Purification and comprehensive utilization of sapphire kerf waste

摘要

Sapphire kerf waste (a fine powder) is a great potential source of high-purity alpha-Al2O3 and is currently discarded without reutilization, which is a waste of this resource and causes environmental problems, such as occupying space and generating dust. Herein, we report a feasible combined method to recycle valuable high-purity alpha-Al2O3 from sapphire kerf waste through the ultrasound-assisted leaching of nickel, diamond removal by bulk heating and a grinding process. The impurities in the waste were collected, and their existence states were characterized as independent metal nickel and diamond. The nickel impurity was removed from the waste by ultrasound-assisted leaching using a mixture of sulfuric acid and nitric acid, and the optimal leaching efficiency reached 99.67% under the conditions of sulfuric acid: nitric acid = 2:1 (v/v), 4 mol/L H+ concentration, 4 mL/g liquid-solid ratio, 45 degrees C, 30 min, 200 rpm, 240 W ultrasonic power and 45 kHz ultrasonic frequency. Subsequently, nickel ions in the lixivium were recycled in the form of nickel sulfate through extraction and stripping treatments. The diamond impurity was removed by bulk heating in flowing oxygen, and the optimal removal ratio was 99.65% under the conditions of 800 degrees C, 30 min and oxygen flow of 400 mL/min. High-purity alpha-Al2O3 was successfully recovered from the sapphire kerf waste after the grinding process, which had a purity higher than 99.99 wt% and an average diameter of 0.6 mu m. In addition, the kinetics of leaching nickel and diamond removal were systematically analysed based on the shrinking model, and the chemical reaction was found to be the control step. The reaction mechanisms of the two processes were also studied. The economic evaluation revealed that the profit from dealing with 1 kg sapphire kerf waste with this method was $13.68. Therefore, the proposed method is promising for providing technical and economical guidance for industrial production. (C) 2019 Elsevier Ltd. All rights reserved.