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Niel Plummer

Publications and source records attributed to Niel Plummer.

At least 91 records · Page 5Linked to original sources
USGS1994

An interactive code (NETPATH) for modeling NET geochemical reactions along a flow PATH, version 2.0

NETPATH is an interactive Fortran 77 computer program used to interpret net geochemical mass-balance reactions between an initial and final water along a hydrologic flow path. Alternatively, NETPATH computes the mixing proportions of two to five initial waters and net geochemical reactions that can account for the observed composition of a final water. The program utilizes previously defined chemical and isotopic data for waters from a hydrochemical system. For a set of mineral and (or) gas phases hypothesized to be the reactive phases in the system, NETPATH calculates the mass transfers in every possible combination of the selected phases that accounts for the observed changes in the selected chemical and (or) isotopic compositions observed along the flow path. The calculations are of use in interpreting geochemical reactions, mixing proportions, evaporation and (or) dilution of waters, and mineral mass transfer in the chemical and isotopic evolution of natural and environmental waters. Rayleigh distillation calculations are applied to each mass-balance model that satisfies the constraints to predict carbon, sulfur, nitrogen, and strontium isotopic compositions at the end point, including radiocarbon dating. DB is an interactive Fortran 77 computer program used to enter analytical data into NETPATH, and calculate the distribution of species in aqueous solution. This report describes the types of problems that can be solved, the methods used to solve problems, and the features available in the program to facilitate these solutions. Examples are presented to demonstrate most of the applications and features of NETPATH. The codes DB and NETPATH can be executed in the UNIX or DOS1 environment. This report replaces U.S. Geological Survey Water-Resources Investigations Report 91-4078, by Plummer and others, which described the original release of NETPATH, version 1.0 (dated December, 1991), and documents revisions and enhancements that are included in version 2.0. 1 The use of trade, brand or product names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.

Water-Resources Investigations Report↗
USGS1993

Stable isotope enrichment in paleowaters of the southeast Atlantic coastal plain, United States

Paleowaters from the Floridan aquifer system in the southeastern Atlantic coastal plain have higher D/H and 18 O/ 16 O ratios than local Holocene ground water. Maximum δ 18 O enrichments in ground water having adjusted radiocarbon ages of 20,000 to 26,000 years are 0.7 to 2.3 per mil. The trend in isotopic enrichment in paleowaters is the reverse of that normally observed in continental glacial age ground water. Dissolved nitrogen and argon concentrations indicate, however, that the average recharge temperature was 5.3°C cooler than that today. The data indicate cool conditions in the southeast Atlantic coastal plain during the last glacial maximum, with recharge limited primarily to late summer tropical cyclones and hurricanes.

Science↗
USGS1992

Reply to Dr. Stoesselfs comment on “Reaction paths and equilibrium end-points in solid-solution aqueous-solution systems”

In reply to the Critical Comment of R. K. Stoessell (this issue), limiting activity coefficients of bromide in halite ( γ NaBr ) have been calculated by least-squares fitting of Simons et al.'s (1952) bromide distribution coefficient data for the Na(Cl,Br)-NaOH-H 2 O system at 35°C. Regular and subregular solidsolution model fits give γ NaBr = 7.4 and γ NaBr = 8.8, respectively. The Br contents of halite at equilibrium with seawater at initial halite saturation, calculated from the regular and subregular fits, are 17 ppm and 14 ppm, respectively. A survey of literature data for trace bromide in halite shows a wide spread in distribution coefficients, with lower values ( D Br ≈ 0.01) reported by Bloch and Schnerb (1953), Puchelt et al. (1972), and Lutz (1975), and higher values ( D Br − ≈ 0.03) reported by Braitsch and Herrmann (1963), Kühn (1968), Herrmann (1972), Herrmann (1980), Mccaffrey et al. (1987), valiashko et al. (1976), Valiashko and Lavrova (1976), and Fontes (pers. commun., 1990). The measurement of stoichiometric saturation states for halite (or sylvite) with trace bromide mole-fractions is not practical, given the insensitivity of the measured solubilities on the bromide mole-fractions. Distribution coefficient measurements, with proof of thermodynamic equilibrium, need to be obtained instead, to conclusively determine the thermodynamic-mixing properties of both Na(Cl,Br) and K(Cl,Br) solidsolution series at very low mole-fractions of bromide. The applicability of the stoichiometric saturation concept to the interpretation of precipitation processes is questionable, primarily because the concept requires solid-solutions to behave as one-component solids with fixed composition. Lippmann diagrams are useful in depicting stoichiometric saturation, endmember saturation, and thermodynamic equilibrium states in binary-solid-solution aqueous-solution systems. Lippmann diagrams can contribute a better understanding of these systems, regardless of the concentration of the endmember components.

