New Evidence of the Brizziite, Sodium Antimonate from the Central Paratethys Sea Strata in Poland

Brizziite, a rare sodium antimonate (NaSb5+O3), and fluorcalcioroméite ((Ca,Na)2Sb5+2O6F), have been identified in two boreholes (Pasternik and Włosienica) which are situated 50 km apart. Both wells are located west of Krakow, Poland, and were drilled in the Miocene strata of the Paratethys Sea (a remnant of the Tethys Ocean). The Sb minerals are scattered in a solidified light blue silica gel within marls and layered clays. They occur most often as anhedral grains up to 20 μm in size. The presence of these phases was confirmed by Raman spectroscopy (RS) and X-ray diffraction (XRD). The brizziite from this study represents a secondary mineral after the alteration of roméite within a supergene zone, or crystallization from Sb-rich solutions derived by the leaching of the weathered primary roméite. Hence, the calcium and fluorine admixtures in their composition, determined by EPMA, indicate intergrowths of brizziite and roméite on the micro- to crypto-scale. The presence of the antimony in the study area is related to rejuvenated Old-Paleozoic polymetallic ore-mineralization occurring in the basement of the Krakow-Silesia Monocline. The phenomenon of the repeatability of brizziite in Pasternik and Włosienica, distant by several tens of kilometers, can be explained by the following three steps: (i) the penetration of the chloride ions from the drying up seawaters of the Paratethys Sea into the Miocene groundwater system, (ii) the mobilization of Sb5+ in the form of chloride complexes, and, finally, (iii) the transportation of the Sb-bearing solutions within the marly and clay sediments.

Bearing Capacity Factor of Circular Footings on Two-layered Clay Soils

Geotechnical engineers often deal with layered foundation soils. In this case, the soil bearing capacity assessment using the conventional bearing capacity theory based on the upper layer properties introduces significant inaccuracies if the top layer thickness is comparable to the rigid footing width placed on the soil surface. Under undrained conditions the cohesion increases almost linearly with depth. A few theoretical studies have been proposed in the literature in order to incorporate the cohesion variation with depth in the computation of the ultimate bearing capacity of the strip and circular footings. Rigorous solutions to the problem of circular footings resting on layered clays with linear increase of cohesion do not appear to exist. In this paper, numerical computations using FLAC code are carried out to assess the vertical bearing capacity beneath rough rigid circular footing resting on two-layered clays of both homogeneous and linearly increasing shear strength profiles. The bearing capacity calculation results which depend on the top layer thickness, the two-layered clays strength ratio and the cohesion increase rates with depth are presented in both tables and graphs, and compared with previously published results available in the literature. The critical depth for circular footing is found significantly less than for strip footing. Doi: 10.28991/cej-2021-03091689 Full Text: PDF

Stability Numbers for Unsupported Conical Excavations in Multi-Layered Cohesive Soils

This paper presents the results of a numerical analysis into undrained stability of conical excavation in multi-layered clays. Stability predictions for a wide range of geometric and material combinations are calculated by finite element analyses. The results from the present analysis are expressed in the familiar form of stability numbers reflecting the effect of (1) angle of inclination, (2) depth ratio, which is relative top layer thickness to excavation depth, (3) strength difference between two layers on the rigid base, (4) width ratio, which is excavation height to radius at the bottom of excavation, and (5) thickness ratio, which is the ratio of the excavation height to thickness of soil 1 layers. The obtained stability numbers are compared with existing solutions published in the literature. The failure mechanism in multi-layered clays are also discussed in terms of the displacement pattern.

Soil flow mechanisms of full-flow penetrometers in layered clays through particle image velocimetry analysis in centrifuge test

This paper reports the soil flow mechanisms observed in centrifuge tests around full-flow (T-bar and ball) penetrometers in layered clays. The layered clay samples consisted of soft–stiff, stiff–soft, soft–stiff–soft, and stiff–soft–stiff soil profiles. Particle image velocimetry (PIV), also known as digital image correlation (DIC), allowed accurate resolution of the flow mechanism around the faces of the T-bar and half-ball penetrated adjacent to a transparent window. For the T-bar, overall, a full symmetrical rotational flow around the T-bar dominated the behavior. A novel “trapped cavity mechanism” was revealed in stiff clay layers, with the evolution of the trapped cavity being tracked. No soil plug was trapped at the base of the advancing T-bar regardless of penetration from stiff to soft layer or the reverse. For the ball, two key features of the soil flow mechanism were identified, including (i) a combination of vertical flow, cavity expansion type flow, and rotational flow for a fully embedded ball and (ii) a stiff soil plug trapped at the base of the ball advancing in a stiff–soft clay deposit. For both penetrometers, a squeezing mechanism mobilized as they approached a soft–stiff layer interface.

