No abstract

Repositories of historical tungsten mining tailings pose environmental risks, but are also potential resources for valuable metals. They still contain large tonnages of useful minerals and metals, reflecting the inefficient extraction methods and/or low metal prices at the time they were mined. The focus of this study is to evaluate the technical viability of reprocessing the tailings to recover some of the contained valuable minerals and metals, as well as reducing the negative environmental impact associated with the tailings. Geometallurgical studies were conducted on drill core samples taken from the Smaltjärnen tailings repository of the closed Yxsjöberg tungsten mine, Sweden. The collected samples were characterized physically, chemically, and mineralogically. Knelson concentrator dry low- and high-intensity magnetic separation methods were tested as potential beneficiation methods. The tailings are dominated by the −600 to +149 µm particles. The highest concentration of tungsten (W) was 0.22% WO3. Using a Knelson concentrator, scheelite (main W mineral) recovery was enhanced, with 75 wt.% tungsten recovered in the 34 wt.% heavy concentrate. Only 1.0 wt.% sulphur (S) reported to the non-magnetic fraction. Based on the findings, a methodology and a preliminary process flowsheet for reprocessing the tailings is proposed.

Innovative tungsten (W) extraction techniques are continually being sought because of challenges of low leaching efficiencies, despite using advanced processing units such as autoclaves operating high temperatures and pressures. Compared to conventional leaching, mechanochemical treatment improves the efficiency of leaching. Therefore, in this study, an innovative mechanochemical treatment method, referred to as leaching while grinding (LWG), was employed as a reprocessing option to optimize W recovery from historical tungsten tailings. Experiments were run using the regular two-level factorial design to screen through the four factors of stirrer speed, liquid/solid ratio, temperature, and digestion time to assess their criticality and effects in the LWG process. The stirrer speed and the liquid/solid ratio were the most critical factors in the optimization of W recovery. The maximum W recovery (91.2%) was attained at the highest stirrer speed (410 rpm), low liquid/solid ratio (0.8), long digestion time (6 h), and low leaching temperature (60 °C). The attained low leaching temperature (60 °C) was due to the mechanical activation of scheelite resulting from the simultaneous grinding and leaching. For such low- grade W material, liquid/solid ratio optimizing is critical for maintaining the digestion mixture fluidity, and for environmental and economic sustainability regarding the sodium hydroxide (NaOH) consumption, which was low.