Cao et al. (1998) had proposed the embedding of all components of multi-dimensional observations by using an optimal Takens embedding for each component (time series). The optimal values of the embedding dimension for each component were found by minimizing the prediction error of a nearest neighbor, locally constant predictor. Optimization of the embedding lag is especially difficult if noise is present in the observations (Lai and Lerner, 1998). The chapter considers a different approach to embed multidimensional observations, which avoids both linear approximations in finding embedding dimensions and potentially suboptimal embedding lags. With this approach, each component of an observation space is treated as a one-dimensional time-series. Each component is embedded individually to generate a set of subspaces. The lag variables are separated and the structure of the attractor is optimized. This results in a reconstructed dynamic attractor based on the observation space. Additionally, the resultant attractor structure is an optimal projection of the original embedding variables.
In the case study discussed in the chapter, the use of surrogate data analysis is demonstrated on a set of artificial curves, generated by the function y = sin(θ) + sin(θ/2) + ɛ, with θ є [0, 20π] and ɛ representing Gaussian noise added to these curves. Three identical curves (y1, y2, and y3) were generated. These curves were consequently corrupted by ɛ1 = N(0, 0.001), ɛ2 = N(0, 0.05), and ɛ3 = N(0, 0.25)—that is, Gaussian noise with zero mean and standard deviations. The three time series curves and the associated correlation dimensions of the curves and their surrogate data sets are illustrated in the chapter. The curves were embedded by the use of singular spectrum analysis, as the use of the average mutual information or autocovariance function criteria could not cope with the noise in the data. The correlation dimension curves associated with the original observations and those associated with the surrogate data derived from the original observations tend to move closer with progressive noise levels, indicating the growing stochastic nature of the observations. Moreover, the noisier the data, the higher the correlation dimension values become at small scales.
In the course of a 6-yr-project in the framework of a German-Romanian scientific cooperation large scale installations were used for controlled expts. on acid rock drainage abatement. These installations imbedded in a waste rock dump were a 4-chamber-percolator (4CP) with a capacity of 65 m3 for each chamber and a 6-column-percolator (6CP) with a capacity of 2.3 m3 for each column. The waste material consisted of about 6-yr old run-off mine waste rock, freshly broken 6-yr old low-grade ore with 4-30 mm grain size, and tailings material from an active pond. The expts. lasted up to now at least 2 yr and were analyzed for depth-dependent cell nos. of leaching bacteria, microbial leaching activity, pH, redox, and total as well as time dependent metal output. Measures to be tested against acid rock drainage were 1 m thick soil/clay covers rich in org. material, layers of alk. materials (mixts. of lime and limestone) for neutralization/hardpan formation, and biocide addn. Two biocides were tested: Na dodecylsulfate (SDS), and isothiazolinone. Each expt. was run with one chamber and/or one column as control. The results demonstrated that org. covers reduce bioleaching transiently, however not completely. About the longevity no information exists. Alk. layers may function as expected, however the thickness has to be sufficient to be able to remain functional after settings. Biocides are an ambiguous measure. They have to be used in a sufficiently high concn. to kill the leaching bacteria, but must not be dangerous to the environment in case of wash-out. Furthermore, they are biodegradable and need to be added constantly. In the case of SDS, the wash-out of metal salts is increased due to the improved wetting, causing a considerable metal output from treated waste. Thus, biocides may possibly be used to stop or rather prevent bioleaching in early stages, but not in case of heaps and dumps with established bioleaching process. Microbial leaching activity measurements performed by microcalorimetry were correlated with the quant. chem. and microbiol. data in order to establish this rapid and simple technique for risk assessment and prediction of the leaching output of a mine waste dump.
Extracellular polymeric substances (EPS) seem to play a pivotal role in bioleaching—the winning of precious metals as well as acid rock drainage. For a better control of both processes structure and function of extracellular polymeric substances from leaching bacteria are of crucial importance. Our research focussed on Acidithibacillus ferrooxidans, the composition of its extracellular polymeric substances and further deduction of their function. The extracellular polymeric substances of Acidithiobacillus ferrooxidans consist mainly of neutral sugars and lipids. The functions of the extracellular polymeric substances of this leaching bacterium seem to be (i) to mediate attachment to a (metal) sulfide surface, (ii) to concentrate iron(III) ions by complexation through uronic acids or other residues at the mineral surface and, thus, allowing for an oxidative attack on the sulfide. Consequently, dissolution of the metal sulfide is enhanced, which may result in an acceleration of 20- to 100-fold over chemical leaching. Experiments were performed to elucidate the importance of the iron(III) ions complexed by extracellular polymeric substances for strain-specific differences in oxidative activity for pyrite. The preliminary data indicate that strains of Acidithiobacillus ferrooxidans, with a high amount of iron(III) ions in their extracellular polymeric substances, possess a higher oxidation activity than those with less iron(III) ions. These data provide new insight into the function of extracellular polymeric substances and the consequent advantage conferred to bacteria involved in bioleaching.
