Solid Elemental Sulfur Research Articles

Quantifying sulfidization and non-sulfidization in long-term in-situ microbial colonized As(V)-ferrihydrite coated sand columns: Insights into As mobility

Sulfide-induced reduction (sulfidization) of arsenic (As)-bearing Fe(III) (oxyhydro)oxides may lead to As mobilization in aquifer systems. However, little is known about the relative contributions of sulfidization and non-sulfidization of Fe(III) (oxyhydro)oxides reduction to As mobilization. To address this issue, high As groundwater with low sulfide (LS) and high sulfide (HS) concentrations were pumped through As(V)-bearing ferrihydrite-coated sand columns (LS-column and HS-column, respectively) being settled within wells in the western Hetao Basin, China. Sulfidization of As(V)-bearing ferrihydrite was evidenced by the increase in dissolved Fe(II) and the presence of solid Fe(II) and elemental sulfur (S0) in both the columns. A conceptual model was built using accumulated S0 and Fe(II) produced in the columns to calculate the proportions of sulfidization-induced Fe(III) (oxyhydro)oxide reduction and non-sulfidization-induced Fe(III) (oxyhydro)oxide reduction. Fe(III) reduction via sulfidization occurred preferentially in the inlet ends (LS-column, 31 %; HS-column, 86 %), while Fe(III) reduction via non-sulfidization processes predominated in the outlet ends (LS-column, 96 %; HS-column, 86 %), and was attributed to the metabolism of genera associated with Fe(III) reduction (including Shewanella, Ferribacterium, and Desulfuromonas). Arsenic was mobilized in the columns via sulfidization and non-sulfidization processes. More As was released from the solid of the HS-column than that of the LS-column due to the higher intensity of sulfidization in the presence of higher concentrations of dissolved S(-II). Overall, this study highlights the sulfidization of As-bearing Fe(III) (oxyhydro)oxides as an important As-mobilizing pathway in complex As-Fe-S bio-hydrogeochemical networks.

Theoretical research on reaction of solid sulfur allotropes with elemental mercury

Element sulfur has proven to be active material for hazardous elemental mercury (Hg0) removal. However, the underlying mechanism of elemental sulfur reacting with Hg0 was still unclear. Generally, solid elemental sulfur exists mainly composed of crown-shaped S8 molecules and traces of S6, S7, and S9 molecules. This research employed quantum chemical calculations and electronic wavefunction analysis to investigate the reaction between branched and cyclic Sn isomers (n = 6–9) with Hg0 at the molecular level. Thermodynamic data and kinetics were also computed. It was found that Hg0 react with branched Sn isomers would proceed spontaneously with heat release by analyzing reaction Gibbs free energies and enthalpies. Reaction rate constants of branched Sn molecules are several orders of magnitude higher than those of cyclic Sn molecules. Moreover, the electronic wavefunction analysis was conducted. The Mayer bond order along the reaction pathway could characterize Hg-S and S-S bonds breaking and formation quantitively. Localized molecular orbitals isosurface maps reflect Hg-S bonds show typical σ bond characteristics in the products. Localized orbital locator color-filled maps reveal electrons begin to concentrate in the region between Hg and S atoms as reactions proceeding forward. In summary, this research would help develop sulfur contained adsorbents with superior Hg0 removal performance in the future.

NEW TECHNOLOGY OF COMPLEX PROCESSING OF PYRITE CONCENTRATE

The paper discusses the benefits of processing pyrite concentrates using a new technology that uses roasting in an atmosphere of water vapor. There are various technologies for the processing of pyrite concentrates containing precious and non-ferrous metals, Au, Ag, Cu and other elements. These technologies often have such disadvantages as undesirable release of sulfur dioxide into the environment, incomplete extraction of useful metals. The optimal modes of technological processes, such as firing temperature, the ratio of steam and solid phases, the duration of the process, the size of the particles, etc. are given. Special attention was paid to the desulfurization of pyrite concentrate with the prevention of the release of sulfur dioxide into the atmosphere, and its transfer into the phase of solid elemental sulfur or sodium sulfide. The developed technology makes it possible to obtain an iron cinder, and with subsequent magnetic separation and reduction in a hydrogen atmosphere to obtain iron in the form of a sponge–a high-quality product for smelting steel or cast iron. The proposed technology provides a closed loop cycle and waste-free with minimal environmental pollution. The technology was tested in a pilot laboratory setup using concentrates from the Kajaran deposit inArmenia.

