Potential Eh Research Articles

Hidrogeoquímica do Arsênio e de Outros Constituintes Inorgânicos Presentes nas Águas Subterrâneas da Cidade de Ouro Preto-MG

Waters with As (arsenic) concentrations above the limits set by environmental control agencies are considered dangerous to human health. As is a toxic and carcinogenic element. The groundwater hydrochemical facies which was studied in Ouro Preto - Minas Gerais is a result of the interaction among different phases presented in the solution, particularly the ionic relationships which are established between the solid phase and the water. Low water mineralization is the result of interaction between weather conditions, rock constituents, relief, and dominant weathering processes. The types and quantities of the solubilized components in the water have been linked directly to their time of residence in the aquifers. Among the main cations, have been predominantly Na+ > Ca2+ > K+ > Mg2+. For the anions, the high presence of HCO3 - >> Cl- > SO4 2- > NO3 - offers water a bicarbonated feature that comes from the system, determined mainly by water circulation near the recharge are and terrain surface. The evolution of the As concentrations during the year occurs as a result of the hydrogeological reactions controlled by the redox potential Eh — pH. The pH values of the analyzed samples ranged from 5.93 to 7.92, with a mean value of 6.72. For Eh values were found between 335 and 532 mV and a mean value of 427. In diagram Eh — pH, under chemical balance conditions, it was found that the types of As presented have been controlled by the conditions of Eh — pH. The As5+ species of oxianions (H2AsO4 - and HAsO4 2-), predominate. The diagram shows that the analyzed waters are from environments close to contact with the atmosphere and that they are of pluvial origin, with circulation close to the topographic surface, which accumulates in a generally discontinuous way along the rock fissures. The main factors in the release, mobilization and evolution of As to the groundwater have been specific and particular to the areas of research, such as the hydrological, geochemic

Speciation and Mobility Assessment of Zinc in Coastal Landfill Sites with MSW Incinerator Ash

The mobility of zinc in coastal landfill sites reclaimed by municipal solid waste incinerator ash (MSWIA) was modeled and investigated by conducting a large column test. Temporal and spatial variations in the pH, redox potential (Eh), total organic carbon, and microbial activity were measured in pore water to observe their influences on the mobility of heavy metals throughout the test. After 502 days, permeation was terminated. Then to determine the content and forms of Zn along the column, MSWIA and marine clay samples were analyzed by the community bureau of reference modified sequential extraction procedure. Zn was partitioned into four defined chemical fractions: exchangeable, reducible, oxidizable, and residual. The results showed that attenuation processes occurred within the ash layer, Zn mobility was minor, and coastal landfill conditions promoted the immobilization of heavy metals. Both pH and Eh were the main factors for controlling the solubility of Zn. Moreover, under reduced-alkaline conditions, the reducible fraction was affected, but the oxidizable fraction was slightly favored. The formation of zinc sulphides might be another attenuation mechanism for Zn.

Novel Electrochemical Approach to Assess the Redox Properties of Humic Substances

Two electrochemical methods to assess the redox properties of humic substances (HS) are presented: direct electrochemical reduction (DER) on glassy carbon working electrodes (WE) and mediated electrochemical reduction (MER) and oxidation (MEO) using organic radicals to facilitate electron transfer between HS and the WE. DER allows for continuous monitoring of electron and proton transfer to HS by chronocoulometry and automated acid titration, respectively, and of changes in bulk HS redox potential E(h). Leonardite Humic Acid (LHA) showed an H(+)/e(-) ratio of unity and a decrease in potential from E(h) = +0.18 to -0.23 V upon transfer of 822 mumol(e-) g(LHA)(-1) at pH 7, consistent with quinones as major redox-active functional moieties in LHA. MER and MEO quantitatively detected electrons in LHA samples that were prereduced by DER to different extents. MER and MEO therefore accurately quantify the redox state of HS. Cyclic DER and O(2)-reoxidation revealed that electron transfer to LHA was largely reversible. However, LHA contained a small pool of moieties that were not reoxidized, likely due to endergonic first electron transfer to O(2). Electron accepting capacities of 13 different HS, determined by MER, strongly correlated with their C/H ratios and aromaticities and with previously published values, which, however, were a factor of 3 smaller due to methodological limitations.

