Bioleaching and bioprecipitation of nickel and iron from laterites

Abstract: Leaching of silicate ores, particularly nickel laterites, with the aid of heterotrophic organisms has been briefly reviewed. Samples of laterite ores from Greece were characterised mineralogically and a number of microorganisms isolated from them. One of these organisms (code FI) was successfully acclimatized to 6400 ppm nickel. Samples of the high-grade Greek Kastoria nickel laterite were leached with sulphuric acid and a number of organic acids. Sulphuric and citric acids extracted over 60 and 40% of the contained nickel, respectively, but the other acids employed were less efficient leachants. Oxalic acid precipitated nickel oxalate. Roughly the same extraction of iron was observed. The main leaching parameter was confirmed to be hydrogen ion concentration, although complexation with organic anions was a contributor. Organism FI (a strain of Penicillium ) was used in comparison with organisms from various culture collections to bioleach nickel from samples of the low-grade Greek Litharakia nickel laterite. The organisms were cultivated in a mixture of a sugar-based nutrient mineral medium and finely ground ore. Several penicillia and aspergilli leached 55–60% of the contained nickel and cobalt, and 25–35% of the iron when sucrose was the carbon source, but FI was not efficient. However, in molasses medium, Fl extracted nearly 40% of the nickel. Biosorption and bioprecipitation reactions were observed. The mechanism of bioleaching or in situ leaching is discussed in terms of close physical and chemical association between the fungal hyphae and mineral phases in the ore. This accounted for the low overall hydrogen ion concentration observed during bioleaching.     

Bioleaching of nickel from equilibrium fluid catalytic cracking catalysts

Summary This study investigates the possibility of reusing metal-contaminated equilibrium fluid catalytic cracking (FCC) catalyst after bioleaching. Leaching with Aspergillus niger culture was found to be more effective in the mobilization of nickel from the catalyst particles compared to chemical leaching with citric acid. Bioleaching achieved 32% nickel removal whereas chemical leaching achieved only 21% nickel removal from catalyst particles. The enhanced nickel removal from the catalysts in the presence of A. niger culture was attributed to the biosorption ability of the fungal mycelium and to the higher local concentration of citric acid on the catalyst surface. It was found that 9% of solubilized nickel in the liquid medium was biosorbed to fungal biomass. After nickel leaching with A. niger culture, the hydrogen-to-methane molar ratio and coke yield, which are the measures of dehydrogenation reactions catalysed by nickel during cracking reactions, decreased significantly.     

Leaching of copper converter slag withAspergillus niger culture filtrate

Leaching of copper converter slag of M/s Hindustan Copper Ltd, Ghatshila (Bihar, India) was carried out usingAspergillus niger culture filtrate. The effects of the duration of leaching, temperature, pulp density and the addition of hydrochloric acid were studied.A. niger culture filtrate solubilized metals from the converter slag at levels of 18.70% copper, 7.40% nickel and 4.00% cobalt. Addition of hydrochloric acid was found to improve copper, nickel and cobalt solubilization to 46.52, 27.90 and 37.96%, respectively. HPLC analysis of the fungal culture filtrate revealed the presence of succinic and citric acids. Therefore, leaching of the slag was also carried out with matching concentrations of these organic acids individually as well as with both mixed together. Results are discussed.     

Mineral leaching of non-sulphide nickel ores using heterotrophic micro-organisms

Laboratory studies were conducted on microbial leaching of non-sulphide nickel ores not amenable to conventional mineral processing operations. The results showed that extensive low-grade laterite domestic sources are generally amenable to bioleaching when micro-organisms were cultivated in the presence of the ore. Nickel recoveries were as high as 60% using hydroxycarboxylic acid producing strains of Aspergillus and Penicillium codes A3, P2. Cobalt recovery achieved was around 50%. Losses of soluble nickel in the fungal biomass were found to be 3.5–10.8%. Chemical analysis of the leach liquors showed the presence of significant amounts of citric, oxalic and other organic acids, indicating that leaching may be ascribed to the production of these metabolic products of fungal activity.     

Chemical and microbiological solubilization of silicates

The solubilization of silicates was investigated using kaolin and quartz sand as model substances. The mineral solubilization was studied in the concentration of solubilized Si and Al. The chemical leaching of the silicates was carried out using inorganic and organic acids as well as sodium hydroxide. The process was more effective in the alkine than in the acid pH range. In the acid medium, oxalic acid showed maximum acidity and a tendency to form complex structures, especially with aluminium, and was most effective in leaching. The microbiological influence on solubilization reactions was tested using a number of microorganisms among them acid, alkali and slime-forming species. The highest leaching activity was observed in the case of Thiobacillus thiooxidans, whereas the heterotrophic microorganisms (among them Bacillus mucilaginosus) did not exercise a sollubilizing effect on the silicates. X-ray phase analysis of leached kaolin samples did not show any differences from the non-leached mineral.     

