Production of potassium dihydrogen phosphate fertilizers

Claim 2

A process according to claim 2 and further comprising the steps of recovering said hydrochloric acid as an aqueous solution, reacting said aqueous hydrochloric acid solution with phosphate rock to form a reaction mixture comprising phosphoric acid, calcium phosphate and calcium chloride; reacting said phosphoric acid, calcium phosphate and calcium chloride reaction mixture with further phosphate rock to form a suspension containing precipitated dicalcium phosphate; reacting said suspension with an alkaline material to form a slurry containing insoluble dicalcium phosphate suspended in a calcium chloride solution; freeing said slurry of said calcium chloride; and feeding the resulting recovered dicalcium phosphate to the reaction mixture produced by the reaction of phosphate rock with said reaction medium.

Claim 3

A process according to claim 3 wherein said alkaline material is selected from the group consisting of limestone, lime and aqueous calcium hydroxide.

Claim 4

A process for the production of potassium dihydrogen phosphate comprising the steps of reacting phosphate rock with a medium containing potassium bisulphate, sulphuric acid and phosphoric acid to form a reaction mixture containing potassium dihydrogen phosphate product; separating calcium sulphate from said reaction mixture to obtain an aqueous solution of potassium dihydrogen phosphate and phosphoric acid; precipitating solid potassium dihydrogen phosphate from said aqueous solution by the addition thereto of a water miscible organic solvent to form a suspension of solid potassium dihydrogen phosphate in a mother liquor containing phosphoric acid, potassium dihydrogen phosphate and organic solvent; recovering solid potassium dihydrogen phosphate from said suspension; distilling organic solvent from said mother liquor, recycling the recovered organic solvent to the precipitation stage of said potassium dihydrogen phosphate; and recycling the remaining solution of potassium dihydrogen phosphate and phosphoric acid from the distillation stage for said organic solvent to said reaction mixture as the phosphoric acid component of said reaction medium.

Claim 5

A process according to claim 5 and further comprising the steps of obtaining said potassium bisulphate and sulphuric acid components of said reaction medium by reaction of potassium chloride and sulphuric acid in a sulphate conversion stage, hydrochloric acid being obtained as a by-product; forming a hydrochloric acid solution from said hydrochloric acid by-product of said sulphate conversion stage; feeding said hydrochloric acid solution together with phosphate rock to a first reaction stage to form a mixture containing phosphoric acid, calcium phosphate and calcium chloride; feeding said mixture together with further phosphaTe rock to a second reaction stage to form a suspension of precipitated dicalcium phosphate in admixture with phosphoric acid and calcium chloride; feeding said suspension to a third reaction stage together with an alkaline material to form a slurry containing insoluble dicalcium phosphate in suspension, in aqueous phosphoric acid and calcium chloride; separating said calcium chloride from said slurry; and feeding the recovered dicalcium phosphate suspension to said reaction mixture containing phosphate rock and said reaction medium.

Claim 6

A process according to claim 1 and further defined wherein said solid potassium dihydrogen phosphate is precipitated from said aqueous solution by the addition thereto of a water miscible organic solvent to form a suspension of solid potassium dihydrogen phosphate in a mother liquor containing phosphoric acid, potassium dihydrogen phosphate and organic solvent.

Claim 7

A process according to claim 7 and comprising the further steps of distilling organic solvent from said mother liquor, recycling the recovered organic solvent to the precipitation stage of said potassium dihydrogen phosphate; and recycling the remaining solution of potassium dihydrogen phosphate and phosphoric acid from the distillation stage for said organic solvent to said reaction mixture as the phosphoric acid component of said reaction medium.

Claim 8

A process according to claim 8 and further comprising the steps of obtaining said potassium bisulphate and sulphuric acid components of said reaction medium by reaction of potassium chloride and sulphuric acid in a sulphate conversion stage, hydrochloric acid being obtained as a by-product.

Claim 9

A process according to claim 9 and further comprising the steps of forming a hydrochloric acid solution from said hydrochloric acid by-product of said sulphate conversion stage; feeding said hydrochloric acid solution together with phosphate rock to a first reaction stage to form a mixture containing phosphoric acid, calcium phosphate and calcium chloride, feeding said mixture together with further phosphate rock to a second reaction stage to form a suspension of precipitated dicalcium phosphate in admixture with phosphoric acid and calcium chloride; feeding said suspension to a third reaction stage together with an alkaline material to form a slurry containing insoluble dicalcium phosphate in suspension, in aqueous phosphoric acid and calcium chloride separating said calcium chloride from said slurry; and feeding the recovered dicalcium phosphate suspension to said reaction mixture containing phosphate rock and said reaction medium.

Claim 10

A process according to claim 10 wherein said alkaline material is selected from the group consisting of limestone, lime and aqueous calcium hydroxide.