Ignited alkali phosphate fertilizer prodn. - by process in which alkali hydroxide is mixed with phosphate and silica prior to ignition in a rotary oven

摘要

Ignited alkali phosphates with fertiliser action are produced by thermal digestion of natural of natural Ca phosphates in a rotary oven at 900-1300 degrees C. with 30-80 wt.% alkali hydroxide soln. in the presence of silicic acid. The molar proportion of alkali hydroxide to P2O5 in the mixt. is 1.1-1.5 : 1, and the amt. of silicic acid is such as to convert CaO present in the starting material as tricalcium phosphate or non-phosphate calcium into calcium orthosilicate. The alkali hydroxide soln. is added to the raw phosphate/sand mixt. in =2 separate streams: the solid starting materials are mixed with 40-90 wt.% of the alkali hydroxide in a suitable mixer outside the rotary oven while waste gases from the oven are passed through the mixt. to give a dry or moist agglomerated mass, then this mass is fed into the rotary oven and at least part of the remaining alkali hydroxide is added at is not 400 degrees C. Mixing alkali hydroxide with the solid raw materials outside the oven but in the presence of oven waste gases gives improved energy utilisation, removes dust and volatiles from the waste gases, and gives a granular material for feeding into the oven. Because of the granular form of the material in the oven, addition of alkali hydroxide soln. to the hot material inside the oven does not give rise to dust formation.