Stabilization/solidification of tailings on traditional gold mining in Kulon Progo using fly ash

Traditional gold mining activity is one of the sources of mercury contamination. Total mercury concentration in tailing ponds in Kulon Progo ranged from 164.49 mg/kg to 383.21 mg/kg, which exceeded the quality standard values set by the government of Indonesia No. 101 of 2014, which is 75 mg/kg. One method that can be applied is stabilization/solidification (S/S). This study aims to determine the optimum composition of the tailing mixture with fly ash in S/S process. The variations of fly ash composition with tailing are 100:0, 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80 and 10:90. The results of the study found that the optimum composition of fly ash: tailings was 10:90, with compression test of 74 ton/m² and TCLP test was 0.0069 mg/L. The obtained compression test results were in accordance with US EPA Standard quality of 35 ton/m². TCLP test results meet the standard of Indonesian Government Regulation no. 101 of 2014, amounting to 0.05 mg/L.