INTERACTION OF SULFIDE MINERALS WITH MIXOTROFIC BACTERIA AND ITS IMPLICATION FOR BIOFLOTATION

• Main Author: Bayangkara Lamandhi, Nuslia
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/47297
• Institution: Institut Teknologi Bandung

Flotation is the separation of minerals by utilizing different surface properties. During its development, flotation is widely used in the mineral processing and metallurgy industries. The flotation process can be carried out with the help of chemical reagents to increase the ability of the minerals to separate. The spread of environmental issues causes the use of chemical reagent to be now limited. Therefore, we need an environmentally friendly and inexpensive treatment method as an alternative to replace chemical reagents by utilizing microorganisms as bioreagents. The bioflotation process using mixotrophic bacteria has been widely studied and developed, but its application to gold sulfide ore is rarely studied. The purpose of this study was to determine the effect of pH, percent bacterial inoculum, bacterial adaptation to pyrite, and type of bacteria on gold sulfide bioflotation. The study began with selecting bacteria and growth media that were suitable for the bioflotation process. Emulsifying index (% EI) testing was also carried out to evaluate the bacteria as a biosurfactant producer, which caused the decrease in surface tension that affects the floatation and sedimentation of pyrite minerals and gold sulfide ores. There were 13 bacteria used in this study, which started from the study of growth curve to the microflotation. The mineral content of the sulfide gold ore was analyzed using X-ray diffraction (XRD) and X-ray fluorescence (XRF). Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analyzes were also carried out to find out gold particles that were included in the pyrite minerals, while the gold content levels were measured using ICP-OES (Inductively coupled plasma-optical emission spectrometry). Two bacterial strains used in the microflotation experiment were Bacillus altitudinis strain SKC/S-8 and Citrobacter freundii strain SKC-4 in which the pure cultures of these two bacteria were compared with other cultures adapted with pyrite and gold sulfide ore. Other variables analyzed in this study were the effect of pH and bacterial inoculum concentration on Au content and recovery in sinks. Each of the study variations was analyzed in terms of Au content and recovery to obtain optimum bioflotation conditions. The result of interaction of Paenibacillus pasadenensis strain SKC/S-3, Bacillus altitudinis strain SKC/S-8 and Citrobacter freundii strain SKC/S-4 with pyrite mineral brought about the increase of pyrite contact angle value. Contradictory results were shown by bacteria that had been adapted to pyrite minerals during the incubation process where Paenibacillus pasadenensis strain SKC/S-3 and Bacillus altitudinis strain SKC/S-8 caused a significant decrease in contact angle, and Citrobacter freundii strain SKC/S-4 caused an increase in contact angle. The microflotation tests of gold sulfide ores with various variations gave different effects. The tendency of bacteria to work at acidic pH with different bacterial cell concentrations (% v/v inoculum) resulted in an optimum bioflotation performance in both grade and recovery. The variation of bacterial adaptation to pyrite minerals and ores did not significantly affect the increase in bioflotation grade. In this experiment, the highest recovery was obtained by using the bacterium Citrobacter freundii strain SKC-4, reaching 93% recovery but with an enrichment ratio (ER) of only 1.073. The best increase in grade was achieved by using Bacillus altitudinis strain SKC/S-8 with an enrichment ratio of almost twice higher than the initial grade (ER = 1.82) at pH 3 with pure culture and bacterial inoculum concentration of 10% v/v.