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 (SPE) properties for the recovery of precious metals from acidic leachate, which is relevant to sustainable metal recovery from tailings or industrial wastewater effluent.