Precipitation Of Zn Research Articles

Low-temperature synthesis and characterization of the Mn–Zn ferrite

Nanocrystalline ferrite with the composition: Mn0.6Zn0.4Fe2O4 was synthesized by two-stage route: the precipitation of Zn, Mn and Fe hydroxides from sulphates solution and the synthesis of a precursor by the sol–gel auto-combustion method. The ferrite powder obtained from the gel by ashing was sintered under air at a temperature of 720, 1150 and 1300 °C. The composition and morphology of the as-obtained phases were examined by ICP-AES, TG/DTA, XRD, FTIR, SEM and low-temperature nitrogen adsorption (BET). It was found that the spinel phase forms after gel combustion. The nanometric ferrite powder obtained as a result of the combustion is soft-agglomerated. The zinc content in the ferrite during ashing and auto-combustion is lower by about 21 mol% than the assumed one and the final product turn out to be Mn0.68Zn0.32Fe2O4.

Arsenic stabilization of calcium arsenate waste by hydrothermal precipitation of arsenical natroalunite

The stabilisation of calcium arsenate waste from a copper smelter by precipitation of arsenical natroalunite has been investigated. This procedure could solve the problem of arsenical gypsum production because it is transformed into arsenic-free anhydrite. Natroalunite precipitation was studied at 180-200 °C from the slurry obtained after H 2SO 4-leaching and ozonation of the original waste - using sodium and aluminum sulfates as reagents. Calcium arsenate waste and final precipitates were characterized by chemical analysis (ICP), SEM-EDS and XRD. Solubility tests were also performed on original waste and selected precipitates. The effects studied in the hydrothermal treatment were: initial pH, Al/As molar ratio, As concentration, reaction time and prior gypsum removal. For (Al/As) aq = 4.5, a complex natroalunite (~(Na,Ca)(Al,Fe) 3((S,As,P)O 4) 2(OH) 6)) was extensively formed. Under these conditions, As-substitution in TO 4 was 7-8% molar. Decreasing (Al/As) aq increased As-substitution in natroalunite (up to ~ 14% molar) but mansfieldite ((Al,Fe)(As,P)O 4.2H 2O) co-precipitated. Other effects such as the arsenic concentration in the range 3.5-7.0 g/L and prior gypsum removal did not significantly alter the arsenic phase ratio and the composition of the arsenic phases. However, treatment at 180 °C increased mansfieldite precipitation. Calcium incorporation in natroalunite was small (~ 0.04 in formula) and for initial pH = 1, precipitation of Cu, Ni and Zn was insignificant. Arsenical natroalunite can be effective for long-term storage. At its natural pH (4-5), arsenic solubility remained stabilized at ~ 0.1 mg/L in 6 months. Mansfieldite was not stable under the same conditions with arsenic solubility between 5-10 mg/L. The major disadvantage of natroalunite is the limited arsenic partition between solid and aqueous phases (~ 0.45 molar). However, as the precipitation rate is fast (< 15 min), it seems technically feasible to improve the arsenic precipitation yield by semi-continuous addition of reagents in a single hydrothermal operation. Cadmium incorporated into the anhydrite structure causes cadmium release in leachates. It seems that this problem can only be overcome through prior removal of cadmium from the plant effluent.

Part I: Removing of Zn(II) from Polluted Water: Determination of Precipitation Limit Of Zn(II) Ion With 2-Hydroxy-1,2,3-Propanetricarboxylic Acid

Problem statement: The goal of this research was to investigate the condition for removing of Zn cation from water, through precipitation method with 2-hydroxy-1,2,3-propanetricarboxylic acid as ligand. Approach: In this study we examined the precipitation of Zn(II) ion in water solutions of ZnSO4 × 7H2O (1×10-2 and 5×10-3 mol L-1) with 2-hydroxy-1,2,3-propanetricarboxylic acid (1×10-1-1×10-3 mol L-1) in constant ionic strength of 0.6 mol L-1 NaCl. We have determined the concentration region at which Zn(II) start to precipitate. Results: From precipitation diagrams of zinc with 2-hydroxy-1,2,3-propanetricarboxylic acid, in ionic force 0.6 mol L-1 NaCl, we have found that during decreasing the concentration of 2-hydroxy-1,2,3-propanetricarboxylic acid, in case of constant concentration of Zn(II), the limit of precipitation is shifted to lower values of pH. The solid phase is analyzed by IR spectroscopy. Conclusion: From the IR spectroscopic analysis we can conclude that Zn(II) ion can precipitate with 2-hydroxy-1,2,3-propanetricarboxylic acid.

