Carbonate equilibria in hydrothermal systems: First ionization of carbonic acid in NaCl media to 300°C

The ionization quotients of aqueous carbon dioxide (carbonic acid) have been precisely determined in NaCl media to 5 m and from 50° to 300°C using potentiometric apparatus previously developed at Oak Ridge National Laboratory. The pressure coefficient was also determined to 250°C in the same media. These results have been combined with selected information in the literature and modeled in two ways to arrive at the best fits and to derive the thermodynamic parameters for the ionization reaction, including the equilibrium constant, activity coefficient quotients, and pressure coefficients. The variation with temperature of the two fundamental quantities $\text{Δ}\text{V}\text{?}{}^{\mathrm{o}}$ and $\text{Δ}\text{C}\text{?}{}^{\mathrm{o}}{}_{\mathrm{p}}$ were examined along the saturation vapor pressure curve and at constant density. The results demonstrated again that for reactions with minimal electrostriction changes the magnitudes and variations of $\text{Δ}\text{C}\text{?}{}^{\mathrm{o}}{}_{\mathrm{p}}$ and $\text{Δ}\text{V}\text{?}{}^{\mathrm{o}}$ with temperature are small and, in addition, $\text{Δ}\text{C}\text{?}{}_{\mathrm{p}}$ and $\text{Δ}\text{V}\text{?}$ are approximately independent of salt concentration.The results have also been applied to an examination of the solubility of calcite as a function of pH (in a given NaCl medium) for the neutral to acidic region both for systems with fixed CO₂ pressure and systems where the calcium ion concentration equals the concentration of carbon. The pH of saturated solutions of calcite with P_CO2 of 12 bars increases from 5.1 to 5.5 between 100° and 300°C.     

Dissolution of secondary copper sulphides using complex-forming agents (EDTA,EDA). Part I: Covellite dissolution in EDTA and EDA

Problems of dissolution of the so-called secondary copper sulphides are very important for dynamic as well as percolation leaching of ores. This paper deals with dissolution kinetics of sulphides in an alkaline medium, using complex-forming agents in connection with possibility to leach basic, partially oxidized ores. Natural minerals and their polydispersions were investigated and the so-called geometrical model was used for evaluation. Basic dependences of the dissolution rate on the reagent concentration and pH value of the leaching solution were found and an attempt at their mathematical expression and physical interpretation was made. The first part of this work refers to the systems of covellite-ethylene diamine tetra-acetic acid (EDTA) and covellite-ethylene diamine (EDA). The established dependences are not only of theoretical but also of practical importance.     

Dissolution of secondary copper sulphides using complex-forming agents (EDTA,EDA). Part II: Chalcocite dissolution in EDTA and EDA

This work is immediate continuation of Part I, using an identical method and evaluation for kinetic studies. The systems chalcocite-ethylene diamine tetra-acetic acid and chalcocite-ethylene diamine were studied. It was necessary to refine the geometrical model method for chalcocite in order to establish dissolution kinetics of polydispersions. This work confirms that chalcocite leaching proceeds through covellite even in the medium of complex-forming agents and kinetic equations for both leaching stages were evaluated with an attempt at physical interpretation.     

Vertical concentration profiles of lead in the Central Pacific at 15°N and 20°S

Concentrations of lead were measured in a surface transect and at two vertical profile stations (15°N and 20°S) in the Central Pacific. These measurements complement similar measurements made earlier in the North Pacific at 33°N and in the Northwest Atlantic at 34°N [1,2], as well as recent measurements of eolian lead input fluxes near each of these locations [3]. The new transect of surface water concentrations of lead corroborates previous measurements, which decrease from 13 ng/kg at 30°N to 4 ng/kg at 17°S in the Central Pacific [4]. This transect gradient is shown to overlie a similar geographic gradient of subsurface maximum concentrations of lead in the three Pacific vertical profile stations, decreasing from 14 ng/kg at 33°N to 11 ng/kg at 14°N to 2.5 ng/kg at 20°S. Lead concentrations at each of those locations exhibit maxima at 400 m, decreasing concentrations to 2500 m and approximately concentrations of 0.8–1.1 ng/kg below that depth. The subsurface maximum at the northwest Atlantic profile station (36 ng/kg at 34°N) is also congruent with surface water lead concentrations which decrease from 806 ng/kg to 32 ng/kg in an offshore transect from Rhode Island to 34°N, 66°W [5], and the shape of the Atlantic profile is congruent with those in the Pacific. There is a positive correlation between the magnitudes of eolian lead input fluxes and the magnitudes of the upper water maxima in lead concentration profiles at corresponding locations as follows: South Pacific easterlies 3 ng/cm² yr vs. 2.5 ng/kg; North Pacific easterlies 6 ng/cm² yr vs. 11 ng/kg; North Pacific westerlies 50 ng/cm² yr vs. 14 ng/kg; and North Atlantic westerlies 170 ng/cm² yr vs. 36 ng/kg.This relationship enables one to view the anthropogenic perturbations of the marine lead cycle on a global scale, since the industrial origin of eolian and seawater lead has been established by correlations between geographic patterns of industrial lead emissions to the atmosphere and isotopic ratios of industrial leads [3] and by geographic patterns of Pb/silicate-dust ratios and lead isotopic ratios in ocean surface waters [3–5]. These new data coupled with earlier biogeochemical data indicate that surface water concentrations of lead in the North Pacific and North Atlantic are now conservatively estimated to be 8 to 20-fold greater and those in the South Pacific are 2-fold greater than natural concentrations because of industrial emissions of lead to the atmosphere.     

