Significant Amounts Of Silver Research Articles

Morphology of the bronze objects from the Pinchuga-6 burial ground

The article is concerned with bronze objects of the end of the Early Iron Age from the fully excavated burial ground of Pinchuga-6 in the Lower Angara River region. The cemetery is dated to the 3rd–4th centuries BC. All burials were made following the rite of burial on the side. Three categories of copper alloy products have been distinguished: belt set parts, jewelry, and cult castings. The components of the belt sets include flat openwork buckles, hoops and bird-shaped overlays. Flat openwork buck-les have no analogues in the neighbouring territories. They appeared on the basis of the circle of post-Hunnic cultures of South-ern Siberia and were used in the Angara taiga until the mid-1st millennium AD. One belt hoop with volutes and an openwork patch is of a typical Tashtyk Culture appearance. At the end of the Early Iron Age, bird-headed belt plates were used across a vast territory that stretched from the Ural Mountains in the west to the banks of the Yenisei and Angara Rivers in the east. The jewelry includes tubular cast and spiral beads, stripes and pendants. The majority of items are multi-functional — they could be worn different ways. All of them were widespread in the first half of the 1st millennium AD, and they do not have a clear cultural and chronological reference. At Pinchuga-6, various objects of cult casting were found, including ornitho-, zoo- and ichthyomor-phic images, and disks with a circular ornament. These items have similarities among the Ishim and Kholmogory collections, materials from the Aidashinskaya cave, and Tomsk and Ust-Abinsk burial grounds. Pinchuga-6 is currently the farthest north-eastern site where such objects have been found. The grave goods of the cemetery contain items of different cultural attribution made of copper-based alloys. In this single complex in the Angara River region, objects from Western Siberia, Khakass-Minusinsk depression, and, possibly, of local origin have been found. XRF analysis of the items has been carried out. Lead-tin and tin bronze prevail, although being in approximately equal quantities, individual objects are made of copper, a small amount of arsenic is traced in two buckles, one ornithomorphic image is cast from an alloy with a significant amount of silver. The clo-sest in this feature, as well as in the amount of tin and lead in the alloys, are the products of the Tomsk burial ground.

Ag2[Fe(CN)5NO]-Fabricated Hydrophobic Cotton as a Potential Wound Healing Dressing: An In Vivo Approach.

There have been reports of different types of wound dressings for various functions and purposes. Cotton being one of the most widely used wound dressing material due to its non-toxic, biodegradable, and other properties is used for fabrication as well as in the form of scaffolds for faster and effective wound closure. Our research team has already demonstrated the role of silver nitroprusside nanoparticles (SNPNPs) for wound healing and antibacterial activity. In the current study, we have developed cotton fabric impregnated with SNPNPs (SNPCFs) which remain photo inert and displayed long-term antimicrobial activity due to the surface modification with the silver nitroprusside complex. These SNPCFs were characterized by various analytical techniques (XRD, FTIR, UV spectroscopy, TGA, TEM, FESEM, EDAX, ICP-OES). The fabricated cotton dressings with nanoparticles showed an improved water contact angle (113-130°) than that of bare cotton gauze (60°) and exhibited more antibacterial property in case of both Gram-negative bacteria (Klebsiella aerogenes and Escherichia coli) and Gram-positive bacteria (Pseudomonas aeruginosa and Bacillus subtilis) even after several washings. The biocompatible nature of SNPCFs was assessed by in vivo chorioallantoic membrane assay that showed no obstruction in the formation of blood vessels. The SNPCFs exhibited better wound healing activity compared to the bare cotton and AgCFs as observed in the C57BL6/J mouse. The histopathological investigation reveals increase in re-epithelialization and deposition of connective tissue. The macrophage (M2) counts in SNPCF-treated skin tissues were supportive of more wound healing activity than mice treated with cotton fabric impregnated with chemically synthesized silver nanoparticles. Based on biodistribution analysis using ICP-OES, the data illustrated that a significant amount of silver is absorbed in the skin tissues of mice as compared to the blood and kidney. Furthermore, the absence of silver from the vital organs (heart, liver, and kidney) corroborates our hypothesis that the SNPCFs can act excellently in treating wounds when topically applied over skin. Thereafter, all these results highlight a strong possibility that SNPCFs exemplify the potential as a new antimicrobial and wound healing agent in future times.

