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.     

Nickel accumulation and nickel oxalate precipitation by Aspergillus niger

A strain of Aspergillus niger isolated from a metal-contaminated soil was able to grow in the presence of cadmium, chromium, cobalt, copper, and unusually high levels of nickel on solid (8.0 mM) and in liquid (6.5 mM) media. This fungus removed >98% of the nickel from liquid medium after 100 h of growth but did not remove the other metals, as determined by inductively coupled plasma spectroscopy. Experiments with non-growing, live fungal biomass showed that nickel removal was not due to biosorption alone, as little nickel was bound to the biomass at the pH values tested. Furthermore, when the protonophore carbonyl cyanide p-(trifluoremetoxy) phenyl hydrazone (FCCP) was added to the actively growing fungus nickel removal was inhibited, supporting the hypothesis that energy metabolism is essential for metal removal. Analytical electron microscopy of thin-sectioned fungal biomass revealed that metal removed from the broth was localized in the form of small rectangular crystals associated with the cell walls and also inside the cell. X-ray and electron diffraction analysis showed that these crystals were nickel oxalate dihydrate.     

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.     

Laugung lateritischer Nickelerze mit heterotrophen Mikroorganismen

Organic acids that are excreted by microorganisms dissolve nickel from lateritic ores. In chemical leaching experiments, fifteen organic acids were tested in the concentration range of 0.05–0.5 M. The most effective were hydroxycarboxylic acids. The leaching of nickel is dependent on the type of mineralization. With completely limonitized ore, no mobilization occurred, while up to 90% of the nickel was extracted from silicate-bearing laterites by 0.5 M citric acid. In biological leaching tests, Penicillium was found to be the most effective microorganism. After improvement of the leaching conditions, up to 70% of the nickel was extracted at considerably lower citric acid concentrations than with the chemical leaching process. Generally, leaching of nickel from lateritic ores with heterotrophic microorganisms is possible and seems to be promising. Possibilities for future investigations are discussed.     

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.     

Optimization of Microbial Leaching of Base Metals from a South African Sulfidic Nickel Ore Concentrate by Acidithiobacillus ferrooxidans

X-ray diffraction analysis revealed that pentlandite and chalcopyrite were the prominent mineral phases in a South African sulfidic nickel ore concentrate that hosted nickel and copper. Cobalt was found to be closely associated with the nickel-bearing pentlandite phase of the ore sample. Microbial batch leaching experiments designed according to a central composite design model were run for 15 days in a shaking incubator (150 rpm) at a constant temperature (30°C) with variations in experimental parameters like ore pulp density, particle size, bacterial inoculum, pH of the culture medium, and residence time. Quadratic mathematical models were developed to predict the rate of metal extractions. The suitability of the model of the microbial leaching process was confirmed from normal probability curves. An analysis of variance indicated that the residence time, pulp density of the ore, and particle size were the most significant factors. Bacterial inoculum size hardly showed any effect on the total metal extractions. Maximum nickel (82%), cobalt (76%) and copper (25.6%) extractions were achieved under optimum conditions, operated for 15 days at pulp density of 2% and particle size of ?75 µm at pH 1.5.     

Compositions of microbial communities in sulfide nickel ore waste piles

Bacterial communities of moderately acidic waste piles of sulfide nickel ore and of the nickel-leaching enrichments obtained from them are analyzed. The structure of bacterial communities was determined by molecular biological techniques. The PCR profiles of bacterial communities were obtained with the primers to a variable 433 bp site of the eubacterial 16S rRNA gene. The differences in community compositions were determined by comparison of their DGGE profiles. Sequencing of the DNA fragments was then carried out and the results were compared with the GenBank gene sequences. Analysis of the 16S rRNA gene sequences revealed few bacterial genera in the moderately acidic waste piles of sulfide nickel ore, with predomination of Acidithiobacillus sp. and Leptospirillum sp. A number of the bacteria revealed belonged to the species never obtained in pure culture. Molecular biological analysis showed the presence of the same groups of bacteria in enriched cultures obtained by inoculating the liquid medium containing ground ore with the waste pile samples (5 : 1). The geochemical activity of these bacteria was confirmed by their capacity for leaching nickel from the sulfide ore in enriched cultures, resulting in nickel solubilization. Thus, new information was obtained concerning the structure composition of the bacterial communities of sulfide ore waste piles: the dominant forms were determined, their leaching activity was confirmed, and the activity of thiobacilli from the waste, which have not been isolated in pure cultures, was confirmed in liquid medium in the presence of ore.     

