GB437833A - Improvements in or relating to the manufacture of phosphoric acid-containing fertilisers - Google Patents

Abstract

<PICT:0437833/III/1> Phosphoric acid containing fertilizers, i.e. superphosphates, are prepared by reacting sulphuric acid and a part of the phosphoric acid containing material to produce phosphoric acid but no monocalcium phosphate and reacting the resulting product with a further quantity of the same or a different phosphoric acid-containing material whereby super phosphate is formed, the reactions being carried out at different times and in different vessels without substantial quantities of the compounds formed during the process being separated. The initial material reacting with sulphuric acid may be tricalcium phosphate or monocalcium phosphate, say in the form of a portion of the superphosphate previously prepared by the process. The two steps may be carried out continuously, the first in a container provided with stirring means and the second in a mixing apparatus such as a mixed screw device. An excess of sulphuric acid may be employed in the first stage corresponding additional phosphate material being added in the second stage. The first stage may be so conducted that the phosphate material first comes into contact with phosphoric acid only. This may be effected by bringing the raw material into the upper part of the decomposition container and the sulphuric acid into the lower part thereof. Either or both of the two steps may themselves be divided into several stages, by introducing the corresponding quantities of the phosphoric-acid containing raw materials in portions and if desired also at different places. According to one example sulphuric acid is fed from a container 9 into the lower part of a reaction vessel 6 and raw phosphate is introduced into the same vessel from a container 10 and a distributer 11. The mass proceeds via a tube 12 to a vessel 7 in which the reaction continues. The paste passes via an overflow 8 into a mixing apparatus 13 where the residual portion of the phosphate flows in from the distributing device 11. The product leaves via 14 and is removed on a conveyer belt 15. The Specification as open to inspection under Sect. 91 describes also a modification of the process in which both raw phosphate and superphosphate previously prepared by the process are reacted with sulphuric acid in the first stage, the resulting product being reacted with further raw phosphate in the second stage. This subject-matter does not appear in the Specification as accepted.