Abstract
At the moment the industrially applied techniques for cemented carbide reclamation feature several deficiencies. Depending on the process route, obstacles consist in high energy and chemical consumption (indirect recycling methods) or a deterioration of the recycled product in comparison with the primary material (direct recycling approach). Therefore, an alternative middle course provided by semidirect recycling processes seems promising. Accordingly, the coating materials as well as the binder metals are leached off the substrate keeping the hard phase unaffected and ready for reuse. However, the literature reports various difficulties like the slow dissolution of the binder, particularly if the scrap consists of larger pieces, contains a low binder metal perecentage or a small grain size. Furthermore, oxidation of the cemented tungsten occurs as an undesired reaction, causing even slower lixiviation and a contamination of the recycled product. Due the fact of an inexistent comparable systematic analysis of the semidirect recycling procedures, this article deals with a primary screening of potential combinations of acids, additives and oxidizing agents found in a literature survey. All experiments took place under the same conditions in a temperature controlled double-walled reaction vessel, varying only the molar concentrations of the different species as used in literature. A crucial point comprised of the development of an appropriate sample preparation, which allowed a simplification of the analysis along with its applicability in future kinetic investigations of selected solutions. As a result, promising combinations of chemicals are ready for further investigations determined by penetration depth and abrasion of the hard metal substrate. Successfully applied mixtures incorporate acids such as HNO3 and HCl followed by some organic acids, all combined with H2O2 as oxidant. Keywords: semidirect hard metal recycling, reclamation of cemented carbides, leaching of cobalt
Highlights
In the past decade China dominated the world production of tungsten ore concentrate with a share of 80 % of the total annual amount [1, 2]
The main issue of the indirect pathway consists of high energy and chemical consumption
The executed experiments without H2O2 did not reveal any detectable influence under the presented parameters (t = 4 h, T = 50 °C, 200 ml) aside from a few single detached WC grains
Summary
In the past decade China dominated the world production of tungsten ore concentrate with a share of 80 % of the total annual amount [1, 2]. Most of the industrially applied techniques for cemented carbide reclamation rest upon on a pretreatment and feed into the primary route (indirect recycling) or the zinc-process (direct route) [2,3,4,5]. At the moment an oxidation process with a combined hydrometallurgical digestion and an alkaline salt fusion treatment constitute the main representatives of this route. Both methods produce water-soluble Na2WO4 and further treatment basically follows the primary production (solution purification, SX, APT crystallization, reduction, carburation) [3, 4]
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