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(How to use both materials together.)
Tungsten Carbide will not dissolve in the Sodium Polytungstate ("SPT") liquid. It will make a two phase slurry with liquid and particles of carbide. The smaller the carbide particles are the better your results will be. Since Tungsten Carbide is a black powder (with a grain size of less then 0.8 m) the suspension of Tungsten Carbide and SPT is dark and opaque.
The polytungstate group is extremely sensitive to reducing agents resulting in a blue color also refered as “tungsten blues”.
If the blue color is only light you can somewhat remedy the situation by adding an oxidation agent. Preferably a small addition of approximate 30% of hydrogen peroxide (H2O2) solution may be required to restore the original color. Use it on small sample first. You may vary the H2O2 percentage up to 30% and experiment with it. Otherwise it is a hopeless situation and you can only discard the SPT solution.
Thus always remove soluble components from your sample by washing respectively rinsing with hot distilled respectively demineralized water. (See how to use SPT).
Following is a list of known reducing agents. Please call Sometu-US if you discover any other agents that cause a bluish discoloration and is not listed below.
Reducing Agents: Iron sulfide (FeS),
Don’t evaporate to dryness ....
One of the strange aspects of the Sodium Polytungstate compound that it dissolves as powder very rapidly when added in batches, it takes very long to redissolve once precipitated.
If the solution evaporates to a hard block add distilled water to the solid and exercise patience. It will take quite some time to redissolve the concrete like precipitation.
To speed up this process you may put the container on a low heat. It is sugguested to use about 150 degrees F. Stir occasionally, it goes into solution fairly rapidly, probably within 20-30 minutes.
Should you encounter difficulties or make observations not mentioned in the brochure, we would appreciate your questions so that we can assist you.
If the solution evaporates to a hard block, just add distilled water and put the container on a low heat. It is sugguested to use about 150 degrees F. Stir occasionally, it goes into solution fairly rapidly, probably within 20-30 minutes.
To achieve a rapid and quantitative separation you can centrifuge the mixture instead of the sink-float procedure, thus easily overcoming viscosity problems.
Only use distilled water! Work only in a dust free environment! Use only glassware or plastic! Add SPT to the water, do not add water to the SPT. Do not use any kind of metal!
Whenever possible use a centrifuge (not a separator funnel) for your work, since it shortens very substantially the separation process also in overcoming problems caused by viscosity in high concentration ranges.
The sample material to be separated should be free of soluble calcium ions. Otherwise, insoluble calcium polytungstate is formed. An example are clay type minerals. If in doubt, wash sample thoroughly in hot water. If experiments show that there is still a reaction, simply use a minor amount of ethylenediamine tetra acetic acid, the common water softening agent. This complex is water soluble.
The solution has come into contact with reducing agents. This, however, does not influence the selected density. If the color is not too dark let the solution stand for a few days under admission of air or add a few droplets of hydrogen peroxide (H2O2). The solution will return to its original color or remain slightly yellow. (See reducing agent information)
These could act as reduction agents. Wash the samples before separation with hot water or decompose the same with a diluted mineral acid.
The samples to be tested should be free of all organic materials which can cause a brownish discoloration. In particular reducing agents must be absent since they cause an irreversible blue discoloration. This can be converted by an oxidation agent like hydrogen peroxide (H2O2) into a brownish-yellow color.
The polytungstate solution can be recovered by washing respective particles with the distilled or demineralized water and then evaporating to the desired density respectively solid polytungstate is added. (See recovery information)
The trace elements can be removed quantitatively from the separated goods by a few washing with water.
Make it to your habit of washing the solid thoroughly several times and the letting it sit in saturated sodium chloride (NaCL) to reconstitute the Na-solidn, then rinse the salt with one bed volume of water.
Rinse samples repeatedly with distilled water, preferably in a funnel with filtration paper.See Recovery of SPT solution.
You can not wash the SPT solution since it would dissolve. See Recovery of SPT solution.
In general the discoloration to yellow is caused by various impurities introduced into the solution by the material to be tested. To remove this yellow color use a little bit of activated carbon. (See reducing agents).
You can use a small addition starting with approximate 3% up to 30% of hydrogen peroxide (H2O2) solution to restore the original color (see reducing agents).
Concerning removal of yellow-brown color from solution by addition of activated charcoal the rule is: The simpler the component, the more difficult it is. The fastest and simplest way to determine is by trail and error, i.e. Make a simple experiment.
(You mentioned something with Carbon isotopes).The extraction does not alter the isotope ratio. If “contamination”is detrimental the sample removed from one solution should be washed before introducing the same into the next solution.
Because any metal might contain compounds that act as reducing agents. Zinc, iron, aluminum and copper are examples of metals which reacts with sodium polytungstate solutions. Use only 100% stainless steel equipment, glass or plastic containers otherwise do not use it.
If calcium carbonate in the form of aragonite (d=2.93) or calcite (d= 2.71) differs sufficiently from the density of the silicate minerals under consideration, a float-sink separation posses no problem. But note that soluble calcium ions will form a precipitate. Otherwise there is no chemical interaction.
Hornblende as such does not cause discoloration. Impurities in the Hornblende can, if they are of a reducing character. Thus samples have to be thoroughly washed before getting into contact with SPT.
Note: Hornblende are very complex minerals, which contains: aluminum, silica, titanium, iron (ferro), magnesia, calcium, potassium (kalium) and sodium (natrium).
As to the precipitate formed with calcium ions this can be avoided by chelating these ions under using ethylenediamine tetra acetic acid used in the household to render tap water soft. Please test first small samples,
To avoid the yellow color after recycling the SPT solution make it to your habit of washing the solid thoroughly several times and the letting it sit in saturated sodium chloride (NaCL) to reconstitute the Na-solid, then rinse the salt with water.
Hydrochloric acid (HCL) can be added slowly in small amounts to the larger precipitate water (ph value = 5). The precipitate will go away within half an hour. Again test first small samples.
The high density solution of sodium polytungstate may turn to a bluish coloration. A small addition approximate 3% of hydrogen peroxide (H2O2) solution may be required to restore the original color.
When the viscosity increases with higher densities, it is recommended to shorten the separation by centrifuging.
One of the strange aspects of the Sodium Polytungstate compound that it dissolves as powder very rapidly when added in batches, it takes very long to redissolve once precipitated. Add distilled water to the solid and exercise patience. It will take quite some time to redissolve the concrete like precipitation, but there is no other way to accelerate.
To speed up this process you may put the container on a low heat. It is sugguested to use about 150 degrees F. Stir occasionally, it goes into solution fairly rapidly, probably within 20-30 minutes.
If crystales appear on top of the beaker the solution is probally over saturated. SPT will actually only crystalize from oversaturated solutions. A work around technique is to work at higher temperatures. The higher the temperature, the more solid SPT will dissolve. You may remove the crystales on top of your beaker and continue to work.
To achieve a rapid and quantitative separation you can centrifuge the mixture instead of the sink float procedure, thus easily overcoming viscosity problems.
It is most important that you use demineralized water, since calcium ions from an insoluble calcium polytungstate precipitate. Also calcium ions diffusing from the glass container into the solution, can cause this, e.g. The solution was stored in a glass container over a long periode of time.
