Silica residual

Another example is the determination of pure silica in an impure ignited silica residue. The latter is treated in a platinum crucible with a mixture of sulphuric and hydrofluoric acids the silica is converted into the volatile silicon tetrafluoride ... 

Hard crystalline scale and deposition also may result from the interaction of silica, residual hardness, and inorganic coagulants carried over into the treated water. Also, pre-boiler system damage by erosion may occur. 

Insoluble silica residues are removed by filtration. The solution now contains beryllium, iron, yttrium, and the rare earths. The solution is treated with oxalic acid to precipitate yttrium and the rare earths. The precipitate is calcined at 800°C to form rare earth oxides. The oxide mixture is dissolved in an acid from which yttrium and the rare earths are separated by the ion-exchange as above. Caustic fusion may be carried out instead of acid digestion to open the ore. Under this condition sihca converts to sodium sihcate and is leached with water. The insoluble residue containing rare earths and yttrium is dissolved in an acid. The acid solution is fed to an ion exchange system for separating thuhum from other rare earths. 

For samples that show significant losses of analyte due to the retention of metals in the silica residues, the sample is first digested thoroughly with... 

The sample was mineralized at 450°C for 8 hours and a 5-g sample was weighed into a platinum dish. Then 15 mL of HNO3 and 10 mL of HCIO4 were added and the sample was leached for 24 hours at room temperature, followed by heating to dryness. The sample was taken up in 25 mL of dilute HC1 and digested on a water bath for an hour. The silica residue was filtered olf and washed with 1% hot HC1 and diluted to 100 mL. 

Pollucite is ground to 120 mesh as described in procedure B above. One hundred grams of the screened material is mixed with 400 ml. of concentrated hydrochloric acid (12 M) in a 1-1. round-bottomed flask, which is connected to a reflux condenser, and refluxed gently for 30 hours. The resulting solution is filtered with suction, using a large Buchner funnel, and the silica residue is washed with about 150 ml. of water. 

Si02 catalyst. Since the surface area of the VPO without PSA is also about 20-30 m /g, the results suggest that the VPO and the PSA are tightly embedded in the periphery of the microsphere. The specific surface area of the silica residue (300-500 m /g) shows how extensively the silica has coalesced from the original 1000-1200 m /g of the PSA dispersion used for the fabrication of the catalyst. 

Under certain conditions, there are definite advantages in using hydrochloric, nitric, or other acids to carry out a dissolution step. In their evaluation of proposed processes for the recovery of alumina, Peters ei al. (P8) cited earlier experimental work which showed that both hydrochloric and sulfuric acid are equally good in extracting alumina from calcined clay (TIO). In the separation of the leach liquor from the silica residue by filtration, the chloride solution rapidly separated, while the sulfate solution did not separate easily. In addition to ease of filtration, the hydrochloric acid leach also made the later removal of iron easier. The insolubility of titanium dioxide in hydrochloric acid also eliminated another separation problem. Under this particular situation, hydrochloric acid was the natural choice. As in most large leaching operations, the acid would be recovered and recycled. 

Identification Talc is added to a melt of anhydrous sodium carbonate and anhydrous potassium carbonate and heated until fused. Hot water and hydrochloric acid are then added to the cooled mixture, and heated to dryness. The remaining solid is boiled in water, and the insoluble silica residue is filtered off. Ammonium chloride and ammonium hydroxide are dissolved in the filtrate. The solution is filtered if necessary and dibasic sodium phosphate TS is added to the filtrate. A white crystalline precipitate of magnesium ammonium phosphate separates. 

Adding ammonium molybdate solution to the silica residue, when a blue colour develops. 

Dissolve the white residue in -30 ml of 4 N HCl, transfer to a 250-ml beaker and make up with alternate 4 N HCl and water washings to about 100 ml to a final acidity of 2 N. Stir until only an insoluble silica residue remains. Add 5 ml of FeClg solution and 10 ml of NHgOH HCl solution followed by a few drops of cresol-red indicator. Adjust the pH of the solution to 1 (with a pH meter until the operator can correctly do it visually) with 2 N NH OH added dropwise from a burette with constant stirring. It is essential that no phosphate precipitate forms, as this may reduce recoveries. Allow the solution to stand for 1 hr to ensure reduction of Pu(VI) to Pu(III). 

The TGA and DTA curves of the polymer in oxygen (Fig. 1) and in nitrogen (Fig. 2) show that the polymer was initially more stable in a nitrogen atmosphere. In an oxygen atmosphere, the DTA curve showed two exothermic peaks at 456°C and 571°C, which corresponded to weight losses of 30% and 84% (maximum), respectively. A silica residue was observed in the Pt reaction pan. 

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