The core of tungsten metal extraction is to extract tungsten compounds (such as tungstic acid and ammonium paratungstate (APT)) from tungsten ores (mainly scheelite (Fe, Mn) WO ₄ and scheelite CaWO ₄), and then reduce them to obtain metallic tungsten (with a purity of over 99.9%). The process is divided into three stages: mineral decomposition, purification, and metal reduction. Due to the low grade and high impurities of tungsten ores, the purification stage is particularly critical. The following is a detailed process analysis:

1、 Preliminary preparation: tungsten ore beneficiation and enrichment

The grade of tungsten ore is usually only 0.1% -0.7%, and it needs to be improved through beneficiation (enriched to 60% -70% tungsten concentrate):

Black tungsten ore: using gravity separation (utilizing density difference, tungsten density is about 19.3g/cm ³, much higher than gangue)+magnetic separation (black tungsten ore has weak magnetism);

White tungsten ore: flotation is used (adding collectors such as oleic acid to make white tungsten ore adhere to bubbles and float up), often combined with heated flotation (40-70 ℃) to improve separation efficiency.

2、 Core step 1: Tungsten ore decomposition (extraction of tungstate)

Select different decomposition processes based on the type of tungsten ore (black tungsten/white tungsten), with the aim of converting tungsten from minerals into soluble tungstate salts:

1. Black tungsten ore: alkaline boiling decomposition method (mainstream process)

Principle: Black tungsten ore reacts with NaOH (caustic soda) at high temperature and high pressure to produce soluble sodium tungstate, and impurities (Fe, Mn) form hydroxide precipitates.

technological process:

Mix black tungsten concentrate with 30% -40% NaOH solution in proportion (ore alkali ratio 1:0.6-1:0.8);

Put it into an autoclave and react for 2-4 hours at 140-160 ℃ and 0.3-0.5MPa pressure. The reaction equation is:

(Fe,Mn) WO₄ + 2NaOH = Na₂WO₄ + Fe (OH)₂↓ + Mn (OH)₂↓；

After the reaction is complete, dilute with water and filter to obtain a sodium tungstate solution (containing about 100-150g/L of WO3), and discard the filter residue (iron manganese hydroxide).

2. scheelite: soda sintering method/hydrochloric acid decomposition method

(1) Soda sintering method (traditional process)

Principle: High temperature sintering of scheelite and Na ₂ CO Ⅲ (soda) produces sodium tungstate, and impurity Ca is converted into CaCO Ⅲ or CaSiO Ⅲ.

technological process:

White tungsten concentrate is mixed with Na ₂ CO ∝ at a ratio of 1:0.4-1:0.6 and sintered in a rotary kiln at 1000-1100 ℃ for 1-2 hours. The reaction equation is:

CaWO₄ + Na₂CO₃ = Na₂WO₄ + CaO + CO₂↑；

The sintered product is leached with water and filtered to obtain a sodium tungstate solution. CaO and SiO ₂ form slag phase separation.

(2) Hydrochloric acid decomposition method (modern and efficient process)

Principle: scheelite reacts with concentrated hydrochloric acid to form tungstic acid (H ₂ WO ₄) precipitate, and impurity Ca is converted to CaCl ₂ (soluble).

technological process:

White tungsten concentrate is mixed with 30% hydrochloric acid in proportion and reacted at 80-90 ℃ for 3-4 hours. The reaction formula is:

CaWO₄ + 2HCl = H₂WO₄↓ + CaCl₂；

Filter to obtain tungstic acid precipitate, wash with hot water to remove soluble impurities such as CaCl ₂.

3、 Core Step 2: Purification Process (Preparation of Ammonium Paratungstate APT)

Sodium tungstate/tungstic acid solution contains impurities such as Si, P, As, Mo, etc. It needs to be purified and purified to obtain high-purity APT (ammonium paratungstate, (NH4) 10W12O41 · xH2O), which is a key intermediate for the production of metallic tungsten

1. Impurity removal

Remove Si, P, and As: Add MgCl ₂ or CaCl ₂ to the sodium tungstate solution to generate precipitates such as Mg ∝ (PO4) ₂ and Mg ₂ SiO4, and filter them out;

Remove Mo: Add ammonium sulfide (NH4) 2S) to convert Mo into thiomolybdate, extract and separate it with an extractant (such as N235), or adjust the pH to 2-3 to precipitate Mo;

Purification of tungstic acid: If tungstic acid is used as the raw material, dissolve tungstic acid in ammonia water to generate ammonium tungstate solution, and repeat the above impurity removal steps.

