Platinum Solubility Research Articles

Platinum solubility in silicate melts: The effects of sulfur (S2–), temperature, and melt composition

Platinum (Pt) solubility in silicate melt (SolPtSil) has been determined to understand its behavior in planetary magmas. However, the effect of sulfur (S) in the silicate melt on SolPtSil was paid little attention. Here we present experiments performed at 1–1.5 GPa, 1300–1700 °C, and oxygen fugacity (fO2) from IW−1.6 to IW+2.3 (IW denotes the iron–wüstite buffer) to determine SolPtSil for silicate melts with major element compositions corresponding to those of rhyolite, mid-ocean ridge basalt, high-FeO basalt, and Martian basalt. The results show that SolPtSil increases from ∼0.1 to 10 μg/g as the S content in silicate melt increases from nominally zero to ∼4000 μg/g, which indicates that Pt dissolves predominantly as Pt-sulfide species in S2–-bearing silicate melt. Our results also show that SolPtSil increases with increasing temperature and/or the silicate melt NBO/T (the ratio of non-bridging oxygens to tetrahedrally coordinated cations). Using our newly obtained SolPtSil and previous data, we developed an empirical model that describes SolPtSil as a multi-function of temperature, fO2, the silicate melt NBO/T, and the S2– content in silicate melt in the case at reducing conditions (fO2 < IW+3.5). The application of our empirical model to mantle partial melting suggests that Pt-rich alloys form only after sulfide liquid exhaustion because of the S-enhanced SolPtSil. We also applied our empirical model to predict the behavior of Pt during arc magmatic differentiation. The results agree with the observations that Pt-rich alloys formed before the saturation of sulfides in the oxidized Pual Ridge lavas. We suggest that the observed coexistence of Pt-bearing alloys and sulfide globules in oxidized arc magmas can be explained by an early formation of Pt-bearing alloys followed by a late formation of sulfide liquids. The strong effect of S2– on SolPtSil also implies that the oxidization of magmatic melts can lead to direct precipitation of Pt-bearing alloys due to the S2– to S6+ transformation, which can also be subsequently entrapped in the sulfide liquids formed later. Finally, our results show a strong effect of S2– in the silicate melt on lowering the metal–silicate melt partition coefficients of Pt, which should be considered when using Pt to trace planetary accretion and differentiation processes. Collectively, our study demonstrates an important role for S2– in controlling the behavior of Pt during planetary core–mantle–crust differentiation.

The solubility of platinum in magmatic brines: Insights into the mobility of PGE in ore-forming environments

Several field-based studies have proposed that late-stage magmatic aqueous brines may be responsible for the transportation and redistribution of platinum-group elements (PGE) in mafic–ultramafic igneous systems. We experimentally studied the solubility of Pt in high-temperature aqueous brines as a function of oxygen fugacity (ƒO2), temperature (T), pH and total chloride concentration (Cltotal) in a S-free system. Experiments were conducted at 800–1000 °C and 200 MPa in an externally-heated rapid-quench Molybdenum-Hafnium Carbide (MHC) pressure vessel assembly. We employed the synthetic fluid inclusion (SFI) technique to trap and sample pre-equilibrated, high-salinity brines in quartz cylinders subjected to in situ fracturing during experimental run conditions. Platinum solubility was observed to have a positive correlation with ƒO2, temperature, fluid acidity and Cltotal (salinity). A log Pt versus log ƒO2 diagram derives a weighted-error linear regression slope (m) = 0.48 ± 0.04 which demonstrates that Pt is present in the 2+ oxidation state over the studied ƒO2 range. At relatively oxidizing conditions, 1.44 log units above the Ni-NiO oxygen buffer (NNO+1.44), aqueous brines (containing 63 NaCl eq. wt.%) with a mildly acidic fluid composition (pH = 6.03) can dissolve up to ∼100 µg/g Pt at 900 °C and 200 MPa. Aqueous brines with identical fluid compositions yield a solubility of 4–13 µg/g Pt under more reducing conditions (NNO–0.41 to NNO–1.42). Thermodynamic model calculations suggest that both PtCl2 and PtCl3− are the dominant Pt(II)-chloride complexes which facilitate the transport of Pt in high-temperature aqueous vapors and brines. In fluid compositions with Cltotal >32 m (mol/kg H2O), PtCl3− complex is expected to be the dominant Pt species. In natural mafic–ultramafic systems, high-salinity, orthomagmatic aqueous brines may be important transporting agents if such magmatic fluids can participate in the dissolution of Pt-enriched base-metal sulfides or react with discrete insoluble Pt phases imposing a relatively high activity of Pt (i.e., Pt3Fe). Furthermore, precipitation of Pt from aqueous brines is promoted by a decrease in ƒO2, temperature, acidity and Cltotal.

