William J. Snodgrass

Flux of reduced chemical constituents (Fe2+, Mn2+, NHinf4sup+ and CH4) and sediment oxygen demand in Lake Erie

Sediment pore water concentrations of Fe2+, Mn2+, NHinf4sup+ and CH4 were analyzed from both diver-collected cores and anin situ equilibration device (peeper) in Lake Eries central basin. Sediment oxygen demand (SOD) was measured at the same station with a hemispheric chamber (including DO probe and recorder) subtending a known area of sediments. The average SOD was 9.4 mM m−2 day−1 (0.3 g m−2 day−1). From pore water gradients within the near-surface zone, the chemical flux across the interface was calculated indirectly using Ficks first law modified for sediments. These calculations, using core and peeper gradients, always showed sediment loss to overlying waters, and variations between the two techniques differed by less than an order of magnitude for Fe2+ and CH4. The transport of these reduced constituents can represent a sizeable oxygen demand, ranging from less than 1% for Fe2+ and Mn2+ to as high as 26% for NHinf4sup+, and 30% for CH4. The average flux of these constituents could account for about a third of the SOD at the sediment-water interface of this station.

Historical Records of Metal Pollution in Sediments of Toronto and Hamilton Harbours

The sediments of Hamilton and Toronto Harbours contain some of the oldest records of metal pollution in the Great Lakes basin. The fluxes of Cd, Cr, Cu, Ni, Pb, Zn, Fe, and Mn into the two harbours have been estimated from the analyses of core samples dated by the Pb-210 technique. The contrasting metal levels in the two harbour sediments are viewed in relation to the differences in the disposal strategies of the dredged spoils and the sources of metal pollution in the harbours. The Zn and Fe concentrations of 5 to 8 mg g−1 and 10 to 13 % dry wt. in Hamilton Harbour sediments, which are among the highest recorded in any harbour, can be related to effluent discharges from the large local iron and steel plants. An inventory of the sources and sinks of pollutant metals in Hamilton Bay shows a substantive export of the metals to Lake Ontario.

Solution Equilibria for Uranium Ore Processing: The BaSO4-H2SO4-H2O System and the RaSO4-H2SO4-H2O System

Abstract A radio-tracer determination of the solubility of BaSO4 in H2SO4-H2O mixtures was undertaken at temperatures of 25°C and 60°C. These were subsequently modelled using the Pitzer model for the activity coefficients, and estimates were made for Ba2+-SO42− and Ba2+-HSO4− interaction parameters. The final model yields an excellent description of the solubility of BaSO4 in H2SO4-H2O mixtures up to 6 mol/kg and at both 25°C and 60°C. The logarithm of the thermodynamic solubility product constant (logKsp) for barite obtained by regression analysis was −10.02 ± 0.02 at 25°C and −9.68 ± 0.01 at 60°C. The values of the ion association constant derived from these data are 2.49 ± 0.03 at 25°C and 2.55 ± 0.1 at 60°C. The enthalpy of dissolution for BaSO4 was estimated to be 17.6 ± 0.2 kJ mol−1. Literature solubility data for the RaSO4-H2SO4-H2O system have also been interpreted, using the Pitzer model for the necessary activity coefficients. The logarithm of the thermodynamic solubility product constant (logKsp) for radium sulfate obtained was −10.21 ± 0.06 at 25°C, while the value of the ion association constant derived is 2.76 ± 0.05 at 25°C. The high negative value of the Pitzer parameter β2 obtained by regression analysis of these data suggests that the explicit recognition of a RaSO4(aq) ion association species is to be preferred in this case.

Experimental measurement of sediment nitrification and denitrification in Hamilton Harbour, Canada

This research examines the role of sediment nitrification and denitrification in the nitrogen cycle of Hamilton Harbour. The Harbour is subject to large ammonia and carbon loadings from a waste-water treatment plant and from steel industries. Spring ammonia concentrations rapidly decrease from 4.5 to 0.5 mg 1−1, while spring nitrate concentrations increase from 1 to 2 mg l−1, by mid-summer. A three-layer sediment model was developed. The first layer is aerobic; in it, oxidation of organics and nitrification occurs. The second layer is for denitrification, and the third layer is for anaerobic processes. Ammonia sources for nitrification include diffusion from the water column, sources associated with the oxidation of organics, sources from denitrification and from anaerobic processes. Diffusion of oxygen, ammonia and nitrate across the sediment-water interface occurs. Temperature effects are modelled using the Arrhenius concept. A combination of zero-order kinetics for nitrate or ammonia consumption with diffusion results in a half-order reaction, with respect to the water column loss rate to sediments.From experimental measurement, the rate of nitrification is 200 mg N 1−1 sediment per day, while that of denitrification is 85 mg N 1–1 sediment per day at 20 °C. The Arrhenius activation energy is estimated as 15 000 cal/ mole-K and 17 000 cal/ mole-K for nitrification and denitrification, respectively, between 10 °C and 20 °C. Calculations of the flux of ammonia with the sediments, using the biofilm model, compare favourably with experimental observations. The ammonia flux from the water column is estimated to account for 20% of the observed decrease in water column stocks of ammonia, while the nitrate flux from the water column is estimated to account for 25% of the total nitrogen produced by the sediments.

