期刊界 All Journals 搜尽天下杂志传播学术成果专业期刊搜索期刊信息化学术搜索

1.

Total individual ion activity coefficients of calcium and carbonate in seawater at 25°C and 35%. salinity,and implications to the agreement between apparent and thermodynamic constants of calcite and aragonite

L.Niel Plummer Eric T. Sundquist 《Geochimica et cosmochimica acta》1982,46(2):247-258

We have calculated the total individual ion activity coefficients of carbonate and calcium,

γ_{TCO_{3}^{2?}}

and

γ_{TCa^{2+}}

, in seawater. Using the ratios of stoichiometric and thermodynamic constants of carbonic acid dissociation and total mean activity coefficient data measured in seawater, we have obtained values which differ significantly from those widely accepted in the literature. In seawater at 25°C and 35%. salinity the (molal) values of

γ_{TCO^{2}_{3?}}

and

γ_{TCa_{2+}}

are

0.038 ± 0.002

and

0.173 ± 0.010

, respectively. These values of

γ_{TCO_{3}^{2?}}

and

γ_{TCa^{2+}}

are independent of liquid junction errors and internally consistent with the value

γ_{TCl^{?}} = 0.651

. By defining

γ_{TCa^{2+}}

and

γ_{TCO_{3}^{2?}}

on a common scale (

γ_{TCl^{?}}

), the product

γ_{TCa^{2+}}

γ_{TCO_{3}^{2?}}

is independent of the assigned value of

γ_{Cl^{?}}

and may be determined directly from thermodynamic measurements in seawater. Using the value

γ_{TCa^{2+}} γ_{TCO_{3}^{2?}} = 0.0067

and new thermodynamic equilibrium constants for calcite and aragonite, we show that the apparent constants of calcite and aragonite are consistent with the thermodynamic equilibrium constants at 25°C and 35%. salinity. The demonstrated consistency between thermodynamic and apparent constants of calcite and aragonite does not support a hypothesis of stable Mg-calcite coatings on calcite or aragonite surfaces in seawater, and suggests that the calcite critical carbonate ion curve of Broecker and Takahashi (1978, Deep-Sea Research25, 65–95) defines the calcite equilibrium boundary in the oceans, within the uncertainty of the data. 相似文献

2.

Dimensionless number and approximate calculation of the upper particle size of floatability in flotation machines

H.J Schulze 《International Journal of Mineral Processing》1982,9(4):321-328

Two simple approximating equations are given for the calculation of the upper particle size of floatability under the turbulent hydrodynamic conditions in a flotation machine (apparatus). They comprise solid density ?_p, fluid density ?_fl, surface tension σ, contact angle θ and a parameter depending on energy dissipation, the vortex acceleration, which we call “machine acceleration”

b_{m}

. Some diagrams are shown for practical purposes. A dimensionless characteristic number analogous to the bond number is introduced in order to characterize the stability of aggregates. 相似文献

3.

Stenols and stanols in the oxic and anoxic waters of the Black Sea

Robert B. Gagosian Franz Heinzer 《Geochimica et cosmochimica acta》1979,43(4):471-486

Water samples collected from a slope station and two deep stations in the western basin of the Black Sea were analyzed for stenols and stanols by glass capillary gas chromatography. These results were used in conjuction with hydrographic, particulate organic carbon, and chlorophyll a data to better understand sterol sources and their transport and transformation mechanisms in anoxic basins.The total free sterol concentrations found in the surface waters were 450–500 ng/l dropping rapidly to values well below 100 ng/l at depths below the

O_{2} H_{2} S

interface. In the upper 200 m of the water column a strong association of sterols with particulate matter is suggested. Structural elucidation by a gas chromatograph-mass spectrometer-computer system revealed the presence of at least sixteen different stenols and stanols in the surface waters of the Black Sea. Cholesterol, 24-methylenecholesterol and 24-methylcholesta-5,22-dien-3β-ol were the major sterols in the surface waters. Cholesterol and 24-ethylcholesterol both exhibited a subsurface maximum at the

O_{2} H_{2} S

interface. In the anoxic deep waters (200–2000 m) only cholesterol and 24-ethylcholesterol were found. Two stenols were found that have not been reported in seawater: a C₂₆ stenol with a saturated C₇H₁₅ side chain (presumably 24-norcholesterol) and 24-ketocholesterol. At least six 5α-stanols could be identified in the surface samples, each of them comprising about 10–20% of the concentration of the corresponding Δ5-stenol. From these comparatively high surface values the stanol concentrations drop rapidly to values near zero at the

O_{2} H_{2} S

interface. Except for very low concentrations of 5α-cholestanol (< 4ng/l) no other stanols could be detected in the anoxic zone.From this data it appears that no detectable stenol → stanol conversion is occurring at the

O_{2} H_{2} S

interface or in the deep anoxic waters of the Black Sea. 相似文献

4.