Biological leaching of sulfide minerals with the use of shake flask,aerated column,air-lift reactor,and percolation techniques

Four different experimental approaches were used to evaluate the microbiological leaching of ore material containing metal sulfides (Fe, Zn, Ni, Cu, Co) and aluminum silicates. A shake flask technique required the shortest contact time for the complete solubilization of the most readily leachable metals (Ni and Zn). Air-lift reactors and aerated column reactors required longer contact times and complete solubilization of either zinc or nickel was not achieved. The air-lift reactor approach was somewhat more effective than the aerated slurry technique. A percolation system was the least effective and yielded the lowest recoveries. Shake flasks (easily autoclavable) offered the advantage of comparison of the microbiological and solely chemical leaching. Aseptic conditions could not be maintained with the air-lift and aerated column reactors because of contamination via aerosol formation. In a relative scale the leaching patterns were similar in that the precipitation of Fe(III) occurred regardless of the technique; zinc and nickel sulfides were solubilized more quantitatively than those of copper and cobalt; aluminum concentrations, although high, indicated low leaching yields relative to aluminum silicates in the ore material; and the pH reached similar final values in the presence of bacteria.     

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.     

Fidelity of metal insertion into hydrogenases.

The fidelity of metal incorporation into the active center of hydrogenase 3 from Escherichia coli was studied by analyzing the inhibition of the maturation pathway by zinc and other transition metals. Hydrogenase maturation of wild-type cells was significantly affected only by concentrations of zinc or cadmium higher than 200 microM, whereas a mutant with a lesion in the nickel uptake system displayed a total blockade of the proteolytic processing of the precursor form into the mature form of the large subunit after growth in the presence of 10 microM Zn(2+). The precursor could not be processed in vitro by the maturation endopeptidase even in the presence of an excess of nickel ions. Evidence is presented that zinc does not interfere with the incorporation of iron into the metal center. Precursor of the large subunit accumulated in nickel proficient cells formed a transient substrate complex with the cognate endoprotease HycI whereas that of zinc-supplemented cells did not. The results show that zinc can intrude the nickel-dependent maturation pathway only when nickel uptake is blocked. Under this condition zinc appears to be incorporated at the nickel site of the large subunit and delivers a precursor not amenable to proteolytic processing since the interaction with the endoprotease is blocked.     

Use of adapted Aspergillus niger in the bioleaching of spent refinery processing catalyst

Spent refinery processing catalyst is listed as a hazardous waste; the toxicity characteristic leaching procedure (TCLP) extracts of the catalyst are found to contain heavy metals at concentrations exceeding the regulated levels. In the present investigation, Aspergillus niger was adapted to single metal ions Ni, Mo or Al (at 100-2,000 mg/L in steps of 100mg/L) and then to a mixture of Ni, Mo and Al (at a mass ratio of 1:2:6, as approximately present in the spent catalyst). Adaptation experiments with single metals showed that the fungus could tolerate up to 1,000 mg/L Ni, 1,200 mg/L Mo and 2,000 mg/L Al. In the presence of a mixture of these metals, the fungus was able to tolerate up to 100mg/L Ni, 200mg/L Mo and 600 mg/L Al. One-step bioleaching experiments with 1 wt% spent catalyst (of particle size <37 microm) were carried out using un-adapted and various adapted fungal strains. In contrast to the adapted strains, the un-adapted strain showed no growth in the presence of the catalyst. Ni:Mo:Al-adapted strain was the most efficient in the leaching of metals from the catalyst (at 78.5% Ni, 82.3% Mo and 65.2% Al) over 30 days due to its tolerance to the toxic elements at 1 wt%. More importantly, the Ni:Mo:Al-adapted strain was capable of bioleaching up to 3 wt% spent catalyst. The TCLP extracts of the spent catalyst after bioleaching using the Ni:Mo:Al-adapted strain showed the concentrations of Ni and Mo were well within the regulated levels.     

