Si Concentration In Solution Research Articles

Evaluating the role of dissolved silica for dolomite formation in evaporitic environments: Insights from prolonged laboratory experiments

The mineral Dolomite CaMg(CO3)2 is a common constituent of sedimentary rocks. Despite centuries of research, the mechanism of its formation remains elusive and debated. Recent studies have shown the presence of silica in solution promote the incorporation of Mg into the carbonate mineral, forming crystal phases that may be precursors to dolomite. The goal of this study was to evaluate with laboratory experiments whether dissolved silica may play a role for dolomite formation in sabkha (i.e., salt flats) environments. Several models for dolomite formation are based on the studies of sabkhas, which are often cited as modern analogue for ancient dolomite-rich sedimentary sequences. We performed long-incubation time (i.e., up to 600 days) laboratory precipitation experiments at 30 °C with solution mimicking the sabkha pore waters (characterized by a salinity of 23 % and Mg: Ca ratio of 15) to which we added different concentrations of Si. Our results revealed a positive correlation (p-value <0.001) between Si concentration in solution and the mol% Mg of the carbonate minerals forming in the experiment. With 2 mM of Si, the bulk precipitate was comprised of 90 % stoichiometric dolomite with possible signs or ordering. Moreover, the rhombohedral morphology of the crystals is analogue to that of natural dolomite previously described from sabkha sediments. Our results suggest that dissolved Si may play an important role for dolomite formation in evaporitic environments.

RELEASE OF SILICON FROM SILICATE MATERIALS AND ITS UPTAKE BY RICE PLANT

&lt;p class="abstrakinggris"&gt;Plants absorb silicon (Si) from soil solution in the form of monosilicic acid, also called orthosilicic acid (H&lt;sub&gt;4&lt;/sub&gt;SiO&lt;sub&gt;4&lt;/sub&gt;). Application of organic and inorganic materials containing readily soluble Si can increase Si supply in the soil and its uptake by plant. The study aimed to evaluate the release of Si from organic and inorganic material sources and its uptake by rice plant. The released phosphorus (P) from those materials was also evaluated. The inorganic materials evaluated included fly ash, steel slag, silica gel and Japanese silica gel (JSG), while the organic materials consisted of rice husk ash (RHA), rice husk burnt (RHB), media of mushroom (MM), cacao shell biochar (cacao SB) and rice straw compost (RSC). The dynamics of Si and P were observed by periodical samplings at 7, 17, 24 and 34 days after transplanting (DAT). Tiller number and plant height were measured at 16, 21 and 36 DAT. The results showed that Si concentration in solution derived from inorganic material was highest for JSG followed by silica gel (1.107 and 0.806 mmol L&lt;sup&gt;-1&lt;/sup&gt;, respectively). The release of Si from organic material was higher for RHB and RHA (0.618 and 0.539 mmol L&lt;sup&gt;-1&lt;/sup&gt;, respectively). Cacao SB, silica gel, JSG and RHB significantly increased plant height at 36 DAT. Meanwhile, Si materials did not significantly affect the tiller number. Of the materials used, steel slag and JSG significantly affected Si uptake by rice plant.&lt;/p&gt;

Formation of siliceous sediments in brandy after diatomite filtration

Brandy is quite a stable spirit but sometimes light sediment appears. This sediment was separated and analysed by IR and SEM-EDX. It was revealed that the sediment is composed mostly of silica and residual organic matter. Silica was present as an amorphous phase and as microparticles. In an attempt to reproduce the formation of the sediment, a diatomite extract was prepared with an ethanol/water mixture (36% vol.) and a calcined diatomite similar to that used in brandy filtration. This extract was added to unfiltered brandy in different amounts. After 1month, the Si concentration decreased in all samples and sediments with similar compositions and features to those found in the unstable brandy appeared. The amounts of sediment obtained were directly related to the decrease in Si concentration in solution. Consequently, it can be concluded that siliceous sediment in brandy originates from Si released during diatomite filtration.

Mineralogical and textural variation of silica minerals in hydrothermal flow-through experiments: Implications for quartz vein formation

We conducted hydrothermal flow-through experiments at 430 °C and 31 MPa to investigate the mechanism of silica precipitation on granite under crustal conditions. Two experiments were performed using different input solutions: a single-component Si solution, and a multi-component solution with minor Al, Na, and K. The degree of supersaturation with respect to quartz, Ω = CSi/CSi,Qtz,eq, where CSi and CSi,Qtz,eq indicate Si concentration in solutions and the solubility of quartz within water, respectively, decreased from 3–3.5 to <1.1 along the flow path. A variety of silica minerals formed during the experiments (opal-A, opal-C, chalcedony, and quartz), and their occurrences and modal abundances changed in response to Ω and the presence of additives in the solution. For near-equilibrium solutions (Ω ∼1.2), silica minerals were deposited on other surfaces in addition to quartz. In the single-component experiment, the dominant silica minerals changed in the order of opal-A → opal-C → quartz with decreasing Si concentration along the flow path. In contrast, in the multi-component experiment, quartz and minor chalcedony formed throughout the entire reaction vessel. This finding indicates that impurities (Na, K, and Al) in the solutions inhibited the precipitation of opal and enhanced the direct nucleation of quartz. The systematic appearance of metastable silica minerals were examined by nucleation processes and macroscopic precipitation kinetics. Our experimental results indicate that different precipitation mechanisms yield contrasting textures, which in turn suggests that vein textures can be used as indicators of solution chemistry within the fracture.

