Production of tungsten boride from CaWO₄ by self-propagating high-temperature synthesis followed by HCl leaching

In this study, the conditions of producing tungsten boride powder from calcium tungstate (CaWO₄) by self-propagating high-temperature synthesis (SHS) followed by HCl leaching techniques were investigated. In the first stage of the experimental study, the SHS products consisting of borides and other compounds were obtained starting with different initial molar ratios of CaWO₄, Mg and B₂O₃. It was found that increasing B₂O₃ content in the initial mixture resulted in an increase of W₂B₅/WB ratio along with Mg ₃B₂O₆ in the SHS product. In the second step, Mg and Ca containing byproducts (i.e. MgO, Mg₃B₂O ₆ and Ca₃B₂O₆) found in the SHS product were leached out by using aqueous HCl solution to obtain a clean tungsten boride product. The effects of particle size, temperature, time, acid concentration and solid/liquid ratio were selected as leaching parameters. The acid leaching experiments of the SHS product synthesized at 1:8:2.5 initial molar ratio of CaWO₄:Mg:B₂O₃ showed that optimum leaching conditions could be achieved by using 2.85 M HCl at 1/10 S/L ratio and the temperature of 80 °C for 60 min.