Short Fluoride Cycle in Tungsten Technology

Abstract

It is found that when a tungsten anode is electrochemically dissolved in a acidic fluorides of alkali metals (K,Na)H2F3 and hydrogen fluoride at a temperature of t ~ 37°C, the resulting atomic fluorine reacts completely with tungsten to form WF6. The latter dissolves in the melt, forming complex compounds (K,Na)2WF8 and (K,Na)WF7, which is accompanied by an increase in the melting point of the electrolyte. The addition of up to 23 mol % LiF and saturation of the electrolyte by WF6 lowered its melting temperature below 18°C, which, in an electrochemical process at a temperature of 35–40°C and an anode current density of 0.3–0.5 A/cm2, made it possible to obtain simultaneously gaseous WF6 at the anode and H2 at the cathode. During the gas-phase deposition of tungsten, dense layers are formed from the resulting gaseous mixture with a stoichiometric ratio of components at a temperature of 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. Based on the results, a short fluoride cycle in tungsten technology is presented. It uses two operations: the electrochemical synthesis of a gaseous mixture of WF6 + H2 in an electrolyzer with a filling anode made of fragments of metal tungsten and the reduction of WF6 by hydrogen with capture the resulting HF, allowing one to reduce the chain of technological devices in the cycle by almost 2 times with a significant reduction in production costs. The hardware and technological scheme of the production chain for the environmentally friendly production of tungsten products with a capacity of ~48.5 t/year, which can be replicated and modified to produce the necessary products, is presented.