Mineral chemistry of the Xiasai Ag–Pb–Zn deposit in the central Yidun Terrane, SW China: Insight into Ni–Ag–Bi mineralization and formation conditions

Sulfides and sulfosalts are major ore minerals for most of Ag–Pb–Zn deposits and can be used to study enrichment and distribution of ore-forming elements and formation conditions. The Xiasai Ag–Pb–Zn deposit (Zn 0.141 Mt @ 4.30%, Pb 0.132 Mt @ 4.03%, Ag 1028 t @ 337.8 g/t, Cu 10058 t @ 0.56%, and Sn 20000 t @ 0.75%) is a hydrothermal vein-type deposit in the central Yindun Terrane, SW China. It consists of proximal quartz-cassiterite veins and distal Ag–Pb–Zn sulfide veins to a Cretaceous monzogranite. Three successive mineralization sub-stages are recognized for Ag–Pb–Zn veins, i.e., arsenopyrite + coarse-grained pyrite (Py1) + pyrrhotite, sphalerite + chalcopyrite + fine-grained pyrite (Py2), and silver-minerals + native bismuth + galena.Nickel-minerals, such as breithauptite and ullmannite were identified as inclusions hosted within pyrrhotite using Energy Dispersive X-ray Spectroscopy (EDS) and Electron probe microscopy (EPM) analysis and mapping. Trace amounts of invisible silver have been detected in chalcopyrite and galena, whereas a significant amount of silver is incorporated in pyrargyrite, freibergite, miargyrite, and electrum as intimate intergrowths with galena or inclusions within galena. A high content of invisible bismuth is detected within galena (0.21–16.95 wt%), as well as numerous grains of native bismuth occur as inclusions in galena. Based on the Bi concentrations determined and the modal composition a large-sized bismuth deposit would be estimated with about 23,800 t of Bi resource. The presence of nickel-minerals and native bismuth, together with Zn/Cd ratios (58–151) of sphalerite, indicate that the ore-forming materials are derived from the Xiasai monzogranite.Based on mineral assemblages and chemical features for sulfides and sulfosalts, the formation of Ag–Pb–Zn ores was triggered by a decrease in temperature, fs2, fO2, and sulfidation. The early episode of arsenopyrite, Py1, pyrrhotite, and nickel-minerals formed at temperature of 320–470°C, lower fs2 and decreasing sulfidation conditions from low alkaline fluids. In contrast, the late episode of silver-minerals, native bismuth, and galena deposited at 160–270 °C with a lower fs2 state and neutral or acidic pH. However, a slight increase of fs2, fO2, and sulfidation (intermediate sulfidation) occurred during precipitation of Zn–Cu.

Antimicrobial finishing of textiles intended for food processing industry by plasma enhanced chemical vapor deposition – physical vapor deposition of Ag-SiOCH composites coated with AlxOy or SiOCH encapsulation layers

In previous work, textiles for the food processing industry were coated with an original deposition technique based on a combination of plasma-enhanced chemical vapor deposition and physical vapor deposition to obtain ~10nm size silver clusters incorporated into a SiOCH matrix (Ag-SiOCH coating). However, the stability of the coating in end-use conditions (abrasion during washing cycles and/or oxidation) is questionable and this work is specifically devoted to study the effect on antimicrobial activity of Ag-SiOCH coatings after deposition of high porosity and low density protective layers. The Ag-SiOCH coating was thus covered with encapsulation layers (either hydrophobic SiOCH or hydrophilic AlxOy). The surface and bulk characterisation results of the multilayer coatings using X-ray Photoelectron Spectroscopy (XPS), Dynamic Secondary Ion Mass Spectrometry (DSIMS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) were used to study the composition of the coating and quantify the presence of the antimicrobial agent (Ag) at the surface and inside of the coating. Antibacterial tests indicated that antimicrobial activity of coated textiles was maintained. However, the antimicrobial activity was not directly correlated with the Ag content detected at the top surface or with the distance from the top surface to the part of the coating containing a significant amount of silver (as detected by XPS) and diffusion mechanisms during antibacterial tests could play a significant role. In particular, the hydrophilic character of AlxOy deposit likely allowed a better availability of the antimicrobial agent (Ag) but it was also observed for SiOCH hydrophobic deposits.