Eletroquímica de flotação de minerais de sulfetos de chumbo e zinco

Esse trabalho foi realizado com amostras provenientes da mina de Morro Agudo, visando a verificar a influência do potencial Eh na flotação de chumbo e zinco. As amostras foram provenientes da britagem primária. Durante o processo de flotação, o potencial redox foi monitorado, continuamente, usando um eletrodo de platina. Nesse estudo, foram avaliados os efeitos da adição de sulfeto de sódio e sulfito de sódio na recuperação de galena e esfalerita na presença e na ausência de nitrogênio, como gás de flotação. Uma análise estatística dos resultados de recuperação foi feita através do software MINITAB. A interação do sulfeto de sódio com o gás nitrogênio diminui a recuperação de chumbo no concentrado e o gás nitrogênio, isoladamente, aumentou a recuperação de zinco no concentrado, para uma flotação composta por dois circuitos em série, recuperação da galena, seguida da esfalerita.

Nutrient Response of Water Hyssop to Varying Degrees of Soil Saturation

ABSTRACT Tissue concentrations of nitrogen (N) and phosphorus (P) were measured in water hyssop (Bacopa monnieri) subjected to four progressive levels of flooding: well-drained Control, Intermittently Flooded, Partially Flooded, and Continuously Flooded. Soil redox potential (Eh), measured at two levels in the mesocosms decreased under flooding. Flooding increased biomass and decreased root growth and N and P concentrations in shoots, with the decreases being most pronounced in the Partially Flooded and Continuously Flooded treatments. The decreased uptake of N and P under flooding underscores the need to better understand how wetland plants function in nutrient-rich environments subjected to variable flooding. Additionally, the apparent decreased translocation of N and P from the root to the shoot in flooding conditions may be indicative of an overall decrease in mineral transport, which would have implications for the design and management of remediation systems.

A Simulated Test of Algal Influence of Formation and Deposition of Phosphates

This paper deals with a simulated test of biogenic mineralization made with a blue- green alga species, Spirulina platensis. The data in the experiment were recorded by a computerized surveying system. The influence of algae on the accumulation of phosphorus by changing their microenvironment to promote the formation and deposition of phosphate was studied. The results show that the pH value of cultural liquor rose up to 10 and the redox potential (Eh) may drop by 100-200 mV during the algal logarithmic growth stage, and the cultrual liquor was changed into a medium with a weakly reducing condition. At the end of the logarithmic growth stage white deposits of Na2Ca(CO3)2 · 5H2O and Ca2Mg (PO4)2 · 2H2O were formed on the floor of cultural containers. The test presented a valuable evidence for the theory of biogenic mineralization.

Behavior of polymeric Pu(IV) in simulated groundwater

The effect of pH, ionic strength, and supporting electrolyte on the speciation of Pu(IV) in simulated groundwater over polymeric plutonium hydroxide at fixed values of the oxidation potential Eh was examined by centrifugal ultrafiltration. Upon dilution of simulated groundwater (SGW) containing highly polymerized polymeric Pu species of high molecular weight, these species transform into those with a lower degree of polymerization. When fresh SGW portions are subjected to ultrafiltration through a compact precipitate of colloidal Pu, this precipitate becomes a source of weakly polymerized Pu species, as in the case of common dissolution of a compact precipitate of colloidal Pu in SGW. In the process, the amount of weakly polymerized forms increases by two orders of magnitude as compared to the initial SGW over polymeric Pu hydroxide. These transformations of the initial Pu species in solutions can affect its migration behavior in subsequent processes.

