The mechanism for the substitution reactions of halopentaaquachromium(III) complexes in the series, [CrX(H2O)(5)](2+), where X = F-, Cl-, Br-, or I- have been investigated using density functional theory. Several different mechanistic pathways were explored including associative interchange (I-a), dissociative (D) and the associatively activated dissociation mechanisms (D-a). The lowest overall activation enthalpy (Delta H-double dagger) obtained for the fluoride system is for the I pathway, with immediate proton abstraction leading to the formation of HF and the conjugate base. For the chloride, bromide and iodide systems the Da pathway has the lowest Delta H-double dagger values. Activation enthalpies determined at the PBE0/cc-pVDZ level, in aqueous solution (PCM), are in excellent agreement with the experimental results (MAD is 1.0 kJ mol(-1)). Reaction profiles were analyzed in terms of activation volumes to explain the observed trends. (C) 2015 Elsevier B.V. All rights reserved.

The influence of nitrate on batch cultures of selected Acidithiobacillus, Sulfobacillus, Acidianus, Sulfolobus and Metallosphaera species capable of utilising iron(II) and reduced sulfur substrates was examined. Nitrate was added to cultures in media containing both ferrous ions and tetrathionate. The presence of nitrate resulted in decreased planktonic cell numbers, increased microbial lag times and lower ferrous ion and tetrathionate utilisation rates. These results varied with nitrate concentration, species and adaptive history. Based on the results of batch culture tests, nitrate was added to chalcopyrite concentrate bioleaching experiments to control the redox potential. Bacteria in bioleaching tests at 30 and 45°C exhibited adaptation to nitrate resulting in high redox potentials. However, when archaea were used in bioleaching tests at 60°C, ferrous ion oxidation was suppressed in the presence of nitrate. At a nitrate concentration of 20–30mM, a redox potential of 430–460mV (vs Ag/AgCl) was maintained during the 10week experiment. At this redox potential copper extraction was increased by 20% compared to a culture without nitrate, potentially offering a method of redox control for high-temperature stirred-tank bioleaching with archaea.

Two nanofiltration membranes, a Dow NF 270 polyamide thin film and a TriSep TS 80 polyamide thin film, were investigated for their retention of ionic species when filtering mine influenced water streams at a range of acidic pH values. The functional iso-electric point of the membranes, characterized by changes in retention over a small pH range, were examined by filtering solutions of sodium sulphate. Both membranes showed changes in retention at pH 3, suggesting a zero net charge on the membranes at this pH. Copper mine drainage and synthetic solutions of mine influenced water were filtered using the same membranes. These solutions were characterized by pH values within 2 and 5, thus crossing the iso-electric point of both membranes. Retention of cations was maximized when the feed solution pH was less than the iso-electric point of the membrane. In these conditions, the membrane has a net positive charge, reducing the transmission rate of cations. From the recoveries of a range of cations, the suitability of nanofiltration was discussed relative to the compliance with mine water discharge criteria and the recovery of valuable commodity metals. The nanofiltration process was demonstrated to offer advantages in metal recovery from mine waste streams, concomitantly enabling discharge criteria for the filtrate disposal to be met.

Heterogeneous bacterial sulphur systems are inherently complicated. However, developing an understanding of the influence of environmental factors such as pH,Iand PCO2is important for a number of fields. Examples of these include minimising acid mine drainage and maximising metal recovery from low-grade sulphide minerals. Measuring the effect of these factors on the extent and rate of sulphur (S) oxidation is complicated by the presence and nature of solid phase elemental S. The rate and extent of S oxidation can be determined indirectly via the reaction product, H2SO4, which was quantified using pH measurements in this study. The method was critically dependent on the quality of pH data but proved effective in providing rate constants for the catalysed S oxidation reaction and yield (biomass/substrate) estimates in the range pH > 1.5. IncreasingIover the range 0.176 0.367 mol L-1decreased bacterial cell yields but increased the rate of sulphur oxidation significantly. Partial pressures of CO2in the range of 0.039 1.18% v/v produced no significant effect on the rates of S oxidation or bacterial cell yields. Bacterial cell yields were not affected in the pH range 1.5 2.5, however the rate of S oxidation increased significantly from pH 2.0 2.5. In the range pH < 1.5 the batch cultures progressed and although no reliable rate data was recorded cell yields decreased from 7.43 to 2.05 (× 1012cells mol-1) at pH 1.5 to 1.0 respectively.

