Iron Hydroxide Precipitation Research Articles

Photo-degradation of di azo dye Bismarck Brown by advanced photo-Fenton process: Influence of inorganic anions and evaluation of recycling efficiency of iron powder

The present research work has demonstrated the usage of zero valent metallic iron (ZVMI) in the photo-Fenton process under UV light as a promising and novel technique for the complete degradation of di azo dye Bismarck Brown (BB) in aqueous medium. The influence of various reaction parameters like concentration of oxidants/dye/iron powder and pH of the solution was investigated and optimum conditions are reported. Ammonium persulfate (APS) proved to be better oxidant in comparison with hydrogen peroxide for enhancing the degradation rate and effectively inhibited the precipitation of iron hydroxides at higher dosages of iron powder which is attributed to the acidity provided by APS which is crucial for Fenton process. The rate constant for the kinetics of degradation using various oxidation processes follows the order: Fe 0/APS/UV > Fe 0/H 2O 2/UV > Fe 0/APS/dark > Fe 0/UV > Fe 0/H 2O 2/dark > Fe 0/dark > H 2O 2/UV > APS/UV. The effects of inorganic anions that are commonly found in the industrial effluents like NaCl, KNO 3, Na 2SO 4, Na 2CO 3 and NaHCO 3 at different concentrations on the degradation rate were studied in detail. The degradation was followed by UV–vis and GC–MS techniques.

Middle Miocene to Pleistocene sedimentary record of rift evolution in the southern Albert Rift (Uganda)

This study presents an almost complete Middle Miocene to Pleistocene sequence of synrift sediments in the western branch of the East African Rift. The studied succession is exposed in several patches on an eastward tilted block between the northern tip of the Rwenzori Block and the eastern shoulder of the Albert Rift. In this position, it reaches a maximum thickness of 600 m of which 350 m have been logged systematically by analysing lithofacies and sediment architecture. Stratigraphic subdivision of the succession relies on published biostratigraphic data of endemic mollusc associations and their correlation across East Africa. The synrift sediments encountered are siliciclastics ranging from clay to coarse gravel with gypsum and ferrugineous interlayers or impregnations. Lithofacies and architectural analysis indicate alluvial plain, delta plain, nearshore, delta front, or lacustrine depositional environments. Based on the vertical stacking pattern, prograding and retrograding trends of the depositional environments, and climatic indicators (e.g. conservation of feldspar, gypsum, and/or iron hydroxide precipitation), four evolutionary phases can be distinguished: (i) a first phase between ca. 14.5 and 10.0 Ma is characterised by bedload-dominated fluvial environment with massive sandy to gravelly bedforms, feldspar-rich sands, rare iron impregnations and relatively low accommodation space. This phase is interpreted as pre- and early synrift sedimentation under a semiarid climate. (ii) From ca. 10.0 to 4.5 Ma predominantly fine-grained siliciclastics were deposited in a distal fluvial plain to lacustrine setting characterised by limited accommodation space. Fluctuation of thin beds, dominance of clay and frequent iron impregnations point to a more humid climate with seasonality and weak tectonic activity. (iii) During the third phase between 4.5 and 2.0 Ma delta plain and nearshore deposits with frequent ferrugineous impregnations and rich mollusc associations occurred, indicating a humid period with lake-level highstands and accelerated subsidence. (iv) During the final sedimentary interval between 2.0 and 1.5 Ma gravel units reoccurred with less iron- but more carbonate and gypsum impregnations, and arkosic sandstones. This phase recorded a general aridisation trend most probably caused by the upcoming rain barrier of the Rwenzori Mountains together with accelerated rift-flank uplift and strong subsidence of the rift floor. The results of this study are of particular importance for delineating key controls on sedimentation in the Albert Rift.

