Production of tungsten boride from CaWO_4 by self-propagating high-temperature synthesis followed by HCl leaching

摘要

In this study, the conditions of producing tungsten boride powder from calcium tungstate (CaWO_4) by self-propagating high-temperature synthesis (SHS) followed by HC1 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 CaWO_4, Mg and B_2O_3. It was found that increasing B_2O_3 content in the initial mixture resulted in an increase of W_2B_5/WB ratio along with Mg_3B_2O_6 in the SHS product. In the second step, Mg and Ca containing byproducts (i.e. MgO, Mg_3B_2O_6 and Ca_3B_2O_6) found in the SHS product were leached out by using aqueous HC1 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 CaWO_4:Mg:B_2O_3 showed that optimum leaching conditions could be achieved by using 2.85 M HC1 at 1/10 S/L ratio and the temperature of 80 °C for 60 min.