GEOLOGICAL EVALUATION OF LAKE VAN (TURKEY) FOR URANIUM-THORIUM DEPOSITION

Purpose of this study is to prove most probable existence of economical U-Th mineralisations within Tatvan Basin which have been hidden among foreign international research project manuscripts of Lake Van and to inform the importance of national exploration studies. Lake Van is a pull-apart basin formed within Quaternary Muş-Zagros suture zone with right lateral movement. Calculations on heat transfer below the Tatvan Basin indicate that a constant heat flow is about fourty times the continental average which have been only reported from some oceanic ridges. Data indicate the heat source below Tatvan Basin bottom represents a steadily collapsing cauldron subsidence of Nemrut volcano’s magma chamber. Lake Van surface water has mean 76ppb dissolved uranium content of hyrothermal and authigenic origin. It is calculated that there is at least 50.000 tons of dissolved uranium exists in the Lake Van waters. Ultimate deposition of U-Th mineralisation within euxinic Tatvan Basin have been expected to be a continuous process during geologic history of Lake Van as long as uranium resources remain and its NaHCO3 water functions as dissolving agent Sodic Lake Van waters continuously dissolve uranium from 1) high 3He/4He and U-Th containing hydrothermal fluxes of mantle origin coming up through cauldron subsidence faults of Tatvan Basin, 2) per-alkaline rhyolitic volcanic ash rain of Nemrut volcanism, 3) Bitlis granitoid Massive basement, 4) repeated authigenic disentegrations of U to (Th and 4He) within the sedimentary deposites of Tatvan Basin through its 600.000 years history. Tatvan Basin is the deepest basin with 450m depth, 300km2 flat area and constant unoxic basal water table undisturbed by currents and has the following verifications for Quaternary U-Th depositions in the unconsolidated porous sediments: 1) organic mass rich levels with reducing microbial activities, 2) evaporitic dolomites deposited during low stand lake levels with high U-Th concentrations, 3) varved, mixed-layered clays with high hectorite content, 4) sub-aquaeous, basic-intermediate volcanic basement intrusions with reducing properties, 5) measured very low redox potentials in basal environment, 6) very high density of U-Th. Drilling core sequence and the gamma ray logs from Ahlat Ridge have been used in the foreign literature published since 1974 until now while the existence or non-existence of uranium has not been mentioned. Gamma ray logs of drilling cores and their pore water analyses from Tatvan Basin were carried out abroad but not published yet. Thus gamma ray logs belonging only to shallow Ahlat Ridge sequence where uranium mineral precipitation is not possible is misleading.

Quantitative and qualitative analysis of segmental dielectric relaxations and space charge by TSDC in nanocomposites of natural rubber/clay

The effect of adding three different layered clays, a sodium montmorillonite and two commercial modified montmorillonites, on the morphology and molecular dynamics of natural rubber characterized by Transmission Electron Microscopy and Thermally Stimulated Depolarization Currents (TSDC) was studied. Carbon black was employed as reinforcing filler in a standard compound prepared and used for comparison purposes. The morphological results revealed that the sample with Cloisite\circledR 15A displays the highest degree of exfoliation, which suggests a stronger compatibility between the organic and inorganic phases. When the dispersion degree increases, a decrease of the activation energy was found from the quantitative analysis of the space charge dielectric relaxations. From the qualitative analysis of the dipolar dielectric relaxations around $T_{g}$, changes in the dielectric relaxation profile and in the peak localization were attributed to probable interactions between the nanofillers and the elastomer in the glass transition region of the NR.

Modification of pillared layered clays for scavenging radiostrontium from acidic aqueous environments

A Pillared Layered Clay (PILC), code-named FREZEN, has been developed as a potential antidote for trapping radiostrontium in the gastrointestinal tract of ruminants. The ion exchange behaviour of FREZEN has been studied, with particular emphasis on Sr+2 exchange in acidic solutions. As for most sorbents and ion ex­ changers, strontium uptake by FREZEN remains sufficiently good over a pH range of 5-11, but a sharp diminution is observed at pH values below 4. Furthermore, at lower pH values, hydronium ions (H3O+) successfully compete with strontium cations already uptaken by FREZEN. An extended "back-exchange" effect, charac­terized by fast kinetics, is thus observed. In order to impede the diffusion and prevalence of Η3Ο+, a modification of the microporous space in FREZEN has been carried out via intercalation of suitable organic molecules. Work currently underway reveals that this approach is capable of improving the performance properties of the PILC. Experimental results with glycerol as the intercalated organic agen will be presented and discussed.

Radioactive contaminants binding on pillared layered clays

The selective sorption of radioactive cesium and strontium on Pillared Layered Clays was investigated. Two reference samples were initially used in experiments, both in vitro and in vivo. An improved nanocomposite-pillared clay with different organization and structural evolution of its building blocks, was constructed, characterized by several methods and employed in exchange experiments. The results derived from the improved material administration in ruminants for strontium and cesium sorption were positive and further investigation is under way.