Adsorption behaviors of Au(III) onto humic acid extracted from gold ore: adsorptive kinetics, isotherm and mechanism

Abstract Humic acid is an important component of carbonaceous matters in the carbon-containing gold ores, which possesses gold-adsorbing capability and leads to the gold loss due to its structural characterization and physicochemical properties. In this paper, the adsorption characteristics of humic acid extracted from refractory carbon-containing gold concentrate were investigated, the adsorption kinetic and isotherm models were established. Simultaneously, the gold-adsorbing process was analyzed employing FTIR, UV-VIS, Raman spectra and XPS. Results showed that the extracted humic acid had the maximum adsorption rate at pH 3.0 and 35℃. The relationship between the amount of adsorption and time was found to be consistent with the pseudo-second-order model, and qe was closer to the measured value. The experimental data were found to conform to the Freundlich model which could better explain humic acid’s adsorbing capability for gold. Thermodynamic study indicated that gold-adsorbing process was spontaneous and endothermic. Isosteric heat of adsorption measured by using Clausius-Clapeyron equation increased with increase in adsorption amount showing that the extracted humic acid possessed heterogeneous surface. The study indicated that the gold-adsorbing behavior of the extracted humic acid was a predominantly chemisorption-driven process corresponding to the complexation between Au (Ⅲ) and N-, O- containing and other functional groups. Changes in the molecular structure of humic acid were detected as a result of adsorption. More importantly, a part of gold went from a trivalent state to a monovalent state during adsorption.