Shuqin Bai

Silicon enhances growth independent of silica deposition in a low-silica rice mutant, lsi1

To examine whether silica bodies are essential for silicon-enhanced growth of rice seedlings, we investigated the response of rice, Oryza sativa L., to silicon treatment. Silicic acid treatment markedly enhanced the SPAD (soil plant analytical development) values of leaf blades and the growth and development of leaves and lateral roots in cvs. Hinohikari and Oochikara, and a low-silicon mutant, lsi1. Combination of ethanol–benzene displacement and staining with crystal violet lactone enabled more detailed histochemical analysis to visualize silica bodies in the epidermis under bright-field microscopy. Supply of silicon induced the development of motor cells and silica bodies in epidermal cells in Hinohikari and Oochikara but not or marginal in lsi1. X-ray analytical microscopy detected silicon specifically in the leaf sheath, the outermost part of the stem, and the leaf blade midrib, suggesting that silicon is distributed to tissues involved in maintaining rigidity of the plant to prevent lodging, rather than being passively deposited in growing tissues. Silicon supplied at high dose accumulated in all rice seedlings and enhanced growth and SPAD values with or without silica body formation. Silicon accumulated in the cell wall may play an important physiological role different from that played by the silica deposited in the motor cell and silica bodies.

Acceleration effect of sulfate ion on the dissolution of amorphous silica

The dissolution rate of amorphous silica is enhanced by sulfate ions. The zeta potential for silica particles in Na(2)SO(4) solution was lower than that in NaCl solution with the same ionic strength. These facts indicate that the specific adsorption of sulfate ions occurred by overcoming repulsion between negative charges of the SO(4)(2-) ion and SiO(-) on the surface of silica. The dissolution rate of amorphous silica may be accelerated by the specific adsorption of SO(4)(2-) ions because of a decrease in the strength of the [triple bond]Si-O-Si[triple bond] bond in amorphous silica due to donation of electron density from the adsorbed SO(4)(2-) ions.

Formation conditions and stability of a toxic tridecameric Al polymer under a soil environment

It is important to study the formation conditions and the stability of the tridecameric Al polymer (Keggin-type Al(13) polycation, [AlO(4)Al(12)(OH)(24)(H(2)O)(12)](7+), known as Al(13)) due to its strong toxicity to living organisms of a soil environment. In order to examine the pH range where toxic Al(13) can exist in aqueous solution, (27)Al NMR spectra for sample solutions containing Al(3+) ions with various pH (pH 3.5-6.1) were measured. The results show that the peak due to Al(13) (peak due to 4-coordinated Al around 63 ppm) appeared at pH 3.6-5.7 and the peak intensity was relatively high at pH 4.1-4.8, suggesting that Al(13) can be formed at pH 3.6-5.7, while it can exist dominantly at pH 4.1-4.8. It was also found that Al(13) can stably adsorb onto a chelate resin, Chelex 100, by weak electrostatic interaction. The Chelex 100, with iminodiacetate groups, served as a model compound for surfaces of microbes covered with carboxyl groups and for surfaces of soil particles covered with humic substances having many carboxyl groups. Additionally, decomposition of Al(13) did not occur even after adsorption, and its pH stability range was wide compared to that in aqueous solution.

Silica deposition induced by isolated aluminum ions bound on chelate resin as a model compound of the surface of microbes

To elucidate the mechanism of silica biodeposition in hot spring water, which is induced by Al(3+) ions bound to the surface of microbes, a chelate resin (Chelex 100) was used as a model compound of the surface of microbes. No silicic acid was adsorbed on the Na type Chelex 100, whereas silicic acids were significantly adsorbed to the Al type Chelex 100. In the Al type Chelex 100, the Al(3+) ions were present as 1:1 tridentate complex with iminodiacetate (IDA) group. After adsorption of silicic acid to Al type Chelex 100, a IDA-Al-O-Si-(OH)(3) site formed. The site acted as a template for the successive adsorption of silicic acids to form silica sheets around Al type Chelex 100 particles. In conclusion, Al(3+) ions bound to the surface of microbes play a key role as a trigger for the biodeposition of silica in hot spring water.

Formation of a silicato complex of zinc in aqueous solution and its accelerating effect on the formation of silica scales in cooling water systems

This study elucidates the effect of zinc (Zn), which is an anticorrosive water additive, on the formation of silica scales from cooling water. In these experiments, the silica scales were analyzed by EPMA, and the results indicate that Zn is sorbed into the silica scales during formation. Measurements of the solubility of Zn(OH)(2) at various concentrations of silicic acid demonstrate that Zn is present as a silicato complex of Zn (SCZ) in cooling water. From adsorption experiments of the SCZ on silica and alumina, which are major components of the silica scales, it can be concluded that the SCZ accelerates the formation of silica scales from cooling water.