Geochimica et Cosmochimica Acta↗
USGS1992

Dissolution of aragonite-strontianite solid solutions in nonstoichiometric Sr (HCO3)2-Ca (HCO3)2-CO2-H2O solutions

Synthetic strontianite-aragonite solid-solution minerals were dissolved in CO 2 -saturated non-stoichiometric solutions of Sr(HCO 3 ) 2 and Ca(HCO 3 ) 2 at 25°C. The results show that none of the dissolution reactions reach thermodynamic equilibrium. Congruent dissolution in Ca(HCO 3 ) 2 solutions either attains or closely approaches stoichiometric saturation with respect to the dissolving solid. In Sr(HCO 3 ) 2 solutions the reactions usually become incongruent, precipitating a Sr-rich phase before reaching stoichiometric saturation. Dissolution of mechanical mixtures of solids approaches stoichiometric saturation with respect to the least stable solid in the mixture. Surface uptake from subsaturated bulk solutions was observed in the initial minutes of dissolution. This surficial phase is 0–10 atomic layers thick in Sr(HCO 3 ) 2 solutions and 0–4 layers thick in Ca(HCO 3 ) 2 solutions, and subsequently dissolves and/or recrystallizes, usually within 6 min of reaction. The initial transient surface precipitation (recrystallization) process is followed by congruent dissolution of the original solid which proceeds to stoichiometric saturation, or until the precipitation of a more stable Sr-rich solid. The compositions of secondary precipitates do not correspond to thermodynamic equilibrium or stoichiometric saturation states. X-ray photoelectron spectroscopy (XPS) measurements indicate the formation of solid solutions on surfaces of aragonite and strontianite single crystals immersed in Sr(HCO 3 ) 2 and Ca(HCO 3 ) 2 solutions, respectively. In Sr(HCO 3 ) 2 solutions, the XPS signal from the outer ~ 60 Å on aragonite indicates a composition of 16 mol% SrCO 3 after only 2 min of contact, and 14–18 mol% SrCO 3 after 3 weeks of contact. The strontianite surface averages approximately 22 mol% CaCO 3 after 2 min of contact with Ca(HCO 3 ) 2 solution, and is 34–39 mol% CaCO 3 after 3 weeks of contact. XPS analysis suggests the surface composition is zoned with somewhat greater enrichment in the outer ~25 Å (as much as 26 mol% SrCO 3 on aragonite and 44 mol% CaCO 3 on strontianite). The results indicate rapid formation of a solid-solution surface phase from subsaturated aqueous solutions. The surface phase continually adjusts in composition in response to changes in composition of the bulk fluid as net dissolution proceeds. Dissolution rates of the endmembers are greatly reduced in nonstoichiometric solutions relative to dissolution rates observed in stoichiometric solutions. All solids dissolve more slowly in solutions spiked with the least soluble component ((Sr(HCO 3 ) 2 )) than in solutions spiked with the more soluble component (Ca(HCO 3 ) 2 ), an effect that becomes increasingly significant as stoichiometric saturation is approached. It is proposed that the formation of a non-stoichiometric surface reactive zone significantly decreases dissolution rates.

