Temperature Effects on Bacterial Leaching of Sulfide Minerals in Shake Flask Experiments

The microbiological leaching of a sulfide ore sample was investigated in shake flask experiments. The ore sample contained pyrite, pyrrhotite, pentlandite, sphalerite, and chalcopyrite as the main sulfide minerals. The tests were performed at eight different temperatures in the range of 4 to 37°C. The primary data were used for rate constant calculations, based on kinetic equations underlying two simplified models of leaching, i.e., a shrinking particle model and a shrinking core model. The rate constants thus derived were further used for the calculation of activation energy values for some of the sulfide minerals present in the ore sample. The chalcopyrite leaching rates were strongly influenced by the interaction of temperature, pH, and redox potential. Sphalerite leaching could be explained with the shrinking particle model. The data on pyrrhotite leaching displayed good fit with the shrinking core model. Pyrite leaching was found to agree with the shrinking particle model. Activation energies calculated from the rate of constants suggested that the rate-limiting steps were different for the sulfide minerals examined; they could be attributed to a chemical or biochemical reaction rather than to diffusion control.     

Mineral and iron oxidation at low temperatures by pure and mixed cultures of acidophilic microorganisms

An enrichment culture from a boreal sulfide mine environment containing a low-grade polymetallic ore was tested in column bioreactors for simulation of low temperature heap leaching. PCR-denaturing gradient gel electrophoresis and 16S rRNA gene sequencing revealed the enrichment culture contained an Acidithiobacillus ferrooxidans strain with high 16S rRNA gene similarity to the psychrotolerant strain SS3 and a mesophilic Leptospirillum ferrooxidans strain. As the mixed culture contained a strain that was within a clade with SS3, we used the SS3 pure culture to compare leaching rates with the At. ferrooxidans type strain in stirred tank reactors for mineral sulfide dissolution at various temperatures. The psychrotolerant strain SS3 catalyzed pyrite, pyrite/arsenopyrite, and chalcopyrite concentrate leaching. The rates were lower at 5 degrees C than at 30 degrees C, despite that all the available iron was in the oxidized form in the presence of At. ferrooxidans SS3. This suggests that although efficient At. ferrooxidans SS3 mediated biological oxidation of ferrous iron occurred, chemical oxidation of the sulfide minerals by ferric iron was rate limiting. In the column reactors, the leaching rates were much less affected by low temperatures than in the stirred tank reactors. A factor for the relatively high rates of mineral oxidation at 7 degrees C is that ferric iron remained in the soluble phase whereas, at 21 degrees C the ferric iron precipitated. Temperature gradient analysis of ferrous iron oxidation by this enrichment culture demonstrated two temperature optima for ferrous iron oxidation and that the mixed culture was capable of ferrous iron oxidation at 5 degrees C.     

Effect of Activated Carbon Addition on the Conventional and Electrochemical Bioleaching of Chalcopyrite Concentrates

The effect of activated carbon addition on the rate and efficiency of copper mobilization from Sarcheshmeh chalcopyrite concentrate was studied in the presence and absence of a mixed culture of moderately thermophilic microorganisms. Conventional leaching at a 10% (w/v) pulp density in 500-ml Erlenmeyer flasks on a rotary shaker at 150 rpm, and electrochemical bioleaching in a stirred bioreactor at an ORP (oxidation-reduction potential) range of 400 to 430 mV measured against a Ag/AgCl reference electrode. The bioreactor contained ore concentrate at a pulp density of 20%, which was stirred at 600 rpm. All experiments were conducted in the presence and absence of 3 g/L activated carbon, at initial pH 1.5, temperature 50°C, in Norris's nutrient medium with an addition of 0.02% (w/v) yeast extract. The results showed that the addition of activated carbon increased the rate and yield of copper extraction from the concentrate especially in the presence of bacteria. Final recovery after 20 days was 52% and 44% in the shake flask experiments with and without carbon addition, respectively. Enhanced rates of copper mobilization were achieved in the electrochemical bioleaching experiments in which copper was leached selectively relative to iron. Final copper recovery after 10 days was 85% and 77% in the presence and absence of activated carbon, respectively. The positive effect of activated carbon on copper extraction could be related to the galvanic interaction between the inert carbon as cathode and chalcopyrite as anode. The bacterial elimination of sulfur produced on the sulfide minerals during chemical leaching is assumed to intensify the galvanic interaction. It seems that maintaining the ORP at a low potential and efficient mixing improves the bacterial and chemical subsystems in the electro-bioreactor that accelerates the rate of copper mobilization from the concentrate.     