Effects of excessive Zn 2+ ions on intrinsic magnetic and structural properties of Ni 0.2Zn 0.6Cu 0.2Fe 2O 4 powder prepared by chemical coprecipitation method

Zn(OH) 2 is a kind of amphoteric compound. Therefore, for chemical coprecipitation method, the precipitation of Zn 2+ ions may be incomplete if using NaOH as precipitator. In this study, single-phase powder specimens with a nominal composition Ni 0.2Zn 0.6Cu 0.2Fe 2O 4 were prepared with chemical coprecipitation method, and the effects of excessive Zn 2+ content ( x, x = 3%, 5%, 7%, 9%) in working solution on intrinsic magnetic and structural properties were studied by vibrating sample magnetometer and X-ray diffractometer, respectively. It was found that the magnetization when H m = 398 kA/m (5000 Oe) reached a maximum when x = 5%, and then decreased with the increase of x, which was attributed to the effect of different amount of Zn 2+ in A sites on the A–B and B–B exchange interaction. Moreover, it was found that the lattice parameter was affected by the Zn 2+ and Fe 3+ ions due to their different ion radius to a certain extent.

Microwave-assisted synthesis of CuO/ZnO and CuO/ZnO/Al 2O 3 precursors using urea hydrolysis

Binary CuO/ZnO and ternary CuO/ZnO/Al 2O 3 catalysts have been rapidly synthesized in a multimode microwave oven by the homogeneous precipitation of aurichalcite and hydrotalcite-like precursors using urea hydrolysis. For purposes of comparison, the same catalysts were prepared under conventional heating. The corresponding metal nitrates were mixed with various amounts of urea to yield different urea/(ΣM +) molar ratios. The precipitation proceeded stepwise, copper being the first metal to be hydrolyzed. It was found that the higher the urea content, the higher the alkalinization of the solution, an effect which favored the precipitation of Zn (II) (the most pH dependent metal), and in turn, the synthesis of aurichalcite and hydrotalcite-like precursors. Microwave-synthesized catalysts presented similar characteristics to those obtained under conventional heating, but in considerably reduced aging times. Microwave radiation proved to be more efficient than conventional heating under harsh conditions of precipitation, i.e., lower molar ratios of urea with respect to the metal cations in the solution.

Field multi-step limestone and MgO passive system to treat acid mine drainage with high metal concentrations

Abstract Passive treatment systems have become one of the most sustainable and feasible ways of remediating acid mine drainage (AMD). However, conventional treatments show early clogging of the porosity or/and coating of the reactive grains when high acidity and metal concentrations are treated. The performance of fine-grained reagents dispersed in a high porosity matrix of wood shavings was tested as an alternative to overcome these durability problems. The system consisted of two tanks of 3 m 3 filled with limestone sand and wood shavings, and one tank of 1 m 3 with caustic magnesia powder and wood shavings, separated by several oxidation cascades and decantation ponds. The system treated about 1.5 m 3 /day of AMD containing an average of 360 mg/L Fe, 120 mg/L Al, 390 mg/L Zn, 10 mg/L Cu, 300 μg/L As and 140 μg/L Pb, a mean pH of 3.08 and a net acidity of 2500 mg/L as CaCO 3 equivalent. The water reached pH 5 and 6 in the first and second limestone tanks, respectively (suitable to remove trivalent metals); and pH 8–9 in the MgO tank (suitable to remove divalent metals). After 9 months of operation, the system achieved an average removal of 100% Al, Cu, As, Pb, more than 70% Fe, about 25% Zn and 80% acidity. Goethite, schwertmannite, hydrobasaluminite, amorphous Al(OH) 3 and gypsum were the main precipitates in the two limestone tanks. Precipitation of divalent metals (Fe (II), Zn, and traces of Cd, Ni and Co) were complete inside the third tank of MgO, but preferential flow along the walls was responsible for its low treatment performance. Goethite, gypsum, Zn-schulenbergite and sauconite are the crystalline solid phases identified in the MgO tank.

