The physical and chemical properties of sodium molybdate and its preparation method

Sodium Molybdate

[Physical and chemical properties] This product is a white rhombus crystal with a molecular formula of Na ₂ MoO ₄ ·2H ₂ O and a density of 3.

[Preparation method] China's sodium molybdate is mainly prepared from waste ammonium molybdate residue, non-standard molybdenum trioxide and waste molybdenum powder

Figure 6-11 Production process of sodium molybdate

(1) Preparation example 1

The calcine was prepared under the roasting conditions of 650℃ and 2.

(2) Preparation example 2

Use ammonium molybdate tailings to produce sodium molybdate

①Molybdenum tailings and soda roasting traditional process is used to treat molybdenum tailings by soda roasting method, that is, the molybdenum slag is mixed with soda and saltpeter in the ratio of 70:40:4, and the molybdenum slag is roasted and melted at 800～1000℃ in the inverter The main reaction equation for turning into soluble sodium molybdate is:

②Water leaching of roasting slag The roasted molybdenum tailings are immersed in water according to a solid-liquid ratio of 1:2, so that sodium molybdate is dissolved in water to generate sodium molybdate aqueous solution, and Fe(OH) ₂ , SiO ₂ , Pb and Ca are removed The carbonate and other impurities

③Concentrated crystallization

Evaporate and concentrate the filtered sodium molybdate solution until the density of the solution reaches 1.

Shi Xingyuan only added soda during roasting, and oxidized molybdenum dioxide and molybdenum disulfide using oxygen in the air, and used soda to convert the insoluble aluminate into sodium molybdate

①Decomposition of roasting slag with hydrochloric acid.

Me is Fe, Ca, Pb and other metals

Due to the excessive amount of hydrochloric acid, part of the molybdenum will remain in the solution as molybdenum oxychloride cations

②The molybdic acid alkali dissolution and purification is based on the solid-liquid ratio of 1:3 to dissolve molybdic acid with liquid alkali, control the alkalinity to 4.

H ₂ MoO ₄ +2NaOH+Na2MoO ₄ +2H ₂ O

The solution contains a small amount of silica , and the pH value needs to be neutralized to 8.

③Adjust the pH value to 10.

The process flow of producing sodium molybdate from molybdenum tailings is shown in Figure 6-12

Figure 6-12 Process flow for producing sodium molybdate from molybdenum tailings

(3) Preparation Example 3 Analyze the preparation of pure sodium molybdate

The conventional process for analyzing pure sodium molybdate is to oxidize and roast molybdenum concentrate to obtain molybdenum trioxide (referred to as molybdenum calcine), leaching with sodium hydroxide solution to obtain industrial sodium molybdate, and then recrystallize industrial sodium molybdate Dissolve in water, add nitric acid to precipitate the dihydrate of molybdenum trioxide, wash thoroughly, dry, and then sublimate at 700°C to obtain high-purity molybdenum trioxide, which is dissolved in pure sodium hydroxide solution and concentrated by evaporation.

Jia Rongbao and others used industrial ammonium tetramolybdate as raw material, washed with pure water to remove impurities, synthesized with pure sodium hydroxide, heated to drive off the ammonia, evaporated and concentrated, cooled and crystallized and recrystallized to prepare analytically pure sodium aluminate
.
The process flow is shown in Figure 6-13
.

Figure 6-13 Analyze the preparation process of pure sodium molybdate