Ferric Sulfate Media Research Articles

Characterization of the Solid Leach Residues from the Iodine-Assisted Chalcopyrite Leaching in Ferric Sulfate Media

Characterization of the Solid Leach Residues from the Iodine-Assisted Chalcopyrite Leaching in Ferric Sulfate Media

Iodine-assisted chalcopyrite leaching in ferric sulfate media: Kinetic study under fully controlled redox potential and pH

The addition of iodide has been found to significantly accelerate chalcopyrite leaching in ferric sulfate media at ambient conditions. Solution potential is the principal factor determining the leaching performance through controlling the iodine speciation. In order to develop a kinetic equation that incorporates the iodine speciation, a series of leaching tests were carried out in specially-designed sealed reactors that allows the solution potential together with other leaching parameters to be fully controlled. The experimental results showed that the rate of copper dissolution was increased by increasing the solution potential in the range of 669 to 769 mV vs. SHE), increasing the total iodide concentration in the range of 50 to 200 mg/L, and increasing the temperature between 25 and 40 °C. The formation of elemental sulfur and jarosite did not hinder the leaching reaction. A kinetic model was developed that relates the rate of copper extraction to the solution potential with a reaction order of 0.32, the diiodine concentration with a reaction order of 1.17, and temperature with an activation energy of 43.1 kJ/mol. The kinetic analysis supported that the leaching process was controlled by surface chemical reaction.

Kinetic modelling of chalcopyrite leaching assisted by iodine in ferric sulfate media

Chalcopyrite leaching at moderate temperature exhibits slow kinetics due to surface passivation. The presence of iodine has been reported to significantly enhance copper dissolution from chalcopyrite in ferric sulfate media at ambient temperature. However, the key factors controlling the reaction rate and the mechanisms have not been well understood. This study quantified the effect of different parameters on the kinetics of copper extraction in the presence of iodine and elucidated the possible rate-limiting steps. A series of leaching tests was carried out in PTFE (polytetrafluoroethylene) bottles with high chemical resistance to investigate the effect of solution potential (673–769 mV vs SHE), total iodide concentration (50–200 mg/L), particle size (53–90 μm), and temperature (25–45 °C) on chalcopyrite concentrate leaching. PTFE bottles were used to prevent iodine loss via evaporation and iodine corrosion of the experimental apparatus. The experimental results show that redox potential was the principal factor determining the leaching performance via controlling the aqueous iodine speciation. In the potential range where triiodide or diiodine dominates, the copper extraction increased with increasing potential, increasing total iodide concentration, and increasing temperature. Particle size did not affect the kinetics, possibly resulting from the narrow size ranged used. A preliminary kinetic model shows that the reaction orders with respect to Fe(III)/Fe(II) concentration ratio and the total iodide concentration were 0.36 and 0.91, respectively. The activation energy (47 kJ/mol) was significantly lower than those reported for the conventional chalcopyrite leaching in ferric sulfate media, suggesting that the presence of iodine changed the reaction mechanism. Further investigation is required to uncover the exact role of different iodine species in the leaching process.

Biooxidation pretreatment of low grade refractory gold tailings using a sulfur-oxidizing mixotrophic bacterium

An inefficient gold leaching in the cyanidation process from refractory gold tailings was caused by gold particle locked in specific minerals. The aim of this study was to harness the ability of a sulfur-oxidizing bacterium to oxidize iron and sulfur and its behaviour on ferrous sulfate heptahydrate (FeSO4.7H2O) and pyrite (FeS2) as the medium in the biooxidation process for gold and silver extraction. The results showed that the gold extracted in ferrous sulfate medium was 20.48%, while that in pyrite medium tended to reduce from direct cyanidation to 14%. The silver extraction increased from 80.96% to 99.26% in ferrous sulfate medium and 91.30% in pyrite medium. This result indicated that ferrous sulfate heptahydrate was more suitable than pyrite, which resulted in the higher extraction of gold.