Nitrate-Cancrinite Precipitation on Quartz Sand in Simulated Hanford Tank Solutions

Caustic NaNO3 solutions containing dissolved Al were reacted with quartz sand at 89 degrees C to simulate possible reactions between leaked nuclear waste and primary subsurface minerals at the U.S. Department of Energy's Hanford site in Washington. Nitrate-cancrinite began to precipitate onto the quartz after 2-10 days, cementing the grains together. Estimates of the equilibrium constant for the precipitation reaction differ for solutions with 0.1 or 1.0 m OH- (log Keq = 30.4 +/- 0.8 and 36.2 +/- 0.6, respectively). The difference in solubility may be attributable to more perfect crystallinity (i.e., fewer stacking faults) in the higher-pH cancrinite structure. This is supported by electron micrographs of crystal morphology and measured rates of Na volatilization under an electron beam. Precipitate crystallinity may affect radionuclide mobility, because stacking faults in the cancrinite structure can diminish its zeolitic cation exchange properties. The precipitation rate near the onset of nucleation depends on the total Al and Si concentrations in solution. The evolution of experimental Si concentrations was modeled by considering the dependence of quartz dissolution rate on AI(OH)4- activity, cancrinite precipitation, and the reduction of reactive surface area of quartz due to coverage by cancrinite.

Response of cotton cultivars to aluminum in solutions with varying silicon concentrations

Abstract Cotton (Gossypium hirsutum L.) is extremely sensitive to Al toxicity. Increasing Si concentration in solution has been reported to alleviate AI toxicity. In this investigation the effects of varying Si concentrations (700, 1400, and 2800 μM Si) on reactive Al (defined as Al reactive with aluminon during 10‐s reaction time, without acidification and heating) was studied in solutions containing either 50, 100 or 200 μM Al during 50 d of aging. An increase in Si concentration had negligible effects on the reactive Al in solutions with 50 or 100 μM Al. However, in solutions with 200 μM Al the reactive Al decreased by 6 to 15% with an increase in Si concentration from 0 to 2800 μM. The effects of either 700, 1400 or 2800 μM Si on root growth of Coker 208, Coker 315, DPL 90, McNair 235, Stoneville 506 and Tifcot 56 cotton cultivars were investigated in solutions containing either 0, 10, 20 or 40 μM Al with 500 μM Ca at pH 4.5. In solutions containing no Al, addition of 700 μM Si improved root growth by...

Chemical Corrosion of Cogema Glass R7T7 in High Saline Brines - Part II

The kinetic results of corrosion experiments of glass R7T7 in brine 2 (high Mg and Ca concentrations) and brine 3 (high Na, low Ca concentrations) in this study are similar to those reported for the corrosion in brine 1 (high Mg concentration, no Ca) in [1]. Further support is lent to the idea that corrosion can be described, by a transient process that depends on the Si concentration in solution (prior to arriving at steady state Si concentration) and another one where this dependence vanishes or becomes small (after constant Si concentration is reached). This is analogous to what is known about corrosion of glass R7T7 and of other glasses in deionized water [4].

Goethite and Hematite Formation in the Presence of Clay Minerals and Gibbsite at 25°C

AbstractAfter 8.4 yr at 25 °C under water, ferrihydrite was almost completely converted into a mixture of goethite and hematite. In contrast, aging in the presence of various clay minerals and gibbsite retarded (kaolinite, illite, smectite, gibbsite) or even blocked (soil smectite, allophane) transformation. The conversion rate was inversely related to the final Si concentration in solution. In addition, the presence of clay minerals resulted in higher hematite to goethite ratios, lower mean crystallite dimensions for both oxides, and the incorporation of Al into the goethite and hematite structures. Similar effects have been observed for coexisting goethite and hematite in soils.

Effects of Phosphorus and Acidity on Levels of Silica Extracted from a Palouse Silt Loam

AbstractConcentrations of Si found in soil solutions are affected both by soil pH and by P availability. Consequently, it was hypothesized that the heavy local use of NH4‐based N fertilizers and of P fertilizers could greatly affect the Si chemistry of soils from the Palouse area of northern Idaho. The objectives of this study were to evaluate the effects of P and acidity on concentrations of Si in water extracts from Palouse silt loam (fine‐silty, mixed, mesic, Pachic Ultic Haploxerolls) soils and to correlate observed effects with possible mechanisms responsible for Si solubility, Soil samples were equilibrated with acid and with P for periods of 0.2 to 150 d in 0.02 M CaCl2 solutions. Increased acidity and the presence of P were both found to increase the concentrations of Si in solution above control levels. These data appear to be additive, suggesting that the mechanisms responsible for increasing solution Si levels for the respective treatments are different. It is postulated that acidity increases Si concentrations in solution by directly affecting the solubility of compounds containing Si, and that P oxyanions compete directly with Si compounds for specific sorption sites.

Electrokinetics, Adsorption and Colloid Study of Simulated Nuclear Waste Glasses Leached in Aqueous Solutions

AbstractZeta potentials of SRL-131-29.8% TOS simulated nuclear waste glasses leached in D.I. water, Al, Ca, Mg, and Zn chloride solutions at 90°C were measured as a function of leaching time. For short term leaching, the adsorption of Ca, Mg, Zn and Al reverses the glass surface potential from negative to positive. Colloids were found to be stable in D.I. water and AICl3 solutions after leaching, presumably due to the electrostatic repulsion between the glass surface and similarly charged particles. Colloids were not found in Mg, Zn or Ca chloride solutions after leaching; instead, a relatively thick metasilicate surface layer was formed on glass surfaces leached in these solutions. The concentration of Si in solution is reduced by the formation of these surface layers.