An overview on different processes for recovery of valuable metals from tungsten carbide scrap.

Abstract

Cemented tungsten carbide material has been widely used in the hard metal industry for the manufacture of cutting tools, drilling tools, mining and machining tools and high wear resistant parts. When these tool bits and components are scrapped, they are collected and processed for recycling following appropriate methods. Tungsten and cobalt both are strategic rare metals and the cost of these metals entrapped in these scraps is estimated to be very high. Therefore, WC scraps have been considered as an important secondary resource of cobalt and tungsten metals. Recycling of hard materials like tungsten carbide scrap require specialised techniques. This paper presents a review of the different processes reported so far to recover valuable metals (W, Co) from cemented tungsten carbide scrap materials. Recycling techniques following either hydro or pyrometallurgical or a combination of them to recover the valuable metals (W, Co) are discussed. Thermal oxidation in presence of air/oxygen generates friable oxides of metals contained in tungsten carbide hard material, which is either leached in acid/alkali to produce tungsten oxide or subjected to reduction by hydrogen to produce tungsten powder. Direct leaching of tungsten scrap in concentrated acid/alkali solutions has also been investigated and different value added materials like ammonium para tungstate, tungstic acid etc are produced in the subsequent processing of leach liquor. The electrochemical route has emerged as an attractive method as it is a single step dissolution process consuming very low energy. However, passivation has been reported to slow down the dissolution rate and hence, some additives have also been tried for continuous dissolution. The environmental and economical aspects of some of the important processes have also been highlighted in this paper.