Precipitation Of Ferric Hydroxide Research Articles

Barium uptake and adsorption in diatoms

Using trace metal-defined culture conditions, we measured the cellular barium concentration in cultures of the diatom Thalassiosira weissflogii. In cultures with low Fe concentration, at a typical surface seawater Ba concentration of 35 to 40 nmol/L, the cellular Ba was 0.5 μmol/mol P (∼0.04 μg/g dw), much below all previously published values for phytoplankton. When the Fe concentration in the growth medium was increased, the measured “cellular” Ba increased proportionally to the particulate Fe. Under conditions of ferric hydroxide precipitation, similar particulate Ba concentrations were measured in the absence and the presence of cells for a given concentration of particulate Fe. Thus, the bulk of the particulate Ba in such experiments was not truly intracellular but adsorbed on precipitated Fe hydroxides associated with the cell surface. A similar mechanism likely explains the high cellular Ba concentrations reported by previous investigators who utilized relatively high ratios of Fe to EDTA concentrations in the growth medium, resulting in Fe precipitation. On the basis of our results, it seems highly unlikely that intracellular uptake by living phytoplankton explains the vertical flux of Ba in oceanic waters. But the adsorption of Ba on Fe hydroxides that is seen in laboratory experiments must also occur in the oceans and contribute to Ba transport in the upper part of the water column. To be significant, however, such a mechanism would require that the particles that transport Ba out of the surface have a markedly lower Ba/Fe ratio than is measured in the average suspended material.

Vertical Flow Systems - Effects of Time and Acidity Relations

The characteristics of the 29 vertical flow systems reported on by Rose and Dietz (2002) have been reevaluated based on 2 years additional experience and revised understanding of acidity. Data on several additional systems have been collected. If measured hot acidity is interpreted as net acidity that includes the effects of alkalinity (vs. net acidity = acidity minus alkalinity), many systems remove slightly less acidity and fewer VFS produce net alkaline water. Rates of acidity removal (g/m 2 /d) are somewhat lower, and the typical value is about 34 rather than 40 g/m 2 /d. If non-Mn acidity is taken as the critical parameter, the sizing parameter for non-acid effluent is about 35 g/m 2 /d. Systems with fine limestone in the compost do about twice as well and appear to be a solution for high-Al discharges. Over the past 2 years, at least 5 of the systems have markedly decreased in effectiveness. Problems have been accumulation of excess ferric hydroxide precipitate on top of the compost, pipe plugging, channeling, and Al coating causing decreased reaction rate with limestone.

Changes of the chemical composition of discharged coal mine water in the Rontok Pond, Upper Silesia, Poland

The natural process of sulphate reduction takes place in the Rontok Pond. During the reduction the concentration of sulphate in the pond water decreases. The changes of δ34S in the pond water are typical for bacterial reduction. The reduction process in the Rontok Pond causes dissolution of barium and the radium from the pond sediments into the water. Concentrations of barium and 226Ra in the discharged water from the Silesia Coal Mine are lower than in water flowing out of the Rontok Pond into the Vistula River. The opposite trend is observed for iron and also Zn, Co, Ni, Mn, Al and Cu because of the precipitation of ferric hydroxide in the stream. The reduction process, which causes dissolution of barium and radium in water, can explain the release of these elements into the Vistula River. The dissolution of toxic elements can be reduced by the precipitation of non-toxic deposits on the sediment of Rontok Pond.

Inhibition of acid generation from sulphidic wastes by the addition of small amounts of limestone