Geochimica et Cosmochimica Acta↗
USGS1990

Reaction paths and equilibrium end-points in solid-solution aqueous-solution systems

Equations are presented describing equilibrium in binary solid-solution aqueous-solution (SSAS) systems after a dissolution, precipitation, or recrystallization process, as a function of the composition and relative proportion of the initial phases. Equilibrium phase diagrams incorporating the concept of stoichiometric saturation are used to interpret possible reaction paths and to demonstrate relations between stoichiometric saturation, primary saturation, and thermodynamic equilibrium states. The concept of stoichiometric saturation is found useful in interpreting and putting limits on dissolution pathways, but there currently is no basis for possible application of this concept to the prediction and/ or understanding of precipitation processes. Previously published dissolution experiments for (Ba, Sr)SO 4 and (Sr, Ca)C̈O 3orth. solids are interpreted using equilibrium phase diagrams. These studies show that stoichiometric saturation can control, or at least influence, initial congruent dissolution pathways. The results for (Sr, Ca)CO 3orth. solids reveal that stoichiometric saturation can also control the initial stages of incongruent dissolution, despite the intrinsic instability of some of the initial solids. In contrast, recrystallisation experiments in the highly soluble KCl-KBr-H 2 O system demonstrate equilibrium. The excess free energy of mixing calculated for K(Cl, Br) solids is closely modeled by the relation G E = χ KBr χ KCl RT [ a 0 + a 1 (2 χ KBr −1)], where a 0 is 1.40 ± 0.02, a 1 , is −0.08 ± 0.03 at 25°C, and χ KBr and χ KCl are the mole fractions of KBr and KCl in the solids. The phase diagram constructed using this fit reveals an alyotropic maximum located at χ KBr = 0.676 and at a total solubility product, ΣΠ = [ K + ]([ Cl − ] + [ Br − ]) = 15.35.

Geochimica et Cosmochimica Acta↗
USGS1987

Thermodynamics of aragonite-strontianite solid solutions: Results from stoichiometric solubility at 25 and 76°C

Dissolution of synthetic strontianite-aragonite solid solutions was followed analytically to stoichiometric saturation using large solid to solution ratios in CO 2 -H 2 O solution at 25 and 76°C. The compositional dependence of the equilibrium constant was calculated from the composition of saturated (stoichiometric) solutions and used to calculate the activities and activity coefficients of CaCO 3 and SrCO 3 in the solid Ca (1− x ) Sr x CO 3 at 25 and 76°C. The results show that the solid-solution is not regular but unsymmetrical. The excess free energy of mixing is closely modeled for all compositions by the relation where A 0 is 8.49 ± 0.30 and 7.71 ± 0.20 KJ/mole and A 1 is −4.51 ± 0.20 and −3.36 ± 0.40 KJ/mole at 25 and 76°C, respectively. The equilibrium constant is denned as a function of the SrCO 3 mole fraction, x , by the relation where R is the gas constant, T is in Kelvins and K A and K S are the aragonite and strontianite equilibrium constants. The experimental results indicate the Henry's law coefficients of SrCO 3 in aragonites containing 0 to 6 mole percent SrCO 3 are approximately 91± 8 and 23 ± 1 at 25 and 76°C, respectively and for strontianites the Henry's law coefficients and applicable compositional ranges are approximately 7.3 ± 0.3 (0.84 ≤ x ≤ 1.00) and 3.3 ± 0.5 (0.50 ≤ x ≤ 1.00) at 25 and 76°C, respectively. Substitution of small amounts of Sr in aragonite and Ca in strontianite initially increases the stability of the solid. The most stable aragonites and strontianites contain 0.58 ± 0.03 and 12.5 ± 1.1 mole percent SrCO 3 and CaCO 3 at 25°C and 3.1 ± 0.3 and 17.2 ± 1.1 mole percent SrCO 3 and CaCO 3 at 76°C, respectively. The spinode occurs over the regions 0.065 ± 0.001 ≤ x ≤ 0.620 ± 0.014 at 25°C and 0.103 ± 0.007 ≤ x ≤ 0.585 ± 0.019 at 76°C where all compositions are unstable. A miscibility gap occurs over the compositional ranges 0.0058 ± 0.0003 ≤ x ≤ 0.875 ± 0.011 at 25°C and 0.031 ± 0.003 ≤ x ≤ 0.828 ± 0.011 at 76°C and is in reasonable agreement with reported compositions of natural aragonites and strontianites. Marine aragonites are neither at equilibrium nor stoichiometric saturation with surface seawater. The experimentally observed distribution coefficient of Sr in aragonite is 12 times larger than the calculated equilibrium value (0.095) at 25°C. Naturally occurring strontianites contain large amounts of calcium primarily because Ca/Sr ratios in natural waters are typically large. Neither equilibrium nor stoichiometric saturation is observed at 76°C during laboratory recrystallization of strontianite-aragonite solid solutions even after apparent 100 percent conversion to a narrow secondary composition and demonstration of a nearly constant composition system for periods of 300 hours.