2. Transformation and Crystallization (Preparation of APT)

Ion exchange/solvent extraction transformation: The purified sodium tungstate solution is passed through a strong alkaline anion exchange resin to adsorb tungstate ions, and then eluted with NH4Cl solution to obtain ammonium tungstate solution; Alternatively, tungsten ions can be extracted with an extractant (such as P204) and then back extracted with ammonia water to obtain ammonium tungstate solution.

Evaporative crystallization: Heat and concentrate ammonium tungstate solution (90-100 ℃), cool and crystallize to obtain ammonium paratungstate (APT) crystals with a purity of 99.99% (4N) and impurity content<10ppm.

4、 Core Step 3: Metal Tungsten Reduction (from APT to Metal Tungsten)

APT is calcined to obtain tungsten trioxide (WO ∝), which is then reduced by hydrogen to obtain metal tungsten powder. If dense tungsten blocks are required, subsequent sintering is also necessary:

1. APT calcination decomposition

Put APT into a rotary kiln or muffle furnace, calcine at 500-600 ℃, remove ammonia and crystal water, and generate yellow tungsten trioxide (WO3), reaction formula: (NH4) 10W12O41 · xH2O → 12WO3+10NH3 ↑+(x+5) H2O ↑.

2. Hydrogen reduction to produce tungsten powder

Principle: WO ∝ is reduced by hydrogen gas at high temperature, and WO ₂ is generated step by step W， Finally, tungsten powder was obtained.

technological process:

Put WO N3 into a tubular reduction furnace and reduce it in two stages in a dry hydrogen atmosphere:

The first paragraph (500-700 ℃): WO ∝→ WO ₂ (tungsten dioxide);

Second paragraph (800-1000 ℃): WO ₂ → W (metal tungsten powder);

The reduced product is cooled, crushed, and classified to obtain tungsten powder of different particle sizes (purity ≥ 99.9%, particle size 0.5-10 μ m).

3. Densification molding (optional)

If it is necessary to prepare finished products such as tungsten blocks and tungsten wires, the tungsten powder needs to be densified:

Powder metallurgy sintering: tungsten powder is pressed into shape (pressure 150-300MPa), pre sintered at 1400-1600 ℃ in a hydrogen atmosphere, and then heated to 2000-2200 ℃ for high-temperature sintering to obtain tungsten billets with a density of ≥ 95%;

Smelting and purification: If ultra-high purity tungsten (above 5N) is required, electron beam melting or plasma melting can be used to remove trace impurities (such as O, N).

5、 Characteristics and Key Control of Tungsten Extraction Process

High purity requirements: When tungsten is used in hard alloys, filaments, and other fields, impurities (such as O, C, Mo) can seriously affect its performance, so the purification process needs to be strictly controlled (APT purity must be ≥ 4N);

High energy consumption: Hydrogen reduction and sintering require high temperatures (800-2200 ℃), usually using electric heating or hydrogen combustion heating;

Environmental requirements: Alkali boiling and sintering processes will generate wastewater (containing NaOH, NH3) and exhaust gas (containing CO ₂) NH3）， A wastewater treatment (neutralization and sedimentation) and exhaust gas recovery (ammonia absorption) system are required.

6、 Comparison of mainstream processes (scheelite vs scheelite)

Advantages and disadvantages of mainstream decomposition processes for mineral types

The alkaline boiling decomposition method of scheelite has a mild reaction and high tungsten recovery rate, and is only suitable for scheelite

The hydrochloric acid decomposition method for scheelite has a short process, easy removal of impurities, strong corrosiveness of hydrochloric acid, and requires anti-corrosion equipment

The soda sintering method of scheelite is suitable for low-grade ores, with high energy consumption and slightly lower recovery rate