Cleaning the Residue of Plasma Pyrolysis of Coal through Alkali-acid Treatment with Recycle of Alkali

Chemical cleaning of the residue of plasma pyrolysis of coal from Karamay, China was investigated through alkali-acid leaching with the recycle of alkaline leachant solution. The ash was optimally removed at a mass ratio of NaOH/residue between 0.5 and 0.6, with about 77% ash removal and 84.4% recovery of carbonaceous material. The recycling method could reduce the NaOH consumption by more than 41% and cut down the alkaline waste water to zero with a convenient operation as compared with that using a common method. Meanwhile, NaCO₃·10H₂O was obtained using the recycling method, as a result of dissolution of carbonates during alkali digestion.