Tungsten and Molybdenum Seperation in High Phosphorus Mixing Solution

Tungsten is an indispensable strategic metal in the defense field and plays an important role in the national military strategic reserve. In view of the current status of resources, the replacement of black tungsten by white tungsten is an inevitable trend. However, China's white tungsten resource endowment is poor, accompanied by more impurities such as molybdenum and phosphorus. 

The group VIB in the periodic table of tungsten and molybdenum is very similar due to the influence of the lanthanide shrinkage. The separation of molybdenum has become a key problem to be solved in tungsten metallurgy.

At present, the industrial tungsten-molybdenum separation method is based on the characteristics of tungsten oxophilic and molybdenum sulphur. First, the alkaline sodium tungstate solution is adjusted to neutral or weakly alkaline with acid, and then S2- or HS- is added to make the solution. The molybdate ion is preferentially converted to the thiomolybdate ion, and then the tungsten-molybdenum separation is achieved by means of precipitation, extraction, ion exchange adsorption, etc. by using the significant difference in the properties of the thiomolybdate and the tungstate.

However, in many cases, such as the secondary resource recovery of tungsten, in the leaching process of decomposing scheelite, phosphorus is inevitably introduced into the leachate to obtain a phosphorus-molybdenum mixed solution containing phosphorus. The phosphorus content of these feed liquids is generally greater than 0.1 mol/L, and the method for separating tungsten molybdenum by the above-mentioned hydrogen peroxide complex extraction extraction cannot be directly treated. Therefore, the direct extraction and separation of this high-phosphorus tungsten-molybdenum feedstock requires further systematic research. Some scholars have tried to solve the tungsten-molybdenum separation problem of high-phosphorus tungsten-molybdenum mixed solution by the following scheme:

Organic phase composition (volume percent): 90% TBP + 10% sulfonated kerosene.

Raw liquid: The leachate obtained by treating high molybdenum scheelite with sulfur-phosphorus mixed acid, containing WO3120.5g/L, Mo 12.05g/L, phosphoric acid concentration 1.3mol/L, sulfuric acid concentration 1.1mol/L.

Feed liquid adjustment: A 30% concentration of H2O2 solution was added thereto, and the amount of H2O2 added was 1.4 times the total number of moles of tungsten molybdenum. A hydrogen peroxide-containing feed liquid containing WO3114.1 g/L, Mo 11.41 g/L, WO3/Mo=10/1, a phosphoric acid concentration of 1.2 mol/L, and a sulfuric acid concentration of 1 mol/L was obtained.

Extraction and separation: The above organic phase and the aqueous phase liquid were subjected to 5-stage countercurrent extraction under conditions of 1/1, and the supported organic phase was subjected to stripping with a 4 mol/L aqueous ammonia solution at a ratio of 1/1. After the organic phase is pickled, it is returned to the extract.

Results: raffinate WO3112.8g / L, Mo 0.1g / L; stripping solution WO31.2g / L, Mo11.3g / L.

The focus of the above method is the addition of hydrogen peroxide, which is the simplest and cleaner way to alter the presence of tungsten and molybdenum ions. With the addition of hydrogen peroxide, the phosphotungstic acid and phosphomolybdic acid in the feed solution complex with hydrogen peroxide to form peroxophosphoric acid and peroxophosphoric acid, which greatly widened the difference in properties of tungsten and molybdenum in the solution. The extraction of tungsten is rapidly suppressed, and the extraction rate of molybdenum is substantially unchanged, so that the separation effect is gradually improved.

By adding hydrogen peroxide and adjusting the total acid concentration in the high-phosphorus tungsten-molybdenum liquid system, and then using tributyl phosphate (TBP) as an extractant, the extraction and separation of tungsten and molybdenum under high phosphorus conditions can be achieved well. The phosphorus-containing high-tungsten-molybdenum leaching solution of tungsten-molybdenum ore provides a new extraction method which is simple in method, low in cost and easy to realize.

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