Modeling continuous bioleach reactors

The results of recent research have shown that the bioleaching of sulfide minerals occurs via a two‐step mechanism. In this mechanism, the sulfide mineral is chemically oxidized by the ferric‐iron in the bioleaching liquor. The ferrous‐iron produced is subsequently oxidized to ferric‐iron by the microorganism. Further research has shown that the rates of both the ferric leaching and ferrous‐iron oxidation are governed by the ferric/ferrous‐iron ratio (i.e., the redox potential). During the steady‐state operation of a bioleach reactor, the rate of iron turnover between the chemical ferric leaching of the mineral and the bacterial oxidation of the ferrous‐iron will define the rate and the redox potential at which the system will operate. The balance between the two rates will in turn depend on the species used, the microbial concentration, the residence time employed, the nature of the sulfide mineral being leached, and its active surface area. The model described proposes that the residence time and microbial species present determine the microbial growth rate, which in turn determines the redox potential in the bioleach liquor. The redox potential of the solution, in turn, determines the degree of leaching of the mineral; that is, conversion in the bioleach reactor. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 64: 671–677, 1999.     

Bioleaching of sulfidic tailing samples with a novel, vacuum-positive pressure driven bioreactor

This study presents a design for a novel bioreactor that uses alternating vacuum and positive pressure cycles to transfer acidic leach solution in and out of contact with finely ground sulfidic mine tailings. These tailings constitute an environmental problem that needs experimental data to support the development of management and control strategies. A conventional stirred tank bioreactor was used as a reference system. Both bioreactors were inoculated with mixed cultures of acidophilic iron and sulfur oxidizers. The rate of the bioleaching of tailings was 0.50 +/- 0.14 g Fe/L . day in the stirred tank bioreactor and 0.17 +/- 0.05 g Fe/L . day in the novel bioreactor. Microbial populations were identified in the two-bioreactor systems by analysis of 16S rRNA genes involving amplification, denaturing gradient gel electrophoresis (DGGE), cloning, and sequencing. The inoculum contained sulfur-oxidizing Acidithiobacillus caldus and Acidithiobacillus thiooxidans, iron oxidizers from the genera Leptospirillum and Ferroplasma, and a chemoorganotrophic Alicyclobacillus sp. During bioleaching of the tailings, the microbial populations in both bioreactors were similar to the inoculum culture, except that At. thiooxidans outgrew At. caldus. Sequences consistent with a Sulfobacillus sp. were amplified from both bioreactor samples although this bacterium was initially below the level of detection in the inoculum. After prolonged operation, Ferroplasma acidiphilum and an uncultured bacterium related to the CFB group were also detected in the novel bioreactor, whereas Sulfobacillus sp. was no longer detected. The novel bioreactor has potential uses in other areas of environmental biotechnology that involves periodic contact of liquids with solid substrates.     

固定化Acidithiobacillus ferrooxidans对Fe2+氧化及其生物反应器研究进展

Acidithiobacillus ferrooxidans 对Fe2+的生物氧化是一个非常重要的反应过程, 在生物浸矿、H2S等废气的脱硫、含重金属污泥和酸性矿坑废水的处理等领域有着重要的应用。近些年来,大量的研究主要集中A. ferrooxidans及其反应过程等方面,然而,A. ferrooxidans对Fe2+的催化氧化速率缓慢和稳定性欠佳等问题仍然限制了其商业应用。因此,对A. ferrooxidans的固定化及其生物反应器研究是该技术进一步发展的关键。本文评述了A. ferrooxidans最新应用、存在的问题和解决办法,重点比较了目前文献中报道的各种A. ferrooxidans固定材料、方法,并对目前采用的各种固定化A. ferrooxidans生物反应系统的效率和结构等方面进行了讨论和分析。     

