Accelerating gold extraction from refractory gold tailings via NH4HF2 pre-treatment

Abstract

Gold tailings are secondary resources, however, a suitable method to extract the remaining gold has not yet been found. Thus, this study investigated that a gold tailings was pretreated with ammonium bifluoride, which promoted recovery of the remaining gold from the tailings. Ammonium bifluoride affecting the leaching effect may be due to the synergistic effect of fluorine and hydrogen ions. The mechanism was researched with the help of scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses. The results indicated that ammonium bifluoride interacted with the silica-bearing mineral in the tailings, which made the surface of the tailings become rougher and more cracks, and thus provided some channels for leaching reagent and exposed the occluded gold, largely facilitating gold dissolution. The preferable pre-treatment conditions were shown as NH4HF2 concentration = 0.7 mol/L, liquid to solid ratio = 5, the temperature = 25 °C, and the time = 4 h. The gold extraction efficiency increased by 48.45 % under the optimized pre-treatment conditions. Additionally, ammonium bifluoride proved to be an environmentally friendly, efficient, and low-costed pre-treatment reagent, being well-suited for promoting gold extraction from gold tailings.