Recovery of gold(III) and iridium(IV) using magnetic layered double hydroxide (Fe₃O₄/Mg-Al-LDH) nanocomposite: Equilibrium studies and application to real samples

In this study for the first time, a magnetic Fe₃O₄/MgAl-layered double hydroxide (LDH) nanocomposite was used as an adsorbent for recovery of gold and iridium from soils around the mining area. The morphological and structural properties of the obtained Fe₃O₄/MgAl-LDH was characterized by transmission electron microscopy, Brunauer-Emmett-Teller, scanning electron microscopy coupled with energy dispersive spectroscopy and X-ray diffraction. The adsorption performance of the magnetic adsorbent was evaluated using isotherm and kinetic models. The equilibrium data best fitted to Langmuir, Sips and pseudo-second order kinetic models. The maximum adsorption capacities of gold(III) and iridium(IV) were found to be 124 mg g⁻¹ and 115 mg g⁻¹, respectively. The selectivity of the nanoadsorbent in the presence of diverse common ions and other platinum group metals (PGMs) were investigated. The adsorbent demonstrated relatively high selectivity towards Au(III) and Ir(IV) ions. The recovery of Au(III) and Ir(IV) ions from the adsorbent was achieved using 2.0 mol L⁻¹ H₂SO₄ solution. Recoveries ranging from 80% to 109% were obtained and the adsorbent was found to be reusable up to ten cycles of adsorption/ desorption processes. The repeatability of the method expressed as relative standard deviation (%RSD) ranged from 2.5–4.9%. The nanocomposite was successfully applied for the recovery of Au(III) and Ir(IV) in South African Reference material (SARM 186, platinum group metal (PGM) concentrate) soil samples collected from a gold mine.