Relationships between pH, colour and heavy metal concentrations in the Tinto and Odiel rivers (southwest Spain)

The relationships between pH, colour, Fe, Mn, Cu, Zn, Cd and sulphates in surface water samples collected from the Tinto and Odiel Rivers (southwest Spain) have been studied. These rivers are adversely affected by the inputs of acid and heavy metals due to Acid Mine Drainage (AMD). Samples were collected from both rivers on a monthly sampling basis from 1995 to 2001. The analytical results showed that pH (mean pH 3.1) in the water samples of the Odiel River presented a greater correlation with heavy metals, colour and sulphates than in the Tinto River (mean pH 2.5). The tidal effect at the sampling point at the Odiel River appears to cause a greater variation of the pH values (2.5–4.4), resulting in the precipitation of iron hydroxide and the co-precipitation of other metals when the pH increased. This phenomenon was not observed in the samples collected from the more acidic Tinto River (pH 2.1–3.2). A similar relationship was observed for the heavy metals and the colour of the surface water of both rivers.

Analysis of hydrolysable neutral sugars in mineral soils: Improvement of alditol acetylation for gas chromatographic separation and measurement

Abstract To understand plant–microbe relationships, a simple method is required for identification of the nature of soil polysaccharides. Acid hydrolysis, reduction of sugar monomers to the corresponding alcohols and subsequent derivatisation with acetic anhydride prior to gas chromatography has often been used for identification and quantification of hydrolysable sugars in plant and soil samples. In mineral soil samples, precipitation of iron hydroxides and dissolved organic substances after addition of ammonia may lead to co-precipitation of the analytes, leading to an underestimation of the neutral sugar content. The aim of this study was to adapt the derivatisation procedure for soil samples with large iron (hydr)oxide contents. This was done by omission of ammonia and addition of ethylenediaminetetraacetic acid (EDTA) to keep iron in solution and to avoid co-precipitation. Standard addition approaches show that the recovery of all sugars is enhanced with the modified method. Application of the EDTA method improves the recovery of added internal standard, increases yields of sugars in mineral soils and reduces the observed standard error compared to the ammonia method. This was shown for a set of various soil samples with different iron (hydr)oxide contents. The EDTA method is also applicable for mineral free samples and therefore suitable for routine use.

Direct Hydrothermal Synthesis of Iron-Containing Mesoporous Silica SBA-15: Potential as a Support for Gold Nanoparticles

The preparation of mesoporous silica SBA-15 with high iron loadings (14−90 wt % Fe2O3) as a suitable support for gold nanoparticles to be used in CO oxidation catalysis has been investigated. The support materials were prepared by a direct hydrothermal two-step pH adjusting method which consisted of the formation of the silica mesophase at low pH and the inclusion of Fe3+ at varying pH in the range 2−7. The materials were characterized by XRD, SEM, and TEM/EDX, N2 porosimetry, and 57Fe Mössbauer spectroscopy. At relatively low Fe loading, the SBA-15 structure is maintained and iron is predominantly surface grafted to the silica surface. Such a mesoporous silica can accommodate up to 40 wt % Fe2O3 with a surface area of 460 m2/g. With increasing Fe content, precipitation of iron hydroxides competes with the surface grafting process and the resulting materials are an intimate mixture of hematite particles embedded in an Fe/SBA-15 matrix. A too high Fe3+ content in the synthesis gel results in a high rate of precipitation and impedes the formation of the silica mesophase. The stabilization of the mesophase at pH 7 is proposed to involve interactions of the surfactant with a surface grafted Fe3+ silica phase. The use of an SBA-15 which contains mainly surface grafted Fe3+ as a support for gold nanoparticles results in a more active catalyst for CO oxidation than gold supported by SBA-15 or iron oxide particles.

Determination of radionuclide levels in rainwater using ion exchange resin and γ-spectrometry

