Reduction of phosphorous content in LD slag through spiral concentrator for industrial utilization

Abstract

Slag generated from basic oxygen converter (LD slag) is one of the recyclable wastes in integrated steel plants. LD slag may be used in refining of steel or in iron-making due to its high metal value and lime content. Presently, it is neither used in steel making nor in iron making. The LD slag processing conducted in waste recycling plant recovers about 20-25% of its total weight. The non-magnetic fraction which is -6mm in size is either discarded or utilized as aggregate in roads construction application. The reject of waste recycling plant, post metal recovery, is virtually stripped of metallic iron content, apart from the fact that the sparse or meagre iron value content mostly happens to be in oxide form. However, these rejects of recycling do contain considerable quantity of calcium bearing mineral phases like mono, di and tri-calcium silicates. These calcium silicates with its inherent advantage in possessing good fluxing value finds productive utilisation in iron ore sintering. However the steel slag rejects cannot be utilized as such since these contains 1.2-1.5% P which is not acceptable for iron ore sintering. Thus, the primary focus and concern lies in its effective recycling for exploiting its utilization for various applications. In the current study, the efficacy of 7-turn coarse spiral followed by 8-turn fine spiral concentrator was evaluated to process fine (-0.5 mm) LD slag for lowering Phosphorus (P) content to the desired level for its application in iron ore sintering. The effect of varying operating parameters on the performance of spiral has been studied through optimization experiments at different feed flow rates ranging from 18-22.2 Kg/min and altering the splitter positions for varying the density of feed pulp from 18-20%. Under optimized conditions, the results indicate that the concentrate product with low phosphorous content of about 0.76% is achieved, which is far too less from industry requirement perspective of <0.90% phosphorous content with a yield of 31%, and this can be effectively utilized for iron ore sintering. However, the yield of concentrate in the experiments undertaken varied proportionally from 31-57%, depending upon the level of phosphorus content desired in the concentrate i.e 0.76-0.90%. The main mineral phases contained in the slag were identified using X-ray diffraction (XRD) and complementary analysis were undertaken using scanning electron microscopy (SEM) coupled with energy dispersive spectrometer (EDS). The results were discussed in the light of our experimental results.