Abstract
The treatment of industrial polycrystalline diamond (PCD) blanks in aqua regia at atmospheric pressure between 333 K and 353 K was performed via the ultrasound-assisted leaching process to investigate whether the influence of ultrasound is beneficial. Cobalt content in the solution and in the blanks was monitored as well as the effects of leaching temperature, solid-to-liquid ratio, and PCD blank size. The use of intermittent and permanent ultrasound helped reduce the leaching time and thus energy consumption by up to 50%. In all trials with ultrasound, higher temperature only has a slight effect. Solid-to-liquid ratio does not have a positive or negative impact. A new process design was tested using an innovative experimental setup for ultrasound-assisted leaching aiming at maximum cobalt and diamond recovery from PCD and final reuse of fine PCD for cutting and polishing other hard materials in different important industrial applications.
Highlights
Cobalt is a ferromagnetic transition metal which is located between iron and nickel in the periodic table of elements and mostly available in lateritic ores [1,2,3]
The results from this study suggest that the leaching of D14 does not require a 353 K bath temperature but can be done at 333 K
In nine experimental runs with a 5 day duration, cobalt containing polycrystalline diamond (PCD) was leached in aqua regia at atmospheric pressure between 333 K and 353 K
Summary
Cobalt is a ferromagnetic transition metal which is located between iron and nickel in the periodic table of elements and mostly available in lateritic ores [1,2,3]. Cobalt is used as a solvent catalyst in the production of polycrystalline diamond (PCD) that would otherwise take even more pressure and a higher temperature to achieve. The wide use of cobalt relative to other metals is associated with the high solubility of carbon in its melt during thermobaric treatment [5]. At temperatures above 800 ◦ C, which are developed during operation of a polycrystalline diamond tool, the cobalt promotes the formation of microcracks and results in significant heat-resistance reduction and subsequent reduction in the abrasion resistance of the polycrystalline diamond [6]. The reduction of the cobalt content in the sintered polycrystalline diamond (PCD) greatly improves the performance of a superhard composite. The removal of cobalt from the used PCD is the most important request in the industry of wire-drawing tools made from diamond materials and tungsten carbide
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