Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
  • C22B3/18—Extraction of metal compounds from ores or concentrates by wet processes with the aid of microorganisms or enzymes, e.g. bacteria or algae
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• This invention relates to a novel process and in particular to biological leaching and to the beneficiation of mineral ores.
• autotrophic bacteria appear to be most important in the field of extractive metallurgy.
• the chemosynthetic autotrophic iron bacteria that are implicated in biological leaching are widely distributed in nature where iron salts, sulfur and hydrogen sulfide are present, particularly in an acid environment.
• the most important member of this group is Thiobacillus ferrooxidans (Colmer, A.R. and Hinkle, M.E. (1974), Science 106. 253).
• T. ferrooxidans derives energy for growth from the oxidation of ferrous iron, sulfur and sulfides (Tuovinen, O.H. and Kelly, D.P. (1974), Z. Allg. Mikrobiol. 12, 311-346)
• This rod-shaped bacterium is aerobic and requires an acid environment between pH 2 and 3.5. Carbon for growth is obtained from atmospheric CO 2 and nitrogen from dissolved ammonia or nitrates.
• Valuable metals are often present in ores as insoluble metal sulfides.
• the leaching process is the end result of the bacteria acting upon the metal sulfide, which serves as an energy source in the presence of other nutrients.
• the mineralogy of the ore minerals and associated gangue are extremely important in establishing the feasibility of leaching.
• Bacterial leaching is associated with the presence of pyrite (FeS 2 ), pyrrhotite or other gangue reduced iron and/or sulfur compounds, representing ubiquitous growth substrates which often occur in association with other more valuable minerals, e.g., copper, uranium, tin.
• pyrite FeS 2
• pyrrhotite or other gangue reduced iron and/or sulfur compounds representing ubiquitous growth substrates which often occur in association with other more valuable minerals, e.g., copper, uranium, tin.
• One mechanism of bacterial leaching is of an indirect nature and is reliant on the presence of pyrite.
• ferrous sulfate produced by the chemical oxidation of pyrite - is oxidised to ferric sulfate by T. ferrooxidans (see equation 1).
• the ferric sulfate then reacts with metallic sulfide minerals as follows -
• the bacteria also oxidise elemental sulfur to sulfuric acid
• iron-oxidizing bacteria also ensures that ferrous iron is oxidised back to ferric iron.
• the products of these reactions ultimately dependent on the presence of pyrite or other iron sulfides, are ferric sulfate and sulfuric acid, a mixture capable of oxidising and dissolving many otherwise insoluble minerals.
• This invention relates to ore types where the valuable metal in question is associated with pyrite, pyrrhotite or other gangue reduced iron and/or sulfur compounds but is present in a highly oxidised state or other recalcitrant state and as such is recalcitrant to the normal mechanisms of bacterially assisted metal solubilization as described above.
• Suitable ores which can be treated according to the invention are cassiterite; pyrite, pyrrhotite or other gangue reduced iron and/or sulfur compound associated laterite deposits, e.g. nickel laterites; and heavy mineral sands, e.g., ilmenite.
• the invention is also applicable to the removal of pyrite, pyrrhotite or other gangue reduced iron and/or sulfur compounds associated with gold etc., or other inert, valuable metals thus, bacterial dissolution of unwanted pyrite, pyrrhotite or other gangue reduced iron and/or sulfur compounds allows beneficiation of the valuable metal required. Such beneficiation may effectively serve to concentrate the desired metal and may also facilitate conventional extractive procedures through reduced ore grinding and more efficient flotation and physical separation techniques.
• the invention therefore provides a process for increasing the concentration of wanted metal values in an ore, ore extract or other like material which contains pyrite pyrrhotite or other gangue reduced iron and/or sulfur compounds.
• the process of the invention comprises cultivating a strain of Thiobacillus ferrooxidans capable of oxidising iron and sulfur under acidic conditions in a medium containing the ore, ore extract or other like material and water under aerobic conditions, in the presence of a source of nitrogen thereby removing iron and sulfur.
• the medium be supplemented by ammonium, potassium, magnesium, calcium, phosphate and nitrate ions. Alternatively, these may be present in the water or the material being treated. If that material or water contains a source of nitrogen, then further nitrogen need not necessarily be added. Some forms of Thiobacillus ferrooxidans appear to fix atmospheric nitrogen. With such forms air may provide the nitrogen source.
• the material to be treated may be pre-ground if necessary, depending on the type of material.
• the process of the invention can be applied to several stages of the beneficiation process.
• the ore can be treated by the process of the invention in situ before mining. This would reduce both mining and conventional beneficiation costs by reducing the amount of material to be mined and beneficiated.
• the ore can be mined and stockpiled and treated according to the invention before the usual beneficiation. In certain cases this will facilitate subsequent grinding of the ore, especially cassiterite, thereby minimising losses through fines.
• the sulfide flotation concentrates can be treated with a strain of Thiobacillus ferrooxidans capable of oxidising iron and sulfur to facilitate their further treatment. Concentrates from other intermediate stages of beneficiation processes may also be treated according to the invention.
• tailings from beneficiation processes can also be treated according to the invention in order to obtain a feedstock with metal values in sufficient concentration to make further beneficiation economic.
• Thiobacillus ferrooxidous may function at moderate or extreme temperatures and processes of the invention employing such organisms may be carried out at temperatures up to the maximum temperature at which the particular organism is viable. Generally, however, the processes will be performed at temperatures of 5°C to 42°C, preferably from 28°C to 32°C.
