Recycling of WC–Co hardmetal sludge by a new hydrometallurgical route Jae-chun Lee a, ⁎, Eun-young Kim a , Ji-Hye Kim a , Wonbaek Kim a , Byung-Soo Kim a , Banshi D. Pandey a,b a Mineral Resources Research Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon 305-350, Republic of Korea b Metal Extraction and Forming Division, National Metallurgical Laboratory ( NML), Jamshedpur-831007, India abstract article info Article history: Received 19 August 2010 Accepted 12 January 2011 Keywords: Hardmetal Tungsten carbide Cobalt Tungstic acid Aqua regia A hydrometallurgical process based on aqua regia treatment of WC–Co hardmetal sludge was developed to simultaneously extract cobalt in solution and forming tungstic acid as residue in a single step. The parameters such as aqua regia concentration, temperature and time of reaction, and pulp density were optimized to process the sludge containing 60.9 wt.% W, 5.99 wt.% Co, 3.38 wt.% Fe and 12.64 wt.% C as the major components. Almost complete leaching of cobalt was achieved with 100 vol.% of aqua regia at 100 °C temperature, 60 min reaction time and 400 g/L pulp density. Complete conversion of tungsten carbide of the sludge to tungstic acid was observed at and below the pulp density of 150 g/L under this condition. The progress of reaction and conversion of tungsten carbide to tunstic acid (H 2 WO 4 ) were investigated by XRD phase identification of the residues under different conditions. The tungstic acid produced from the acid treatment was purified by dissolving tungsten in 11.20 mol/L of ammonia solution at 60 °C while rejecting insoluble metallic impurities as a residue. Tungsten from the ammoniacal solution was recovered by evaporation–crystallization process as high purity (99.97%) ammonium paratunstate (APT, (NH 4 ) 10 ·- H 2 W 12 O 42 ·4H 2 O) with low levels of impurities. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction WC–Co hardmetals have been widely used as cutting tools, mining tools, machining tools of various metals, and hard-surface coating materials because of their excellent hardness and toughness. Generally, the WC–Co hardmetals contain tungsten carbide and carbides of metals such as Ti, Ta, Nb, Cr, V, Mo, Re etc and binders such as cobalt, nickel, iron etc, depending on their applications. Coating and surface treatment of the hardmetals have further added other metals as carbide, nitride, alumina, brass (Cu/Ni/Zn alloys), Ag etc to extend the life of tools. More recently, submicron grain hardmetals with even better wear and anti-flaw properties were developed for high-tech usage such as dies and micromachining of PCBs in semiconductor and cutting machines of LCD glass contributing to the high precision and long-life of tools [1–3]. The hardmetal tools are manufactured by sintering of WC powders, with/ or without other carbides, mixed with metallic binders and machining the sintered products for final usage. Inevitably, a large amount of hardmetal sludge is generated in the machining step of the manufacturing process. The sludge contains valuable metals such as W, Co, Ni etc and thus its recycling is necessary from the view point of metal reclamation and environmental protection. A variety of methods, such as chemical modification, melting metallurgy, zinc process, coldstream process, bloating/crushing, electrochemical/hydrothermal and hydrometallurgical processes have been developed for recycling hard (solid pieces) and soft (cutting or grinding sludges, sweeps, powders, turning, etc.) scraps of hardmetals [1,4–14]. Usually, the soft scraps of impure quality are treated by hydro-/electro- metallurgical methods to recover the valuable components including tungsten, because other methods are suitable for the scraps of high purity and with small variation in the grain size of WC. As regards the recycling of hardmetal sludges, processes based on either alkaline treatment or acid treatment are mostly followed. The alkali treatment methods have been executed typically in two ways: (i) transformation of WC to sodium tungstate (Na 2 WO 4 ) which is soluble in water, by alkali fusion process using sodium nitrate/nitrite and sodium carbonate, and (ii) dissolution of pre-oxidized sludge using sodium hydroxide solution followed by removal of impurities, precipitation of tungstic acid and ammonia dissolution, crystallization of ammonium paratungstate (APT), and finally hydrogen reduction to recover tungsten or tungsten compound. In this process, cobalt remains as oxide in the residue and returns to the recovery process. These alkaline treatment methods require high temperature fusion or oxidation which consumes large amount of energy. In addition, a separate processing method has to be applied for the recovery of cobalt from the residue [4,7,8,13,15]. In acid treatment methods [6,14,16], soluble metals in acid particularly cobalt is extracted first leaving insoluble WC in residue. Int. Journal of Refractory Metals and Hard Materials 29 (2011) 365–371 ⁎ Corresponding author. Tel.: +82 42 868 3613; fax: +82 42 868 3415. E-mail address: jclee@kigam.re.kr (J.-c. Lee). 0263-4368/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijrmhm.2011.01.003 Contents lists available at ScienceDirect Int. Journal of Refractory Metals and Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM