value of below about 8 agitating the slurry while treating the slurry with oxygen or an oxygen containing gas to convert the pyrite in the coal to a soluble alkali metal sulfate reacting lime with the so formed alkali metal sulfate to regenerate the alkali metal hydroxide and then recycling the hydroxide for use in the process application_number US 11979 A description the process of pyrite removal from coal by chemical oxidation in an alkaline medium e g sodium hydroxide proceeds according to the following equation equ1 it will be seen from equation 1 above that the pyritic sulfur in the coal is oxidized to sulfate which is soluble in the reaction medium the iron remains in the treated coal as an insoluble oxide or hydroxide this desulfurization process may be carried out at high rates of pyrite removal from the coal under certain optimum conditions e g temperatures of between 50 and 60 u00b0 c ph values of about 10 or 11 and at atmospheric pressure approximately 90 of the pyrite can be removed from the coal in about two days under these conditions conventional solids liquid separation techniques can be employed to recover the treated or desulfurized solid coal it has been proposed to modify the desulfurization process described above by adding lime e g cao or ca oh 2 to the reaction product in order to convert the sodium sulfate to sodium hydroxide and thereby to regenerate additional sodium hydroxide for use in.