Extension of the empirical Alyavdin equation for representing batch grinding data

L.G Austin K Shoji V.K Bhatia F.F Aplan 《International Journal of Mineral Processing》1974,1(2):107-123

The Alyavdin equation for batch grinding data is:

1 ? P(χ, t) = [1 ? P(χ, 0)] exp ? c(x)t^{p}]

where P(χ,t) is the weight fraction less than size χ after grinding time t, c (χ) is constant with t and p is a constant close to one. It is shown that this equation is illogical (except for a single size of feed) unless c (χ) varies with P(χ,0), which makes the equation of little utility. A new empirical equation is developed for finite size intervals:

1 ? P(χ_{i+1}, t) = exp ? tK_{i}^{1γ} + ln 1 1 ? P(χ_{i+1},0)^{1γ_{i}}^{γ_{i}}

which reduces to the Alyavdin equation for a single size of feed, and which gives consistent computations for any feed size distribution. Techniques are given for determining K_i, γ values from sets of batch grinding data. The values are then used to predict size distributions for other times and other feed size distributions. The equation was quite successful in predicting size distributions in batch milling: (a) providing the feed size distribution was not un-natural, that is, not truncated or (b) if a truncated feed was used, the values of K_i and γ are determined from size distributions of grinding of the same type of feed. Thus, K_i, γ are not, unfortunately, completely independent of the starting feed size distribution. 相似文献

5.

The geochemical evolution of the Pleistocene Lake Lisan-Dead Sea system

Amitai Katz Yehoshua Kolodny Arie Nissenbaum 《Geochimica et cosmochimica acta》1977,41(11):1609-1626

The geochemical history of Lake Lisan, the Pleistocene precursor of the Dead Sea, has been studied by geological, chemical and isotopic methods.Aragonite laminae from the Lisan Formation yielded (equivalent) Sr/Ca ratios in the range 0.5 × 10^?2?1 × 10^?2, Na/Ca ratios from 3.6 × 10^?3 to 9.2 × 10^?3,

δ^{18} O_{PDB}

values between 1.5 and 7%. and

δ^{13} C_{PDB}

from ?7.7 to 3.4%..The distribution coefficient of Na⁺ between aragonite and aqueous solutions,

λ^{A}_{Na}

, is experimentally shown to be very sensitive to salinity and nearly temperature independent. Thus, Na/Ca in aragonite serves as a paleosalinity indicator.Sr/Ca ratios and

δ^{18} O

values in aragonite provide good long-term monitors of a lake's evolution. They show Lake Lisan to be well mixed, highly evaporated and saline. Except for a diluted surface layer, the salinity of the lake was half that of the present Dead Sea (15 vs 31%).Lake Lisan evolved from a small, yet deep, hypersaline Dead Sea-like, water body. This initial lake was rapidly filled-up to its highest stand by fresh waters and existed for about 40,000 yr before shrinking back to the present Dead Sea. The chemistry of Lake Lisan at its stable stand represented a material balance between a Jordan-like input, an original large mass of salts and a chemical removal of aragonite. The weighted average depth of Lake Lisan is calculated, on a geochemical basis, to have been at least 400, preferably 600 m.The oxygen isotopic composition of Lake Lisan water, which was higher by at least 3%. than that of the Dead Sea, was probably dictated by a higher rate of evaporation.Na/Ca ratios in aragonite, which correlate well with

δ^{13} C

values, but change frequently in time, reflect the existence of a short lived upper water layer of varying salinity in Lake Lisan. 相似文献

6.

