Introduction of ammonium molybdate

May 24, 2022

Ammonium molybdate easily purified, readily soluble, susceptible to thermal dissociation, and the thermal dissociation of the NH ₃ gas can be sufficiently heated with the escape, no product contamination molybdenum. Thus, ammonium molybdate is widely used as a basic raw material for producing high-purity molybdenum products. For example, pyrolytic ammonium molybdate produces high-purity molybdenum trioxide, hydrogen sulfide ammonium molybdate solution is used to produce high-purity molybdenum disulfide, and various molybdenum-containing chemical reagents are produced by ammonium molybdate. Ammonium molybdate is also commonly used as a basic raw material for producing molybdenum catalysts such as molybdenum catalysts and molybdenum pigments.

In the primary molybdenum products, molybdenum calcine ammonium second only to iron and molybdenum, occupies an important position.

Industrial ammonium molybdate is not a single compound, it is a mixture of a series of molybdenum and ammonium polyacids, which varies with the ratio of (NH ₃ ) ₂ /MoO ₃ . However, they can all be summarized into a general formula, and several common ammonium molybdates and general formulas are shown in Table 1. Dnval Rode et al. proposed a new conversion route for ammonium paramolybdate from the test results:

(NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O	△	(NH ₄ ) ₄ Mo ₅ O ₁₆	△	(NH ₄ ) ₄ Mo ₈ O ₂₆	△	MoO ₃
	→		→		→

Here again, the presence of a = 5 or 8, b = 2 or 2, c = 0 or 0 ammonium molybdate heteropolyacids is confirmed. However, regardless of the presence of several heteropolyacids, the main component of industrial ammonium molybdate is usually ammonium paramolybdate.

Table 1 Common characteristics of several ammonium molybdate

Name	Molecular formula	Parameter			(NH ₃ ) ₂ /MoO ₃	%Mo	Transformation
Name	Molecular formula	a	b	c	(NH ₃ ) ₂ /MoO ₃	%Mo	Transformation
Ammonium molybdate	(NH ₄ ) ₂ MoO ₄	1	1	0	1:1	48.94
Ammonium paramolybdate	(NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O	7	3	4	3:7	54.34	Decalcification water at 130 ° C, converted to ammonium tetramolybdate at 230 ° C (release NH ₃ ↑)
Ammonium tetramolybdate	(NH ₄ ) ₂ Mo ₄ O ₁₃	4	1	0	1:4	61.12	Conversion to molybdenum trioxide at 315 ° C (release of NH ₃ ↑)
general formula	(NH ₄ ) _2b Mo _a O _3a _+b CH ₂ O				b:a

Starting from molybdenum concentrate, there are many processes for preparing industrial ammonium molybdate. From the decomposition mode of molybdenite in molybdenum concentrate, these processes can be classified into two categories, namely (1) fire method: the molybdenum concentrate is converted into molybdenum calcine by oxidative roasting, and then treated by wet method. (2) Wet method: The molybdenum concentrate is directly leached, and the molybdenite is converted into a soluble molybdenum salt.

The difference between the fire method and the wet method is only that the MoS _{2 is} oxidized differently, the former is calcined, and the latter is decomposed by an oxidizing agent solution. Finally, both make Mo ⁴ ⁺ →Mo ⁶⁺ , S ² →S ⁰ or S ⁴⁺ .

Ammonium molybdate has different molybdenum contents due to different proportions of heteropolyacids, but the content of impurities is often small and the requirements are strict. The technical requirements for industrial ammonium molybdate are shown in Table 2.

Table 2 Ammonium molybdate quality standards

standard content(%) Ingredients		Chinese national standard GB3460-82			Claymax 1971 Standard
standard content(%) Ingredients		MSA-1	MSA-2	MSA-3	standard	Product typical analysis
Mo
Si	( miscellaneous quality ) ≯	0.0006	0.0010	0.002	0.0025	0.0013
Al		0.0006	0.0006	0.002	0.0010	0.0005
Fe		0.0006	0.0008	0.005	0.0020	0.0007
Cu		0.0003	0.0005		0.0010	0.0006
Mg		0.0006	0.0006	0.002	0.0005	0.0005
Ni		0.0003	0.0005	0.001	0.0005	0.0005
Mn		0.0003	0.0006
P		0.0005	0.0005	0.001
K		0.01	0.080
Na		0.001	0.003
Ca		0.0008	0.0010		0.0015	0.0007
Pb		0.0005	0.0005	0.0006	0.0005	0.0005
Bi				0.0006
Sn		0.0005	0.0005	0.0006	0.0035	0.0010
Sb				0.0006
Cd				0.0006
Cr					0.0010	0.0005
Ti					0.0010	0.0005
Particle size <		40 mesh