Geochimica et Cosmochimica Acta↗
USGS1985

Kinetic and thermodynamic factors controlling the distribution of SO32- and Na+ in calcites and selected aragonites

Significant amounts of SO 4 2− , Na + , and OH − are incorporated in marine biogenic calcites. Biogenic high Mg-calcites average about 1 mole percent SO 4 2− . Aragonites and most biogenic low Mg-calcites contain significant amounts of Na + , but very low concentrations of SO 4 2− . The SO 4 2− content of non-biogenic calcites and aragonites investigated was below 100 ppm. The presence of Na + and SO 4 2− increases the unit cell size of calcites. The solid-solutions show a solubility minimum at about 0.5 mole percent SO 4 2− beyond which the solubility rapidly increases. The solubility product of calcites containing 3 mole percent SO 4 2− is the same as that of aragonite. Na + appears to have very little effect on the solubility product of calcites. The amounts of Na + and SO 4 2− incorporated in calcites vary as a function of the rate of crystal growth. The variation of the distribution coefficient ( D "> D ) of SO 4 2− in calcite at 25.0°C and 0.50 molal NaCl is described by the equation D = k 0 + k 1 R "> D = k 0 + k 1 R where k 0 "> k 0 and k 1 "> k 1 are constants equal to 6.16 × 10 −6 "> 6.16 × 10 −6 and 3.941 × 10 −6 "> 3.941 × 10 −6 , respectively, and R "> R is the rate of crystal growth of calcite in mg·min −1 ·g −1 of seed. The data on Na + are consistent with the hypothesis that a significant amount of Na + occupies interstitial positions in the calcite structure. The distribution of Na + follows a Freundlich isotherm and not the Berthelot-Nernst distribution law. The numerical value of the Na + distribution coefficient in calcite is probably dependent on the number of defects in the calcite structure. The Na + contents of calcites are not very accurate indicators of environmental salinities.

Geochimica et Cosmochimica Acta↗
USGS1984

The solubility of strontianite (SrCO 3 ) in CO 2 -H 2 O solutions between 2 and 91°C, the association constants of SrHCO + 3 (aq) and SrCO 0 3 (aq) between 5 and 80°C, and an evaluation of the thermodynamic properties of Sr 2+ (aq) and SrCO 3 (cr) at 25°C and 1 atm total pressure

