Deposition Behavior of Supersaturated Silicic Acid in the Condition of Relatively High Ca or Na Concentration

2014 ◽  
Vol 1665 ◽  
pp. 55-60
Author(s):  
Taiji Chida ◽  
Yuichi Niibori ◽  
Hayata Shinmura ◽  
Hitoshi Mimura
Keyword(s):  
Deposition Rate ◽  
Silicic Acid ◽  
Solid Phase ◽  
Cementitious Materials ◽  
Buffer Solution ◽  
Deposition Behavior ◽  
Ca Ions ◽  
Na Ions ◽  
Materials Used ◽  
Coexisting Ions

ABSTRACTAround the radioactive waste repository, the pH of the groundwater greatly changes from 8 to 13 and the groundwater contains a relatively large quantity of calcium (Ca) and sodium (Na) ions due to cementitious materials used for the construction of the geological disposal system. Under such conditions, the deposition behavior of silicic acid is one of the key factors for the migration assessment of radionuclides. The deposition and precipitation of silicic acid with the change of pH and coexisting ions may contribute to the clogging in flow paths, which is expected as the retardation effect of radionuclides. Thus, this study focused on the deposition behavior of silicic acid under the condition of relatively high Ca or Na concentration.In the experiments, Na2SiO3 solution (250 ml, 14 mM, pH>10, 298 K) was prepared in a polyethylene vessel containing amorphous silica powder (0.5 g) as the solid phase. Then, a buffer solution (to adjust to 8 in pH), HNO3, and Ca(NO3)2 as Ca ions or NaCl as Na ions were sequentially added. Such a silicic acid solution becomes supersaturated, gradually forming colloidal silicic-acid and/or the deposit on the solid surface. In this study, the both concentrations of soluble and colloidal silicic-acid were monitored over a 40-day period. As a result, the deposition rate of silicic acid decreased with up to 5 mM in Ca ions. Besides, Na ions with up to 0.1 M slightly increased the deposition rate. Under the conditions of [Na+]>0.1 M or [Ca2+]>5 mM, the supersaturated silicic acid immediately deposited. These suggest that Na or Ca ions strongly affect the deposition behavior of supersaturated silicic-acid, depending on the surface alteration of solid phase, the change of zeta potential and the decrease of water-activity due to the addition of electrolytes (coexisting ions).

Effects of Temperature on Deposition Rate of Supersaturated Silicic Acid on Ca-Type Bentonite

2016 ◽  
Author(s):  
Tsuyoshi Sasagawa ◽  
Taiji Chida ◽  
Yuichi Niibori
Keyword(s):  
Deposition Rate ◽  
Silicic Acid ◽  
Cementitious Materials ◽  
Effect Of Temperature ◽  
Alkaline Condition ◽  
High Concentration ◽  
Flow Paths ◽  
Effects Of Temperature ◽  
Materials Used ◽  
High Level

For the disposal system of high-level radioactive waste in Japan, Na-type bentonite is used as one of backfilling and buffer materials for preventing the migration of groundwater and radionuclide. However, the alteration to Ca-type bentonite will cause the degradation of the barrier performance. On the other hand, silicate minerals around the repository dissolve under the high alkaline condition of groundwater (about pH 13) altered by alkaline components leaching from cementitious materials used for the construction of the repository. Such high-concentration silicic acid becomes supersaturated with the decrease in pH by mixing with natural downstream groundwater (pH 8) because of the change in the solubility of silicic acid. So far, the authors have examined the deposition rates of supersaturated silicic acid on Ca-type bentonite under the condition of room temperature, showing the clogging effect of flow-paths with the deposition. However, the dynamic behaviors of silicic acid are much sensitive to temperature change. Therefore, the present study focuses on the effect of temperature on the deposition rate of silicic acid on Ca-type bentonite. As a result, in the range up to 323 K, the deposition of supersaturated silicic acid on Ca-type bentonite was promoted with the increase in temperature. This suggests that the deposition of silicic acid will clog the flow-paths in Ca-type bentonite in this temperature range.