The effect of various carbon sources on stimulating bioprecipitation of heavy metals in the saturated zone

In situ bioprecipitation (ISBP) seems to be one of the most promising processes for immobilization of heavy metals in soil. It is mainly performed by Sulfate Reducing Bacteria (SRB) that are anaerobic heterotrophs utilizing a range of organic substrates and sulphates as a terminal electron acceptor. Sulphides produced from sulphates reduction form insoluble complexes with a metal, which results in its immobilisation. SRB can be stimulated by the addition of various carbon (C) sources. The aim of this study was to evaluate the effect of various C sources on stimulating bioprecipitation of heavy metals (Zn, Ni, Cu, Pb, Cd) in the saturated zone. As C – sources, molasses, whey and ethanol were used to induce the ISBP process. Column tests were performed with natural aquifer materials from Piekary Slaskie, Poland and synthetic groundwater containing Zn, Ni, Cd, Pb, Cu. Two controls included: an abiotic control containing formaldehyde, and a natural attenuation control (not amended with an extra C – source). In the molasses and ethanol amended columns, redox potential decreased to -163 and -189 mV, the initial pH of ca. 6 decreased to 4.6 and heavy metals (Zn, Cd, Cu, Pb) were immobilized . In the NA column and abiotic control, almost no metals were immobilized. In the whey amended column precipitation of Zn was observed and no significant immobilized of Cu, Cd, Ni, Pb took place. The tested C sources promoted sulfate reduction within seven weeks, with average efficiencies of 60%. keywords: heavy metals, in situ bioprecipitation, sulphate reducing bacteria, carbon sources

Biological hydrogen sulfide production in an ethanol–lactate fed fluidized-bed bioreactor

Sulfate-reducing fluidized-bed bioreactor (FBR) fed with ethanol–lactate mixture was operated at 35 °C for 540 days to assess mine wastewater treatment, biological hydrogen sulfide production capacity and acetate oxidation kinetics. During the mine wastewater treatment period with synthetic wastewater, the sulfate reduction rate was 62 mmol SO 4 2 - L −1 d −1 and Fe and Zn precipitation rates were 11 mmol Fe L −1 d −1 and 1 mmol Zn L −1 d −1. After this, the hydrogen sulfide production was optimized, resulting in sulfate reduction rate of 100 mmol SO 4 2 - L −1 d −1 and H 2S production rate of 73.2 mmol H 2S L −1 d −1. The limiting step in the H 2S production was the rate of acetate oxidation, being 50 mmol acetate L −1 d −1. Therefore, FBR batch assays were designed to determine the acetate oxidation kinetics, and following kinetic parameters were obtained: K m of 63 μmol L −1 and V max of 0.76 μmol acetate g VSS −1 min −1. The present study demonstrates high-rate hydrogen sulfide production and high-rate mine wastewater treatment with ethanol and lactate fed fluidized-bed bioreactor.

Separate recovery of copper and zinc from acid mine drainage using biogenic sulfide

Precipitation of metals from acid mine drainage (AMD) using sulfide gives the possibility of selective recovery due to different solubility product of each metal. Using sulfate reducing bacteria to produce sulfide for that purpose is advantageous due to in situ and on-demand sulfide production. In this study, separate precipitation of Cu and Zn was studied using sulfide produced in anaerobic baffled reactor (ABR). ABR fed with ethanol (1340 mg/L chemical oxygen demand (COD)) and sulfate (2000 mg/L) gave a stable performance with 65% sulfate reduction, 85% COD removal and around 320 mg/L sulfide production. Cu was separately precipitated at low pH (pH < 2) using sulfide transported from ABR effluent via N 2 gas. Cu precipitation was complete within 45–60 min and Zn did not precipitate during Cu removal. The Cu precipitation rate increased with initial Cu concentration. After selective Cu precipitation, Zn recovery was studied using ABR effluent containing sulfide and alkalinity. Depending on initial sulfide/Zn ratio, removal efficiency varied between 84 and 98%. The low pH of Zn bearing AMD was also increased to neutral values using alkalinity produced by sulfate reducing bacteria in ABR. The mode of particle size distribution of ZnS and CuS precipitates was around 17 and 46 μm, respectively.