Seventy new measurements (Sr T -P co2 of the solubility of strontianite were used to evaluate the equilibrium constant for the reaction SrCO 3 ( cr ) = Sr 2+ ( aq ) + CO 2− 3 ( aq ) between 2 and 91 °C. The temperature dependence of the equilibrium constant is given by the expression Log K = 155.0305 − 7239.594/ T − 56.58638 log T where T is in degrees Kelvin. The log K of strontianite, the Gibbs energy, enthalpy and entropy of the reaction at 25°C are −9.271 ± 0.020, 52.919 ± 0.08 kJ · mol −1 , −1.67 ± 1.30 kJ · mol −1 , and −183.1 ± 4.0 J · mol −1 · K −1 , respectively. The equilibrium constants are consistent with an aqueous model that includes the ion pairs SrHCO + 3 (aq) and SrCO 0 3 (aq) which were evaluated by potentiometric methods between 5 and 80°C. The equilibrium constant for the association reaction Sr 2+ ( aq ) + HCO − 3 ( aq ) = SrHCO + 3 aq ) is given by the expression Log K SrHCO + 3 = −3.248 + 0.014867 T . The log of the association constant, the Gibbs energy, enthalpy and entropy of the reaction at 25°C are 1.18, −6.76 kJ · mol −1 , 25.30 kJ · mol −1 , and 107.5 J · mol −1 · K −1 , respectively. The equilibrium constant for the association reaction Sr 2+ ( aq ) + CO 2− 3 ( aq ) = SrCO 0 3 aq ) is given by the expression Log K SrCO 0 3 = −1.019 + 0.012826 T . The log of the association constant, the Gibbs energy, enthalpy, and entropy of the reaction at 25°C are 2.81, −16.01 kJ · mol −1 ,21.83 kJ · mol −1 , and 126.9 J · mol −1 · K −1 , respectively. These results lead to reliable calculation of the aqueous speciation and solubility of strontianite in the system SrCO 3 -CO 2 -H 2 O from 0 to more than 90°C. Literature data on the solubility of strontianite have been evaluated and compared with these results. Our new data for strontianite have been used in an evaluation of the thermodynamic properties of Sr 2+ (aq), SrCO 3 (cr) and related compounds. The following values are recommended for the standard enthalpy (kJ · mol −1 ), Gibbs energy (kJ · mol −1 ), and entropy (J · mol −1 · K −1 ), respectively, of Sr 2+ aq): −550.90 ± 0.50, −563.83 ± 0.8 and −31.50 ± 2.0, and for SrCO 3 (cr): −1225.77 ± 1.1, −1144.73 ± 1.0 and 97.2.

Geochimica et Cosmochimica Acta↗
USGS1984

Partial compilation and revision of basic data in the WATEQ programs

Several portions of the basic data in the WATEQ series of computer programs (WATEQ, WATEQF, WATEQ2, WATEQ3, and PHREEQE) are compiled. The density and dielectric constant of water and their temperature dependence are evaluated for the purpose of updating the Debye-Huckel solvent parameters in the activity coefficient equations. The standard state thermodynamic properties of the Fe2+ and Fe3+ aqueous ions are refined. The main portion of this report is a comprehensive listing of aluminum hydrolysis constants, aluminum fluoride, aluminum sulfate, calcium chloride, magnesium chloride, potassium sulfate and sodium sulfate stability constants, solubility product constants for gibbsite and amorphous aluminum hydroxide, and the standard electrode potentials for Fe (s)/Fe2+(aq) and Fe2 +(aq)/Fe3+(aq). (USGS)

Water-Resources Investigations Report↗
USGS1983

Development of reaction models for ground-water systems

Methods are described for developing geochemical reaction models from the observed chemical compositions of ground water along a hydrologic flow path. The roles of thermodynamic speciation programs, mass balance calculations, and reaction-path simulations in developing and testing reaction models are contrasted. Electron transfer is included in the mass balance equations to properly account for redox reactions in ground water. The mass balance calculations determine net mass transfer models which must be checked against the thermodynamic calculations of speciation and reaction-path programs. Although reaction-path simulations of ground-water chemistry are thermodynamically valid, they must be checked against the net mass transfer defined by the mass balance calculations. An example is given testing multiple reaction hypotheses along a flow path in the Floridan aquifer where several reaction models are eliminated. Use of carbon and sulfur isotopic data with mass balance calculations indicates a net reaction of incongruent dissolution of dolomite (dolomite dissolution with calcite precipitation) driven irreversibly by gypsum dissolution, accompanied by minor sulfate reduction, ferric hydroxide dissolution, and pyrite precipitation in central Florida. Along the flow path, the aquifer appears to be open to CO 2 initially, and open to organic carbon at more distant points down gradient.