Gold Solubility in Reduced Carbon-Bearing Fluid

The paper presents first experimental data on gold solubility in CO–CO2 and C–O–S fluids with a low H2O concentration under reduced conditions, a pressure of 200 MPa, and a temperature of 950°C. Gold solubility in C–O–S fluid is approximately 27 ppm. The estimate of gold solubility in CO–CO2 fluid with 10–15 mol % CO is less accurate, and the solubility is no lower than 2–3 ppm but may reach 200–300 ppm. The high gold solubility in reduced CO2 fluid determined in the course of this research, and our earlier estimates of high platinum solubility (Simakin et al., 2016), may explain the deposition of mineralization of these noble metals in the Guli intrusion, polar Siberia, as a result of fluid extraction of these metals and their redeposition at a temperature slightly below the solidus. The reduction of the largely oxidized CO2 fluid, which was determined using mineralogical sensors, was likely related to the subsolidus oxidation of olivine.

Solubility of platinum-arsenide melt and sperrylite in synthetic basalt at 0.1 MPa and 1200 °C with implications for arsenic speciation and platinum sequestration in mafic igneous systems

To better understand the Pt-As association in natural magmas, experiments were done at 1200°C and 0.1MPa to measure the solubility of Pt and Pt-arsenide phases (melt and sperrylite, PtAs2), as well as to determine the oxidation state, and identify evidence for Pt-As complexing, in molten silicate. Samples consisting of synthetic basalt contained in chromite crucibles were subject to three experimental procedures. In the first, platinum solubility in the synthetic basalt was determined without added arsenic by equilibrating the sample with a platinum source (embedded wire or bead) in a gas-mixing furnace. In the second, the sample plus a Pt-arsenide source was equilibrated in a vacuum-sealed fused quartz tube containing a solid-oxide oxygen buffer. The third approach involved two steps: first equilibrating the sample in a gas-mixing furnace, then with added arsenide melt in a sealed quartz tube. Oxygen fugacity was estimated in the latter step using chromite/melt partitioning of vanadium.Method two experiments done at high initial arsenic activity (PtAs melt+PtAs2), showed significant loss of arsenic from the sample, the result of vapour transfer to newly-formed arsenide phases in the buffer. Method three experiments showed no loss of arsenic, yielding a uniform final distribution in the sample. Analyses of run-product glasses from experiments which did not show arsenic loss reveal significant increase in arsenic concentrations with fO2, varying from ∼10ppm (FMQ-3.25) to >10,000ppm (FMQ+5.5). Despite very high arsenic loadings (>1000ppm), the solubility of Pt is similar in arsenic-bearing and arsenic-free glasses. The variation in arsenic solubility with fO2 shows a linear relationship, that when corrected for the change in the activity of dissolved arsenic with the melt ferric/ferrous ratio, yields a solubility-fO2 relationship consistent with As3+ as the dissolved species. This result is confirmed by X-ray absorption near edge structure (XANES) determination on run-product glasses.Levels of arsenic required for Pt-arsenide saturation are 50–500ppm over the fO2 range of most terrestrial basalts (FMQ to FMQ-2), >100× higher than the arsenic concentrations typical of such magmas, indicating significant enrichment of arsenic is required if Pt-arsenide saturation is to occur. In contrast, the level of dissolved Pt required to saturate in sperrylite is >8× lower than for pure Pt, suggesting that arsenic enrichment could lead to Pt removal at concentrations much less than required for pure metal saturation.

1573KにおけるFeOx- SiO&lt;sub&gt;2 &lt;/sub&gt;系スラグの白金の溶解度

There is an increasing trend in the copper smelters to recycle electronic materials, which contain relatively high concentration of platinum group metals. Platinum group metals lost in the slag is increasing with increasing of treated scrap amount. To determine the portion of the platinum group metals chemically dissolved in the slag will be a key factor to improve the recovery of those metals. An experimental study was carried out to determine the solubility of platinum in FeOx-SiO2 slag equilibrated with a pure platinum and the liquid Pt-Cu alloy at 1573 K and the range of oxygen partial pressure from 10-9 to 10-6. The solubility of platinum in the slag tends to increase with increasing oxygen partial pressure and content of copper in the slag. Based on the measured platinum solubility, activity coefficients of platinum oxide in the FeOx-SiO2 slag were derived. The activity coefficients decrease by increasing copper contents in slag. Therefore, lower copper content in the slag tend to lower precious metals dissolution in the slag.

