Sodium tungstate solution

The sodium tungstate solution is filtered from the resulting slurry. Similarly, in the alkaH roasting process, the concentrate, either scheeHte or wolframite, is heated with sodium carbonate in a rotary kiln at 800°C and then leached using hot water to remove the sodium tungstate. Wolframite ores are also decomposed by reaction with a sodium hydroxide solution at 100°C. 

Refer the readings to a calibration curve prepared from a solution containing spectrographically pure iron to which suitable amounts of standard sodium tungstate solution have been added. 

Estimation of Absorption Effects in Sodium Tungstate Solutions... 

Sodium tungstate solutions have provided data for the testing of Equation 7-6. These data, obtained in the authors laboratory, show that absorption effects can be calculated for a series of solutions in which the calculated critical thickness (Equation 6-8) decreases from 0.4 cm for water, the solvent, to only 0.1 cm for the most concentrated solution tested. In order not to confuse the issue here, the details of the cor-... 

The constancy of the quotient in the last line of Table 7-2 is greatly improved over that in the line above the last, proving that Equation 7-5 holds. So far as we know, this is the first case in which the absorption effects for a series of solutions have been obtained so precisely. Examples of this kind place on a firmer basis the calculation of semiquantitative analytical results from measured intensities when the composition of the matrix (all of S but E, the element sought) in a sample is approximately known. For example, tungsten contents could be estimated from measurements of L7I intensity for sodium tungstate solutions even when other salts are present in the absence of such salts, tungsten contents... 

Recent results from the authors laboratory69 on the x-ray emission spectrography of tungsten or molybdenum in solution illustrate some of the points made in Section 7.13. The also show the usefulness of internal standards (7.12). Finally, the work on tungsten is closely related to the experiments on the absorption effect in sodium tungstate solutions, the results of which are summarized in Table 7-2. 

Sodium tungstate solutions, estimation of absorption effects in, 168-170 Soft x-rays, 11... 

If tungsten is recovered from the wolframite group mineral, the wolframite concentrate is boiled or pressure-digested with 50% caustic soda solution. Alternatively, they may be fused or sintered with caustic soda, caustic potash or sodium carbonate and the fused mass then leached with water. The solution is filtered to separate sodium tungstate solution. The fdtrate is subjected to various treatments to remove molybdenum, phosphorus, and arsenic impurities. The filtrate at this point is essentially a solution of sodium tungstate and is treated in the same way as that obtained from the scheehte concentrate discussed above. 

Thiosalts and Sulphides of Molybdenum and Tungsten. Pour 2-3 ml of an ammonium molybdate solution into one test tube and 2-3 ml of a sodium tungstate solution into another one. Add 2-3 drops of a 25 % ammonia solution to each solution and pass a stream of hydrogen sulphide through them from a Kipp gas generator. What compounds form Acidify the solutions with a 10% hydrochloric... 

Molybdenum and Tungsten Peroxide Compounds. Pour ammonium molybdate and sodium tungstate solutions into separate test tubes, acidify them with sulphuric acid, and add several drops of a 1 % hydrogen peroxide solution to each tube. How does the colour of the solutions change Write the equations of the reactions. 

Amine salts have been used for more than 25 years in the manufacture of pure ammonium paratungstate from sodium tungstate solutions obtained from the leaching of tungsten ores with alkali.211 Such solutions are produced by the leaching of scheelite with sodium carbonate solution at 190 to 225 °C... 

In a typical solvent-extraction process,211 the pH value of the sodium tungstate solution is adjusted to about 2.5 with sulfuric acid, and the tungsten is extracted into a 7% solution of the tertiary amine Alamine 336 plus 7% isodecanol in kerosene in two countercurrent stages at a temperature of 50 °C. Distribution data are consistent with the extraction of species such as H2W1204o6 and Wi2O408- in reactions of the type208-212... 

Tungsten Sodium tungstate solution at pH 2 High-molecular weight amine extractant in kerosene mixer-settler system... 

Treatment of a sodium tungstate solution with hydrochloric acid at boiling-point (as described above) until only faintly alkaline to litmus. ... 

Electrolysis of sodium tungstate solution in a cell in w hich the electrodes are separated by a diaphragm (see above). 

Sodium -nonatungstosilicate (5.8 g, 2 mmol, from the procedure in Section B) and sodium tungstate solution (1.42g, 4mmol in 40 mL of water) are placed... 

Derivation By adding a sodium tungstate solution to a solution of a cobalt salt. 

Here is an example A sodium tungstate solution acidified to pH 2.5 behaves differently during further processing via solvent extraction in comparison to the same solution after some days. 

Addition of sodium tungstate solution to 1 molar nitric acid until pH 1 is reached. 

The preparation of insoluble tungstates (divalent or trivalent metal ions with the exception of Mg) is carried out by reacting aqueous sodium tungstate solutions with the corresponding soluble metal salt. 

Addition of calcium chloride solution to sodium tungstate solution. This reaction was used on a large scale in former times as purification step (precipitation of artificial scheelite). 

PP Solutions of lithiiun tungstate are even more dense than sodium tungstate solutions, although lithium is the least dense alkali metal maximum density is about... 

PR Sodium tungstate solution is saturated with H2Se, whereby selenotungstate ions [WSe4] are formed which are subsequently decomposed to WSes by acidification. PP Black, amorphous powder. 

Impure sodium tungstate solution containing gangue and/or precipitates... 

These includes the following main steps separation of the undissolved digestion residue by filtration, and separation of the impurities dissolved in the sodium tungstate solution. Sometimes, the first step can be combined with the first precipitation step (silica precipitation). 

Silica Precipitation [5.1,5.31,5.32]. Silicate ions may be precipitated by addition of aluminum sulfate or magnesiiun sulfate solution to the sodium tungstate solution. Also, mixtures of both reagents are used. The addition is made to the slightly alkaline or neutral solution. The respective chemical reactions are complex but can be described in a simplified matmer by the following equations ... 

Molybdenum Separation [5.1,5.31,5.33,5.35]. If sodium sulfide is added to the neutral or slightly alkaline sodium tungstate solution, the molybdate ion is converted to... 

A continuous operation using a multistage stirred-tank reactor system and hydrogen sulfide recycling by absorption in the sodium tungstate solution substantially reduces the amount of sulfuric acid. 

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. 

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