Study on reaction mechanism of bioleaching of nickel and cobalt from lateritic chromite overburdens

Depletion of high-grade ores and presence of significant quantities of metals in low-grade oxide ores has enforced to utilize the overburdens (COB) and wastes (low-grade ores) generated during mining operations. The impact of ore mineralogy and mineral–microbe interaction during bioleaching could not be ignored. Seeking to the need, a systematic study was performed to establish the reaction mechanism involved for recovery of nickel and cobalt from chromite overburden (COB), Sukinda, Orissa using pure culture of Aspergillus niger. Mineralogical analysis reveals a complete conversion of goethite into hematite phase leading to exposure of nickel particles into the micro-pores and cracks developed in the matrix which was initially found to be intertwined in the goethite lattice. As a result, it became more susceptible to attack by the fungal bio acids which in turn accelerate the dissolution rate. Organic acids like oxalic and citric acids were detected in the culture filtrate using HPLC. TEM analysis of the leached samples shows that nickel dissolute into the solution leaving a porous space in the matrix of the hematite by forming nickel oxalate or nickel citrate. Kinetics of the nickel bioleaching was studied to support the mechanism of the reaction. It was observed that the initial rate of reaction follows the chemical control dissolution reaction where as the later part fits to shrinking core model. 18% of nickel and 37.8% of cobalt was recovered from pre-treated COB at 2.5% pulp-density with 10% (v/v) fungal inoculum at 30 °C within 25 days in shake flask while 32.5% of nickel and 86% of cobalt was recovered in bioreactor.     

Leaching of zinc from an industrial filter dust withPenicillium,Pseudomonas andCorynebacterium: Citric acid is the leaching agent rather than amino acids

Summary Heterotrophic microorganisms are able to solubilize metals via excreted metabolites-most often di- or tricarboxylic acids but also amino acids. With amino acids Cu, Zn, Au, Ni, U, Hg and Sb have been solubilized from metal oxides, metal sulfides or elementary metals. In this work it was investigated if excreted amino acids play a role in the leaching of zinc from a zinc oxide containing industrial filter dust. Two bacteria-Pseudomonas putida andCorynebacterium glutamicum-and a fungus-Penicillium simplicissimum were used.P. putida andP. Simplicissimum have already been used to solubilize zinc oxide, whereasC. glutamicum was used because of its known ability to excrete amino acids. Amino acids in culture fluids were analyzed via derivatization with phenyl isothiocyanate, separation on a RP-18 column and UV-detection. All three microorganisms solubilized zinc from the filter dust and excreted much more citric acid than amino acids. Thus citric acid rather than amino acids was regarded to be the leaching agent. Of the two bacteriaP. putida was more resistant towards the heavy metalcontaining filter dust.     

Use of heterotrophic microorganisms in mineral biotechnology

A process for biological removal of iron from quartz sands, kaolins and clays was developed in which these industrial minerals were leached at 90°C with lixiviant produced as a result of the cultivation of acid-producing heterotrophic microorganisms, mainly strains of Aspergillus niger, at 30°C in a nutrient medium containing molasses as a source of carbon and energy. The lixiviant, i.e. the fermentation fluid, contained oxalic and citric acids as main components and after the cultivation was acidified to a pH of 0.5 by means of hydrochloric acid. The leaching was carried out in mechanically stirred acid-resistant vats for a period of from 1 to 5 hours. The iron content of some sands treated by this method was lowered from 0.035–0.088 to below 0.012% Fe₂O₃ making them suitable for the preparation of high quality glass. The iron content of different kaolins was lowered from 0.65–1.49 to 0.44–0.75% Fe₂O₃ and as a result of this their whiteness was increased from 55–87 to 86–92%. The iron content of a clay was lowered from 6.25 to 1.85% Fe₂O₃ and this increased the fireproofness of the clay from 1 670 to 1 750°C. Similar process was used for leaching of aluminium from aluminosilicates, mainly clays and kaolins. However, after the cultivation the fermentation fluid was acidified either by means of sulfuric or hydrochloric acid or by means of different mixtures of inorganic acids. For enhancing aluminium solubilization the aluminosilicates were heated before leaching at 600–650°C for 1–2 hours. Over 90% of the aluminium present in different clays and kaolins was leached within 3–6 hours in this way. “Silicate” bacteria related to the species Bacillus circulans and B. mucilaginosus were used to leach silicon from low-grade bauxite ores containing aluminosilicates as impurities. The bacterial action was connected with the formation of mucilaginous capsules consisting of expolysaccharides. The solid residues after leaching were characterized by higher values of alumina content and were suitable for processing by means of the BAYER process for recovering aluminium. Heterotrophic bacteria were used to leach manganese from oxide ores using different organic compounds as reducing agents.     