Model for Lake-Bay Exchange Flow

Abstract Transient inflows and outflows of water between Lake Ontario and Hamilton Harbor, driven by lake seiches, can be parameterized as a two-directional exchange flow. Estimates of exchange flows made from current measurements by others result in unlikely values. A model is developed for exchange flow during summer stratification in which two distinct flow patterns exist — (i) lake water enters the harbours hypolimnion, displacing an equal volume of hypolimnetic water to the epilimnion and then of epilimnetic water to the lake and (ii) lake water exchanges directly with the harbours epilimnion. The temporal variation of exchange flows are estimated from a TDS budget and temperature data. They suggest that weekly estimates of epilimnetic exchange vary from 1 to 5 times Q (the average annual flow rate) while hypolimnetic exchange varies from 0 to 15 times Q for a 3-year period. The calculations suggest that stratification and lake seiches significantly increase the “pumping” action of exchange flow in summertime compared to the remainder of the year.

The aqueous dissolution kinetics of the barium/lead sulfate solid solution series at 25 and 60°C

Abstract The dissolution behavior of the BaxPb(1−x) SO4 solid solution series and pure endmembers was investigated. The solids were precipitated from sulfuric acid solutions, then dissolved in slightly acidified water at 25 and 60°C for 24 h. Endmembers equilibrated within several h at 25°C and several min at 60°C. At 25°C the solid solutions dissolved congruently up to 30 min, then the Ba2+ concentration decreased and Pb2+ concentration increased for the duration of the experiments. At 60°C the results were similar except the region of congruent dissolution was over before the first samples were taken at 3 min. Solid solution-aqueous solution (SSAS) reaction paths were followed on Lippmann diagrams. During congruent dissolution the reaction paths dissolved toward stoichiometric saturation. During incongruent dissolution the systems moved toward two-component thermodynamic equilibrium at lower aqueous mole fractions of Ba2+, while maintaining steady states of undersaturation with respect to the stoichiometric saturation. At 60°C the solutions maintained steady states closer to stoichiometric saturation than at 25°C. The 25 °C results were fit to the two parameter kinetic model of Denis and Michard (1983) with an additional parameter to account for the precipitation rate dependence of the distribution coefficient. The 60°C results could not be modelled due to a complete lack of data in the congruent dissolution region. The model was able to generate close fits to our Ba2+ data, but not our Pb2+ data. The model was unable to generate steady states significantly below the stoichiometric saturation given the observed rates of congruent dissolution. This indicates a process occurs which acts to decrease the congruent dissolution rate after the formation of a secondary phase.

Preparation, characterization and aging of δ-MnO2, for use in trace metal speciation studies

Abstract Well characterized synthetic δ-MnO2 can be used successfully for trace metal speciation studies in natural waters. Characteristics and adsorption behavior of δ-MnO2 depend on the preparation method and subsequent treatment and aging. Three different recipes were used to prepare δ-MnO2. Methods involving a redox reaction between Mn2+ and Mn7+ at neutral pH (δ-MnO2-redox), and reduction of Mn7+ at low pH (δ-MnO2-red), yielded compounds with characteristics in agreement with literature data; they also have a high adsorption capacity for Cu. A method involving oxidation of Mn2+ at high pH yielded a δ-MnO2(ox), with some variant characteristics and a lower adsorption capacity for Cu. An artificial aging process, using heat treatment at neutral pH, produced cryptomelane from δ-MnO2(ox), but not from δ-MnO2(redox) or δ-MnO2(red). Conversion of δ-MnO2(redox) to cryptomelane and loss of approximately one-half of the adsorption capacity, as a result of a natural aging process, can be avoided for at least four years if the K content is 10% in the solid, and the solid is stored at low temperature. Potassium content, and not a low pH, appears to control the conversion to cryptomelane. Adsorption capacity of δ-MnO2 for Cu appears to be related to the K and H2O content of the solid, which is structure dependent. Because of their higher adsorption capacity for Cu, δ-MnO2(redox) or δ-MnO2(red) are more suitable for trace metal studies in natural waters, than δ-MnO2(ox).

Modelling solution equilibria for uranium ore processing: The PbSO4-H2SO4-H2O and PbSO4-Na2SO4-H2O systems

Abstract Solution equilibria in the PbSO4-H2SO4-H2O and PbSO4-Na2SO4-H2O systems have been modelled using the Pitzer formalism for the determination of activity coefficients over the temperature range from 0–60°C, and up to 6 m in H2SO4. The available literature, common ion solubility data, and our own experimental data at 60°C have been analysed to determine the various ion interaction parameters needed to provide a description of the solution equilibria. The resulting array of Pitzer parameters yield an accurate description of the solubility equilibria over the temperature range 0–60°C, and concentration conditions up to 6 m in H2SO4.

The formation of hetero-epitaxial deposits of lead, barium and (barium/lead) sulfates on quartz surfaces

As a continuation of an investigation concerning the fate of226Ra during uranium ore milling and long-term tailings storage we have grown hetero-epitaxial deposits of barium sulfate, lead sulfate and mixed barium/lead sulfate on sawn quartz surfaces of differing crystallographic orientations. The deposits formed readily on the substrate from supersaturated aqueous solutions of the parent ions and appear to be strongly adherent. Calcium sulfate formed deposits on quartz at very much greater levels of supersaturation than lead or barium sulfate.

A new model describing the adsorption of copper on manganese dioxide

The use of delta-MnO/sub 2/ in determining conditional stability constants (CSC) for trace metal-organic complexes depends upon the precise modeling of trace metal uptake by delta-MnO/sub 2/. Cu adsorption deviates from Langmuir linearity at low surface coverages due to a nonconstant binding energy. Adsorption isotherms for various delta-MnO/sub 2/ batches, obtained in the pH range 6-8.5, fit the implicit model well. CSC values obtained for Cu-NTA by using this model agree with literature data. 14 references, 6 figures.