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1.
The sphalerite oxidative kinetics under hypergene condition was simulated and studied by means of a mixed flow reactor over a pH range of 1.0 7.8,and at dissolution temperatures from 20 to 55℃,ferric ion concentrations from 1.0×10-5 to 1.0×10-2 mol/L,O 2 flux of 0.5 L/min,and oxidants of ferric ion and O 2.It is indicated that with ferric ion as oxidant,the oxidation rate of sphalerite increases with increasing ferric ion concentration,temperature and decreasing pH value,and under the studied conditions,the dissolution rates of Zn and Cd are approximately identical,with the values of activation energy being 41.75 and 42.51 kJ·mol-1,respectively,suggesting that the oxidation rate of sphalerite is controlled by chemical reactions on mineral surface.However,with O 2 as oxidant,the oxidation mechanism of sphalerite varies with pH value.Oxidation rate decreases with increasing pH value when pH is lower than 5.95,whereas the increase of pH value results in an increase in oxidation rate when pH value is higher than 7.The oxidation rate of sphalerite can be expressed as:R Zn =10 1.1663 [Fe3+] 0 0.154 ·[H+] 0.2659 ·e-41.75/RT or R Cd =10 1.7292 [Fe3+] 0 0.170 ·[H+] 0.2637 ·e-42.51/RT 相似文献
2.
3.
Radomir Petrović 《Contributions to Mineralogy and Petrology》1973,41(2):151-170
Coherency stress and coherency strain energy generated by Na+?K+ ion exchange in alkali feldspars are calculated using an isotropic model, and deformation of single crystals of alkali feldspars exposed to molten alkali chlorides at \(P_{H_2 O} \) < 1 bar is described. Coherency stress in alkali feldspars can reach 10–20 kb. When it is large, partial relaxation by fracture and/or plastic deformation takes place under anhydrous conditions, but temporary build-up of stress is unavoidable even under hydrothermal conditions. Because of coherency strain energy, a thin layer of an end-member alkali feldspar produced by cation exchange on a grain of the other end-member alkali feldspar would be unstable with respect to dissolution. Therefore, under hydrothermal conditions one end-member alkali feldspar replaces the other by dissolution and precipitation. The mechanism of the reaction $$Na_x K_{1 - x} AlSi_3 O_{8_{(feld.)} } + yK^ + \rightleftharpoons Na_{x - y} K_{1 + y - x} AlSi_3 O_{8_{(feld.)} } + yNa^ + $$ is primarily controlled by \(P_{H_2 O} \) and by ΔK/(Na + K), the difference between the equilibrium value and the initial value of the atomic K/(Na + K) ratio of the feldspar. When ¦ΔK/(Na + K)¦ is small, the reaction proceeds by cation exchange. When ¦ΔK/(Na + K)¦ is large, cation exchange still occurs if \(P_{H_2 O} \) is very low, but under hydrothermal conditions replacement by dissolution and precipitation occurs. 相似文献
4.
The equilibrium position of the reaction $$\begin{gathered} 1.5 KAlSi_3 O_8 + HCl = 0.5 KAl_3 Si_3 O_{10} (OH)_2 \hfill \\ + 3SiO_2 + KCl \hfill \\ \end{gathered} $$ has been located at 1 and 2 kb pressure and temperatures between 600° and 670° C using the Ag-AgCl buffer. These data can be combined with information on the dissociation of KC1, HC1 and H2O to determine species abundances in supercritical aqueous fluids in equilibrium with muscovite — K-feldspar — quartz assemblages. Chloride species become increasingly associated with increasingT, increasing total molality, (m tot or \(m_{Cl_{tot} } \) ), and decreasing \(P_{H_2 O} \) . Master variable diagrams indicate that the pH of the solutions may vary from near neutral to quite acid. Published data on the paragonite-albite-quartz reaction and exchange reactions involving feldspars and micas were included to calculate speciation in mica-feldspar-NaCl-KCl-HCl-H2O fluids at 2kb pressure and temperatures between 300° and 600° C. The data are not accurate enough to distinguish different feldspar structural states. Concentration gradients were calculated for individual species between K-feldspar+quartz, muscovite+quartz and andalusite+quartz assemblages at 500° C, 2 kb. Assuming that the proton diffuses most rapidly and that there are no [H+] gradients, the molality of the solution must vary 30-fold, with feldspar+quartz at the more concentrated side. The data on mica-feldspar-chloride equilibria are used to interpret the spacial distribution of micas, feldspar and quartz in microfolds. This distribution can be accounted for by pressure solution, due to the fact that non-hydrostatic pressure affects congruently dissolving minerals, auch as quartz, differently from minerals which dissolve incongruently, such as micas and feldspars. We postulate, that during folding at constant \(P_{H_2 O} \) ,T and \(m_{Cl - } \) , gradients in KC1 and SiO2 are created by stress differences between hinge and limb of a microfold, such that both migrate to the hinge area where quartz precipitates and muscovite is converted to K-felspar, thus accounting for the observed mineral distribution. 相似文献
5.