The process chemistry and mineralogy of brannerite leaching

Brannerite (UTi2O6) is the most important uranium mineral after uraninite and coffinite, and the most common refractory uranium mineral. As the more easily leachable uranium ores are becoming exhausted, it is necessary to process the complex and refractory ores in order to meet the growing demand for uranium as an energy source. This typically requires either more intense leaching conditions or a better-designed process based on sound understanding of feed mineralogy and reaction chemistry. The present study was carried out to provide information that will enable the development of a more effective processing strategy for the extraction of uranium from ores containing brannerite. The leaching behaviour of brannerite in sulphate media under moderate temperature conditions was investigated and compared with its relative leachability in alternative acid and alkaline systems. The feed and the leached residues were characterized by XRD and SEM-EDX techniques. Brannerite dissolutions of up to 95% after 5 hours of leaching in ferric sulphate media, up to 89% in ferric chloride media under similar conditions, and up to 82% in 24 hours in sodium carbonate media were obtained. Since alkaline leaching was considered promising for acid-consuming ores, leaching was repeated with a high-carbonate brannerite-bearing ore, with comparable extractions. Mineralogical characterization showed that altered and amorphous regions are a regular feature of brannerite, and that pitting is typically observed on the surface of the leached grains. The leaching results, coupled with mineralogical data, showed that the uranium and titanium in brannerite generally dissolve congruently, with faster dissolution of the altered and amorphous regions in the brannerite grains than of the crystalline regions. We conclude that the extent of brannerite alteration is a key factor in process selection, along with the grade, liberation size, and gangue mineralogy.

Patterned Copper Sulfide Thin Films: a Method for Studying Leaching Behaviour

An experimental study on copper leaching from Cu1.85S thin films is presented, wherein copper extraction is quantitatively evaluated by changes in film thickness measured by white light interferometric profilometry. Changes in the film morphology and elemental composition, as assessed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, are used to confirm that the loss in film thickness is due to changes in the copper content and that the resultant film species is consistent with the mechanism of copper dissolution. The Cu1.85S thin films were synthesized by chemical bath deposition. The leaching behaviour of copper from the films was investigated in acidic ferric sulfate media at pHs 1, 2, and 3, and pH 1 at redox potentials of ~350–650 mV versus Ag/AgCl in 3 M KCl. The changes in the film thickness and copper sulfur ratio were shown to reflect copper dissolution behaviour from chalcocite. Leaching of the Cu1.85S films demonstrated a greater decrease in film thickness as pH decreased. In addition comparison of the order of reaction as a function of proton concentration in non-oxidative dissolution of Cu1.85S (0.06) and as a function of iron(iii) concentration in ferric oxidation of Cu1.85S (0.40) shows that the proton dissolution reaction is negligible. Leaching of the Cu1.85S films at redox potentials of up to ~476.4 mV versus Ag/AgCl in 3 M KCl produced covellite and demonstrated greater decreases in film thickness with increases in the redox potential. Leaching of the films above ~476.4 mV resulted in the formation of spionkopite and demonstrated a much lesser decrease in film thickness. These results are consistent with Eh-pH diagrams for the Cu–S–H2O system.

The role of silver-enhanced pyrite in enhancing the electrical conductivity of sulfur product layer during chalcopyrite leaching in the Galvanox™ process

The rate of chalcopyrite leaching in ferric sulfate media during the Galvanox™ process increases significantly in the presence of silver-enhanced pyrite. The increase in the kinetics of leaching is attributed to the galvanic interaction between pyrite and chalcopyrite. Pyrite provides an additional surface area for the cathodic reaction. The oxidation reaction rate increases to compensate for the increased consumption of electrons. Pyrite is more noble than chalcopyrite; hence chalcopyrite leaches preferentially under oxidizing conditions. This leads to the acceleration of the rate of copper extraction. However, an insulating product layer of elemental sulfur forms on the surface of chalcopyrite as leaching proceeds. Formation of this non-conductive layer limits the electrical contact between pyrite and unleached chalcopyrite. In the presence of silver-enhanced pyrite, a very small proportion of the added silver to pyrite dissolves in the leaching solution and reacts with chalcopyrite particles to form silver sulfide. In this study, increases in the conductivity of the sulfur layer sufficient to allow the rapid transfer of electrons are observed, in spite of very low levels of silver in the sulfur product layer (60–100ppm). Hence, it is shown that in the presence of silver-enhanced pyrite, the resistivity of the sulfur layer is lowered, allowing the electrical contact between pyrite and chalcopyrite to be maintained.

