Efficient extraction and determination of Au(iii) ions from acid mine drainage and water samples using silica gel immobilized with Brevibacillus borstelensis

The analysis of gold, which is a precious metal with limited resources, in environmental samples is crucial for the sustainable utilization of natural resources. Therefore, in the present research we have aimed to develop a novel and environmentally friendly bioadsorbent, Brevibacillus borstelensis loaded on silica gel (BB@Si), with outstanding adsorptive properties that can be implemented for quantitative recovery of Au(III) ions via the solid phase extraction (SPE) technique. After characterizing the developed adsorbent using FTIR and SEM techniques, we conducted a detailed investigation of the critical parameters that influence the extraction performance of Au(III) ions. Optimum parameters were observed as follows: pH 3.0, adsorption contact time 30 min, eluent type 0.1% (w/v) thiourea in 0.5 M HNO₃, elution time 60 min, BB@Si amount 1.0 g L⁻¹, and sample volume 400 mL. Some of the well-known isotherm and kinetic models were applied to the results observed from the adsorption studies. Equilibrium adsorption capacity of BB@Si was estimated to be 66.2 mg g⁻¹ utilizing the Langmuir isotherm model while the limit of detection (LOD) and relative standard deviation (RSD%) were established as 0.99 μg L⁻¹ and 3.7%, respectively. The developed method was utilized smoothly for the quantification of Au(III) ions in mining wastewater, acid mine drainage (AMD), streams and seawater.