Sodium thiomolybdates

Sodium Thiomolybdates.—Two are knowm the normal salt, NajMoS, prepared as dark reddish crystals by the action of hydrogen sulphide upon a solution of sodium molybdate, and the acid salt, NagMogSy, obtained as a dark grey mass by treatment of the normal salt with a deficiency of acid. Oxythiomolybdates are obtained by the action of sodium hydrosulphide upon sodium tri- and para-molybdates. 

The neutral sodium tungstate solution (pH 7.2-7.4) is treated with sodiiun sulfide to convert the molybdate to thiomolybdate and then adjusted to pH 8.2-8.4. Activated carbon is added and mixed for about 30 minutes. The loss of tungsten by coadsorption is less than 0.1%. Specific adsorption of Mo varies between 4.5 and 6.1 mg Mo/g carbon, depending on the carbon quality. A multistage crossflow adsorption is proposed for industrial application, leading to higher specific adsorption in the earlier stages. 

The resin in the chloride form exchanges chloride against tungstate and thiomolybdate. In the case of tungstate the equation is idealized, because in reality isopolytungstates are present Sodium ions as well as the anions silicate, phosphate, and arsenate are not retained and pass the column. The pH is too high for heteropolytungstate formation with these anions. 

So far, two synthetic methods for the preparation of the di- -sulfido cysteinato complex have been reported (1) bubbling H2S gas into the di-/i-oxo complex, [Mo204(cys)2] , in water, (2) reduction of a one-to-one (1 1) mixture of thiomolybdate and molybdate by sodium dithionite, followed by the addition of the ligand. ... 

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