The effects of temperature and pH on the growth rates (based on rates of ferrous iron oxidation) of the type strain of Thiobacillus ferrooxidans and an isolate (strain CF12) of 'Leptospirillum ferrooxidans' were compared. The temperature optimum of T, ferrooxidans (at similar to 30 degrees C) was found to be higher than that of this particular strain of `L. ferrooxidans' (less than or equal to 25 degrees(C)), but the latter iron-oxidiser was shown to be the more acidophilic of the two bacteria. Tn cultures adjusted to an initial pH of 1.25, the culture doubling time of T. ferrooxidans (at about 100 hours) was about four times that of 'L. ferrooxidans', though growth rates of both bacteria could be increased by adaptation to extremely acidic conditions. Both isolates displayed poor growth in media adjusted to pH 1.0. The mortality rates of T. ferrooxidans and 'L. ferrooxidans' in oxidised ferrous sulphate medium were similar in cultures set at pH 2.0, but cell viability of T, ferrooxidans declined much more rapidly than that of the `L. ferrooxidans' isolate in pH 1.25 cultures.
The micro-organisms used in the processes of sulphur elimination from coal by bioleaching are currently considered to play an important part in the dissolving of other elements (Cu, V, Ni, Pb, Cr, Se, As, etc.). In this study an analysis is carried out a process of biodesulphurization of coal and the elimination of certain heavy and trace elements. An 8.4-litre reactor was used, comprising three columns connected in series with a volume of 2.8 litres each.Twenty elements were studied, in three groups according to the criteria of the National Research Council of the USA, major components found in most coals in large quantities, elements harmful to the environment and elements of medium and low environmental impact. Of the major components, only iron, calcium and phosphorous are leached throughout the process. Of the harmful elements, it can be said that almost all the cadmiun released is due to bioleaching. Arsenic and boron are also bioleached in the process. Of the elements of medium and low environmental impact, it is our opinion that only copper is dissolved, at least to any great extent, by bioleaching.
In this study, we demonstrated that the logarithmic growth of Thiobacillus ferrooxidans could be maintained under conditions of efficient Fe(II) regeneration with the potential controlled reduction of Fe(III) and sufficient aeration. The potential controlled electrolysis produced a high efficiency (80%) reduction of Fe(III). The use of a glassy microbubbler showed that it was possible to maintain a dissolved oxygen concentration in the medium adequate for a 7.0 x 10(9) cells/cm(3) cell suspension. Using this system, the logarithmic growth of T. ferrooxidans was maintained for 4 days reaching a final cell density of 1 x 10(10) cells/cm(3) within 6 days. This concentration was a 50-fold increase over the conventional batch culture.
To clarify the role of crystallographic orientation of the ore on the reaction mechanism of bacterial oxidation, single crystals of pyrite were oxidized by using Thiobacillus ferrooxidans and representative plane orientations of (100) and (111) of pyrite were adopted for this purpose. According to SEM and AFM characterization, the surface corrosion associated with microbial oxidation seems different between (100) and(111) planes.
The bacterial leaching of refractory arsenic-bearing gold ores from different deposits were investigated to determine the effects of mineralogy on the fate of arsenic during processing and to assess the effectiveness of biological pre-treatment on gold extraction. Experiments were conducted using a mixed culture of iron and sulphur oxidising bacteria dominated by Thiobacillus ferrooxidans. The speciation of arsenic during bioleaching was studied using polarography. Leaching of a concentrate which was predominantly arsenopyrite resulted in 80% of the leached arsenic reporting in solution as arsenic(III) at the end of the bacterial oxidation stage. Study of the oxidation of concentrates from different ore deposits with various ratios of pyrite to arsenopyrite showed that the amount of pyrite was an important factor in determining the dominating arsenic oxidation state in the leach solutions. Iron(III) alone was found not to be able to oxidise arsenic(III), instead pyrite was needed as a catalyst. It was found that adding pyrite and iron(III) to arsenopyrite concentrates promotes the formation of arsenic(V) leaving less than 1% of the extracted arsenic as arsenic(III). Furthermore a strong dependence of pyrite leaching and arsenic(III) oxidation was demonstrated. These results demonstrate the importance of ore composition in terms of pyrite to arsenopyrite ratio in the production of environmentally acceptable biooxidation residues containing arsenic(V).
