Mobilization analysis of the dolmen of Dombate (Northwest Spain)

This paper presents an analysis of the mobilization of the dolmen of Dombate, a megalithic monument situated in the Northwest of Spain. The study is founded on simple static principles, with the application of basic concepts of soil mechanics (soil reactions were computed by the reaction modulus method) and rock mechanics (a simple secant approach was adopted to model the contact between orthostats). In addition, a simplified geometric model for dolmens was adopted. On the basis of these concepts, a numerical solver able to provide quick estimations of the system's mobilization was developed. Using this tool, a number of sensitivity analyses were conducted to estimate the mobilization that could be caused by a conservation project currently under consideration. It was found that mobilization might be excessive, and therefore, a safer procedure is proposed. In short, this paper puts forth a new rational approach for archaeological practices which may help to estimate the possible consequences of excavations and rehabilitations on megalithic structures.     

Mobilisierbarkeit von hydrophoben organischen Schadstoffen in belasteten Böden und Abfällen. Teil I: Mobilisierbarkeit von PCB,PAK und n-Alkanen durch Lösungsvermittler

Mobilization Potential of Hydrophobic Organic Compounds (HOCs) in Contaminated Soils and Waste Materials. Part I: Mobilization Potential of PCBs, PAHs, and Aliphatic Hydrocarbons in the Presence of Solubilizing Substances When using an elution procedure for organic pollutants to estimate the leaching behaviour of contamined soils and waste deposits, the influence of organic matter in solids and eluates adequately has to be considered. In batch tests with a solid/liquid ratio of 1:10, various aqueous solutions were composed, the solubilizing effect of which can be attributed to ubiquitous natural compounds (e. g., phospholipids, humic and carbonic acids). These solutions were evaluated in regard to the mobilization of PAHs, PCBs, and aliphatic hydrocarbons in soil and waste samples. The results were compared with batch tests containing sodium dodecyl sulfate (SDS), the properties and applications of which are selected and optimized in order to simulate the chemical interactions between pollutant and solubilizing substances of natural sources. Under alkaline conditions, the part of eluated pollutants was high because of the release of humic substances indigenous to the sample. Low concentrations of phospholipids and humic acid could decrease the mobility of aliphatic hydrocarbons. The extend of HOC mobilization is affected by specific interdependences between solubilizing substances and reactive matter of the samples. For most samples, 5.0 g/L concentrated SDS solution was able to simulate the most effective natural solutizer potential in regard to the mobilization of PAHs, PCBs, and aliphatic hydrocarbons within the system of batch tests. Whereas elution with pure water caused significant deviations in pollutant composition and too low yields, the use of SDS effected à good conformity. Modified in such a manner, the elution procedure can follow DIN 38414 part 4, when loss of pollutants will be minimized; e. g., centrifugation is needed to separate phases.     

中国地区沙尘气溶胶输送过程的数值模拟

本文建立了一个包含沙尘起沙、输送、干沉积和湿沉积过程的气溶胶输送扩散模式．并和中尺度气候模式RIEMS相连接研究了1998年1月、4月、7月和1997年10月的沙尘起沙、输送、干沉积和湿沉积的过程。计算1998年1月、4月、7月和1997年10月气溶胶浓度及其分布．并和这四个月份的平均起沙分布以及北京、郑州和南京的实例沙尘分布作了比较．结果表明我国起沙多发生在春季．同时春季也是我国沙尘强度最大的季节。沙尘在我国西北的沙地和沙漠地区起沙后．向我国的东南方向输送．在输送过程中沙尘浓度逐渐降低。     

Bindungsverhalten ausgewählter Elemente in Sedimenten eines sauren Tagebaurestsees/FNR>

Binding Character of Selected Elements in Acidic Mining Lake Sediments To investigate the vertical element distribution in an acidic mining lake the concentrations of selected elements were measured by ICP‐MS and ICP‐OES. By knowing the metal concentrations in different depths it is possible to divide these metals into three groups. While the concentrations of iron, manganese, and zinc decline with decreasing depth, those of aluminium, copper, and nickel rise up. For lead and cobalt no distinct tendency could be determined. The limit value for all measured elements was not exceeded in any sampling location. The binding character of the metals is, besides the seasonal conditions of the lake (circulation in spring and stagnation in summer), influenced by the sediment depth. The addition of Carbokalk® for lake water neutralization had no significant effect on binding character of the analyzed metals. The application of a sequential extraction procedure enabled a classification of the available metal binding forms. All analyzed metals occurred mainly in compounds which are difficult to mobilize and for environment only slightly available.     

华南T岩体白云母化与铀活化的关系

白云母化是华南许多花岗岩型铀矿床常见的“前提蚀变”。T岩体白云母化呈面型分布,黑云母转变为白云母后,单位晶胞体积缩小,在等容交代条件下,粒间空隙增多,导致岩石孔隙度增加,为活化出来的铀准备了空间和迁移通道。黑云母在结晶过程中,吸附和隐晶捕获的铀及所包裹的副矿物中的铀也部分活化,引起铀配分的调整,使分散、吸附形式的铀增加。铀存在形式的转变和初步浓集,对花岗岩型铀矿床的形成是不可少的成矿机制之一。     

Zn/Cd ratios in calcsilicate-hosted sphalerite ores at Tumurtijn-ovoo, Mongolia

As other calcsilicate-hosted ore deposits the Tumurtijn-ovoo Fe–Mn–Zn deposit is subdued to the question how the ore elements took place, whether linked to epigenetic silicification of a limestone host or bound to syngenetic precipitation during the deposition of a calcareous-siliceous sediment. The comparison of high Zn/Cd ratios of ores from Tumurtijn-ovoo ranging from 514 to 724 with those of other ore deposits relates Tumurtijn-ovoo to the group of submarine hydrothermal deposits which got their ore elements from basaltic source rocks by subseafloor leaching. Hence, respecting geological and textural features of the ores, a synsedimentary precipitation of zinc and cadmium in a volcano-sedimentary environment is suggested for Tumurtijn-ovoo. A group of low Zn/Cd ratios (274–297) is correlated with processes of mobilization and redeposition of sphalerite.     

