Papers by Keyword: Refractory Gold Ore

Abstract: Reserves of high-grade gold ore worldwide are decreasing, and some industries have started processing refractory gold ore. Refractory gold ore contains sulfide minerals such as pyrite (FeS₂), chalcopyrite (CuFeS₂), galena (PbS), and sphalerite (ZnS). Gold in refractory ores occurs as fine-size gold-bearing sulfide minerals. In this study, the microwave-assisted roasting method has been investigated as a pretreatment for a refractory gold ore. This method can provide rapid heating radiation, cause micro-cracks, and trigger the decomposition of sulfide minerals. The presence of additive helps in the oxidation of sulfide minerals. The microwave-assisted roasting was carried out using variations in microwave power and time. Microwave power between 300 - 600 watts significantly affected the increase in roasting temperature and weight loss of refractory gold ore. The highest temperature reached 567°C in roasting at 800 watts for 30 minutes. The optimum condition for microwave roasting was achieved at 400 watts of power with a roasting time of 30 minutes. Metals extraction of Cu, Zn, Pb, and Fe reached 97.2%, 82.7%, 16.1%, and 2.1% in water leaching.

Abstract: This paper describes the oxidative dissolution kinetics of sulfides with gold occlusion within pyrite and arsenopyrite. Shake flasks tests and column leaching of a low grade gold ore from China were carried out with domesticated mixed acidophiles isolated from acid mine drainage. Both test show that the main factors accelerating sulfide oxidation was mainly temperature and redox potential. Column bio-oxidation of mineral with a particle size less than 10 mm at 60°C resulted in higher mineral decomposition, finer fractions and eventually higher sulfide oxidation than that at 30°C. Sulfide-S dissolution increased from 58% to 77% from 30°C to 60°C after 247 ds of bio-oxidation. Further investigation into microbial community attached to the ore surface and in the leachate during the bio-oxidation was done by Real-time PCR assays. Organism of genera Acidithiobacillus was the most dominant species in both leachate and ore surface at lower temperature. For the Archaea, the iron oxidizing microbial Ferroplasma showed its predominance of 60°C. Mineral dissolution kinetics and microbial community in bio-oxidation was lucubrated in this work and suggestions were provided for pre-treatment of refractory gold ore.

Abstract: The Sawayardun Gold Mine, the first Muruntau type gold mine in China, was located in the south Tianshan Mountain, Xinjiang Province. The gold reserve was 127 t with an average gold grade of 2.36 g/t. Due to the high content of arsenic and antimony, the traditional flotation-roasting-cyanidation process was not suitable. The direct cyanidation gold extraction for the raw ore was 44.70 %. Thus, biooxidation experiments in shaker flasks were conducted for this ore. The optimum conditions were obtained as inoculation volume 10 %, initial pH 1.7, pulp density 15 %, temperature 33 °C, leaching time 10 days, with the arsenic oxidation rate of 75.12 %. Then the biooxidation residues were test for gold leaching using NaCN, green gold leaching agent and thiourea. After 24 h leaching rate at pulp density of 33%, gold leaching agent dosage of 2 kg/t ore, the gold extraction for NaCN, green gold leaching agent and thiourea were 91.50 %, 86.23 % and 91.09 %, respectively. The high gold extraction showed a bright future for the whole-ore heap biooxidation of this refractory gold ore.

Abstract: Refractory sulfide ores are ubiquitous resources of gold around the world. It was demonstrated that biooxidation pretreatment of refractory whole ores could be conducted in heaps. The effectiveness of column biooxidation of off-balance gold ores from Bakyrchik and Bolshevik deposits (northeast Kazakhstan) containing pyrite and arsenopyrite was examined in the laboratory. Bakyrchick ore contained 1.5% of pyrite, 3% of arsenopyrite and 4.5 g/t of gold. Bolshevik ore contained 1% of pyrite, 1% of arsenopyrite and 10.7 g/t of gold. The recovery rates of gold from the Bakyrchik and Bolshevik ores by direct cyanidation were 4.5% and 8.2%, respectively. Representative samples of each ore were processed in air-lift percolators. A bioleaching experiment was performed in duplicate. The enrichment culture was obtained from the pyrite flotation wastes and used as an inoculum. Bioleaching was conducted for 60 days at ambient temperature (20-25°C). The recovery rates of gold from the bioleaching residues of Bakyrchik and Bolshevik ores by cyanidation were 21.0% and 48.5%, respectively. The results obtained in the present work may be used to estimate perspectives of heap bio-oxidation for the recovery of gold from these sulfide ores.

