The formation of sulfur is predicted by the current understanding of the mechanisms involved in mineral sulfide oxidation and observed in studies of the leaching products that accumulate on the surface of the mineral. Sulfur oxidising bacteria can exploit this energy source and can remove a potentially 'rate-limiting' diffusion barrier. In this study on the activity of sulfur oxidising bacteria cultured on mixed solid sulfur allotropes, it was observed that a heterogeneous culture preferentially oxidised the orthorhombic allotrope and no significant growth on the polymeric allotrope could be demonstrated.

ÔØ Å ÒÙ× Ö ÔØSpecific iron oxidation and cell growth rates of bacteria in batch culture This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT ABSTRACTThe increase in cell number during a batch culture cycle of iron oxidizing 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 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.

ÔØ Å ÒÙ× Ö ÔØThis is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT AbstractContinuous 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 Na 2 SO 4 which produced no toxic effects and allowed a flourishing culture. There was however significant inhibition of the specific iron oxidation rates which were reduced by more than 75% by the increase in TDS from 0.05 to 0.4 M. 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 0.4 M 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.Keywords: Iron oxidation, Chemolithotrophic bacteria, Inhibition, Total dissolved solids. IntroductionHydrometallurgical processes are concerned with iron chemistry because of the ubiquitous distribution of iron in minerals. Some control over the presence, concentration and oxidation state of iron is almost always required at some point in a process flow sheet. The oxidation of iron is the most important step in that control because the ferric state (Fe +3 ) is the immediate precursor to forming solid iron phases which allow for its removal from the process circuit. It is often a problematic step because although reaction 1 is spontaneous, the rate is slow and becomes slower as the solution becomes more acidic (Lowson, 1982). The Fe +3 state is also required for the oxidation of some minerals where the target metal (M) is released as the solid is oxidatively dissolved (Eq. 2). The iron Fe +3 /Fe +2 couple in these cases du Plessis et al., 2011; Johnson 1998, 2000;Brock and Gustafson, 1976).Rapid oxidation of Fe +2 can be achieved by raising the pH or by addition of oxidising agents, peroxide (H 2 O 2 ) for example. Raising the temperature of the process solution also increases the rate of reaction 1. It's also possible to catalyse reaction 1 by the growth of chemolithotrophic cells which can be achieved by providing the solution with small amoun...

Abstract. Heterogeneous bacterial sulphur systems are inherently complicated. However, developing an understanding of the influence of environmental factors such as pH, I and P CO2 is 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 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, H 2 SO 4 , 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. Increasing I over the range 0.176 -0.367 mol L -1 decreased bacterial cell yields but increased the rate of sulphur oxidation significantly. Partial pressures of CO 2 in 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 pH data were recorded, cell yields decreased from 7.43 × 10 12 to 2.05 × 10 12 cells mol -1 at pH 1.5 to1.0 respectively.