The effect of Cl on Pt solubility in haplobasaltic melt: Implications for micronugget formation and evidence for fluid transport of PGEs

Platinum solubility was determined in a haplobasaltic, diopside–anorthite melt at 1523 K and 0.2 GPa as a function of oxygen fugacity and chlorine content. Synthetic glass powder of an An 42Di 58 composition was sealed in a platinum or platinum–iridium alloy capsule and equilibrated with a solid CaCl 2 and MgCl 2 chlorine source, water and the noble-metal capsule. All experiments were run in an internally-heated pressure-vessel equipped with a rapid-quench device with oxygen fugacity controlled by the water content and intrinsic hydrogen fugacity of the autoclave (MnO–Mn 3O 4). Resultant glasses were analyzed by isotope dilution ICP-MS and LA-ICP-MS to determine the solubility and distribution of Pt and assess potential Cl-complexation of Pt in the melt. Experiments with run durations longer than 96 h show Pt solubilities consistent with solubilities determined for the equivalent Cl-free diopside–anorthite system, under the same P– T conditions. These results indicate that chlorine has no discernable effect on Pt solubility and there is no evidence of Pt–Cl complexing in the silicate melt from 0.6 to 2.75 wt% Cl (saturation). However, products from short run duration experiments (<96 h) contain Pt concentrations which are orders of magnitude higher than those of the Pt-free starting glass and of the experimental products of the longer run duration experiments. These anomalously high levels are most pronounced in the shortest experiments and Pt concentration decreases with increasing run duration. It is suggested that this excess platinum is dissolved within the Cl-bearing fluid during the heating stages of the experiment and is left behind as the fluid dissolves into the melt leaving small amounts of Pt as “micronuggets”, increasing the bulk Pt concentration. With increasing run duration the platinum appears to migrate out of the melt, back to the capsule walls, decreasing the amount of Pt contained within the glass. This behavior offers compelling evidence that Cl-bearing fluids have the capacity to transport significant amounts of Pt under magmatic conditions. Mass balance calculations on the excess amount of Pt in the glass (above inherent solubility) in short duration experiments lead to an estimation of Pt concentration in the Cl-bearing fluid ranging from tens to a few hundred ppm, versus ppb levels in the melt. The correspondingly high estimated apparent partition coefficients of 10 3–10 4 suggest that Cl-bearing fluids can be highly efficient at enriching and transporting platinum in mafic magmatic–hydrothermal ore-forming systems. These values strongly contrast with recent experimental results in felsic systems, highlighting the potential importance of melt composition on partitioning, the need for composition specific partitioning experiments, as well as a detailed understanding of Pt distribution in experimental products.

Mn(II) → Mn(III) oxidation kinetics and its effect on crystallization of nanodisperse platinum at 200–300°C and 1 kBar

In the Mn-H2O-Cl-Pt system, phase transitions in Mn(II)-Mn(III) solid compounds were experimentally shown to affect platinum solubility and platinum crystallization at 200–300°C (ptot = 1 kBar). Platinum dissolution rate curves feature a cooperative synergistic effect that results from overlapping of a concentration wave and a crystallization wave. The process is accompanied by crystallization of nonequilibrium intermediate phases, which are represented by flexivalent manganese hydroxides. Metallic platinum crystallizes as a result of a strong increase in platinum concentration in the solution during MnO oxidation to Mn3O4. With an electron microscope we observed precipitation of aggregates of isometric metallic platinum nanocrystals with cross sections of 60–550 nm on facets of hausmannite (Mn3O4) crystals. Walls of sealed platinum ampoules served as the platinum source during dissolution in the Mn-H2O-Cl system. As the run duration increased, Mn and manganese hydroxides were converted to hausmannite, which is stable at these p, T parameters. As a result, the platinum solubility dropped to equilibrium values (logmPt = −6.00 at T = 300°C), thereby inhibiting precipitation of crystalline platinum from solutions.