A novel method for the quantitative assessment of the percolation of <Emphasis Type="Italic">Metarhizium anisopliae</Emphasis> conidia through horticultural growing media

Incorporation of fungal biological control agents (BCAs) into plant growing media has considerable ergonomic and economic benefits for growers. These agents usually give prophylactic control of target pests and diseases. However, their efficacy is dose dependent and loss of inoculum through leaching could influence the degree of protection they provide. At present there are no protocols to determine the loss of inoculum in the disparate growing media used in horticulture. We describe a method based on a nutrient leaching column to quantify leaching of conidia of the insect-pathogenic fungus Metarhizium anisopliae in a range of growing media. Conidia of this biocontrol agent were applied as a drench or premixed into the medium. Both the application method and growth medium influenced conidial leaching. Inoculum losses were greater following drench application than premixing (95% vs. 15%) irrespective of media type. Comparatively more inoculum was lost from bark and coir following drench application whereas losses were relatively high in peat following premixed application. The leaching column assay provided a simple and accurate method to quantify inoculum loss in real time. This assay could help determine leaching of other fungal BCAs in growing media. It could help in improving pest and disease control by optimizing the rate and frequency of conidial application as well in the design of more efficacious formulations.     

Short Communication: Leaching of Chromite overburden with various native bacterial strains

Four heterotrophic bacterial strains were isolated from soil and water samples from a chromite mine in Sukinda valley in Orissa. They were identified as Lactobacillus acidophilus, Staphylococcus lactis, Lactobacillus sp. and Propionibacterium acnes. Each strain was used for leaching of metals from chromite overburden of Sukinda. Comparatively, Lactobacillus sp. showed maximum capability for metal solubilization. It leached a maximum of 5.98% of nickel in 35 days of contact time.     

Influence of Arbuscular Mycorrhizal (AM) Symbiosis on Phosphorus Leaching through Soil Cores

Two experiments with soil cores were carried out to investigate the effects of arbuscular mycorrhizal (AM) fungal colonization on mobility of phosphorus (P) during leaching of repacked columns of a soil with a loamy sand texture. Trifolium subterraneum plants inoculated with an AM fungus or not inoculated were grown in cores with low or high P concentrations for 8 or 10 weeks in the glasshouse. Cores were then irrigated with 2500 mL water and the leachate collected. Plant growth and the amounts of P removed by plants, remaining in soil as available P and removed dissolved in leachate were measured. Mycorrhizal fungal colonization and development of external hyphae were also determined. Inoculation and/or P application significantly increased plant growth and plant P removal and decreased P leaching. In low P soils AM fungal colonization significantly increased plant P uptake and decreased soil available P and total dissolved P in leachates. Lower P leaching from cores with AM plants under low P conditions was related to enhancement of plant growth and to scavenging and removal of P from the soil by roots and/or external hyphae. When P was applied AM effects were not observed and available P remaining in the soil after leaching was much higher, regardless of AM fungal colonization.     

An Automated High-Throughput Cell-Based Multiplexed Flow Cytometry Assay to Identify Novel Compounds to Target Candida albicans Virulence-Related Proteins