Intrinsic oxygen fugacity measurements: techniques and results for spinels from upper mantle peridotites and megacryst assemblages

Richard J. Arculus John W. Delano 《Geochimica et cosmochimica acta》1981,45(6):899-913

A new technique for the determination of intrinsic oxygen fugacities (

?_{O_{2}}'s

) of single and polyphase geological samples with solid ZrO₂, oxygen-specific electrolytes is described. Essentially the procedure involves isolating the emf signal from the sample from that unavoidably imposed by the residual atmosphere inside the sample-bearing sensor. By varying the

?_{O_{2}}

of the residual atmosphere, it is possible to determine a ‘plateau’ value of constant

?_{O_{2}}

recorded from the sensor which represents a reversed intrinsic

?_{O_{2}}

measurement for the sample alone, and where the extent of the plateau reflects the innate buffering capability of the sample. A measure of the precision and accuracy of the data obtained is the fact that identical

?_{O_{2}}

values are obtained whether on a heating or cooling cycle of the sample + compatible atmosphere system.These techniques have been applied to measurements of the intrinsic

?_{O_{2}}

of spinels from peridotites and megacryst assemblages from Australia, West Germany and the U.S.A. Oxidation states range from ～- 0.25 log₁₀ units more oxidized to 1 log₁₀ unit more reduced than the iron-wüstite (IW) buffer. The overall reduced nature of the spinels and the range of

?_{O_{2}}

's obtained are striking features of the data. One implication of the results is that the majority of mantle-derived magmas are initially highly reduced, and the relatively oxidized values observed at surface (～- 4–5 log₁₀ orders more oxidized than IW) reflect late-stage alteration, perhaps by H₂ loss (Sato, 1978). 相似文献

7.

Speciation of boron with Cu2+, Zn2+, Cd2+ and Pb2+ in 0.7 M KNO3 and in sea-water

Constant M.G. van den Berg 《Geochimica et cosmochimica acta》1984,48(12):2613-2617

The stability constants,

K^{1}_{MB}

, for borate complexes with the ions of Cu, Pb, Cd and Zn are determined in this work by DPASV in 0.7 M KNO₃ at metal concentrations of 10^?7 M. The acidity constants of the Cu²⁺ ion are determined by DPASV in the same conditions. The following values for log

K^{1}_{MB}

(

β^{1}_{MB_{2}}

) have been obtained: CuB: 3.48, CuB₂: 6.13, PbB: 2.20, PbB₂: 4.41, ZnB: 0.9, ZnB₂: 3.32, CdB: 1.42, and CdB₂: 2.7, while the values for the acidity constants of Cu are

pK^{1}_{CuOH} = 7.66

and

pβ^{1}_{Cu(OH_{2})} = 15.91

. At the low concentration of boron in 35%. S sea-water complexes with borate represent only about 0.2% Cu, 0.03% Pb, 0.02% Zn and 0.003% Cd. 相似文献

8.

Correction of ground-water chemistry and carbon isotopic composition for effects of CO₂ outgassing

F.J. Pearson Donald W. Fisher L.N. Plummer 《Geochimica et cosmochimica acta》1978,42(12):1799-1807

Direct

P_{co_{2}}

measurements on water samples from several CO₂-charged warm springs are significantly higher than

P_{co_{2}}

values calculated from field pH and alkalinity (and other constituents). In addition, calcite saturation indices calculated from field pH and solution composition indicated supersaturation in samples which, on the basis of hydrogeologic concepts, should be near saturation or undersaturated. We attribute these discrepancies to uncertainties in field pH, resulting from CO₂ outgassing during pH measurement. Because samples for direct

P_{co_{2}}

measurement can be taken with minimal disturbance to the water chemistry, we have used the measured

P_{co_{2}}

to back calculate an estimate of the field pH and the carbon isotopic composition of the water before outgassing. By reconstructing water chemistry in this way, we find generally consistent grouping of

δ^{13} C

, pH, and degree of calcite saturation in samples taken from the same source at different times, an observation which we expect based on our understanding of the hydrogeology and geochemistry of the ground-water systems. This suggests that for very careful geochemical work, particularly on ground-waters much above ambient temperature,

P_{co_{2}}

measurements may provide more information on the system and a better estimate of its state of saturation with respect to carbonate minerals than can field measurements of pH. 相似文献

9.