We find clear intrinsic anharmonicity in the NaCl-B1 phase by examining the equation of state (EoS) based on previous ultrasonic velocity data for pressures up to 0.8 GPa and temperatures up to 800 K. The experimental EoS for this phase shows that its specific heat at constant volume (C V ) is significantly smaller than that based on a harmonic model. Also, the sign of $\left( {{{\partial C_{V} } \mathord{\left/ {\vphantom {{\partial C_{V} } {\partial P}}} \right. \kern-0pt} {\partial P}}} \right)_{T} ,$ which is normally negative in the quasi-harmonic approximation, is unexpectedly positive. The thermodynamic Grüneisen parameter (γ), which has frequently been assumed to be a single-variable function of molar volume, shows not only volume dependence but also negative temperature dependence. To understand these features of C V and γ, we introduce a thermodynamic model including positive quartic anharmonicity. To make an anharmonic model advancing the ordinarily quasi-harmonic approximation model, we introduce two parameters: anharmonic characteristic temperature (θ a ) and its volume derivative. In the anharmonic model, the value of C V is calculated along an isochore using classical statistical mechanics and a harmonic quantum correction. At high temperatures, the decrease in C V from the Dulong-Petit limit is related to the value of T/θ a . For infinitely large θ a , the system is approximately quasi-harmonic. The temperature dependence of γ is related to C V by the thermodynamic identity $\left( {{{\partial C_{V} } \mathord{\left/ {\vphantom {{\partial C_{V} } {\partial \ln V}}} \right. \kern-0pt} {\partial \ln V}}} \right)_{T} = C_{V} \left( {{{\partial \gamma } \mathord{\left/ {\vphantom {{\partial \gamma } {\partial \ln T}}} \right. \kern-0pt} {\partial \ln T}}} \right)_{V} + \gamma \left( {{{\partial C_{V} } \mathord{\left/ {\vphantom {{\partial C_{V} } {\partial \ln T}}} \right. \kern-0pt} {\partial \ln T}}} \right)_{V}.$ Even though our modification of the quasi-harmonic approximation is simple, our anharmonic model succeeds in reproducing the experimental γ and C V simultaneously for the NaCl-B1 phase. 相似文献
6.
S. B. Dwivedi 《Journal of Earth System Science》1996,105(4):365-377
The non-ideal regular Mg-Fe binary in cordierite has been derived through multivariate linear regression of the expressionRT InKD +(P- 1)ΔVK 1 0 , 298 along with updated subfegular mixing parameter of almandine-pyrope solution (Hackler and Wood 1989; Berman 1990). The data base used for multivariate analyses consists of published experimental data (n = 177) on Mg-Fe partitioning between garnet and cordierite in theP-T range 650–1050°C and 4–12 K bar. The non-ideality can be approximated by temperature-dependent Margules parameters. The retrieved values of ΔH<T> o and ΔH<T> o of exchange reaction between garnet and cordierite and enthalpy and entropy of mixing of Mg-Fe cordierite were combined with recent quaternary (Fe-Mg-Ca-Mn) mixing data in garnet to obtain the geothermometric expressions to determine temperature (T Kelvin): $$\begin{gathered} T(WH) = 6832 + 0.031(P - 1) - \{ 166(X_{Mg}^{Gt} )^2 - 506(X_{Fe}^{Gt} )^2 + 680X_{Fe}^{Gt} X_{Mg}^{Gt} + 336(X_{Ca} + X_{Mn} ) \hfill \\ (X_{Mg} - X_{Fe} )^{Gt} - 3300X_{Ca}^{Gt} - 358X_{Mn}^{Gt} \} + 954(X_{Fe} - X_{Mg} )^{Crd} /1.987\ln K_D + 3.41 + 1.5X_{Ca}^{Gt} \hfill \\ + 1.23(X_{Fe} - X_{Mg} )^{Crd} \hfill \\ \end{gathered} $$ $$\begin{gathered} T(Br) = 6920 + 0.031(p - 1) - \{ 18(X_{Mg}^{Gt} )^2 - 296(X_{Fe}^{Gt} )^2 + 556X_{Fe}^{Gt} X_{Mg}^{Gt} - 6339X_{Ca}^{Gt} X_{Mg}^{Gt} \hfill \\ - 99(X_{Ca}^{Gt} )^2 + 4687X_{Ca}^{Gt} (X_{Mg} - X_{Fe}^{Gt} ) - 4269X_{Ca}^{Gt} X_{Fe}^{Gt} - 358X_{Mn}^{Gt} \} + 640(X_{Fe} - X_{Mg} )^{Crd} \hfill \\ + 1.90X_{Ca}^{Gt} (X_{Mg} - X_{Ca} )^{Gt} . \hfill \\ \end{gathered} $$ 相似文献
7.