Limestone addition is a commonly applied technique to prevent acid generation from sulphidic wastes containing 1–10% S. In the present paper, the effectiveness of small amounts, lower than the stoichiometric requirement, of this alkaline additive in inhibiting acid generation from a pyrite concentrate material is studied. Long term laboratory column tests were conducted on a partially oxidised pyrite concentrate, where limestone was added by thoroughly mixing. The amount of alkaline additive ranged from 6.4 to 29% wt. corresponding to 5–30% of the stoichiometric quantity. The performance of the pyrite-limestone mixtures was evaluated by monitoring the drainage quality of the columns. Furthermore, a detailed geochemical characterisation of the column solid residues was performed after a monitoring period of 270 days. The effect of secondary oxidation-neutralisation products on the hydraulic conductivity of material was also examined. Dissolution of previously formed oxidation products occurred in the control column during the monitoring period, resulting in the release of a significant amount of Fe, Zn, Mn, Cd, As and SO 4 and to a lesser extent Pb. However, due to the presence of secondary products, further oxidation of pyrite particles was delayed. The experimental results showed that homogeneous mixing of pyrite with limestone amounting to only a fraction of the contained acidity inhibited the generation of acidic drainage and significantly reduced the dissolved amount of metals and sulphates for a test period of 270 days. Under the alkaline conditions prevailing in the limestone amended columns, secondary precipitation of ferric hydroxides and gypsum occurred. A ten fold decrease of hydraulic conductivity was observed for the material amended with 207 kg CaCO 3/t, corresponding to 15% of the contained acidity.

Pollution prevention in the semiconductor industry through recovery and recycling of gallium and arsenic from GaAs polishing wastes

A process was developed for the recovery of both arsenic and gallium from gallium arsenide polishing wastes. The economics associated with the current disposal techniques utilizing ferric hydroxide precipitation dictate that sequential recovery of toxic arsenic and valuable gallium, with subsequent purification and in-house reuse of both, is to the benefit of the gallium arsenide crystal grower. The developed process involves first the removal of the majority of the arsenic and suspended polish as a mixed precipitate of calcium arsenate and polish. This first process step is performed at ambient temperatures and at a pH>11 using NaOH. At these pH regimes, gallium is retained in solution as a sodium gallate species. Precipitation of virtually pure gallium hydroxide is then accomplished in the next process step through pH adjustment to between 6 and 8 with waste acids. The commonly used ferric hydroxide coprecipitation step is retained as a final treatment step, but because of the removal of the majority of the arsenic, gallium, and polish in the two prior steps, far less waste is land disposed. A patent application has been filed with the United States Patent Office.

A robust multisyringe system for process flow analysis. Part II. A multi-commuted injection system applied to the photometric determination of free acidity and iron(III) in metallurgical solutions.

A new software-controlled volume-based system for sample introduction in process flow injection analysis was developed. By using a multi-syringe burette coupled with one or two additional commutation valves, the multi-commuted injection of precise sample volumes was accomplished. Characteristics and performance of the injection system were studied by injecting an indicator in a buffered carrier. Three configurations were implemented in order to achieve two different tasks: the single injection of a sample in a two- or three-channels manifold, and the dual injection into different streams. The two channel flow system using the single injection was applied to the determination of free acidity in diluted samples containing high levels of iron(III), by employing the single point titration methodology. The precipitation of ferric hydroxide was prevented using the ammonium and sodium salts of oxalate and acetate as buffer titrant. Methyl Red was employed as indicator. The procedure allows determination of acid concentration in solutions with a Fe(III)/H+ molar ratio up to 0.2. Samples with higher Fe(III)/H+ molar ratios were spiked with a known strong acid at dilution. The three-channel configuration was applied to the determination of ferric ions, using, as reagent, a merging mixture of sulfuric acid and potassium thiocyanate. The double injection system was implemented in series in a single (three-channel) manifold in such a way that a different injection volume and a changed reagent were used for each analyte. It was applied to the separated or sequential determination of free acidity and ferric ions. In this configuration, iron(III) was determined using 0.5-0.7% (w/v) sodium salicylate solution as reagent. The systems can operate at up to 100, 84 and 78 injections per hour, respectively. Determinations on synthetic and process samples compared well with the reference values and procedures. Recoveries of 95-102% with a maximum RSD value of 5.4% were found for acidity. The respective values obtained for iron determinations were 96-105% and 4.3%.