Platinum solubility and partitioning in a felsic melt–vapor–brine assemblage

The solubility and partitioning of Pt in a S-free vapor – brine – rhyolite melt – Pt metal assemblage has been quantified at 800 °C, f O 2 = NNO and pressures of 100 and 140 MPa. Vapor and brine were sampled at run conditions by trapping these phases as glass-hosted fluid inclusions as the melt cooled through the glass transition temperature. The vapor and brine were in equilibrium with the melt at the time of trapping and, thus, represent fluids which were sampled at the termination of each experimental run. The microthermometrically determined salinities of vapor and brine are ∼2 and ∼63 wt.% NaCl eq. and ∼9 and ∼43 wt.% NaCl eq. at 100 and 140 MPa, respectively. Platinum solubilities in vapor, brine and glass (i.e., quenched melt) were quantified by using laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS). Equilibrium is discussed with reference to the major and trace element concentrations of glass-hosted fluid inclusions as well as the silicate melt over run times that varied from 110 to 377 h at 140 MPa and 159 to 564 h at 100 MPa. Platinum solubility values (±1σ) in H 2O-saturated felsic melt are 0.28 ± 0.13 μg/g and 0.38 ± 0.06 μg/g at 140 and 100 MPa, respectively. Platinum solubility values ( ± 1 σ x ¯ ) at 140 and 100 MPa, respectively, in aqueous vapor are 0.91 ± 0.29 μg/g and 0.37 ± 0.17 μg/g and in are brine 16 ± 10 μg/g and 3.3 ± 1.0 μg/g. The measured solubility data were used to calculate Nernst-type partition coefficients for Pt between vapor/melt, brine/melt and vapor/brine. The partition coefficient values ( ± 1 σ x ¯ ) for vapor/melt, brine/melt and vapor/brine at 140 MPa are 2.9 ± 1.0, 67 ± 27, and 0.13 ± 0.05 and at 100 MPa are 1.0 ± 0.2, 6.8 ± 2.4, and 0.15 ± 0.05. The partitioning data were used to model the Pt-scavenging capacity of vapor and brine during the crystallization-driven degassing (i.e., second boiling) of a felsic silicate melt over a depth range (i.e., 3–6 km) consistent with the evolution of magmatic-hydrothermal ore deposits. Model calculations suggest that aqueous vapor and brine can scavenge sufficient quantities of Pt, and by analogy other platinum group elements (PGE), to produce economically important PGE-rich magmatic-hydrothermal ore deposits in Earth’s upper continental crust.

Dissolution of platinum in acidic media

To understand the degradation of the Pt/C cathode for use in polymer electrolyte fuel cells, the solubility and the dissolution mechanism of platinum in acidic media was very important fundamentally. In this study, the platinum solubility has been determined in acidic electrolytes as a function of temperature and pH. The solubility was 3 × 10 −6 mol dm −3 at 25 °C in 1 mol dm −3 of H 2SO 4, HClO 4, and CF 3SO 3H under air. It increased at higher temperature and decreased in pH. The apparent enthalpy of the dissolution reaction was ca. 25 kJ mol −1, and the solubility was proportional to [H +] in these acids. The platinum solubility in oxygen was slightly higher than that in air. The detected dissolved Pt species was 4 valent. On the other hand, the solubility of platinum in nitrogen was much lower than the oxygen-containing atmosphere. Based on these results, the platinum solubility in an oxygen-containing atmosphere would mainly be the following acidic dissolution reaction: PtO 2 + H + + H 2O = Pt(OH) 3 +.

Diammine Dicarboxylic Acid Platinum Enhances Cytotoxicity in Platinum-Resistant Ovarian Cancer Cells through Induction of Apoptosis and S-Phase Cell Arrest