Hydrothermal evolution and ore genesis of the Beiya giant Au polymetallic deposit, western Yunnan, China: Evidence from fluid inclusions and H–O–S–Pb isotopes

The Beiya porphyry–skarn gold-polymetallic deposit is one of the largest gold deposits in China, and also contains significant amounts of silver and base metals. The estimated reserve at the end of 2015 was 130million metric tonnes (Mt) of ores, grading 2.42g/t Au, 0.48wt.% Cu, 25.5wt.% Fe, 38.85g/t Ag, 1.24wt.% Pb, and 0.53wt.% Zn. The deposit is located in the Jinshajiang–Ailaoshan porphyry–skarn Cu–Mo–Au metallogenic belt in western Yunnan province, southwest China. Skarn alteration and mineralization are spatially and temporally associated with Eocene monzogranite porphyries, which were emplaced into Triassic carbonates. Field evidence and petrographic observations indicate there are four stages of hydrothermal activity, i.e. prograde (Stage I), iron oxide (Stage II), sulfide (Stage III) and carbonate stage (Stage IV). Stage I is characterized by the formation of garnet and pyroxene by high-temperature (398–560°C) hypersaline (48.81–67.24wt.% NaCl equiv.) hydrothermal fluids with H-O isotopic compositions that are similar to typical magmatic fluids. These fluids were most likely generated by the separation of brine from a silicate melt. In Stage II garnet and pyroxene was replaced by epidote, amphibole, chlorite, quartz and magnetite. Associated hydrothermal fluids are preserved in coexisting L-type and V-type fluid inclusions and are characterized by anomalously low δD values (approximately −80‰), and lower δ18O than Stage I fluids. The decrease in ore fluid δ18OH2O values with time coincided with marked decreases in fluid salinity and temperature. Based on the fluid inclusion and stable isotopic data, we suggest that the ore fluid evolved by boiling of the magmatic brine. Stage III is characterized by the development of pyrite, chalcopyrite, galena, and sphalerite. Fluids inclusions associated with Stage III display and continuous range of salinities, with the majority being low-salinity inclusions (1.28–3.54wt.% NaCl equiv.). These fluids yield lower δ18OH2O values (−0.85 to 5.52‰) and moderate δD values (−78.6 to −88.6‰). Altogether, these data indicate that Stage III fluids originated from the mixing of residual Stage II fluids with meteoric water. The sulfur isotope (δ34S) values of Stage III sulfides cover a narrow range of −4.2 to 1.2‰ (mean=−1.1‰), and boiling also occurred at low temperatures (165–347°C) during Stage III. In Stage IV, only L-type fluid inclusions are present, which yielded the lowest homogenization temperatures (157–272°C) and the lowest salinities (1.06–12.20wt.% NaCl equiv.). The H–O isotope data indicate that the ore-forming fluids were dominated by magmatic water in Stage I and Stage II, and that the magmatic water gradually mixed with circulating meteoric water during Stage III and Stage IV. This conclusion is further supported by the isotopic composition of lead of the ores, which is similar to that of the monzogranite porphyries, but differs significantly from Permian basalts and Triassic wall rocks.

Determination of silver release from antibacterial finished cotton and polyester fabrics into water

Silver compounds have extensive use among the antimicrobial agents in textiles. Silver particles are released into the water during washing processes in particular and they are released from the textile in time due to use. In this work, silver ion release from cotton and polyester antimicrobial fabrics which are the most widely used textiles have been studied. Two well-known silver-based commercial agents and silver-doped calcium phosphate powder-based antibacterial finishing agent which was developed in our previous work were applied to the fabric samples. The release of silver from the fabric samples during washing and incubation was determined by ICP-OES. The effects of fabric composition, time and laundering process on the silver release were studied. It was found that significant amount of silver was released from textile fabrics during washing due to the mechanical forces exerted on the fabrics. The total released silver varied from 73.43 to 92.27% for cotton fabrics and 76.49 to 89.70% for PES fabrics after 20 washing cycles. Results also showed that calcium phosphate can reduce the amount of silver release significantly. It was also found that even a smaller quantity of nanosilver particles was sufficient for strong antibacterial activity.

THE GEOLOGY AND MINERALOGY OF THE BEIYA SKARN GOLD DEPOSIT IN YUNNAN, SOUTHWEST CHINA

The Beiya skarn gold deposit is located in the eastern Tethyan orogenic belt in western Yunnan province, China. It is one of the largest gold deposits in China, with significant amounts of silver and base metals. To the end of 2014, the estimated resources are 125 million tonnes (Mt) of ore, grading 2.42 g/t Au, 0.48 wt % Cu, 25.5 wt % Fe, 38.85 g/t Ag, 1.24 wt % Pb, and 0.53 wt % Zn. Skarn alteration and mineralization are related to shoshonitic quartz monzonite porphyries that were emplaced in Triassic carbonates (Beiya Formation). Re-Os dating on molybdenite from a skarn orebody indicates an ore-forming age of 36.82 ± 0.48 Ma, which is consistent with previous dating results of the quartz monzonite porphyries. At least two paragenetic stages of skarn minerals and associated sulfides were recognized, with the early stage typified by garnet ± pyroxene, magnetite, and calcite, and the late stage characterized by epidote, amphibole, chlorite, quartz, and calcite, containing up to 70% sulfides (pyrite, chalcopyrite, and minor pyrrhotite). The early skarn is dominated by anhydrous minerals, which were replaced by hydrous minerals formed during the late stage. The garnet in the Beiya deposit is andradite rich (Ad36–97Gr3–61), and pyroxene is relatively diopside rich (Di8–91Hd7–89). This mineral assemblage indicates an oxidized skarn system, similar to other Au-Cu, Fe-bearing skarn deposits around the world. Fluid inclusions from pyroxene indicate precipitation from high-temperature and high- to moderate-salinity fluids (420°–530°C, 11.1–43.3 wt % NaCl equiv), which probably results from boiling of a moderately saline magmatic fluid. Cooler (180°–365°C) and moderate- to low-salinity fluids (1.6–16.5 wt % NaCl equiv) were trapped in garnet and quartz and are interpreted to be responsible for gold deposition. Chlorite chemistry indicates ore-forming temperatures between 300° and 340°C, in agreement with fluid inclusion data. It appears that gold was transported as chloride complexes under oxidized conditions and was deposited at temperatures of about 300°C, when transport of chloride complexes as gold carriers was less efficient.

A comparative study of the effect of α-, β-, and γ-cyclodextrins as stabilizing agents in the synthesis of silver nanoparticles using a green chemistry method

This paper describes the effect of different types of cyclodextrins (CDs) in the synthesis of silver nanoparticles (Ag-NPs), using an easy green chemistry method. The Ag-NPs were obtained using an aqueous silver nitrate solution (AgNO3) with α-, β-, or γ-CDs (aqueous solutions) as stabilizing agents, employing the chemical reduction method with citric acid as a reducing agent. A comparative study was done to determine which cyclodextrin (CD) was the best stabilizing agent, and we found out that β-CD was the best due to the number of glucopyranose units in its structure.The formation of the Ag-NPs was demonstrated by analysis of UV–vis spectroscopy, atomic force microscopy (AFM), scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS) and transmission electron microscopy (TEM). SEM–EDS showed the formation of a cluster with a significant amount of silver, for β-CD-Ag-NPs, spherical agglomerates can be observed. However, for α-, γ-CD, the agglomerates do not have a specific form, but their appearance is porous. TEM analysis shows spherical nanoparticles in shape and size between ~0.5 to 7nm. The clear lattice fringes in TEM images and the typical selected area electron diffraction (SAED) pattern, showed that the Ag-NPs obtained were highly crystalline with a face cubic center structure (FCC).