Although three major classes of systemic antifungal agents are clinically available, each is characterized by important limitations. Thus, there has been considerable ongoing effort to develop novel and repurposed agents for the therapy of invasive fungal infections. In an effort to address these needs, we developed a novel high-throughput, multiplexed screening method that utilizes small molecules to probe candidate drug targets in the opportunistic fungal pathogen Candida albicans. This method is amenable to high-throughput automated screening and is based upon detection of changes in GFP levels of individually tagged target proteins. We first selected four GFP-tagged membrane-bound proteins associated with virulence or antifungal drug resistance in C. albicans. We demonstrated proof-of-principle that modulation of fluorescence intensity can be used to assay the expression of specific GFP-tagged target proteins to inhibitors (and inducers), and this change is measurable within the HyperCyt automated flow cytometry sampling system. Next, we generated a multiplex of differentially color-coded C. albicans strains bearing C-terminal GFP-tags of each gene encoding candidate drug targets incubated in the presence of small molecules from the Prestwick Chemical Library in 384-well microtiter plate format. Following incubation, cells were sampled through the HyperCyt system and modulation of protein levels, as indicated by changes in GFP-levels of each strain, was used to identify compounds of interest. The hit rate for both inducers and inhibitors identified in the primary screen did not exceed 1% of the total number of compounds in the small-molecule library that was probed, as would be expected from a robust target-specific, high-throughput screening campaign. Secondary assays for virulence characteristics based on null mutant strains were then used to further validate specificity. In all, this study presents a method for the identification and verification of new antifungal drugs targeted to fungal virulence proteins using C. albicans as a model fungal pathogen.     

Development of an in vitro model for the multi-parametric quantification of the cellular interactions between Candida yeasts and phagocytes

We developed a new in vitro model for a multi-parameter characterization of the time course interaction of Candida fungal cells with J774 murine macrophages and human neutrophils, based on the use of combined microscopy, fluorometry, flow cytometry and viability assays. Using fluorochromes specific to phagocytes and yeasts, we could accurately quantify various parameters simultaneously in a single infection experiment: at the individual cell level, we measured the association of phagocytes to fungal cells and phagocyte survival, and monitored in parallel the overall phagocytosis process by measuring the part of ingested fungal cells among the total fungal biomass that changed over time. Candida albicans, C. glabrata, and C. lusitaniae were used as a proof of concept: they exhibited species-specific differences in their association rate with phagocytes. The fungal biomass uptaken by the phagocytes differed significantly according to the Candida species. The measure of the survival of fungal and immune cells during the interaction showed that C. albicans was the more aggressive yeast in vitro, destroying the vast majority of the phagocytes within five hours. All three species of Candida were able to survive and to escape macrophage phagocytosis either by the intraphagocytic yeast-to-hyphae transition (C. albicans) and the fungal cell multiplication until phagocytes burst (C. glabrata, C. lusitaniae), or by the avoidance of phagocytosis (C. lusitaniae). We demonstrated that our model was sensitive enough to quantify small variations of the parameters of the interaction. The method has been conceived to be amenable to the high-throughput screening of mutants in order to unravel the molecular mechanisms involved in the interaction between yeasts and host phagocytes.     

Mitigation of amphotericin B nephrotoxicity by mannitol.

Renal transplant recipients are susceptible to a number of fungal infections amenable to therapy with amphotericin B, but azotaemia is an almost invariable sequel to the use of this agent. As intravenous mannitol has been shown to minimize nephrotoxicity induced by amphotericin B in dogs we treated four kidney transplant recipients who had systemic fungal infections with mannitol and amphotericin B. None showed significant reduction in renal function though a mild metabolic acidosis did develop.     

Responses of embryogenic mango cultures and seedling bioassays to a partially purified phytotoxin produced by a mango leaf isolate of Colletotrichum gloeosporioides penz

Summary Colletotrichum gloeosporioides Penz., the causal agent of mango anthracnose, produces a phytotoxin in vitro. The partially purified phytotoxin, presumably colletotrichin, caused anthracnose-like symptoms on young mango leaves, was toxic to embryogenic suspension cultures of two mango cultivars, ‘Hindi’ and ‘Carabao,’ and inhibited in vitro seed germination of two nonhosts, lettuce and tobacco. There were linear relationships between concentration of the partially purified phytotoxin and mortality of mango embryogenic cultures. Embryogenic cultures grown in the presence of the partially purified phytotoxin showed significantly lower growth rates than the controls. Similarly, embryogenic cultures grown in the presence of 40% (vol/vol) fungal culture filtrate showed significantly lower growth rates than unchallenged controls. Medium containing 40% (vol/vol) Czapek-Dox fungal broth did not reduce growth of embryogenic cultures, indicating the production of phytotoxin in vitro. The results suggest that either fungal culture filtrate or purified phytotoxin can be used as in vitro selection agents to screen for resistance to this fungus.