Separation of W and Mo from their peroxoacids solutions by thermal decomposition

A separation method for W and Mo from peroxoacids solution by thermal decomposition wasstudied. Thermal decomposition of peroxotungstic acid and peroxomolybdic acid was investigated respectively. The results confirmed that peroxomolybdic acid showed a preferable stability compared with peroxotungstic acid. This thermal stability difference was the basic principle of theseparationof W and Mo. Experiments were performed to study the effects of temperature, stirring speed, free acid concentration and Mo concentration on the separation efficiency. The results indicated that peroxotungstic acid decomposed into tungstic acid（H2WO4） and precipitated selectively,while Mo was rejected in aqueous solution,realizing good separation of W and Mo. The separation factorof W and Moreached 112 under the studied conditions, which indicated that this method has potential for use in separating W and Mo.

studies on the Mechanism of Producing Tungstic Acid by Complex-Homogeneous Precipitation Method

A new method of producing tungstic acid with a yield over 98% at room temperature and low acidity is advanced and referred to as Complcx -Homogeneous Precipitation Method. If combined with the treatment of activated charcoal in recovering the remnant tungsten left in the filter liquor, a perfect closed technological process can be obtained. The key to this method is to prevent the formation of pseudo-metatungstatc during scdium rungstate being acidified directly with the aid of the complexing-protecting agent H2O2, The perexo-mtermediate, which was prepated and identified as dipcroxytetratnngstate by IR and Raman analysis by comparison with diperorytetramolybdate, can be decomposed by SO2 tapidly and quantitatively. The tungstic acid precipitate can be filtered and washed easily. The related mechanisin is studied.

Organic solvent-and phase transfer catalyst-free oxidation of cyclohexanol to cyclohexanone with dilute H_2O_2

The oxidation of cyclohexanol to cyclohexanone with 30% aqueous hydrogen peroxide by using peroxotung-state complexes formed in situ from sodium tungstate di-hydrate and various bidentate organic ligands as the catalysts, without organic solvents, halide and phase transfer catalyst has been carried out. The influence of 13 ligands on the oxidation is investigated. The maximum yield of cyclohexanone is obtained when using 1,10-phenanthroline (96%) and oxalic acid (95%) as the ligand. Very high yields (around 90%) have also been obtained for the instances of using salicylic acid, 3,5-dibromosalicylic acid, and 8-hydro- xylquino-line as ligands. A research to improve the reaction condition using cheap oxalic acid as the ligand indicates that the optimum condition is that the reaction mixture with a molar ratio of cycohexanol:tungstate dihydrate:oxalic acid: 30% H2O2=100:2:2:120 was stirred at 85-90℃ for 12 h.

The Preparation and Crystal Structure of Ammonium Oxalatooxodiperoxotungstate(NH_4)_2[WO(O_2)_2(C_2O_2)]

In H2O2 solution of different concentrations or various pH, Mo can form various kinds of peroxodydates with different polymeric states and structures of most of them have been determined.They have also been successfully used as oxidation cata-