Tritium and Plutonium in Waters from the Bering and Chukchi Seas

During the summer of 1993, seawater in the Bering and Chukchi Seas was sampled on a joint Russian-American cruise [BERPAC] of the RV Okean to determine concentrations of tritium, 239Pu and 240Pu. Concentrations of tritium were determined by electrolytic enrichment and liquid scintillation counting. Tritium levels ranged up to 420 mBq L(-1) and showed no evidence of inputs other than those attributed to atmospheric nuclear weapons testing. Plutonium was recovered from water samples by ferric hydroxide precipitation, and concentrations were determined by thermal ionization mass spectrometry. 239+240Pu concentrations ranged from < 1 to 5.5 microBq L(-1). These concentrations are lower than those measured in water samples from other parts of the ocean during the mid-1960's to the late 1980's. The 240Pu:239Pu ratios, although associated with large uncertainties, suggest that most of the plutonium is derived from world-wide fallout. As points of comparison, the highest concentrations of tritium and plutonium observed here were about five orders of magnitude lower than the maximum permissible concentrations allowed in water released to the off-site environs from licensed nuclear facilities in the United States. This study and others sponsored by the International Atomic Energy Agency and the Office of Naval Research's Arctic Nuclear Waste Assessment Program are providing data for the assessment of potential radiological impacts in the Arctic regions associated with nuclear waste disposal by the former Soviet Union.

Contaminant source and mobilization in industrial wastes in Dalälven river drainage area, Sweden

From a summary of mineralogical and geochemical studies, this paper presents patterns of contaminant source, mobilization, and retention in three types of industrial wastes deposited in the Dalälven river drainage area in central Sweden. These industrial wastes contain significant amounts of sulfides and have been subjected to atmospheric oxidation for several tens to hundreds of years. They are the major sources of metals and non-metal contaminants discharged into the Dalälven river. The collected data are of considerable value toward the remedial management of this kind of industrial wastes. The mill-tailings initially contain carbonate minerals which neutralize the acidity and maintain the leachate pH at near neutral values at the bottom of the oxidation zone (about 40 cm deep beneath the surface). The acid neutralization results in a great deal of precipitation of ferric iron hydroxides, leading to the formation of Fe-precipitated layers - a potential barrier to metal movement and O2 diffusion downward through the tailings. The mine waste dump is composed of coarse-grained rock fragments and has been covered by crushed limestone since 1985 in an attempt to neutralize the acid leachate. However, limestone cover has much less buffering effect than expected. As a result, the underlying soil and ground water contains high levels of SO4, Fe, and other metals, and have low pH values. The sulfuric acid industry wastes consist of 70-80% iron oxides which are porous in texture. The porous texture provides a large surface area for the adsorption of SO4. During roasting, sphalerite acquired alteration rim which is composed of Zn-oxides. The mineralogical properties of the SAI wastes play an important role in the formation of hydrated sulfates of Fe and Zn. Due to the occurrence of these highly soluble sulfates, in situ flushing is a practical remedial approach for the SAI wastes, and a cleansing project is carrying out in Falun.

In-situ alteration of minerals by acidic ground water resulting from mining activities: preliminary evaluation of method

The chemical composition of the Cu-mining-related acidic ground water (pH ∼ 3.5 to near neutral) in Pinal Creek Basin, Arizona has been monitored since 1980. In-situ experiments are planned using alluvial sediments placed in the ground-water flow path to measure changes in mineral and chemical composition and changes in dissolution rates of subsurface alluvial sediments. The test results should help refine developed models of predicted chemical changes in ground-water composition and models of streamflow. For the preliminary test, sediment from the depth of the well screen of a newly drilled well was installed in three wells, the source well (pH 4.96) and two up-gradient wells (pHs 4.27 and 4.00). The sediment was placed in woven macrofilters, fastened in series to polyvinyl chloride (PVC) pipes, and hung at the screened level of each well. After interacting with the slowly moving ground water for 48 days, the test sediments were removed for analysis. There was no evidence that any of the materials used were biologically or chemically degraded or that the porosity of the filters was diminished by ferric hydroxide precipitation. These materials included 21-μm-pore (21PEMF) and 67-μm-pore polyester and the 174-μm-pore fluorocarbon Spectra/mesh macrofilters containing the in-situ sediment, the polypropylene (PP) macrofilter support structures, and the Nylon (NY) monofilament line used to attach the samples to the PVC pipe. Based on chemical and mineral composition and on particle-size distribution of the sediment before and after ground-water exposure, the 21PEMF macrofilter was chosen as the most suitable macrofilter for the long-term in-situ experiment. Tests also showed that the PP support structures and the NY monofilament line were sufficiently durable for this experiment.