Effects of Supersaturated Silicic Acid Concentration on Deposition Rate Around Geological Disposal System

2017 ◽  
Vol 3 (4) ◽  
Author(s):  
Tsuyoshi Sasagawa ◽  
Taiji Chida ◽  
Yuichi Niibori
Keyword(s):  
Deposition Rate ◽  
Silicic Acid ◽  
Dispersion Model ◽  
Cementitious Materials ◽  
Alkaline Condition ◽  
Radionuclide Migration ◽  
Flow Paths ◽  
Advection Dispersion ◽  
Geological Repository ◽  
The One

Cementitious materials for the construction of a geological repository of radioactive waste alter the pH of groundwater to a highly alkaline condition (pH ≈ 13). While this alkaline groundwater dissolves silicate minerals, the soluble silicic acid polymerizes or deposits on the surface of rock with the decrease in pH by mixing with the surrounding groundwater (pH = 8). In particular, the deposition of silicic acid leads to a clogging effect in flow-paths, which retards the migration of radionuclides. This study estimated the clogging of silicic acid in flow-paths with the one-dimensional advection–dispersion model considering the deposition rate constants evaluated in our previous study. As some of the most important parameters, these estimations focused on the initial supersaturated concentration of silicic acid and the density of deposited minerals. As a result, the aperture of flow-paths (initial width: 0.1 mm, flow-rate: 5 m/y, initial supersaturated concentration of silicic acid: 0.01, 0.1 and 1.0 mM) was almost clogged within about 200 y by the deposition of silicic acid. The period for the clogging became shorter under the conditions of higher initial supersaturated concentration and lower density of deposited minerals. In other words, the use of cementitious materials for constructing the repository might produce a retardation effect of radionuclide migration by the deposition/clogging processes of the supersaturated silicic acid.

Dependence of the Dynamic Behavior of Supersaturated Silicic Acid on the Surface Area of the Solid Phase

2008 ◽  
Author(s):  
Yuichi Niibori ◽  
Yasunori Kasuga ◽  
Hiroshi Kokubun ◽  
Kazuki Iijima ◽  
Hitoshi Mimura
Keyword(s):  
Surface Area ◽  
Dynamic Behavior ◽  
Silicic Acid ◽  
Solid Phase

Detection of Hepatitis a Virus in Drinking Water by Enzyme -Immunoassay Using Ultracentrifugation for Virus Concentration

1985 ◽  
Vol 17 (10) ◽  
pp. 39-41 ◽  
Author(s):  
A. Schnattinger
Keyword(s):  
Membrane Filtration ◽  
Hepatitis A ◽  
Hepatitis A Virus ◽  
Solid Phase ◽  
Phosphate Buffer Solution ◽  
Enzyme Linked Immunosorbent Assay ◽  
Virus Concentration ◽  
Buffer Solution ◽  
Solution Ph ◽  
Two Stage

Ten litres of tapwater were seeded with 200 µl (8×108 HAV particles) of a commercial (Organon Teknika) suspension of hepatitis A virus. Following WALTER and RÜDIGER (1981), the contaminated tapwater was treated with a two-stage technique for concentration of viruses from solutions with low virus titers. The two-stage technique consists of aluminium hydroxideflocculation (200 mg/l Al2(SO4)3. 18 H2O, pH 5,4-5,6) as first stage, the second stage of a lysis of aluminium hydroxidegel with citric acid/sodium citrate-buffer (pH 4,7; 1 ml/l sample), separation of viruses from the lysate by ultracentrifugation and suspension in 1 ml phosphate buffer solution (pH 7,2). A commercial solid phase enzyme-linked immunosorbent assay (ELISA) was used for the detection of HAV. HAV was detecterl in the 10.000:1 concentrates, but not in the seeded 101 samples. Approximately 4×108 of the inoculated 8×108 HAV particles were found in the 1 ml concentrates. The efficiency of detection is about 50%, the virus concentration 5000-fold. Although the percentage loss of HAV in comparison with concentration by means of membrane filtration is similar, the ultracentrifugation method yields a larger sample/concentrate ratio, so that smaller amounts of HAV can be detected more efficiently because of the smaller end-volume.

