Patent GB-826234-A (GB)
Title: Improvements in and relating to phosphate fertilizers
IPC: C05B1/04
Filed: 1956-03-02
Abstract: A phosphate fertilizer comprising dicalcium phosphate and mono-calcium phosphate is prepared by hydrolysing monocalcium phosphate (e.g. in the form of superphosphate or triple superphosphate) to form dicalcium phosphate and phosphoric acid and then evaporatively heating the mixture at 125-280 DEG  C. in the presence of phosphate rock whereby said rock is dissolved in the form of monocalcium phosphate.  The hydrolysis and heating stages may be carried out in the same zone or in separate zones.  The phosphate rock may be present in the initial mixture or added afterwards; the process may thus be performed by reacting phosphate rock with an acid such as sulphuric, nitric, phosphoric or oxalic in which it dissolves to form a monocalcium phosphate, in an amount less than that necessary for complete reaction, storing to increase the monocalcium phosphate content if desired, hydrolysing the monocalcium phosphate and dissolving the remainder of the rock.  Thereafter if desired, water may be added and the last two steps referred to above repeated to obtain a product richer in dicalcium phosphate.  Suitable temperatures for the hydrolysis reaction are 50-120 DEG  C., and if the mixture is (as preferred) in the form of an easily agitated slurry, temperatures approaching the boiling point are preferred, though it is important to maintain sufficient water concentration for hydrolysis; preferably this is sufficient to maintain the monocalcium phosphate in solution.  The dissolution of the phosphate rock in the final stage is preferably done at at least 125 DEG  C. under atmospheric pressure and 150-260 DEG  C. is preferred; it is desirable to carry out the heating to the final temperature rapidly. Agitation and grinding is desirable during the hydrolysis and/or heating steps and in an illustrated embodiment steam heating is employed.  The process can be carried out continuously if desired, and a part of the ground product can be recycled to the hydrolysis stage, together with make-up water. Examples are given in which the temperatures and proportions of reactants are varied.  Specification 300,965, [Class 1 (iii)], is referred to.ALSO:A phosphate fertilizer comprising dicalcium phosphate and monocalcium phosphate is prepared by hydrolysing monocalcium phosphate, (e.g. in the form of superphosphate or triple superphosphate) to form dicalcium phosphate and phosphoric acid and then evaporatively heating the mixture at 125-280 DEG C. in the presence of phosphate rock whereby said rock is dissolved in the form of monocalcium phosphate.  The phosphate rock may be present in the initial mixture or added afterwards: the process may thus be performed by reacting phosphate rock with an acid such as sulphuric, nitric, phosphoric or oxalic in which it dissolves to form a monocalcium phosphate, in an amount less than that necessary for complete reaction, storing to increase the monocalcium phosphate content if desired, hydrolyzing the mono calcium phosphate and dissolving the remainder of the rock. Thereafter if desired, water may be added and the last two steps referred to above repeated to obtain a product richer in dicalcium phosphate.  Specification 300,965 [Class 1(iii)] is referred to.