Papers by Keyword: Biooxidation

Abstract: Inhibition of iron oxidation by Leptospirillum ferriphilum in the presence of thiocyanate (SCN^-) was studied in small-scale batch experiments. The L. ferriphilum culture was challenged with SCN^- over a range of 0 mg/l to 10 mg/l. The data showed that L. ferriphilum was able to utilise ferrous iron at low-level concentrations of SCN^- (0.25 mg/l to 1.75 mg/l), however exhibited a reduction in oxidation rate relative to the control (0 mg/l). Moreover, introduction of SCN^- at low-level concentrations resulted in a lag in iron oxidation activity, specifically at concentrations of 1 mg/l, 1.25 mg/l and 1.75 mg/l. No iron oxidation was observed at SCN^- concentrations above 1.75 mg/l, indicating complete inhibition. As L. ferriphilum is the dominant iron oxidising bacteria within biooxidation tanks, evidence of sustained iron oxidation activity at low-level SCN^- concentrations affirms the potential of recycling bioremediated cyanidation wastewater within biooxidation circuits in bioprocesses for gold recovery from sulfidic minerals as residual SCN^- concentrations in remediated effluent are reportedly lower than 0.25 mg/l. The inhibition kinetics of this system need to be explored further in order to develop a deeper understanding of the system such that it may be applied to inform process operation.

Abstract: This study investigated the biooxidation of a high-grade refractory gold ore from the Zarshouran mine (West Azarbaijan, Iran) in shake flasks and a stirred tank bioreactor (STBR) using a mixed culture of moderately thermophilic microorganisms. The influence of four critical parameters including, pH, biooxidation time, nutrient medium type and pulp density on the iron and arsenic extraction as well as gold cyanidation were evaluated in a full factorial design in shake flasks at 45 °C. Maximum iron extraction was obtained in M9K medium, pulp density of 5% (w/v), 15 days of biooxidation time and the pH of 1.6. Biooxidation in the STBR was carried out at the pulp densities of 10% and 20% (w/v), the pH of 1.7 in the M9K medium, in which dissolved oxygen, pH, redox potential, iron and arsenic concentrations were measured during the process. It was found that 61% decrement of sulphur content in the STBR led to recover 80% of gold, which was 43% higher than that in the conventional cyanidation process. It can be concluded that the oxidation of refractory arsenopyrite gold ore can achieved using a moderately thermophilic biooxidation culture.

Abstract: While bioleaching is a proven technology for the efficient recovery of base metals from sulphide minerals, its sustenance is dependent on the continuous availability of ferric ion, Fe³⁺, in soluble form, in bioleach liquor. However, the solubility of ferric ion is low at higher pH thus resulting in the formation of various types of ferric ion precipitates, which decreases leaching efficiency by trapping the leached metals in solution through an adsorption. The effect of initial solution pH on the surface properties of ferric ion precipitates was investigated with a view to establish a relationship between operational pH and surface charge on precipitate and to relate this to the precipitates metal adsorption properties. Ferric ion precipitates recovered from a typical biooxidation process were characterized by XRD, SEM, PSD and zeta potential. Potassium-hydronium jarosite were the main phases identified by X-ray diffraction (XRD) analyses. The SEM results revealed that the precipitates had smooth surfaces with development of sharp edges on the precipitates formed at high pH. The precipitates formed at higher pH had less positive charge and scavenged more copper ions due to the high electrostatic attraction forces. The results from this study revealed that surface charge on a precipitate can give an indication of its metal adsorption capacity and that in order to prevent metal loss and improve extraction efficiency, solution conditions should be maintained such that the resulting precipitates have high positive surface charge to promote high electrostatic repulsion forces.

Abstract: Since the discovery of bioleaching microorganisms and their role in metal extraction in the 1940s, a number of technical approaches have been developed to enhance microbially catalysed solubilisation of metals from ores, concentrates and waste materials. Biomining has enabled the transformation of uneconomic resources to reserves, and thus help to alleviate the challenges related to continually declining ore grades. The rapid advancement of microbial characterisation methods has vastly increased our understanding of microbial communities in biomining processes. The objective of this paper is to review the recent advances in biomining processes and microbial characterisation.

Abstract: The first production shop in Russia of refractory gold ores biooxidation using chemoautotrophic microorganisms association was launched in 2001 at Olimpiada gold recovery plant. The shop was designed for treatment of 3 million tons of Olimpiada deposit “Vostochniy” pit primary sulphide ore per year. In 2007 the BIO-2 shop designed for treatment of 5 million tons of primary sulphide ore was launched. Total capacity of the two bio-processing unit is 8 million tons of sulphide ores per year. A more advanced concept of BIO-3 shop was developed based on industrial operation and performance analysis of BIO-1 and BIO-2. The concept was based on biooxidation process automatisation with displaying control and managing parameters of the process on the monitors in control room. This allows to keep main process parameters within the specified limits and maintain process in a stable high-performance state. Installation of the automatisation systems in BIO-1 and BIO-2 shops allowed increasing the throughput of all flotation concentrate treatment shops from 870 t/day to 1200-1300 t/day. This led to production of more than 26 tons of gold in 2016. Currently JSC “Polyus” is copyright holder of patented refractory gold sulphide ores concentrate treatment technology, patented microbial association carrying out the process, and the technology itself is protected by the trademark "BIONORD".

