An optimized recovery of cobalt and tungsten carbide (WC) from a binary-phase WC-6 wt%Co cemented tungsten carbide hardmetal using design of experiments

Abstract

Tungsten extraction from scheelite and wolframite ores is a well-established process. However, continuous exploitation has led to more complex ore compositions and lower WO₃ concentrations in tungsten concentrates, posing significant challenges for sustainable extraction. Primary and secondary tungsten sources often contain valuable metals such as Sn, Ta, Nb, Mo, Sc, and Co; however, current industrial processes focus predominantly on tungsten recovery, neglecting other metals and compromising sustainability. This study aimed to develop a process for the co-recovery of tungsten carbide (WC), cobalt (Co), and tungsten (W) from cemented carbide scrap using a sulphate-based leaching system. A statistical Design Of Experiments (DOE) approach was employed to screen and optimize process variables, including acid concentration, leaching time, solid-to-liquid ratio, temperature, and agitation rate. Characterization revealed the material contained 85.95 wt% W, 8.77 wt% C, and 5.28 wt% Co. Optimal leaching occurred with 2 M H₂SO₄, a 1:10 S/L ratio, at 82 °C, and 750 rpm agitation, achieving 25.13 % Co extraction in 10 h and 97.6 % after 4.2 days. Increasing the temperature to 92 °C improved extraction, reaching 31.7 % in 10 h. Temperature was identified as the primary factor influencing cobalt dissolution kinetics. The recovered WC powder consisted of well-defined, fine particles comparable in quality to ‘virgin’ WC. Electroplated cobalt achieved 91.9 % current efficiency over 3 h, producing metal with 98.0 wt% purity and good morphological integrity. Synthetic tests confirmed that tungsten recovery as scheelite (CaWO₄) is highly feasible.