Isolation of Humic Acid from Peat Soil and Its Application as an Adsorbent for AuCI4- in Solution

Humic acid (HA) has been isolated from South Kalimantan (Indonesia) peal soil using alkali extraction method. The isolated HA then was applied on the adsorption process of AuCI4- in solution. Parameters investigated in the adsorption process consisted of the effect of initial pH, adsorption rate constant (k) and the adsorption capacity of AuCPIon peat soil HA. The adsorption rate constant was determined according to the kinetic model proposed by Santosa (2007). The adsorption of AtiCI(4)(-) on peat soil HA was optimum at pH 2. The adsorption rate constant (k) was 1.11 x 10(-3) min(-1). Adsorption of AuCli on peat soil HA fitted the Langmuir isotherm with the adsorption capacity of 90.91 mg.g(-1). The adsorption of AuCI4- on peat soil HA was accompanied by the reduction of AuCI4- to Au(0), claritied by the existence of several peaks belonging to Au(0) in the XRD pattern of HA after the adsorption process.