Biooxidation of a refractory gold concentrate in a continuous culture operation utilising a Thiobacillus ferrooxidans strain was studied. The experiments were conducted in a 5 I, bioreactor using a 6% (w/v) pulp density in the feed stream, dilution rate of solids between 0.088 and 0.92 d(-1), pH 1.5 and 33 degrees C. Main sulphur compounds of the concentrate were 41% enargite and 43% pyrite. Cell, ferric ion and sulphate productivity present a maximum at a solids dilution rate in the range of 0.6 - 0.8 d(-1). The presence of iron and negligible amounts of arsenic in solution are indicative that cells utilises pyrite as energy source rather than enargite. Specific growth rate and cell yield associated to solids present a saturation type curve as a function of solids dilution rate. The increment of cell growth and mineral dissolution as consequence of step changes, either lowering particle size or air enrichment with CO2, reflect a condition of a double limitation of the continuous culture, energy and carbon sources respectively.
This study was concerned with a biosorption by biomass of the brown marine alga Sargassum polycystum in a batch system. The optimum condition for cadmium removal was investigated by determination of cadmium uptake capacity of alga which were dried at different temperatures; 80 and 100 degrees C. In each case of algal preservation, three different conditions of pH; 4.0, 4.6, and 5.6 were studied. A sodium acetate buffer was used in a system to maintain constant pH. The results showed that S. polycystum had the highest cadmium uptake at pH 4.0 at both different drying temperatures. The cadmium uptake capacity estimated from Langmuir isotherm were 103.36 and 95.49 mg Cd/g biomass for the alga dried at 80 and 100 degrees C, respectively. The biomass which were dried at 80 degrees C had a cadmium uptake capacity of 71.39 mg Cd/g biomass at pH 4.6 and 70.66 mg Cd/g biomass at pH 5.6. The cadmium uptake capacity of alga dried at 100 degrees C in the conditions of pH 4.6 and 5.6 were 56.78 and 56.67 mg Cd/g biomass respectively. Alga dried at 80 degrees C was found to have slightly higher cadmium uptake capacity per gram dry weight than that of alga dried at 100 degrees C.The recovery of cadmium loaded alga with 0.2 M HCl resulted in no changes of the algal cadmium uptake capacity through five cycles of regenertion process. The dry biomass of S. polycystum exhibited high swelling volume. The values of distention index were 13.8 and 11.1 ml/g for alga dried at 80 and 100 degrees C, respectively. These results indicated the low stability of biosorbent. However, its high cadmium uptake capacity and abundant availability indicated that S. polycystum can be used for the development of biosorbent for heavy metal removal from wastewater.
When developing technologies of ionselective biomineral sorbents produced by dark-colored micromycetes cultivation in media containing clay minerals, it is of a great importance to define processes taking place on the boundary of mineral phase and organic phase. Particularly, the interaction between sorption-active components of dark-coloured microfungi melanins and surface of clay minerals (montmorillonite, kaolinite) was studied by infrared spectroscopy. Keeping in view that the melanin structure closely resembles that of humic acids, we examined humic acids and clay minerals associates obtained by heterocoagulation of peat humic acid hydrosol with clay mineral particles. It was established that the organic phase fixation on the clay minerals surface occurred as a result of (I) the interaction between -COOH groups of the organic phase and exchange groups of mineral after the ligand exchange and (II) hydrogen bonds formation between corresponding groups of organic and mineral phase. The direct interaction between the organic phase and mineral surface with coordination bonds is also possible.