Effects of L-cysteine on Ni-Cu sulfide and marmatite bioleaching by Acidithiobacillus caldus

The effect of L-cysteine in different concentrations on the bioleaching of Ni-Cu sulfide and marmatite were studied with a moderately thermophilic, sulfur-oxidizing bacterium, strain of Acidithiobacillus caldus. X-ray diffraction (XRD) observations showed the change of bioleached solid residues and the effect of L-cysteine on the surface charges of minerals. It was found that adding certain amounts of L-cysteine to the leaching system of Ni-Cu sulfide largely enhanced the leaching rate, while L-cysteine inhibited the bioleaching of marmatite by A. caldus. The mechanism of L-cysteine interaction with mineral surfaces was studied by means of zeta potential determination and IR spectra.     

Microbiological and geochemical dynamics in simulated-heap leaching of a polymetallic sulfide ore

The evolution of microbial populations involved in simulated-heap leaching of a polymetallic black schist sulfide ore (from the recently-commissioned Talvivaara mine, Finland) was monitored in aerated packed bed column reactors over a period of 40 weeks. The influence of ore particle size (2-6.5 mm and 6.5-12 mm) on changes in composition of the bioleaching microflora and mineral leaching dynamics in columns was investigated and compared to fine-grain (<2 microm) ore that was bioprocessed in shake flask cultures. Both column reactors and shake flasks were inoculated with 24 different species and strains of mineral-oxidizing and other acidophilic micro-organisms, and maintained at 37 degrees C. Mineral oxidation was most rapid in shake flask cultures, with about 80% of both manganese and nickel and 68% of zinc being leached within 6 weeks, though relatively little of the copper present in the ore was solubilised. The microbial consortium that emerged from the original inoculum was relatively simple in shake flasks, and was dominated by the iron-oxidizing autotroph Leptospirillum ferriphilum, with smaller numbers of Acidimicrobium ferrooxidans, Acidithiobacillus caldus and Leptospirillum ferrooxidans. Both metal recovery and (for the most part) total numbers of prokaryotes were greater in the column reactor containing the medium-grain than that containing the coarse-grain ore. The bioleaching communities in the columns displayed temporal changes in composition and differed radically from those in shake flask cultures. While iron-oxidizing chemoautotrophic bacteria were always the most numerically dominant bacteria in the medium-grain column bioreactor, there were major shifts in the most abundant species present, with the type strain of Acidithiobacillus ferrooxidans dominating in the early phase of the experiment and other bacteria (At. ferrooxidans NO37 and L. ferriphilum) dominating from week 4 to week 40. With the coarse-grain column bioreactor, similar transitions in populations of iron-oxidizing chemoautotrophs were observed, though heterotrophic acidophiles were often the most abundant bacteria found in mineral leach liquors. Four bacteria not included in the mixed culture used to inoculate the columns were detected by biomolecular techniques and three of these (all Alicyclobacillus-like Firmicutes) were isolated as pure cultures. The fourth bacterium, identified from a clone library, was related to the Gram-positive sulfate reducer Desulfotomaculum salinum. All four were considered to have been present as endospores on the dried ore, which was not sterilized in the column bioreactors. Two of the Alicyclobacillus-like isolates were found, transiently, in large numbers in mineral leachates. The data support the hypothesis that temporal and spatial heterogeneity in mineral heaps create conditions that favour different mineral-oxidizing microflora, and that it is therefore important that sufficient microbial diversity is present in heaps to optimize metal extraction.     

嗜酸氧化亚铁硫杆菌的高效培养及浸出黄铜矿初探

采用向硫化矿培养基中补加FeSO4的方式以维持Fe2+ 浓度为4～8 g/L,可使嗜酸氧化亚铁硫杆菌菌浓在培养39 h时达到6.25×108 cells/mL,并在比生长速率几乎不降低的前提下提高了转化率和生产强度.然后对低氧化还原电位下低品位黄铜矿的浸出进行初步研究,结果表明经过30 d浸出,铜的浸出率可达28.5%...     

