Comprehensive treatments of tungsten slags in China: A critical review

As a critical and strategic metal, tungsten is widely used in the fields of machinery, mining and military industry. With most of the tungsten resources reserves in the world, China is the largest producer and exporter of tungsten. This has resulted in the generation of a huge amount of tungsten slag (slag) stored in China. This slag always contains not only valuable elements, such as tungsten (W), scandium (Sc), tin (Sn), niobium (Nb) and tantalum (Ta), but also toxic elements, such as arsenic (As), lead (Pb), chromium (Cr) and mercury (Hg). Due to a lack of developed technologies, most of these slags cannot be treated safely, which results in a waste of resources and serious environmental and ecological risks. In this review we briefly describe the distribution and proportion of tungsten deposits in China, the tungsten extraction process and the properties of tungsten slag. We also mainly discuss the comprehensive treatments for the valuable and toxic slag, including the amounts of valuable metal elements that can be recovered and the stabilization of toxic elements. These aspects are summarized in a comparison of their advantages and disadvantages. In particular, we focus on the efforts to analyze the relationship between the existing processes and attempts to establish a comprehensive technology to treat tungsten slag and also suggest areas for future research.