Key factors controlling the size, biomass, and sprouting of Japanese alder swamp forest in Kushiro Mire, Hokkaido, Japan

The interrelation among size, biomass, and sprouting of alder trees was studied to extract the most important hydrochemistrical factors controlling the growth of alder forest in Kushiro Mire, northern Japan. The gradient was mostly explained by chemical variables such as pH, ash content, and P2O5, which showed strong positive correlation with each other, and secondarily by fluctuation of the water table (WL, i.e., water level range). These variables are more important than other hydrochemical ones, because neutral and turbid flood water replaces acidic mire water and conveys fine sediment with adsorbed phosphorus, which in turn could regulate the pH and amount of phosphorus. Also, the number of sprouts showed negative correlation mainly with tree size and redox potential (Eh), which suggested a flooded environment. Because of this, the size of alder was suppressed by hydrochemical variables; however, alder individuals producing new sprouts were maintained. We conclude that variation in size, biomass, and sprouting of alder was mainly controlled by acidity and phosphorus availability, and was significantly influenced by water fluctuation.

Heavy metals availability (Fe, Mn, Zn, Cu and Cr) in Aden Gulf sediments under aerobic and anaerobic conditions

The present study aims to analyse the chemical speciation of heavy metals in relation to aerobic and anaerobic conditions. Two sediment samples (from the Gulf of Aden, Yemen) were incubated under flooded conditions. In particular, the chemical forms of Fe, Mn, Zn, Cu and Cr under the experimental conditions were studied using a sequential chemical extraction method. The pH and Eh of the suspension were measured as critical parameters controlling the fate of the metals in the environment. The results showed that the metals concentration in the different forms varied with time incubation and affected by the variation of redox potential and pH value. Also, the changes in both redox potential (Eh) and pH values had evident effects on heavy metals transformation. It is obvious that the highest redox potential affected the amount of iron and manganese in the oxides form. When the redox potential decreased to−133 and−170 mV, it caused a significant transformation of the Fe-Mn oxide form to the water-soluble and exchangeable fractions. Under anaerobic conditions, the relative percentage of all five metals including the summation of four fractions (the water-soluble and exchangeable, carbonate, oxides and organic fractions) constituted 45–60% of the total amount of iron, 33–50% for manganese, 33–63% for Zn, 63–74% for Cu and 19–43% for Cr. Both zinc and copper among water-soluble and exchangeable fraction were high at the end of incubation period, this accompanied by a significant decrease in the content of the organically bound fraction. In general, the reducing conditions were more favorable for metal bound to water soluble and exchangeable fraction.

Diagenesis of a bioclastic oyster deposit from the Lower Cretaceous (Chachao Formation). Neuquén basin. Mendoza Province, Argentina

The Lower Cretaceous Chachao Formation in the Malargue anticline area consists of wackestone, packstone, and minor grainstone and mudstone rich in benthonic fauna that were deposited in a carbonate ramp. The carbonate diagenesis in the Valanginian Chachao Formation contains many processes with conspicuous effects, including micritization, dissolution, neomorphism, and cementation. The early diagenetic process is characterized by micritization, dissolution and mineralogic stabilization of components, and earlier cement phase represented by micrite cement and isopachous calcite cement, which have petrographic characteristics consistent with precipitation in a marine-phreatic diagenetic environment. Later diagenetic phenomena include granular calcite and syntaxial cement. Both of cement types are interpreted as typical of a meteoric-phreatic environment. Concentric-zoning pattern of alternating dull, and blotchy- to bright luminescent zones is interpreted as being caused by a decrease in redox potential (Eh), under conditions of a progressive marine burial meteoric-phreatic diagenetic environment. Geochemical data (Sr++, Na+, Mg++, Fe++, Mn++) and SEM features of the micrite suggest that original calcareous mud could have been calcite dominated (CDP). The δ18O composition of the granular calcite cement ranging from −2.84‰ to −4.27‰ PDB and the δ13C values of the cement between −2.46‰ and −3.50‰ PDB are compatible with precipitation from a fluid that evolved meteoric-phreatic composition. The high depleted δ18O values of theGryphaea oyster shells can be related to the dilution of the marine water with a fresh water influx, whereas shells with the heaviest δ13C isotopic compositions are probably related to the original marine signal, which suggest a closed diagenetic system for carbon.