Interaction of Aqueous Zn(II) with Hematite Nanoparticles and Microparticles. Part 1. EXAFS Study of Zn(II) Adsorption and Precipitation

Sorption of Zn(II)(aq) on hematite (alpha-Fe2O3) nanoparticles (average diameter 10.5 nm) and microparticles (average diameter 550 nm) has been examined over a range of total Zn(II)(aq) concentrations (0.4-7.6 mM) using Zn K-edge EXAFS spectroscopy and selective chemical extractions. When ZnCl2 aqueous solutions were reacted with hematite nanoparticles (HN) at pH 5.5, Zn(II) formed a mixture of four- and six-coordinated surface complexes [Zn(O,OH)4 and Zn(O,OH)6] with an average Zn-O distance of 2.04+/-0.02 A at low sorption densities (Gamma<or=1.1 micromol/m2). On the basis of EXAFS-derived Zn-Fe3+ distances of (3.10-3.12)+/-0.02 A, we conclude that both Zn(O,OH)6 and Zn(O,OH)4 adsorb on octahedral Fe3+(O,OH)6 or pentahedral Fe3+(O,OH)5 surface sites on HN as inner-sphere, mononuclear, bidentate, edge-sharing adsorption complexes at these low sorption densities. It is possible that polynuclear Zn complexes are also present because of the similarity of Zn and Fe backscattering. At higher Zn(II) sorption densities on hematite nanoparticles (Gamma>or=3.38 micromol/m2), we observed the formation of Zn(O,OH)6 surface complexes, with an average Zn-O distance of 2.09+/-0.02 A, a Zn-Zn distance of 3.16+/-0.02 A, and a linear multiple-scattering feature at 6.12+/-0.06 A. Formation of a Zn(OH)2(am) precipitate for the higher sorption density samples (Gamma>or=3.38 micromol/m2) is suggested on the basis of comparison of the EXAFS spectra of the sorption samples with that of synthetic Zn(OH)2am. In contrast, EXAFS spectra of Zn(II) sorbed on hematite microparticles (HM) under similar experimental conditions showed no evidence of surface precipitates even at the same total [Zn(II)(aq)] that resulted in precipitate formation in the nanoparticle system. Instead, Zn(O,OH)6 octahedra (d(Zn-O)=2.10+/-0.02 A) were found to sorb dominantly in an inner-sphere, bidentate, edge-sharing fashion on Fe3+(O,OH)6 octahedra at hematite microparticle surfaces, based on an EXAFS-derived Zn-Fe3+ distance of 3.44+/-0.02 A. CaCl2 selective extraction experiments showed that 10-15% of the sorbed Zn(II) was released from Zn/HN sorption samples, and about 40% was released from a Zn/HM sorption sample. These fractions of Zn(II) are interpreted as weakly bound, outer-sphere adsorption complexes. The combined EXAFS and selective chemical extraction results indicate that (1) both Zn(O,OH)4 and Zn(O,OH)6 adsorption complexes are present in the Zn/HN system, whereas dominantly Zn(O,OH)6 adsorption complexes are present in the Zn/HM system; (2) a higher proportion of outer-sphere Zn(II) surface complexes is present in the Zn/HM system; and (3) Zn-containing precipitates similar to Zn(OH)2(am) form in the nanoparticle system but not in the microparticle system, suggesting a difference in reactivity of the hematite nanoparticles vs microparticles with respect to Zn(II)(aq).

Determination of Precipitation Limit of Zn(II) Ion with (2S)-2-Aminobutanedioic Acid

Problem statement: In this study we examined the precipitation of Zn(II) ion in water solutions of ZnSO4.7H2O (1.10-2 and 5.10-3 mol L-1) with (2S)-2-aminobutanedioic acid (1.10--1.10-3 mol L-1) in constant ionic strength of 0.6 mol L-1 NaCl. We have determined the concentration region where we have found the clear solution and solid phase. The solid phase is analyzed by IR spectroscopy. Approach: From precipitation diagrams of zinc with (2S)-2-aminobutanedioic acid in ionic force 0.6 mol L-1 NaCl, we have found that during decreasing the concentration (2S)-2-aminobutanedioic acid in case of constant concentration of Zn(II) the limit of precipitation is shifted to lower values of pH. Results: Also from precipitation diagrams we can see that when the concentration of zinc increases, in case of constant concentration of (2S)-2-aminobutanedioic acid the limit of precipitation will shift at lower values of pH. Conclusion: From the IR spectroscopic analysis we can conclude that Zn (II) ion has reacted with (2S)-2-aminobutanedioic acid.