Swelling pressure and microstructure of an activated swelling clay with temperature

Clay Minerals ◽  
1998 ◽  
Vol 33 (2) ◽  
pp. 255-267 ◽  
Author(s):  
D. Tessier ◽  
M. Dardaine ◽  
A. Beaumont ◽  
A. M. Jaunet
Keyword(s):  
Room Temperature ◽  
Swelling Pressure ◽  
Radioactive Waste Disposal ◽  
Basic Medium ◽  
Hydraulic Pressure ◽  
Swelling Behaviour ◽  
Transmission Electron ◽  
Ca Ions ◽  
Na Ions ◽  
Marked Drop

AbstractClay from Fourges has been selected by the Commissariat à l'Energie Atomique as a support in radioactive waste disposal studies. This material was activated by adding Na2CO3, then compacted at 60 MPa. Subsequently, its swelling behaviour was monitored at 90°C and 145°C for 330 days and at the end of this period the samples were examined by transmission electron microscopy (TEM). For this, they were embedded in a resin then sectioned with an ultramicrotome for mineralogical and chemical analyses. The initial material is essentially composed of kaolinite and smectite. Addition of Na2CO3 at room temperature induces a replacement of Ca ions by Na ions and the precipitation of finely divided carbonates on the surface of the constituents. At the end of 330 days at 90°C under a hydraulic pressure of 1 MPa, the initial particles combine and the material exerts a swelling pressure of 20 MPa. A complete reorganisation of the clay crystallites is observed without significant dissolution of the solid phases. After the same time at 145°C under a hydraulic pressure of 10 MPa, in a basic medium, the combined conditions are such that a high proportion of the clay is dissolved with formation of amorphous aluminosilicates correlated with a marked drop in the swelling pressure to 5 MPa. This work establishes the advantages of following the macroscopic properties in parallel with the microstructure variations for understanding the changes in the properties of clays.

scholarly journals Improved method for determination of waxes in olive oils: reduction of silica and use of a less hazardous solvent

OCL ◽  
2020 ◽  
Vol 27 ◽  
pp. 20
Author(s):  
Andrea Milani ◽  
Paolo Lucci ◽  
Martina Sedran ◽  
Erica Moret ◽  
Sabrina Moret ◽  
...  
Keyword(s):  
Silicic Acid ◽  
Solid Phase ◽  
Internal Standard ◽  
Solvent Mixture ◽  
Official Method ◽  
Improved Method ◽  
Capillary Gc ◽  
Olive Oils ◽  
Solid Phase Extraction Cartridge

The evaluation of the content of waxes is request both by IOC Trade Standard and by Regulation (EEC) 2568/91 and its further amendments. The official method uses 15 g of silicic acid and elutes several fractions by using huge volumes of dangerous solvent (n-hexane). The developed method uses 1 g of silicic acid with a different particle size and less than 20 mL of solvent mixture, substituting n-hexane with less toxic isooctane. Briefly, after spiking with a suitable internal standard, oil sample is fractionated by SPE (Solid Phase Extraction) cartridge with 1 g of silica, waxes are eluted with 14 mL of isooctane/ethyl ether 99/1 (6 mL discarded and 8 mL collected), then, after elution sample is reconstitute in 200 μL of n-heptane and analysed by capillary GC. Data of “In home” validation, (repeatability, accuracy and recovery) and relative chromatograms are reported in this paper.

Effect of Curing Temperature on Hardened Concrete Properties

2005 ◽  
Vol 1914 (1) ◽  
pp. 97-104 ◽  
Author(s):  
W. Micah Hale ◽  
Thomas D. Bush ◽  
Bruce W. Russell ◽  
Seamus F. Freyne
Keyword(s):  
Fly Ash ◽  
Cementitious Materials ◽  
Curing Temperature ◽  
Supplementary Cementitious Materials ◽  
Cold Weather ◽  
Strength Development ◽  
Hardened Concrete ◽  
Hardened Properties ◽  
Hot Weather ◽  
Materials Used

Often, concrete is not mixed or placed under ideal conditions. Particularly in the winter or the summer months, the temperature of fresh concrete is quite different from that of concrete mixed under laboratory conditions. This paper examines the influence of supplementary cementitious materials on the strength development (and other hardened properties) of concrete subjected to different curing regimens. The supplementary cementitious materials used in the research program were ground granulated blast furnace slag (GGBFS), fly ash, and a combination of both materials. The three curing regimens used were hot weather curing, standard curing, and cold weather curing. Under the conditions tested, the results show that the addition of GGBFS at a relatively low replacement rate can improve the hardened properties for each curing regimen. This improvement was noticeable not only at later ages but also at early ages. Mixtures that contained both materials (GGBFS and fly ash) performed as well as and, in most cases, better than mixtures that contained only portland cement in all curing regimens.