S. F. Tombros K. St. Seymour A. E. Williams-Jones P. G. Spry 《Mineralogy and Petrology》2008,94(3-4):175-194
Precious metals accompany all types of epithermal deposits. In general, the largest of these deposits occur in intrusive or extrusive rocks of alkaline or calc-alkaline affinity. The Apigania Bay vein system and Au–Ag mineralization is hosted in Mesozoic marbles and schists, and is composed primarily of five nearly parallel, high-angle quartz veins that extend for at least 200 m. Gold–silver mineralization, in association with more than thirty ore and vein minerals, is developed in three stages and occurs at the contact of marbles and schists. Zones of epidote–chlorite–calcite and sericite–albite alteration are associated with precious metal-bearing milky and clear quartz veins. Fluid inclusion studies suggest that hydrothermal mineralization was deposited under hydrostatic pressures of ~100 bars, at temperature of 120–235°C, from low to moderate, calcium-bearing, saline fluids of 0.2 to 6.8 equiv. wt.% NaCl. Calculated isotope compositions (δ18O?=??4.7‰ to 1.7‰ and δD?=??120‰ to ?80‰) for waters in equilibrium with milky and clear quartz are consistent with mixing with dilute, low temperature meteoric ore fluids. Calculated δ 13CCO2 (0.6‰ to 1.1‰) and δ 34SH2S (?7.3 to ?0.3‰) compositions of the ore fluids indicate exchange, in an open system, with a metasedimentary source. Gold and silver deposition was associated with degassing of hydrogen due to intense uplift of the mineralizing area. The physicochemical conditions of mineralization stages I to III range between 200°C and 150°C, $f_{{\text{S}}_2 } = 10^{ - 18.1} $ to 10?16.8, $f_{{\text{O}}_2 } = 10^{ - 44.0} $ to 10?41.5, pH?=?6.9 to7.6, $f_{{\text{H}}_{\text{2}} {\text{S}}} = 10^{ - 3.4} $ to 10?2.6 and $a_{{\text{H}}_{\text{2}} {\text{S}}} = 10^{ - 2.7} $ to 10?2.6. Apigania Bay could be possibly considered the latest evolutional phase of Tinos hydrothermal system. 相似文献
8.
A number of experimental CO2 solubility data for silicate and aluminosilicate melts at a variety of P- T conditions are consistent with solution of CO2 in the melt by polymer condensation reactions such as SiO 4(m 4? +CO2(v)+Si n O 3n+1(m) (2n+1) ?Si n+1O 3n+4(m) (2n+4)? +CO 3(m )2? . For various metalsilicate systems the relative solubility of CO2 should depend markedly on the relative Gibbs free change of reaction. Experimental solubility data for the systems Li2O-SiO2, Na2O-SiO2, K2O-SiO2, CaO-SiO2, MgO-SiO2 and other aluminosilicate melts are in complete accord with predictions based on Gibbs Free energies of model polycondesation reactions. A rigorous thermodynamic treatment of published P- T-wt.% CO2 solubility data for a number of mineral and natural melts suggests that for the reaction CO2(m) ? CO2(v)
- CO2-melt mixing may be considered ideal (i.e., { \(a_{{\text{CO}}_{\text{2}} }^m = X_{{\text{CO}}_{\text{2}} }^m \) );
- \(\bar V_{{\text{CO}}_{\text{2}} }^m \) , the partial molal volume of CO2 in the melt, is approximately equal to 30 cm3 mole?1 and independent of P and T;
- Δ C p 0 is approximately equal to zero in the T range 1,400° to 1,650 °C and
- enthalpies and entropies of the dissolution reaction depend on the ratio of network modifiers to network builders in the melt. Analytic expressions which relate the CO2 content of a melt to P, T, and \(f_{{\text{CO}}_{\text{2}} } \) for andesite, tholeiite and olivine melilite melts of the form
9.
