A GEOCHEMICAL STUDY ON THE IMPACT OF OXIDATION AND DISSOLUTION RATES IN ALTERED ROCKS ON WATER QUALITY

• Main Author: Fitrah
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/87107
• Institution: Institut Teknologi Bandung

Porphyry deposits formed through the interaction of hydrothermal solutions with host rocks, typically consist of silicate, aluminosilicate, and sulfide minerals. These deposits are often mined using open-pit methods, which can leave behind voids that have the potential to form pit lakes during the post-mining phase. This process [frequently leads to environmental issues, such as acid mine drainage (AMD), which arises from the oxidation of sulfide minerals in the presence of water. The reactive characteristics of the host rocks can also result in varying water quality within the pit lakes, characterized by acidic or alkaline pH conditions. In this study, sixteen rock column samples were utilized, consisting of nine volcanic rock samples, five diorite rock samples, and two tonalite rock samples. The testing methods employed included several approaches: static tests, mineralogical analysis using X-ray diffraction (XRD) and X-ray fluorescence (XRF), and kinetic tests using the free-draining column leaching test (FDCLT) method with three leaching cycles: a 1-day cycle (daily) for 28 days, a 3-day cycle for 30 days, and a 7-day cycle for 56 days. The chemical analysis of leachate water involved Ion Chromatography (IC) and Inductively Coupled Plasma Mass Spectrometry (ICPMS), along with geochemical reaction modeling using PHREEQC sofiware to understand and predict the leachate water quality and its long-term geochemical impacts. The oxidation rates, based on the molar approaches of iron (Fe), sulfate (SO.), and pyrite transfer (FeS2), indicated that oxidation rates tend to increase under acidic pH conditions, particularly in the weekly leaching cycle. Meanwhile, the dissolution rates approached through calcium (Ca) and bicarbonate (HCO:”) concentrations, also play a role in controlling AMD potential. The relationship between oxidation and dissolution rates shows that if the oxidation rate exceeds the dissolution rate, the polentiaflor acid mine drainage formation will increase. Over the long term, the sulfide concentrations with the highest oxidation rates in volcanic, diorite, and tonalite rocks will be depleted in approximately 49 years, 66 years, and 94 years, respectively. Within the same lithologies, the carbonate dissolution parameters with the highest rates will be depleted in approximately 78 years, 136 years, and 108 years, respectively.