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

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, <i>Brevibacillus borstelensis</i> loaded on silica gel (BB@Si), with outstanding adsorptive properties that can be implemented for quantitative recovery of Au(III) ions <i>via</i> 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.