐PVC polymer dose = 0.2 g L⁻¹, initial PM ion concentration (C _i) = 200 mg L⁻¹, pH = 2). b) PM adsorption isotherms (equilibrium PM adsorption capacity (q _e) as a function of the equilibrium PM ion concentration (C _e)) of the h‐PVC polymer and their fits to established isotherm models (h‐PVC polymer dose = 0.2 g L⁻¹, pH = 2, contact time = 3 h). c) PM adsorption performance (maximum PM adsorption capacity (q _max) and equilibrium time (t _eq)) of the h‐PVC polymer and other reported PM adsorbents. d) PM recovery (R _e) and desorption (D _e) efficiency of the h‐PVC polymer as a function of the adsorption–desorption cycle number (h‐PVC polymer dose = 0.2 g L⁻¹, C _i = 10 mg L⁻¹, pH = 2, contact time = 3 h). Data represents the mean ± standard deviation (n = 3).

Figure 3

a) Schematic of the fabrication of the h‐PVC plastic film via benign solvent treatment and subsequent hydrazination. b,e,h) Photographs and c,f,i) surface and d,g,j) cross‐sectional SEM images of the b–d) pristine PVC, e–g) d‐PVC, and h–j) h‐PVC films. k–m) Photographs illustrating the PM adsorption and collection processes of the h‐PVC film.

Figure 4

a) Cross‐sectional TEM (top) and corresponding EDS (bottom) images of the PM@h‐PVC plastic films. The PM@h‐PVC films were collected using tweezers after PM (200 mg L⁻¹) aqueous solutions (pH = 2) containing the h‐PVC film (1.0 g L⁻¹) were shaken for 12 h. b) Deconvoluted Au4f XPS peak of the Au@h‐PVC film. c) PM adsorption kinetics (q _t as a function of t) of the h‐PVC film (h‐PVC film dose = 1.0 g L⁻¹, C _i = 200 mg L⁻¹, pH = 2). d) Cross‐sectional SEM (top) and corresponding EDS (bottom) images of the Au@h‐PVC film over three‐step adsorption (1^st step at 10 min, 2^nd step at 2 h, and 3^rd step at 12 h). e) PM adsorption isotherms (q _e as a function of C _e) of the h‐PVC film and their fits to established isotherm models (h‐PVC film dose = 1.0 g L⁻¹, pH = 2, contact time = 12 h). f) PM adsorption performance (q _max and t _eq) of the h‐PVC film and other reported macroscale PM adsorbents.

Figure 5

a–c) Recovery efficiency (R _e) of the h‐PVC plastic film with real‐world leachates (h‐PVC film dose = 1.0 g L⁻¹, pH = 2, contact time = 12 h): a) CPU and spent b) Pd and c) Pt catalyst leachates (insets: photographs of the real‐world samples). d) PM R _e and desorption efficiency (D _e) of the h‐PVC film with real‐world leachates as a function of the adsorption–desorption cycle number (h‐PVC film dose = 1.0 g L⁻¹, pH = 2, contact time = 12 h). e) Photographs of the PM particles obtained by calcinating the PM@h‐PVC films. f) Photographs illustrating the reduction of organic dyes (pNP and MeO) catalyzed by the Au@h‐PVC film. Data represents the mean ± standard deviation (n = 3).

Figure 6

a) Construction of the subsystems and their contributions to the total cost of the complete processes. The processes also include storage (capital and operating costs are 0.5 × 10⁶ and 0.1 × 10⁶ $ year⁻¹, respectively, for both film calcination and film regeneration) and utility (capital and operating costs are 0.8 × 10⁶ and 0.2 × 10⁶ $ year⁻¹, respectively, for film calcination, while capital and operating costs are 0.6 × 10⁶ and 0.2 × 10⁶ $ year⁻¹, respectively, for film regeneration) subsystems. b) Minimum selling price (MSP) of Au. c) Environmental impacts. Contributions of the process inputs and outputs to the global warming potential for the d) film calcination and e) film regeneration processes. Negative numbers are highlighted with dashed borders.