An improved process for the production of metal phosphates

摘要

In the production of metal phosphates from an oxidation product of phosphorus and a molten metal salt, the reaction is carried out in an internally heated revolving furnace, the inner surface of which is lined with a solid layer of a metal phosphate which during the process is covered by a molten layer of metal salt surrounding the reaction zone. The process is particularly concerned with the production of alkali metal phosphates from alkali metal chlorides, but may be used also for the production of phosphates of calcium, magnesium, zinc and lead. As shown the shell 1 of a rotary furnace is provided with a lining 2 of alkali metal phosphate, for instance sodium metaphosphate. This may be gradually built up by melting the phosphate while chilling the metal shell by water sprays 3, or be formed from solid blocks of phosphate which are fitted in place and then united by melting at the surface, or comprise superposed layers of phosphates of different melting points. Liquid phosphorus is supplied to a burner 4 by a pipe 8 together with air or oxygen from a pipe 9, and vaporized phosphorus is burnt in the furnace by means of preheated air or oxygen supplied by a pipe 11. Steam is supplied from a pipe 5, and sodium or potassium chloride by a worm feed 5. Gaseous products of the reaction, comprising unreacted phosphoric acid and hydrochloric acid are recovered respectively in chambers 13, 14 and the molten phosphate formed is discharged continuously or intermittently. By omitting the supply of steam and adjusting the oxygen supply elemental chlorine may be obtained. If desired, the alkali metal chloride may be conveyed through the furnace in counter-current to the flow of heated gases. If the reaction product still contains alkali metal chloride it may be further heated in a second similar furnace to allow the reaction to be completed. The furnace may be used for the production of metal phosphates from phosphoric acid. In this case heating is effected electrically or by an oil or gas burner. For instance aqueous phosphoric acid recovered in the refining of crude oil may be reacted with potassium chloride to form a eutectic mixture of KCl and K3PO4 for use as a fertilizer.ALSO:Aqueous phosphoric acid recovered in the refining of crude oil is reacted with potassium chloride to form a eutectic mixture of KCl and K3PO4 for use as a fertilizer. Reaction is effected in an internally heated revolving furnace lined with a solid layer of a metal phosphate.