Effects of sodium carbonate on the carbothermic reduction of siderite ore with high phosphorus content

Minerals & Metallurgical Processing , 2013, Vol. 30, No. 2, pp. 100-107

Bai, Shaojun; Lv, Chao; Wen, Shuming; Liu, Dianwen; Zhang, Wenbin; Cao, Qinbo

Siderite ore with high phosphorus content was reduced isothermally at 1,050° C with pulverized coal and different dosages of sodium carbonate. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive analysis of X-rays (EDAX) were used to characterize the samples. The influence of sodium carbonate on the carbothermic reduction process was investigated. Sodium carbonate and its dosage played a considerable role in the carbothermic reduction. The iron particle size in the reduced ore was below 20 μm, and fayalite was abundant without sodium carbonate additive. With a mass ratio of Na₂CO₃-to-ore of 5% additive, the iron particle size in the reduced ore was generally above 50 μm, and the diffraction intensity associated with metallic iron in the XRD pattern increased. The effect of sodium carbonate on the phase transformation of fluorapatite during carbothermic reduction was also addressed via thermodynamic calculations and aqueous leaching experiments. The results showed that the fluorapatite was not reduced to P₂ at 1,050° C, and a portion of the fluorapatite was converted to soluble phosphate. The reduction of siderite can be catalyzed by adding an appropriate amount of sodium carbonate. This catalytic activity was caused by an increase in the reducing reaction activity of FeO and the acceleration of the carbon gasification reactions. The decrease in phosphorous content in the iron concentrate was attributed to an improvement in the separation of the iron phase from the slag phase when sodium carbonate was added and with the formation of soluble phosphate.