Mineral chemical investigation on sulfide mineralization of the Istala deposit, Gümüşhane, NE-Turkey

The mineralogy of the Istala deposit, Gümüşhane, northeastern Turkey, was studied in detail, and a geochemical investigation was carried out using electron probe micro-analysis (EPMA). Sphalerite, galena, chalcopyrite and pyrite are the major sulfide minerals found in the Istala deposit, with minor amounts of bornite, idaite, tetrahedrite–tennantite, anilite, yarrowite, mckinstryite, covellite and chalcocite. In addition to these, barite and a small quantity of quartz occur as gangue minerals. Based on the textural relations and mineral assemblages, five different stages of crystallization have been recognized. Mineral paragenesis of the first four stages has been found to be similar, whereas clear enrichment has been observed in the modal abundance of the copper sulfide mineral assemblage at the fifth-stage ore formation. Whole-rock geochemical analyses of the Istala ore show an enrichment of Ag content up to 3328ppm. Optical observations and EPMA study indicated that abundant silver mineralization was found in the Istala ore, especially during the later-stage ore deposition. Repetition to the presence of native silver in the samples, a significant amount of silver was incorporated in bornite, idaite, tetrahedrite–tennantite, anilite, yarrowite, mckinstryite, covellite and chalcocite, whereas a trace amount of silver has been detected in sphalerite, galena, chalcopyrite and pyrite. The homogenization temperatures (Th) of the primary fluid inclusions were measured between 98 and 284°C, with frequency peaks around 140°C, 190°C and 240°C. All data obtained support the theory that later stage copper-rich sulfides, formed under the low temperature conditions, are responsible for the large amounts of silver content in the Istala mine.

Gold and Silver Cyanidation from a Residue Produced by Leaching Dead-Roasted Copper White Metal

The present work discusses the gold and silver recovery by cyanidation from a solid leach residue produced by a new alternative of processing copper matte or white metal. The leach residue contains mainly hematite, cupric ferrite, insolubles and precious metals. By cyanide leaching this residue, over 95% of gold can be extracted with solutions containing 0.06 g/L of KCN at 45°C in 24 hours, while silver extraction was less than 2.5% for the same conditions. Significant amounts of silver (45%) can be extracted only under a strong KCN concentration of 1.2 g/L.Cyanidation temperature affects the gold and silver dissolution. An increase in temperature increases the gold dissolution, while the opposite effect was found for silver. The low silver dissolution appears to be the result of the roasting step of the copper white metal. Although no direct evidence of a silver-iron ferrite or silver-copper double oxide was found in the residue, results indicate that metallic silver dissolves in the ferrite both by intergranular diffusion and Fick's diffusion, with a diffusion coefficient of 5 × 10-4 sq.cm2/s at 800°C.

Silver Absorption on Burns After the Application of Acticoat™: Data From Pediatric Patients and a Porcine Burn Model