The Relationship between Metabolic Pathways of Bacteria and Pyrrhotite Bioleaching Behavior

The effect of Sulfobacillus thermosulfidooxidans, cultured respectively in the substratum containing ferrous ion or solid elemental sulfur in a long term, on the leaching behavior of pyrrhotite was revealed through leaching test and surface analysis of pyrrhotite leaching residues using XRD and SEM. It was demonstrated that there was significant difference in growth characteristic of S. thermosulfidooxidans, the leaching behavior and surface products of pyrrhotite when pyrrhotite bioleaching was conducted using S. thermosulfidooxidans cultured in different mediums, and it suggested that the difference was chiefly due to different energy metabolism pathways. The pyrrhotite leaching behavior using S. thermosulfidooxidans grown on ferrous ion in a long term was similar to that in the sterile acidic system, and only leaching yield was slightly improved. This was attributed to the ability to oxidize sulfur of S. thermosulfidooxidans was weakened and thus the effect of the generated sulfur could not be eliminated, which leads to low iron extraction and low S. thermosulfidooxidans reproduced ability for lack of growth energy. In the case of S. thermosulfidooxidans cultured in medium containing sulfur, The ability to oxidize sulfur was enhanced, the bacterium grew rapidly in the mid-term of leaching, which weakened the suppressing effect of sulfur film and improved significantly pyrrhotite leaching. However, a large number of jarosite was generated owing to the accumulation of ferric ions with the bioleaching processing, and the formed wrapping layer by jarosite and minor sulfur on mineral surface suppressed further leaching of pyrrhotite.

Elemental sulfur in northern South China Sea sediments and its significance

Elemental sulfur (ES) is one of the intermediates in the inorganic sulfur cycle and thus plays a key role in the fractionation of stable sulfur isotopes in different reservoirs and the marine environment. In this study, solid ES is discovered in sediments near the Jiulong Methane Reef in the northern South China Sea by scanning electron microscopy and Raman spectroscopy. Combining the morphology and distribution of ES, pyrite concentrations, and sulfur isotopes, we conclude that: (1) solid ES coexists with pyrite microcrystals and sulfide (oxyhydr)oxides as well as clay minerals, and they are mainly distributed on the surface of mineral aggregates; (2) ES mainly occurs within and near the sulfate-methane transition zone (SMTZ) despite little morphological diversity; (3) ES formation might be related to hydrogen sulfide oxidation and is therefore linked with fluctuations in the SMTZ. Within the SMTZ, hydrogen sulfide is produced and pyrite precipitates because of enhanced anaerobic oxidation of methane coupled with dissimilatory sulfate reduction. This enhances the efficiency of the inorganic sulfur cycle and provides favorable conditions for ES formation. The discovery of solid ES in sediments near the Jiulong Methane Reef suggests an important relationship with SMTZ fluctuations that could have implications for the evolution of methane hydrate in the South China Sea.

A large column analog experiment of stable isotope variations during reactive transport: I. A comprehensive model of sulfur cycling and δ34S fractionation

