Utilization of Portland Cement and Fly Ash for Treatment of Mercury Polluted Soil through Stabilization/Solidification

Abstract Traditional gold mining contributes significantly to soil mercury pollution. Stabilization/Solidification (S/S) Technology offers a remediation solution for soils contaminated with heavy metals. Besides the low cost of the technology, the S/S technology can be carried out in situ and ex-situ with material pozzolanic properties, such as Portland cement and fly ash, effectively bind these metals. This study aims to identify the proportion of mercury-contaminated soil mixed with a combination of Portland cement and fly ash. Artificial soil samples with a mercury content of 150 mg/kg were used, and test specimens were formed into 5 cm cubes. In the first phase, different ratios of Portland cement to fly ash were tested: 100:0, 90:10, 80:20, 70:30, 60:40, and 50:50. The second phase focused on the optimal mix ratio based on compressive strength tests for combinations of Portland cement and fly ash with mercury-contaminated soil, with the same ratios as in the first phase. Subsequent compressive strength and specimens were tested using the Toxicity Characteristic Leaching Procedure (TCLP). The first phase identified the optimal 50:50 ratio of Portland cement to fly ash, achieving a compressive strength of 5559 tons/m 2 . In the second phase, the same 80:20 ratio for the mix of Portland cement, fly ash, and mercury-contaminated soil yielded a compressive strength of 2902 tons/m 2 and a TCLP result of 0.0062 mg/L. All samples met the criteria set by the United States Environmental Protection Agency (US EPA), with variations ranging from 17 MPa for residential concrete to 28 MPa and the TCLP-B quality standard. According to Regulation by Government No. 22 of 2021, the permissible concentration is 0.05 mg/L. The study concludes that increasing the proportion of soil and fly ash Included in the mixture reduces the quality of S/S products.