Silver dressings have been widely used to successfully prevent burn wound infection and sepsis. However, a few case studies have reported the functional abnormality and failure of vital organs, possibly caused by silver deposits. The aim of this study was to investigate the serum silver level in the pediatric burn population and also in several internal organs in a porcine burn model after the application of Acticoat. A total of 125 blood samples were collected from 46 pediatric burn patients. Thirty-six patients with a mean of 13.4% TBSA burns had a mean peak serum silver level of 114 microg/L, whereas 10 patients with a mean of 1.85% TBSA burns had an undetectable level of silver (<5.4 microg/L). Overall, serum silver levels were closely related to burn sizes. However, the highest serum silver was 735 microg/L in a 15-month-old toddler with 10% TBSA burns and the second highest was 367 microg/L in a 3-year old with 28% TBSA burns. In a porcine model with 2% TBSA burns, the mean peak silver level was 38 microg/L at 2 to 3 weeks after application of Acticoat and was then significantly reduced to an almost undetectable level at 6 weeks. Of a total of four pigs, silver was detected in all four livers (1.413 microg/g) and all four hearts (0.342 microg/g), three of four kidneys (1.113 microg/g), and two of four brains (0.402 microg/g). This result demonstrated that although variable, the level of serum silver was positively associated with the size of burns, and significant amounts of silver were deposited in internal organs in pigs with only 2% TBSA burns, after application of Acticoat.

The recovery of silver from mining wastewaters using hybrid cyanidation and high-pressure membrane process

The main objective of this work was to investigate the recovery of silver from mining wastewaters using a hybrid cyanidation and high-pressure membrane process. The tested hybrid process in lab-scale experiments includes the concentration and recovery of silver by nanofiltration (NF) or reverse osmosis (RO) after the silver is taken into solution as AgCN employing re-cyanidation and subsequent sedimentation and/or pre-filtration of wastewaters. Synthetic water experiments were conducted in this work. In synthetic water experiments (in distilled and deionized water), the soluble AgCN complex was formed after cyanidation of low-soluble AgCl particles which were added to the leach tank. Two different NF membranes and one RO membrane were tested in a lab-scale flat-sheet configuration test unit. The results indicated that although a significant amount of silver was lost on the RO membrane due to irreversible sorption, RO membrane performed better than NF membranes based on higher silver rejections, thus higher mass recoveries. Therefore, RO membrane was found to be more effective in terms of precious metal recovery and production of high quality permeate that can be reused in the leaching process. The tested hybrid cyanidation (leaching) and high-pressure membrane process in this work may be an effective approach in recovering precious metals and producing reusable water from wastes or wastewaters of mining industry.

Enhanced leachability of gold and silver in cyanide media: Effect of alkaline pre-treatment of jarosite minerals

Composite samples of tailings containing gold (1.35 g/t) and significant amounts of silver (155 g/t) were subjected to batchwise cyanide leaching to assess the feasibility of extracting gold and silver. The tailings are waste solids arising from flotation and leaching operations whereby the flotation product (sphalerite concentrate) is calcined and then solubilised into dilute sulphuric acid solution and eventually sequestered from the electrolyte by electrowinning. Silver and gold are part of the zinc refinery residue, flotation tailings and to a limited extent the calcine leach tailings. Mineralogical results showed that composite tailings are refractory in nature (44% quartz, 17% silico aluminates and 12% jarosites). The concept of enhancing gold and silver recovery from the tailings focused on firstly decomposing the jarosite minerals by alkaline pre-treatment and then secondly leaching with cyanide solution. These two steps ensured that free gold and silver found in the zinc refinery residue and in the jarosite minerals could be leached simultaneously. The composite tailings were treated with Ca(OH) 2 solutions and then heated to 90 °C for 2 h to decompose the silver-bearing mineral (Ag,PbFe 3(SO 4) 2(OH) 6). The alkaline pre-treated tailings were then subjected to cyanide leach tests at different NaCN dosages (2.5–10 kg/t) and particle size (96–200 μm). Without an alkaline pre-treatment stage, leach efficiencies achieved were 41% and 25% for gold and silver, respectively at 40 °C and 8 h mixing time. But, better leach efficiencies (55% for Au, 81% for Ag) were achieved after the feed was pre-treated with Ca(OH) 2. The leaching mechanism of gold was explained by the shrinking sphere model denoted by surface chemical reaction.

