Silicic acid, soluble

Silica fouling is the accumulation of insoluble silica on anion resins. It is caused by improper regeneration which allows the silicate (ionic form) to hydrolyze to soluble silicic acid which in turn polymerizes to form colloidal silicic acid with the beads. Silica fouling occurs in weak-base anion resins when they are regenerated with silica-laden waste caustic from the strongbase anion resin unless intermediate partial dumping is done. 

For analytical purposes silicates may be conveniendy divided into the following two classes (a) those ( soluble silicates) which are decomposed by acids, such as hydrochloric acid, to form silicic acid and the salts (e.g. chlorides) of the metals present and (b) those ( insoluble silicates) which are not decomposed by any acid, except hydrofluoric acid. There are also many silicates which are partially decomposed by acids for analytical purposes these will be included in class (b). 

The setting reaction of dental silicate cement was not understood until 1970. An early opinion, that of Steenbock (quoted by Voelker, 1916a,b), was that setting was due to the formation of calcium and aluminium phosphates. Later, Ray (1934) attributed setting to the gelation of silicic acid, and this became the received opinion (Skinner Phillips, 1960). Wilson Batchelor (1968) disagreed and concluded from a study of the acid solubility that the dental silicate cement matrix could not be composed of silica gel but instead could be a silico-phosphate gel. However, infrared spectroscopy failed to detect the presence of P-O-Si and P-O-P bonds (Wilson Mesley, 1968). 

With chemical treatment, the natural surfactants in crude oil can be activated [1384]. This method has been shown to be effective for highly viscous crude oil from the Orinoco Belt that has been traditionally transported either by heating or diluting. The precursors to the surfactants are preferably the carboxylic acids that occur in the crude oil. The activation occurs by adding an aqueous buffer solution [1382,1383]. The buffer additive is either sodium hydroxide in combination with sodium bicarbonate or sodium silicate. Water-soluble amines also have been found to be suitable [1506]. 

Isolation of toxins. The digestive glands of shellfish were extracted with acetone at room temperature. After removal of the acetone by evaporation, the aqueous suspension was extracted with diethyl ether. The ether soluble residue was successively chromatographed twice over silicic acid columns with following solvents benzene to benzene-methanol (9 1), and diethyl ether to diethyl ether-methanol (1 1). To avoid degradation of dinophysistoxin-3 by contaminant acid, the silicic acid was washed with dilute sodium hydroxide solution and then with water prior to activation at 110 C. Toxic residue obtained in the second eluates was separated into two fractions... 

Beckwith, R.S. Reeve, R. (1963) Studies on soluble silica in soils. I. The sorption of silicic acid by soils and minerals. Aust. J. Soil Res. 

Colorless fuming liquid suffocating odor density 1.52 g/mL freezes at -68.9°C boils at 57.7°C vapor pressure 235 torr at 25°C critical temperature 235°C critical pressure 35.45 atm critical volume 326 cm /mol decomposes in water forming silicic acid and HCl soluble in benzene, toluence, chloroform, and ether. 

Silica and silicates are soluble in aqueous alkali.9,15-17 The silicate anions produced in solution may be regarded as derived from silicic acid [H4Si04 or Si(OH)4], which has a first pK of 9.47 at 0.6 mol L"1 ionic strength ... 

Hydrogel of Silicic Acid. Pour 5 ml of a concentrated solution of soluble glass into a test tube, rapidly pour 3 ml of a 24% hydrochloric acid solution into it, and stir with a glass rod. What is observed Write the equation of the reaction. How can you explain the formation of a gel ... 

Hydrosol of Silicic Acid. Add 1 ml of soluble glass to 6 ml of a 37% hydrochloric acid solution. Why does no gel form in this case Does the acid solution obtained... 

