Growth and attachment of Thiobacillus ferrooxidans during sulfide mineral leaching

The growth of Thiobacillus ferrooxidans, their attachment to sulfide minerals and detachment during bacterial leaching are discussed in this paper. Growth of the bacteria has been measured by cell count of the supernatants of the mineral suspensions while attachment to minerals and detachment were measured by periodic protein estimations for both the solid and liquid phases, Even in the absence of the nutrients, bacterial growth occurs and increases the available cell population during leaching; such growth was greater in sphalerite suspensions than in galena suspensions, The bacterial attachment studies suggest that more cells are attached onto galena mineral surface than to sphalerite surface. The mechanisms of bacterial attachment and detachment are discussed.

Structure and magnetotransport properties of the layered manganites REl.2Srl.8Mn,07(R E = La, Pr, Nd)

We have examined the magnetotransport properties and the structure, by Rietveld refinement of powder X-ray data, of the phases RE(1.2)Sr(1.8)Mn(2)O(7) (RE = La, Pr, Nd). We find that on cooling, La1.2Sr1.8Mn2O7 undergoes a transition to a nearly perfect ferromagnet with 90% magnetization at 1.45 T, as reported by earlier workers, but the Pr and Nd phases show only a small magnetization that grows gradually as the temperature is decreased. There seems to be significant correlation between electrical transport and the Jahn-Teller elongation of the apical Mn-O bonds in these systems. The elongation of the apical Mn-O bonds forces the nine-coordinate rock-salt site to be occupied preferentially by the smaller rare-earth-metal cations. This preferential occupation is reliably obtained from the X-ray refinement. All three title phases show a magnetoresistance ratio of about 4(corresponding to a magnetoresistance, [R(0)-R(H)]/R(0), of about 75%) at a field of 7 T and temperatures around 100 K.

Estimation of mineral-adhered biomass of Thiobacillusferrooxidans by protein assay-some problems and remedies

Enumeration of adhered cells of Thiobacillus ferrooxidans on sulphide minerals through protein assay poses problems due to interference from dissolved mineral constituents. The manner in which sulphide minerals such as pyrite, chalcopyrite, sphalerite, arsenopyrite and pyrrhotite interfere with bacterial protein estimation is demonstrated. Such interferences can be minimised either through dilution or addition of H2O2 to the filtrate after hot alkaline digestion of the biotreated mineral samples.

Codoping Effect of Zn and Pr in YBa2Cu3O7-delta

In this paper we present the resistivity data for Pr and Zn codoped compound Y1-xPrxBa2[Cu1-yZny](3)O7-delta with 0 < y < 0.1 and x = 0.0, 0.1 and 0.2. The data is analysed in terms of the superconducting critical temperature T-c, residual resistivity rho(0) and the resistivity slope d rho/dT corresponding to the linear rho-T region. It is found that for x = 0.1 Pr has a minimal influence on the in-plane processes for Zn impurity alone affecting slightly T-c and rho(0). The slope dp/dT becomes larger for 0.03 < y < 0.06 leading to larger depining effect and hence slower fall of T, as a function of y. For x = 0.2 there is a drastic change, rho(0) becomes abnormally large, d rho/dT becomes negative implying absence of depinning and a totally pinned charge stripes. Superconductivity vanishes at y = 0.03. It is concluded that for x = 0.2 Pr converts the system from overdoped to underdoped region leading to the universal superconductor-insulator transition.

Structure of the noncubic phase in the ferroelectric state of Pr-substituted SrTiO3

Sr1−xPrxTiO3 has recently been shown to exhibit ferroelectricity at room temperature. In this paper powder x-ray and neutron-diffraction patterns of this system at room temperature have been analyzed to show that the system exhibits cubic (Pm-3m) structure for x<=0.05 and tetragonal (I4/mcm) for x>0.05. The redundancy of the noncentrosymmetric structural model (I4cm) in the ferroelectric state suggests the absence of long-range ordered ferroelectric domains and supports the relaxor ferroelectric model for this system.