Organoheterotrophe Laugung resistenter Materialien

Leaching processes can be classified in chemolithotrophic and organoheterotrophic mechanisms. In the case of chemolithotrophic leaching sulphide minerals, elemental sulphur, ferrous iron and a number of different reduced metals will be oxidized in a solution containing sulphuric acid of bacterial and/or chemical origin. Organoheterotrophic leaching however is connected with the accumulation of microbial metabolites such as organic acids, proteins, peptides and polysaccharides, which are capable to disintegrate ores, minerals or industrial wastes through dissolution, formation of complexes or chelates. Whereas at the present time chemolithotrophic leaching processes are in operation in industrial scale for the winning of copper, uranium and some other special metals, organoheterotrophic processes, their problems and technical applications are still under study. Therefore problems of organoheterotrophic leaching of chemical high resistant materials such as phosphorus furnace slag and zircon from the Baltic shield have been investigated with regard to possible technical applications for the winning of rare earth elements (REE) and other precious metals. Using a strain of Acetobacter methanolicus which is able to accumulate large amounts of gluconic acid on the basis of glucose or glucose containing by-products, leaching effects up to 90% of REE could be realized in the case of phosphorus furnace slag and up to 45% in the case of zircon.     

Microbial community study of the iron ore concentrate of the Sishen Iron Ore Mine, South Africa

As a result of the advancing global technologies and civilisation, there has been a progressive depletion of high-grade mineral deposits. Consequently, it has become increasingly important to process lower-grade ores. Phosphorous (P) and particular potassium (K) contained in the iron ore concentrates of the Sishen Iron Ore Mine have a detrimental effect on the steel making process, whereby these alkali’s cause cracks to form in the refractory lining of blast furnaces. It is initially essential to determine which microbes are indigenously present at the Sishen Iron Ore Mine before strategising how best to employ them to industrial advantage. Therefore, the objective of this study was to determine which microorganisms are indigenous to the iron ore and soil of the Sishen Iron Ore Mine. The bacterial 16S PCR and fungal ITS PCR revealed several bacterial and fungal species present in the mine environment. The bacterial isolates were found to be closely related to Herbaspirillum species, as well as Acidithiobacillus ferrooxidans, while the fungal isolates were closely related to Aureobasidium pullulans, Phaeosphaeria nodorum, Aspergillus fumigatus, and Candida parapsilosis. Isolating A. fumigatus from the iron ore/soil of the mine may indicate that A. niger, the most common fungi used for the production of citric acid, can adapt to the stringent mine environment. This would allow the application of A. niger for the production of citric acid, which may be used for the chemical leaching of the P and K from the iron ore concentrate of the Sishen Iron Ore Mine.     

Uranium mobilization from low-grade ore by cyanobacteria

Summary Three cyanobacterial isolates (two LPP-B forms and one Anabaena or Nostoc species) from different environments could mobilize uranium from low-grade ores. After 80 days, up to 18% uranium had been extracted from coal and 51% from carbonate rock by the filamentous cyanobacterium OL3, a LPP-B form. Low growth requirements with regard to light and temperature optima make this strain a possible candidate for leaching neutral and alkaline low-grade uranium ores.     

Extraction of Zinc from Industrial Waste by a Penicillium sp

Zinc was extracted from a filter residue of a copper works (58.6% zinc) by a Penicillium sp. isolated from a metal-containing location. By isotachophoresis citric acid was identified as the leaching agent. Citrate was only formed when the leaching substrate was present. This production of citrate was different in several ways from that achieved by Aspergillus niger: glucose was utilized before fructose; the initial concentration of zinc was 50 to 500 times higher than usual in citrate fermentations with A. niger; citrate production stopped when 80 to 90% of the zinc was leached, although sufficient sugar for further synthesis was still present; and in synthetic media citrate production by A. niger needs an acidic environment (pH 2), while the formation of citric acid by Penicillium sp. occurred in a pH range of 7 to 4. Tests with different concentrations of waste material (0.5, 2.5, and 5%) showed that the highest yield of solubilized zinc occurred with a 2.5% substrate (93% zinc extracted after 13 days).     