Thermodynamic model for sorption of bivalent heavy metals on calcite in natural-technogenic environments

Approaches to the construction of thermodynamic models for sorption of trace-element cations on carbonates are considered. To calculate thermodynamic equilibria by the method of Gibbs free-energy minimization, the existing database of reaction constants and thermodynamic potentials was extended. Different types of models are illustrated by the example of precipitation of Cd, Cu, Pb, and Zn from the water of a drainage stream flowing out of the impoundment of barite-polymetallic ore-dressing wastes. It is shown that the mobility of metals in such cases can be controlled by their sorption by calcite present in bottom sediments and suspension. Any approach can be successfully applied to both the modeling of experimental data on cation sorption and the prediction of the ecologo-geochemical situation in the districts of dressing works.

Electrochemical behaviour of some transition metal acetylacetonate complexes as corrosion inhibitors for mild steel

Corrosion inhibition of some metal acetylacetonate complexes including Co(acac) 2, Cu(acac) 2, Mn(acac) 2 and Zn(acac) 2 was evaluated using electrochemical impedance spectroscopy (EIS) in 3.5% NaCl for mild steel. The results were compared to zinc potassium chromate (ZPC) solution in 3.5% NaCl. Corrosion inhibition of these metal complexes followed the order: ZPC > Co(acac) 2 > Zn(acac) 2 > Mn(acac) 2 while Cu(acac) 2 displayed corrosion catalytic activity. Solutions containing metal acetylacetonate complexes had an increase in pH compared to Blank and ZPC solutions, which indicated partial dissociation of ligand and metallic cations. However, after 24-h contact with the mild steel samples the solutions pH were dropped which implied decrease of the complex concentration in the test solutions. SEM images showed no detectable deposited film on the surface exposed Co(acac) 2 solution while EDX analysis revealed precipitation of a layer containing 4.14% Co. SEM-EDX results for samples immersed in Zn(acac) 2 and Mn(acac) 2 solution showed precipitation of Zn and Na components and Mn complex on the surface, respectively.

Removal of Mn(II) and Zn(II) ions from flue gas desulfurization wastewater with water-soluble chitosan

Heavy metals are the most important pollutants in wastewater from dual-alkali flue gas desulfurization (FGD) system. Mn(II) and Zn(II) could predominate in the catalyzed oxidation of sulfite. So the feasibility of precipitation of heavy metal ion (Mn(II) and Zn(II)) by water-soluble chitosan was studied in a lab scale experiment. The association between chitosan and metal ions was verified through FT-IR. The pH investigation revealed that at the pH ranged from 5 to 9, there were three stages for different actions: chelation of chitosan for metal ion, precipitation of metal hydroxide and coprecipitation of metal hydroxide and chitosan–metal complex. The selective chelation of chitosan for Mn(II) and Zn(II) mixture solution was also studied. The results showed that the chelation of chitosan for Mn(II) was prior to Zn(II) in multiple component solution. Compared with the settling of metal hydroxide, the chitosan–metal complex had better separating performance. Application of chitosan solution for chelation could remove Mn(II) and Zn(II) efficiently and make it easily to separate sediment from dual-alkali FGD wastewater. On the other hand co-precipitation of the complicate heavy metal in the FGD wastewater enhanced the heavy metal removal of chitosan chelation.

