Thiocarbamoyl chitosan: Synthesis, characterization and sorption of Au(III), Pt(IV), and Pd(II)

Here we suggest a new method of chitosan sulfur derivatives (thiocarbamoylchitosans, TC-chitosans) synthesis via reaction in eutectic two-component system ammonium rodanide-thiourea that allows significant increase of substitution degrees at the reduced time and reagent consumption as compared to conventional synthetic procedures. The sorption properties of TC-chitosans with substitution degrees (DS) from 0.4 to 0.9 toward Au(III), Pt(IV), Pd(II) ions were studied in chloride solutions, including systems with 10 to 1000-fold excess of Fe(III), Cu(II), and Zn(II) over the precious metal ions content. The sorption capacities of TC-chitosans increase with DS and change in the row: Au(III) > Pd(II) > Pt(IV) ≫ Cu(II) > Fe(III) > Zn(II). The maximum sorption capacities of TC-chitosan with DS 0.9 for Pt(IV), Pd(II), and Au(III) were 1.24 mmol/g, 3.43 mmol/g, and 3.81 mmol/g, respectively. Characterization of precious metals oxidation states by the XPS method after the sorption on TC-chitosan revealed that the platinum and gold recovery occurred with reduction of Au(III) to Au(I)/Au(0) and Pt(IV) to Pt(II).