3RD INTERNATIONAL CONGRESS ON TECHNOLOGY - ENGINEERING & SCIENCE - Kuala Lumpur - Malaysia (2017-02-09)

Investigating The Formation Of Acid Mine Drainage Of Toledo Pyrite Concentrate Using Column Cells
Acid mine drainage (AMD) is one of the problematic and expensive consequences of mining. AMD is produced when, in a mine site, a sulfide mineral is exposed to oxygen and water, creating an acidic environment. Different ore compositions lead to different AMD formation, thus, in this study, the mechanisms of formation of AMD of Toledo pyrite was investigated using two-stage column cell experiment. Specifically, it aimed to determine the effects of particle size, water volume and amount of pyrite sample to pH change due to pyrite oxidation using column cells, and to determine the effects of pH change to the surface of pyrite via scanning electron microscopy (SEM). For the column setup, there were twelve column cells packed with samples with different particle size range, volume of solution and mass of pyrite. Air was constantly pumped below the glass frit using the air pump. For the parameter levels, the mass used were 5 g and 10 g. The volumes of the deionized water solution were 50 mL and 100 mL, and for the particle size, the levels were greater than 149 µm for P1, 149 -106 µm for P2 and ≤105 µm for P3. A total of 12 column cells were set up and were run for 30 days. Moreover, SEM was used to see the pyrite surface before and after the column experiment. Results showed that for the first 6 hours, there was a rapid decrease in pH in all column cells, from pH 5.6 to about 3.5 to 3.3. It was also noted that the smallest particle size range had the lowest attained pH. This may be explained due to the cracks seen at the surface of the unreacted pyrite, increasing the surface area of the pyrite to be reacted. These cracks served as reactivity points where it’s easiest to oxidize pyrite (Lottermoser, 2007). Moreover, for 30 days, gradual drop of pH was observed also for every column. This may be explained by the amorphous precipitates attached to the pyrite’s surface covering parts of the externals surface that could be oxidized, thus making the pH drop slower than the first hours. Studies by Ribiero et al. (2004) and Cruz et al. (2000) also observed a layer of precipitates after a period of time of leaching, and identified it as iron oxyhydroxides and amorphous precipitates using SEM-EDX. It was concluded that the formation of acid mine drainage in Toledo pyrite in column cell experiment was initiated by the formation of Fe(OH)3 precipitates which increased the formation of hydrogen ions. The fast decrease of pH at the start was due to the cracks formed from the beneficiation process that increased the surface area of the pyrite available for reaction.
Diosa Marie Aguil