Citric acid production from sucrose by recombinant Yarrowia lipolytica using semicontinuous fermentation

The genetically modified yeast strain Yarrowia lipolytica H222‐S4(p67ICL1)T5 is able to utilize sucrose as a carbon source and to produce citric and isocitric acids in a more advantageous ratio as compared to its wild‐type equivalent. In this study, the effect of pH of the fermentation broth (pH 6.0 and 7.0) and proteose‐peptone addition on citric acid production by the recombinant yeast strain were investigated. It was found that the highest citric acid production occurred at pH 7.0 without any addition of proteose‐peptone. Furthermore, two process strategies (fed‐batch and repeated fed‐batch) were tested for their applicability for use in citric acid production from sucrose by Y. lipolytica. Repeated fed‐batch cultivation was found to be the most effective process strategy: in 3 days of cycle duration, approximately 80 g/L citric acid was produced, the yield was at least 0.57 g/g and the productivity was as much as 1.1 g/Lh. The selectivity of the bioprocess for citric acid was always higher than 90% from the very beginning of the fermentation due to the genetic modification, reaching values of up to 96.4% after 5 days of cycle duration.     

Physicochemical and Mineralogical Characterization of Uranium-Contaminated Soils

Physicochemical and mineralogical properties of the contaminants should be taken into account to decide a remediation strategy for a given radionuclide because development and optimization of soil remedial technologies are based on physicochemical and mineralogical separation techniques. The objectives of this study are to (1) demonstrate how a priori physicochemical and mineralogical characterization of soil contaminants can direct the development of remediation strategies and their performance evaluation for soil treatments and (2) understand the nature of uranium contamination and its association with the soil matrix by chemical extractions. This study examined two U-contaminated sites (K311 and K1300) at the DOE K-25 site, presently located at East Tennessee Technology Park, Oak Ridge, Tennessee. Uranium concentrations of the soils ranged from 1499 to 216,413 Bq kg^?1 at both sites. Scanning electron microscopy with backscattered electron spectroscopy and X-ray diffraction analysis showed that the dominant U phases are U oxides (schoepite), U-Ca-silicate (uranophane) and U silicate (coffinite) from the K311 site soils, whereas U-Ca-oxide and U-Ca-phosphate dominate in the K1300 site soils. Sodium carbonate/bicarbonate leaching was effective on the K1300 site soils, whereas citric acid leaching is effective on the K311 site soils. Sequential leaching showed that the majority of the uranium in the contaminated soils was contained in carbonate minerals (45%) and iron oxides (40%). Conventional leaching showed that citric acid treatment was most effective on the K311 site soils, whereas the sodium carbonate/ bicarbonate treatment was most effective on the K1300 site soils.     

Characterization by high performance liquid chromatography (HPLC) of the solubilization of phosphorus in iron ore by a fungus

Summary The value of iron ore is adversely affected by phosphorus in concentrations over 0.03% by weight. The present research concerns the use of metabolic products of aPenicillium-like fungus to leach insoluble phosphates (hydroxyapatite) from ores. Ion chromatography was used to measure metabolism of glucose into acidic fragments. The rate and products of glucose degradation depended on both the chemical composition of the growth medium (buffered or not) and incubation conditions (shaken or quiescent). The principal products were identified as oxalic acid and isomers of propylene dicarboxylic acid, mainly itaconic acid. Continued, slow metabolism of itaconic acid generates more oxalic acid. Aliphatic acids were not detected. Both iron ore phosphate and calcium phosphate were partially solubilized by either the spent broth or aqueous oxalic acid. Solubilization of ore phosphorus was greatly assisted by hydrochloric acid added to the spent broth in small increments. The data suggest biological alternatives to costly leaching procedures that use only mineral acids.     

Chemical leaching of copper-zinc concentrate with ferric iron biosolution

The process of leaching of copper-zinc concentrate with a solution containing biogenic iron, which is a product of the metabolism of iron-oxidizing microorganisms, was studied. The dependence of leaching rate of metals on temperature and pH was determined. It was shown that up to 98% of zinc and 70% of iron could be removed from the concentrate, while up to 7 and 4 g/L of zinc and copper, respectively, were accumulated in the liquid phase, which was sufficient for metal recovery. It was established that a copper concentrate with copper content up to 16% and only 0.5% of zinc could be obtained after chemical leaching for 340 min at 80°C.     

