There’re many kinds of method of eliminating the molybdenum from the sodium tungstate solution. But when we use the differences of tungsten, molybdenum and S2- producing sulfide acid radical ion to separate tungsten and molybdenum, the vulcanization step is the key. No matter what method is used, good or bad vulcanization reaction directly affects the effect of molybdenum. Sodium tungstate system eliminating the molybdenum mainly adopts molybdenum sulfide precipitation, which is divided into two process of sulfuration and acid precipitation (add pH acid). But this kind of excessive vulcanization process of high temperature and long time, the processing cost is higher and the operation is also strict. It restricts the production greatly. At the same time, after vulcanization, the acid eliminating molybdenum remains unstable phenomenon. Because excessive vulcanization agent, although the tungsten sulfide is very limited, it leads to a certain degree of tungsten sulfide. In the next acid process, with the MoS3 precipitation, WS3 will precipitate, resulting in the loss of tungsten. So a kind of improved Na2S eliminating molybdenum process-acid adjustment precipitation eliminating molybdenum will be introduced as follws:

 

For the system of sodium tungstate, general sulfide method eliminating molybdenum process emphasizes sulfuration completely. It makes all molybdenum turn into Na2MoS4 to acid treatment. Molybdenum separates from solid and liquid as MoS3 precipitation. In vulcanization process, Na2M004 transforming into Na2MoS4 is a balance of ions in the solution. This requires larger excessive sodium sulphide and strict curing conditions to ensure cure completely. 

1. For the acid process, through the experiment we discovered when the pH value is 6.5, the molybdenum precipitation is about 60% (it refers to relative to the remaining in the solution which can remove the proportion of molybdenum and it also known as precipitation rate). When pH value is 5.5, the molybdenum precipitation is about 75%. When PH value is 3.5, the molybdenum precipitation is about 95%. Finally, adjusting the pH value to 2-3, molybdenum precipitation rate is above 95% and the precipitation of molybdenum decreased mostly in the process of pH value. 

2. The original sulfide method can be fully improved as follows: under the condition of incomplete sulfide, acid treatment after being part molybdenum sulfide preliminarily, sulphur molybdenum to settle first, as to the MoS3 Na2MoS4 consumption, accelerate to Na2M Na2M004 oS4 transformation, the molybdenum sulfide quickly, and satisfies the requirement of precipitation, sulfide and precipitation. 

3. Sulfide, acid precipitation process is not a contradiction between the two. Preliminary, acid treatment with molybdenum acid precipitation consumption, the pH value decreased slowly, generally maintained between 6 to 7, the condition of vulcanization, quickest and most efficient can further promote quick response; With pH value decreased, the most of molybdenum precipitation down, finally the pH fell to 2 to 3, which achieve depth molybdenum. 

 

The improved fast precipitation eliminating molybdenum can greatly reduce the conditions needed for the vulcanization process. The dosage of curing agent can be reduced. The molybdenum process is greatly simplified. In a nutshell, sodium tungstate system normal Na2S eliminating molybdenum method can be improved. Improved Na2S fast eliminating molybdenum method is greatly simplified and thoroughly with low dosage of Na2S, small tungsten loss. The products of APT come up to come up to the APT-0 standard.