Bioleaching of zinc sulfide concentrate by Thiobacillus ferrooxidans

The kinetics of the bioleaching of ZnS concentrate by Thiobacillus ferrooxidans was studied in a well-mixed batch reactor. Experimental studies were made at 30 degrees C and pH 2.2 on adsorption of the bacteria to the mineral, ferric iron leaching, and bacterial leaching. The adsorption rate of the bacteria was fairly rapid in comparison with the bioleaching rate, indicating that the bacterial adsorption is at equilibrium during the leaching process. The adsorption equilibrium data were correlated by the Langmuir isotherm, which is a useful means for predicting the number of bacteria adsorbed on the mineral surface. The rate of chemical leaching varied with the concentration of ferric iron, and the first-order reaction rate constant was determined. Bioleaching in an iron-containing medium was found to take place by both direct bacterial attack on the sulfide mineral and indirect attack via ferric iron. In this case, the ferric iron was formed from the reaction product (ferrous iron) through the biological oxidation reaction. To develop rate expressions for the kinetics of bacterial growth and zinc leaching, the two bacterial actions were considered. The key parameters appearing in the rate equations, the growth yield and specific growth rate of adsorbed bacteria, were evaluated by curve fitting using the experimental data. This kinetic model allowed us to predict the liquid-phase concentrations of the leached zinc and free cells during the batch bioleaching process.     

三种浸矿细菌协同作用的回顾及展望

生物浸矿技术相比于传统的矿物加工技术具有成本低、易操作和污染小的特点,可以用来处理金精矿、低品位金矿、难处理金矿或者是高硫煤炭。为了更好地利用多种浸矿细菌的协同作用,本文综合阐述了生物浸矿的协同作用优势和存在的一些问题,对今后协同浸矿的发展做了预测。本文首先分析了3种主要浸矿细菌,包括氧化亚铁硫杆菌、氧化亚铁钩端螺旋菌和氧化硫硫杆菌等各自的生物学特性,接着重点分析了国内外近些年来浸矿细菌的协同作用研究进展情况和作用机制,最后展望了未来二十年内浸矿技术研究的发展方向。     

Cultural and phylogenetic analysis of mixed microbial populations found in natural and commercial bioleaching environments.

A range of autotrophic and heterotrophic enrichment cultures were established to determine the cultural bacterial diversity present in samples obtained from the acidic runoff of a chalcocite overburden heap and from laboratory-scale (1- to 4-liter) batch and continuous bioreactors which were being used for the commercial assessment of the bioleachability of zinc sulfide ore concentrates. Strains identified as Thiobacillus ferrooxidans, Thiobacillus thiooxidans, "Leptospirillum ferrooxidans," and Acidiphilium cryptum were isolated from both the natural site and the batch bioreactor, but only "L. ferrooxidans," a moderately thermophilic strain of T. thiooxidans, and a moderately thermophilic iron-oxidizing bacterium could be recovered from the continuous bioreactor running under steady-state conditions. Sequence analysis of the 16S rRNA genes of 33 representative strains revealed that all of the strains were closely related to strains which have been sequenced previously and also confirmed the phylogenetic diversity of bacteria present in bioleaching environments.     

Effect of applied potentials on the activity and growth of Thiobacillus ferrooxidans

The effect of applied DC potentials both in the positive and negative range, on the activity and growth of Thiobacillus ferrooxidans, is discussed. In general, application of positive potentials up to +1000 mV in an acid bioleaching medium was found to be detrimental to bacterial activity, while the impression of negative potentials enhanced both their activity and growth through electrochemical regeneration of ferrous ions and an increase in the biomass. Ferrous-ferric ratios in a bioleaching medium could be monitored through Eh measurements.Among the base sulfide minerals such as pyrite, chalcopyrite, and sphalerite, sphalerite could be selectively bioleached if an impressed potential of -500 mV (SCE) could be maintained in the leaching medium. Electrochemical bioleaching tests carried out under an applied potential of -500 mV with sphalerite in the presence and absence of noble minerals such as pyrite and chalcopyrite indicated enhanced zinc dissolution with negligible copper and iron in solution. Probable mechanisms and advantages of the electrochemical bioleaching process developed in the laboratory are outlined.     