Seasonal variation in stable oxygen and carbon isotope values recovered from modern lacustrine freshwater mollusks: paleoclimatological implications for sub-weekly temperature records

A fingernail clam (Sphaerium simile, Sphaeriidae) from Science Lake, a small watershed located in Allegany State Park, New York, USA and a zebra mussel (Dreissena polymorpha, Dreissenidae) from Keuka Lake, New York, the third largest Finger Lake of central New York, were selected to evaluate the applicability of using ¹⁸O_(CaCO3) and ¹³O_(CaCO3) values for sub-weekly climate records. Seasonal variation in ¹⁸O_(CaCO3) values was compared with predicted equilibrium values to test the hypothesis that lacustrine molluscs produce shell aragonite according to environmental variables. For the purpose of comparison, aragonite temperature-fractionation equations determined by Grossman& Ku (1986) and Patterson et al. (1993) were used. Sphaerium simile appears to produce ¹⁸O_(CaCO3) values predicted by Patterson et al. (1993), while Dreissena polymorpha produces ¹⁸O_(CaCO3) values in agreement with Grossman & Ku (1986). We attribute the difference to family-specific temperature-fractionation relationships. Because both types of mollusc record climate variables with a high degree of integrity, they should each serve as excellent paleoclimate proxies.The fingernail clam collected from a small watershed exhibits higher variation about the seasonal pattern than did the zebra mussel collected from a large watershed. This is attributed to the increased sensitivity of the small watershed to storm perturbation. Analysis of fossil molluscs from such watersheds might be useful in discerning paleo-storminess.     

Embedding reach-scale fluvial dynamics within the CAESAR cellular automaton landscape evolution model

We introduce a new computational model designed to simulate and investigate reach-scale alluvial dynamics within a landscape evolution model. The model is based on the cellular automaton concept, whereby the continued iteration of a series of local process ‘rules’ governs the behaviour of the entire system. The model is a modified version of the CAESAR landscape evolution model, which applies a suite of physically based rules to simulate the entrainment, transport and deposition of sediments. The CAESAR model has been altered to improve the representation of hydraulic and geomorphic processes in an alluvial environment. In-channel and overbank flow, sediment entrainment and deposition, suspended load and bed load transport, lateral erosion and bank failure have all been represented as local cellular automaton rules. Although these rules are relatively simple and straightforward, their combined and repeatedly iterated effect is such that complex, non-linear geomorphological response can be simulated within the model. Examples of such larger-scale, emergent responses include channel incision and aggradation, terrace formation, channel migration and river meandering, formation of meander cutoffs, and transitions between braided and single-thread channel patterns. In the current study, the model is illustrated on a reach of the River Teifi, near Lampeter, Wales, UK.     

Assessing spatial and attribute errors in large national datasets for population distribution models: a case study of Philadelphia county schools

Geospatial technologies and digital data have developed and disseminated rapidly in conjunction with increasing computing efficiency and Internet availability. The ability to store and transmit large datasets has encouraged the development of national infrastructure datasets in geospatial formats. National datasets are used by numerous agencies for analysis and modeling purposes because these datasets are standardized and considered to be of acceptable accuracy for national scale applications. At Oak Ridge National Laboratory a population model has been developed that incorporates national schools data as one of the model inputs. This paper evaluates spatial and attribute inaccuracies present within two national school datasets, Tele Atlas North America and National Center of Education Statistics (NCES). Schools are an important component of the population model, because they are spatially dense clusters of vulnerable populations. It is therefore essential to validate the quality of school input data. Schools were also chosen since a validated schools dataset was produced in geospatial format for Philadelphia County; thereby enabling a comparison between a local dataset and the national datasets. Analyses found the national datasets are not standardized and incomplete, containing 76 to 90 percent of existing schools. The temporal accuracy of updating annual enrollment values resulted in 89 percent inaccuracy for 2003. Spatial rectification was required for 87 percent of NCES points, of which 58 percent of the errors were attributed to the geocoding process. Lastly, it was found that by combining the two national datasets, the resultant dataset provided a more useful and accurate solution.