A novel desulphurization process of coal water slurry via sodium metaborate electroreduction in the alkaline system

The present work investigated an alternative desulfurization process for coal water slurry (CWS) using sodium metaborate (NaBO2) electroreduction under the ambient conditions. Desulfurization efficiency improved with the increases of NaBO2 concentration, electrolytic time, and electrolytic voltage, while with the decreases of coal particle size and CWS concentration. Up to 50% desulfurization efficiency was obtained in the ⩽109 μm (140 mesh) coal under the optimized conditions of CWS (50 g/L), NaBO2 (13.2 g/L), NaOH (1 g/L), electrolytic voltage (3.5 V), and electrolytic time (4 h). Furthermore, the possible reaction mechanism of electrochemical desulfurization (ED) was that NaBO2 was converted into NaBH4 by means of the electrochemical reduction (ER) on the cathode, which induced transformation of pyritic sulfur (PS) and organic sulfur (OS) in the coal into H2S and S2−, and S2− in the solution was further oxidated into SO 4 2 - (SS) on the anode.