When presented with ferrous ions and tetrathionate in growth media, individual archaeal species, Acidianus brierleyi, Metallosphaera hakonensis and Sulfolobus metallicus, exhibited different patterns of substrate utilisation and cell growth. Total cell numbers for A. brierleyi were about 60% of those for M. hakonensis and S. metallicus after complete substrate utilisation, and specific growth rates were affected by substrate concentration and cell growth history. High iron(II) concentrations inhibited S. metallicus growth. In relation to mixed microbial communities in high-temperature bioleaching reactors, the results are consistent with the hypothesis that specific growth rates of different species grown on different substrates strongly influence community structure. The combination of T-RFLP with substrate analysis and cell counts is a valuable analytical tool for the discrimination and semi-quantitative estimation of species in mixed cultures that can be used to gain better understanding of community structures and population dynamics in complex bioleaching systems.

A detailed electrochemical study of cubic α-Fe2O3 microparticles has been carried out in strong aqueous LiOH electrolyte. The α-Fe2O3 was synthesized hydrothermally and investigated in the form of an electrochemical cell using an alkaline solution, ‘α-Fe2O3|LiOH (saturated), ZnSO4 (1 M)|Zn’. In this cell, the α-Fe2O3 cathode showed a reversible capacity of ca 220 mAh/g within cut-off voltages of 0 and 1.5 V under the constant current of 0.3 mA. The electrochemical performance was attributed to the reversible formation of both proton and lithium intercalation products (FeOOH and LiFeO2) detected in the cathode material. Interestingly, at a lower discharge current of 0.1 mA, some of the hematite phase was reduced to metallic iron after yielding 336 mAh/g. The various possible electro-reduction reactions, which have direct electro-hydrometallurgical implications, are analyzed and discussed.

Ferrous sulfate was added to batch cultures ofSulfobacillus (Sb.) acidophilus,Sb. thermosulfidooxidansandSb. sibiricusduring growth on tetrathionate. Soluble ferrous ion and polythionate concentrations were used as a measure of substrate utilisation.Sb. thermosulfidooxidansswitched from utilising polythionates to exclusively oxidising ferrous ions, only then oxidising the remainder of the polythionates.Sb. sibiricusandSb. acidophilusdid not cease polythionate oxidation but utilised both substrates concurrently after ferrous ion addition. None of the cultures tested exhibited preferential polythionate utilisation, even though they were utilising polythionate prior to the addition of ferrous ions.

Energy storage is always an important issue and will be far more important in the future than at any time in the past. Storing large amounts of electricity cheaply, something that will be essential for making renewable energy the primary source, rather than just the supplemental source it is a current challenge. Such storage will make it practical to store energy from wind turbines and solar farms for later use. To achieve these, sodium-based energy storage systems have been identified as a key technology for the future as the lithium technology is more expensive. Existing sodium technologies work at high temperature, where molten sodium and molten sulphur are the anode and cathode respectively and they have never found widespread use. An alternative strategic approach used in this study is water-based sodium-ion intercalation cell (MnO2|NaOH|NaCo1/3Ni1/3Mn1/3PO4) for a promising low temperature energy storage device.

Membrane technology is an established strategy to treat acid mine drainage (AMD). Nanofiltration offers economical advantages over reverse osmosis, and allows for concentrating and recovering valuable metals from AMD waters. Understanding the relationship between AMD pH and membrane charge is required to ensure compliance with stringent discharge criteria, and to maximize metal recovery for profit. The membrane iso-electric point (IEP) is a significant parameter in the rejection of ions. Maximum metal recovery was observed when the pH was lower than IEP. Ongoing research is exploring the opportunity to customize the position of the IEP by membrane surface modification.

In batch cultures, the presence of nitrate inhibited iron(II) oxidation by iron(II)- or tetrathionate-adapted Acidianus (A.) brierleyi and Sulfolobus (S.) metallicus cells and tetrathionate oxidation by iron(II)-adapted A. brierleyi cells. Tetrathionate-adapted cell lines of A. brierleyi and S. metallicus oxidised tetrathionate in the presence of up to 40 mM nitrate but cell numbers were lower than those in uncontaminated tests. The results of the bioleaching tests indicated a possible window of enhanced copper extraction in the presence of 20-30 mM nitrate that might be exploited in tank bioleaching. The build up of nitrate above 40 mM in bioleaching solutions must be avoided

The structural characteristics of olivine-type lithium orthophosphate Li(Mg0.5Ni0.5)PO4 synthesized via solid-state reaction have been studied using X-ray diffraction, ion beam technique, scanning electron microscopy, infrared spectroscopy, transmission electron microscopy and energy dispersive X-ray analysis. The parent LiNiPO4 compound can be synthesized in olivine structure without any evidence of secondary phases as impurities. The structural quality of the parent LiNiPO4 in the absence of secondary component phases resulted in the formation of hexagonal closed packed structure. The olivine analogue compound containing mixed M (M = Mg, Ni) cations, Li(Mg0.5Ni0.5)PO4 contained Li3PO4 as a second phase upon synthesis, however a carbothermal reduction method produced a single-phase compound. The redox behaviour of carbon-coated Li(Mg0.5Ni0.5)PO4 cathode in aqueous lithium hydroxide as the electrolyte showed reversible lithium intercalation.

