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1.
《Geochimica et cosmochimica acta》1987,51(10):2757-2767
Highly supersaturated solutions of Ca2+ and CO2−3 ions rapidly precipitate amorphous calcium carbonate, ACC, the logarithmic thermodynamic solubility product of which is about −6.0 at 25°C. The ACC initially formed is transformed to a mixture of several crystalline calcium carbonate polymorphs within several minutes. The transformed polymorphs are vaterite and calcite at low temperature (14 to 30°C), and aragonite and calcite at high temperature (60 to 80°C). At intermediate temperatures (40 to 50°C) the formation of all three polymorphs was observed. Metastable polymorphs are gradually transformed to the stable form, calcite. It takes about 200 min at 25°C and 370 min at 30°C for the complete transformation of vaterite to calcite, and 1000–1300 min for that of aragonite to calcite at 60–80°C. At 50°C, vaterite is predominantly transformed at first to aragonite within 60 min, and then the aragonite is transformed to calcite in about 900 min. The results of the change in the ion activity product of the solution and the abundances of the polymorphs strongly suggest that the polymorphic transformation of vaterite and aragonite to calcite takes place through dissolution of the metastable phase and growth of the stable phase, calcite. The rate-determining step of the transformation is the growth of calcite. The relative abundance of vaterite becomes higher at 25°C with increasing concentrations of calcium and carbonate ions in the supersaturated solution. When the ion activity product of the initial supersaturated solution is lower than the solubility product of ACC at 25°C, only vaterite directly precipitates after some induction period. The vaterite crystals formed are free of calcite seeds and the vaterite saturated solutions are stable for several days. 相似文献
2.
Lurdes Fernández-Díaz Ángeles Fernández-González 《Geochimica et cosmochimica acta》2010,74(21):6064-6076
The nucleation and growth of CaCO3 phases from aqueous solutions with SO42−:CO32− ratios from 0 to 1.62 and a pH of ∼10.9 were studied experimentally in batch reactors at 25 °C. The mineralogy, morphology and composition of the precipitates were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and microanalyses. The solids recovered after short reaction times (5 min to 1 h) consisted of a mixture of calcite and vaterite, with a S content that linearly correlates with the SO42−:CO32− ratio in the aqueous solution. The solvent-mediated transformation of vaterite to calcite subsequently occurred. After 24 h of equilibration, calcite was the only phase present in the precipitate for aqueous solutions with SO42−:CO32− ? 1. For SO42−:CO32− > 1, vaterite persisted as a major phase for a longer time (>250 h for SO42−:CO32− = 1.62). To study the role of sulfate in stabilizing vaterite, we performed a molecular simulation of the substitution of sulfate for carbonate groups into the crystal structure of vaterite, aragonite and calcite. The results obtained show that the incorporation of small amounts (<3 mole%) of sulfate is energetically favorable in the vaterite structure, unfavorable in calcite and very unfavorable in aragonite. The computer modeling provided thermodynamic information, which, combined with kinetic arguments, allowed us to put forward a plausible explanation for the observed crystallization behavior. 相似文献
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4.
通过缓慢分解Ca2+-Mg2+-HCO3--Cl--H2O溶液和以菱锶矿(或碳钡矿、白铅矿)为晶种的附晶生长法,在0-90℃温度范围内定向合成了碳酸钙同质多象变体.矿物合成实验结果表明,随着温度升高,有利于亚稳态文石和不稳定六方方解石的生成;随着溶液中Mg2+离子浓度增大和Ca(HCO3)3溶液浓度减小,均有利于亚稳态文石的形成.以XRD和SEM技术为实验手段,详细研究了碳酸钙同质多象转变过程.结果显示:在流体参与的情况下,文石→方解石和六方方解石→方解石的同质多象转变速率很快,并且其转变的矿物学机理为溶解/再沉淀. 相似文献
5.
