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 Mg3B2O6 in the SHS product. In the second step, Mg and Ca containing byproducts (i.e. MgO, Mg3B2O6 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.