STUDY OF BIOXIDATION BEHAVIOUR OF GOLD CONCENTRATE FROM SUMBAWA ISLAND USING IRON AND SULFUR OXIDIZING MIXOTROPHIC BACTERIA

• Main Author: BAKHTIAR - Nim: 12513050, ARSYAD
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/21262
• Institution: Institut Teknologi Bandung

Mineral processing of refractory gold has begun recently. This was done because the non-refractory gold ore begins to diminish its supply in nature because of its massive exploitation. One of the refractory gold ores is sulphide gold ore. Sulphide gold ores can not be extracted by direct cyanidation so it is necessary to do the pre-treatment to produce an optimal yield of gold extraction. One of sulphide gold concentrate’s pre-treatment methods is biooxidation. In this research, biooxidation experiments of sulphide gold concentrate was using iron and sulfur oxidizing mixotrophic bacteria such as Citrobacter youngae strain SKC-5 and Alicyclobacillus ferrooxidans. The concentrate used in this research is refractory gold ore concentrate from Sumbawa Island from flotation product. <br /> <br /> <br /> Series of experiment was begun with preparation of sulphide gold ore with crushing, grinding, homogenization, and sampling to get -75 µm composite. The composite was floated to get gold sulphide concentrate. The concentrate were characterized by Fire Assay, Inductively Coupled Plasma Optical Emission Spectrometry (ICP-EOS), LECO analysis, X-Ray Diffraction (XRD), mineragraphy polishing, and diagnostic leaching experiment. Preliminary experiments were performed to obtain the most optimal bacterial incubation time, the best species of bacteria, and make concentrates of gold sulphide were treated adaptively with pH 2 and were compared to non-adapted concentrates. Direct cyanidation experiment was done and used as a comparison. Several variations of bioxidation were an addition of iron sulphate (FeSO4.7H2O) 6 g/l, 10 g/l, 15 g/l; pyrite (FeS2) 3 g/l, 6 g/l, 9 g/l; and molasses 2 g/l, 4 g/l, 6 g/l. Intensive cyanidation process in bottle roll test at 10% (w/w) solid percentage, 5% sodium cyanide (NaCN), 0,7% sodium hydroxide (NaOH) and 2% leachwell (PbNO3) for 24 hours was conducted on solid residue of bioxidation. <br /> <br /> <br /> The result of experiment showed that gold is inclusive at <5µm in sphalerite. In addition, gold is also present in arsenopyrite, pyrite, and silica. Optimal bacterial incubation times for Citrobacter youngae strain SKC-5 and Alicyclobacillus ferrooxidans are 5.25 and 3.75 days, respectively. The best iron and sulfur oxididizing bacterium is Citrobacter youngae SKC-5. The concentrate does not need to be adapted at pH 2. The result of percent extraction gold in direct intensive cyanidation is 52,67%. The highest percentage of gold extraction is found in the addition of 10 g/l iron sulphate, 9 g/l pyrite, and 4 g/l molasses with percent extraction of gold respectively are 64.57%, 52.23%, and 62.46%.