Bacterial Oxidation of Sulfide Minerals in Column Leaching Experiments at Suboptimal Temperatures

The purpose of the work was to quantitatively characterize temperature effects on the bacterial leaching of sulfide ore material containing several sulfide minerals. The leaching was tested at eight different temperatures in the range of 4 to 37°C. The experimental technique was based on column leaching of a coarsely ground (particle diameter, 0.59 to 5 mm) ore sample. The experimental data were used for kinetic analysis of chalcopyrite, sphalerite, and pyrrhotite oxidation. Chalcopyrite yielded the highest (73 kJ/mol) and pyrrhotite yielded the lowest (25 kJ/mol) activation energies. Especially with pyrrhotite, diffusion contributed to rate limitation. Arrhenius plots were also linear for the reciprocals of lag periods and for increases of redox potentials (dmV/dt). Mass balance analysis based on total S in leach residue was in agreement with the highest rate of leaching at 37 and 28°C. The presence of elemental S in leach residues was attributed to pyrrhotite oxidation.     

Bacterial Oxidation of Refractory Sulfide Ores for Gold Recovery

Abstract

The microbiological leaching of refractory sulfide ores (pyrite, arsenopyrite) for recovery of gold is reviewed in this article. The underlying physiological, biochemical, and genetic fundamentals of the bacteria involved (Thiobacillus and Sulfolobus spp.) are complex and have yet to be elucidated in depth. The chemistry of acid and biological leaching of pyrite and arsenopyrite minerals is also complex, and many of the individual reactions are not known in detail. Bacterial leaching is discussed in relation to chemical speciation at acid pH values. Attempts to develop models for a better understanding of bioleaching processes are summarized. The importance of pH, redox potential, temperature, sulfur balance, and toxic metals is evaluated for optimizing conditions for bacterial activity. Gold is finely disseminated in refractory sulfide ores, thereby decreasing Au recoveries upon conventional cyanidation for gold dissolution. In the bioleaching process, bacteria remove the sulfide minerals by oxidative dissolution and thus expose Au to extraction with cyanide solution. Stirred tank reactors appear most suited for this biological leaching process. The overall oxidation of the sulfides is an important variable for gold recovery. Pilot- and commercial-scale bioleaching processes for gold-containing pyrite and arsenopyrite ores are reviewed. This application of mineral biotechnology competes favorably with pressure leaching and roasting processes, both of which are problematic and energy-intensive alternatives for pretreatment of auriferous pyrite/arsenopyrite ores.     

Hydrodynamic and mass transfer characteristics of three-phase gaslift bioreactor systems.

This review focuses on the hydrodynamic and mass transfer characteristics of various three-phase, gaslift fluidized bioreactors. The factors affecting the mixing and volumetric mass transfer coefficient (k(L)a), such as liquid properties, solid particle properties, liquid circulation velocity, superficial gas velocity, bioreactor geometry, are reviewed and discussed. Measurement methods, modeling and empirical correlations are reviewed and compared. To the authors' knowledge, there is no 'generalized' correlation to calculate the volumetric mass transfer coefficient, instead, only 'type-specific' correlations are available in the literature. This is due to the difficulty in modeling the gaslift bioreactor, caused by the variation in geometry, fluid dynamics, and phase interactions. The most important design parameters reported in the literature are: gas hold-up, liquid circulation velocity, 'true' superficial gas velocity, mixing, shear rate, aeration rate and volumetric mass transfer coefficient, k(L)a.     

Progress in bioleaching: part B: applications of microbial processes by the minerals industries

This review presents developments and applications in bioleaching and mineral biooxidation since publication of a previous mini review in 2003 (Olson et al. Appl Microbiol Biotechnol 63:249–257, 2003). There have been discoveries of newly identified acidophilic microorganisms that have unique characteristics for effective bioleaching of sulfidic ores and concentrates. Progress has been made in understanding and developing bioleaching of copper from primary copper sulfide minerals, chalcopyrite, covellite, and enargite. These developments point to low oxidation–reduction potential in concert with thermophilic bacteria and archaea as a potential key to the leaching of these minerals. On the commercial front, heap bioleaching of nickel has been commissioned, and the mineral biooxidation pretreatment of sulfidic-refractory gold concentrates is increasingly used on a global scale to enhance precious metal recovery. New and larger stirred-tank reactors have been constructed since the 2003 review article. One biooxidation–heap process for pretreatment of sulfidic-refractory gold ores was also commercialized. A novel reductive approach to bioleaching nickel laterite minerals has been proposed.     

