Development of polyethylenimine-functionalized cellulose fibers for recovery of Au(0) from Au(III)-containing acidic solutions through an adsorption–reduction–detachment–aggregation mechanism

The aim of this study was to develop cellulose-based, fibrous adsorbents for the selective recovery of gold (Au) and to reveal the adsorption–reduction–attachment–aggregation mechanism. Polyethylenimine (PEI)-functionalized cellulose fibers (PCFs) were fabricated by extruding a mixture of PEI and cellulose into a sulfuric acid solution. To maximize the performance of the PCFs, the amounts of PEI and ethylene glycol diglycidyl ether, a crosslinking agent, were optimized. The maximum uptake of Au(III) by PCFs was 1108.2 ± 58.8 mg/g obtained based on adsorption isotherm experiments. PCFs characterization and mechanistic investigations were carried out using FT-IR, XPS, XRD, FE-SEM, EDX, and HR-TEM. After 0.5 h of Au(III) adsorption on the PCFs, Au(III) was reduced to Au(I) owing to electron transfer when –NH3+/−NH2+‒, functional groups of PCFs, were oxidized to = NH+‒ and = N‒. After 12 h, –NH3+/−NH2+‒ were oxidized to = N‒, and C–N was oxidized to CO; therefore, Au(I) present on the fibers was reduced to Au(0) owing to the oxidation–reduction reaction. The released nitrogen was detected as NO2− and NO3− in the solution. Subsequently, the Au particles detached from the PCFs, and the aggregated Au particles on the vessel wall were recovered. In addition, the prepared PCFs showed outstanding selectivity for Au(III) in a solution containing the main metals found in electronic waste. PCFs maintain the Au(III) adsorption performance even in the 10 times adsorption-desorption cycles. These results indicated the application potential of PCFs as efficient adsorbents for Au recovery.