Abstract: The fungus Phanerochaete chrysosporium has been proven to biotransform refractory gold ores, leading to increase in gold recovery. This transformation has been attributed to enzymes secreted by the microbe. This paper reports the findings of preliminary investigations aimed at assessing the use of hydrogen peroxide and cell-free extracts from the fungus, P. chrysosporium, to effect biotransformation of sulphidic refractory gold ores. The investigations show that the total dissolved arsenic, iron and sulphur in solution were up to 5.2 wt%, 0.9 wt% and 6.0 wt% respectively from flotation concentrate after 72 hrs of treatment. Analysis for sulphide sulphur in the residual solids of the gold concentrate indicated about 25 wt% oxidation within 24 hours of treatment. In general, cell-free decomposition of the samples did not increase beyond 24 hours of contact time, possibly due to exhaustion of the active components. Gold extraction by cyanidation increased by 24% after 24-hr treatment with the cell-free extracts. Comparatively, cell-free (in vitro) treatment recorded 66% overall gold recovery as against 61% for whole cell (in vivo) after 72 hours of treatment. These initial results indicate clearly that in vitro processing is a promising alternative to in vivo processing of refractory gold ores using P. chrysosporium.

Abstract: Low-grade, finely disseminated refractory sulfide gold ores associated with high arsenic are ubiquitous resources all over the world. Since heap bio-oxidation is an economic and promising biotechnology to recover gold, low grade, high organic carbon and arsenic bearing gold ores from Zhesang Mines in China were chosen for this purpose to study the key factors that would affect biooxidation. Pyrite and arsenopyrite (particle size 0.002-0.22 mm) were the main minerals from Mineral Liberation Analysis (MLA). Column biooxidation and cyanidation of mineral size < 10 mm were evaluated for its potential for gold extraction. Results showed that temperature was the main factor influencing sulfide oxidation. 58-67 % of sulfide was oxidized at 35-45°C after > 240 days of biooxidation with mixed mesophiles, while higher sulfide-S dissolution (77%) was obtained at 60°C. Sulfide-S fraction distribution revealed higher mineral decomposition, finer fractions and eventually higher sulfide oxidation at 60°C. Jarosite and scorodite were found from the residues at 60°C by SEM and EDX, which implies higher temperature accelerated arsenic precipitation. No elemental sulfur was detected during the biooxidation at 35-60°C. After bio-oxidation, column cyanidation was successfully demonstrated recovery of gold from the residues, with gold extraction rate reaching 66%.

Abstract: Dissolution of pyrite by chemical oxidation and bioleaching were studied with using short-term batch experiments. The results show that the rate of oxidative dissolution of pyrite increases with the increasing concentration of ferric in ferric sulfate solutions. With the corresponding in the bioleaching, the leaching rate of pyrite is markedly affected by the Eh of the solution. The ferric/ferrous ratio controls the relative rate of the oxidation reactions involved in the process. Additionally, the leaching rate of pyrite is controlled by the pH. The phase analysis of products indicated that S2- 2oxidation can produce S0 and SO2- 4under these conditions. On the basis of predecessors and using these species，the simplest expected oxidation mechanism is S2O2- 3regarded as the intermediate mechanism during the oxidation process.

Abstract: An attempt has been made to study the pretreatment of sulfidic refractory gold ore with pyrolusite. The influences of various parameters were studied to optimize the conditions. The optimum leaching conditions were pyrolusite/gold ore mass ratio of 3.0, H₂SO₄ concentration of 3.0 M, temperature of 100°C, particle size of 45μm, stirring speed of 200 rpm. After the pretreatment, gold and silver were exposed, these made the extraction of the precious metal in the gold ore much easier.

Abstract: This paper summarizes the result of experiment that was fourced on investigation of oxidation pretreatment on sulfide mineral for leaching of refractory gold concentrate by hydrogen peroxide in sulfuric acid. For a viable option, extraction rate of Fe, Cu was low, but extraction rate of arsenic reached nearly 100%. As the result of oxidation, elemental sulfur was not produced.

Abstract: Bacterial preoxidation of refractory gold ore has showed many advantages, such as lower operation cost and environmental friendly. In this paper, biooxidation of refractory gold ore by mixed moderate thermophiles culture in airlift bioreactor has been well studied. Firstly, a laboratory scale airlift bioreactor unit has been designed for bacterial preoxidation of refractory gold ore, a mixed moderate thermophilic culture was incubated. The orthogonal experiment was performed to investigate the effects of particle size, pulp density, aeration rate and initial pH. The results showed that when particle size 37micrometer，pulp density 5%，aeration rate 4 dm3•s-1 and initial pH 1.2, the arsenic leaching rate achieved to 93.5%. On the base of the airlift bioreactor unit, a continuous airlift bioreactor was designed. The preoxidation of refractory gold ore by a mixed culture of moderately thermophilic bacteria also was investigated in this equipment. The results showed that, under the conditions of pulp density 8% and stay time 60h, it can deal with 0.256 kg refractory gold ore per day, and the arsenic leaching rate can reach to 95.25%. During the experiment, some leaching liquor has been sampled from the second sect the fourth column of the continuous airlift bioreactor. The composition of microbial communities in this sample has been investigated using culture-independent 16S rDNA based cloning approach- restriction fragment length polymorphism. The phylogenetic analysis revealed that Leptospirillum ferriphilum and Acidithiobacillus caldus are the main organisms in this system. Both of them are moderate thermphilic bacteria and can resist relatively high concentration of arsenic ion.