This study demonstrates a mechanistic incorporation of the stable isotopes of sulfur within the CrunchFlow reactive transport code to model the range of microbially-mediated redox processes affecting kinetic isotope fractionation. Previous numerical models of microbially mediated sulfate reduction using Monod-type rate expressions have lacked rigorous coupling of individual sulfur isotopologue rates, with the result that they cannot accurately simulate sulfur isotope fractionation over a wide range of substrate concentrations using a constant fractionation factor. Here, we derive a modified version of the dual-Monod or Michaelis–Menten formulation (Maggi and Riley, 2009, 2010) that successfully captures the behavior of the 32S and 34S isotopes over a broad range from high sulfate and organic carbon availability to substrate limitation using a constant fractionation factor. The new model developments are used to simulate a large-scale column study designed to replicate field scale conditions of an organic carbon (acetate) amended biostimulation experiment at the Old Rifle site in western Colorado. Results demonstrate an initial period of iron reduction that transitions to sulfate reduction, in agreement with field-scale behavior observed at the Old Rifle site. At the height of sulfate reduction, effluent sulfate concentrations decreased to 0.5mM from an influent value of 8.8mM over the 100cm flow path, and thus were enriched in sulfate δ34S from 6.3‰ to 39.5‰. The reactive transport model accurately reproduced the measured enrichment in δ34S of both the reactant (sulfate) and product (sulfide) species of the reduction reaction using a single fractionation factor of 0.987 obtained independently from field-scale measurements. The model also accurately simulated the accumulation and δ34S signature of solid phase elemental sulfur over the duration of the experiment, providing a new tool to predict the isotopic signatures associated with reduced mineral pools. To our knowledge, this is the first rigorous treatment of sulfur isotope fractionation subject to Monod kinetics in a mechanistic reactive transport model that considers the isotopic spatial distribution of both dissolved and solid phase sulfur species during microbially-mediated sulfate reduction.

An Experimental Study on Fracture Conductivity Influenced by Sulfur Deposition

Deposition of solid elemental sulfur may arouse severe damage to the formation and significantly affect the gas deliverability in sour gas reservoirs. As one main measure of stimulation, hydraulic fracturing always ceases to work due to the sulfur deposition in the fractures. To have a better understanding of the failure of fracture conductivity caused by sulfur deposition and learn the degree of fracture conductivity improved by acidification, an experimental was implemented and studied. In this paper, both the sulfur powder and an artificial fractured core were employed to simulate the process of sulfur deposition in the fractures. A further step was made to inject some hydrochloric acid into the blocked fracture caused by sulfur powder. The result showed that the fracture conductivity could be greatly reduced by the sulfur deposition. The fracture conductivity can be decreased by 17%~47% due to sulfur deposition. However, to some degree, acid-fracturing can improve the conductivity of fracture by eroding the surface of fracture. This means the failure of fracture blocked by sulfur deposition can be improved by acidification.

An NPT Monte Carlo Molecular Simulation-Based Approach to Investigate Solid-Vapor Equilibrium: Application to Elemental Sulfur-H2S System

In this work, a method to estimate solid elemental sulfur solubility in pure and gas mixtures using Monte Carlo (MC) molecular simulation is proposed. This method is based on Isobaric-Isothermal (NPT) ensemble and the Widom insertion technique for the gas phase and a continuum model for the solid phase. This method avoids the difficulty of having to deal with high rejection rates that are usually encountered when simulating using Gibbs ensemble. The application of this method is tested with a system made of pure hydrogen sulfide gas (H2S) and solid elemental sulfur. However, this technique may be used for other solid-vapor systems provided the fugacity of the solid phase is known (e.g., through experimental work). Given solid fugacity at the desired pressure and temperature, the mole fraction of the solid dissolved in gas that would be in chemical equilibrium with the solid phase might be obtained. In other words a set of MC molecular simulation experiments is conducted on a single box given the pressure and temperature and for different mole fractions of the solute. The fugacity of the gas mixture is determined using the Widom insertion method and is compared with that predetermined for the solid phase until one finds the mole fraction which achieves the required fugacity. In this work, several examples of MC have been conducted and compared with experimental data. The Lennard-Jones parameters related to the sulfur molecule model (ɛ, σ) have been optimized to achieve better match with the experimental work.

Sulfur metabolism in the extreme acidophile acidithiobacillus caldus.