SUBSTITUTIONAL EFFECT OF Zn AND Pr IN YBa2Cu3O7-delta

The co-doping effect of Zn and Pr impurities in the compound of composition Y1-xPrxBa2[Cu1-yZny](3)O7-delta with x = 0.1, x = 0.2 and 0 <= y <= 0.1 has been investigated by analyzing the results of electrical resistivity measurements. It is found that for Pr substitution at x = 0.1, there is a minimal influence on in-plane processes, thereby slightly affecting T-c and residual resistivity rho(0), but with the resistivity slope d rho/dT becoming large for the range of y from 0.03 to 0.06, leading to a larger depinning effect. For x = 0.2 a drastic change is observed whereby rho(0) becomes abnormally large, and d rho/dT becomes negative, implying totally pinned charge stripes and no depinning. The second observation therefore suggests that Pr substitution converts the overdoped system to an optimally doped system, leading to the universal superconductor-insulator transition.

Anderson transitions in Ln1-xSrxCoO3 (Ln=Pr or Nd)

Electrical conductivity measurements show that Ln1-xSrxCoO3, (Ln = Pr or Nd) undergoes a non-metal-metal transition when x-0 3. The d.c. conductivity of compositions with 0

Role of cell attachment in leaching of chalcopyrite mineral by Thiobacillus ferrooxidans

Experiments on the leaching of copper from chalcopyrite mineral by the bacterium Thiobacillus ferrooxidans show that, in the presence of adequate amounts of sulphide, iron-grown bacteria preferentially oxidise sulphur in the ore (through direct attachment) rather than ferrous sulphate in solution. At 20% pulp density, the leaching initially takes place by a predominantly direct mechanism. The cell density in the liquid phase increases, but the Fe2+ is not oxidised. However, in the later stages when less solid substrate is available and the cell density becomes very high, the bacteria start oxidising Fe2+ in the liquid phase, thus contributing to the indirect mechanism of leaching. Contrary to expectations, the rate of leaching increased with increasing particle size in spite of the decreasing specific surface area. This has been found to be due to increasing attachment efficiency with increase in particle size.

Tendency to promote ferroelectric distortion in Pr-modified PbTiO3

Structural, microstructural, and dielectric studies have been carried out on Pr-modified PbTiO3. A comparative analysis with La-modified PbTiO3 suggests that for chemical modification by same amount, the Pr-modified system has larger tetragonal strain and Curie point. No clear feature of relaxor ferroelectric state is observed for Pr concentration as high as x=0.35, suggesting that Pr modification is less effective, as compared to La-modification, in inducing a relaxor ferroelectric state. Results suggest that inspite of increased chemical disorder, Pr modification partly tends to restore the ferroelectric distortion of the lattice through partial occupancy of the Pr4+ ions on the Ti4+ sites.

Chelating and bridging diphosphinoamine (PPh2)(2)N(Pr-i) complexes of copper(I)

The ligand bis(diphenylphosphino) isopropylamine (dppipa) has been shown to be a versatile ligand sporting different coordination modes and geometries dictated by copper(I). Most of the molecular structures were confirmed by X-ray crystallography. It is found in a chelating mode, in a monomeric complex when the ligand to copper ratio is 2:1. A tetrameric complex is formed when low ratios of ligand to metal (1: 2) were used. But with increasing ratios of ligand to metal (1: 1 and 2: 1), a trimer or a dimer was obtained depending on the crystallization conditions. Variable temperature P-31{H-1} NMR spectra of these complexes in solution showed that the Cu-P bond was labile and the highly strained 4-membered structure chelate found in the solid state readily converted to a bridged structures. On the other hand, complexes with the ligand in a bridging mode in the solid state did not form chelated structures in solution. The effect of adding tetra-alkylammonium salts to solutions of various complexes of dppipa were probed by P-31{H-1} NMR and revealed the effect of counter ions on the stability of complexes in solution. (C) 2008 Elsevier B.V. All rights reserved.

Microbially Induced Mineral Beneficiation

The divergent role of microbes in the field of mineral processing starting from mining and beneficiation to efficient waste disposal has been well recognized now. The roles of various microorganisms and bioreagents in the beneficiation of minerals are illustrated in this paper. Various types of microorganisms useful in bringing about selective flotation and flocculation of various oxide and sulfide minerals are illustrated. Interfacial phenomena governing microbe-mineral interactions are discussed with reference to bacterial cell wall architecture, cell surface hydrophobicity, electrokinetic data, and adsorption behavior on various minerals. Applications of microbially induced mineral beneficiation are demonstrated with respect to beneficiation of iron ores, bauxite, limestone, and complex multimetal sulfides.