The significance of metamorphic fluorite in the Adirondacks

S.R. Bohlen E.J. Essene 《Geochimica et cosmochimica acta》1978,42(11):1669-1678

Thermodynamic calculations for selected silicate-oxide-fluorite assemblages indicate that several commonly occurring fluorite-bearing assemblages are restricted to relatively narrow

?_{O_{2}} -?_{F_{2}}

fields at constant P?T. The presence of fayalite-ferrohedenbergite-fluorite-quartz ± magnetite and ferrosalite-fluorite-quartz-magnetite assemblages in orthogneisses from Au Sable Forks, Wanakena and Lake Pleasant, New York, buffered fluorine and oxygen fugacities during the granulite facies metamorphism in the Adirondack Highlands. These buffering assemblages restrict

?_{F}_{2}

to 10^{?29 ± 1} bar and

?_{0}_{2}

to 10^{?16 ± 1} bar at the estimated metamorphic temperature of 1000K and pressure of 7 kbar. The assemblage biotite-magnetite-ilmenite-K-feldspar, found in the same Au Sable Forks outcrop as the fayalite-fluorite-ferrohedenbergite-quartz-magnetitie assemblage, restricts H₂O fugacities to less than 10^3·3 bar. These fugacities limit H₂ and HF fugacities to less than 10¹ bar for the Au Sable outcrop. The data indicate that relative to H₂O, O₂, H₂, F₂ and HF are not major species in the fluid equilibrated with Adirondack orthogneisses. The calculated F₂ fugacilies are similar to the upper limits possible for plagioclase-bearing rocks and probably represent the upper

?_{F}_{2}

limit for metamorphism in the Adirondacks and in other granulite facies terranes. 相似文献

10.

The kinetics of silica-water reactions

J.D. Rimstidt H.L. Barnes 《Geochimica et cosmochimica acta》1980,44(11):1683-1699

A differential rate equation for silica-water reactions from 0–300°C has been derived based on stoichiometry and activities of the reactants in the reaction SiO₂(s) + 2H₂O(l) = H₄SiO₄(aq)

(?a_{H_{4}SiO_{4}} ?t)_{P.T.M.} = (A M)(γ_{H_{4}SiO_{4}})(k+a_{SiO_{2}} a^{2}_{H_{2}O} ? k_a_{H_{4}SiO_{4}})

where (

A M

) = (the relative interfacial area between the solid and aqueous phases/the relative mass of water in the system), and k₊ and k_? are the rate constants for, respectively, dissolution and precipitation. The rate constant for precipitation of all silica phases is

log k_{?} = ? 0.707 ? 2598 T (T, K)

and E_act for this reaction is 49.8 kJ mol^?1. Corresponding equilibrium constants for this reaction with quartz, cristobalite, or amorphous silica were expressed as

log K = a + bT + c T

. Using

K = k_{+} k_{?}

, k was expressed as

log k_{+} = a + bT + c T

and a corresponding activation energy calculated:

相似文献

11.

Partial molal volume calculations for the dissolution of aged amorphous silica in salt water and seawater at 0–2°C

Joan D. Willey 《Geochimica et cosmochimica acta》1982,46(7):1307-1310

Measurement of solubility as a function of pressure allows calculation of

3 V ?_{1}

. Using this experimental approach, the best estimate of

3 V ?_{1}

for the dissolution of aged amorphous silica in salt water or seawater at 0–2°C is ?9.9 cm³ mol^?1 (standard error = 0.4 cm³ mol^?1). This gives

V ?_{Si(OH)_{4}(aq)} = 55 ± 5 cm^{3} mol^{?1}

, which compares well with other published values of

V ?_{Si(OH)_{4}(aq)}

. 相似文献

12.

Some mineral stability relations in the system CaOMgOSiO₂H₂OHCl

R.W Luce G.L Cygan J.J Hemley W.M D&#x;angelo 《Geochimica et cosmochimica acta》1985,49(2):525-538

