Patent GB-787016-A (GB)
Title: Production of fertilizer materials
Inventor: DEE THOMAS PRIDE
IPC: C01B17/50
Filed: 1954-06-23
Abstract: A fertilizer and sulphur oxides are produced by reacting a mixture comprising an alumino phosphate rock and calcium sulphate in the absence of alkali metal salts at a temperature in excess of 1000 DEG C. and recovering the evolved sulphur oxides.  The mixture contains 2-7 mols. of CaO per mol. P2O5, and is preferably granulated.  The alumino phosphate is probably converted to calcium phosphate and aluminium sulphate, the latter being de-composed to alumina and sulphur oxides.  Suitable alumino phosphate rocks are pseudo-wavellite or other calcium alumino phosphates which are preferably ground and granulated with calcium sulphate hemihydrate in the presence of water, after which the granules are dried at 60-80 DEG  C., thereby retaining their shape after calcination.  Suitable reaction temperatures are 1250-1300 DEG  C.  In order to obtain a high P2O5 availability the tricalcium phosphate formed should be retained in the alpha form and to this end, at the termination of the reaction, the product should be rapidly cooled through the transition temperature, namely 1250-1150 DEG  C. thereby preventing appreciable formation of the beta form.  Steam may be added during the calcination to remove fluorine.  According to an example, an alumino phosphate rock was mixed with ground calcium phosphate and the mixture heated to 1250 DEG  C. for one hour in an atmosphere of steam.  The furnace effluent gases were purified by passage through a series of scrubbers and the sulphur dioxide obtained was collected in the usual manner.  After reaction the product was cooled rapidly through the temperature range 1250-1150 DEG  C.  A further example relates to the employment of waste gypsum hemihydrate which was granulated with the alumino phosphate rock in the presence of water in excess of that required to form the gypsum dihydrate.  The resulting granular material after drying at 60 DEG  C. was heated in steam as before.ALSO:A calcium phosphate/alumina fertilizer and sulphur oxides are produced by reacting a mixture comprising an alumino-phosphate rock and calcium sulphate in the absence of alkali metal salts at a temperature in excess of 1000 DEG C. and recovering the evalued sulphur oxides.  The mixture contains 2-7 mols of CaO per mol P2O5 and is preferably granulated.  The aluminophosphate is probably converted to tri-calcium phosphate and aluminium sulphate the latter being decomposed to aluminia and sulphur oxides.  Suitable alumino-phosphate rocks are pseudo-wavellite or other calcium aluminophosphates which are preferably ground and granulated with calcium sulphate hemihydrate in the presence of water, after which the granules are dried at 60 DEG -80 DEG C., thereby retaining their shape after calcination. Suitable reaction temperatures are 1250 DEG -1300 DEG C.  In order to obtain a high P2O5 availability the tri-calcium phosphate formed should be retained in the alpha form and to this end, at the termination of the reaction, the product should be rapidly cooled through the transition temperature namely 1250 DEG -1150 DEG C. thereby preventing appreciable formation of the beta form.  Steam may be added during the calcination to remove fluorine. According to an example, an aluminophosphate rock was mixed with ground calcium phosphate and the mixture heated to 1250 DEG C. for one hour in an atmosphere of steam.  After reaction the product was cooled-rapidly through the temperature range 1250 DEG -1150 DEG C. The phosphate product had a citric acid solubility of 91,4 per cent, and was sulphur-free.