Short fluoride cycle in tungsten technology

It was found that when the tungsten anode is electrochemically dissolved in a melt of acidic alkali metal fluorides (K,Na)H₂F₃ and hydrogen fluoride at t ~ 37 °C, the resulting atomic fluorine reacts completely with tungsten to form tungsten hexafluoride (WF₆). The latter dissolves in the melt to form complex compounds (K,Na)₂WF₈ and (K,Na)WF₇, which is accompanied by an increase in the melting electrolyte point. Adding up to 23 mol.% LiF and WF₆ electrolyte saturation lower the electrolyte melting point below 18 °C making it possible to obtain simultaneously gaseous WF₆ at the anode and H₂ at the cathode in an electrochemical process at t = 35÷40 °C and an anode current density of 0.3–0.5 A/cm². During gas-phase deposition of tungsten, dense layers are formed from the resulting gas-containing mixture with a stoichiometric ratio of components at t = 550÷600 °C, and the resulting HF is captured by an electrolyte and used to produce a mixture of WF₆+H₂ , ensuring the circulation of reagents and the absence of stored waste. A short fluoride cycle in the tungsten technology is presented based on the results obtained. It uses two operations: electrochemical synthesis of the WF₆+H₂ gaseous mixture in an electrolyzer with a bulk anode made of metal tungsten fragments, and WF₆ reduction by hydrogen with capture the resulting HF. This cycle reduces the chain of process units in the cycle by almost 2 times with a corresponding investment reduction and significant production cost saving. The paper provides process flow diagram of the production chain for environmentally friendly tungsten production with a capacity of ~48.5 tons per year, which can be replicated and modified to produce the necessary products.

tungsten, fluorine, fluorination, tungsten hexafluoride, hydrogen, reduction, hydrogen fluoride, complex alkali metal fluorides, electrochemical dissolution, reagent cycle, ecological safety, tungsten products, productivity, energy consumption, cost

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