Metavanadates Basic

Catalyst. A pure precipitated Si02 sample (grade Si 4-5P, AKZO product BET S.A., 395 m g" Pore Volume, 1.14 cm -g" ) has been used "as received", while 4% MoOj/SiOj (BET S.A., 187 m g-l) and 5% V205/Si02 (BET S.A., 231 m2.g-i) catalysts have been prepared by incipient wetness impregnation of the "Si4-5P" Si02 with a basic solution (pH=11) of ammonium heptamolybdate and ammonium metavanadate respectively (23). The impregnated samples were dried at 90°C for 24h and then calcined at 6C)0°C for 16h. 

Lead Pyrovanadate, PbaVa07.—This salt is of interest in that it is the artificial form of descloizite, one of the important natural ores of vanadium. It is obtained by boiling mixed solutions of lead nitrate and ammonium metavanadate in the presence of acetic acid.11 A pale yellow basic pyrovanadate of lead, 2PbaVa07.PbO, is obtained by... 

Several vanadates are known the compositions of whieh are intermediate between that of the pyrovanadates, 2R 2O.V2Os, and that of the metavanadates, R 2O.V205. They can be looked upon as basic metavanadates. The following have been described —... 

Basic Lithium Metavanadate, 3Li20.2Va05.15H20 or Lia0.4LiV03. 15H20, is obtained by crystallising lithium ortho vanadate from dilute nitric acid.3... 

Basic Potassium Metavanadate, 5K20.4V20S.7H20 or K20. KV03. 7H20, separates in white crystals when a solution of potassium pyrovanadate, K4V207, is acidified with acetic acid and concentrated.4... 

Basic Thallium Metavanadates, 3T120.2V205 or T120.4T1V03, is obtained as a sparingly soluble, yellow powder by the action of thallium sulphate on the corresponding sodium compound.6... 

Basic Silver Metavanadate, SAg20.2V205 or Ag20.4AgV03, is prepared by the action of silver nitrate on the corresponding sodium salt. It is a dark yellow compound, almost insoluble in water.8... 

Basic Lead Metavanadate, 8Pb0.2V206.2H20 or Pb0.2Pb(V03)a. 2H20, is obtained as a yellow powder by the action of lead nitrate on an acid manganese vanadate.9... 

Basic Strontium Metavanadate, 8Sr0.2V205.2Ha0 or Sr0.2Sr(V03)2. 2H20, has also been prepared.10... 

Beryllium Metavanadate, Be(V03)2.4H20.—Addition of solutions of beryllium salts to alkali vanadates gives rise to basic vanadates of indefinite composition. The pure salt is obtained by boiling beryllium hydroxide and vanadium pentoxide in water in the required proportions. The solution is filtered, concentrated to a syrup and poured into alcohol, whereupon isometric cubes, modified by an octahedron, are obtained. The larger crystals polarise light. Density, 2-273. One gram dissolves in a litre of water at 25° C.s... 

Lead Metavanadate, Pb(VOg)2.—Acid solutions of vanadates on being treated with lead salts give rise to yellow basic vanadates the composition of which varies with the conditions. The precipitation of normal lead vanadate is, therefore, difficult. It has been accomplished by the addition of lead acetate to ammonium metavanadate solution in the presence of acetic acid.2 The lead precipitates contain all the vanadic acid originally present in solution, and precipitation of vanadates with lead salts has, therefore, been employed for the quantitative estimation of vanadium.3 The mineral deschenite consists chiefly of lead metavanadate a portion of the lead is, however, frequently replaced by zinc.4... 

Magnesium Metavanadate, Mg(V03)2.6H20, is obtained as transparent crystals by boiling an excess of basic magnesium carbonate with vanadium pentoxide and concentrating the filtered solution in a vacuum.7 It is easily soluble in water. 

A marked improvement in separation is less frequently achieved with other complex-forming salts like sodium arsenite, tungstate, molybdate or metavanadate or basic lead acetate. Boric acid or borax are more often employed as impregnation agents for complex-formation. Mobeis [317 a] and Schorn [615 a] have undertaken good compilations of the results so far obtained in this field. 

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