Abstract
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.
Highlights
Tungsten (W) is a critical raw material for the European Union [1], with scheelite (CaWO4 ) and wolframite ((Fe,Mn)WO4 ) being the most important tungsten ore minerals [2,3]
It was documented that mechanochemical treatment can improve the efficiency of leaching [7,8]
It was observed that the stirrer speed (D), temperature (A), and digestion time (B) had positive effects, meaning an increase in these main factors would increase the W recovery
Summary
Tungsten (W) is a critical raw material for the European Union [1], with scheelite (CaWO4 ) and wolframite ((Fe,Mn)WO4 ) being the most important tungsten ore minerals [2,3]. Different hydrometallurgical techniques have been used for W extraction from these ores, mostly from high-grade W concentrates, and synthetic concentrates (scraps) [2]. Different leaching reagents, being either alkaline or acidic or a combination of the two, applied at different stages of the leaching process and reactors have been considered to enhance W extraction efficiency [4,5,6]. In the leaching while grinding (LWG) process, the reaction ability of the mineral to be leached is increased (mechanical activation) by grinding using high-energy mills, and in the presence of a leaching reagent, a mechanochemical reaction occurs. The mechanical activation in the high-energy mills is achieved by impact (stroke or collision), attrition (shear), and compression. In the LWG process, several factors influence the grinding process and the leaching process; for grinding, the factors include the filling extent of the milling chamber, ball-to-powder ratio (BPR), and grinding speed and time, while for leaching, the factors include temperature, reagent concentration, stirring speed, and leaching time [8,9,10,11,12]
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