Meta oxides precipitation

Alkali Meta.IPhospha.tes, A significant proportion of the phosphoric acid consumed in the manufacture of industrial, food, and pharmaceutical phosphates in the United States is used for the production of sodium salts. Alkali metal orthophosphates generally exhibit congment solubility and are therefore usually manufactured by either crystallisation from solution or drying of the entire reaction mass. Alkaline-earth and other phosphate salts of polyvalent cations typically exhibit incongment solubility and are prepared either by precipitation from solution having a metal oxide/P20 ratio considerably lower than that of the product, or by drying a solution or slurry with the proper metal oxide/P20 ratio. 

Iron Vanadate is, metallurgically, the most important vanadate. Precipitation of a solution of a vanadate with ferrous sulphate gives rise to a precipitate of indefinite composition, ortlio-, pyro-, meta-, and perhaps a poly-vanadate being present, as well as ferric or ferrous oxide. Reduction of the vanadate to a vanadyl salt may also ensue. The precipitate is usually colloidal and carries down with it some sodium vanadate. The dried powder may be either green, yellow, brown, or red the more nearly the precipitate approximates to a red colour the lower is its vanadium content. An iron vanadate has also been prepared by electrolysis of a solution of sodium vanadate between iron poles.1... 

Peracids such as m-chloroperbenzoic acid (MCPBA) clearly illustrate the redox nature of oxidative addition. In this reaction the olefin is oxidized and the MCPBA is reduced to meta-chlorobenzoic acid, which precipitates slowly from solution. 

Actually, during the reactions, the meta-titanic acid H2Ti03 is precipitated first, which adsorbs considerably large amounts of water and soluble impurities such as ammonium sulfate, ammonium chloride etc, and also contains some insoluble impurity particles such as oxides of iron, strontium, and calcium etc. Therefore, it is essential to fully wash the precipitate to obtain a product of high purity. The insoluble and part of the soluble impurities can be removed by multiple washings ammonium chloride and ammonium sulfate are decomposed and released as the precipitate is later heated to 300°C and 700°C, respectively, during the calcination. 

Synthesis of WO3 /ZrOz samples was performed by co-precipitation method. To solution of ZrOCIz SHaO (30 g in 300 ml of water) 2.60 ml of aqueous meta-tungstate solution (containing 800 mg W in 1 ml) was added. This proportion of reagents corresponds to an atom ratio Zr W = 8.25 1 and mass content of WO3 in oxide material (ZrOa-tWOs) of 18,6%. The mixed solution was heated to boiling and then solution of 5.6 g of urea in 10 ml of water was added. The reaction solution was boiled under reflux 6 h. Then 11 ml of 12 M ammonia was added to the solution at room temperature (pH 9.2 - 9.6), precipitate was filtered off and washed with water up to disappearance of chloride in water. The product was dried first in stream of hot air and then for 24 h in drying box at 100 C. The dried product was then calcined for 2 h at 800°C. Surface area of W03/Zr02 sample after 800 C was 53 m /g. 

Stannic hydroxide can be prepared from the chloride by precipitation by a base or it may be formed by oxidation of the metal in presence of water, when a hydrated oxide results. The former compound is called a-stannic acid, the latter / -, or meta stannic acid. 

Reactions of Colloidal Iron Oxide. — Colloidal iron oxides obtained from the acetate are turbid in reflected light and clear in transmitted. Sulfuric acid or its salts coagulate the hydrosol immediately, and the precipitate is not soluble in concentrated acid in contradistinction to the precipitate from Graham s solutions. When the hydrosol is poured into concentrated acid a precipitate is formed that is again dissolved by water. There exist several analogies between the hydrosol of meta-stannic acid and those of these ferric acetate hydrosols this accounts for the name, inetairon oxide. The hydrosol deserves more elaborate investigation the apparent isomerism of the two modifications is probably due to the difference in the size of the particles. 

Graham s iron oxide differs from the meta variety in that the former is more stable and its precipitate is more soluble in acids. Colloidal iron oxide on the market has properties that lie between these two extremes. It is precipitated by moderately concentrated HCl but the solid gradually goes into solution again to form a chloride. This colloid therefore bears the same relation to Graham s and raetairon oxide that colloidal stannic oxide prepared by the author s method bears to the ct and p varieties. 

Phosphane quickly reduces AU2CU to Au but excess PH3 precipitates black AU3P, stable in warm H2O, and leaves ortho- and meta-phosphates in solution. Drying leads to oxidation. Excess AU2CU, however, yields some Au. A small... 

Tin(ll) oxide and oxalate are soluble in acids. Freshly precipitated ortho-tin(IV) hydroxide is soluble or peptized in many acids, even giving [Sn(OH) (H20)6.n] " in HCIO4. Tin dioxide and meta-tin(lV) oxide/hydroxide are insoluble in most acids except concentrated H2SO4. 

Meta-Sn salts with alkalis precipitate meta-Sn02-aq less acidic than the ortho form not readily soluble in NaOH insoluble in NH3 and COs l soluble in not-too-concentrated KOH excess KOH precipitates potassium meta-stamiate(TV), soluble in water. Tartrate prevents the precipitation of Sn hydrous oxide by OH" and C03 similarly (ortho) SnCU gives no precipitate, but the action of meta-Sn" chlorides is unaffected—see 14.4.3 Reduced halogens below about some of these. 

Tin(II) sulfide is oxidized by HNO3 to meta-tin(lV) hydrous oxide. Other Sn salts and SnO, as well as freshly precipitated (ortho) SnO(OH)2-aq, when heated with HNO3 likewise yield the much less soluble Sn02 aq. Nitrous acid gives similar results. 

Different methods of preparation were also envisaged to avoid from using the complex sulfidation of oxides into sulfides that sometimes do not allow a perfect activation of sulfide catalysts. For example, Seiver and Chianelli [112] used low-temperature precipitation method for the preparation of group IVB, VB, and VIB binary sulfides. This low-temperature meta-thetical reaction allows controlling particle size and composition and occurs as follows ... 

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