The lack of quality water supplies in the Western Australian gold fields is a limiting factor in the use of biological oxidation to treat refractory gold ores prior to the extraction of gold by cyanidation. Clearly, the recycling of water from the CIP process back to a biological oxidation plant is desirable in regions where supplies of fresh water are a limiting resource. However, thiocyanate, a by-product of the cyanidation process and a major contaminant in tailings dams, must be removed if water is to be recycled because it is toxic to sulphide-oxidising bacteria.Two strains of bacteria that were capable of degrading thiocyanate were isolated from the Youanmi mine in Western Australia. Both strains demonstrated the ability to utilise thiocyanate as their sole energy and nitrogen source. Physiological characterization of the strains indicated that both species of bacteria had the potential to tolerate the variable conditions encountered in Youanmi tails water. Phylogenetic analysis showed that one strain was a member of the genus Thiobacillus and the other was a member of the genus Halomonas but neither could be accommodated within any described species. Phosphate was the only additional nutrient required for thiocyanate degradation.Both strains were inoculated into a laboratory-scale Rotating Biological Contactor (RBC). The success and extent of colonization was confirmed by recovery of signature lipids of both strains from the fixed-film biomass. The bacteria degraded thiocyanate to ammonium, sulphate and carbon dioxide. The biomass supported on the reactor surface area (20 m(2)) was capable of degrading approximately 2800 mg L-1 to less than 1 mg L-1 thiocyanate at a flow rate of 30 mt min(-1). The process operated in saline, low nutrient water.
While only weakly radioactive, traces of natural uranium in surface waters represent a danger because of high toxicity. Mine drainage brings enough uranium into the environment as to cause concern. Acid washed, protonated, non-living biomass of Sargassum seaweed sequestered uranyl ions from solution extremely effectively. At pH 4.0, pH 3.2 and pH 2.6, the maximum uranium uptake values were 560 mg/g, 330 mg/g and 150 mg/g, respectively. The uranium biosorption mechanism was affected by the solution pH through the hydrolysis of uranyl ions in aqueous solution. At low pH value, the uranium is present in the solution mainly in the form of free UO22- ions, and it was competing with protons for the binding sites on the biomass. The high uranium biosorption at higher pH was attributed to the ion exchange between the hydrolyzed uranyl ions, UO2OH+, (UO2)(3)(OH)(5+), (UO2)(2)(OH)(2)(2+) and protons. Experimental sorption isotherms could be reliably fitted by conventional Langmuir and/or Freundlich models. A flow-through biosorption column demonstrated a high overall column uranium sorption capacity of 105 mgU/g at pH 2.5. About 36 bed volumes of 238 mg/L uranium solution was purified before the breakthrough (at 1 mgU/L in the column effluent). The regeneration of the column by elution with 0.1 N HCl resulted in a very narrow peak of the elution curve reflecting a high efficiency in uranium recovery.
Structural changes in chromosomal DNA of Thiobacillus ferrooxidans strains that occur under the influence of varied growth conditions were studied by pulsed-field gel electrophoresis. Strain diversity of T. ferrooxidans was manifested in different,growth rates and oxidation rates of inorganic substrates under extreme conditions, in different resistance to metal ions and low pH values, and also in polymorphism of the chromosomal DNA fragments generated by the macrorestriction endonucleases. Adaptation of some strains to growth on media containing new substrates was accompanied by changes in the number and size of restriction fragments. Thus, new 177 and 164 kb DNA fragments were revealed after the substitution of the oxidation substrate from Fe2+ to FeS2 or from Fe2+ to SO, respectively, whereas 115 and 77 kb DNA fragments disappeared. The switching from Fe2+ to S-0 resulted in the change in the number of 27 kb DNA fragments. Another type of chromosomal DNA variability was found in the strains adapted to high concentrations of metal ions. A comparison of Xbal-restriction patterns in parent strains and in strains with acquired enhanced resistance to zinc (from 40 to 70 g/l) or arsenic (from 1.5 to 4.0 g/l) revealed amplification of 98 and 28 kb fragments, respectively. When both strains were subcultured on medium with Fe2+ without the inducing factors, amplification of DNA fragments was no longer detectable. However, the strain adapted tp 50 g/l of Fe2+/Fe3+ had a mutation in the structure of chromosomal DNA. The data obtained on the natural and experimental genomic variability of T. ferrooxidans strains provide biotechnologists with practical recommendations for selection aimed at the intensification of bioleaching processes and testify about possibilities of strain monitoring in natural and technological conditions. Strains with the labile genome have an advantage in biohydrometallurgy.
Significant concentrations of thiocyanate are generated in effluent from the CIP/CIL gold extraction process. As thiocyanate is toxic to iron- and sulphide-oxidising bacteria, the effluent cannot be returned directly to a bacterial oxidation plant. To overcome this problem, a rotating cage laboratory-scale bioreactor was inoculated with two strains of known thiocyanate-degrading bacteria. The reactor, which had a 20 L solution volume and surface area of 20 m(2) available for biomass support, degraded thiocyanate from a concentration of 2000 to <1 mg L-1 (flow rate 30 mt min(-1); residence time 11 h).The efficiency of the thiocyanate-degrading bioreactor to detoxify process water was evaluated in bacterial oxidation tests using Fe2+ and arsenopyrite as energy sources. The er;peri mental results indicated that water detoxified using the thiocyanate-degrading bioreactor could be recycled to a biological oxidation plant.