Continuous growth of an acidophilic, chemolithotrophic bacterial culture in minimal iron media, was investigated over a range of TDS values. The specific cell parameters, iron oxidation rates, growth rates and observed yields at fixed solution potentials were compared over a range of TDS values but with the same total iron concentrations. By perturbing the steady state at any set point it was possible to estimate the population of sessile cells and calculate values for the specific cell parameters. The TDS was increased by addition of Na2SO4 which produced no toxic effects and allowed a flourishing culture. There was however a significant inhibition of the specific iron oxidation rates which were reduced by more than 75% by the increase in TDS from 0.05 to 0.4M. A framework for understanding the observed result, based on the ionic strength (I) rather than TDS, is suggested. The oxidation of iron is an important sub-process in hydrometallurgy and TDS values of 0.4M are modest from an operational perspective so these results may point to potential problems during long term operation where TDS can accumulate without otherwise interfering.

Cubic α-Fe2O3 (hematite) microparticles (side lengths=0.3–1.3μm) have been synthesized using glycine and ferric chloride via a simple one-step hydrothermal reaction. Their morphological, mineralogical and surface properties have been determined using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). XRD analysis indicated that the synthesized α-Fe2O3 microparticles were minerallogically pure. An increase in hydrothermal reaction duration from 10 to 24h increased the atomic percentages of α-Fe2O3 on the surface of the microparticles by almost 8%. The mechanism concerning reactions of species to produce this microparticles precipitate was elucidated based on thermodynamics and ionic equilibrium aspects. In the electrochemical analysis, the synthesized α-Fe2O3 microparticles (as cathode material) exhibit an approximate charge capacity of 160mAh/g and excellent coulombic efficiency of 94%.

Acidithiobacillus caldus (DSM 8584) grew aerobically in minimal medium at 45 degrees C with potassium tetrathionate as the sole energy source. Oxidation of tetrathionate during batch culture involved the production of sulfite, thiosulfate, penta- and hexathionate which were then consumed after the tetrathionate was exhausted. Average growth yields over the batch were 3.5 g(dry wt.) mol(S(4)O(6))(-1), somewhat less than yields reported for continuous growth on the same substrate. Thiosulfate was unstable under sterile culture conditions and reacted spontaneously to give tetra-, penta- and hexathionate. It is suggested that the occurrence of polythionates during growth of A. caldus on tetrathionate is due to formation of thiosulfate as the first step in tetrathionate oxidation. Observed growth yields were compared with a thermodynamic framework which suggested a growth efficiency of ca. 10%. The pattern of growth yield and thermodynamic analysis suggest the formation of elemental sulfur although this was not observed. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Considering the safety, cost and low ohmic resistance issues with respect to the non-aqueous electrolytes that are generally used in rechargeable lithium ion batteries, aqueous electrolytes attract wide interest. A traditional Zn-MnO2 battery in which potassium hydroxide (KOH) has been replaced with a lithium hydroxide (LiOH) electrolyte is discussed. As lithium intercalation materials are of special interest as cathode in rechargeable batteries, the new concept has been extended to use lithium nickel phosphate as cathode for aqueous rechargeable batteries. Here, we show reversible extraction and insertion of lithium from and into olivine LiNiPO4 in aqueous solutions. These cells are found to be cheap, rechargeable and safe. The unique sol-gel synthesis has been used to synthesize LiNiPO4 which has been characterized in order to evaluate a new potential cathode for aqueous rechargeable batteries.