Polysaccharides such as chondroitin play a potent role in tumor growth, tissue repair and angiogenesis. These properties make chondroitin a good candidate for novel drug delivery systems. Diammine dicarboxylic acid platinum (DDAP), a novel polymeric platinum compound, was developed by conjugating the platinum analogue to aspartate-chondroitin for drug delivery to tumor cells. DDAP improves platinum solubility which may reduce systemic toxicity and be more efficacious than cisplatin in killing tumor cells. We tested and compared the cytotoxic effects of DDAP and CDDP on the platinum-sensitive 2008 and A2780 ovarian cancer cell lines and their platinum-resistant sublines 2008.C13 and A2780cis; we also investigated DDAP's mechanism of action. In the platinum-sensitive cell lines, the cytotoxic effects of DDAP and CDDP were comparable. However, in the platinum-resistant sublines, significantly greater cell-growth inhibition was induced by DDAP than by CDDP, especially at lower doses. DDAP also induced more apoptosis than CDDP did in the 2008.C13 subline, which was partially mediated by the caspase 3-dependent pathway. In addition, lower (but not higher) doses of DDAP arrested 90% of S-phase 2008.C13 cells, which might be associated with up-regulation of p21 and maintenance of low cyclin A expression. Furthermore, greater cellular uptake of DDAP was seen in platinum-resistant than in platinum-sensitive ovarian cancer cells. Low-dose DDAP enhances drug delivery to platinum-resistant ovarian cancer cells and substantially inhibits their growth by inducting apoptosis and arresting cells in the S-phase, suggesting that DDAP may overcome platinum resistance in ovarian cancer.

Experimental study of the influence of sulfur on platinum solubility in hydrous haplobasaltic melts

Experimental study of the influence of sulfur on platinum solubility in hydrous haplobasaltic melts

Dissolution Mechanism of Platinum in Acidic Media

The platinum solubility in a polymer electrolyte would be a key issue in order to improve and guarantee the durability of PEFCs. In this study, the platinum solubility has been determined in acidic electrolytes as a function of temperature and pH. The solubility was ca. 3 x 10-6 mol dm-3 at 25oC in 1 mol dm-3 of H2SO4, HClO4, and CF3SO3H under air, and increased with temperature and with the decrease in pH. The platinum solubility in oxygen was slightly larger than that in air. However, the solubility in nitrogen was much smaller than the mixtures. Based on these results, the dissolution of platinum in an acidic medium would follow an acidic dissolution mechanism.

Solubility of Platinum in Acidic Media (I)-in Sulfuric Acid

Platinum depositions have been observed in the electrolyte membrane of polymer electrolyte fuel cells (PEFCs) as in other types of fuel cells; PEFCs, MCFCs. The platinum solubility in the membrane must be a key issue to improve and guarantee the durability of PEFCs. In this basic study, the platinum solubility has been determined in an acidic medium as a function of temperature, pH, and potential which was controlled by the oxygen partial pressure. The solubility was 3.0×10−6 mol dm−3 at 23°C in 1 mol dm−3 H2SO4 under air, and increased with temperature and the decrease in pH. The platinum solubility slightly increased with the oxygen partial pressure in oxygen–nitrogen mixtures. However, the solubility in nitrogen was much smaller than the mixtures. Based on these results, the dissolution of platinum in an acidic medium would follow the acidic dissolution mechanism.

Dissolution of Platinum in Acidic Media

Platinum dissolves chemically after the formation of oxide in oxygen atmosphere, such as the cathode of polymer electrolyte fuel cells(PEFCs). Considering the platinum depositions in the membrane electrolyte of PEFCs, the solubility of platinum (oxide) in the electrolyte might be one of key issues, in order to improve the durability of PEFCs. In this study, platinum solubility has been determined in acidic medium as a function of temperature, pH, and potential which was controlled with oxygen partial pressure. The solubility was 2.9x10-6mol dm-3 at 23oC in 1mol dm-3 H2SO4 under air, and increased with temperature and with the decrease of pH. The platinum solubility significantly increased with the presence of oxygen. From these results, the dissolution of a platinum oxide in acidic medium would follow an acidic dissolution mechanism.

Experimental study of platinum solubility in silicate melt to 14 GPa and 2273 K: Implications for accretion and core formation in Earth