Use of chloride–hypochlorite leachants to recover gold from tailing

This study evaluated the speciation of various gold and silver chloride species to determine their stability of gold and silver in a chloride solution. Optimum conditions were then chosen to leach a mine tailing containing gold and silver. If chlorinated sea water (approximately 0.5 M NaCl and pH5.5 and Eh of less than 1.00 V vs Ag–AgCl reference) was used for leaching, both gold and silver could not be fully extracted due to the formation of gold hydroxide and silver chloride. The pH is better kept below pH4 and the solution potential Eh is kept over 1.00 V to maintain gold in solution. An increase in sodium chloride concentration in the range 0.5–3 M will enhance the stability of gold chloride. However, within this range, more than 50% of silver still remains in solid AgCl form. Leaching of gold and silver using both stirred reactors and in static tests confirmed that maximum gold and silver extractions were governed by these constraints. Nevertheless, the gold and silver extractions reached 80% and 50% in reactor leaching. Static tests simulating the in-situ leaching of the tailing show lower extractions for both gold and silver, reaching 70% and 30%, respectively after at least 6 days.

Process Enhancement of Bioleaching of Covellite Concentrate through Modification of Solution Potential

Based on the bioleaching mechanism and electrochemical studies of covellite, the dissolution rate of covellite mineral is accelerated through increasing the redox potential (Eh) of the leach. In the present work, some methods were adopted to enhance the bioleaching of covellite concentrate (collected from Zijinshan copper mine, Fujian province, China) by adding different oxidants such as pure pyrite, ferric ions and H2O2. The goal of this study was to provide appropriate operating parameters for the industry application and increase the efficiency of the bioleaching of copper mine. The results showed that the optimal way to increase the redox potential (Eh) level was the addition of pure pyrite. This method could effectively raise the Eh of bioleaching process while the effect of environmental change was negligible. It could quicken the leaching process and enhance the final copper recovery through the addition of pyrite by 1:1 or 1:2 ratio of covellite concentrate to pyrite.

Electron Transfer Capacities and Reaction Kinetics of Peat Dissolved Organic Matter

Information about electron-transfer reactions of dissolved organic matter (DOM) is lacking. We determined electron acceptor and donor capacities (EAC and EDC) of a peat humic acid and an untreated peat DOM by electrochemical reduction and reduction with metallic Zn and H2S (EAC), and by oxidation with complexed ferric iron (EDC) at pH 6.5. DOC concentrations (10-100 mg L(-1)) and pH values (4.5-8) were varied in selected experiments. EAC reached up to 6.2 mequiv x (g C)(-1) and EDC reached up to 1.52 mequiv-(g C)(-1). EDC decreased with pH and conversion of chelated to colloidal iron, and the electron-transfer capacity (ETC) was controlled by the redox potential Eh of the reactant (ETC = 1.016x Eh - 0.138; R(2) = 0.87; p = 0.05). The kinetics could be adequately described by pseudo first-order rate laws, one or two DOM pools, and time constants ranging from 2.1 x 10(-3) d-1 to 1.9 x 10(-2) d(-1) for the fast pool. Reactions were completed after 24-160 h depending on the redox couple applied. The results indicate that DOM may act as a redox buffer over electrochemical potentials ranging from -0.9 to +1.0 V.

Environmental assessment of water-courses of the Turvo Limpo River basin at the Minas Gerais State, Brazil

