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Calcium molybdate
With molybdenum, molybdenum oxide, as often as calcium molybdate molybdenum steel alloy additives. Its use is far from extensive ferromolybdenum and molybdenum oxide. Pure calcium molybdate contains 48.0% molybdenum. The table below lists the former Soviet Union calcium molybdate standards for reference.
Table Calcium molybdate (former Soviet Union) standard UMTY-4523-65ROC
model
Mo
≥
Ca
≤
P
≤
S
≤
MДK-1
44
twenty two
0.1
0.2
MДK-2
40
twenty four
0.2
0.3
The production of calcium molybdate can be calcined by molybdenum calcination with lime (CaO), and the molybdenum concentrate is mixed with lime (CaO) and then calcined. However, more is made by precipitating MoO 4 2- with calcium chloride (CaCl 2 ) when processing low-grade molybdenum concentrate. The conventional process is shown in the following figure.
Figure Low-grade molybdenum concentrate to produce calcium molybdate
When the molybdenum calcine is leached with soda liquid, it can react not only with molybdenum trioxide but also with molybdenum molybdate and iron molybdate (but ammonia cannot dissolve and react):
MoO 3 +Na 2 CO 3 â†â†’Na 2 MoO 4 +CO 2 ↑
CaMoO 4 + Na 2 CO 3 â†â†’Na 2 MoO 4 +CaCO 2 ↓
FeMoO 4 + Na 2 CO 3 +H 2 Oâ†â†’Na 2 MoO 4 +Fe(OH) 2 ↓CO 2 ↑
In order to dissolve fully and save soda, four to five stages of countercurrent leaching are usually employed. After the immersion liquid after the mashing is heated and concentrated by steam, the molybdenum concentration of the sodium molybdate solution exceeds 50-70 g/L, and calcium chloride (CaCl 2 ) can be added at 80-90 ° C to form a calcium molybdate precipitate. The precipitation should be carried out in a neutral or alkaline solution, and the amount of CaCl 2 added should be 10-15% more than the theoretical reaction. After the resulting precipitate is washed with water to remove sulfate, the steel industry calcium molybdate can be obtained by filtration and calcination (600-700 ° C).
The low-grade molybdenum concentrate and even the ammonium leaching residue of ammonium molybdate can be mixed with soda and calcined to produce the following reaction:
MoS 2 +Na 2 CO 3 +O 2
â–³
Na 2 MoO 4 +CO 2 ↑+SO 2 ↑
â†â†’
SiO 2 + Na 2 CO 3 →Na 2 SiO 3 +CO 2 ↑
The resulting soluble sodium molybdate and sodium silicate (or sodium metasilicate) can be separated at a certain pH range. The mother liquor after separation of silicic acid is added with calcium chloride to form a precipitate of calcium molybdate. After the precipitate is washed and dried, it becomes industrial grade calcium molybdate.
The production process of bismuth molybdate is similar to the production process of calcium molybdate. The only difference is that the calcium in the sodium molybdate solution is precipitated with barium chloride without using calcium chloride:
Na 2 MoO 4 +BaCl 2 →2NaC1+BaMoO 4 ↓
Bismuth molybdate is used in the enamel industry. At the time of production, there are many domestic applications of ammonia leaching slag and soda roasting. The key to its production is the full separation of metasilicate and sodium molybdate in solution.