Investigation of phosphate removal from aqueous solution by both coal gangues

Equilibrium studies were carried out for the adsorption of phosphate onto newly discharged coal gangue and spontaneous combustion coal gangue, which are industrial solid residues. The experimental data were fitted to the two-parameter equations of Freundlich, Langmuir, Temkin, and Dubinin-Radushkevich and the three-parameter equations of the Redlich-Peterson, Sips and Toth isotherms by non-linear method. All three-parameter isotherm equations have a higher correlation coefficient than the two-parameter isotherm equations. For new discharged coal gangue, the maximum phosphate adsorption capacity is over 2.504 mg/g (as P), and the best two-parameter isotherm is Freundlich, which indicated multilayer adsorption takes place on the surface. For spontaneous combustion coal gangue, the maximum phosphate adsorption capacity is 7.079 mg/g (as P), two times larger than new discharged coal gangue, and the best two-parameter isotherm is Langmuir, suggesting that the adsorption process occurs on a homogenous surface by monolayer adsorption. The three-parameter isotherm model of Redlich-Peterson shows the best fitting in both cases, but parameter g is 0.6138 in new discharged coal gangue (the parameter g is nearly 1, which means that the equilibrium isotherm behaves as the Langmuir, not as the Freundlich isotherm), g approaches to unity in spontaneous combustion coal gangue, suggesting that the two kinds of coal gangues have different adsorption properties.

A study on the interaction between ferric ion and silicic acid in hydrosphere： Si-containing ferruginous deposits formed in neutral hot spring waters

Five ferruginous deposit samples formed from neutral hot springs were analyzed to determine whether they consisted of a mixture of silica, hydrous iron oxide or iron silicate by differential thermal analysis (DTA), infrared (IR) spectroscopy, powder X-ray diffraction (XRD), and 57Fe Mössbauer spectroscopy. The Si/Fe atomic ratios of the deposits ranged from 0.25 to 0.45, and were smaller than those of hisingerite (1–2), but apparently close to those of siliceous ferrihydrite (0.25–0.5). Si was confirmed to be present as monomeric or oligomeric silicate from the Si-O stretching vibration frequencies on the IR spectra. Judging from the results of DTA, which minerals starting to produce after heating, and a relationship between Si-O stretching vibration frequency and Si/Fe atomic ratio proposed by Henmi et al. (1981), all the deposits in this study were concluded to be mixtures of various siliceous ferrihydrites with low and high Si/Fe atomic ratios. Moreover, by comparing the chemical properties of hot spring waters, the formation conditions of siliceous ferrihydrite were also discussed.

Distribution and Status of Silicon in Rice Plant

The content,distribution and existing form of silicon in tissues of rice plant were analyzed by UV-Vis spectrophotometer,X-ray analytical microscope and scanning electron microscope(SEM),and the chemical properties of silicic acid were investigated,which will provide a scientific basis for comprehensive utilization of silicon in rice plant.The results showed that silicic acid in soil was absorbed by rice plant in the form of monosilicic acid and transferred to different organs.The contents of the silicic acid varied with the growing periods,reaching 912 mg/L(expressed as SiO2) in maturity.The comparison of silicic acid concentrations in xylem sap and in soil solution showed that the silicic acid was selectively absorbed and concentrated during the transportation from soil to xylem,and the concentration ratio of silicic acid was considerably high being 85 fold at maximum.X-ray characteristic images of silicon showed that silicon existed widely in each tissue and its content was higher in the rigid parts.SEM image suggested that the silicon colloid deposited in different organs had specific shapes and was insoluble in strong acid.The content of silicic acid in each tissue was determined after decomposition of organic material with mixed acids,indicating that the highest content of silicic acid of 13.3% was observed in rice hull.As a result,the rice hull is one of the most potential nature resources to produce elemental silicon and silicon carbide materials.

Synthesis of mesoporous silica from geothermal water recycling system

To prevent the silica scale formation in the geothermal water recycling process, the silicic acid perfectly removed from geothermal water as calcium silicate by calcium nitrate. Ordered mesoporous silica was synthesized at strong acidic condition by using low cost calcium silicate as silicon source, which was separated from geothermal water recycling process.