Dicalcium phosphate is known to be an effective fertilizer, particularly for direct application and blending (Superphosphate, Its History, Chemistry and Manufacture, chapter 7, page 172, U.S. Department of Agriculture, 1964); however, it has not been widely used, in part because no process has heretofore been available for its preparation at a cost competitive with other fertilizer materials. A major reason for its relatively high cost is that existing processes either require excess mineral acids in its preparation or require multiple heating, grinding, and filtration steps, unit operations which, like the use of excess acid, significantly add to manufacturing costs of dicalcium phosphate.
The prior art teaches that phosphate rock can be converted to dicalcium phosphate by acidulating the rock with an excess of mineral acid to dissolve the P2 O5, then neutralizing the excess acid in the separated extract with ammonia, limestone, lime, or other basic material to precipitate dicalcium phosphate.
Phosphate rock is the fertilizer industry's name for beneficiated apatitic phosphate ore. The unbeneficiated ore is commonly called matrix, particularly in the United States. Phosphorus occurs in the matrix and phosphate rock as fluorapatite, Ca10 (PO4)6 F2. Excess acid is defined as that over the theoretical amount needed to directly convert phosphorus in the phosphate rock to dicalcium phosphate. For example, with pure fluorapatite and nitric acid, the amount is defined by equation 1.
Our invention relates to a novel method of converting beneficiated or unbeneficiated apatitic phosphate ore to dicalcium phosphate, substantially free of most of the impurities present in the phosphate ore and eminently suitable for use as a fertilizer or as a feedstock for the production of high quality phosphoric acid, more particularly to the conversion of apatitic phosphate ore to dicalcium phosphate by treatment with sulfur dioxide, water, and a carbonyl-containing material, and still more particularly to the conversion of apatitic phosphate ore to dicalcium phosphate with consumption of essentially the minimum theoretical amount of sulfur dioxide.
Dicalcium phosphate is known to be an effective fertilizer, particularly for direct application and blending (Superphosphate, Its History, Chemistry and Manufacture, chapter 7, page 172, U.S. Department of Agriculture, 1964); however, it has not been widely used, in part because no process has heretofore been available for its preparation at a cost competitive with other fertilizer materials. A major reason for its relatively high cost is that existing processes either require excess mineral acids in its preparation or require multiple heating, grinding, and filtration steps, unit operations which, like the use of excess acid, significantly add to manufacturing costs of dicalcium phosphate.
The prior art teaches that phosphate rock can be converted to dicalcium phosphate by acidulating the rock with an excess of mineral acid to dissolve the P2 O5, then neutralizing the excess acid in the separated extract with ammonia, limestone, lime, or other basic material to precipitate dicalcium phosphate.
Phosphate rock is the fertilizer industry's name for beneficiated apatitic phosphate ore. The unbeneficiated ore is commonly called matrix, particularly in the United States. Phosphorus occurs in the matrix and phosphate rock as fluorapatite, Ca10 (PO4)6 F2. Excess acid is defined as that over the theoretical amount needed to directly convert phosphorus in the phosphate rock to dicalcium phosphate. For example, with pure fluorapatite and nitric acid, the amount is defined by equation 1. Ca10 (PO4)6 F2 + 6HNO3 ➝ 6CaHPO4 + CaF2 + 3Ca(NO3)2 ( 1)
The prior art teaches that phosphate rock can be converted to dicalcium phosphate by acidulating the rock with an excess of mineral acid to dissolve the P2 O5, then neutralizing the excess acid in the separated extract with ammonia, limestone, lime, or other basic material to precipitate dicalcium phosphate.
Phosphate rock is the fertilizer industry's name for beneficiated apatitic phosphate ore. The unbeneficiated ore is commonly called matrix, particularly in the United States. Phosphorus occurs in the matrix and phosphate rock as fluorapatite, Ca10 (PO4)6 F2. Excess acid is defined as that over the theoretical amount needed to directly convert phosphorus in the phosphate rock to dicalcium phosphate. For example, with pure fluorapatite and nitric acid, the amount is defined by equation 1.
Our invention relates to a novel method of converting beneficiated or unbeneficiated apatitic phosphate ore to dicalcium phosphate, substantially free of most of the impurities present in the phosphate ore and eminently suitable for use as a fertilizer or as a feedstock for the production of high quality phosphoric acid, more particularly to the conversion of apatitic phosphate ore to dicalcium phosphate by treatment with sulfur dioxide, water, and a carbonyl-containing material, and still more particularly to the conversion of apatitic phosphate ore to dicalcium phosphate with consumption of essentially the minimum theoretical amount of sulfur dioxide.
Dicalcium phosphate is known to be an effective fertilizer, particularly for direct application and blending (Superphosphate, Its History, Chemistry and Manufacture, chapter 7, page 172, U.S. Department of Agriculture, 1964); however, it has not been widely used, in part because no process has heretofore been available for its preparation at a cost competitive with other fertilizer materials. A major reason for its relatively high cost is that existing processes either require excess mineral acids in its preparation or require multiple heating, grinding, and filtration steps, unit operations which, like the use of excess acid, significantly add to manufacturing costs of dicalcium phosphate.
The prior art teaches that phosphate rock can be converted to dicalcium phosphate by acidulating the rock with an excess of mineral acid to dissolve the P2 O5, then neutralizing the excess acid in the separated extract with ammonia, limestone, lime, or other basic material to precipitate dicalcium phosphate.
Phosphate rock is the fertilizer industry's name for beneficiated apatitic phosphate ore. The unbeneficiated ore is commonly called matrix, particularly in the United States. Phosphorus occurs in the matrix and phosphate rock as fluorapatite, Ca10 (PO4)6 F2. Excess acid is defined as that over the theoretical amount needed to directly convert phosphorus in the phosphate rock to dicalcium phosphate. For example, with pure fluorapatite and nitric acid, the amount is defined by equation 1. Ca10 (PO4)6 F2 + 6HNO3 ➝ 6CaHPO4 + CaF2 + 3Ca(NO3)2 ( 1)