• the invention is especially applicable to the treatment of tin ores such as cassiterite, the beneficiation of which can be effected by dissolution of pyrite, pyrrhotite or other gangue reduced iron and/or sulfur compounds by a strain of Thiobacillus ferrooxidans capable of oxidising iron and sulfur.
• Tin is not solubilised by the micro-organism.
• the biological dissolution of pyrite, pyrrhotite or other gangue reduced iron and/or sulfur compounds may favourably affect subsequent metallurgical extractive procedures by making the ore more amenable to grinding. Leaching of cassiterite in situ would simplify mining operations and provide feed to the mill with a lesser comminution energy requirement.
• Suitable organisms have been isolated from surface waters and ore samples located within cassiterite containing dolomite host rock at a tin minesite.
• the cultures which have been temporarily designated BA-MBW3, BA-MBW9, BA-MBS2 and BA-MBS3 consist of gram-negative rods of varying sizes (0.5 - 2 micron) with rounded ends, which occur singly and frequently in pairs.
• the morphology of these cultures are consistent with the presence of both "typical" Thiobacillus ferrooxidans as described extensively in the literature and a typical "Thiobacillus ferrooxidans like" rods of greater length.
• the organisms designated BA-MBW3, BA-MBW9, BA-MBS2 and BA-MBS3 are mixtures of Thiobacillus ferrooxidans strains.
• BA-MBW9 is capable of chemoautotrophic growth in the absence of an organic carbon substrate.
• artificial minewater medium designated 9K salts medium (Silverman, M.L. and Lundgren, D.G. (1959), J. Bacteriol. 78., 326) under aerobic conditions, BA-MBW9 rapidly oxidizes ferrous suifate, oxidation being complete in approximately 72 hours.
• 9K salts medium Silverman, M.L. and Lundgren, D.G. (1959), J. Bacteriol. 78., 326
• BA-MBW9 was isolated from a site characterized by a pH of 2.45 and at 16°C. The culture grows rapidly within the range 20° to 32°C, however the limits of growth have not been determined. It is acidophilic, growth being most rapid in the region pH 2-2.5. Growth has also been observed at pH 1.7. Maintenance of BA-MBW9 on synthetic medium does not result in loss of ability to oxidize naturally occurring sulfides.
• EXAMPLE 1 This example illustrates the ability of a Thiobacillus ferrooxidans containing culture to remove pyrite from a cassiterite containing porphyry ore. The culture was isolated from the minesite.
• a cassiterite containing quartz porphyry ore composite was used in this example.
• the ore was crushed to -3.2mm and an iatad analysis conducted (Table 1).
• the contents of the flask were inoculated (5% v/v/) with either sterile acid water or a T. ferrooxidans containing culture designated MBW-9.
• the flasks were incubated on an orbital shaker at 120opm at 28°C. Samples (5ml) were taken asceptically at appropriate time intervals. The samples were centrifuged (3,000 rpm) to remove debris and the supernatants retained for analyses. The following analyses were conducted.
• Soluble metals (tin, iron) were determined by Atomic Absorption Spectrophotometry. Soluble ferric iron was monitored by reaction with acid thiocyanate (20%, w/v) and spectrophotometric absorption at 480nm. The pH was followed using a standard laboratory pH meter. Microscopic examination of culture flasks was conducted using a standard research microscope. Ore residues remaining after leaching were analysed by standard chemical tests. X-ray diffraction and microscopic examination.
• This example demonstrates the ability of the same Thiobacillus ferrooxidans containing culture cited in Example 1 to remove pyrite from a different cassiterite containing quartz porphyry ore. Details of this ore were not supplied.
• Sterilised ore (10g) was dispensed into Erlenmeyer flasks (500ml) containing either mineral salts medium or acidified distilled water. Details of medium addition and composition are outlined in Example 1. The flasks were inoculated (1% v/v) with a T. ferrooxidans containing culture designated MBW9. The conditions of flask incubation, content sampling and analysis are given above (Example 1). The results are shown in Table 5.
• This example shows the ability of a Thiobacillus ferrooxidans containing culture not isolated from the minesite to remove iron from a cassiterite containing quartz porphyry ore similar to the ore sample used in Example 2.
• Example 2 Sterilized ore (4g) was dispensed into Erlenmeyer flasks (500ml) containing mineral salts medium. Details of the medium addition and composition are outlined in Example 1. The flasks were inoculated (5% v/v) with either sterile acid water or a culture containing Thiobacillus ferrooxidans. The conditions of flask incubation, content sampling and analysis are given above (Example 1). The results are shown in Table 6.
• Table 6 Iron solubilization from porphyry ore by a culture containing Thiobacillus ferrooxidans not isolated from the minesite.

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• 1983
  • 1983-12-16 WO PCT/AU1983/000186 patent/WO1984002355A1/fr not_active Application Discontinuation
  • 1983-12-16 EP EP19840900004 patent/EP0129564A4/fr not_active Withdrawn
  • 1983-12-16 AU AU23348/84A patent/AU565144B2/en not_active Ceased
  • 1983-12-16 JP JP59500148A patent/JPS60500239A/ja active Pending
  • 1983-12-19 ZA ZA839394A patent/ZA839394B/xx unknown
• 1984
  • 1984-08-17 OA OA58370A patent/OA07796A/xx unknown

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