Olivine-type lithium orthophosphate Li(Co0.5Ni0.5)PO4 was synthesized in a solid state reaction at 800 degrees C in air. Infra-red spectroscopy, x-ray and neutron powder diffraction were used to characterize the as-prepared compound and its electro-oxidized analogue. Rietveld analysis was used to illustrate that the synthesized compound is isostructural with LiNiPO4 and LiCoPO4 with lattice parameters larger than the former and smaller than the latter. The Rietveld-refined Ni:Co ratio was found to be 0.498(4):0.502(4) and no evidence for long-range Ni: Co ordering or mixed Li/Ni/Co cation sites was found. The electro-oxidised electrode showed a mixture of two phases i.e. parent Li(Co0.5Ni0.5)PO4 and lithium extracted Li1-x(Co0.5Ni0.5)PO4 suggesting a delithiation process in aqueous electrolytes. Reversible Li transfer between a Li(Co0.5Ni0.5)PO4 electrode and an aqueous LiOH electrolyte was demonstrated. (C) 2011 The Electrochemical Society. [DOI:10.1149/1.3561764] All rights reserved.

In this paper, a brief outline is presented on acidic ferric ion oxidation of mineral sulphides for the extraction of metals in both stirred tank reactors for mineral concentrates and heaps for low-grade ores. The identities and capabilities of the relatively few acidophiles that assist the oxidative processes are summarized and their responses to selected extremes in their growth environments described. Individually, the organisms adapt to the presence of high concentrations of heavy metals and other elements in the bioleaching environment, tolerate a wide range of acidities and can recover from prolonged exposure to temperatures significantly above their preferred temperatures for growth. However, the presence of chloride in their acidic environment presents a significant physiological challenge. Species that exhibit a chemotactic response and attachment to sulphide surfaces, where they can create their own micro-environments, would be favoured in both heap bioreactors with low availability of energy substrates and physically aggressive, agitated continuous stirred-tank reactor environments treating concentrates.

Concurrent ferrous ion and tetrathionate utilisation by Sulfobacillus acidophilus, Sb. thermosulfidooxidans, Sb. thermotolerans, and Sb. sibiricus grown separately in batch culture in dual-substrate media containing ferrous ion and tetrathionate was investigated. For all species, tetrathionate-adapted cells oxidised both substrates concurrently, achieving at least 20% oxidation of the second substrate before the first substrate was exhausted. Sequential substrate utilisation was observed for iron(II)-adapted cells for three of the four species and all iron(II)-adapted cell lines commenced oxidation of ferrous ions ahead of tetrathionate. Adaptation to iron(II) or tetrathionate of the test species had little impact on subsequent ferrous ion oxidation. However, tetrathionate oxidation was affected by growth history. Compared with their respective tetrathionate-adapted cell lines, cells adapted to iron(II) exhibited either significantly longer lag times and/or longer periods to complete tetrathionate oxidation once it had commenced. Polythionate intermediates measured during tetrathionate oxidation to sulfate included thiosulfate, pentathionate and hexathionate for the four species. The intermediate trithionate was only detected in Sb. thermotolerans cultures.

A novel process was developed using sulfur-oxidizing bacteria to extract metal values like Ni, V and Mo from spent petroleum catalyst. Bacteria were grown in elemental sulfur media for five day and after filtering, the filtrate was used for leaching purpose. Effect of different parameters such as contact time, particle size, pulp density and lixiviant composition were studied to find out the extent of metal leaching during the leaching process. XRD analysis proved the existence of V in oxide form, Ni in sulfide form, Mo both in oxide as well as sulfide forms, and sulfur in elemental state only. In all the cases studied Ni and V showed higher leaching efficiency compared to Mo. The low Mo leaching rate may be either due to formation of impervious sulfur layer or refractoriness of sulfides or both. Leaching kinetics followed dual rate, initial faster followed by slower. Dissolution mechanism was explained on the basis of both surface and pore diffusion rate. The leaching kinetics followed 1st order reaction rate. Finally, multiple linear regression analysis was carried out to compare the observed and calculated leaching percentage values for three metals.

The increase in cell number during a batch culture cycle of iron oxidising bacteria was measured by an optical probe that operated on the principle of light scattering by cells within the optical path. These data together with the redox potential measured in the growth media allowed the parameters of culture activity, specific substrate oxidation and cell replication rates to be determined throughout the cycle. The technique was used to examine the effect of increased ionic strength by the addition of sodium sulfate to minimal iron media. Both the presence of excess sulfate and the potential of the iron couple at the time of inoculation were shown to affect the first half of the batch culture cycle where the potential of the iron couple was less than 0.65 V. Addition of sulfate above the minimal media values did not produce any adverse effects on cell activity when the potential of the iron couple was greater than 0.65 V. The complexation or inhibition of the iron-centred components of the electron transport chain is proposed to explain the observed specific substrate oxidation rates. The yield of cells produced from a given amount of substrate was not significantly affected by sulfate addition. Rates of substrate utilisation and yield were directly compared to values obtained by other workers. (C) 2009 Elsevier B.V. All rights reserved.