TEMPERATURE EFFECT ON PRECIPITATION OF CALCIUM CARBONATE FROM CALCIUM BICARBONATE SOLUTIONS AND ITS APPLICATION TO CAVERN ENVIRONMENTS 总被引：1，自引：0，他引：1
Solutions of calcium bicarbonate were allowed to lose carbon dioxide and evaporate to dryness under controlled temperature conditions. With filtered solutions prepared from spar calcite, precipitates were 100% calcite in the 2° to 100°C temperature range. When, in analogous experiments, coralline aragonite was the starting material, the precipitates were 100% calcite. Essentially the same was true when carbonate rocks from karst areas were used to prepare the experimental solutions. An artificially prepared mixture (maximum crystal size of about 7 u) of 70% aragonite and 30% calcite was also used in the study. The precipitates from this starting material were apparently affected by seed nuclei which passed through the filter. The stability of calcium carbonate seed nuclei appears to vary with temperature. Natural calcium bicarbonate solutions from caves yielded only calcite at 25°C. Calcite should be the dominant or only polymorph of CaCO3 formed by the loss of carbon dioxide and evaporation of natural calcium bicarbonate solutions if temperature is the controlling factor. Since appreciable amounts of aragonite are found in many cave deposits, factors other than temperature must influence the polymorphs formed. POBEGUIN (1955) proposed that rapid evaporation and slow diffusion of solutions favor aragonite. If so, layers of aragonite and calcite in speleothems may reprsent alternate wet and dry paleoclimates. During these periods, rate of introduction of solution and rate of evaporation would change markedly. 相似文献
6.
Alan G. Turnbull 《Geochimica et cosmochimica acta》1973,37(6):1593-1601
Vaterite is shown to be unstable with respect to calcite at 25°C by measurements of the enthalpies of solution in 0·1 N HCl under 0·97 atm CO2 and the solubilities in water under 0·97 atm CO2 of the two polymorphs. For a pure, synthetic vaterite ΔH (tr) = ?1036 ±16 cal mol?1 and ΔG(tr) = ?790 ± 25 cal mol?1 for the transition to calcite. For other vaterites aged longer during preparation ΔH(tr) is smaller and shows a linear relationship with the X-ray line broadening which extrapolates to ΔH(tr) = ?545 ± 30 cal mo?1 for zero broadening. The use of X-ray line broadening as a measure of crystal imperfection and stability is discussed for various synthetic and natural vaterites. 相似文献
7.
The results of experiments on the hydrothermal dolomitization of calcite (between 252 and 295°C) and aragonite (at 252°C) by a 2 M CaCl2-MgCl2 aqueous solution are reported and discussed. Dolomitization of calcite proceeds via an intermediate high (ca. 35 mole %) magnesian calcite, whereas that of aragonite is carried out through the conversion of the reactant into a low (5.6 mole %) magnesian calcite which in turn transforms into a high (39.6 mole %) magnesian calcite. Both the intermediate phases and dolomite crystallize through a dissolution-precipitation reaction. The intermediate phases form under local equilibrium within a reaction zone surrounding the dissolving reactant grains. The volume of the reaction zone solution can be estimated from Sr2+ and Mg2+ partitioning equations. In the case of low magnesian calcite growing at the expense of aragonite at 252°C, the total volume of these zones is in the range of 2 × 10?5 to 2 × 10?4 1., out of 5 × 10?3 1., the volume of the bulk solution.The apparent activation energies for the initial crystallization of high magnesian calcite and dolomite are 48 and 49 kcal/mole, respectively.Calcite transforms completely into dolomite within 100 hr at 252°C. The overall reaction time is reduced to approximately 4 hr at 295°C. The transformation of aragonite to dolomite at 252°C occurs within 24 hr. The nature of the reactant dictates the relative rates of crystallization of the intermediate phases and dolomite. With calcite as reactant, dolomite growth is faster than that of magnesian calcite; this situation is reversed when aragonite is dolomitized.Coprecipitation of Sr2+ with dolomite is independent of temperature (within analytical error) between 252 and 295°C. Its partitioning, with respect to calcium, between dolomite and solution results in distribution coefficients in the range of 2.31 × 10?2 to 2.78 × 10?2. 相似文献
8.
The kinetics of spontaneous precipitation of CaCO3 from aqueous solution in the presence of dissolved silica was investigated by recording pH as a function of time. The presence of dissolved silica, at concentrations below saturation with respect to the amorphous phase, decreases induction time for CaCO3 nucleation, but does not affect CaCO3 polymorphism. For a “pure” system without silica, the surface free energy, σ, determined from classical nucleation theory is 42 mJ m−2. This agrees well with values reported in the literature for vaterite and indicates some degree of heterogeneous nucleation, which can occur because of the relatively low degree of supersaturation used for the experiments. In the presence of 1 and 2 mM silica, σ is 37 and 34 mJ m−2, indicating an increasing degree of heterogeneous nucleation as the amount of polymeric silica increases. The ratio of Ca2+ to CO32− activity was a governing parameter for determining which CaCO3 polymorph precipitated. At high Ca2+ to CO32− activity ratios, almost all initial solid was vaterite, whereas at low ratios, a mixture of vaterite and calcite was observed. In solutions with low Ca2+ to CO32− activity ratios, the presence of silica at concentrations above saturation with respect to amorphous silica led to formation of only calcite and strongly influenced the crystalline structure and morphology of the precipitates. At high Ca2+ to CO32− ratios, system behaviour did not differ from that without silica. 相似文献
9.