Matteo Lelli Sergio Grassi Michele Amadori Fabrizio Franceschini 《Environmental Earth Sciences》2014,71(9):3907-3919
A detailed hydrogeochemical study of groundwater in the Cecina coastal plain (Livorno province, Italy) and its inner sectors was undertaken in 2008, as chemical analyses carried out on groundwater since 2006 have revealed Cr(VI) concentrations of up to 49 μg/L (well above the permissible limit of 5 μg/L). Ophiolite outcrops are present throughout the study area, and their fragments likely represent a significant portion of the existing multilayered aquifer skeleton. Waters delivered by the serpentinite outcrops have a typically Mg–HCO3 composition, whereas those of the coastal plain are prevailingly of the Ca/Mg–HCO3 type with significant Mg contents. Significant NO3 contamination characterises the studied coastal plain, and an interesting negative correlation exists between Cr(VI) and both NO3 and SO4 deriving from the widespread use of (NH4)2SO4 as a farm fertilizer. Chromium speciation calculations carried out using the EQ3NR code reveal that the prevailing Cr(VI) species in solution is CrO4 2?; however, CaCrO4° and MgCrO4° neutral complexes represent significant percentages (up to 42 %). These findings suggest that the mobility and consequently the bioavailability of Cr(VI) can be significantly enhanced by these neutral complexes, which are not considered to be affected by adsorption/desorption processes. The Cr(VI) source, investigated by means of the Mg/SiO2 molar ratio, seems to be represented mainly by Mg-bearing minerals of the chlorite group. Petrographic observations confirm the occurrence of this mineral group. The interaction between rainwater and the local serpentinite rock was simulated at different $P_{{{\text{CO}}_{ 2} }}$ and $P_{{{\text{O}}_{ 2} }}$ conditions by reaction path modelling using the EQ3/6 software package. $P_{{{\text{O}}_{ 2} }}$ was varied in accordance with the assumption that redox conditions are determined in part by NO3. Results are in good agreement with experimental data on spring waters and subordinately with data on some coastal plain groundwater, which plot in a rather wide $P_{{{\text{CO}}_{ 2} }}$ and $P_{{{\text{O}}_{ 2} }}$ field. Although the dissolved Cr content is mostly of natural origin, fertilization may affect its fate. 相似文献
10.
Z. H. Zhang Y. J. Feng P. Gao J. F. Liu N. Q. Ren 《International Journal of Environmental Science and Technology》2012,9(2):247-256
The adsorption and desorption behaviors of 17??-ethinylestradiol on various sludges derived from different treatment units of a sewage treatment plant were investigated using batch equilibration experiments. The results showed that adsorption process could be well described by pseudo-second-order kinetic model and fast adsorption played a main role. Adsorption ability varied as the order of aerobic sludge????anoxic sludge????primary sludge?>?sludge cake?>?anaerobic sludge. Adsorption/desorption isotherms were well fitted by the modified Freundlich model, and $ K_{f}^{\prime } $ values increased with the organic matter content. Thermodynamic analysis indicated that 17??-ethinylestradiol adsorption/desorption was exothermic and conducted spontaneously. After heat treatment for removing the organic carbon, $ K_{f}^{\prime } $ values decreased by more than 78%, but organic carbon normalized adsorption constant was 7.76?C29.51?mg/g. The 17??-ethinylestradiol adsorption capacity was found to decrease from 0.95?C1.39 to 0.44?C0.49?mg/g with sludge concentration increasing from 500 to 4,000?mg/L, being almost unchanged at pH 3?C10 and sharply decreasing with pH?>?10. The adsorption capacity was also found to fluctuate in the range of 2.0?C3.0?mg/g when Ca2+ concentration was <0.5?mol/L and increased rapidly above 0.5?mol/L. Addition of methanol and acetonitrile could improve 17??-ethinylestradiol desorption effect, which increased with the content of organic solvents, and the desorption degree of acetonitrile was higher than methanol. 相似文献
11.