Selective precipitation of Cu from Zn in a pS controlled continuously stirred tank reactor

Copper was continuously and selectively precipitated with Na 2S to concentrations below 0.3 ppb from water containing around 600 ppm of both Cu and Zn in a Continuously Stirred Tank Reactor. The pH was controlled at 3 and the pS at 25 (pS = −log(S 2−)) by means of an Ag 2S sulfide selective electrode. Copper's recovery and purity were about 100%, whereas the total soluble sulfide concentration was below 0.02 ppm. X-ray diffraction (XRD) analysis showed that copper precipitated as hexagonal CuS (covellite). The mode of the particle size distribution (PSD) of the CuS precipitates was around 36 μm. The PSD increased by high pS values and by the presence of Zn. Depending on the turbulence, the CuS precipitates can grow up to 200 μm or fragment in particles smaller than 3 μm in a few seconds. Zn precipitation with Na 2S at pH 3 and 4, in batch, always lead to Zn concentrations above 1 ppm. Zn precipitated as cubic ZnS (spharelite).

Study on reaction kinetics and selective precipitation of Cu, Zn, Ni and Sn with H 2S in single-metal and multi-metal systems

Determination of reaction kinetics and selective precipitation of Cu, Zn, Ni and Sn with H 2S in single-metal and multi-metal systems were studied to develop a process of metal recovery from plating wastewater. As samples, single-metal model wastewaters containing Cu, Sn, Zn or Ni, and multi-metal model wastewater containing Cu–Zn–Ni or Sn–Zn mixtures were used. In both single-metal and multi-metal systems, the pH value was precisely controlled at a value of 1.5 for CuS and SnS precipitation, 4.5 for ZnS precipitation and 6.5–7.0 for NiS precipitation. Subsequently, the sulfidation of Cu, Sn, Zn and Ni was evaluated. It was found that an amount of H 2S equimolar to a given metal was sufficient to achieve almost complete precipitation of the particular metal. Further, the selectivity of metal precipitation was found to be higher than 95% in the Cu–Zn–Ni multi-metal system and higher than 91% in the Sn–Zn system. It was also found that the sulfidation reaction proceeded in accordance with Higbie’s penetration theory and reaction rate constants and mass-transfer coefficients under various experimental conditions were determined. Finally, the reaction rate constants obtained in single-metal and multi-metal systems were found to be almost the same indicating that the precipitation of a particular metal was not significantly affected by the presence of other components.

Preparation and performance of ZnO nanoparticle aggregation with porous morphology

ZnO nanoparticle aggregations with porous morphology were prepared by the direct precipitation of Zn(OH) 2 coats on the surface of Zn powders, and succedent calcination of Zn/Zn(OH) 2 composites. The coating and calcination reaction mechanism was given to explain the formation of the novel structure. The samples were characterized by X-ray diffraction, energy-disperse X-ray spectrometry, scanning electron microscopy and ultraviolet–visible spectrometry. It was found that ZnO nanoparticle aggregations were irregular porous microspheres consisting of ZnO nanoparticles with hexagonal wurtzite structure, and the diameters of bores in the microspheres ranged from tens to hundreds nanometers. The gas sensing properties of the samples were investigated. Sensors based on the samples showed high sensitivity and short response time to the H 2S gas. These characteristics make the sensors to be excellent potential candidates for detecting H 2S. The electrochemical performance of samples as anode materials for Li-ion battery was also investigated.