Amitai Katz 《Geochimica et cosmochimica acta》1973,37(6):1563-1586
Calcite crystals were grown in a closed system by recrystallization of synthetic and natural aragonite crystals, in the presence of various CaCl2-MgCl2 solutions with and without NaCl.The distribution of Mg2+ between calcite and solution at the entire temperature range is heterogeneous, closely following the Doerner-Hoskins (Doerner and Hoskins, 1925) distribution law. λMg2+C is strongly dependent on temperature, being: 0·0573 ± 0·0017 at 25°C, 0·0681 ± 0·0019 at 35°C, 0·0778 ± 0.0022 at 50°C, 0·0973 ± 0·0021 at 70°C, and 0·1163 ±0 ·0034 at 90°C. λMg2+C is independent of the absolute concentration of Ca2+ in solution as well as of the presence of NaCl.Relatively high λMg2+C values are obtained during the initial reaction stages when too-highly reactive synthetic aragonites are recrystallized. SEM micrographs show that calcite crystals grown from such aragonites are imperfect and that their earlier formed Mg-rich cores redissolve later, resulting in apparently inconsistent λMg2+C values.Calculations applying the new λMg2+C value for 25°C and the solubility data for magnesian calcites (Chaveet al., 1962) demonstrate that although no calcite should be expected to precipate directly from open sea water, its direct precipitation (or recrystallization from aragonite) is possible in closed diagenetic systems which still contain marine solutions, provided a temporary increase in the dissolved calcium concentration takes place.The λMg2+C values obtained allow for a new insight into processes of calcite cementation of reefs and a variety of other carbonate sediments, and for a more precise definition of dedolomitization chemistry. 相似文献
10.
The thermodynamic properties of monohydrocalcite, CaCO3 · H2O, have been obtained using a well-characterized natural specimen. Equilibration of the solid with water at 25°C under 0.97 atm CO2 led to an activity product [Ca2+][CO32?] = 10?7.60±0.03 and a free energy of formation ΔGfo = ?325,430 ± 270 calmol?. The enthalpy of solution of monohydrocalcite in 0.1 N HCl at 25°C led to a standard enthalpy of formation ΔHfo = ?358,100 ± 280 cal mol?1. Estimates of the variation of ΔGf with temperature and pressure showed monohydrocalcite to be metastable with respect to calcite and aragonite. 相似文献
11.
The dissolution behavior of two biogenic Mg-calcites, the echinoid, Tripneustes (12 mol% MgCO3), and the red alga, Neogoniolithon (18 mol% MgCO3 plus brucite), was studied using free-drift methods in distilled water and phosphate-spiked solutions at 25°C and PCO2 = 1 atm. Small concentrations of phosphate strongly inhibit dissolution rates. Inhibition increases with increased phosphate levels and with approach toward saturation. Near saturation, dissolution rates are reduced by 103 by the presence of 0.6 μmol adsorbed-P/m2. The magnitude of phosphate inhibition is similar to that observed for low-Mg calcite, and like calcite, the mechanism of inhibition is probably by adsorption of P at surface kink sites. Phosphate appears to inhibit removal of Mg and Ca equally during Mg-calcite dissolution. Rates of brucite dissolution are unaffected by phosphate.Mg-calcites containing >8.5 mol% MgCO3 should be thermodynamically unstable relative to aragonite in most natural waters. Recent work, however, shows that in contrast to its effect on the behavior of Mg-calcites. phosphate does not inhibit aragonite dissolution. The presence of phosphate might thus reverse the relative stability of these two minerals during diagenesis of shallow marine carbonate sediments. 相似文献
12.