The mechanism of chalcopyrite leaching in the presence of silver-enhanced pyrite in the Galvanox™ process

A dramatic improvement in the leaching kinetics of chalcopyrite in ferric sulfate media was observed upon the addition of silver-enhanced pyrite. In this process, pyrite samples are pretreated with a miniscule amount of silver and used as a catalyst in atmospheric leaching of chalcopyrite. The aim of this study was to understand the mechanism of this process and to reveal the role of silver and pyrite in accelerating the rate of chalcopyrite leaching. It is shown that this process, known as Galvanox™, is the galvanically assisted leaching of chalcopyrite, where pyrite provides an alternative surface for ferric reduction. As the leaching reaction proceeds, in the absence of silver-enhanced pyrite, a non-conductive sulfur layer forms on the surface of chalcopyrite. This layer prevents electrical contact between pyrite and chalcopyrite particles in the slurry. However, it is observed that, in the presence of silver-enhanced pyrite, a small proportion of the added silver to the pyrite dissolves and reacts with the elemental sulfur around chalcopyrite particles to form silver sulfide. In spite of the very low silver level in this layer, its conductivity increases significantly and allows the transfer of electrons from chalcopyrite to pyrite. In this study, it is shown that pyrite and silver have critical roles in enhancing the kinetics of chalcopyrite leaching. Pyrite provides an alternative surface area for ferric reduction. Silver increases the catalytic properties of pyrite and therefore, the rate of ferric reduction on the surface of silver-enhanced pyrite is faster than this rate on the surface of natural pyrite. Another role of silver is to decrease the resistivity of the sulfur product layer and to facilitate the electrical contact between pyrite and chalcopyrite.

Kinetics of chemical leaching of chalcopyrite from low grade copper ore: behavior of different size fractions

The kinetics of the chemical leaching of copper from low grade ore in ferric sulfate media was investigated using the constrained least square optimization technique. The experiments were carried out for different particle sizes in both the reactor and column at constant oxidation-reduction potential (Eh), pH values, and temperature. The main copper mineral was chalcopyrite. About 40% of Cu recovery is obtained after 7 d of reactor leaching at 85°C using −0.5 mm size fraction, while the same recovery is obtained at 75°C after 24 d. Also, about 23% of Cu recovery is obtained after 60 d of column leaching for +4-−8 mm size fraction whereas the Cu recovery is as low as about 15% for +8-−12.7 and +12.7-−25 mm size fractions. A 4-stage model for chalcopyrite dissolution was used to explain the observed dissolution behaviors. The results show that thick over-layers of sulphur components cause the parabolic behavior of chalcopyrite dissolution and the precipitation of Fe3+ plays the main role in chalcopyrite passivation. In the case of coarse particles, transformation from one stage to another takes a longer time, thus only two stages including the initial reaction on fresh surfaces and S0 deposition are observed.

A novel acidophilic, thermophilic iron and sulfur-oxidizing archaeon isolated from a hot spring of tengchong, yunnan, China.

A novel thermoacidophilic iron and sulfur-oxidizing archaeon, strain YN25, was isolated from an in situ enriched acid hot spring sample collected in Yunnan, China. Cells were irregular cocci, about 0.9–1.02 µm × 1.0–1.31 µm in the medium containing elemental sulfur and 1.5–2.22 µm × 1.8–2.54 µm in ferrous sulfate medium. The ranges of growth and pH were 50–85 (optimum 65) and pH 1.0–6.0 (optimum 1.5–2.5). The acidophile was able to grow heterotrophically on several organic substrates, including various monosaccharides, alcohols and amino acids, though the growth on single substrate required yeast extract as growth factor. Growth occurred under aerobic conditions or via anaerobic respiration using elemental sulfur as terminal electron acceptor. Results of morphology, physiology, fatty acid analysis and analysis based on 16S rRNA gene sequence indicated that the strain YN25 should be grouped in the species Acidianus manzaensis. Bioleaching experiments indicated that this strain had excellent leaching capacity, with a copper yielding ratio up to 79.16% in 24 d. The type strain YN25 was deposited in China Center for Type Culture Collection (=CCTCCZNDX0050).

