As for inorganic inhibitors, sodium silicate, water glass + metal ions, water glass + ammonium salt, salufer, pyrophosphate, calgon and phosphorous acid are mostly used. Each of them has its advantage. Inorganic depressing agent of tungsten ore –phosphite is basically introduced in this part.

 

The inorganic compound – phosphate(H₃PO₃) soluble in water and alcohol. It will be slowly oxidized and turn to phosphoric acid when it is exposed to the air. And when the heating temperature rises to 180℃, it will turn into phosphoric acid and phosphine (toxic and explosive). As a kind of diprotic acid, phosphate has a little more acidic than phosphate acid. Someone pointed out that the inhibitory effect of phosphite is better than that of calcite and fluorite and other phosphate inhibitors.

 

In the research process of phosphorous acid, the researchers found that when using the sodium phosphate as a depressing agent, the inhibitory action of scheelite’s floatability is influenced by the pH value and the quantities. When the dosage of sodium phosphite is more than 20 mg/L, phosphate can inhibit fluorite floating. And when it is more than 80 mg/L, it can inhibit calcite floating. It can achieve maximum effectiveness, separating the most calcic minerals from scheelite when the value of pH is about 10.

 

As an important inorganic phosphate compound, the mechanism of phosphite is similar to pyrophosphate. Phosphite used as inhibitor can be ionized in water, generating anions to form complex with Ca2+ which is on the mineral surface. And then the complex transformed into soluble complexes, thereby inhibiting calcite and fluorite. In fact, when using the phosphate compounds as inhibitors, it is advised to supplemented with sodium silicate to achieve better flotation effect of auxiliary.