This study measures the reaction rate of dolomite and aragonite (calcite) into Mg-calcite at 800, 850, and 900°C and 1.6 GPa. The dry synthetic dolomite-aragonite aggregate transformed very rapidly into dolomite-calcite polycrystalline aggregate while Mg-calcites formed at a relatively slow rate, becoming progressively richer in Mg with run time. We modeled the reaction progress semi-empirically by the first-order rate law. The temperature dependence of the overall transport rate of MgCO3 into calcite can be described by the kinetic parameters (E?=?231.7 kJ/mol and A o ?=?22.69 h?1). Extrapolation using the Arrhenius equation to the conditions during exhumation of UHPM rocks indicates that the reaction of dolomite with aragonite into Mg-saturated calcite can be completed as the P-T path enters the Mg-calcite stability field in a geologically short time period (<1 Ky). On the other hand, the extrapolation of the rate to prograde metamorphic conditions reveals that the Mg-calcite formed from dolomitic marble in the absence of metamorphic fluid may not reach Mg-saturation until temperatures corresponding to high-grade metamorphism (e.g., >340°C and >10 My). SEM-EDS analysis of individual calcite grains shows compositional gradients of Mg in the calcite grains. The Mg-Ca inter-diffusion coefficient at 850°C is around 1.68?×?10?14 m2/sec if diffusion is the major control of the reaction. The calculated closure temperatures for Ca-Mg inter-diffusion as a function of cooling rate and grain size reveal that Ca/Mg resetting in calcite in a dry polycrystalline carbonate aggregate (with grain size around 1 mm) may not occur at temperatures below 480°C at a geological cooling rate around 10°C/My, unless other processes, such as short-circuit interdiffusion along grain boundaries and dislocations, are involved. 相似文献
13.
The solubilities of synthetic, natural and biogenic aragonite and calcite, in natural seawater of 35%. salinity at 25°C and 1 atm pressure, were measured using a closed system technique. Equilibration times ranged up to several months. The apparent solubility constant determined for calcite of 4.39(±0.20) × 10?7 mol2 kg?2 is in good agreement with other recent solubility measurements and is constant after 5 days equilibration. When we measured aragonite solubility we observed that it decreased with increasing time of equilibration. The value of 6.65(±0.12) × 10?7 mol2 kg?2, determined for equilibration times in excess of 2 months, is significantly less than that found in other recent measurements, which employed equilibration times of only a few hours to days. No statistically significant difference was found among the synthetic, natural and biogenic material. Solid to solution ratio, contamination of aragonite with up to 10 wt% calcite and recycling of the aragonite made no statistically significant difference in solubility when long equilibration times were used.Measured apparent solubility constants of aragonite and calcite are respectively 22( ± 3)% and 20( ± 2)% less than apparent solubility constants calculated from thermodynamic equilibrium constants and seawater total activity coefficients. These large differences in measured and calculated apparent solubility constants may be the result of the formation of surface layers of lower solubility than the bulk solid. 相似文献
14.
The oxygen isotope fractionation accompanying the hydrothermal dolomitization of CaCO3 between 252 and 295°C has been investigated. Dolomitization (which occurs via the crystallization of one or more intermediate magnesian calcite phases) is characterised by a progressive lowering in δ8O, which smoothly correlates with the change in the Mg/(Mg + Ca) and the ratios and with the sequential phase formation. The data support the proposals of Katz and Matthews (1977) that (a) all reaction occurs by solution and reprecipitation, (b) intermediate phases and dolomite form sequentially and (c) the intermediate phases form within limited solution zones surrounding the dissolving precursor. Calculated volumes of the solution zone for the aragonite → low magnesian calcite transformation are within the range 3.7–6.7 × 10?5 liters (out of 5 × 10?3 liters, the volume of the bulk solution used in the present study), and agree well with those calculated from strontium and magnesium partitioning data. Dolomite precipitates in apparent isotopic equilibrium with the bulk solution. The temperature dependence of the fractionation is defined by the equation 1000 InαD-H2O = 3.06 × 106T?2 ? 3.24 Dolomite-water fractionations from this equation are significantly lower than those obtained by extrapolation of the Northrop And Clayton (1966) calibration. The reaction zone model can be applied to explain near zero dolomite-calcite oxygen isotope fractionations reported by Epsteinet al. (1964). 相似文献
15.