微生物接种密度和矿物收集时间对生物沥浸中次生铁矿物形成的影响

在嗜酸性氧化亚铁硫杆菌Acidithiobacillus ferrooxidans作用下, 污泥生物沥浸体系中常会有次生铁矿物形成, 这些矿物对污泥脱水和重金属溶出有重要影响。在FeSO4-K2SO4-H2O生物成矾临界点模拟生物沥浸过程, 考察了Acidithiobacillus ferrooxidans菌接种密度和矿物收集时间对次生铁矿物的影响。结果表明, 微生物接种密度和矿物收集时间对生物沥浸过程中次生铁矿物的重量及其类型均有一定影响, 随矿物收集时间的推迟, 溶液中含有的一价阳离子(如K+等)可导致施氏矿物向黄铁矾发生转变, 并成为影响铁矿物类型的主导因素。     

Thermoacidophilic microbial community oxidizing the gold-bearing flotation concentrate of a pyrite-arsenopyrite ore

An aboriginal community of thermophilic acidophilic chemolithotrophic microorganisms (ACM) was isolated from a sample of pyrite gold-bearing flotation concentrate at 45–47°C and pH 1.8–2.0. Compared to an experimental thermoacidophilic microbial consortium formed in the course of cultivation in parallel bioreactors, it had lower rates of iron leaching and oxidation, while its rate of sulfur oxidation was higher. A new thermophilic acidophilic microbial community was obtained by mutual enrichment with the microorganisms from the experimental and aboriginal communities during the oxidation of sulfide ore flotation concentrate at 47°C. The dominant bacteria of this new ACM community were Acidithiobacillus caldus (the most active sulfur oxidize) and Sulfobacillus thermotolerans (active oxidizer of both iron and sulfur), while iron-oxidizing archaea of the family Ferroplasmaceae and heterotrophic bacteria Alicyclobacillus tolerans were the minor components. The new ACM community showed promise for leaching/oxidation of sulfides from flotation concentrate at high pulp density (S : L = 1 : 4).     

Scale-up impacts on mass transfer and bioremediation of suspended naphthalene particles in bead mill bioreactors

Scale-up effects on mass transfer and bioremediation of suspended naphthalene particles have been studied in 20 and 58L bead mill bioreactors and compared to data generated earlier with a laboratory scaled bioreactor. The bead mill bioreactor performance with respect to naphthalene mass transfer rate was dependent on the size and loading of the inert particles, as well as the rotational speed of the roller apparatus. The optimum operating conditions were found to be 15mm glass beads at a loading of 50% (total volume of particles/working volume of bioreactor: v/v%) and a bioreactor rotational speed of 50rpm. The highest naphthalene mass transfer coefficients obtained in the large scale system under these optimum conditions (19.6 and 22.4h(-1) for 20 and 58L vessels, respectively) were higher than those determined previously in a 2.5L bead mill bioreactor (0.7h(-1)). The acute toxicity tests indicated that the bioreactor effluent was less toxic than the untreated naphthalene suspension. Biodegradation rates obtained in these large scale bead mill bioreactors under optimum conditions (36-37.4mgL(-1)h(-1)) were higher than those achieved in the control bioreactors of similar sizes (11.4 and 11.6mgL(-1)h(-1)) but were slower than those previously determined in a 2.5L bead mill bioreactor (59-61.5mgL(-1)h(-1)). The limitation of oxygen in the large scale systems and damage of the bacterial cells due to the crushing effects of the large beads are likely contributing factors in the lower observed biodegradation rates. The optimum conditions with respect to naphthalene mass transfer might not necessarily translate to optimum performance with regard to bioremediation.