The evaluation of radioactivity accidentally released into the atmosphere involves determining the radioactivity levels of rainwater samples. Rainwater scavenges atmospheric airborne radioactivity in such a way that surface contamination can be deduced from rainfall rate and rainwater radioactivity content. For this purpose, rainwater is usually collected in large surface collectors and then measured by γ-spectrometry after such treatments as evaporation or iron hydroxide precipitation. We found that collectors can be adapted to accept large surface (diameter 47 mm) cartridges containing a strongly acidic resin (Dowex AG 88) which is able to quantitatively extract radioactivity from rainwater, even during heavy rainfall. The resin can then be measured by γ-spectrometry. The detection limit is 0.1 Bq per sample of resin (80 g) for 137Cs. Natural 7Be and 210Pb can also be measured and the activity ratio of both radionuclides is comparable with those obtained through iron hydroxide precipitation and air filter measurements. Occasionally 22Na has also been measured above the detection limit. A comparison between the evaporation method and the resin method demonstrated that 2/3 of 7Be can be lost during the evaporation process. The resin method is simple and highly efficient at extracting radioactivity. Because of these great advantages, we anticipate it could replace former rainwater determination methods. Moreover, it does not necessitate the transportation of large rainwater volumes to the laboratory.

Kinetics of iron(III) hydrolysis and precipitation in aqueous glycine solutions assessed by voltammetry

The kinetics of iron(III) hydrolysis and precipitation in aqueous glycine solutions were studied by cathodic voltammetry with a mercury drop electrode. The kinetics was controlled by changing ionic strength (I), pH and glycine concentration. Voltammetric measurements clearly showed formation and dissociation of a soluble Fe(III)–glycine complex, formation of iron(III) hydroxide and its precipitation. The rate constants of iron(III) hydroxide precipitation were assessed. The precipitation is first-order with respect to dissolved inorganic iron(III). The calculated rate constants of iron(III) precipitation varied from 0.18 × 10–5 s–1 (at 0.2 M total glycine, pH 7.30, I = 0.6 mol dm–3) to 2.22 × 10–3 s–1 (at 0.1 M total glycine, pH 7.30, I = 0.2 mol dm–3). At 0.5 M total glycine and I = 0.6 mol dm–3, the iron(III) precipitation was not observed.

Ferrimagnetic magnetite hollow microspheres prepared via enzymatically precipitated iron hydroxide on a urease-bearing polymer template

Hollow magnetite (Fe3O4) microspheres a few tens micrometers in diameter were fabricated by calcining iron hydroxide precipitated on spherical polydivinylbenzene (PDVB) template with enzymatically supplied ammonia. Monophasic Fe3O4 hollow spheres were obtained by calcining the precursor at 1073 K for 3.6 ks in an equimolar mixed gas of CO2 and H2. The prepared Fe3O4 hollow spheres had smooth surfaces. The particle size and monodispersity of Fe3O4 spheres reflected those of the PDVB template, and the latter was controllable 10-30 μm in diameter during the process of the polymerization. The Fe3O4 spheres showed ferrimagnetic behavior. The use of urease to precipitate the precursor was found to be effective for preparing template-directed microspheres, and the Fe3O4 microspheres synthesized are considered to be promising thermoseeds for hyperthermic treatment.

The geochemical evolution of water coproduced with coalbed natural gas in the Powder River Basin, Wyoming

Water produced with coalbed natural gas (CBNG) attains its characteristic sodium-bicarbonate composition through a series of processes, including dissolution of salts, precipitation of salts, pyrite oxidation, ion exchange, sulfate reduction, and methanogenesis. After CBNG-produced water is discharged to the surface, interaction with the atmosphere will initiate the precipitation of calcite, iron hydroxide, and barite among other minerals. The interaction of CBNG-produced waters with semiarid Powder River Basin soils can mobilize accumulated salts, which, through infiltration, can then reach the water table, potentially affecting the quality of the groundwater. The mobilization of the soil-based salts may render the composition of the water recharging the near-surface groundwater very different from the initial chemical composition of the CBNG-produced water. Additionally, prolonged exposure to CBNG-produced water can cause the salinization and sodification of soils surrounding CBNG-produced water ponds and streams carrying CBNG-produced water. This can impact the quantity of biomass and the species composition of the vegetation in proximity to CBNG-produced water discharge locations. The high sodium to calcium and magnesium ratio in CBNG-produced water requires careful management to prevent sodification of irrigated soils when it is used as an irrigation source. In many instances, irrigation with CBNG-produced water requires the addition of soil amendments such as gypsum and sulfur to maintain the fertility and physical qualities of the soil. An understanding of the geochemical evolution of CBNG-produced water is necessary to anticipate and address these potential environmental issues associated with production of CBNG.