We determined the solubility limit of Pt in molten haplo-basalt (1 atm anorthite-diopside eutectic composition) in piston-cylinder and multi-anvil experiments at pressures between 0.5 and 14 GPa and temperatures from 1698 to 2223 K. Experiments were internally buffered at ∼IW + 1. Pt concentrations in quenched-glass samples were measured by laser-ablation inductively coupled-plasma mass spectrometry (LA-ICPMS). This technique allows detection of small-scale heterogeneities in the run products while supplying three-dimensional information about the distribution of Pt in the glass samples. Analytical variations in 195Pt indicate that all experiments contain Pt nanonuggets after quenching. Averages of multiple, time-integrated spot analyses (corresponding to bulk analyses) typically have large standard deviations, and calculated Pt solubilities in silicate melt exhibit no statistically significant covariance with temperature or pressure. In contrast, averages of minimum 195Pt signal levels show less inter-spot variation, and solubility shows significant covariance with pressure and temperature. We interpret these results to mean that nanonuggets are not quench particles, that is, they were not dissolved in the silicate melt, but were part of the equilibrium metal assemblage at run conditions. We assume that the average of minimum measured Pt abundances in multiple probe spots is representative of the actual solubility. The metal/silicate partition coefficients ( D met/sil) is the inverse of solubility, and we parameterize D met/sil in the data set by multivariate regression. The statistically robust regression shows that increasing both pressure and temperature causes D met/silto decrease, that is, Pt becomes more soluble in silicate melt. D met/sil decreases by less than an order of magnitude at constant temperature from 1 to 14 GPa, whereas isobaric increase in temperature produces a more dramatic effect, with D met/sil decreasing by more than one order of magnitude between 1623 and 2223 K. The Pt abundance in the Earth’s mantle requires that D met/sil is ∼1000 assuming core-mantle equilibration. Geochemical models for core formation in Earth based on moderately and slightly siderophile elements are generally consistent with equilibrium metal segregation at conditions generally in the range of 20–60 GPa and 2000–4000 K. Model extrapolations to these conditions show that the Pt abundance of the mantle can only be matched if oxygen fugacity is high (∼IW) and if Pt mixes ideally in molten iron, both very unlikely conditions. For more realistic values of oxygen fugacity (∼IW − 2) and experimentally-based constraints on non-ideal mixing, models show that D met/sil would be several orders of magnitude too high even at the most favorable conditions of pressure and temperature. These results suggest that the mantle Pt budget, and by implication other highly siderophile elements, was added by late addition of a ‘late veneer’ phase to the accreting proto-Earth.

Constraints on core formation from Pt partitioning in mafic silicate liquids at high temperatures

A new high temperature piston cylinder design has enabled the measurement of platinum solubility in mafic melts at temperatures up to 2500 °C, 2.2 GPa pressure, and under reducing conditions for 1–10 h. These high temperature and low f O 2 conditions may mimic a magma ocean during planetary core formation. Under these conditions, we measured tens to hundreds of ppm Pt in the quenched silicate glass corresponding to D Pt met / sil ≈ 10 3 – 4 , 4–12 orders of magnitude lower than extrapolations from high f O 2 experiments at 1 bar and at temperatures no higher than 1550 °C. Moreover, the new experiments provide coupled textural and compositional evidence that noble metal micro-nuggets, ubiquitous in experimental studies of the highly siderophile elements, can be produced on quench: we measure equally high Pt concentrations in the rapidly quenched nugget-free peripheral margin of the silicate as we do in the more slowly quenched nugget-bearing interior region. We find that both temperature and melt composition exercise strong control on D Pt met / sil and that Pt 0 and Pt 1+ may contribute significantly to the total dissolved Pt such that low f O 2 does not imply low Pt solubility. Equilibration of metal alloy with liquid silicate in a hot primitive magma might not have depleted platinum to the extent previously believed.

Platinum solubility in water-bearing magnesian basaltic melts at 1200°C and 2 kbar

Platinum solubility in water-bearing magnesian basaltic melts at 1200°C and 2 kbar

Platinum solubility in a haplobasaltic melt at 1250°C and 0.2 GPa: The effect of water content and oxygen fugacity

Haplobasaltic melts with a 101 kPa dry eutectic composition (An 42Di 58) and varying water contents were equilibrated with their platinum capsule at 1523 K and 200 MPa in an internally heated pressure vessel (IHPV) equipped with a rapid quench device. Experimental products were inclusion-free glasses representative of the Pt-saturated silicate melts at the experimental conditions. Platinum concentrations were determined using an isotope dilution multicollector inductively coupled plasma mass spectrometer and water contents and distribution by Karl Fischer titration and Fourier transform infrared spectroscopy, respectively. The water content of the melt has no intrinsic effect on platinum solubility, for concentrations between 0.9 wt.% and 4.4 wt.% H 2O (saturation). Platinum solubility increases with increasing water content, but this effect is an indirect effect because increasing water content at fixed f H 2 (imposed by the IHPV) increases the oxygen fugacity of the experiment. The positive oxygen fugacity dependence of Pt solubility in a hydrous silicate melt at 200 MPa is identical to that in anhydrous melts of the same composition determined in previous studies at 101 kPa. This study extends the range of platinum solubilities to oxygen fugacities lower than was previously possible. Combining the data of this and previous studies, Pt solubility is related to oxygen fugacity (in bar) at 1523 K by the equation: [ P t ] t o t a l ( p p b ) = 1389 × f O 2 + 7531 × ( f O 2 ) 1 / 2