Fungal leaching of nickeliferous laterites

Extraction of nickel by microbial leaching of Greek laterites is feasible by using ofAspergillus andPenicillium. The effectiveness was found to depend on the ability of the microorganism to produce hydroxycarboxylic acids, especially citric acid, as well as other metabolites. The nickel recoveries achieved were as high as 60%, in 48 d, when the ore was leached in the presence of the living fungi, in a sucrose medium, and as high as 70%, in a much shorter time, when the ore was leached by their metabolic products after pH adjustment by means of sulfuric acid. The use of much cheaper, factory grade, Greek beet molasses as a growth medium proved promising, giving the possibility of making the process more attractive in economic terms.     

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.     

Bioleaching of Uranium From Egyptian Rocks Using Native Actinomycete Strains

Bioleaching is an economic, novel practice for extraction of metals from their sources by microorganisms. The current study aimed to extract uranium from Egyptian ores using native strains of actinomycetes. Two types of rocks and one ore sample were collected from west-central Sinai, Egypt. Major oxides of the samples and fourteen heavy metals, including uranium, were determined. X-ray diffraction analysis proved that uranium was present in the samples in various structures. Uranium was present in different concentrations, 220, 770, and 550 mg/kg in sandstone, granite, and manganese ore, respectively. Thirty-four actinomycete isolates were recovered from the studied samples using four different isolation media. Acid production capabilities were employed to select isolates for further leaching experiments. Bioleaching experiments were carried out using sterile and non-sterile ore samples. Using sterile ore samples, the highest solubilization percentages of U₃O₈ were 44.5, 38.55, and 16.76% from sandstone, manganese ore, and granite sample, achieved by isolates UA12, UA5, and U7, respectively. Lower solubilization percentages of U₃O₈ were recorded by using non-sterile ore samples. Investigating the factors affecting the bioleaching abilities of the tested organisms revealed that 10 days of incubation with 4% pulp density were the best conditions for U₃O₈ solubilization. The most efficient isolates were identified using 16S rRNA gene sequence analysis. UA12 identified to be Streptomyces bacillaris, while UA5 could not be identified, and U7 was assigned as uncultured bacterium clone. Scanning electron microscope examination of the bioleaching experiment showed different growth intensity within the active isolates. For larger-scale extraction purposes, a kilogram of sandstone, containing 220 mg of U₃O₈, was used in the form of a truncated cone in a heap leaching experiment. After 20 cycles, 14.72 mg/l (6.7%) of U₃O₈ was leached by S. bacillaris, while 19.36 mg/l (8.8%) of U₃O₈ was leached by chemical leaching using sulfuric acid. The results of this study prove that the extraction of uranium using actinomycetes could be exploited as less polluting, more economical, and more effective than traditional chemical extraction especially from low-grade ores or mining wastes.     

Buffer-stimulated citrate efflux in Penicillium simplicissimum: an alternative charge balancing ion flow in case of reduced proton backflow?

Organic acids excreted by filamentous fungi may be used to win metals from industrial secondary raw materials. For a future commercial use a high production rate of organic acids is necessary. The conditions under which the commercially used fungus Aspergillus niger excretes high amounts of citric acid can not be maintained in metal leaching processes. However, Penicillium simplicissimum showed an enhanced citric acid efflux in the presence of an industrial filter dust containing 50% zinc oxide. Because Good buffers of high molarity were able to mimic the effect of zinc oxide, the high buffering capacity of zinc oxide and not an effect of the zinc ions was held responsible for the enhanced citric acid efflux. The presence of ammonium and trace elements reduced this buffer-stimulated citric acid efflux, whereas the plant hormone auxine canceled this reduction. This citric acid efflux was influenced by a depolarization of the membrane: the freely permeable compound tetraphenylphosphoniumbromide decreased the citric acid efflux, without decreasing intracellular citric acid or consumption of glucose and oxygen. Vanadate, an inhibitor of the plasma membrane H⁺-ATPase also reduced the buffer-stimulated citric acid efflux. The role of the efflux of citrate anions as an alternative charge balancing ion flow in case of impaired backflow of extruded protons because of a high extracellular buffering capacity is discussed.Abbreviations CCCP carbonyl cyanide m-chlorophenylhydrazone - delta electrochemical potential gradient - DES diethylstilbestrol - DMSO dimethyl sulfoxide - TAPS N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid - TEA triethanolamine - TFP trifluoperazine - TPP tetraphenylphosphonium bromide