GEORGE R. DIX 《Sedimentology》1995,42(5):711-724
At burial depths of 800-1000 m, within the epicontinental Queensland Trough of north-east Australia (ODP Site 823), microcrystalline inter- and intraskeletal mosaics of anhedral (loaf-shaped, rounded) calcite have Sr2+ values ranging from below microprobe detection limits (<150 ppm) to 8100 ppm. Host rocks are well lithified, fine-grained mixed sediment to clayey wackestone and packstone of Middle and Late Miocene age. Petrography demonstrates that calcite precipitation has spanned shallow to deep burial, overlapping formation of framboidal pyrite in the upper 50 m; shallow-burial dolomitization (<300 m); and dedolomitization during sediment consolidation and incipient chemical compaction at greater (>400–500 m) depths. Petrographic observations illustrate that the calcite microfabric formed through coalescing crystal growth resulting from one or a combination of displacive growth in clay, porphyroid neomorphism of aragonite/vaterite, and clay replacement by calcite. Sr2+ mean concentrations in calcite between depths of 800 and 1000 m are similar to an expected equilibrium pore-water concentration, using a Dsr of 0.06, and may indicate active calcite precipitation. However, Sr2+ variation (2000–5000 ppm) within and among crystals, and concentrations that range well above predicted equilibrium values for a given depth, illustrate either variable Sr2+ retention during recrystallization of shelf-derived aragonite (and authigenic local vaterite) or relative uptake of Sr2+ during calcite precipitation with burial. Within the context of calcite formation during burial to 1 km, diagenetic attributes that affect the latter process include increased concentrations of pore-water Sr2+ with depth associated with aragonite recrystallization/dissolution; upward migration of Sr-rich pore water; and increased DSr related to local variation in precipitation/recrystallization rates, differential crystal sector growth rates and/or microvariation in aragonite distribution. 相似文献
16.
Pseudohexagonal aragonite crystals are common components in some hot-spring travertines at Chemurkeu on the western shore of Lake Bogoria, Kenya. Beds, lenses and pods of aragonite crystals are intercalated with beds of white non-crystallographic calcite dendrites. The pseudohexagonal aragonite crystals, which are up to 4 cm long and 4 mm wide, are formed of nested skeletal crystals. Each skeletal crystal is formed of cyclical twinned crystals that are constructed of stacked subcrystals. The latter are inclined at a consistent angle of 40° to the long axis of the pseudohexagonal aragonite crystal. Intense competition for space during growth modified the crystal morphology with the result that many of the pseudohexagonal crystals are distorted. Intercrystalline and intracrystalline pores are filled or partly filled by epitaxial aragonite overgrowths and/or reticulate microbial coatings that have a high concentration of Si and Mg. In places, this extracellular mucus induced etching of the underlying aragonite crystal. Today the hot (T>95 °C) Na-HCO3-Cl spring waters at Chemurkeu have a salinity of 5–6 g L?1 TDS, a pH of 8·1–9·1, Ca2+ concentrations of <2 mg L?1 and Mg2+ concentrations of <0·7 mg L?1, The springs of the Lake Bogoria Geothermal Field are fed by a shallow aquifer (T～100 °C) and a deeper aquifer (T～170 °C). Springs at Chemurkeu derive from meteoric groundwater, lake water and condensed steam, and are fed mainly from the shallow thermal aquifer. Much of the aragonite may have formed when the spring waters contained more dissolved Ca2+ than today, possibly under more humid conditions during the Holocene. 相似文献
17.
Gregg Marland 《Geochimica et cosmochimica acta》1975,39(1):83-91
Experimental runs were made in cold-seal pressure vessels using synthetic CaCO8·6H2O, calcite and aragonite as starting materials. The reaction CaCO3·6H2O (ikaite) ? CaCO3 (calcite I) + 6H2O was reversed across its metastable extension into the aragonite stability field and the phase boundary is defined by brackets at 4.14kb, 14.3°C and 2.96 kb, ?3.0°C. An invariant point for CaCO3·6H2O, calcite I, aragonite and water thus occurs at about 3.02 kb and ?2.0°C. No other reaction could be reversed. Calculations based on the equilibrium phase boundary between calcite and ikaite and the available thermochemical data for calcite and water yield the stadard free energy of formation, standard enthalpy of formation and third law entropy of CaCO3·6H2O at 25°C and 1 bar total pressure; ?607.3 kcal/mole, ?705.8 kcal/mole, and 88.4 cal/deg mole, respectively. 相似文献
18.