Recovery of precious metals from electronic scrap by hydrometallurgical processing routes

Although copper is the principal metal in most electronic scrap, printed circuit boards in mobile phones also contain a significant amount of silver, gold and palladium. A bench-scale extraction study was carried out on the applicability of economically feasible hydrometallurgical processing routes to recover these precious metals. The starting material contained 27.37% copper, 0.52% silver, 0.06% gold and 0.04% palladium. In a first step, the following leaching solutions were applied: an oxidative sulfuric acid leach to dissolve copper and part of the silver; an oxidative chloride leach to dissolve palladium and copper; and cyanidation to recover the gold, silver, palladium and a small amount of the copper. A thiourea leach, as an alternative to cyanidation, was also investigated but did not give a sufficiently high yield. To recover the metals from each leaching solution, the following methods were evaluated: cementation, precipitation, liquid/solid ion exchange and adsorption on activated carbon. Precipitation with NaCl was preferred to recuperate silver from the sulfate medium; palladium was extracted from the chloride solution by cementation on aluminum; and gold, silver and palladium were recovered from the cyanide solution by adsorption on activated carbon. The optimized flowsheet pe united the recovery of 93% of the silver, 95% of the gold and 99% of the palladium.

Efficiency and characteristics of solid-phase (ion-exchange) extraction for removal of Cl − matrix

Certain types of samples contain chloride in concentrations that are too high to accurately determine other anions by ion chromatography without any pretreatment. One of the most widely used approaches for such samples is matrix elimination using disposable cartridges containing a cation-exchange resin in the Ag + form. The efficiency and characteristics of the commercially available cartridge for Cl − removal were tested by the on-line connection of the cartridge effluent to an inductively coupled plasma mass spectrometer. Displacement efficiency of Ag + ions and loading capacity of the cartridges were studied at different flow-rates. Significant amounts of silver were detected in the effluent, which were attributed to colloidal AgCl as well as dissolved Ag + ions. Because silver ions can cause irreversible damage to the analytical column, an Ag cartridge followed by an on line filter (pore size 0.22 μm) and cartridge in the H 3O + form were proposed for improvement of this sample pretreatment technique for chloride removal.

Nanoleakage at the dentin adhesive interface: a new application for laser ablation-sector field-ICPMS

Laser ablation-sector field-inductively coupled plasma mass spectrometry has been used for in situ determination of silver concentration in treated human teeth. Silver nitrate has long been used to trace the presence of micro sized gaps between the walls of dental restorations and teeth, and more recently, to trace the presence of nanometer sized voids within resin-bonded restorations. This study examines the diffusion of silver nitrate into submicron voids beneath resin-bonded composite restorations. The silver treated-teeth were analyzed for 43Ca, 107Ag, and 109Ag isotopes. Elemental data were obtained by ablation with Nd:YAG laser operating in the UV region 266 nm and 213 nm by New Wave-Merchantek and isotopic analysis with a sector field ICP MS by Finnigan MAT. A 50 ppm glass standard (NIST-612) was also analyzed for the same isotopes. Quantification was performed by assuming a uniform nominal calcium concentration value of 27 g per 100 g of dry dentin across the root and using the 43Ca signal for internal calibration. The precision (RSD%) of measurements for 43Ca for the NIST-612 glass standard was found to be within 1.8% to 2.5% and for the tooth samples within 2.8% to 7.1%. The precision of analysis for 107Ag for the NIST-612 glass standard was between 2.6% and 4.4%. The analysis revealed a significant penetration of resin-bonded dentin by silver, ranging from ∼35000 ppm at the very bottom of the resin-infiltrated demineralized dentin to only 10 s of ppm in the areas within the underlying mineralized dentin. The analysis revealed that a significant amount of silver penetrated through resin-dentin bonds, and that the amount of silver increased with increased acid-etching time. The results from this study suggest that current adhesive resin system do not create perfect bonds and that laser ablation sector field ICPMS can be used to quantify the amount of nanoleakage of bonded restorations.

