Advanced Materials Research Vols. 71-73

Abstract: The past number of years has seen a sharp rise in the gold price. This has led to renewed activity in the gold sector and especially in refractory ore-bodies that are not economically feasible at lower gold prices. There have, historically, been a total of eleven BIOX® plants commissioned world wide with eight currently in operation. The most recent plants to be commissioned were Bogoso and Jinfeng in 2007 and Kokpatas in Uzbekistan in 2008. Design of the Bogoso BIOX® plant was started by Minproc in 2005. The design throughput of the sulphide BIOX® circuit is 820 tpd concentrate at a feed sulphide sulphur grade of 20 %. The Bogoso BIOX® plant has the largest biooxidation reactors with a live capacity of 1,500 m3 each. Plant design on the Jinfeng project started in 2005 and the engineering was performed jointly by Ausenco and Nerin. The BIOX® plant has a design capacity of 790 tpd concentrate at 9.4 % sulphide sulphur. The Kokpatas plant will be the largest BIOX® plant in the world with a Phase 1 design concentrate treatment capacity of 1,069 tpd at 20 % sulphide sulphur. The throughput will be doubled during Phase 2. Interestingly, unlike other BIOX® Plant, this plant will use a resin-in-pulp circuit for gold recovery, but the design will allow the plant to be converted to Carbon-in-pulp if required. There are currently three BIOX® projects in various stages of design or construction. This includes two expansions to existing BIOX® operations and one new BIOX® project. There are a number of major R&D projects currently under investigation with some very positive results. Most R&D is focussed on the main capital and operating cost items in the process, but there are also projects focussed purely on process optimisation and improvement.

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.

Abstract: In this report we evaluate the oxidative capacity of native microorganisms from Copahue geothermal system applied to a gold concentrate (71.1 g/t) compared to that showed by some culture collection strains. The sulphide ore, in which gold is present as submicroscopic particles contained in a pyrite matrix, came from several reservoirs of polymetallic ores located in Neuquén, Patagonia Argentina. The ore was processed in Andacollo treatment plant for gold concentration. After biooxidation tests, the highest percentages of solubilised iron were reached in the inoculated system (100% mixed native cultures, 47.8% Leptospirillum ferrooxidans ATCC 29047 and 28.5% for Acidithiobacillus ferrooxidans DSM 11477) while in the sterile control it was only 8.8%. The gold recovery was 96.3% and 45.3% for the treated and untreated concentrate respectively.

Abstract: Results of research on technological processes for treatment of refractory gold-arsenic ores using bioleaching of concentrates are presented. In October 2001 the first line of bioreactors on Mill-2 began operation with projected throughput of 3 million tons a year. In July 2007 Mill-3 began operation with projected throughput of 5 million tons a year. At present the closed joint stock company Gold Mining Company «Polyus» occupies a leading position in gold extraction from hard rocks in the Russian Federation. Processing of refractory gold-arsenic ores is conducted on Mill-2 and Mill-3 by a flotation-cyanide scheme using a unique biooxidation technology, BIONORD®, designed to process concentrates in the extreme climatic conditions of the North, . The achieved productivity of the Olympiada Mining Combine, from the processing of both oxidized and refractory ores of the Olympiada deposit, is 26.7 tons of gold a year. The gold is mostly present as finely dispersed and submicroscopic particles in close association with sulfide minerals, usually pyrite, pyrrhotite, arsenopyrite and antimonite. The average productivity of the lines is 1000 t/day. The process time is 100-150 h. The pulp density is 150-200 g/l. The working temperature is 39-40oC. The microbial association is represented by three species of chemolithotrophs: “Sulfobacillus olympiadicus”, Leptospirillum ferrooxidans, and Ferroplasma acidiphilum present in proportions 60-80%, 10-20%, and 10-17%, respectively. During the process 87% of sulfide minerals are oxidized. Thus, 98% of the pyrrhotite, 95.4% of the arsenopyrite, 70% of the antimony sulfides and 60% of the pyrite is oxidised. Biooxidation enables 97% of the gold to be released.

Abstract: The mining district of Zaruma-Portovelo of southern Ecuador is a deposit of polymetallic sulfides worked since 1908. Currently the small traditional mining operation processes 1800 tons of ore a day, generating environmental waste that is accumulated and systematically discharged into the Calera and Amarillo Rivers. In this watershed area of Puyango-Tumbes, where samples were taken and subjected to gravimetric concentration, a mineralogical analysis of the concentrate was made. Samples of sediments taken from areas of weathered mining shafts were used to isolate native microorganisms for subsequent molecular and physiological characterization. The mineral concentrate contains 66.63 % of pyrite, 175 ppm Ag and 6.9 ppm Au (with 80 % of refractory gold). This mineral was subjected to biooxidation by the isolated native organisms. In experiments with pulp density of 10%, the solubility of the sulfides was very significant, reaching concentrations of Fe3 + 30 g/L and sulfate 60 g/L.

