A sample of Tabas coal from Iran was oxidized using air, peroxyacetic acid (PAA), and PAA + air as a pretreatment for desulfurization with sodium butoxide in a batch reactor. The effects of air oxidation temperature, PAA oxidation time, sodium butoxide reaction time and temperature, solvent concentration and particle size on the reduction of sulfur were investigated. The PAA + air oxidation pretreatment was the most effective method for enhancing sulfur removal. This procedure increased pyritic sulfur removal by approximately 15% and organic sulfur removal by 20% in leaching with sodium butoxide. Increasing the temperature from 25 (unoxidized) to 100 degreesC on air oxidized samples, increased sulfur reduction for organic and inorganic sulfur by 7% and 11%, respectively. Further increases in temperature decreased the sulfur removal. For PAA oxidized samples that dried at room temperature, penetration of PAA into the coal pores blocked them, leading to a reduction in the diffusion of sodium butoxide. For oxidized/desulfurized samples, depending on the desulfurization conditions, the reduction in pyritic, organic and total sulfur ranged from 28% to 84%, 8% to 49% and 19% to 67%, respectively. The particle size reduction had a positive effect on the efficiency of the leaching process. For particle sizes <300 mum, after oxidation and desulfurization at 150 degreesC for 90 min, pyritic, organic and total sulfur decreased from 0.9%, 0.82% and 1.72% to 0.18%, 0.45% and 0.64%, a reduction of 81%, 49% and 65%, respectively. The results show that PAA + air oxidation pretreatment can be used as an effective method for enhancing the removal of organic and inorganic sulfur without severe dissolution of the coal organic matrix. (C) 2004 Elsevier Ltd. All rights reserved.