A study was performed to evaluate the environmental contamination in the Turvo Limpo River basin which receives effluent discharges from domestic (residential and commercial) activities. The watercourses examined were the São Bartolomeu Stream, Turvo Sujo River, and Turvo Limpo River, located in the Minas Gerais State, Brazil. Water samples were collected at the river-side and analyzed for evaluation of pollutant inputs. The pH, temperature, electrical conductivity, redox potential (Eh), dissolved oxygen (DO), total and settleable solids, visual color, hardness, chemical oxygen demand (COD), biochemical oxygen demand (BOD), chloride, total phosphate, total nitrogen, ammonia nitrogen, nitrate, total coliforms and E. coli, as well as the Cd, Pb, Cu, and Zn speciation were determined in the watercourses. The data obtained were compared with those of the Brazilian Environmental Standards and with data from non-contaminated areas. River water characteristics in some sites were far from the limit values established for superficial waters with satisfactory quality. For instance, the BOD values reached 411 mg L(-1) for a maximum limit of 10.0 mg L(-1), while the ammonia nitrogen concentration reached 28 mg L(-1) for a maximum limit of 13.3 mg L(-1). Some sites showed E. coli values above those of non-contaminated regions. Besides the effects of sewage discharges into the water-courses, agriculture activities and the use of the area for cattle husbandry influenced the quality of the river waters, for instance, the pH of a spring-water sample reached the value of 4.3. The São Bartolomeu Stream has been contributing to the deterioration of the water quality of the Turvo Sujo River, while the Turvo Limpo River has also been affected by anthropogenic discharges in the Turvo Sujo River. The speciation of Cd, Cu and Pb showed that these metals were mainly found in the particulate fraction (i. e., associated with the suspended material). Fifty five percent of the water samples showed labile Zn concentrations greater than that of the nonlabile Zn.

Noncontinuous Development of Reducing Conditions in Wetland Soils

Soil aeration status in relation to water table was analyzed by contour mapping in a forested wetland, an emergent marsh, and an irrigated rice field. Two soil aeration status indicators, oxygen (O2) and redox potential (Eh), showed a significant correlation (P<0.01). Soil O2 and Eh levels generally decreased with the water table rise in the forested wetland and marsh, but with a noncontinuous pattern. The results indicate that soil aeration status could be temporally improved at an optimum water table level, probably due to O2 transport by wetland plants. The soil Eh in the rice fields clearly showed a seasonal pattern regardless of the water tables.

Electrochemical investigation of copper–DTPI interactions

The electrochemical behavior of copper in the absence and presence of a dithiophosphinate type collector, sodium diisobuthyldithiophosphinate (NaDTPI), was determined to investigate the interactions between a copper surface and NaDTPI as a function of pulp potential (Eh) and pH. The electrochemical studies were performed by Cyclic Voltammetry (CV) in the )355 to +1550 mV (SHE) potential range and at different pHs from slightly acidic to strongly alkaline conditions. The electrochemical studies were carried out for copper and DTPI alone as well as with DTPI added copper system. DTPI addition had considerable effects on the electrochemical behavior of copper. CuDTPI formation was the main reaction at all pHs through a mixed mechanism and oxidation of the copper surface was followed by a chemical reaction between copper and DTPI ions. Formation of a cupric metal-collector complex, Cu(DTPI)2, was observed only in acidic conditions in the form of an unstable surface compound.

Modeling Studies on Microbial Effects on Groundwater Chemistry

AbstractThe overall goal of this project is to develop a model to predict microbial effects on the performance of a high-level radioactive waste (HLW) repository. As a first step, the effects of microbes on groundwater chemistry have been evaluated with the numerical code 'MINT', using data collected from the borehole HDB-6 in the Horonobe underground research laboratory (URL) in Japan. The MINT code models biochemistry and geochemical equilibrium, with consideration of transport of solute and microbial activity. The MINT code simulates the activities of 6 major groups of microbes, classified by their metabolism as 'aerobic', 'denitrifying', 'manganese reducing', 'iron reducing', 'sulfate reducing' and 'methanogenic'. The specific activity of each of these groups will depend on the redox potential (Eh) of the groundwater.Sensitivity analyses were performed to investigate the consequences of changes in groundwater composition on the effects of microbial activity. This indicates that the activities of Sulfate Reducing Bacteria (SRB) and methanogens are relatively high. The concentration of dissolved methane produced by such microbial activity is seen to be influenced by sulfate concentration. Based on the observed data from Horonobe URL, the concentration in oxygen is relatively high and the activity of denitrifying bacteria is the highest of the major 6 groups of microbes. This can, however, be attributable to chemical / microbial contamination of the groundwater during sampling. The modeling results indicate that the concentration of dissolved oxygen and nitrate ion should be quickly reduced by microbial metabolism, reducing the redox potential to a level low enough for active methanogenesis to commence. Such assessment can be important to evaluate the reliability of sampling and measurement techniques for sensitive geochemical parameters in general - and microbiology in particular.