Plasma induced graft polymerization of acrylic acid onto polypropylene monofilament

AbstractPlasma induced graft polymerization of acrylic acid onto polypropylene (PP) monofilament was carried to introduce carboxyl functionality on its surface. The monofilament was treated with oxygen plasma to create hydroperoxide groups and subsequent graft polymerization was initiated on this exposed monofilament. It was observed that in the absence of an added inhibitor, the grafting did not proceed because of the extensive homopolymerization which left behind hardly any monomer for the grafting reaction. The addition of ferrous sulfate to the grafting medium led to the homopolymer free grafting reaction. The addition of organics, such as methanol, butanone, and acetone led to complete inhibition of the homopolymerization at 60% content. However, the addition of butanone led to much lower degree of grafting than methanol and acetone. The contact angle of the monofilament showed drastic reduction by plasma treatment and by the subsequent grafting of acrylic acid. The grafting in ferrous sulfate medium showed higher contact angles as compared to the grafting in organic medium. The surface morphology was significantly influenced by the nature of the additive in the grafting medium. © 2007 Wiley Periodicals, Inc. JAppl Polym Sci, 2008

Characterization of New Iron Oxidizing Bacteria from an Acid Mine Water Treatment Plant

In the Lusatia area a pilot plant for the treatment of acidic mine waters by microbial iron oxidation and a concomitant iron hydroxysulfate precipitation is operated. Molecular based studies of acidic waters from this iron hydroxysulfate producing pilot plant revealed the presence of 16S rRNA gene sequences from undescribed iron-oxidizing bacteria. Most of these were related to autotrophic Betaproteobacteria (see Heinzel et al. IBS 2007, poster number 98). For cultivating different iron-oxidizing bacteria water samples from this pilot plant were directly plated on various solid media. Double-layer plates were used, with a heterotrophic Acidiphiliumstrain in the underlayer, because of the high sensitivity of autotrophic bacteria towards organic substances. The media contained different iron-substrates with and without organic carbon sources. Colonies appeared at the latest after three weeks and they were encrusted with ferric iron. The phylogeny of the isolated strains was determined and the physiological requirements, like temperature, pH optima, preferred carbon source and iron concentrations, were analyzed. Many isolates which were related to Acidithiobacillus ferrooxidans strains could be cultivated, as well as an isolate related to the genus Thiomonas and one isolate related to a Ferribacter polymyxa species. The Thiomonas-like isolate showed best growth in media containing tryptone soya broth, sodium thiosulfate and ferrous sulfate at pH 2.5 and 30°C. The other Betaproteobacterium grew on ferrous sulfate medium at pH 2.5 between 16 and 37°C. In liquid culture experiments the cells of both isolates were attached to the iron minerals built in the medium. These physiological characteristics of the isolates helped to vary parameters in the pilot plant to optimize the process of iron oxidation and improved waste water remediation.

The dissolution of sphalerite in ferric sulfate media

The dissolution of sphalerite, (Zn,Fe)S, in ferric sulfate media was investigated using closely sized fractions of crushed sphalerite crystals. Linear kinetics were observed, and the rate increased in proportion to the surface area, as the average particle size of the sphalerite decreased. The predominant reaction products are ZnSO4, FeSO4, and elemental sulfur. The leaching rate increases with increasing temperature, and the apparent activation energy is 44 kJ/mol. The relatively high apparent activation energy suggests that the rate is chemically controlled, a conclusion supported by the insensitivity of the rate of the rotation speed that was observed in complementary rotating disk experiments. The rate increases as the 0.3 to 0.4 power of the Fe(SO4)1.5 concentration, and is nearly independent of the pulp density, in the presence of a stoichiometric excess of ferric sulfate. In 0.3 M Fe(SO4)1.5 media, the rate increases with increasing acid concentrations >0.1 M H2SO4, but is insensitive to more dilute acid concentrations. In the absence of ferric ions, the rate increases rapidly with increasing H2SO4 concentrations, and relatively rapid rates are observed in solutions containing >0.5 M H2SO4. The rate decreases with increasing initial concentrations of ZnSO4, MgSO4, or FeSO4 in the ferric sulfate leaching solution, and this emphasizes the importance of maintaining the dissolved iron in a fully oxidized state in a commercial leaching operation.

