GEOCHEMICAL MODELING OF MIXING SCENARIO BETWEEN POTENTIALLY ACID FORMING (PAF) MATERIAL AND FLY ASH IN LABORATORY SCALE KINETIC TEST

• Main Author: A. P. Silalahi, Herbert
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/69320
• Institution: Institut Teknologi Bandung

One method that can be applied to prevent the formation of acid mine drainage (AMD) is by mixing rocks that have the potential to neutralize the acid with rocks that are potentially acid forming (PAF). Research on using coal ash as a non-acid forming (NAF) material in mixing scenarios to prevent the formation of AMD has been carried out, both in laboratory scale and field scale kinetic tests. However, the kinetic testing procedure is complex, timeconsuming, and requires operator expertise to obtain consistent results. Hence geochemical modeling is needed, which can be an alternative method that can describe the characteristics of the geochemical reaction as a reference in determining the estimation of the performance of the coal ash mixing system. In this study, the effect of fly ash addition on the mixing of PAF materials was evaluated through an analytical approach, and geochemical modeling was carried out to obtain information about the formation and neutralization behavior of AMD using PHREEQC software. Secondary data consists of the results of physical tests, static tests, mineralogy & elemental tests, and kinetic tests of the free draining column leach test (FDCLT) method were used in this study. The grain size characteristic of fly ash which is smaller than PAF material plays a role in filling the pore space in the mixed material, which theoretically can prevent the formation of acid mine drainage by reducing the sulfide minerals reaction surface area from water and oxygen. On the other hand, the presence of alkali in fly ash will increase the potential of hydroxide-iron deposition on the surface of the PAF rock, which over time, will reduce the surface area of the sulfide mineral reaction. The mole transfer obtained from the geochemical modeling shows that the mole transfer of pyrite, which reflects the occurrence of pyrite oxidation, is the most dominant reaction in the mixing column, with ranges from 4.64×10-4 to 7.89×10-3 mol, while the neutralization reaction indicated by the transfer of moles of calcite (4.12×10-4 – 2.07×10-3 mol), followed by periclase (1.95×10-4 – 1.19×10- 3 mol) and kaolinite (9.27× 10-8 – 1.41×10-4 moles). Both conditions will simultaneously gradually suppress the rate of pyrite oxidation, which is indicated by the increasing trend of solution pH value so that the formation of AAT can be minimized.