Functionalized agriculture-derived biomass-based adsorbent for the continuous recovery of gold from a simulated mobile phone leachate

Electronic waste has become a global concern, as it has been steadily increasing over the years. The lack of regulation and appropriate processing facilities has rendered these wastes an environmental hazard. However, they represent excellent alternative sources of precious metals, which are highly in demand in various industries. Adsorption has been a popular method for metal removal/recovery because of several advantages, such as ease of use and low cost. In this regard, it is crucial to develop an inexpensive and functionalized adsorbent to selectively adsorb precious metals. Thus, silica, which is derived from rice husk and is abundantly present in Indonesia, was functionalized using an ionic liquid (SiRH_Im) and used for Au(III) adsorption from a simulated mobile phone leach liquor. SiRH_Im exhibited a high adsorption capacity (232.5 mg g⁻¹). The Au(III) adsorption kinetic suitably fitted with the pseudo-second-order kinetic model. The Au(III) adsorption followed a chemisorption route that suited the monolayer model. Thomas’ and Yoon-Nelson's models were well suited for the continuous Au(III) behavior. Selective recovery of Au(III) from SiRH_Im was achieved via sequential desorption. SiRH_Im also showed excellent reusability, as indicated by a negligible decrease in adsorptive performance over three cycles. The functionalization of silica derived from rice husk using an ionic liquid led to the successful creation of a solid adsorbent with a high adsorption capacity toward precious metals present in a simulated leach solution. Our results highlight the benefit of the functionalization of biomass through the immobilization of an ionic liquid toward the enhancement of its adsorption capability.