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INDUSTRIAL A N D ENGINEERING CHEMISTRY
E. P.. Hioks. V.. . . Partrid-. S O C . . ~&e ~, (isai).
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DEFLUORINATION OF PHOSPHATE ROCK IN THE MOLTEN STATE Factors Affecting Rate of Defluorination KELLY L. ELMORE, ERNEST 0. HUFFMAN. AND WILLIAM W. WOLF Tennessee Valley Authority, Wilson Dam, Ala.
DOMEgTIC . phosphate . . rocka are essentially fluorapatite adrmxed m t h various proportions of other compounds of calcium, fluorine, iron, aluminum, and silicon (1, 8). Since the greater fraction of the phosphorus is present ES fluorapatite, the phosphorus of raw phosphate rock is not assimilated by plant life. If the apatite lattice is destroyed and the fluorine is eliminated, however, most of the phosphorus is made availahle. Various inveatigators (6, 7) have shown that the fluorine can be removed by heating the phosphate rock at temperatures above 130O0 C. in the presence of silica and water vapor; their work suggested the possibility of producing a phosphatic fertilizer by calcining the rock in a rotary
kiln. Calcination experiments carried out in this laboratory, however, showed that defluorination below the fusion point of phosphate rock containing the oxides of silicon, iron, and aluminum lowered the melting point to that of a eutectic mixture which sintered. The sintering p r o w s caused the rate of removal of the fluorine to be prohibitively slow and favored the formation of rings in the kiln. Accordingly, studies of defluorination in the molten state were undertaken with the hope of eliminating the difficultieg arising from sintering and developing a p r o w s suitable for largescale operation, in which the deflnorinated product could be tapped from the furnace. The kinetics of the removal of fluorine from the melt waa determined by systematically investigating the specific effects of the composition of the charge, the concentration of water vapor in the furnace atmosphere, the velocity of the furnace atmosphere, the temperature of defluorination, and the depth of charge.
Apparatus and Procedure The work was carried out by fusing S to 4apram charges in 60 per cent platinum40 per cent rhodium boats in a high-ternture furnace. eauinwd with a tubular silicon carbide heatins element 24
