Physical property-based screening of polyurethane foam for gold enrichment from rock gold ores

To address the technical challenges of significant variations in gold extraction efficiency and the absence of a scientific screening basis for commercially available unmodified polyurethane foam (U-PUF) in gold enrichment from rock gold ores, this study systematically investigated the correlations between six physical properties of 18 U-PUF samples and the gold extraction efficiency in accordance with General flexible polyurethane cellular plastics (GB/T 10802-2023). The gold enrichment mechanism was elucidated by combining adsorption kinetics, competitive adsorption characteristics, and microscopic characterization techniques. The results demonstrated that the optimal physical parameters of U-PUF with a gold adsorption rate of ≥95% were determined as follows: white color, density of 30-40 kg m^-3, 25% indentation hardness of 105-140 N, 40% indentation hardness of 130-150 N, rebound rate of 50-65%, and pore size of 100-400 µm (fine pore). This type of U-PUF exhibited an optimal adsorption capacity of 3.91 mg g^-1, and its adsorption process followed the three-stage intraparticle diffusion model, reaching adsorption equilibrium within 30 min with excellent homogeneous adsorption performance. FTIR analysis confirmed that no chemical bonding was involved in the gold adsorption by U-PUF, while SEM-EDS characterization revealed that the gold existed as multi-scale aggregates with sizes ranging from 300 nm to 15 µm on the porous framework of U-PUF. The enrichment mechanism was clarified as follows: in an acidic system, the secondary amino groups on U-PUF were protonated, which then captured [AuCl₄]^- anions via electrostatic interaction and subsequently reduced them to elemental gold in situ. The U-PUF screened by the optimal parameters showed good consistency between the determined values and the certified values for 26 gold ore reference materials, and the determined values for actual rock gold ore samples were not significantly different from those obtained by the activated carbon enrichment method and fire assay. The screening standard for U-PUF physical properties established in this study resolves the dilemma of material selection in gold enrichment for batch geological samples, and provides theoretical support and technical specifications for the standardized application of U-PUF.