Calorimetric and fourier transform infrared spectrophotometric studies of potassium elimination by dunite
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I.
INTRODUCTION
BLASTfurnace extraction of pig iron from iron ore is effected when the content of alkaline elements, principally sodium and potassium, goes above certain levels. These elements undergo a series of cyclical reactions that lead to their accumulation in the furnace, giving rise to the formation of scaffolding on the furnace body, canalization of gases, and loss of permeability in the load. ~ Furthermore, when the alkalis are deposited over the load, they provoke the swelling of iron ore agglomerates and catalyze the gasification of coke, inducing its breakup and reducing its ability to support the load. tej The elimination of potassium with the slag can be increased by adjusting of the slag volume, which dilutes the K20 content down to lower and more acceptable levels; decreasing the slag basicity index, which stabilizes K20 in the slag; increasing the MgO content of the slag, which, for the same total basicity index and identical sulfur capacity, decreases the thermodynamic activity of potassium; and finally, cold operating (low silicon) and high top pressuring to slow down the reduction of potassium and the formation of vapors when the slag trickles on the high-temperature coke. f3-7~ Other methods for the elimination of potassium are the addition of calcium chloride to the furnace loadt8,91 and of olivine, either during the sintering of the iron ore, in which case a synthetic olivine obtained from serpentines is used, t~~ or in the agglomeration of the iron ore for its direct use in the blast fumace, t~l~ F.A. LOPEZ, Principal Researcher, A. CORES, Researcher, and E. SAINZ and M. ALONSO, Postdoctoral Associates, are with the Department of Materials Recycling, National Center of Metallurgical Research (CSIC), Avenida Gregorio Del Amo, 8, E-28040 Madrid, Spain. Manuscript submitted March 7, 1994.
METALLURGICAL AND MATERIALS TRANSACTIONS B
With regard to dunite, a preliminary investigation using cylinders of 13-mm diameter and 10-mm length, surrounded by coke and heated to 1250 ~ has shown that it is capable of fixing between 6 and 13 wt pct potassium (expressed as K 2 0 ) . [12,|31 In this investigation, calorimetry and infrared spectroscopy were used to study the effects of coke impregnated with K2CO3 on partially serpentinized dunite. The mode of action of dunite was determined to be the fixation and formation of potassium silicates. II.
EXPERIMENTAL
A. Methods and Materials
Samples of commercial grade dunite (Pasek, Ortegal, Spain) were ground to grains of less than 20/zm. A sample of commercial grade industrial coke (National Iron and Steel Works, Seixal, Portugal) was impregnated with a saturated solution of K2CO3, which was prepared by dissolving 112 g of analytical grade carbonate (previously dried at 110 ~ for 24 hours) per 100 mL of distilled water. The impregnated coke was dried in an oven also at 110 ~ for 24 hours before use and was ground to grains of less than 20/xm. The sample was composed of 50.5 wt pct potassium carbonate and 47.5 wt pct coke (humidity, 2 pct). Initially, a sam
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