An Experimental Approach on the Effect of Rock Alteration on Sorption Behavior

2006 ◽  
Vol 932 ◽  
Author(s):  
Yuichi Niibori ◽  
Yasunori Kasuga ◽  
Hiroaki Yoshikawa ◽  
Kouichi Tanaka ◽  
Osamu Tochiyama ◽  
...  
Keyword(s):  
Silicic Acid ◽  
Experimental Approach ◽  
Solid Phase ◽  
Sorption Behavior ◽  
Flow Paths ◽  
Geological Disposal ◽  
Long Time ◽  
Degree Of Crystallization ◽  
Rock Alteration ◽  
Alkaline Groundwater

ABSTRACTIn the geological disposal of radioactive wastes, cement used for the repository construction alters the condition of groundwater to highly alkaline of pH about 13. Such alkaline groundwater around the repository would alter the surfaces of the rocks in the flow paths to the amorphous phase. Once the surface is altered, it takes a geological period (so much long time) to restore the surface to its former condition. This study examined the sorption behavior of europium (Eu-152 (tracer), Eu-151 (5×10-5 M, carrier) onto some silica minerals with polymeric silicic acid. Polymeric silicic acid also affects the alteration of the solid surface.The results showed that the kinds of silica minerals strongly affect the sorption behavior in the range of 5<pH<8. The main difference was due to the degree of crystallization of the solid phase, the specific surface area and the concentration of polymeric silicic acid. Since the amorphous silica or polymeric silicic acid takes a loose structure, the isoelectric point is high compared to the crystal ones such as opal-CT and cristobalite, which in turn decreases the sorption. The crystalline silica with polymeric silicic acid remarkably decreased the sorption of europium. This suggested that the surface of solid phase was altered by polymeric silicic acid.

Ca and Na selectivity of the active membrane of rabbit AV nodal cells

1979 ◽  
Vol 236 (1) ◽  
pp. C1-C8 ◽  
Author(s):  
T. Akiyama ◽  
H. A. Fozzard
Keyword(s):  
Outward Current ◽  
Rabbit Heart ◽  
Ionic Channel ◽  
Slow Inward Current ◽  
Constant Field ◽  
Total Removal ◽  
Similar Dependence ◽  
Inward Currents ◽  
Ca Ions ◽  
Na Ions

The atrioventricular (AV) node is thought to have a slow ionic channel. These experiments were designed to measure the relative contributions of Na and Ca ions to inward currents in the AV nodal cells of rabbit heart superfused with Tyrode solution. The effects of tetrodoxin (TTX), Mn2+, and verapamil observed in this study were in agreement with reports by others. The overshoot of AV nodal (N) cells was related to external Ca, with a slope of 12 mV/decade, unchanged by addition of TTX. Similar dependence of overshoot on external Na was seen, with a slope of 20 mV/decade. The slope did not change on addition of TTX. Total removal of either Na or Ca from the solution abolished excitability. Using a constant field equation, we estimated relative permeability (P) of the membrane at the time of maximal overshoot to be PCa/PNa congruent to 60 similar to or approximately 100 and PK/PNa congruent to 1. Relative contributions of these ions to the currents were estimated as ICa congruent to 17%, INa congruent to 33% (inward currents), and IK congruent to 50% (outward current). In conclusion, AV nodal cells have "slow inward-current channels" that are selective for Ca over Na ions.

Polymerization behavior of silicic acid with Fe3+, Al3+, and Ca2+ coexisting ions

2017 ◽  
Vol 85 (2) ◽  
pp. 480-485
Author(s):  
Xingmei Shen ◽  
Jun Ge ◽  
Ping Wang ◽  
Xingrong Wu ◽  
Liaosha Li
Keyword(s):  
Silicic Acid ◽  
Polymerization Behavior ◽  
Coexisting Ions
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