Given the challenges to life at low pH, an analysis of inorganic sulfur compound (ISC) oxidation was initiated in the chemolithoautotrophic extremophile Acidithiobacillus caldus. A. caldus is able to metabolize elemental sulfur and a broad range of ISCs. It has been implicated in the production of environmentally damaging acidic solutions as well as participating in industrial bioleaching operations where it forms part of microbial consortia used for the recovery of metal ions. Based upon the recently published A. caldus type strain genome sequence, a bioinformatic reconstruction of elemental sulfur and ISC metabolism predicted genes included: sulfide–quinone reductase (sqr), tetrathionate hydrolase (tth), two sox gene clusters potentially involved in thiosulfate oxidation (soxABXYZ), sulfur oxygenase reductase (sor), and various electron transport components. RNA transcript profiles by semi quantitative reverse transcription PCR suggested up-regulation of sox genes in the presence of tetrathionate. Extensive gel based proteomic comparisons of total soluble and membrane enriched protein fractions during growth on elemental sulfur and tetrathionate identified differential protein levels from the two Sox clusters as well as several chaperone and stress proteins up-regulated in the presence of elemental sulfur. Proteomics results also suggested the involvement of heterodisulfide reductase (HdrABC) in A. caldus ISC metabolism. A putative new function of Hdr in acidophiles is discussed. Additional proteomic analysis evaluated protein expression differences between cells grown attached to solid, elemental sulfur versus planktonic cells. This study has provided insights into sulfur metabolism of this acidophilic chemolithotroph and gene expression during attachment to solid elemental sulfur.

Electrochemical sulfide removal and recovery from paper mill anaerobic treatment effluent

Sulfide can be removed from wastewater and recovered as elemental sulfur using an electrochemical process. Recently, we demonstrated this principle of product recovery on synthetic feeds. Here, we present a lab scale electrochemical reactor continuously removing sulfide from the effluent of an anaerobic treatment process operated on paper mill wastewater. The effluent contained 44 ± 7 mg of sulfide-S L −1. Sulfide was reduced to 8 ± 2 mg-S L −1, at a removal rate of 0.845 ± 0.133 kg-S m −3 of total anodic compartment (TAC) d −1. The removed sulfide was recovered (75 ± 4% recovery) as pure concentrated alkaline sulfide/polysulfide solution, from which solid elemental sulfur was obtained. The electrochemical sulfide removal was not affected by different soluble constituents or particulate materials present in the wastewater. However, over time sulfide removal decreased due to biological sulfur reduction using the organics present in the wastewater. Therefore, a periodic switching strategy between anode and cathode was developed. Biofilm formation was avoided as the pH of the cathode solution increased to inhibitory levels during cathodic operation, while still allowing full recovery of the sulfur as end product.

Protocol for Quantitative Detection of Elemental Sulfur and Polysulfide Zero‐Valent Sulfur Distribution in Natural Aquatic Samples

A HPLC‐based protocol has been developed for the determination of zero‐valent sulfur (ZVS) speciation, including solid, colloidal elemental sulfur and individual inorganic polysulfides in natural aquatic samples. The protocol includes four experimental procedures: (1) determination of polysulfide speciation by rapid single‐phase derivatisation with methyl trifluoromethanesulfonate; (2) determination of the sum of polysulfide and colloidal sulfur by reaction with hydrogen cyanide (cyanolysis); (3) determination of total zero‐valent sulfur by treatment with zinc chloride followed by extraction with chloroform; and (4) chromatographic determination of polythionates without sample pre‐treatment. With proper sampling and preservation techniques in the field or on board ship, this combination of methods allowed the quantitative determination of: (a) individual polysulfide species; (b) dispersed colloidal sulfur; (c) dispersed solid elemental sulfur; and (d) tetra‐, penta‐ and hexathionates. With minor modification, the method could be expanded to include other polythionates. Sixteen various wet chemical and liquid chromatographic methods were tested on nine synthetic reference samples (including solid elemental sulfur, colloidal elemental sulfur, inorganic polysulfides and polythionates) to establish the optimal protocol. The protocol was further evaluated by analysing the zero‐valent sulfur content in microbially‐produced sulfur and in sulfur from two natural samples of sulfide‐rich seawater from tidal flats pools of the Wadden Sea (Germany).