Elimination of arsenic traces contained in liquid effluents by chromatographic treatment

Our present work is included in a development plan of a two-step detoxication process of arsenical by-products orig- inated from chemical warfare destruction effluents (1). The first method studied was classical anion exchange chromatography. Less than 1% of the anion exchanger capacity is used to fix arsenate ions for a Cl -/AsO4 concentration ratio equal to 100. Because of the lack of anion exchanger selectivity, the use of more selective adsorbents has been investigated, namely a macro- porous cation exchange resin (BioRad AGMP-50 resin). We confirm that the As III and AsV retention does not depend on the nature of the resin functional groups and that only the ferric hydroxide precipitate is involved in the retention. We also show that t he arsenic available exchanger capacity is not significantly affected by high concentrations in chloride ions (1 mol L -1), and it seems that the kinetics of arsenite and arsenate ions fixation is better in presence of chlorides. The use of the exchanger for the c om- plete detoxication of arsenic trace (10 ppm) solutions in presence of high contents in chlorides (1 to 3 mol L -1) leads to an efflu- ent volume equal to 280 and 540 times the resin bed volume, for As III and AsV respectively. The effluent thereby obtained has an arsenic concentration lower than the M.C.L. (100 ppb).

Diversity of bacterial iron mineralization

Bacterial cells, growing naturally in freshwater and marine environments or experimentally in culture, can precipitate a variety of authigenic iron minerals. With the vast majority of bacteria biomineralization is a two-step process: initially metals are electrostatically bound to the anionic surfaces of the cell wall and surrounding organic polymers, where they subsequently serve as nucleation sites for crystal growth. The biogenic minerals have crystal habits and chemical compositions similar to those produced by precipitation from inorganic solutions because they are governed by the same equilibrium principles that control mineralization of their inorganic counterparts. As the latter stages of mineralization are inorganically driven, the type of biomineral formed is inevitably dependent on the available counter-ions, and hence, the chemical composition of the waters in which the microorganisms are growing. In oxygenated waters, iron hydroxides are a common precipitate and can form passively through the binding of dissolved ferric species to negatively charged polymers or when soluble ferrous iron spontaneously reacts with dissolved oxygen to precipitate as ferric hydroxide on available nucleation sites (e.g. bacteria). Alternatively, the metabolic activity of Fe(II)-oxidizing bacteria can induce ferric hydroxide precipitation as a secondary by-product. Ferric hydroxide may then serve as a precursor for more stable iron oxides, such as goethite and hematite via dissolution–reprecipitation or dehydration, respectively, or it may react with dissolved silica, phosphate or sulphate to form other authigenic mineral phases. Under suboxic to anoxic conditions, ferric hydroxide may be converted to magnetite, siderite, and iron sulphides through various reductive processes associated with organic matter mineralization. Under biologically controlled conditions, where mineralization is completely regulated, magnetotactic bacteria form magnetite and greigite as navigational tools to guide themselves into their preferred habitat. In general, the formation of iron biominerals is not difficult to achieve, bacteria simply provide charged surfaces that bind metals and they excrete metabolic waste products into the surrounding environment that induce mineralization. The ubiquitous presence of bacteria in aquatic systems and their inherent ability to biomineralize, therefore, makes them extremely important agents in driving both modern and ancient geochemical cycles.