Jacques Schott Robert A Berner E.Lennart Sjöberg 《Geochimica et cosmochimica acta》1981,45(11):2123-2135
The short term (2–40 days) dissolution of enstatite, diopside, and tremolite in aqueous solution at low temperatures (20–60°C) and pH 1–6 has been studied in the laboratory by means of chemical analyses of reacting solutions for Ca2+, Mg2+, and Si(OH)4 and by the use of X-ray photoelectron spectroscopy (XPS) for detecting changes in surface chemistry of the minerals. All three minerals were found to release silica at a constant rate (linear kinetics) providing that ultrafine particles, produced by grinding, were removed initially by HF treatment. All three also underwent incongruent dissolution with preferential release of Ca and/or Mg relative to Si from their outermost surfaces. The preferential release of Ca, but not Mg for diopside at pH 6 was found by both XPS and solution chemistry verifying the theoretical prediction of greater mobility of cations located in M2 structural sites. Loss mainly from M2 sites also explains the degree of preferential loss of Mg from enstatite at pH 6; similar structural arguments apply to the loss of Ca and Mg from the surface of tremolite. In the case of diopside and tremolite initial incongruency was followed by essentially congruent cation-plus-silica dissolution indicating rapid formation of a constant-thickness, cation-depleted surface layer. Cation depletion at elevated temperature and low pH (~ 1) for enstatite and diopside was much greater than at low temperature and neutral pH, and continued reaction resulted in the formation of a surface precipitate of pure silica as indicated by solubility calculations, XPS analyses, and scanning electron microscopy.From XPS results at pH 6, model calculations indicate a cation-depleted altered surface layer of only a few atoms thickness in all three minerals. Also, lack of shifts in XPS peak energies for Si, Ca, and Mg, along with undersaturation of solutions with respect to all known Mg and Ca silicate minerals, suggest that cation depletion results from the substitution of hydrogen ion for Ca2+ and/or Mg2+ in a modified silicate structure and not from the precipitation of a new, radically different surface phase. These results, combined with findings of high activation energies for dissolution, a non-linear dependence on aH+ for silica release from enstatite and diopside, and the occurrence of etch pitting, all point to surface chemical reaction and not bulk diffusion (either in solution or through altered surface layers) as the rate controlling mechanism of iron-free pyroxene and amphibole dissolution at earth surface temperatures. 相似文献
12.
Experimental results show that skarns can—800°C and 500–1,000 bars. Starting materials include intermediate-acidic igneous rocks, volcanic rocks, metamorphic rocks, carbonates of various purities and chemical reagents of analytical purity-grade. Experimental media are: NaCl, NaCl+CaCl2, NaCl+CaCl2+MgCl2, Na2CO3 and Na2SiO3 solutions. Experimental results show that skarns can be formed under wide physico-chemical conditions:T=400°–800°C,P=500–1,000 bars,pH=4–11, and \(f_{O_2 } = 10^{ - 23} - 10^{ - 11} \) bar. The mineralogy of skarns and the chemical compositions of skarn minerals are generally controlled by the combined factors: the chemical composition of the original rocks, pH values, redox conditions, temperatures and pressures. Isomorphous substitution may have agreat effect on the temperature of formation andfo 2 of some major skarn minerals. It is found that skarnization occurs preferentially in NaCl and NaCl+CaCl2 solutions and subortinately in MaCO3 and Na2SiO3 soiutions. 相似文献
13.
The experiments of the dissolution kinetics of fluorite were performed in aqueous HCl solutions over the temperature range
of 25–100 °C using a flow-through experimental apparatus. With a constant input of aqueous HCl solution through the reactor,
output concentrations of the dissolved species Ca, F, Cl vary with flow rate, as well as with the surface compositions. Measured
output concentrations of dissolved species and the pH can be used to determine a rate law for fluorite dissolution. Fluorite
dissolution rates are found to be pH dependent. Usually, dissolution rates of fluorite decreases with increasing dissolved
Ca in the output solution at 25 and 100 °C. Dissolution rate can be expressed as
where k is the rate constant and α is the order with respect to the hydrogen ion activity vs. the activity of dissolved Ca. The α was obtained from kinetic experiments. For the fluorite sample passed through 18–35 mesh, α =1.198 at 100 °C and k = 10−0.983, while fluorite dissolved in HCl–H2O solution at pH 2.57 of input solution. Adsorption of a proton and Cl−1onto the fluorite surface, surface cation exchange and the formation of the surface complex Ca(F, Cl)2 and/or (H2x, Ca1−x)(F, Cl)2 control dissolution rates. Investigation of the fluorite surface before and after dissolution by using X-ray photoelectron
spectroscopy (XPS) indicate that surface modifications affect reaction rates. 相似文献
| (1a) |
14.