Influence of Growth Substrate and Attachment Substratum on EPS and Biofilm Formation by <i>Acidithiobacillus ferrooxidans</i>

Extracellular polymeric substances (EPS) of Acidithiobacillus ferrooxidans and other leaching microorganisms mediate the attachment of cells to pyrite and other minerals. They also play a pivotal role in indirect leaching of base and precious metals via the contact mechanism. The aim of this study is to get more insight on the influence of the growth substrates iron(II) ions, pyrite, chalcopyrite and elemental sulfur on EPS formation, attachment and biofilm formation. The synthesis of EPS by cells of A. ferrooxidans strain A2 is strongely influenced by the growth substrate or attachment substratum of the cells. Cells grown with soluble iron(II) ions generally generate less EPS than cells grown with solid pyrite, chalcopyrite or elemental sulfur. Planktonic cells grown in the presence of solid substrate produce two to four times more EPS than iron(II) ion grown cells. With sessile cells, this factor is further increased to 50 to 240 depending on the specific substrate. The EPS of all the differently grown planktonic and sessile cells of A. ferrooxidans strain A2 contained neutral sugars, fatty acids, uronic acids, proteins and metal ions. The composition of these compounds varied with the growth substrate and type (planktonic or sessile). The attachment behavior of cells of A. ferrooxidans strain A2 also differed with the substrate of the pre-culture. Cells grown on iron(II) ions, pyrite or chalcopyrite attached rapidly to pyrite and chalcopyrite, while attachment to elemental sulfur was poor. On the contrary, sulfur grown cells attached well to elemental sulfur but weakly to pyrite and chalcopyrite. Attachment of EPS-free cells to all substrates was also diminished. Cells of A. ferrooxidans strain A2 cover mineral surfaces with a dense biofilm after a few days of cultivation, as visualized by fluorescence microscopy and AFM. Large amounts of EPS are formed, which eventually cover the cells and the mineral surface. Even after a few weeks of cultivation the biofilm remained monolayered on all substrates.

Effect of biologically produced sulfur on gas absorption in a biotechnological hydrogen sulfide removal process

Absorption of hydrogen sulfide in aqueous suspensions of biologically produced sulfur particles was studied in a batch stirred cell reactor, and in a continuous set-up, consisting of a lab-scale gas absorber column and a bioreactor. Presence of biosulfur particles was found to enhance the absorption rate of H(2)S gas in the mildly alkaline liquid. The mechanism for this enhancement was however found to depend on the type of particles used. In the gently stirred cell reactor only small hydrophilic particles were present (d(p) < 3 microm) and the enhancement of the H(2)S absorption rate can be explained from the heterogeneous reaction between dissolved H(2)S and solid elemental sulfur to polysulfide ions, S(x) (2-). Conditions favoring enhanced H(2)S absorption for these hydrophilic particles are: low liquid side mass transfer (k(L)), high sulfur content, and presence of polysulfide ions. In the set-up of gas absorber column and bioreactor, both small hydrophilic particles and larger, more hydrophobic particles were continuously produced (d(p) up to 20 microm). Here, observed enhancement could not be explained by the heterogeneous reaction between sulfide and sulfur, due to the relatively low specific particle surface area, high k(L), and low [S(x) (2-)]. A more likely explanation for enhancement here is the more hydrophobic behavior of the larger particles. A local increase of the hydrophobic sulfur particle concentration near the gas/liquid interface and specific adsorption of H(2)S at the particle surface can result in an increase in the H(2)S absorption rate.

THE ELUSIVE C60S: THREE ATTEMPTED SYNTHESES

Results of semiempirical energy calculations suggested that a [6,6]-closed C60S fullerene sulfide might be stable. Attempts were therefore undertaken to synthesize the compound by UV photolysis of C60 in CS2 and by the heating of mixtures of C60 and S8 to 325 and 400°C. Any sulfide, if formed, was present in undetectably small quantities. However, [12C60 34S]− ions were observed when a mixture of solid C60 and elemental sulfur was analyzed by Laser Desorption Ionization Time-of-Flight mass spectrometry.