Hydro(radio)chemical relationships in the giant Guarani aquifer, Brazil

This investigation was carried out within the Paraná sedimentary basin and involved the sampling of 78 pumped tubular wells for evaluating the hydrochemistry and radioactivity due to the nuclides 238U, 234U, 222Rn, 226Ra, and 228Ra in the Brazilian part of Guarani aquifer. Several significant correlations were found involving the geostatic pressure, for instance, specific flow rate, temperature, dissolved O2, free CO2, pH, redox potential Eh, conductivity, Na, HCO3−, CO32−, SIcalcite, Cl−, F−, SO42−, and B. Carbonates precipitation was evidenced by inverse correlation between CO32− and Ca, Mg, Sr, and Ba, whereas Na exhibited an opposite trend, dissolving rather than precipitating with increasing CO32− concentration. An inverse correlation between CO32− and K was found, possibly related to the increasing tendency of K to recombine with the thickness of the clayey layers. HCO3− played an important role on Na, Ca, Mg, and Sr dissolution. The dissolved U content and 234U/238U activity ratio data were plotted on a two-dimensional diagram that was successfully utilized on identifying an unreported zone of U accumulation, though not necessarily of economic size and grade. The variability in chemical and radionuclides data indicated an important influence of the underlying Paleozoic sediments in the composition of waters from Guarani aquifer. The available data allowed estimate the groundwater residence time by two U-isotopes disequilibrium methods. Values of 45–61 ka were initially calculated, depending on the adopted porosity (15–20%), but a longer residence time (∼640 ka) was also estimated, which is more compatible with the hydraulic conductivity data in Guarani aquifer and groundwater flow velocity occurring at Milk River aquifer, Alberta, Canada. Such time range agrees with previously reported 14C ages exceeding 30 ka BP at the more central parts of the Paraná sedimentary basin.

Influence of pH and oxidation-reduction potential (Eh) on the dissolution of mercury-containing mine wastes from the Sulphur Bank Mercury Mine

This study was undertaken as a part of the development of treatment alternatives for waste materials, primarily waste rock and roaster tailings, from sites contaminated by mercury (Hg) mining wastes. Leaching profiles of waste rock over a range of pH and oxidation-reduction (Eh) conditions were performed. Because iron (Fe) is present in large quantities in mining wastes, the effect of Fe on the leaching of Hg was also determined. Results show that the Hg concentration increased as the pH of the suspension increased until a pH value of 10.65. Thereafter, the Hg concentration decreased sharply. The Hg concentration in the presence of Fe decreased significantly (1/10th to 1/100th). Kinetics results show a relatively slow rate of leaching in the presence of ferric ions. The results obtained from the present study are being used to predict the fate and stability of Hg present in the environment and will, therefore, be useful in dictating the nature and suitability of any remediation treatment.

Pyrite–DTPI interaction as a function of pulp potential and pH

This study aims to investigate the nature of interactions between pyrite and sodium diisobutyldithiophosphinate (DTPI), a dithiophospinate type collector, with respect to the pulp potential (Eh), and pH. Cyclic voltammetry (CV) technique was employed at certain potential ranges and slightly acidic, neutral and alkaline solutions in order to identify the electrochemical behaviour of pyrite and DTPI individually, as well as the possible mutual reactions occurring among pyrite surface and DTPI. In addition, the change in the hydrophobicity of the pyrite surface was also evaluated in the absence and presence of DTPI as a function of Eh and pH through electrochemical contact angle measurements. These two phases were complemented by DRIFT spectroscopy analysis with polarized and DTPI induced pyrite samples at various potential values so as to determine the origin of species forming on pyrite surface. At the end of the study, all these three distinct methods indicated that the adsorption of DTPI on the pyrite surface relied on chemical mechanisms rather than an electrochemical interaction.