Theoretical Basis for Measuring Small Radon Diffusion Coefficients for a Radium-Bearing Porous Material Generated by Precipitation of Iron (III) Hydroxide

In order to remove a very small amount of a certain substance (such as radium) which is contained in a solution in a dissolved or suspended form, iron nitrate or iron chloride is often used to separate the substance as a precipitate. Such a precipitate consists of very small polycrystals of iron (III) hydroxide and is porous and contains much moisture. The polycrystals have very complicated forms and link with each other irregularly. In this precipitate, radon diffuses so slowly that measuring its diffusion coefficients is very difficult. However if the small amount of the substance in the solution is radium, it is possible to measure the radon diffusion coefficients by putting the precipitate in a can and measuring the amount of emanated radon in the can. The present paper established a theoretical basis for this measurement and applied it to a simulated ferrous uranium-bearing waste.

Properties of iron nanosized powders obtained by chemicometallurgical method using surface-active substances

In this paper, we have studied the effect of water-soluble surfactants (C2H5OH and C12H25NaO4S) on the processes of iron hydroxide precipitation and reduction and have showed the possibility of controlling the dispersity of the initial hydroxides and the reduced nanocrystalline metal particles and their size distributions upon the production by chemicometallurgical method.

Theoretical Basis for Measuring Small Radon Diffusion Coefficients for a Radium-Bearing Porous Material Generated by Precipitation of Iron (III) Hydroxide

Theoretical Basis for Measuring Small Radon Diffusion Coefficients for a Radium-Bearing Porous Material Generated by Precipitation of Iron (III) Hydroxide

Radiochemical procedure and quantitative determination of the activation product, 63Ni, in environmental soft water samples with high Ca and Mg phosphate concentration

Nickel-63 is a low energy beta-emitter needing a radiochemical separation before β-counting. Several papers described the separation and the detection of 63Ni in environmental samples. The method used in our work was first developed by Skwarzec and Holm. The main steps of this separation are the selective precipitation of nickel with dimethylglyoxime (DMG) and the use of the non-sorption of nickel on anion resin in hydrochloric acid solutions. In this paper, a new step is added to eliminate high quantities of calcium and magnesium phosphate disturbing the iron hydroxide precipitation step. The procedure has been applied to soft water samples: sediments, plants and fishes. The chemical yields are 60, 70 and 20%, respectively. The detection limit of 63Ni by liquid scintillation spectrometer is 10 mBq.

Jarosite-related chemical processes and water ecotoxicity in simplified anaerobic microcosm wetlands

Simulation experiments were conducted to examine whether jarosite is decomposed and toxic products are produced under anaerobic microcosm wetland conditions. The results show that jarosite was stable under water inundation in the microcosm wetland for a period of at least 56 days when no organic substance was added. However, jarosite became increasingly unstable with increasing amount of added organic matter. This resulted in entry of ferrous Fe into the soil solutions. Concentration of other heavy metals in the leachates was extremely low except for Mn. This is attributed to the maintenance of a high pH in the microcosm wetlands, which might cause re-precipitation of originally jarosite-borne heavy metals, if any. No acute toxicity was observed for leachate from the control (non organic matter-added treatment). However, leachates from various organic matter-added treatments show varying degrees of toxicity to the test organism and soluble Fe was likely to be the dominant metal of potential toxicity. Atmospheric exposure of leachate led to oxidation of ferrous Fe and precipitation of iron hydroxide, which caused a drop in leachate pH. This, in turn, inhibited further oxidation of ferrous Fe.