Ferric hydroxide and ferric hydroxysulfate precipitation by bacteria in an acid mine drainage lagoon

The spontaneous precipitation of amorphous iron hydroxide and ferric hydroxysulfate has generally been considered to be an inorganic process involving the oxidation of ferrous iron with or without the presence of sulfate. However, our study of bacterial communities growing in an acid mine drainage lagoon sediment has confirmed that microorganisms were also capable of facilitating this mineral precipitation. Transmission electron microscopy revealed that bacteria growing at the surface had iron-rich capsules, along with detectable amounts of Zn, Ti, Mn and K incorporated into the mineralised matrix. In the subsurface, more cells were associated with granular, fine-grained mineral precipitates, composed almost exclusively of iron and sulfur. Pore water profiles indicated that no discernible sulfate reduction had taken place, suggesting that these authigenic minerals were ‘ferric hydroxysulfate’, and not iron sulfide. Energy dispersive X-ray spectroscopy further indicated that the subsurface minerals had variable composition, with the Fe:S ratio decreasing with depth from 3.5:1 at 15 cm to 1.9:1 at 30 cm. This indicates the high reactivity of ferric hydroxide for dissolved sulfate. Because iron reduction was limited to sediment depths between 3–10 cm, it is conceivable that these minerals are not amenable to bacterial reduction, and hence, the ability of bacteria to bind and form such precipitates may provide a natural solution to cleansing acidified waters with a high dissolved metal content.

Cycling of iron, manganese, and phosphate in a meromictic lake

Lake Nordbytjernet (Southeast Norway) had up to 40 mg liter−1 dissolved iron and 67 mg liter−1 dissolved manganese in a stagnant layer. The ratio between iron and manganese loading was around 3:1, while the inventory of manganese was six times higher than for iron. High concentrations of dissolved iron occurred solely under strictly anoxic conditions, while dissolved manganese was unaffected by intrusion of oxygen during the autumnal partial circulation. Mixed potentials caused by oxidation of ferrous iron and reduction of manganic oxide or O2 controlled the redox potential values, while dissolved manganese appeared to have no influence. The following main processes controlled the sedimentation rates: fluvial supply of suspended material, precipitation of ferric hydroxide and manganese oxide from the water column, and plankton production. Sorption to ferric hydroxide in the oxic zone and reductive desorption in the anoxic zone controlled the deep water stratification of phosphorus, dissolved organic carbon, and some major cations. No similar effects were seen for manganese sedimentation. The iron sedimentation rate was enhanced in the anoxic zone due to redox coupling of iron oxidation and manganese reduction. Phosphorus was depleted in the anoxic zone during periods of substantial ferric hydroxide sedimentation. Sedimentation of manganese under anoxic conditions seemed to be governed by precipitation of carbonate and phosphate. Residence times in the lake were 0.2 yr for iron and phosphorous vs. 3.3 yr for manganese and 1.4 yr for water.

Removal of Organic Pollutants by Coprecipitation with Metallic Hydroxides and Photochemical Treatment

Effluents from textile, and paper and cellulose industries were treated combining the precipitation of Zn (II), Fe (III) and Zr (IV) hydroxides with photochemical treatment with UV light. By using zinc hydroxide precipitation, colour, total phenols and total organic carbon are greatly reduced in effluents from the paper industry. With further irradiation in the presence of the precipitate, colour is almost completely reduced and the phenol concentrations are reduced to < 20% of their original value without additional reduction of organic carbon concentration. Irradiation permits an additional decrease of the organic matter adsorbed on to the precipitate surface. The results for textile effluent are not satisfactory because the decolorization obtained by the ferric hydroxide precipitation is accompanied by a considerable generation of phenolic forms when the system is submitted to irradiation.

An assessment of isotopic equilibrium in goethites from a bog iron deposit and a lateritic regolith

