Physical-chemical and electrochemical characterization of Fe-exchanged natural zeolite applied for obtaining of hydrogen peroxide amperometric sensors

This work demonstrates that a Fe-exchanged zeolitic volcanic tuff from Cepari (Fe/CV) (Bistrita-Nasaud County, Romania) is suitable for the amperometric detection of H₂O₂, using new modified carbon paste electrodes based on this material (Fe/CV-CPEs). The physical-chemical characterization of natural (CV) and modified (Fe/CV) forms was realized using chemical analysis, optical microscopy, scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), energy dispersive X-ray spectroscopy (EDX) and Fourier transformed infrared (FTIR) spectroscopy. The resulting electrodes (Fe/CV-CPEs) were investigated using cyclic voltammetry and chronoamperometry measurements. The new electrodes showed good electrocatalytic activity toward H₂O₂ reduction. The calibration curve for H₂O₂ determination was linear up to 0.1 mM, with a detection limit (signal to noise ratio of 3) of 20 μM.     

Gas phase measurements of hydrogen peroxide in Greenland and their meaning for the interpretation of H2O2 records in ice cores

The gas phase concentration of hydrogen peroxide at Summit, Central Greenland, has been measured continuously during June/July 1990 using a coil scrubber technique combined with liquid phase fluorometry. The concentrations ranged between 0.3 ppbv and 3.5 ppbv, which is considerably higher than expected from model calculations and can be explained by low deposition rates. The record shows pronounced diurnal variations with minimum concentrations during night and maximum concentrations in the afternoon. The nocturnal minima can be explained by scavenging of H₂O₂ by hoarfrost. The scavenging mechanisms of H₂O₂ by snow and the redistribution of H₂O₂ during firnification are discussed. There is indirect evidence, that H₂O₂ is uniformly distributed in the ice lattice and that the fractionation between H₂O₂ and H₂O is small during diffusional crystal growth from the vapor phase (co-condensation).     

钴的赋存状态及其在找矿和资源评估中的意义

通过分析含钴矿物类型的多样性 ,得出地球系统中钴呈硫化物、类硫化物、铁氧化物和呈类质同像代替铁多种赋存状态及其受晶体化学因素控制特点。基于钴赋存状态的不同 ,提出当前钴的地球化学找矿和矿产资源评估中仅以钴量化丰度值作为化探异常和矿石品位判据的局限性。指出元素状态丰度提供资源信息的重要意义     

Hydrogen diffusion in natural and synthetic orthopyroxene

 Hydrogen diffusion coefficients in natural orthopyroxenes and synthetic enstatite were determined by dehydration and hydration experiments at 700 and 900 °C. In natural Opx (approximately En₉₀Fs₁₀) small but significant differences in diffusivities along the three crystallographic axes were observed, [001] being the fastest direction, followed by [100] and [010]. Hydrogen diffusion in pure enstatite proved to be about 2 orders of magnitude slower and isotropic. The activation energy for hydrogen diffusion in pure enstatite was determined to be −295 (±55) kJmol⁻¹, and −213 (±47) kJmol⁻¹ for orthopyroxene from Kilbourne Hole. Long-term hydration experiments did not lead to saturation in hydrogen. Instead, after an initial increase in hydrogen concentration, a slow but continuing decrease could be observed in all cases. It is suggested that the investigated samples lose their ability to store hydrogen even when heated in a hydrogen atmosphere. This loss in storage ability can itself be described by a diffusion equation, its diffusion coefficients being more than 1 order of magnitude slower than the diffusion of hydrogen. Received: 22 February 2002 / Accepted: 18 October 2002     

河南内乡板厂铜多金属硫化物矿床地质特征及成因分析

板厂铜矿床位于东秦岭造山带内,区内出露地层主要为二郎坪群细碧岩类及秦岭群大理岩类。矿体地表呈带状分布,倾向上矿体呈层状、似层状、叠瓦状重复出现。矿体与围岩呈渐变过渡关系,矿层随含矿地层硅质岩展布而展布。对24种微量元素编制的配分图解中可以看出矿化层、矿化硅质岩、无矿化硅质岩、无矿化大理岩中的微量元素配分曲线有一定的相似性,同时发现矿化硅质岩中碳酸岩条带δ18 O结果为18.809‰～21.572‰,和海底喷流沉积δ18 O范围相近。通过研究分析,认为板厂铜多金属硫化物矿床成因为海底喷流沉积金属硫化物矿床。     

锍镍试金-等离子体质谱法测定地球化学勘探样品中的铂族元素和金Ⅰ．分析流程的简化

报道了一个改进的锍镍试金一等离子体质谱测定铂族元素和金的分析流程，用封闭溶解贵金属硫化物滤渣与同位素稀释法测锇相结合，解决了包括锇在内的全部铂族元素和金的测定，避免了锇的蒸馏分离和（或）单独测定，简化了分析流程，以适应大批量化探样品的要求，用所拟方法分析了标准物质中铂族元素和金，其结果与参考值相符。     

论华南块状硫化物矿床成矿规律与找矿方向

华南块状硫化物矿床，在成因上同生喷气沉积为主，兼具后期叠加改造特点。在成矿时代上具多期成矿特征，尤以中－晚元古代，泥盆纪，石岩纪和晚侏罗世－白垩４个时代为主。在空间分布上具“成带分布，分段集中，成群产出”的规律，受拉张性明背景，火山或热泉活动及特殊岩相古地理环境控制。重要矿床集中于一些特殊成矿结中。成矿作用表现出明显的继承性和新生性，成矿物质组合也随着时间和空间而发生规律性变化。需指出，江南古陆周     