Microbial Alkalinity Production to Prevent Reacidification of Neutralized Mining Lakes

Microbial alkalinity production was evaluated as a method to prevent reacidification of neutralized mining lakes by acidic ground and seepage water. We used 60 L mesocosms to represent the sediment and water column of a shallow acidic mine lake. To enhance alkalinity production, acidic and neutralized lake waters were treated with either phosphorus (controlled eutrophication) or organic matter (controlled saprobization). Controlled eutrophication could not produce enough autochthonous biomass as substrate for microbial alkalinity production to change the acidity of the water. Chemical pre-neutralization of the acidic water caused the inorganic carbon concentration to increase, but at the same time, hindered algae growth by reducing the availability of phosphate by sorption to the freshly precipitated iron hydroxide. This effect was so strong that even high phosphorus additions could not increase the algae biomass production. In contrast to controlled eutrophication, controlled saprobization produced significant alkalinity. Despite inhibition of the most important alkalinity producing process, namely microbial sulfate reduction, by low pH values, the microbial alkalinity production rate was not affected by pre-neutralization of the water column. Other alkalinity producing processes raised the pH in the reactive zone until sulfate reduction was no longer inhibited.

In-situ electrochemical measurements of total concentration and speciation of heavy metals in acid mine drainage (AMD): assessment of the use of anodic stripping voltammetry

We assessed the use of anodic stripping voltammetry (ASV) for in-situ determinations of both total concentration and speciation of dissolved heavy metals (Cd, Cu, Pb and Zn) in acid mine drainage (AMD). In the Kwangyang Au-Ag mine area of South Korea, different sites with varying water chemistry within an AMD were studied with a field portable anodic stripping voltammeter. Anodic stripping voltammetry after wet oxidation (acidification) was very sensitive enough to determine total concentration of dissolved Cd because Cd was dominantly present as 'labile' species, whilst the technique was not so effective for determining total Cu especially in the downstream sites from the retention pond, due to its complexation with organic matter. For dissolved Pb, the concentrations determined by ASV after wet oxidation generally agreed with those by ICP-AES. In the downstream samples (pH>5), however, ASV data after wet oxidation were lower than ICP-AES data because a significant fraction of dissolved Pb was present in those samples as 'inert' species associated with colloidal iron oxide particles. The determination of total dissolved Zn by ASV after wet oxidation appeared to be unsatisfactory for the samples with high Cu content, possibly due to the interference by the formation of Zn-Cu intermetallic compounds on the mercury coated electrode. In AMD samples with high dissolved iron, use of ultraviolet irradiation was not effective for determining total concentrations because humate destruction by UV irradiation possibly resulted in the removal of a part of dissolved heavy metals from waters through the precipitation of iron hydroxides.

Comparative evaluation of short-term leach tests for heavy metal release from mineral processing waste

Evaluation of metal leaching using a single leach test such as the Toxicity Characteristic Leaching Procedure (TCLP) is often questionable. The pH, redox potential ( E h), particle size and contact time are critical variables in controlling metal stability, not accounted for in the TCLP. This paper compares the leaching behavior of metals in mineral processing waste via short-term extraction tests such as TCLP, Field Leach Test (FLT) used by USGS and deionized water extraction tests. Variation in the extracted amounts was attributed to the use of different particle sizes, extraction fluid and contact time. In the controlled pH experiments, maximum metal extraction was obtained at acidic pH for cationic heavy metals such as Cu, Pb and Zn, while desorption of Se from the waste resulted in high extract concentrations in the alkaline region. Precipitation of iron, caused by a pH increase, probably resulted in co-precipitation and immobilization of Cu, Pb and Zn in the alkaline pH region. A sequential extraction procedure was performed on the original waste and the solid residue from the E h–pH experiments to determine the chemical speciation and distribution of the heavy metals. In the as-received waste, Cu existed predominantly in water soluble or sulfidic phases, with no binding to carbonates or iron oxides. Similar characteristics were observed for Pb and Zn, while Se existed mostly associated with iron oxides or sulfides. Adsorption/co-precipitation of Cu, Se and Pb on precipitated iron hydroxides was observed in the experimental solid residues, resulting in metal immobilization above pH 7.