For the reaction: 1 diopside+3 dolomite ?2 forsterite+4 calcite+2 CO2 (14) the following P total?T-brackets have been determined experimentally in the presence of a gasphase consisting of 90 mole%CO2 and 10 mole%H2O∶1 kb, 544°±20° C; 3kb, 638°±15° C; 5kb, 708°±10° C; 10kb, 861°±10° C. The determination was carried out with well defined synthetic minerals in the starting mixture. The MgCO3-contents of the magnesian calcites formed by the reaction in equilibrium with dolomite agree very well with the calcite-dolomite miscibility gap, which can be recalculated from the activities and the activity coefficients of MgCO3 as given by Gordon and Greenwood (1970). The equilibrium constant K 14b was calculated with respect to the reference pressure P 0=1 bar using the experimentally determined \(P_{total} TX_{CO_2 }\) brackets, the activities of MgCO3 and CaCO3 (Gordon and Greenwood 1970; Skippen 1974) and the fugacities of CO2 Holloway (1977) considering the correction of Flowers (1979). Results are plotted as function of the absolute reciprocal temperature in Fig. 1. For the temperature range of 530° to 750° C the following linear expression can be given for the natural logarithm of K14b: (g) $$[ln K_{14b} ]_T^P = - \frac{{18064.43}}{{T\left( {^\circ K} \right)}} + 38.58 + \frac{{0.308(P - 1 bar)}}{{T\left( {^\circ K} \right)}}$$ where P is the total pressure in bars and T the temperature in degrees Kelvin. Combining Equation (g) with the activities of MgCO3 and CaCO3 gives the equilibrium fugacity \(f_{CO_2 }\) : (i) $$[ln f_{CO_2 } ]_T^P = - \frac{{11635.44}}{{T\left( {^\circ K} \right)}} + 21.09 + \frac{{0.154(P - 1 bar)}}{{T\left( {^\circ K} \right)}}$$ Equation (i) and the fugacities of CO2 permit to calculate the equilibrium data in terms of \(P_{CO_2 }\) and T (see Fig. 3) or P total, T and \(X_{CO_2 }\) (see Fig. 5). Combining the \(P_{total} TX_{CO_2 }\) equilibrium data of the above reaction with those of the previously investigated reaction (Metz 1976): 1 tremolite+11 dolomite ?8 forsterite+13 calcite+9 CO2+1 H2O yields the stability conditions of the four-mineral assemblage: diopside+calcian dolomite+forsterite +magnesian calcite and the stability conditions of the five-mineral assemblage: tremolite+calcian dolomite+forsterite +magnesian calcite+diopside both shown in Fig. 6. Since these assemblages are by no means rare in metamorphic siliceous dolomites (Trommsdorff 1972; Suzuki 1977; Puhan 1979) the data of Fig. 6 can be used to determine the pressure of metamorphism and to estimate the composition of the CO2-H2O fluid provided the temperature of the metamorphic event was determined using the calcite-dolomite geothermometer. 相似文献
15.
Groundwater samples (n = 163) were collected across Kashmir Valley in 2010 to assess the hydrogeochemistry of the groundwater in shallow and deep aquifers and its suitability for domestic, agriculture, horticulture, and livestock purposes. The groundwater is generally alkaline in nature. The electrical conductivity (EC) which is an index to represent the total concentration of soluble salts in water was used to measure the salinity hazard to crops as it reflects the TDS in groundwater ranging from 97 to 1385 μS/cm, except one well in Sopore. The average concentration of major ions was higher in shallow aquifers than in deeper aquifers. In general, Ca2+ is the dominant cation and HCO \(_{3}^{-}\) the dominant anion. Ca–HCO3, Mg–HCO3, Ca–Mg–HCO3, Na–HCO3 were the dominant hydrogeochemical facies. High concentration of HCO3 and pH less than 8.8 clearly indicated that intense chemical weathering processes have taken place in the study area. The groundwater flow pattern in the area follows the local surface topography which not only modifies the hydrogeochemical facies but also controls their distribution. The groundwater in valley flows into four directions, i.e., SW–NE, NE–W, SE-NW and SE–NE directions. The results suggest that carbonate dissolution is the dominant source of major ions followed by silicate weathering and ion-exchange processes. The concentrations of all the major ions determined in the present study are within the permissible limits of WHO and BIS standards. The results of Total Hardness, SAR, Na%, Kelly Index, USDA classification, Magnesium absorption ratio, residual sodium carbonate, and PI suggested that groundwater is good for drinking, livestock, and irrigation purposes. 相似文献
16.
