GB743190A - Manufacture of phosphate usable as fertilizer or as cattle-food - Google Patents

Abstract

A phosphate suitable for fertilizer or cattle food is prepared by subjecting a mixture of crude calcium phosphate, phosphoric acid and an alkali-metal chloride in amounts such as to give a calcium and alkali-metal phosphate corresponding to the empirical composition P2O5. 2 CaO.Na2O (and/or K2O), to a two-stage heat treatment, in the first stage of which the mixture is gradually calcined at 600 to 800 DEG C. for 1 to 2 hours in the presence of water vapour and in the immediately subsequent second stage of which the mixture is gradually heated to a temperature from 1000 to 1200 DEG C. for a shorter duration. A small amount of silica may be incorporated which, in fixing a portion of the lime in the phosphate as silicate lowers the free lime content thereby permitting the quantity of P2O5 to be added to be decreased. It is preferred to mix the chloride and the phosphate before the addition of phosphoric acid whereby on addition of phosphoric acid preferably containing 40 per cent of P2O5, the paste may be granulated to set into hard granules. The calcination may be effected in a revolving furnace having lifting bricks and suitably the two stages of the heating may be effected in different sections of the same rotary furnace. The furnace effluent gases contain recoverable hydrochloric acid and fluorine partly as hydrofluoric acid and partly as hydrofluosilicic acid depending on the silica content of the phosphase used. The product leaving the furnace is preferably suddenly cooled by a violent air current or a mist of atomized water or by an internally cooled drum. According to an example dried fragments of a paste obtained by adding phosphoric acid to a mixture of phosphate and sodium chloride was calcined in two stages in two revolving furnaces arranged in series the first of which operated at 750 to 800 and the second at about 1150 DEG C. 3 kgs. of steam for every 100 kgs. of phosphate were added to the first furnace but the addition of steam is not necessary to the second furnace. The product was received in a revolving drum cooled by internal water circulation. The products may contain from 35 to 44 per cent of phosphoric acid of which 90 to 100 per cent is soluble in neutral or alkaline ammonium citrate and the fluorine content may be as low as 0.2 to 0.3 per cent.ALSO:A phosphate suitable for fertilizer or cattle food is prepared by subjecting a mixture of crude calcium phosphate, phosphoric acid and an alkali-metal chloride in amounts such as to give a calcium and alkali-metal phosphate corresponding to the empirical composition P2O5.2CaO.Na2O (and/or K2O), to a two-stage heat treatment, in the first stage of which the mixture is gradually calcined at 600 DEG to 800 DEG C. for 1 to 2 hours in the presence of water vapour and in the immediately subsequent second stage of which the mixture is gradually heated to a temperature from 1000 DEG to 1200 DEG C. for a shorter duration. A small amount of silica may be incorporated which, in fixing a portion of the lime in the phosphate as silicate, lowers the free lime content thereby permitting the quantity of P2O5 to be added to be decreased. It is preferred to mix the chloride and the phosphate before the addition of phosphoric acid whereby on addition of phosphoric acid, preferably containing 40 per cent of P2O5, the paste may be granulated to set into hard granules. The calcination may be effected in a revolving furnace having lifting bricks and suitably the two stages of the heating may be effected in different sections of the same rotary furnace. The furnace effluent gases contain recoverable hydrochloric acid and fluorine partly as hydrofluoric acid and partly as hydrofluosilicic acid depending on the silica content of the phosphate used. The product leaving the furnace is preferably suddenly cooled by a violent air current or a mist of atomized water or by an internally cooled drum. According to an example, dried fragments of a paste obtained by adding phosphoric acid to a mixture of phosphate and sodium chloride was calcined in two stages in two revolving furnaces arranged in series, the first of which operated at 750 DEG to 800 DEG C. and the second at about 1150 DEG C. 3 kgs. of steam for every 100 kgs. of phosphate were added to the first furnace, but the addition of steam is not necessary to the second furnace. The product was received in a revolving drum cooled by internal water circulation. The products may contain from 35 to 44 per cent of phosphoric acid of which 90 to 100 per cent is soluble in neutral or alkaline ammonium citrate and the fluorine content may be as low as 0.2 to 0.3 per cent.