The principle Zr ore, zircon (Zr silicate) is processed by caustic fusion or by direct chlorination of milled coke and zircon mixts. Washing of the Na fusion cake leave an acid soluble hydrated Zr oxide, whereas chlorination yields mixed Si and Zr tetrachlorides which are separated by distillation. Removal of the Hf from the Zr takes place through counter current liq-liq extraction (Ref 33), For this purpose the oxide or the tetrachloride is dissolved in dil hydrochloric acid to which ammonium thiocyanate is added as a complexing agent. The organic extracting phase is methyl isobutylketone... 

The ether extract containing the catalyst and neutral products was fractionally distilled (130°-160°C at 0.01 mm Hg). The soluble catalyst was concentrated in the pot residues. The distillation fractions were then chromatographed through a silicic acid column. Monoesters and cyclic ketones were eluted successively with 5 95 and 10 90 diethyl ether petroleum ether, and more polar material was eluted with 15 85 diethyl ether. -petroleum ether followed by pure diethyl ether. 

Two inorganic water-soluble polymers, both polyclcctrolytcs in their sodium salt forms, have been know ll for some time poly(phosphoric acid) and poly(silicic acid). A more exciting inorganic water-soluble polymer with nonionic characteristics has been reported. This family of phosphazene polymers is prepared by the ring-opening polymerization of a heterocyclic monomer (6) followed by replacement of the chlorine atoms in Ihe resultant polymer. 

When fine powders of vitreous silica, quartz, tridymite, cristobalite, coesite, and stishovite of known particle-size distribution and specific surface area are investigated for their solubility in aqueous suspensions, final concentrations at and below the level of the saturated concentration of molybdate-active silicic acid are established. Experimental evidence indicates that all final concentrations are influenced by surface adsorption of silicic acid. Thus, the true solubility, in the sense of a saturated concentration of silicic acid in dynamic equilibrium with the suspended silica modification, is obscured. Regarding this solubility, the experimental final concentration represents a more or less supersaturated state. Through adsorption, the normally slow dissolution rates of silica decrease further with increasing silicic acid concentrations. Great differences exist between the dissolution rates of the individual samples. 

Figure 1. Solubility (saturation concentration) of oligomeric silicic acid at different pH values. Curve established by Alexander et al. (1) data points by Baumann (2), arrows indicating pH shift during dissolution experiment...

With regard to a solubility equilibrium, the fact that vitreous silica behaves like a precipitate of polymeric silicic acid must be caused by the similarity between polymeric silicic acid and the hydrated surface of vitreous silica. Both forms can release silicic acid by hydrolysis and desorption, and likewise both forms are able to adsorb and condense silicic acid by means of silanol groups randomly distributed on their surfaces. Thus, in order to explain equal final states, the only assumption necessary is that the condensates will not attain the degree of dehydration of the bulk of the vitreous silica. The resulting equilibrium then relates to the two-phase system silicic acid—polymeric precipitate, and strictly speaking, this system is in a supersaturated state with respect to vitreous silica, which can be considered as an aged form of silica gel. 

Polymer structures that hold silanols at the interface. Good examples of hydrolytically stable crosslinked structures are silica and silicate rocks. Although every oxane bond in these structures is hydrolyzable, a silicate rock is quite resistant to water. Each silicon is bonded to four oxygens under equilibrium conditions with a favorable equilibrium constant for bond retention. The probability that all four bonds to silicon can hydrolyze simultaneously to release soluble silicic acid is extremely remote. With sensitive enough analytical techniques it is possible to identify soluble silica as it -leaches from rocks, but an individual rock will survive in water for thousands of years. 

Si(OH)4. When silica, in the form of flint, or fine sand, or powdered rock-crystal is either fused with caustic soda or potash, or heated under pressure with a solution of one or other of the alkalies, an orthosilicate is produced, possessing the formula Si(ONa)4 or Si(OK)4. These silicates are soluble in water, 2nd as they resemble glass in appearance, they are usually named soluble glass. If hydrochloric acid is added to the solution of one of... 

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