Existence of an iron-oxidizing bacterium Acidithiobacillus ferrooxidans resistant to organomercurial compounds

Acidithiobacillus ferrooxidans MON-1 which is highly resistant to Hg2+ could grow in a ferrous sulfate medium (pH 2.5) with 0.1 microM p-chloromercuribenzoic acid (PCMB) with a lag time of 2 d. In contrast, A. ferrooxidans AP19-3 which is sensitive to Hg2+ did not grow in the medium. Nine strains of A. ferrooxidans, including seven strains of the American Type Culture Collection grew in the medium with a lag time ranging from 5 to 12 d. The resting cells of MON-1, which has NADPH-dependent mercuric reductase activity, could volatilize Hg0 when incubated in acidic water (pH 3.0) containing 0.1 microM PCMB. However, the resting cells of AP19-3, which has a similar level of NADPH-dependent mercuric reductase activity compared with MON-1, did not volatilize Hg0 from the reaction mixture with 0.1 microM PCMB. The activity level of the 11 strains of A. ferrooxidans to volatilize Hg0 from PCMB corresponded well with the level of growth inhibition by PCMB observed in the growth experiments. The resting cells of MON-1 volatilized Hg0 from phenylmercury acetate (PMA) and methylmercury chloride (MMC) as well as PCMB. The cytosol prepared from MON-1 could volatilize Hg0 from PCMB (0.015 nmol mg(-1) h(-1)), PMA (0.33 nmol mg(-1) h(-1)) and MMC (0.005 nmol mg(-1) h(-1)) in the presence of NADPH and beta-mercaptoethanol.

Monitoring of bacteria in acid mine environments by reverse sample genome probing

A variety of microorganisms can exist in acid mine drainage (AMD) environments, although their contribution to AMD problems is unclear. Environmental strains of Thiobacillus ferrooxidans and Thiobacillus acidophilus were purified by repeated plating and single-colony isolation on iron salts and tetrathionate media, respectively. Thiobacillus thiooxidans was enriched on sulfur-containing media. For the isolation of Leptospirillum ferrooxidans, iron salts and pyrite media were inoculated with environmental samples. However, L. ferrooxidans was never recovered on solid media. Denatured chromosomal DNAs from type and (or) isolated strains of T. ferrooxidans, T. acidophilus, T. thiooxidans, and L. ferrooxidans were spotted on a master filter for their detection in a variety of samples by reverse sample genome probing (RSGP). Analysis of enrichments of environmental samples by RSGP indicated that ferrous sulfate medium enriched T. ferrooxidans strains, whereas all thiobacilli grew in sulfur medium, T. thiooxidans strains being dominant. Enrichment in glucose medium followed by transfer to tetrathionate medium resulted in the selection of T. acidophilus strains. DNA was also extracted directly (without enrichment) from cells recovered from AMD water or sediments, and was analyzed by RSGP to describe the communities present. Strains showing homology with T. ferrooxidans and T. acidophilus were found to be major community components. Strains showing homology with T. thiooxidans were a minor community component, whereas strains showing homology with L. ferrooxidans were not detected.

Factorial experiments for selective leaching of zinc sulphide in ferric sulphate media

The zinc-recovery results obtained in leaching tests run on a complex sulphide ore of Caribbean origin have been statistically processed. The raw material contained 6.95% Zn, 2.41% Pb and traces (0.05%) of Cu. The study was conducted by means of consecutive factorial plans which permitted determination of the manner in which the leaching was influenced by the following factors: (1) oxidizing agent (Fe 2(SO 4) 3) concentration; (2) temperature; (3) ore particle size characteristics; and (4) solid/liquid ratio. A regression equation was calculated by the results obtained from the tests; this permitted the derivation of a response surface which provides zinc recovery levels in relation to the levels of the factors adopted in the experiments. It is important to understand the parameters which exert most influence on zinc recoveries during leaching, especially when the presence of finely distributed polluting agents in the useful phase, pyrite in this case, prevents zinc enrichment by the usual physical means.