Adhesion of Acidithiobacillus ferrooxidans to mineral surfaces

Direct contact mechanism in bioleaching implies prior mineral adhesion of Acidithiobacillus ferrooxidans and subsequent enzymatic attack.Prior bacterial adaptation to sulfide mineral substrates influences bacterial ferrous ion oxidation rates. It is highly beneficial to understand major biooxidation mechanisms with reference to solution- and mineral-grown cells in order to optimize bioleaching reactions. For A. ferrooxidans grown in the presence of solid substrates such as sulfur, pyrite and chalcopyrite, bacterial adhesion is required for its enzymatic machinery to come into close contact for mineral dissolution.But when grown in solution substrate such as ferrous ions and thiosulfate, such an adhesion machinery is not required for substrate utilization. Proteinaceous compounds were observed on the surface of sulfur-grown cells. Such an induction of relatively hydrophobic proteins and down regulation of exposed polysaccharides leads to changes in cell surface chemistry. Sulfur-grown and pyrite- and chalcopyrite-grown bacterial cells were found to be more efficient in the bioleaching of chalcopyrite than those grown in the presence of ferrous ions and thiosulfate. (C) 2010 Elsevier B.V. All rights reserved.

New family of thallium cuprate superconductors not containing calcium or barium: TlSrn+1−xLnxCunO2n+3+δ (Ln=La, Pr, or Nd)

The first two members of the new TlSrn+1−xLnxCunO2n+3+δ (Ln=La, Pr, or Nd) series of superconducting cuprates possessing 1021 and 1122 type structures are described. The n=1 (1021) members with Tcs around 40 K have electrons or holes as the majority charge carriers depending on x. The n=2 (1122) cuprate (Ln=Pr or Nd) shows a Tc in the 80–90 K range.

Am unexpected entry into the silver(I) chemistry of diphosphazane ligands: Crystal and molecular structures of [Ag{Ph2PN(Pr-i)PPh2}(CF3SO3)](2), [Ag{Ph2PN(Pr-i)PPh(OC6H3Me2-2,6)}(2)]PF6, and [Ag-3(mu-Cl)(2){Ph2PN(R)PPh2}(3)]PF6 (R = H, Pr-i)

Mononuclear, binuclear and trinuclear silver(l) complexes were obtained unexpectedly while probing the reactivity of diphosphazane ligands of the type X2PN(Pr-i)PXY towards the ruthenium-based precursor Ru(bipy)(2)Cl-2 center dot 2H(2)O, in the presence of a silver salt as a chloride scavenger. Subsequently, the reactions of AgX [X = Cl, NO3 or CF3SO3] with Ph2PN(R)PPh(Y) [R = H, Y = Ph; R = Pr-i, Y = Ph or OC6H3Me2-2,6] in a 1: 1 or 1:2 molar ratio have been investigated. Mononuclear or binuclear Ag(I) complexes containing either chelating or bridging diphosphazane ligands are obtained. Trinuclear silver(l) complexes are accessible by the treatment of diphosphazane ligands, Ph2PN(R)PPh2 [R = H, Pr-i] with AgCl using piperidine as the solvent. In the presence of a suitable chloride donor species, the mononuclear and binuclear complexes of Ph2PN(Pr-i)PPh2 are transformed slowly to the trinuclear complex [Ag-3(mu-Cl)(2){Ph2PN(Pr-i)PPh2}(3)]X, over a period 20 h. The structures of representative complexes have been confirmed by X-ray crystallography and the salient structural features are discussed

Surface Chemistry of Thiobacillus ferrooxidans Relevant to Adhesion on Mineral Surfaces

Thiobacillus ferrooxidans cells grown on sulfur, pyrite, and chalcopyrite exhibit greater hydrophobicity than ferrous ion-grown cells. The isoelectric points of sulfur-, pyrite-, and chalcopyrite-grown cells were observed to be at a pH higher than that for ferrous ion-grown cells. Microbe-mineral interactions result in change in the surface chemistry of the organism as well as that of the minerals with which it has interacted. Sulfur, pyrite, and chalcopyrite after interaction with T. ferrooxidans exhibited a significant shift in their isoelectric points from the initial values exhibited by uninteracted minerals. With antibodies raised against sulfur-grown T. ferrooxidans, pyrite- and chalcopyrite-grown cells showed immunoreactivity, whereas ferrous ion-grown cells failed to do so. Fourier transform infrared spectroscopy of sulfur-grown cells suggested that a proteinaceous new cell surface appendage synthesized in mineral-grown cells brings about adhesion to the solid mineral substrates. Such an appendage was found to be absent in ferrous ion-grown cells as it is not required during growth in liquid substrates.