Evaluation of the Adsorption and Reduction of Au(III) on Esterified Humic Acid

Electronic waste is increasing every year, one of which is electronic waste metal. Gold mining is less profitable than taking gold from electronics. One of the adsorbents that can be used is humic acid. To study the effect of functional groups on the adsorption of Au (III) ions, the adsorptionreduction of Au (III) ions using esterified humic acid was studied. Humic acid that will be esterified is isolated from peat soil from Rawa Pening, Central Java. Esterification was performed by reaction with ethanol in acidic conditions and doing repeated. Estesterified humic acid was characterized by Fourier-Transform Infrared spectroscopy (FTIR), X-Ray Diffraction (XRD), ash content, total acidity, -COOH content, and -OH content, then used for adsorption-reduction of Au (III). Esterified humic acid has studied the effect of pH adsorption, adsorption kinetics, and adsorption isotherm on adsorption reduction process of Au (III). The Au metal formed was confirmed by XRD diffractogram and photo-optical microscope. Esterified humic acid has 0.78% ash content, total acidity of 1022 cmol/kg, COOH content of 217 cmol/kg, and OH content of 805 cmol/kg. pH optimum on adsorption reduction Au(III) using esterified humic acid was 6. The adsorption capacity is 625 mg/g with Langmuir isotherm model esterified humic acid. The adsorption rate constant (k) is 1.50.10-3 g/mg min with Ho kinetic model for esterified humic acid. Peaks of gold particles in the diffractogram are detected on 2θ = 38, 44, and 64. Keywords—adsorption, reduction, Au (III), humic acid, esterification