A Pilot Study of Trophic Level and Human Origins at the Xiaoshuangqiao Site, China (ca. 1400 BC) Using δD Values of Collagen

We present here a pilot study to examine trophic level effects and migration patterns at the middle Shang Dynasty site of Xiaoshuangqiao in Henan Province using δD results combined with δ13C and δ15N values. A total of 33 specimens (17 humans, 7 cattle, 5 pigs, 3 sheep, 1 dog) of bone collagen were isotopically analyzed for δ13C, δ15N, and dD values. A strong positive correlation (R2 = 0.94) between mean δ15N and δD values of herbivores (cattle and sheep), omnivores (pig), carnivores (dog) and humans was observed. The δD results were found to increase by ~10‰ to 20‰ from herbivores to omnivores to carnivorous, evidence that collagen δD results are a useful indicator for the study of trophic levels and dietary patterns at archaeological sites. The δD results were also used to examine the origins of two different groups of individuals buried at Xiaoshuangqiao. Individuals buried in sacrificial pits of district V had mean δD values (?47.0 ± 2.9‰, n = 11) that were significantly (p = 0.049) elevated compared to the people buried in the stratigraphy of district IX (?51.3 ± 3.3‰, n = 3), indicating that they were ingesting water from different locations. In addition, the D values of the people buried in the stratigraphy were similar to the pigs (?54.5 ± 4.2‰, n = 5) at Xiaoshuangqiao, suggesting that they were most probably of the local population, and that the individuals buried in the sacrificial pits were most possibly from the coast and prisoners of the Dongyi (“东夷”) people. Thus, δD results have the potential to examine human origins and migration patterns and should be increasingly used in conjunction with δ13C and δ15N values at archaeological sites.     

Monitoring of the integrated column of hydrogen fluoride above the Jungfraujoch Station since 1977 — the HF/HCl column ratio

The amount of hydrogen fluoride (HF) above the International Scientific Station of the Jungfraujoch (Switzerland) has been monitored during the last 8 years. The results deduced spectro-scopically from solar IR absorption measurements near 2.48 m indicate a cumulative trend equivalent to (8.5±1)% increase per year, as well as short-term variability which appears to be strongly correlated with meridional circulation patterns during the February–April months. Based on intensified measurements made over the last three years, it is found that the integrated content of HF undergoes a seasonal change with a minimum occurring in the fall. The HF/HCl ratio derived from simultaneous HF and HCl measurements was found equal to 0.15 during the period 1977–79, and 0.24 for the 1983–85 timespan.     

Platinum-Group Elements in Sulphide Minerals, Platinum-Group Minerals, and Whole-Rocks of the Merensky Reef (Bushveld Complex, South Africa): Implications for the Formation of the Reef

The concentrations of platinum-group elements (PGE), Co, Re,Au and Ag have been determined in the base-metal sulphide (BMS)of a section of the Merensky Reef. In addition we performeddetailed image analysis of the platinum-group minerals (PGM).The aims of the study were to establish: (1) whether the BMSare the principal host of these elements; (2) whether individualelements preferentially partition into a specific BMS; (3) whetherthe concentration of the elements varies with stratigraphy orlithology; (4) what is the proportion of PGE hosted by PGM;(5) whether the PGM and the PGE found in BMS could account forthe complete PGE budget of the whole-rocks. In all lithologies,most of the PGE (65 up to 85%) are hosted by PGM (essentiallyPt–Fe alloy, Pt–Pd sulphide, Pt–Pd bismuthotelluride).Lesser amounts of PGE occur in solid solution within the BMS.In most cases, the PGM occur at the contact between the BMSand silicates or oxides, or are included within the BMS. Pentlanditeis the principal BMS host of all of the PGE, except Pt, andcontains up to 600 ppm combined PGE. It is preferentially enrichedin Pd, Rh and Co. Pyrrhotite contains, Rh, Os, Ir and Ru, butexcludes both Pt and Pd. Chalcopyrite contains very little ofthe PGE, but does concentrate Ag and Cd. Platinum and Au donot partition into any of the BMS. Instead, they occur in theform of PGM and electrum. In the chromitite layers the whole-rockconcentrations of all the PGE except Pd are enriched by a factorof five relative to S, Ni, Cu and Au. This enrichment couldbe attributed to BMS in these layers being richer in PGE thanthe BMS in the silicate layers. However, the PGE content inthe BMS varies only slightly as a function of the stratigraphy.The BMS in the chromitites contain twice as much PGE as theBMS in the silicate rocks, but this is not sufficient to explainthe strong enrichment of PGE in the chromitites. In the lightof our results, we propose that the collection of the PGE occurredin two steps in the chromitites: some PGM formed before sulphidesaturation during chromitite layer formation. The remainingPGE were collected by an immiscible sulphide liquid that percolateddownward until it encountered the chromitite layers. In thesilicate rocks, PGE were collected by only the sulphide liquid. KEY WORDS: Merensky Reef; Rustenburg Platinum Mine; sulphide; platinum-group elements; image analysis; laser ablation ICP-MS