Mineral-aqueous solution equilibria for the assemblages talc-quartz, tremolite-talc-quartz, diopside-tremolite-quartz, wollastonite-diopside-quartz and wollastonite-quartz have been studied at 2 kb total pressure, 500° to 700°C and chloride concentrations from 0.03 to 6.0 molal. Most work was at 1 m chloride. Both buffered and unbuffered data were obtained and a recalibration of the Ag-AgCl buffer is presented. Log equilibrium quotients at 500°, 600° and 700°C are respectively: Ta-Qz (

m_{MgCl_{2}} m_{HCl}^{2}

) 2.57, 1.71, 0.73; Tr-Ta-Qz and Di-Tr-Qz (

m_{CaCl_{2}} m_{MgCl_{2}} m_{HCl}^{2}

) 4.98, 3.99, 2.21 and 7.29, 5.30, 3.56; WoDi-Qz (

m_{CaCl_{2}} m_{MgCl_{2}}

) 3.30, 3.00, 2.79: Wo-Qz (

m_{CaCl_{2}} m_{HCl}^{2}

) 5.15, 3.95, 2.68. Mineral stability fields plotted in terms of these concentration data more tangibly represent the compositional character of real systems and the mass transfer capabilities of their fluids than do the analogous theoretical activity diagrams.Overall dissociation constants of MgCl₂ and CaCl₂ were calculated from the experimental data using the calculated ionic activity constants for the reactions and the established dissociation constants of HCl. The negative log values are respectively: 3.88. 6.63, 9.20 for CaCl₂ and 4.60, 7.54, 10.37 for MgCl₂ at 500°, 600° and 700°C, 2 kb. The Ca values are about an order of magnitude more positive than the conductance-derived values by Frantz and Marshall (1982).The phase relations developed in this study have application to the genesis of talc, tremolite, and diopside-bearing assemblages in some regional metamorphic rocks, but more specifically to the calcsilicate skarn assemblages of many metasomatic aureoles. The equilibrium fluids are characterized by high concentrations of Ca relative to Mg and increasing

Ca Mg

ratios with decreasing temperatures. The stability fields of talc, tremolite, and quartz expand relative to those of diopside and wollastonite with decreasing temperature, hence their more common appearance as retrograde products in skarn systems. 相似文献

13.

Polyunsaturated fatty acids in a lacustrine sediment as a possible indicator of paleoclimate

Kimitaka Kawamura Ryoshi Ishiwatari 《Geochimica et cosmochimica acta》1981,45(2):149-155

Polyunsaturated fatty acids (C_18:2 and C_18:3ω3 were analyzed in the upper 20m layer of a 200 m long sediment core taken from Lake Biwa. Concentration maxima occur in layers at depths of 0.2, 1–5, 11–12, and 16m. The vertical changes in the

(C_{18:2} C(C_{18:0}

ratio appear to correlate with paleoclimatic condition suggested from palynological evidence. On the basis of

C_{18:2} C_{18:0}

ratios, it was suggested that it has been colder at 200, 1000–4000, 15,000 and 20,000 yr BP than at other times. 相似文献

14.

Steady diffusion model for olivine-plagioclase corona growth

Tadao Nishiyama 《Geochimica et cosmochimica acta》1983,47(2):283-294

This paper describes an application of a steady diffusion model (Joesten, 1977) to an olivineplagioclase corona and some new results about a theoretical background on the steady diffusion equations.The olivine-plagioclase corona in a metanorite from Mt. Ikoma. Japan, has a layer sequence of olivinecummingtonite-hornblende + spinel-plagioclase. An analysis of a set of steady diffusion equations for the corona in the four-component system, MgO-AlO_$32$-SiO₂-Na_0.1Ca_0.9O_0.95 (NC) with excess H₂O. successfully gives the exchange cycle (Fisher, 1973) in the layer sequence with specific values of the phenomenological coefficients' ratios;

L_{MgMg} L_{SiSi}

,

L_{MgMg} L_{AlAl}

and

L_{MgMg} L_{NCNC}

. The factor which controls most strictly the stability of the layer sequence under isobaric-isothermal conditions is

L_{MgMg} L_{AlAl}

.Theoretical considerations on the steady diffusion equations show that the L-ratios does not depend on concentrations even if the phenomenological coefficients themselves are functions of concentrations. Equivalence of the steady state condition and the minimum rate of entropy production law (Prigogine, 1967) is also proved for the system with fixed chemical potential gradients under isobaric-isothermal conditions, such as reaction bands. These results give a strong background for the model. 相似文献

15.

