An innovative microextraction material for efficient and selective extraction of gold: Magnetic oil-based gel microspheres containing Aliquat 336

Abstract

The recovery of low-concentration Au(III) from industrial wastewater holds significant economic and environmental value. Therefore, developing materials for the efficient extraction of low-concentration Au (III) is of great importance. In this study, we propose a novel microextraction scheme that combines the characteristics of microextraction with an extractant curing technique. Magnetic polystyrene microspheres serve as containers to encapsulate the extraction phase, which consists of the extractant (Aliquat 336) and the diluent (1,2-dichloroethane). Magnetic polystyrene microspheres with a diameter of 3.69 μm were swollen using an emulsion containing Aliquat 336 and 1,2-dichloroethane, resulting in the formation of magnetic oil-based gel microspheres with a diameter of 10.14 μm. These magnetic oil-based gel microspheres, which also contain Aliquat 336, are composed of 1,2-dichloroethane (81.73 wt%), Aliquat 336 (11.52 wt%), polystyrene (4.36 wt%), and iron tetroxide (1.69 wt%). At a low oil-to-water (O:A) ratio (ranging from 1:40 to 1:100), the microspheres achieved extraction equilibrium within 8 min. An eluent solution containing 0.1 mol·L⁻¹ hydrochloric acid and 0.05 mol·L⁻¹ thiourea was able to completely reverse the extraction of AuCl₃ from the microspheres, facilitating their regeneration. The microspheres demonstrated stable and effective extraction capabilities over four cycles. In the presence of impurity ions (Ca²⁺, Fe³⁺, Cu²⁺, and Ni²⁺), the extraction rate of gold by the microspheres exceeded 95 %, while the extraction rate of the impurity ions remained below 10 %. This indicates the excellent selective extraction ability of the microspheres for Au(III).