Raman spectroscopic and laser scanning confocal microscopic analysis of sulfur in living sulfur-precipitating marine bacteria

Laser Raman microprobe spectroscopy and laser scanning confocal microscopy were used to determine the presence and speciation of sulfur in sulfur-oxidizing, marine bacteria from Monterey Bay, CA. The bacteria studied include: large, filamentous Thioploca and Beggiatoa, endosymbionts in the vesicomyid clam Calyptogena kilmeri, and a filamentous bacterium of undetermined species. All of these bacteria were shown spectroscopically to store elemental sulfur in submicrometer to several micrometer diameter vesicles. More detailed Raman spectroscopic study of the vesicles in Thioploca and Beggiatoa provided further chemical and structural characterization of the elemental sulfur. The sulfur is bonded in the common, stable S 8 ring configuration and is of an extremely fine-grained microcrystalline form. No additional (organo) sulfur compounds were detected spectroscopically in the vesicles under the low laser powers required to preserve the molecular structure of the sulfur. The present spectroscopic and optical data stand in contrast to reports and inferences of liquid-like elemental sulfur or homogeneous, complex sulfur compounds in other sulfur-oxidizing bacteria. The findings of this study are compatible with a model of sulfur vesicles as dominated by microcrystalline solid elemental sulfur, perhaps embedded in a matrix and/or confining membrane of organic material. The high reactivity and solubility observed in these vesicles is attributed to the extremely fine grain size of the solid elemental sulfur.

亜鉛精鉱の直接浸出と浸出残さからの元素硫黄の回収に関する研究

Zinc concentrate is usually roasted as pretreatment in zinc hydrometallurgy and the produced SO2 is changed to sulfuric acid. However, recently in Japan the utilization of sulfuric acid has been limited and it is more costly to store. In this study, a zinc concentrate (sphalerite) was leached with ferric sulfate at about 373 K for 3 to 6 hours. Then, zinc was leached about 94% and after a solid-liquid separation, the leach residue containing solid elemental sulfur was obtained. After direct leaching, the leach residue was filtrated and the elemental sulfur rich solids were recovered as float product by sink-float separation followed by flotation. In the flotation, lignine sulfonic acid salt as dispersant and MIBC as frother were effective to float sulfur at pH4. The solid elemental sulfur of approximately 97% was recovered as float product by sink-float separation and flotation. The dried mixed float product by sink-float separation and flotation was heated at 413 K for 2 hours and about 87.7% of solid elemental sulfur produced by direct leaching was recovered as pure sulfur.

Determination of trace and platinum-group elements in high ionic-strength volcanic fluids by sector-field inductively coupled plasma mass spectrometry (ICP-MS)

The accurate measurement of ultra-trace concentrations of rare metals and platinum group elements in volcanic fluids is complicated by interferences, complex matrices, and preferential element partitioning. We analyzed condensed, high-temperature magmatic fluids collected from Kudryavy volcano (Kurile Islands, Russia) for Be, B, Rb, Sr, Mo, Ru, Rh, Pd, Cd, W, Re, Pt, Pb, Bi, and U using ICP-MS. The samples had three different matrices: 5 mol L–1 sodium hydroxide (NaOH, pH = 11), gas condensates of sulfuric acid (H2SO4, pH = 0), and solid elemental sulfur. Interferences and suppression/enhancement effects were investigated using standards in concentrated NaOH and H2SO4 solutions to determine adequate dilution for sample analyses, which then required very low levels of element detection (< 1 μg L–1 for most elements). Depending on the field sampling technique of volcanic gas vents, our results show significant differences in concentrations of some trace elements due to the precipitation of solid sulfur during gas condensation and variations in element volatility as a function of temperature.

The Effect of Sulfur Deposition on Gaswell Inflow Performance

Summary Deposition of solid elemental sulfur in the formation may significantly reduce the inflow performance of sour-gas wells. The key operational and reservoir parameters that influence the magnitude of impairment by sulfur deposition were identified through the derivation of an analytical expression for the rate of sulfur buildup assuming idealized flow conditions. A methodology for the use of conventional, black-oil reservoir simulators was subsequently developed to permit the investigation of sulfur-deposition processes for specific reservoir descriptions and well operations. The rate of sulfur buildup in the formation was shown to be inversely proportional to the square of the radial distance from the well. As a consequence, the magnitude of sulfur deposition is highly sensitive to well skin— the lower the skin, the farther away from the well the deposition occurs and the lower the sulfur-buildup rate. Nonuniform deposition over the pay interval (owing to reservoir layering or uneven stimulation) was shown to accelerate the impact of sulfur deposition. A field case involving early decline in well production caused by sulfur deposition was successfully history-matched with the simulation model developed in this study.