Tveitite,a new calcium yttrium fluoride

Sveinung Bergstøl Brenda B. Jensen Henrich Neumann 《Lithos》1977,10(1):81-87

Tveitite is a new mineral with formula of the type

Ca_{1?x} (Y, RE)_{x} F_{2+x} where x

is approximately 0.3. It is found in a cleavelandite pegmatite at Høydalen in Tørdal, Telemark, S. Norway. The sub-cell is thought to be monoclinic,

a ′=3.924, b ′=3.893, c ′=5.525, ß=90°26′, Z =2

. The structure is very similar to that of fluorite and can be described in terms of a pseudo-cubic cell

[1 1 0]_{0} = 5.527, [110]_{0} = 5.527, c = 5.525, α = 90°18′, γ = 89°37′

which contains approximately 1[YCa₃F₉]. The mineral shows twinning in at lest three different directions giving a grating structure probably due to high-low inversion. DTA studies show an inversion point at about 670°C. Material heated above this temperature gives X-ray diffraction patterns corresponding to yttrofluorite (a₀ 5.528). The effect of trivalent ions on the stability of fluorite is discussed. 相似文献

16.

Solubility product of galena at 298°K: A possible explanation for apparent supersaturation in nature

A.D. Uhler G.R. Helz 《Geochimica et cosmochimica acta》1984,48(6):1155-1160

The synthetic chelating agent ethylenediaminetetraacetic acid (EDTA) has been used to evaluate the stoichiometric solubility product of galena (PbS) at 298°K:

K_{s2} =^{a} Pb^{2+}^{a} HS^{?}^{a} H^{+}

This method circumvents the possible uncertainties in the stoichiometry and stability of lead sulfide complexes. At infinite dilution,

Log K_{s2} = ?12.25 ±0.17

, and at an ionic strength corresponding to seawater (

I = 0.7 M

),

Log K_{s2} = ?11.73 ± 0.05

. Using the value of

K_{s2}

at infinite dilution, and the free energies of formation of HS^? and Pb²⁺ at 298°K (literature values), the free energy of formation of PbS at 298°K is computed to be

?79.1 ± 0.8 KJ/mol (?18.9 Kcal/mol)

. Galena is shown to be more than two orders of magnitude more soluble than indicated by calculations based on previous thermodynamic data. 相似文献

17.

The system pargasite-H₂O-CO₂: a model for melting of a hydrous mineral with a mixed-volatile fluid—I. Experimental results to 8 kbar

J.R Holloway 《Geochimica et cosmochimica acta》1973,37(3):651-666

The stability of the amphibole pargasite [NaCa₂Mg₄Al(Al₂Si₆))O₂₂(OH)₂] in the melting range has been determined at total pressures (P) of 1.2 to 8 kbar. The activity of H₂O was controlled independently of P by using mixtures of H₂O + CO₂ in the fluid phase. The mole fraction of H₂O in the fluid (

X_{H}_{2} O^{1fl}

) ranged from 1.0 to 0.2.At P < 4 kbar the stability temperature (T) of pargasite decreases with decreasing

X_{H}_{2} O^{1fl}

at constant P. Above P ? 4 kbar stability T increases as

X_{H}_{2} O^{1fl}

is decreased below one, passes through a T maximum and then decreases with a further decrease in

X_{H}_{2} O^{1fl}

. This behavior is due to a decrease in the H₂O content of the silicate liquid as

X_{H}_{2} O^{1fl}

decreases. The magnitude of the T maximum increases from about 10°C (relative to the stability T for

X_{H}_{2} O^{1fl} = 1

) at P = 5 kbar to about 30°C at P = 8 kbar, and the position of the maximum shifts from

X_{H}_{2} O^{1fl} ? 0.6

at P = 5 kbar to

X_{H}_{2} O^{1fl} ? 0.4

at P = 8 kbar.The H₂O content of liquid coexisting with pargasite has been estimated as a function of

X_{H_{2}O}^{1fl}

at 5 and 8 kbar P, and can be used to estimate the H₂O content of magmas. Because pargasite is stable at low values of

X_{H}_{2} O^{1fl}

at high P and T, hornblende can be an important phase in igneous processes even at relatively low H₂O fugacities. 相似文献

18.

