Thiourea-functionalized chitosan for highly selective and high-capacity recovery of gold from leaching solutions

To overcome the limitations of chitosan in gold recovery, a novel adsorbent (TU-CTS) was strategically designed by grafting thiourea onto chitosan molecular chains. This modification engineered multiple active sites, incorporating sulfur (S) atoms alongside the inherent amine (-NH₂) groups, to enhance the capture of gold ions. The maximum adsorption capacity for Au(III) of 1388.40 mg/g, as determined by the Langmuir model. TU-CTS demonstrated selectivity and practical efficacy in an actual gold-bearing leaching solution, achieving recovery efficiency of 93.54% without interference from co-existing metal ions. The adsorption mechanism was elucidated, revealing a synergistic process involving the electrostatic attraction of anionic AuCl₄^- to protonated amine groups, followed by coordination complexation with both -NH₂ and S, and subsequent reduction of Au(III) to elemental gold Au(0). These findings confirm that the thiourea-grafting strategy effectively creates a powerful adsorbent with great potential for the efficient and selective recovery of gold from complex industrial leaching solution.