Compositional Mapping of Jupiter's Satellite Io Utilizing High Speed Multifilter Photometry during Mutual Satellite Occultations, 1990–1991

We observed selected mutual occultations of Jupiter's satellites in 1990–1991 at four wavelengths and we used the occultation profiles to constrain the areal distribution of selected spectrally active compounds on Io's surface. We performed high speed photometry of Io at four wavelengths while it was being occulted by another Galilean satellite. The wavelengths of the filters that we used for this work were 0.305, 0.345, 0.45, and 0.56 μm. These wavelengths were selected to constrain the areal distribution of sulfur and/or sulfur-bearing compounds and sulfur dioxide (SO2) frost, believed to be the two major surface constituents on Io. During a typical occultation, a Galilean satellite whose spectral properties are well defined passed in front of Io, gradually blocking the sunlight reflected by Io from reaching an Earth-based observer. In the observations reported here the occulting satellite was always Europa. Europa's contribution to the combined signal was removed and the remaining Io occultation brightness variations were compared to curves produced by synthesized occultations that would be expected assuming a two component surface, where one component is an unknown mixture of sulfur bearing materials and the other is SO2frost. We utilized the results of previous IUE derived ultraviolet longitudinal phase angle variation studies (Nelson, R. M., A. L. Lane, D. L. Matson, F. P. Fanale, D. B. Nash, and T. V. Johnson 1980.Science210, 784–786) which localized the distribution of SO2on Io in longitude. Thus, we were able to vary the distribution of SO2in latitude and produce a synthetic lightcurve based on the reflectance properties of solid SO2and elemental sulfur. This was done by simulating different distributions of sulfur bearing materials and SO2frost on Io's surface and minimizing the difference between the synthetic lightcurve and the observed lightcurve. On Io's trailing hemisphere, we find that the region north of the equator between latitudes 0° and 60° and between 180° and 270° longitude to be highest in concentration of SO2frost. It also coincides with the highly reflective “white areas” seen in the Voyager spacecraft television images. All of the observations reported are of Io's trailing hemisphere.

Bacterial leaching of complex sulfide ore samples in bench-scale column reactors

Several variables were examined in column bioleaching of a complex sulfide ore material which contained chalcopyrite, pentlandite, pyrite, pyrrhotite and sphalerite as the main sulfide minerals. Samples were used with varying proportions of pyrrhotite, pyrite, quartzite (low acid consumption) and skarn (high acid consumption). The experiments were carried out using bench-scale column leaching reactors which were inoculated with acidophilic, Fe- and S-oxidizing bacteria, initially derived from the source mine water. Leaching rates in sterile controls were negligible. In inoculated columns new solid phases (covellite, jarosite, Fe (III) oxide and elemental sulfur) were formed. Acid consumption was highest under low pH and low redox potential conditions. The solubility of ferric iron was controlled by jarosite and an Fe (III) hydroxide (initially amorphous). The leaching rates of Co (from pyrite and pentlandite), Cu (chalcopyrite), and Zn (sphalerite) showed a tendency to increase with dissolved ferric iron concentration. The leaching of Ni (from pyrrhotite and pentlandite) did not correlate with the concentration of ferric iron in solution. Microscopic counts of bacteria in solution, deemed insufficient to represent total bacterial counts, showed a tendency to be higher at the lower pH and intermediate redox potential ranges. Trickle-leaching conditions yielded higher acid production and redox-potential values compared with flood leaching. The leaching rates of Co, Cu, Ni and Zn each responded differently to redox potential and pH regimes. The accelerating effect of a decreasing particle size on the metal leaching rates was amplified by low pH values.