Thermodynamic modeling of selenide matte converting

A by-product of the electrorefining of anode copper is a slime that contains significant amounts of silver, as well as selenium, copper, and other minor elements such as gold. Slimes are usually smelted to recover silver and gold. The thermodynamics of the smelting of such selenium-rich materials have received scant attention, and the little that has been done leads to erroneous predictions. In this work, a chemical potential diagram is developed that successfully explains previously published observations. The smelting of slimes was also modeled with a computational thermodynamics package. Despite the simplicity of the model, which assumed that the activity coefficients of all species remained constant throughout oxidation, it gave good agreement with experimental results published elsewhere for the compositions of all phases during smelting. The model was used to demonstrate that using air rather than pure oxygen significantly affected only the selenium content of the slag, reducing it to low levels. Smelting temperature in the range tested was shown not to be an important process variable.

Stratigraphic and structural controls on gold mineralization in the Pilgrim's Rest goldfield, eastern Transvaal, South Africa

Since 1872, approximately 185 metric tons of gold and a significant amount of silver have been won from numerous stratiform ore bodies within the Pilgrim's Rest goldfield. The epigenetic stratiform ore bodies are found primarily in the Malmani Dolomite Subgroup, a laterally extensive Lower Proterozoic carbonate platform succession. A strong relationship exists between the presence of stratiform ore bodies and environment of deposition and structural deformation. Analysis of the host sediments indicates deposition in a retrogradational, followed by an aggradational, sequence that comprises supratidal (sabkha) siliciclastic sediments to midshelf carbonates. The retrogradational and aggradational sequences are characterized by numerous higher frequency transgressive and regressive cycles. Mineralization is, with few exceptions, restricted to shallow-water siliciclastic sediments; deeper water carbonates are barren. More importantly, siliciclastic mudstones and sandstones have acted as zones of detachment for thin-skinned thrust-fault deformation, resulting in the development of conformable passageways in which fluids concentrated their auriferous lodes. Evidence of shallow hinterland-dipping duplex, antiformal stack, and imbricate thrust systems abounds in several underground and field exposures. The gold-silver emplacement model for the Pilgrim's Rest goldfield infers fluids derived from a deep-seated magmatic source. Oxygen-isotopic compositions of the mineralizing fluids, recalculated from δ 18O quartz (+ 12.1‰ to + 19.5‰), point to a magmatic source and subsequent mixing with saline, evolved formation water. A magmatic origin is also supported by the high homogenization temperature gradient displayed by the fluid inclusions (100°C/km). The Bushveld Igneous Complex (Rustenburg Layered Suite) to the west of Pilgrim's Rest is thought to be the source of the auriferous hydrothermal solutions, and its emplacement was the driving mechanism of thrust-fault deformation in the Pilgrim's Rest goldfield.

Silver release from metal-reinforced glass ionomers

The release of silver from two metal-reinforced glass ionomers, Ketac-Silver and Miracle Mix, was studied in artificial saliva by the anodic stripping voltammetry technique. It was observed that a significant amount of silver (∼10 −5 g/cm 2) was released from both materials in 10 days. The concentration of silver released from Miracle Mix was about 20% lower than that from Ketac-Silver.

The spherical form of gold; man-made or secondary?

An unusual spherical form of gold is described from a number of widely distributed sites: the Abitibi clay belt of Canada, the Lakekamu gold field of Papua New Guinea, the Naraguta placer tin mine in Nigeria, French Creek in British Columbia, Chateau-Gontier in France, the Dorlin area of French Guiana, a gossan in Cyprus, and three placers in South America. The spheres range in size from 20 to 300 mu m and are characterized by a microcrystallite structure, variable gold contents from site to site, and significant amounts of silver and copper. Some of the spheres are interpreted as secondary or supergene chemical precipitates produced by the reduction of gold in ground water and soil water by iron and manganese oxides: most are interpreted as man-made melt droplets accidentally introduced into otherwise normal placer samples, and some may be interpreted either way. Whenever they are found during a gold exploration program, the geologist should suspect that the samples concerned have been contaminated with man-made melt droplets.