scheelite tungsten processing united kingdom

Scheelite (CaWO₄) is a primary tungsten ore mineral, and its processing in the United Kingdom involves several stages, from mining to refining. Here’s an overview of the key steps and relevant UK context:

1. Mining & Extraction
– Historical Context: The UK had active tungsten mines in the past, such as the Hemerdon Mine in Devon (operated briefly in the 2010s by Wolf Minerals) and the Drakelands Mine. However, these are currently inactive due to economic challenges.
– Current Status: The UK imports most of its tungsten concentrate (including scheelite) from China, Vietnam, and other global producers.

2. Processing Scheelite into Tungsten Concentrate
Scheelite ore is processed through:
– Crushing & Grinding: Ore is reduced to fine particles.
– Gravity Separation: Scheelite is dense (6.1 g/cm³), so methods like jigging or shaking tables are used.
– Flotation: If needed, froth flotation separates scheelite from gangue minerals (e.g., quartz, sulfides).
– Magnetic Separation: Removes magnetic impurities.

3. Chemical Processing (UK Refining)
The UK has tungsten chemical processing facilities that convert scheelite concentrate into usable forms:
– Digestion: Scheelite reacts with sodium carbonate (Na₂CO₃) or hydrochloric acid (HCl) to form soluble sodium tungstate or tungstic acid.
\[
\text{CaWO}_4 + \text{Na}_2\text{CO}_3 → \text{Na}_2\text{WO}_4 + \text{CaCO}_3
\]
– Purification: Impurities (e.g., phosphorus, arsenic) are removed via precipitation or solvent extraction.
– Conversion to APT (Ammonium Paratungstate):
\[
\text{Na}_2\text{WO}_4 + 2\text{HCl} → \text{H}_2\text{WO}_4 + 2\text{NaCl}
\]
\[
\text{H}_2\text{WO}_4 + 2\text{NH}_4\text{OH} → (\text{NH}_4)_2\text{WO}_4 + 2\text{H}_2\text{O}
\]
– Calcination to WO₃ (Tungsten