Geochemistry and mineralogy of arsenic in (natural) anaerobic groundwaters

Here new data from field bioremediation experiments and geochemical modeling are reported to illustrate the principal geochemical behavior of As in anaerobic groundwaters. In the field bioremediation experiments, groundwater in Holocene alluvial aquifers in Bangladesh was amended with labile water-soluble organic C (molasses) and MgSO 4 to stimulate metabolism of indigenous SO 4 -reducing bacteria (SRB). In the USA, the groundwater was contaminated by Zn, Cd and SO 4 , and contained <10 μg/L As under oxidized conditions, and a mixture of sucrose and methanol were injected to stimulate SRB metabolism. In Bangladesh, groundwater was under moderately reducing conditions and contained ∼10 mg/L Fe and ∼100 μg/L As. In the USA experiment, groundwater rapidly became anaerobic, and dissolved Fe and As increased dramatically (As > 1000 μg/L) under geochemical conditions consistent with bacterial Fe-reducing conditions. With time, groundwater became more reducing and biogenic SO 4 reduction began, and Cd and Zn were virtually completely removed due to precipitation of sphalerite (ZnS) and other metal sulfide mineral(s). Following precipitation of chalcophile elements Zn and Cd, the concentrations of Fe and As both began to decrease in groundwater, presumably due to formation of As-bearing FeS/FeS 2 . By the end of the six-month experiment, dissolved As had returned to below background levels. In the initial Bangladesh experiment, As decreased to virtually zero once biogenic SO 4 reduction commenced but increased to pre-experiment level once SO 4 reduction ended. In the ongoing experiment, both SO 4 and Fe(II) were amended to groundwater to evaluate if FeS/FeS 2 formation causes longer-lived As removal. Because As-bearing pyrite is the common product of SRB metabolism in Holocene alluvial aquifers in both the USA and Southeast Asia, it was endeavored to derive thermodynamic data for arsenian pyrite to better predict geochemical processes in naturally reducing groundwaters. Including the new data for arsenian pyrite into Geochemist’s Workbench, its stability field completely dominates in reducing Eh–pH space and “displaces” other As-sulfides (orpiment, realgar) that have been implied to be important in previous modeling exercises and reported in rare field conditions. In summary, when anaerobic bacterial metabolism is optimized by providing both electron donors and acceptors, As is mobile under Fe-reducing conditions, immobile under SO 4 -reducing conditions, and arsenian pyrite is the likely stable mineral phase formed under SO 4 -reducing conditions, instead of pure As–S phases such as realgar or orpiment.

Dissolved and particulate metals (Fe, Zn, Cu, Cd, Pb) in two habitats from an active hydrothermal field on the EPR at 13°N

The distribution of Fe, Cu, Zn, Pb, Cd between the dissolved (< 2 μm) and the particulate (> 2 μm) fractions was measured after in-situ filtration in two hydrothermal habitats. The total metal concentration ranges exhibit a clear enrichment compared with the seawater concentration, accounting for the hydrothermal input for all the metals considered. Iron is the predominant metal (5–50 μM) followed by Zn and Cu. Cd and Pb are present at the nM level. At the scale studied, the behavior of temperature, pH and dissolved iron is semi-conservative whereas the other dissolved and particulate metals are characterized by non-conservative patterns. The metal enrichment of the > 2 μm fraction results from the settlement and accumulation of particulate matter close to the organisms, acting as a secondary metal source. The enrichment observed in the dissolved fraction can be related to the dissolution or oxidation of particles (mainly polymetallic sulfide) or to the presence of small particles and large colloids not retained on the 2 μm frit. SEM observations indicate that the bulk particulate observed is characteristic of crystalline particles settling rapidly from the high temperature smoker (sphalerite, wurtzite and pyrite), amorphous structures and eroded particles formed in the external zone of the chimney. Precipitation of Zn, Cu, Cd and Pb with Fe as wurtzite, sphalerite and pyrite is the main process taking place within the area studied and is semi-quantitative. The distribution of the dominant observed fauna has been related to the gradient resulting from the dilution process, with the alvinellids worms colonizing the hotter and more variable part of the mixing zone, but also to the metallic load of the mixing zone. Dissolved and particulate metal concentrations are therefore necessary abiotic factors to be studied in a multiparametric approach to understand the faunal distribution in hydrothermal ecosystems.

Determination of historical emission of heavy metals into the atmosphere: Celje case study

The research shows that in the Celje area (Slovenia), the historical anthropogenical emissions are 1,712 tons of Zn and 9.1 tons of Cd. For Zn, this value represents approximately 0.3% of the total Zn production in that area. Close to the former zinc smelting plant, the “Zn precipitation” has been estimated to be up to 0.036 mm. The 100-year Zn production left behind a heavily contaminated area with maximum concentrations of Zn of up to 5.6% in attic dust and 0.85% in the soil, and 456 mg/kg of Cd in attic dust and 59.1 mg/kg in the soil. The calculation of historical emissions is based on the data of heavy metals concentration in the attic dust at 98 sampling points and on the data from 19 measurement sites of the weight of total monthly air deposit. The main idea behind determining past emissions is that when the weight of the deposited dust on a small area is multiplied by the concentration of the element in that area, the mass of the polluter which has been transported to the place of interest by air can be calculated. If we sum up all the weight over the whole geochemical anomaly, we get the quantity of historical emissions.