A chromate reducing strain, Pseudomonas mendocina transformed hexavalent chromium to its trivalent form which precipitated as chromic hydroxide in the medium. Studies with respiratory inhibitors in conjunction with molar growth yield data indicated that chromate is not used as the terminal electron acceptor by this organism but probably serves as an auxiliary oxidant that helps in generation of oxidized cofactors necessary in cellular metabolism. Chromate reduction by P. mendocina is mediated by a periplasmic chromate reductase having molecular weight of approximately 183 KDa. The temperature and pH optima of the enzyme are 70 degrees C and 8.5, respectively. Purified enzyme exhibited a K-m of 289 mu M chromate and a V-max of 625 mu M chromate reduced/min/mg protein.
A new process for copper ion removal was studied, coupling electrochemistry and biology. An electrochemical reactor using a packed bed cathode of 10 x 2.5 x 30 cm of activated carbon was selected and built. The electrochemical deposition of copper was studied in this reactor in the absence and in the presence of biomass adsorbed on the cathode. A preconcentration phase of copper ion on the surface of the activated carbon was shown to increase of 30 % the deposition efficiency. In the presence of biomass this efficiency was increased of 20 % more. An elimination of 54% was achieved in this latter case.
The quantitative study of the adsorption of metallic ions on both organic and mineral surfaces showed that sorption is strongly dependent on chemical parameters such as pH or competing ions. An increase in pH yields to a greater amount of fixed metals whereas the competition between ions tends to decrease the relative amount of each sorbed element. Moreover, the behaviour of the adsorption sites and the binding capacity of each material (at different pH) and their selectivities have been studied for complex solutions including up to 7 cations introduced at the same starting concentration. Sorption of cations is very fast and up to 90% of the fixation is achieved in less than 10 minutes. However, fluctuation in the total of sorbed ions is observed for greater times. Results show that biomasses bound more efficiently uranium than rare earth elements, and that the final amounts of sorbed rare earth elements depends on the nature of the elements, with the following order of increasing sorbed quantities: Ce, Nd, La, Pr and Dy. The same order is found during the sorption of rare earth elements on clays. Finally, kinetics analysis of sorption were done in order to fit experimental results by Freundlich or Langmuir adsorption model which seems more appropriated.
Biohydrometallurgical solubilization cannot yet compete with conventional pyrometallurgical processes for recovering metals from sulphide concentrates, though the benefits deriving from its being much more environmentally friendly make it extremely attractive. Up to now, the main reason has been the relatively large size of the bioreactors and consequently the higher investment and power costs per unit mass of metal recovered compared to conventional processing. Bioreactor size is directly related to the biosolubilization process kinetics that, in turn, depend upon the suitability of the bioreactor to the process and on the prevailing biochemical conditions in the system. The Biorotor - the first reactor purpose built to match biohydrometallurgical requirements and developed by the authors - yields much faster biosolubilization kinetics than conventional bioreactors. It has been demonstrated that sulphur and iron biooxidation kinetics can be further enhanced, even in conventional bioreactors, by adding to the mineral suspension small amounts of substances capable of removing at least part of the metabolites. One of such substances is bentonite, a clay mineral that is already used as a scavenger in some commercial processes. Ferrous sulphate kinetics at least one order of magnitude higher than those reported in the literature can easily be obtained in the biorotor when the reaction takes place in the presence of bentonite. The concentration of oxidizable solids is more of a performance-limiting factor for conventional reactors than for the Biorotor and less harmful when bentonite is present in the solids suspension. Tests have been carried out in two identical Pachuca tanks operated in parallel using pure pyrite in concentrations increasing from 4.78% to 20.58% through 13.35%, one (No.1) containing a pyrite suspension and the other (No. 2) the same suspension admired with bentonite. The ratio of pyrite solubilization rates in Pachuca No. 2 to those in Pachuca No. 1 increased almost linearly with increasing pyrite concentration. For 30% solids in Biorotor, without bentonite, the iron solubilization rate was 561 mgAdm(-3)Ah(-1). Testing of Biorotor performance with bentonite confirmed the results obtained in the Pachuca, although less pronouncedly.