Hydrogen and oxygen isotope ratios have been measured in goethites from a lateritic regolith in the eastern Amazon Basin of Brazil and a young bog iron deposit in New Jersey, USA. The presence of exchangeable hydrogen and admixed minerals required the use of material-balance calculations to determine relevant δD and δ 18O values. For the Brazilian goethite, δD is −121‰ and δ 18O of −1.2‰ (adjusted for Al content). These values yield a calculated temperature of formation of 24 ± 3°C, which is in good agreement with the modern average annual temperature in that locale. Goethite from the New Jersey bog has a δD of −134‰ and δ 18O of −0.9‰. Its calculated temperature of formation (23 ± 3°C) resembles summer temperatures in southeastern New Jersey. Bacterially mediated rates of precipitation of ferric hydroxide appear to be higher in the bog during the summer months (Crerar et al., 1979). Thus, the temperature calculated for the New Jersey goethite could indicate that the conversion of ferric hydroxide to goethite also occurs predominantly in the summer. δ 13C values of the Fe(CO 3)OH component in goethite (−21.7‰ for Brazil and −19.3‰ for New Jersey) reflect the δ 13C values of the associated organic carbon (−28.4‰ for Brazil and −26.3‰ for the New Jersey). Values of P CO 2 in the regolith (0.063 bar) and bog (0.039 bar) were calculated from the measured abundances of the Fe(CO 3)OH component. The values of δ 13C and P CO 2 obtained from the goethites suggest that the ambient CO 2 in these systems originated primarily from oxidized organic matter. In the low-pH, high- P CO 2 waters characteristic of bogs and laterites, isotopic equilibrium may be closely approached during the formation of goethite from ferric hydroxide (ferrihydrite), even if the initial precipitation of the ferric hydroxide precursor is bacterially mediated. Therefore, meaningful paleotemperatures might commonly be calculated from stable isotope ratios of nonexchangeable oxygen and hydrogen in geothites from such environments.

Sorption of Cd to colloidal ferric hydroxides—impact of pH and organic acids

ABSTRACTThe sorption (both ad- and desorption) of Cd to or from colloidal ferric hydroxides as a function of pH, the concentration of organic acids (acetic acid (AA), EDTA, fulvic acid (FA) and malonic acid (MA)), the precipitation procedure for the ferric hydroxide as well as the contact time were investigated in the present study. The concentrations of Cd, colloids and organic acids were chosen to be representative of natural surface waters. The ferric hydroxide were either precipitated in presence of FA or the acid was mixed with the colloids after the purification steps. The presence of FA during the precipitation of ferric hydroxide, had an impact on the size distribution of the solid phase, but it did not have any influence on the sorption behaviour of Cd. The adsorption process was found to be relatively fast and largely pH-dependent. It was fully reversible when the pH was decreased, however, with somewhat slower kinetics. The addition of up to 1 mmol L−1 AA or MA did not cause any measurable desorption of Cd, probably due to the relatively weak complexes formed between Cd(II)-ions and the anions of the acids. Thermodynamic calculations of the distribution between different soluble Cd-species indicated that EDTA and FA would form stronger complexes with Cd. This was indicated in the experiments as enhanced adsorption at low pH-values due to the adsorption of Cd(II)-organic species, and an increase in the soluble fraction at high pH-values caused by competition for Cd(II)-ions between complex forming groups on the surfaces and the soluble organic ligands.

Modeling cadmium and sulfate adsorption by [formula omitted] mixed oxides

Adsorption of cadmium and sulfate in a mixed Fe(OH) 3 SiO 2 system was studied using the triple-layer model. The uptake of H 4SiO 4 dissolved from the SiO 2 particles was considered in modeling the cation and anion adsorption. The mixed oxides were formed with a range of Fe(OH) 3:SiO 2 ratios by controling the precipitation of ferric hydroxide in a suspension of fumed silica (Cab-O-Sil). Observation of the micromorphology of the mixed oxides by transmission electron microscopy showed that Fe(OH) 3 formed separately from the SiO 2 particles, therefore, an independent oxide model was used to simulate cation and anion adsorption. In this model Cd adsorption occurred on separate Fe(OH) 3 and SiO 2 surfaces. When the pH was lower than 8, Fe(OH) 3 dominated Cd adsorption in the mixed system. Sulfate adsorption on the independent Fe(OH) 3 surface was modeled for the mixed oxide system because no sulfate was adsorbed by the SiO 2 surface at pH > 4. The uptake of H 4SiO 4 reduced sulfate adsorption, but it had a negligible effect on cadmium absorption due to a combination of sorbate competition and electrostatic interactions.