{M[UO2¦AsO4]2 · nH2O} with M=Cu2+, Co2+, Ni2+ has been synthesized from reagent grade chemicals and by ion exchange of trögerite {HUO2AsO4 · 4 H2O}. Synthetic meta-zeunerite (M=Cu2+), meta-kirchheimerite (M=Co2+) and nickel-uranylarsenate are all tetragonal. The cell parameters determined from Guinier-Hägg diffraction data for {Cu[UO2¦AsO4]2 · 8 H2O} are a=b=7.10 Å and c=17.42 Å, with Z=2 and the measured density 3.70 g cm?3. The cell parameters for {Co[UO2¦AsO4]2 · 7 H2O} and {Ni[UO2¦AsO4]2 · 7 H2O} are a=b=20.25 Å and c=17.20 Å, with Z=16 and the measured density 3.82 and 3.74 g cm?3, respectively. The solubility products for synthetic Cu-, Co- and Ni-uranylarsenate at 25° C are 10?49.20, 10?45.34 and 10?45.10, respectively. The zeta-potential remains negative between pH=2 and pH=9 and is strongly affected by the presence of different cations. 相似文献
19.
Ronny Boch Xianfeng Wang Tobias Kluge Albrecht Leis Ke Lin Hannes Pluch Florian Mittermayr Andre Baldermann Michael E. Bttcher Martin Dietzel 《Sedimentology》2019,66(2):604-635
The well‐known Erzberg site represents the largest siderite (FeCO3) deposit in the world. It consists of various carbonates accounting for the formation of prominent CaCO3 (dominantly aragonite) precipitates filling vertical fractures of different width (centimetres to decimetres) and length (tens of metres). These commonly laminated precipitates are known as ‘erzbergite’. This study focuses on the growth dynamics and environmental dependencies of these vein fillings. Samples recovered on‐site and from mineral collections were analyzed, and these analyses were further complemented by modern water analyses from different Erzberg sections. Isotopic signatures support meteoric water infiltration and sulphide oxidation as the principal hydrogeochemical mechanism of (Ca, Mg and Fe) carbonate host rock dissolution, mobilization and vein mineralization. Clumped isotope measurements revealed cool formation temperatures of ca 0 to 10°C for the aragonite, i.e. reflecting the elevated altitude Alpine setting, but unexpectedly low for aragonite nucleation. The 238U–234U–230Th dating yielded ages from 285·1 ± 3·9 to 1·03 ± 0·04 kyr bp and all samples collected on‐site formed after the Last Glacial Maximum. The observed CaCO3 polymorphism is primarily controlled by the high aqueous Mg/Ca ratios resulting from dissolution of Mg‐rich host rocks, with Mg/Ca further evolving during prior CaCO3 precipitation and CO2 outgassing in the fissured aquifer. Aragonite represents the ‘normal’ mode of erzbergite formation and most of the calcite is of diagenetic (replacing aragonite) origin. The characteristic lamination (millimetre‐scale) is an original growth feature and mostly associated with the deposition of stained (Fe‐rich) detrital particle layers. Broader zonations (centimetre‐scale) are commonly of diagenetic origin. Petrographic observations and radiometric dating support an irregular nature for most of the layering. Open fractures resulting from fault tectonics or gravitational mass movements provide water flow routes and fresh chemical reaction surfaces of the host rock carbonates and accessory sulphides. If these prerequisites are considered, including the hydrogeochemical mechanism, modern water compositions, young U‐Th ages and calculated precipitation rates, it seems unlikely that the fractures had stayed open over extended time intervals. Therefore, it is most likely that they are geologically young. 相似文献
20.
The solubilities of PbCO3(s), 2PbCO2·Pb(OH)2(s), and of 3PbCO3 2Pb(OH)2(s) have been studied at 25°C ± 0.1°C in solutions of the constant ionic strength I = 0.3 mol/dm3, consisting primarily of sodium perchlorate. A few experiments with hydrocerussite were performed in solutions of 0.1 M KNO3. The concentrations of lead and hydrogen ions have been determined in solution in contact with the solid phase. From experimental data the following values for equilibrium constants are obtained: log [Pb2+]·pCO2·[H+]?2 = 5.20log [Pb2+]·pCO0.672·[H+]?2 = 6.80log [Pb2+]3·[CO2?3]2·[OH?]2 = ?44.08 (and ?44.8 forI = 0.1 M)log [PbCO03]·[Pb2+]?1·[CO2?3]?1 = 5.40log [Pb(CO3)2?2]·[Pb2+]?1·[CO2?3]?2 = 8.86 The data indicate that hydrocerussite is the most stable solid phase in natural waters. Comparison with the literature and needs for further research are also presented. 相似文献