The leaching of galena in ferric sulfate media

The leaching of galena (PbS) in ferric sulfate media was investigated over the temperature range 55 °C to 95 °C and for various Fe(SO4)1.5, H2SO4, FeSO4, and MgSO4 concentrations. Relatively slow kinetics were consistently observed; in most instances, the 1-2/3α-(1−α)2/3 vs time relationship, indicative of a diffusion-controlled reaction, was closely obeyed. The diffusion-controlled kinetics were attributed to the formation of a tenacious layer of PbSO4 and S0 on the surface of the galena. The generation and morphology of the reaction products were systematically determined by scanning electron microscopy, and complex growth mechanisms were illustrated. The leaching rate increased rapidly with increasing temperature, and the apparent activation energy is 61.2 kJ/mol. The rate increases as the 0.5 power of the ferric ion concentration but is nearly independent of the concentration of the FeSO4 reaction product. The rate is insensitive to H2SO4 concentrations <0.1 M but increases at higher acid levels. The presence of neutral sulfates, such as MgSO4, decreases the leaching rate to a modest extent.

Physiological diversity amongst some moderately thermophilic iron-oxidising bacteria

Three strains of moderately thermophilic and acidophilic bacteria capable of oxidising ferrous iron, isolated from different sources, were compared with each other and with an earlier isolate, TH1. The isolates displayed different rates of carbon dioxide fixation and incorporation of glucose and glycine; only one could be subcultured continuously in organic-free ferrous sulfate medium. Two of the isolates readily oxidised elemental sulfur, and all were capable of solubilising pyrite and chalcopyrite, though at different rates; there was no correlation between rates of ferrous iron and pyrite oxidation. Reduction of ferric iron by two of the isolates was observed in unshaken cultures containing 10 mM glucose. The DNA base composition of the isolates varied from 43–68 mol% G + C.

Occurence, identification and possible significance of ornithine lipid in Thiobacillus ferrooxidans

An ornithine containing aminolipid has been found in Thiobacillus ferrooxidans grown in ferrous sulfate medium, which was purified and estimated at four main phases of growth. GLC analysis of ornithine lipid has revealed the existence of mainly C 18:1 and C 22:1 fatty acids. The infrared spectra showed the existence of both amide and ester linkages in the aminolipid. The major ester linked fatty acid was C 22:1. The interaction of ornithine lipid with membrane was investigated by delipidation of the membrane particles, which resulted in the perturbation of the activities of the three enzymes of iron oxidation system. The activities could be restored to the lipid depleted particles by preincubation with a dispersion of purified ornithine lipid together with coenzyme Q 8. The kinetic parameters of the enzyme activities were also affected by delipidation which was significantly altered in the reconstituted particles by this lipid, thus indicating a possible role of ornithine lipid in iron oxidation system.

Enhancement of growth and ferrous iron oxidation rates of T. Ferrooxidans by electrochemical reduction of ferric iron

Thiobacillus ferrooxidans, the bacterium most widely used; in bioleaching or microbial desulfurization studies, was grown in an electrolytic bioreactor containing a synthetic, ferrous sulfate medium. Passage of current through the medium reduced the bacterially generated ferric iron to the ferrous iron substrate. When used in conjunction with an inoculum that had been adapted to the electrolytic growth conditions, this technique increased the protein (cell) concentration by 3.7 times, increased the protein (cell) production rate by 6.5 times, increased the yield coefficient (cellular efficiency) by 8.0 times, and increased the ferrous iron oxidation rate by 1.5 times at 29 degrees C, compared with conventional cultivation techniques. A Monod-type equation with accepted values for the maximum specific growth rate could not account for the increased growth rate under electrolytic conditions.