Microbial ecology of Thiobacillus ferrooxidans

FINAL TECHNICAL REPORT TO U.S. DEPARTMENT OF THE INTERIOR Geological Survey Washington. D.C.The contents of this report were developed in part under a grant from the Department of the Interior, U.S. Geological Survey. Grant number 14-08-0001-61313

Processing double refractory gold-arsenic-bearing concentrates by direct reductive melting

Iron arsenides may be the key to extraction of gold from existing refractory ores such as that at Bakyrchik, Kazakhstan, an ore body containing an estimated £8.5 billion reserve of gold. Gold is not extractable without significant ecological contamination from the associate arsenopyrite mineralisation. A new method for gold recovery from refractory gold-arsenic-bearing materials, based on direct reductive melting (DRM) of the concentrate has been developed, which locks As into relatively benign iron arsenide phases, whilst gold is extracted into lead alloy. The method has been filed as a patent with the Patent Office of the Republic of Kazakhstan.Islamic Development Bank - Cambridge International Scholarship Programm

Bio-reduction of sulfide minerals to recover invisible gold

Sulfide minerals, like pyrite and arsenopyrite, are of economical interest due to the presence of invisible gold locked inside these minerals. As fine grinding is often not sufficient to liberate the gold from these minerals, additional destruction techniques, based on chemical and biological oxidation processes, are required to access the gold via cyanidation. These techniques have proven to be successful to reach satisfactory gold recoveries, but operation costs are high and challenging waste streams (sulfuric acid) are produced. As an alternative to the oxidation methods in this thesis the bio-reduction of sulfide minerals was proposed and investigated. Bio-reduction, the use of hydrogen to convert mineral-sulfur to hydrogen sulfide, has as major advantage that the hydrogen sulfide can be recovered from the solution (to produce bio-sulfur) leaving a waste stream without diluted sulfuric acid. Furthermore, electrical energy will be saved. Theoretically, this more environmental friendly alternative should work, but no bio-reduction reaction was observed in practice. It appeared that sulfur/sulfate reducing bacteria were not able to use sulfur when fixed in the crystal lattice of pyrite and arsenopyriteat the selected conditions (pH 5, 35ºC). In order to make the mineral-sulfur bio-available for these bacteria the sulfur should first enter the solution. As alternative the combination between partial bio-oxidation and bio-reduction was therefore investigated. Partial bio-oxidation at pH 2 results in the formation of elemental sulfur, which can serve as a substrate at pH 5 for the sulfur/sulfate reducing bacteria. This combined method was found to be successful at 35°C, as the gold leachability of the used concentrate was increased from 6% to 39%. Optimization of this process is needed to reach gold recoveries >90% in 1 or 2 ox/red cycles, but when successful a new method (called the Paroxsul process) with a lower environmental impact, less costs, and application to a large number of minerals, is ready to be introduced to the precious metal industry. </p

Biooxidation of a gold bearing arsenopyrite/pyrite concentrate

The objectives of this project have been to characterise the biooxidation of an auriferous pyrite/arsenopyrite flotation concentrate, and to interpret laboratory batch and continuous pilot plant data in the light of the logistic model. Furthermore, the possibility of predicting continuous biooxidation plant performance from batch data was considered. The batch testing was carried out on five narrowly sized fractions of Fairview concentrate, as well as on the bulk concentrate. Extents of removal of iron, arsenic and sulphide-sulphur were described by the logistic equation and values of the kinetic parameters obtained. Maximum rates of removal of these components, predicted by the logistic parameters, correlated well with experimentally determined rates of removal obtained from the linear portions of the fractional removal versus time curves. Bibliography: pages 93-98

Bioprocessing of ores: Application to space resources

The role of microorganisms in the oxidation and leaching of various ores (especially those of copper, iron, and uranium) is well known. This role is increasingly being applied by the mining, metallurgy, and sewage industries in the bioconcentration of metal ions from natural receiving waters and from waste waters. It is concluded that bioprocessing using bacteria in closed reactors may be a variable option for the recovery of metals from the lunar regolith. Obviously, considerable research must be done to define the process, specify the appropriate bacteria, determine the necessary conditions and limitations, and evaluate the overall feasibility

Treatment of Arsenic-Bearing Minerals and Fixation of Recovered Arsenic Products: An Updated Review

Mineral processing and extractive metallurgical operations have created and are creating appreciable arsenic bearing wastewater and waste solid products that have to be handled, treated for recycle, or treated for environmentally safe disposal. At present there are intense research and operational activities being conducted to provide the best viable processing procedures to ensure that the mineral processing and extractive metallurgical industries are profitable and environmentally secure. The focus of this presentation is on the element arsenic, even though many other deleterious elements may also be present in ores and concentrates. Numerous base metal resources contain arsenic bearing minerals, especially resources containing mineral sulfides. Information on presently treated metal-bearing resources and potential new resources is voluminous, especially for those containing arsenic mineralization. The influence of elevated arsenic concentrations in the treatment of copper-arsenic sulfides and to a lesser extent the treatment of copper-gold-arsenic sulfides are considered in this presentation. Because of chapter page limitations not all treatment processes are discussed, however, examples are provided to illustrate arsenic problems and industrial solutions. The major emphasis of this presentation has been placed on the present state-of-the-art for arsenic immobilization/fixation and long-term storage considerations

Improving gold recovery from a refractory ore via Na₂SO₄ assisted roasting and alkaline Na₂S leaching

Gold recovery from refractory gold ores with controlled roasting remained well below 80%. Na2SO4 was added in an O-2-enriched single stage roasting of a refractory gold ore to improve its gold recovery. Changes in physicochemical properties of the calcines suggested that this reduced the sintering as well as facilitated the formation of pores and a water soluble phase within the calcine. Thermodynamic analysis and leaching results demonstrated that Na2S solutions could effectively remove Sb species from the calcine. An extraction process that includes Na2SO4 assisted roasting and alkaline Na2S leaching is shown to be able to achieve a gold recovery of over 95% from the refractory ore

Advances in Mineral Processing and Hydrometallurgy

This is a Special Issue of Metals devoted to aspects of Advances in Mineral Processing and Hydrometallurgy. This includes a global call for article submissions that also included Characterization along with Recycling and Waste Minimization. As such, both primary and recycled aspects will be considered. Possible specific topics included Mineralogy, Geometallurgy, Thermodynamics, Kinetics, Comminution, Classification, Physical Separations, Liquid–Solid Separations, Leaching, Solvent Extraction, Ion Exchange, Activated Carbon, Precipitation, Reduction, Process Economics and Process Control. Suggested application areas were in Gold, Silver, PGM’s, Aluminum, Copper, Zinc, Lead, Nickel, and Titanium. Critical Metals articles on topics such as Lithium, Antimony Tellurium, Gallium, Germanium, Cobalt, Graphite, Indium, and Rare Earth were also welcome. As such, this Special Issue of Metals was well supported by diverse submissions and the final publication of high-quality peer-reviewed articles