Arsenic remobilization from sediments contaminated with mine tailings near the Adak mine in Västerbotten district (northern Sweden)

Weathering of mine tailings have resulted in high As concentrations in water (up to 2900 μg l^− 1) and sediment (up to 900 mg kg^− 1) samples around the Adak mine. Notably, As occurs as As(III) species (15–85%) in the oxic surface and ground water samples, which is not common. Time-series based sediment incubations were set up in the laboratory with contaminated sediments to study the microbial processes involved in transformation and remobilization of As across the sediment–water interface. The microcosm experiments indicate that microorganisms are capable of surviving in As-rich sediments and reduce As(V) to As(III). A decrease in total As concentration in sediments is coupled to an increase in As(III) concentration in the aqueous media. In contrast, the controls (treated with HgCl₂ and formaldehyde) did not show growth, and As(V) concentrations increased steadily in the sediments and aqueous medium. The results imply that active metabolism is necessary for As(V) reduction. These microorganisms possess reduction mechanisms that are not necessarily coupled to respiration, but most likely impart resistance to As toxicity.     

Arsenic mobilization in an oxidizing alkaline groundwater: Experimental studies,comparison and optimization of geochemical modeling parameters

Arsenic (As) mobilization and contamination of groundwater affects millions of people worldwide. Progress in developing effective in-situ remediation schemes requires the incorporation of data from laboratory experiments and field samples into calibrated geochemical models.In an oxidizing aquifer where leaching of high pH industrial waste from unlined surface impoundments led to mobilization of naturally occurring As up to 2 mg L⁻¹, sequential extractions of solid phase As as well as, batch sediment microcosm experiments were conducted to understand As partitioning and solid-phase sorptive and buffering capacity. These data were combined with field data to create a series of geochemical models of the system with modeling programs PHREEQC and FITEQL. Different surface complexation modeling approaches, including component additivity (CA), generalized composite (GC), and a hybrid method were developed, compared and fitted to data from batch acidification experiments to simulate potential remediation scenarios. Several parameters strongly influence the concentration of dissolved As including pH, presence of competing ions (particularly phosphate) and the number of available sorption sites on the aquifer solids. Lowering the pH of groundwater to 7 was found to have a variable, but limited impact (<63%) on decreasing the concentration of dissolved As. The models indicate that in addition to lowering pH, decreasing the concentration of dissolved phosphate and/or increasing the number of available sorption sites could significantly decrease the As solubility to levels below 10 μg L⁻¹. The hybrid and GC modeling results fit the experimental data well (NRMSE<10%) with reasonable effort and can be implemented in further studies for validation.     

Platinum-group elements in the serpentinite lateritic mantles of the Kongo–Nkamouna ultramafic massif (Lomié region,South-East Cameroon)

The behaviour of PGE in a rainforest ecosystem were investigated in four lateritic profiles (Nkamouna, Napene, West and East Mada) developed on serpentinites in the Kongo–Nkamouna massif (Lomié region, South-East Cameroon). In serpentinites, the total PGE content attains 22 ppb whilst it ranges between 26 and 200 ppb in the weathering blanket. Amongst the analyzed elements (platinum, iridium, ruthenium, rhodium, palladium), platinum and ruthenium contents are high in the saprolite zone and in the hardened materials of some weathering profiles (40–66 ppb for platinum, 50–71 ppb for ruthenium). Apart from the hardened materials, the total PGE content decreases from the coarse saprolite towards the clayey surface soil. The Fe₂O₃-PGE diagram indicates a relatively similar behaviour in these iron-rich samples. The Pt–Ir, Pt–Pd, Pt–Ru, Pt–Rh diagrams portray positive correlations between platinum and other PGE. This fact is supported by the positive correlation noticed between IPGE and PPGE. The Pt/Ir, Pt/Pd, Pt/Ru and Pt/Rh values indicate that iridium, palladium, ruthenium and rhodium are more mobile than platinum. These data confirm the mobility of PGE in laterites and the positive correlation reveals that PGE might be accommodated in the interfaces of iron oxides. The mass balance assessment shows that PGE are strongly leached from the Kongo–Nkamouna weathering blanket except in the coarse saprolite of the Nkamouna profile.     

Gas exsolution and flow during supersaturated water injection in porous media: I. Pore network modeling

Degassing and in situ development of a mobile gas saturation take place when an aqueous phase saturated with gas at a pressure higher than the subsurface pressure is injected in water-saturated porous media. In the first part of this work, a pore network model is used to study the key physical aspects of this novel and hitherto unexplored way of introducing a gas phase in the subsurface. Following heterogeneous nucleation, growth of gas phase clusters driven by convective diffusion of solute from the bulk aqueous phase, is shown to result in a ramified pattern of gas-occupied pores, which is controlled by capillary and buoyancy forces. The interplay between mass transfer and immiscible displacement processes, namely gas cluster coalescence, mobilization under the action of buoyancy forces and fragmentation resulting from capillary instabilities, is seen to favour the propagation of a stable gas saturation front. Pore network model predictions of the macroscopic mass transfer rate coefficient are in fair agreement with a recently published empirical correlation.