Geochimica et Cosmochimica Acta↗
USGS1982

The solubilities of calcite, aragonite and vaterite in CO2-H2O solutions between 0 and 90°C, and an evaluation of the aqueous model for the system CaCO3-CO2-H2O

Calculations based on approximately 350 new measurements (Ca T -PCO 2 ) of the solubilities of calcite, aragonite and vaterite in CO 2 -H 2 O solutions between 0 and 90°C indicate the following values for the log of the equilibrium constants K C , K A , and K V respectively, for the reaction CaCO 3 (s) = Ca 2+ + CO 2− 3 : where T is in o K. At 25°C the logarithms of the equilibrium constants are −8.480 ± 0.020, −8.336 ± 0.020 and −7.913 ± 0.020 for calcite, aragonite and vaterite, respectively. The equilibrium constants are internally consistent with an aqueous model that includes the CaHCO + 3 and CaCO 0 3 ion pairs, revised analytical expressions for CO 2 -H 2 O equilibria, and extended Debye-Hückel individual ion activity coefficients. Using this aqueous model, the equilibrium constant of aragonite shows no PCO 2 -dependence if the CaHCO + 3 association constant is between 0 and 90°C, corresponding to the value log K Cahco + 3 = 1.11 ± 0.07 at 25°C. The CaCO 0 3 association constant was measured potentiometrically to be between 5 and 80°C, yielding log K CaCO 0 3 = 3.22 ± 0.14 at 25°C. The CO 2 -H 2 O equilibria have been critically evaluated and new empirical expressions for the temperature dependence of K H , K 1 and K 2 are , and log K 2 = −107.8871 − 0.03252849 T + 5151.79/ T + 38.92561 log T − 563713.9/ T 2 which may be used to at least 250°C. These expressions hold for 1 atm. total pressure between 0 and 100°C and follow the vapor pressure curve of water at higher temperatures. Extensive measurements of the pH of Ca-HCO 3 solutions at 25°C and 0.956 atm PCO 2 using different compositions of the reference electrode filling solution show that measured differences in pH are closely approximated by differences in liquid-junction potential as calculated by the Henderson equation. Liquid-junction corrected pH measurements agree with the calculated pH within 0.003-0.011 pH. Earlier arguments suggesting that the CaHCO + 3 ion pair should not be included in the CaCO 3 -CO 2 -H 2 O aqueous model were based on less accurate calcite solubility data. The CaHCO + 3 ion pair must be included in the aqueous model to account for the observed PCO 2 -dependence of aragonite solubility between 317 ppm CO 2 and 100% CO 2 . Previous literature on the solubility of CaCO 3 polymorphs have been critically evaluated using the aqueous model and the results are compared.

Geochimica et Cosmochimica Acta↗
USGS1982

BALANCE : A computer program for calculating mass transfer for geochemical reactions in ground water

BALANCE is a Fortran computer program designed to define and quantify chemical reactions between ground water and minerals. Using (1) the chemical compositions of water samples from two points along a flow path and (2) a set of mineral phases hypothesized to be the reactive constituents in the system, the program calculates the mass transfer (amounts of the phases entering or leaving the aqueous phase) necessary to account for the observed changes in composition between the two water samples. Additional constraints can be included in the problem formulation to account for mixing of two end-member waters, redox reactions, and, in a simplified form, isotopic composition. The computer code and a description of the input necessary to run the program are presented. Three examples typical of groundwater systems are described.

Water-Resources Investigations Report↗
USGS1981

Crystal growth of calcite from calcium bicarbonate solutions at constant P CO 2 and 25°C: a test of a calcite dissolution model

A highly reproducible seeded growth technique was used to study calcite crystallization from calcium bicarbonate solutions at 25&deg;C and fixed carbon dioxide partial pressures between 0.03 and 0.3 atm. The results are not consistent with empirical crystallization models that have successfully described calcite growth at low P CO 2 (< 10 &minus;3 atm). Good agreement was found between observed crystallization rates and those calculated from the calcite dissolution rate law and mechanism proposed by Plummer et al . (1978).

Geochimica et Cosmochimica Acta↗