Experimental exchanges between plagioclases (synthesized from gels) and aqueous solutions (0.5N–8N) were carried out according to the reaction $$\begin{gathered} 2NaA1Si_3 O_8 + CaC1_2 \hfill \\ \leftrightarrow CaA1_2 Si_2 O_8 + 4SiO_2 + 2NaC1. \hfill \\ \end{gathered}$$ Distribution coefficients defined by $$K_D = \frac{{X_{An} }}{{(X_{Ab} )^2 }}\frac{{(X_{NaC1} )^2 }}{{X_{CaC1_2 } }}$$ were determined at 700° C and 1 kbar. From previous studies it is known that variations in the concentration of the aqueous solutions have no influence upon K D if the fluid is a single phase. In this study, variation of K D with the concentration of the solutions is interpreted as the result of fluid unmixing to vapour and brine phases. This implies boiling of CaCl2-NaCl-H2O fluids analogous to that known for the system NaCl-H2O. Experimental data permit calculation of the compositions of vapours and estimation of those of the brines for fluids in which Ca/Na<0.5. Boiling has an effect upon the exchange between feldspars and solutions (metasomatism) and must be considered when determining the activity coefficients. 相似文献
17.
Alexander A. JeschkeWolfgang Dreybrodt 《Geochimica et cosmochimica acta》2002,66(17):3055-3062
Experimentally observed dissolution rates of minerals in an aqueous solution are determined by surface reaction rates, mass transport by molecular diffusion through a diffusion boundary layer (DBL) and the morphology of the mineral’s surface. By solving the transport equation in the presence of a diffusion boundary layer for surfaces containing open pores their contribution to the observed dissolution rates can be quantified. Furthermore dissolution rates are calculated for fractal surfaces. A general solution is given. Two extremes are discussed. If the surface controlled rate constant k is small compared to the mass transport constant kt = D/ε (ε thickness of DBL, D coefficient of diffusion), the rates are surface controlled and the entire surface contributes to the observed dissolution rate. In this case rates must be normalized to the B.E.T.-surface area. When k ? kt the observed rates are limited by diffusion and information on k cannot be obtained. In intermediate cases a careful analysis is required. If ink bottle pores are present their contribution to the observed rates can be neglected and rates must be normalized to the geometrical envelope surface area, although in such cases the B.E.T.-surface area can be much larger. 相似文献
18.
Caroline L. Peacock 《Geochimica et cosmochimica acta》2005,69(15):3733-3745
We measured the adsorption of Cu(II) onto kaolinite from pH 3-7 at constant ionic strength. EXAFS spectra show that Cu(II) adsorbs as (CuO4Hn)n−6 and binuclear (Cu2O6Hn)n−8 inner-sphere complexes on variable-charge ≡AlOH sites and as Cu2+ on ion exchangeable ≡X--H+ sites. Sorption isotherms and EXAFS spectra show that surface precipitates have not formed at least up to pH 6.5. Inner-sphere complexes are bound to the kaolinite surface by corner-sharing with two or three edge-sharing Al(O,OH)6 polyhedra. Our interpretation of the EXAFS data are supported by ab initio (density functional theory) geometries of analog clusters simulating Cu complexes on the {110} and {010} crystal edges and at the ditrigonal cavity sites on the {001}. Having identified the bidentate (≡AlOH)2Cu(OH)20, tridentate (≡Al3O(OH)2)Cu2(OH)30 and ≡X--Cu2+ surface complexes, the experimental copper(II) adsorption data can be fit to the reactions
19.
A multisite solid solution of the type (A, B) (X, Y) has the four possible components AX, AY, BX, BY. Taking the standard state to be the pure phase at the pressure and temperature of interest, the mixing of these components is shown not to be ideal unless the condition: $$\Delta G^0 = (\mu _{AX}^0 + \mu _{BY}^0 - \mu _{AY}^0 - \mu _{BX}^0 = 0$$ applies. Even for the case in which mixing on each of the individual sublattices is ideal, ΔG 0 contributes terms of the following form to the activity coefficients of the constituent components: $$RT\ln \gamma _{AX} = - X_{B_1 } X_{Y_2 } \Delta G^0$$ (X Ji refers to the atomic fraction of J on sublattice i). The above equation, which assumes complete disorder on (A, B) sites and on (X, Y) sites is extended to the general n-component case. Methods of combining the “cross-site” or reciprocal terms with non-ideal terms for each of the individual sites are also described. The reciprocal terms appear to be significant in many geologically important solid solutions, and clinopyroxene, garnet and spinel solid solutions are all used as examples. Finally, it is shown that the assumption of complete disorder only applies under the condition: $$\Delta G^0 \ll zn_1 RT$$ where z is the number of nearest-neighbour (X, Y) sites around A and n 1 is the number of (A, B) sites in the formula unit. If ΔG 0 is relatively large, then substantial short range oder must occur and the activity coefficient is given by (ignoring individual site terms): $$\gamma _{AX} = \left( {\frac{{1 - X'_{Y_2 } }}{{1 - X_{Y_2 } }}} \right)^{zn_1 }$$ where X′Y2 is the equilibrium atomic fraction of Y atoms surrounding A atoms in the structure. The ordered model may be developed for multicomponent solutions and individual site interactions added, but numerical methods are needed to solve the simultaneous equations involved. 相似文献
20.