Abstract: Acidithiobacillus ferrooxidans was acclimatized to 1000 mg/L arsenic(V) and then used for the bioleaching of enargite (Cu3AsS4) at pH 2. Secondary minerals formed during the bioleaching of enargite were characterized by X-ray diffraction, FT- infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Oxidative dissolution of enargite resulted in the formation of elemental sulfur, arsenate and oxidized sulfur species including jarosites and possibly also schwertmannite at pH 2.

Abstract: In previous studies it has been showed that sulphuric bio-acid is a good leaching agent for laterite tailings. In this work we evaluated nickel and cobalt recoveries from tailings of Caron technology process using sulphuric acid produced by Acidithiobacillus thiooxidans cultures under different conditions. In studies where tailings were initially added to the cultures, high nickel and cobalt recoveries (about 60 % for cobalt and 85-100 % for nickel) were reached after 13 days when low pulp densities (1 % and 2.5 %) of laterite tailings were used. These high recoveries fitted very well with the low pH values measured in these cultures. However, metal recoveries were negligible when higher pulp densities were used. Due to such reason, the performance of pre-cultivation configuration was evaluated; for that laterite tailings were added to the cultures after 24 or 48 hours of bacterial growth. This configuration was very efficient even at high pulp density (like 10 %) reaching recoveries (almost 50 % for cobalt and 80 % for nickel) close to those observed where tailings at low pulp densities were initially added to the cultures.

Abstract: Nickel laterite contains metal values but is not capable of participating in the primary chemolithotrophic bacterial oxidation because it contains neither Fe2+ iron nor substantial amount of reduced sulphur. Its metal value can, however, be recovered by allowing the primary oxidation of FeS2, or similar iron/sulphur minerals to provide H2SO4 acid solutions, which solubilise the metal content. This study investigated the possibility of treating nickel laterites using chemolithotrophic microorganisms. Preliminary studies conducted using H2SO4 acid, citric acid and acidified Fe2(SO4)3 gave an insight on the use of chemolithotrophic bacteria in this process,. Results showed that H2SO4 acid performed better, in terms of nickel recovery, than citric acid or acidified Fe2(SO4)3. In the bacterial leaching test works, mixed cultures of Acidithiobacillus ferrooxidans, Acidithiobacillus caldus and Leptospirillum ferrooxidans were used in the presence of elemental sulphur and FeS2 as energy sources. The sulphur substrate exhibited better effects in terms of bacterial growth, acidification and nickel recovery than the FeS2 substrate. Using response surface methodology, the theoretical optimum conditions for maximum nickel recovery (79.8%) within the conditions studied was an initial pH of 2.0, 63μm particle size and 2.6% pulp density.

Abstract: Quartz sands contain various iron and clay minerals which coat silicate grains or are impregnated in silicate matrix. Treatment by basin water bioleaching in combination with electromagnetic separation can substantially improve the quality of quartz sands. The purpose of this in-situ study was to evaluate the feasibility of using a biological basin treatment process to improve the quality of quartz sands. The environmental conditions involved the changes of climate temperature, using fresh surface water without disinfection, inhibition of algae and fungi, and promoting bacteria. Analyses of the solution phase were used to monitor the dissolution of iron during the bioleaching of the quartz sands and to optimize the in-situ conditions for the bacterial activity. The rate of iron dissolution varied with environmental conditions, with the addition of nitriloacetic acid (NTA)/l and organic feedstock in the form of molasses. Bacterial removal of clay and iron minerals can be used to expose the white surfaces of quartz grains. The quartz sands from the Šaštín deposit (Slovakia) were used in glass industry after decreasing the Fe content.

Abstract: The biological reduction rate of Fe(III) was studied using dissimilatory ferric reducing bacterial cultures (FeRB) in an attempt to establish a biotechnological via for the metallurgical treatment of iron ores. Enrichment cultures of dissimilatory ferric reducers were obtained from samples collected from a flooded acidic open pit in an abandoned Pb and Zn sulphide mining site nearby La Unión (Murcia, Spain). Adapted cultures were able to reduce 3 g/L of soluble Fe(III) with 100 efficiency in 36 hours. The growth of mixed cultures was also tested in solids. Ferrihydrite and ammonium jarosite served as electron acceptors in cultures where lactate acted as electron donor. Bacterial growth was also positive in both cases. This result represents an effective alternative to the chemical reduction of ferric minerals that avoids extreme temperatures when pyrometallurgical reactors are used. In addition, three species of FeRB were isolated and identified as Serratia fonticola, Aeromonas hydrophila and Clostridium celerecrescens. One of them, Aeromonas hydrophila, results of particular interest and, at the present moment, is being studied in depth. The particular significance of Aeromonas hydrophila is related to the characteristics of its exhausted cultures, where ferrous iron remains solved at pH values next to 7. At the present moment, the identification and characterization of the Fe(II) soluble complex is being account.