Long-term evaluation of FABA utilization to prevent AMD generation – a review of barrel kinetic test

Abstract The utilization of fly ash and/or bottom ash (FABA) to prevent the generation of acid mine drainage is present in several mining companies to maximize geochemical and geotechnical potentials of FABA. Geochemically, FABA has the potential as a neutralizing material due to its high acid-neutralizing capacity, therefore it can be used as a sealing material for the potentially acid-forming (PAF) overburden in coal mining activities, which has the potential to produce acid drainage. This study aims to ensure that the potential leachate runoff at PAF disposals through neutralizing and sealing is not in acidic condition. A series of kinetic geochemical tests were carried out using a 200-liter volume column, applying various compositions of non-acid forming (NAF) rocks, a mixture of FABA, and PAF to ensure the method reliability. Leachate leaking out of the column was subjected to pH and EC analysis. The test results for a period of 3 years (Jan 2021 – June 2024) showed that the NAF-PAF-FABA sealing system produced a neutral pH compared to the FABA-PAF and NAF-FABA-PAF-NAF sealing. The position of FABA under the PAF layer triggered the carbonate released by acidic water, enabling neutralization. The 9:1 ratio of FA to BA in NAF-PAF-FABA sealing system showed better results than 4:1 ratio, indicative of greater neutralizing capacity of FA than BA. Compositions with smaller amounts of PAF produced better results due to less potential acidity that must be neutralized.