D.E. Ralph

The resilience and versatility of acidophiles that contribute to the bio‐assisted extraction of metals from mineral sulphides

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.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.

Dynamic redox potential measurement for determining the ferric leach kinetics of pyrite

The bioleaching of pyrite has been found to occur via an indirect mechansim. Ferric iron leaches the pyrite, and is reduced to ferrous iron. Bacteria such as Thiobacillus ferrooxidans oxidise the ferrous iron to ferric iron, thus maintaining a high redox potential. The effect of the redox potential on the ferric leach rate was investigated by developing an experimental technique where dynamic redox potential measurements were used to study the kinetics of the sub process. The ferric leach rate of pyrite was found to be of the order of 3 × 10−7 moles pyrite per mole pyrite per second, which is of the same order of magnitude as rates reported for the bioleaching of pyrite over similar ranges of redox potential. The rate decreased as the redox potential decreased, in what appeared to be a Butler-Volmer-like manner. This, along with the observation that there was no significant effect of the total iron concentration, suggested the likelihood of an electrochemical mechanism being operative, with charge transfer at the pyrite surface being rate limiting.

Dissolution kinetics of spent petroleum catalyst using sulfur oxidizing acidophilic microorganisms

Bioleaching studies of spent petroleum catalyst were carried out using sulfur oxidizing, Acidithiobacillus species. Leaching studies were carried out in two-stage, in the first stage bacteria were grown and culture filtrate was used in the second stage for leaching purpose. XRD analysis of spent petroleum catalyst showed oxides of V, Fe and Al and sulfides of Mo and Ni. The leaching kinetics followed dual rate, initial faster followed by slower rate and equilibrium could be achieved within 7 days. The leaching rate of Ni and V were high compared to Mo. The low Mo leaching rate may be either due to formation of impervious sulfur layer or refractoriness of sulfides or both. The leaching kinetics followed 1st order rate. Using leaching kinetics, rate equations for dissolution process for different metal ions were evaluated. The rate determining step observed to be pore diffusion controlled.

Pyrite surfaces after bio-leaching : a mechanism for bio-oxidation

A pyrite mineral surface was exposed to a mixed culture of the lithotrophic bacteria Thiobacillus ferrooxidans (Tf). The surface structure of this sample was compared to surfaces exposed to uninoculated solutions of either sulphuric acid or ferric and ferrous sulfate dissolved in sulfuric acid solution at equivalent concentrations as the inoculated solution. All surfaces were examined using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). A chemical profile of the surfaces, as a function of depth, was obtained by surface ablation. The colonised surface produced an oxidised phase extending to a depth of more than 4 μm. A carbonaceous phase was not observed within the oxide layer. No oxide layers of significant depth were observed for samples exposed to uninoculated solutions. The importance of the sessile cells in bio-oxidation of pyrite is demonstrated and a qualitative model is proposed.

Tricyclic sesquiterpenes from Eremophila georgei

Abstract The structures of three new tricyclic sesquiterpenes from Eremophila georgei are described. The absolute stereochemistry of these sesquiterpenes is shown to be antipodal to that of the zizane sesquiterpenes of vetiver oil.

The role of bacteria in well clogging

The effect of ochreous sludge from blocked irrigation bores on the oxidation rate of soluble Fe(II) was studied. Solutions of Fe(II) at an initial concentrations of 12-15 ppm were held at 19°C under an oxygen partial pressure of ca 1.4% and the decline in Fe(II) concentration observed. Solutions were buffered with 2-(N-morpholino) ethanesulfonic acid (MES) at pH values of 5.8, 6.0, 6.3 and 6.5. Sterile flasks showed agreement with the expected 1st order behaviour (with respect to [Fe(II)]) while flasks inoculated with ochreous sludge deviated significantly from this pattern. Rates of Fe(II) oxidation were significantly enhanced in the inoculated flasks with the greatest increase observed at pH 5.8. The effect of ochreous sludge from blocked irrigation bores on the oxidation rate of soluble Fe(II) was studied. Solutions of Fe(II) at an initial concentrations of 12-15 ppm were held at 19 °C under an oxygen partial pressure of ca 1.4% and the decline in Fe(II) concentration observed. Solutions were buffered with 2-(N-morpholino) ethanesulfonic acid (MES) at pH values of 5.8, 6.0, 6.3 and 6.5. Sterile flasks showed agreement with the expected 1st order behaviour (with respect to [Fe(II)]) while flasks inoculated with ochreous sludge deviated significantly from this pattern. Rates of Fe(II) oxidation were significantly enhanced in the inoculated flasks with the greatest increase observed at pH 5.8.

Nanofiltration of Mine Water: Impact of Feed pH and Membrane Charge on Resource Recovery and Water Discharge

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.

Synthesis and Characterization of Li(Co0.5Ni0.5)PO4 Cathode for Li-Ion Aqueous Battery Applications

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.

The shear degradation of high-molecular-weight flocculant solutions

Solutions of polyacrylamide and poly(acrylamide-co-sodium acrylate) flocculants with varying molecular weights were shear degraded under a range of mixing conditions. The viscosity and flocculant activity of the solutions generally decreased with time to limiting values dependent on the mixing intensity. The activity of 10 and 20% anionic flocculants displayed quite different trends from those for nonionic flocculants of equivalent molecular weight, with less apparent degradation due to mixing, particularly at low dosages. However, viscosity measurements on sheared solutions diluted with a salt buffer suggest that nonionic and anionic flocculants with similar initial molecular weights were degraded to the same degree. Multiangle laser light-scattering measurements were used to confirm that the shearing process resulted in a reduction in molecular weight which was independent of anionic character. The apparent shear resistance of anionic flocculation mechanisms for the nonionic and anionic flocculants.

Structural characteristics of olivine Li(Mg0.5Ni0.5)PO4 via TEM analysis

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.