Synthesis of Amino Polyurethane Foam and Its Application in Trace Gold Enrichment in Geological Samples

The common method for the determination of Au in geological samples is by Atomic Absorption Spectrometry (AAS) and Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) after enrichment by polyurethane foam (PUF). Compared with activated carbon, PUF has a good selectivity but has a low absorption capacity. PUF loaded by different extraction agents or modified with different functional groups can improve the absorption capacity. PUF was treated with hydrochloric acid to prepare PUF-NH₂. Infrared Spectrum and Scanned Electron Microscope results show the peak of PUF-NH₂ shows obvious red shift, and the amount of amino group increases obviously. Macromolecule of PUF-NH₂ shows obvious fracture. The amino group after hydrolysis is reduced, which is easy to achieve in an oxide-reduction reaction with Au ions during the absorption of Au to form Au nanoparticles. Modified PUF-NH₂ achieved absorption capacity of 96 mg/g, which is an 8-fold improvement compared to PUF. Using PUF-NH₂ to enrich Au in geological samples, the samples were first ashed and then digested by 50% aqua regia. Gold was determined by ICP-OES. The recovery by standard-addition ranged from 95.0% to 105.0% and the detection limit was 0.15 μg/g. The experimental results show that the enrichment degree and analytical sensitivity are improved by using PUF-NH₂, which is suitable for the determination Au in low grade ores.