Molybdenum is hard and tough silvery white metal which is one of the important alloy elements in steel. It is also the essential trace minerals in human body, animals and plants. It is a kind of beneficial element. Adding molybdenum in steel to increase the harden ability, hot hardness, thermal strong ability, prevent the temper brittleness and improve magnetism. Factory practical analysis methods are: the quality method, spectrophotometry. Quality method is currently one of the common methods. Thiocyanate spectrophotometry analysis method is applied widely. The method is simple, rapid, and can be measured in aqueous phase and with organic solvent extraction. 

 

In this paper, the traditional measuring molybdenum method has been improved. Using oxalic acid to replace citric acid in sodium tungstate solution and reducing the concentration of thiourea in the color liquid, overcome the phenomenon of turbid solution and improve the stability of color liquid. It also shortens the process and saves reagent.

 

1. The masking effect and dosage of the oxalic acid on tungsten: Original method uses citric acid as a masking agent, but now we use oxalic acid. Putting the oxalic acid in sulfuric acid can save one step. For the determination of sodium tungstate solution, tungstic acid will not be precipitated under prescribed amount.

2. Adding thiourea has a certain effect on chromophoric intensity and stability. Using oxalic acid as a masking agent can reduce the concentration of thiourea, overcome the opacity. 

3. The acidity of medium has a certain influence on absorbance. Thiocyanate has a certain effect on chromophoric intensity and stability. Thiocyanate concentration should be in 1.5% ~ 2.5%.

4. The copper ion has the effect of catalytic reduction and can accelerate molybdenum reduction. The more copper ions are, the faster the reduction is. Copper ions can also accelerate the reduction of thiourea on iron.

 

We can draw the following conclusions: 

1. After improving traditional measuring molybdenum method with thiourea reduction, thiocyanate coloration, the new method of measuring 0.004% ~ 0.5% molybdenum has the quick and convenient advantages.

2. Compared with citric acid, oxalic acid can effectively eliminate a large number of tungsten interference to make the liquid color stable and measurement results accurate. The process is short. Cost is low. 

3. The method can be applied in control and analysis of factories' production process.