Silanol-rich ordered mesoporous silica modified thiol group for enhanced recovery performance of Au(III) in acidic leachate solution

Herein, we present a new approach to enhance the recovery performance of Au(III) using thiol-functionalized adsorbents in acidic leachate solution of urban mining. Ordered mesoporous silicas (OMS) with abundant surface silanol were obtained from mine tailings by solvent extraction. Overall, the surface silanol groups had the greatest effect on sulfur density and content under the conditions for functionalization with 3-mercaptopropyl-trimethoxysilane (3-MPTMS). Furthermore, silanol-rich OMS functionalized with thiol exhibited greater sulfur content and higher Au(III) adsorption capacity (231 mg/g) in a single-component solution. The adsorption rates follow the pseudo-second-order model, and the Au(III) adsorption isotherms fit well with the Langmuir adsorption model. These are attributed to the high sulfur content and its increased uniformity in silanol-rich OMS adsorbents, which increased the inward diffusion of Au(III) and effectively improved its accessibility to the activated sites. The adsorbents of Au(III) in acidic leachate solution achieved an adsorption efficiency of 213 mg/g. Moreover, they maintained the Au(III) selectivity of the functionalized thiol on surface silanol in acidic leachate solution, suggesting minimal non-selective metal ion adsorption. As a result of the regeneration, the adsorption efficiencies of Au(III) was maintained at over ca. 97.2%, even after five recovery cycles. These results demonstrate the potential application and recyclability of the developed adsorbent for Au(III) recovery in acidic leachate solution of urban mining and other prospective sources.This work was supported by the National Research Foundation of Korea Grant funded by the Korean Government (NRF-2014R1A1A2004176), (NRF-2017R1C1B2011235) and (NRF-2017R1A6A3A11033645)