The high-grade assemblage Cd-Ga-Si-Qz can be thermodynamically modelled from available calorimetric data on the metastable reaction: (I) $$3 MgCd \rightleftarrows 2 Py + 4 Si + 5 Qz$$ naturalK D Fe-Mg between garnet and cordierite and experimental results on cordierite hydration. In the system SiO2-Al2O3-MgO-H2O, reaction (I) becomes (II) $$3 MgCd \cdot nH_2 O \rightleftarrows 2 Py + 4 Si + 5 Qz + 3 nH_2 O$$ . However, hydrous cordierite is neither a hydrate nor a solid solution between water and anhydrous cordierite and when nH2O (number of moles of H2O in Cd) is plotted against \(P_{H_2 O} \) , the resulting isotherms are similar to adsorption isotherms characteristic of zeolitic minerals. Reaction (II) can thus be considered as a combination of reaction (I) with a physical equilibrium of the type nH2O (in Cd)?nH2O (in vapor phase). Starting from a point on equilibrium (I), introduction of H2O into anhydrous Mg-cordierite lowers the chemical potential of MgCd and hence stabilizes this mineral to higher pressure relative to the right-hand assemblage in reaction (I). The pressure increment of stabilization,ΔP, above the pressure limit of anhydrous cordierite stability at constantT, has been calculated using the standard thermodynamics of adsorption isotherms. Cordierite is regarded as a mixture of Mg2Al4Si5O18 and H2O. The activity of H2O in the cordierite is evaluated relative to an hypothetical standard state extrapolated from infinite H2O dilution, by using measured hydration data. The activity of Mg2Al4Si5O18 in the cordierite is then obtained by integration of the Gibbs-Duhem equation, and the pressure stabilization increment,ΔP, computed by means of the relation: $$\Delta V_s \Delta P \cong - RT\ln a_{MgCd}^{MgCd \cdot nH2O} \left( {\Delta V indepentdent of P and T} \right)$$ . Thus, one may contour theP-T plane in isopleths of nH2O=constant within the area of Mg-cordierite stability allowed by the hydration data for \(P_{H_2 O} = P_{total} \) . The present model indicates greater stabilization of cordierite by H2O than the model of Newton and Wood (1979) and the calculated curve for metastable breakdown of hydrous MgCd is consistent with experimental data on cordierite breakdown at \(P_{H_2 O} = P_{total} \) . Mg/(Mg+Fe) isopleths have been derived for cordierites of varying nH2O in the SiO2-Al2O3-MgO-FeO-H2O system using the additional assumptions that (Fe, Mg) cordierite and (Fe, Mg) garnet behave as ideal solutions, and that typical values of the distribution coefficient of Fe and Mg between coexisting garnet and cordierite observed in natural parageneses can be applied to the calculations. The calculated stable breakdown curve of Fe-cordierite under conditions of \(P_{H_2 O} = P_{total} \) to almandine, sillimanite, quartz and vapor has a positive slope (dP/dT) apparently in contrast to the experimental negative slope. This may be explained by hydration kinetics, which could have allowed systematic breakdown of cordierites of metastable hydration states in the experiments. The bivariant Cd-Ga fields calibrated from the present model are, potentially, good petrogenetic indicators, as, given the iron-magnesium ratio of garnet and cordierite and the hydration number of cordierite, the temperature, pressure and water fugacity are uniquely determined. As this geothermobarometer is in part based on the water content of cordierite, it can be used only if there is some assurance that the actual hydration is inherited from high-grade metamorphic conditions. Such conditions could be realised if the slope of unloading-cooling retrograde metamorphism is more or less parallel to a cordierite isohydron. 相似文献