Alteration Mineralogy and Stable Isotope Geochemistry of Paleoproterozoic Basement-Hosted Unconformity-Type Uranium Deposits in the Athabasca Basin, Canada

Unconformity-type uranium deposits are characterized by mineralization developed along the contact between younger sandstone cover and underlying crystalline basement rocks. Mineralization may extend up to 400 m into the underlying basement rocks. Whereas sandstone-hosted unconformity-type deposits have been well studied, deposits hosted primarily in the basement have not. This study examines the deposits at Rabbit Lake, Dawn Lake, and McArthur River, in the Athabasca basin of Canada, which are hosted by the metamorphic Archean and Early Paleoproterozoic rocks forming the basement to younger Late Paleoproterozoic sandstones. Alteration is similar in the three deposits and is characterized by three distinct paragenetic stages: (1) preore alteration involving illitization of plagioclase and amphibole, followed by chloritization of biotite and illite, which formed at ca. 230°C; (2) ore-stage alteration, characterized by uraninite and coarse-grained illite, which formed at ca. 240°C; (3) postore alteration comprising spherulitic dravite, vein chlorite, quartz, calcite, and Fe, Cu, Co, and Pb sulfides, which formed at ca. 135°C. Fluid circulation associated with emplacement of later Mackenzie dikes initiated partial recrystallization of uraninite. A later stage of alteration includes kaolinite and iron hydroxide precipitation formed at much lower temperatures of ca. 50°C. Stable isotope compositions of the alteration minerals in conjunction with their paragenesis indicate that oxidized basinal fluids (δD = ‐43 to ‐21‰., δ18O = 3‐8‰) were derived primarily from evolved seawater and leached uranium from the overlying sandstones of the Athabasca Formation and transported it into the basement via infiltration along fracture zones associated with reverse faults. Graphitic units in the basement and preore alteration served as both physical (fractured zones) and chemical (reductants) traps for the uranium mineralization. The basinal fluids were responsible for the preore illite-chlorite, synore uraninite-illite, and the early postore alteration events; this differs from many other sandstone-hosted deposits, where both oxidized basinal and reduced basement-derived fluids were responsible for uranium precipitation.

Assessment of the ecological potential of mine-water treatment wetlands using a baseline survey of macroinvertebrate communities

A baseline survey of macroinvertebrate populations in two mine-water treatment wetlands, one treating a net acidic spoil heap discharge and one a net alkaline ferruginous pumped mine water, was undertaken to assess the potential of these systems to provide habitats for faunal communities. Both wetlands were found to be impoverished in comparison to natural wetlands but did sustain a macroinvertebrate community that could support higher organisms. Wetland size and water quality in terms of pH, conductivity and metal concentrations were found to be important factors in determining the quality of the populations supported. Direct toxicity to organisms was unlikely to be the main cause of lower diversity, but the smothering of organisms via the precipitation of iron hydroxides particularly in the early parts of the treatment systems affected macroinvertebrate communities. The presence of areas of open water within the planted systems was found to be important for providing habitats for macroinvertebrates and this should be both a future design and maintenance consideration for environmental managers.

Electrical properties of iron-sand columns: Implications for induced polarization investigation and performance monitoring of iron-wall barriers

We investigate the electrical response (0.1–1000 Hz) of reactive iron barriers by making measurements on zero valent iron ([Formula: see text])-sand columns under the following conditions: (1) variable [Formula: see text] surface area (0.1–100% by volume [Formula: see text] under constant electrolyte chemistry; (2) variable electrolyte activity (0.01–1 mol/liter), valence (mono trivalent), and pH under constant [Formula: see text]-sand composition; and (3) forced precipitation of iron hydroxides and iron carbonates on the [Formula: see text] surface. We model the measurements in terms of conduction magnitude, polarization magnitude, and polarization relaxation time. Our key findings are: (a) Polarization magnitude exhibits a linear relation to the surface area of [Formula: see text], whereas conduction magnitude is only weakly dependent on the [Formula: see text] concentration below 30% by volume [Formula: see text]. (b) Polarization magnitude shows a power law relation to electrolyte activity, with exponents decreasing from 0.9 for monovalent solutions to 0.7 for trivalent solutions. (c) The relaxation time parameter depends on activity and valence in a manner that is partly consistent with the variation in double layer thickness predicted from theory. (d) pH exerts minor control on the electrical parameters. (e) Polarization magnitude and relaxation time both increase as a result of precipitation induced on the surface of [Formula: see text]. Our results show that induced polarization parameters systematically change in response to changes in the [Formula: see text]-electrolyte interfacial chemistry.