Estimation of the dielectric constant of H2O from experimental solubilities of quartz,and calculation of the thermodynamic properties of aqueous species to 900°C at 2 kb

William F. McKenzie Harold C. Helgeson 《Geochimica et cosmochimica acta》1984,48(11):2167-2177

Experimental quartz solubilities in H₂O (Anderson and Burnham, 1965, 1967) were used together with equations of state for quartz and aqueous species (Helgesonet al., 1978; Walther and Helgeson, 1977) to calculate the dielectric constant of H₂O (

?_{H_{2}O}

) at pressures and temperatures greater than those for which experimental measurements (Heger, 1969; Lukashovet al., 1975) are available (

0.001 ? P ? 5 kb

and

0 ? T ? 600°C

). Estimates of

?_{H_{2}O}

computed in this way for 2 kb (which are the most reliable) range from 9.6 at 600°C to 5.6 at 800°C. These values are 0.5 and 0.8 units greater, respectively, than corresponding values estimated by Quist and Marshall (1965), but they differ by <0.3 units from extrapolated values computed from Pitzer's (1983) adaptation of the Kirkwood (1939) equation. The estimates of

?_{H_{2}O}

generated from quartz solubilities at 2 kb were fit with a power function of temperature, which was then used together with equations and data given by Helgeson and Kirkham (1974a,b, 1976) Helgesonet al. (1981), and Helgeson (1982b, 1984) to calculate Born functions, Debye Hückel parameters, and the thermodynamic properties of Na⁺, K⁺, Mg⁺⁺, Ca⁺⁺, and other aqueous species of geologic interest at temperatures to 900°C. 相似文献

19.

Improved method for estimating the standard free energies of formation (

ΔG_{f,298.15}^{0}

) of smectites

Shas V. Mattigod Garrison Sposito 《Geochimica et cosmochimica acta》1978,42(12):1753-1762

Two alternative empirical methods were developed for estimating the standard free energies of formation of layer silicate minerals with cation exchange capacity due to isomorphous substitutions. These methods involve the summation of either hydroxide or oxide components to form the desired smectite mineral similarly to a method developed by Nriagu, but differ in that (1) no ad hoc ‘calibrations’ are necessary for the

ΔG_{f,298.15}^{0}

values of alkali hydroxides and (2) a three-parameter equation is used for the correction factor, with the charge on the mineral due to isomorphous substitutions and the ionic radius and charge on the exchangeable cation taken as independent variables.A comparison between experimental and estimated

ΔG_{f,298.15}^{0}

values indicated that one of the methods (that involving the summation of hydroxide components) was significantly better than all other methods in predicting

ΔG_{f,298.15}^{0}

values of smectites while at the same time requiring no ad hoc thermochemical assumptions. 相似文献

20.

A recycle flow flotation machine model

C.C Harris A Chakravarti S.N Degaleesan 《International Journal of Mineral Processing》1975,2(1):39-58

Residence time measurements were made on a Denver laboratory flotation machine with and without the DR ring assembly. Soluble and insoluble tracers were used (a dye and fine quartz, respectively), and the variables studied were tank liquid volume,

V

, water and air volumetric flow rates, Q and Q_A respectively, and some geometric and design variables.By analogy with nominal residence time,

t_{N} (= V Q)

, a term “effective residence time”

t_{E}

is defined by:

f (t)= exp [? t t_{E}

where f(t) is the fraction of tracer remaining in the tank at time t. Perfect mixing is indicated if and only if: (i) data satisfies the exponential relationship; and (ii)

t_{E} t_{N} = 1

.Using the soluble tracer the machine behaved substantially as a perfect mixer under all operating conditions, except with the DR ring at values of Q_A nearly double the natural aeration capacity of the machine; condition (i) above was satisfied, but

t_{E} t_{N} ～ 1.1

.With the insoluble tracer the machine behaved as a perfect mixer only without air. As Q_A increased,

t_{E} t_{N}

increased from unity to about 1.2, and the effect was emphasized by the DR ring. In all cases condition (i) above was satisfied.A model in which the flow pattern in the tank includes a large component of pulp recirculation through the impeller region is developed. This model can account for the experimental findings but the details remain to be elucidated. 相似文献

	a	b	c	E_act(kJ mol ^-1)
Quarts	1.174	-2.028 x 10³	-4158	67.4–76.6
α-Cristobalite	-0.739	0	-3586	68.7
β-Cristobalite	-0.936	0	-3392	65.0
Amorphous silica	-0.369	-7.890 x 10^-4	3438	60.9–64.9