Reservoir Sensitivity to Water Flooding: An Experimental Study of Seawater Injection in a North Sea Reservoir Analog

In this paper we report results from laboratory experiments designed to study the permeability sensitivity of reservoirs to seawater flooding. Core flood experiments using a new recirculating flow apparatus were conducted on the Hopeman Sandstone (Clashach Sandstone) which was used as an analog of carbonate-free North Sea sandstone reservoirs. The samples were confined to 345 bars and flooded at 0.3 cm3min-1 under 207 bars pore pressure. During flooding, the fluid was regularly sampled for analysis of cations using high-performance liquid chromatography. The cores were examined for textural, mineralogical, and petrophysical changes after flooding using scanning electron microscopy (SEM), x-ray diffraction (XRD), probe minipermeametry, and ion and ele tron microprobe imaging. During the tests, which lasted for 5 to 6 weeks, the permeability of the cores declined by as much as 50%. Over the same period, Mg, Ca, and K were removed from the fluid. Integration of fluid data, SEM, XRD, and ion imaging suggests that permeability reductions resulted from (1) pore-throat blockage by clays and other fine mineral particles, (2) precipitation of potassium feldspar (K-feldspar), and (3) precipitation of ferric hydroxide via reduction of ferrous iron. Although permeability damage from pore plugging by fine particles commonly recovered to near starting values, chemical reactions induced permanent permeability damage. Permeability and pore-area measurements conducted on the core after flooding have shown that permeability actually increased near the inlet end of the core but decreased in both the middle and outlet end. These findings suggest that in reservoirs, permeability reduction due to seawater flooding would be restricted to the near-injector area, leading to loss of injectivity; however, the net effect on productivity in a particular field will depend on the relative magnitude of vertical drive due to compaction, and permeability decline within the reservoir due to creation or reactivation of faults.

Preparation of porous materials by bacterially enhanced corrosion of Fe in iron-titanium hot-pressed plates

Sintered iron-titanium plates, presenting several titanium-rich and iron-rich phases, were submitted to bacterial corrosion in acidic media containing dissolved oxygen in order to produce a porous material to be infiltrated by lithium and used as an anode for thermalbatteries. The iron-rich phases were selectively attacked, and the presence of Thiobacillus ferroxidans bacteria in the electrolyte accelerated the corrosion. The postulated mechanism involved an anodic reaction of Fe, yielding Fe 2+ ions, which underwent rapid bacterial oxidation to Fe 3+ in the electrolyte. Reduction of these Fe 3+ ions to Fe 2+ ions constituted the cathodic reaction. The corrosion reaction rate was limited by ferric hydroxide precipitation. The largest pore volume obtained was 3.1 × 10 −4 m 3 kg −1.

Groundwater transport of arsenic and chromium at a historical tannery, Woburn, Massachusetts, U.S.A.

The geochemical environment in hide piles at a historical tanning and rendering site (Woburn, Massachusetts, U.S.A.) is strongly reducing, as reflected by the presence of H 2S and CH 3HS in the pile offgas. The presence of a reducing environment in the Subjacent groundwater, along with DOC (≥ 100mg/l) from hide breakdown, results in reduction of As(V) to As(III), and subsequent methylation to monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA). The reducing conditions also result in precipitation of FeS (am), while hydrophilic organic acids have increased Cr(III) solubility. Three spatially sequential geochemical redox facies were recognized in groundwater downgradient from the hide piles. Typically, a reduced core zone was present adjacent to the hide piles, characterized by S 2− ≥ 1mg/l, Fe 2+ <5mg/l,NH 3 ≥ 200mg/l and the presence of MMAA in conjunction with DOC (−30mg/l). This facies transitions through an intermediate zone, represented by Fe 2+ > 20mg/l, NH 3 (5–200 mg/l) and the sporadic presence of measurable S 2− (1–2 mg/l), to an oxidizing peripheral zone characterized by conditions representative of background (i.e. DO> 1mg/l, Eh> 0mV, Fe 2+ < 20mg/l, S 2− < 1mg/l,NH 3 < 5mg/l and NO 3 − >NH 3), accompanied by precipitation of amorphous ferric hydroxide, sorption of As and co-precipitation-sorption of Cu, Pb and Zn. Electron microprobe analysis of hide-pile materials demonstrated authigenic precipitation of amorphous ferric hydroxide and gypsum, in agreement with the results of geochemical modeling.