EFFECT OF DIRECT AND INDIRECT PRE-OXIDATION OF GOLD ORE FROM DOUP NORTH SULAWESI USING OZONE GAS ON THE GOLD EXTRACTION DURING CYANIDATION PROCESS

• Main Author: Chrisna, Chanovanto
• Format: Final Project
• Language: Indonesia
• Subjects: Metalurgi
• Online Access: https://digilib.itb.ac.id/gdl/view/68571
• Institution: Institut Teknologi Bandung

Refractory gold ore is a type of gold ore that is difficult to process and produces gold recovery <95%, even <50% for the highly refractory category, when dissolved in conventional cyanidation. Gold recovery can be improved by pre-treatment of sulfide-type refractory gold ores where the gold grains are encapsulated in difficultto- dissolve sulfide minerals. One of the pre-treatment methods that may be applied is the use of ozone gas as an oxidizing agent. Ozone has a high standard reduction potential, which is +2.07 V (vs SHE), which can be produced from pure oxygen gas or air. In this study, gold ore samples from Doup, North Sulawesi were used to study the effect of direct and indirect pre-oxidation using ozone gas on the increasing gold recovery in the subsequent cyanidation process. Gold ore was dried, grinded and sifted until the ore particle size distribution was 100% <74 microns, and samples were taken using the coning-quartering method. The ore samples were then analyzed by X-ray Diffraction (XRD), X-ray Fluorescence (XRF), fire assay, and Scanning Electron Microscope (SEM). After that, diagnostic leaching is carried out to study the quantitative distribution of gold within certain mineral groups in the ore. Then, a series of direct and indirect preoxidation experiments were carried out with various pH and ozone raw materials (pure air and O2). Temperature, pH, dissolved ozone (DO3), dissolved oxygen (DO2), oxidation-reduction potential (ORP) changes were recorded and the solution was sampled for a certain pre-oxidation time. The pre-oxidized filtrate was then analyzed for the concentration of dissolved Cu, Fe, and Zn using Atomic Absorption Spectroscopy (AAS). Meanwhile, the residue from each pre-oxidation experiment was then leached by a cyanidation to obtain a leaching solution (PLS) then analyzed the concentration of dissolved gold using AAS. The percentages of dissolved Cu, Fe, and Zn during pre-oxidation was found to increase with the pre-oxidation time, acidity setting at pH 2, and the use of pure O2 as ozone raw material. The direct pre-oxidation process with acidity setting at pH 2 and air as raw material for ozone for 240 minutes was able to increase gold extraction from 79.08% to 82.78% in the cyanidation process. Pre-oxidation conditions without acidity setting resulted in lower gold than the pre-oxidation conditions at pH 2 due to the formation of an ferric hydroxide layer inhibiting further oxidation of sulfide minerals. Besides that, the formation of elemental sulfur as a result of the direct pre-oxidation method can result in a slow rate of gold leaching and increase cyanide consumption.