Sustainability in the Metallurgical Industry: Chemically Modified Cellulose for Selective Biosorption of Gold from Mixtures of Base Metals in Chloride Media

In an effort to develop sustainable materials and methods for the recovery and recycling of precious metals, we recently developed two different adsorbents by cross-linking pure cellulose with either epichlorohydrin or concentrated sulfuric acid and then modifying the surface with N-aminoguanidine functional groups. The adsorption behavior of these sorption materials toward Au(III) from a multicomponent mixture of Pt(IV), Pd(II), and some base-metal ions was studied in hydrochloric acid media. Both of the adsorbents exhibited outstanding selectivity toward precious metals, with a selectivity order of Au(III) >> Pd(II) > Pt(IV), over base metals in a wide range of acid concentrations. These materials contain a number of positive centers in HCl media that function as sorption active sites for chloroanionic species of Au(III), Pd(II), and Pt(IV). The chloroanionic species of the corresponding precious metals were thus adsorbed on these materials through anion-exchange-coupled electrostatic interaction. The sulfuric acid cross-linked material exhibited improved selectivity and greater adsorption capacity compared to the epichlorohydrin cross-linked adsorbent. As equilibrium was achieved within an hour with quantitative adsorption, the effectiveness of the sulfuric acid cross-linked material with regard to Au(III) was exemplified by the fact that 1 kg of the dry adsorbent material had a capacity to load 9.2 mol, that is, nearly 1.8 kg of Au(III). Moreover, the adsorbed Au(III) was subsequently reduced to the elemental form, yielding metallic gold particles, thereby demonstrating the considerable improvements in efficiency and effectiveness of the novel adsorbents for the recovery of gold in comparison to current commercial resins.