Abstract: Mineral separation by froth flotation is widely used around the world for the beneficiation of sulfide ores. Flotation products (typically concentrate) are subjected to metallurgical processes for metal extractions. Bioleaching as a metallurgical procedure indicated many advantages over other traditional techniques (pyro- and hydro-metallurgy). However, organic flotation reagent residuals on the surface of minerals are effective on biological activities of microorganisms. In this work, to extensively study these effects, typical sulfide flotation collectors (Sodium ethyl-xanthate, Potassium isopropyl-xanthate, Potassium isobutyl-xanthate, Potassium amyl-xanthate, and Dithiophosphate (Aero)), and frothers (pine oil (PO) and methyl isobutyl Carbinol (MIBC)) were used in the presence of various bacteria (Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans) to investigate their effects on bio-oxidation. The results of this investigation can be used to better understand the mechanisms of bio-activities when reagent residues are on the surface of flotation products and they will feed to the bioleaching process.

Abstract: In a mine owned by the company Orenas S.A. (Equador), a biooxidation process for gold recovery has been developed. Refractory gold ore was crushed, milled and 500 ton of flotation concentrate was agglomerated by coating a support rock. This was piled up on a liner and the biooxidation process in the heap of 35x25x6 m³ was run for approximately 150 days. The oxidized material was subsequently removed for further processing. An outcrop allowed for depth dependent sampling of altogether 36 samples at three sites over the complete depth of 6 m. The fine fraction was removed from the host rock and sent to the laboratory for analysis of the microbial community. The pH ranged between 2.2 and 2.9. Total cell counts determined via counting under a fluorescence microscope after SYBR Green staining indicated a high microbial colonialization of the heap in all depths between 10⁶ to 10⁹ cells per g concentrate, however the highest cell numbers were mainly found in the upper 50 cm. Most-probable-number determination of living, acidophilic iron (II)-oxidizers for one site also revealed a decrease of cell numbers with depth (between 10⁴ to 10⁸ cells per g concentrate). Further molecular analyses of the community composition based on extracted DNA and 16S rRNA gene analyses by TRFLP and qPCR revealed a complex archaeal and bacterial community within the heap. It can be stated that an active community of acidophiles runs the biooxidation process in all sampled parts of the heap.

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: The ability of an iron-sulfur-oxidizing mixotrophic bacterium to treat two types of sulfide-rich carbonaceous refractory gold concentrates from Sulawesi and Sumatra in Indonesia was studied in comparison with an acidophilic chemolithotrophic bacterium Acidithiobacillus ferrooxidans. Over the course of the biooxidation experiments, the pH of the solution tended to rise (pH>5) due to the high content of acid-consuming minerals such as carbonates in both concentrates. Ferric ions were frequently observed to precipitate due to high solution pH. The BIOX^skc employed in this study was able to increase the gold extraction from low sulfidic carbonaceous refractory gold concentrates by ~15% higher than that by using At. ferrooxidans. It was also capable of treating carbonaceous matters which causes preg-robbing effect and retaining iron in ionic form due presumably to the production of extracellular polymeric substances (EPS) under high solution pH. Nevertheless, BIOX^skc also reduced the gold extraction yield of high sulfidic gold concentrates because of passivation effect. It is suggested that the precipitation of iron and sulfur on the surface of sulfide minerals during biooxidation may prevent cyanide ion contact with gold.

Abstract: The BIOX^® process was developed in the late 1980’s for the treatment of refractory gold concentrates. The process has since developed into a commercially proven process with 12 successful installations of which 6 are currently still in operation. During this time development of the technology continued to improve the efficiency of the process, improve the reliability of the equipment used and to reduce the capital and operating cost for the implementation and operation of the process.This paper will look at some critical aspects in the selection of the BIOX as the preferred technology for the treatment of a refractory gold. Process selection will include technical criteria, for example the amenability of a concentrate to biooxidation and process design criteria, but will also include the overall project economic evaluation, a study of the project risks, the impact of the project and technology on the environment and local communities, operability of the process and implementation strategy.It is important that these aspects be taken into consideration in the design of any testwork program, be it fundamental research in the biooxidation field or in the development of a specific project. The impact of decisions taken during the execution of the program must also be tested continuously to gauge the impact on the overall process viability.The selection of biooxidation as the preferred process route for any project, be it gold, copper or any other mineral, will in most cases be based on the overall project economics compared to other processes, rather than technical considerations.