Experimental Study of Gold and Platinum Solubility in a Complex Fluid under Hydrothermal Conditions

Abstract: The solubility of gold was studied in water and aqueous NaCl (1– 5 m) solutions under oxygen and sulfur buffered conditions between 300–500C at a constant pressure 1 kb. Two buffer assemblages HMP and PPM were used. Analysis of the scatter in measured values in log mAu–mNaCl–T frame fixed linear dependence between log mAu and T at any studied iso-pleth (mNaCl) in the form of log mAu = a. T(C) + b. Coefficients of the equation were calculated for water and NaCl (1, 3, 5 m) solutions. The maximum solubility characterizes the NaCl-free system in the presence of HMP. In the case, Au solubility increases from (log mAu) –6. 72 to –5. 04 at 300 and 500C, respectively. In the presence of PPM, maximum of Au solubility was obtained for the 5 mNaCl solution. In a similar manner solubility rises from –6. 54 to –5. 77 at 300 and 500C, accordingly. In studied fO2/fS2 area the behavior of Au solubility testified that: (i) – a composite interaction between chloride and hydrosulfide speciation of gold affects its total solubility; (ii) – in addition of NaCl up to about 1. 5 m the solubility decreases, more pronounced in the presence of HMP; (iii) – the contribution of chloride in total Au solubility is more for PPM despite of lower fO2value, than for HMP. The solubility of platinum was studied in the Pt–Cl–S–H2O system between 300 and 500C, 1 kb. PPM solid buffer controlled oxidation state, pH and sulfur activity of solutions (H2O, 1 mNaCl and 0. 1 mHCl). Under the conditions, PtS precipitated from the solutions with increasing temperature and acidity. The PtS solubility in the 0. 1 mHCl solutions lowers slightly in the range of 300–500C from –5. 30 to –5. 60 (in log mPt) that is typical to the hydrosulfide species. It was deduced that reducing media, regulated by the PPM assemblage, suppress activity of chloride species of Pt. More oxidizing conditions were modeled in runs using mixtures of Mn(II), Mn(III) and Mn(IV) oxides to buffer the aqueous-chloride solutions between 300 and 500C, 1 kb. It was found that MnO tends to oxidize at T below 400C forming intermediate Mn-hydroxides (β–MnOOH, Mn (OH)2 and Mn2(OH)3Cl). These phases are metastable and transfer to Mn3O4 with increasing duration. Generation of the Mn-hydroxides leads to a change of physical-chemical parameters of the solutions, such as water activity, pH and Eh. The last results in abrupt increase in the noble metals dissolution. At stable existence of only Mn3O4, the solubility of both Pt and Au lowers to equilibrium values. Essential catalysis effect of Pt on intensity and rate of Mn(II) oxidation was found. The dominant role of chloride of Pt and Au was defined under most oxidized conditions, specified by Mn2O3–MnO2 buffer. So at 400C, dissolved Au (log mAu) increases from –4. 40 in water to –1. 00 in 0. 1 mHCl, and ones of Pt (log mPt) from –4. 80 to –2. 90 accordingly. Thus, mixing of hydrosulfide and chloride solutions, as well as transformation of the systems to the stable state act upon total solubility of the noble metals.

Structural investigation of platinum solubility in silicate glasses

The coordination environment of 20-200 ppm Pt in yellowish glasses from the CaO-Al 2O3-SiO2 (CAS) ternary was studied using X-ray absorption fine structure spectroscopy at the Pt-L III edge. Analysis of the Pt-L III edge region suggests that Pt in these glasses is mainly tetravalent and sixfoldcoordinated by O (with a mean Pt-O distance of 2.08 ± 0.02 A). No evidence for Pt 2+ or Pt 6+ was found in any of the glasses studied, suggesting that one can not derive valence information easily from solubility data. No second-neighbor contribution was observed around Pt 4+ O6 polyhedra. However, bond-valence modeling suggest that these polyhedra are likely to bond mostly to [VI] Ca 2+ , which should promote high positional disorder of second -neighbor cations around Pt. This particular bonding arrangement may explain the relatively high solubility of Pt in these relatively depolymerized melts, as CaPtO3-type units.