Decomposition of tungsten mineral raw materials - direct preparation of tungsten carbide from tungsten concentrate

March 08, 2022

Mainly divided into high temperature melt extraction and gas injection carbonization two stages.
A tungsten concentrate was extracted Melt (mixture of wolframite concentrates or Scheelite and wolframite concentrate) and the Na ₂ Si0 _3, NaCl mixed, at 1050 ~ 1100 ℃ melted and the following reaction occurs:

2(Fe, Mn)W0 ₄ +3Na ₂ Si0 ₃ +16NaC1====(Na ₂ W0 ₄ ·8NaCl)+Na ₂ (Fe,Mn) ₂ Si ₃ 0 ₉

The obtained Na ₂ W0 ₄ ·8NaC1 phase is immiscible with the silicate phase, so it is layered by density, the lower layer is a chloride-tungstate phase, and the upper layer is a silicate phase. After two phases are separated by decantation, typically 98% to 99% WO ₃ and a small amount of iron impurities into the manganese tungstate, typical conditions are:
Ingredients: black tungsten concentrate NaCl: Na ₂ Si0 ₃ = 33:47:20, when using white tungsten as raw material, generally should add A1 ₂ 0 ₃ and NaF as flux, but white tungsten and black tungsten according to 1:3 ~3:1 ratio addition can also avoid adding flux.
Temperature and holding time: 1050~1100 °C, 2h.
Chloride-tungstate phase composition: 25% to 30% WO ₃ , about 0.24% FeO, about 0.3% MnO.
Silicate phase composition: about 0.5% WO ₃ , about 36% (FeO + MnO).
B Gas injection carbonization The chloride-tungstate phase is supplemented with NaCl to adjust the ratio. At 1050~1090 °C, natural gas is introduced into the following reaction:

Na ₂ W0 ₄ +4CH ₄ ==== Na ₂ 0+WC+3C0+8H ₂

WC, WC was washed with 10% HCl and 3% NaOH.
Typical conditions are: chloride-tungstate phase composition: containing 25% to 30% W0 ₃ (ie, Na ₂ W0 ₄ is 31.7% to 38%).
Reaction temperature: 1050~1070 °C.
Carbon utilization rate in CH ₄ : about 2.2% (semi-industrial scale data, the same below).
The recovery rate of W0 ₃ into WC; about 90%.
The total cost of WC powder: about 30% less than the traditional method.
After the above-mentioned carbonized product is ground, it is leached three times with 6 mol/L hydrochloric acid at 65 ° C to remove impurities, and the composition of the obtained product is roughly: total carbon of 5.99% to 6.14%; free carbon of 0.06% to 0.08%; S: 0.003%~0.014%; 0: 0.53%~0.55%, A1: 0.001%~0.005%; Ca: 0.005%~0.01%; Cr: 0.05%~0.3%; Cu: 0.007%~0.01%; Fe: 0.001%~0.05%; Mg: 0.001%~0.01%; Mo: 0.01%~0.1%; Si: 0.001%~0.01%; Ni: 0.03%~0.1%, the particle size is 1~20μm, accounting for 85%~90% .

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Mr. zhichun Fu

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