Perpustakaan Digital ITB

The formation of acid mine drainage (AMD) could be prevented by several methods, including mixing/blending of neutralizing material with potentially acid forming (PAF) material. Studies on coal fly ashes usage in mixing with PAF material to prevent AMD generation using various mixture ratios and scenarios have been conducted, both in laboratory-scaled and field-scaled kinetic tests. Nevertheless, the test procedures are complex, time- consuming and reguire experienced personnel to obiain meaningful and consistent results. Hence, geochemical modelling can serve as an alternative method to predict and describe the possible characteristics of geochemical reactions, so that performance of fly ash and PAF mixing scenarios could be assessed In this study, the effect of various ratio addition of fly ash with PAF material on leachate water guality and performance of prevention on AMD generation using laboratory kinetic test data were studied. There are three kinetic columns with different mixing compositions (by weight), namely PAF: FA 5:1, PAF: FA 2:1, and PAF:FA 1:1. The data obtained from these kinetic columns were results of physical tests, Static tests, mineralogy & elemental tests and also physicochemical characteristic of water (2 data from the daily wet-dry cycle and 3-days cycle. The data is used as inputs for geochemical modelling using PHREEOC software to compute reaction including the rate of reaction prevailed. The smaller particle size of fly ash compared to PAF material plays an important role to reduce total pore space by filling the space which could theoretically prevent the formation of AMD through reduction of effective surface area for sulphide minerals oxidation and decreasing diffusivity of water and oxygen. On the other hand, the presence of alkali oxides and other compounds would increase the potency of iron hydroxide deposition which in turn further reduces the total pore space. Geochemical modelling of various mixing scenarios results shows that the most dominant reaction is pyrite oxidation in the presence of oxygen with calculated mol transfer values ranging from 4.64x10“ to 7.89x10 mol. Neutralization reactions are indicated by calculated mol transfer values ranging from 4.12x10-? — 2.07x103 mol, 1.95x104 — 1.19x10” mol and 9.27x 104 — 1.41x10“ moles for calcite, periclase and kaolinite, respectively. Both reactions take place simultaneously and suppress gradually the oxidation of pyrite reaction which is indicated by increasing in pH values trend, hence the formation of AMD could be minimized.