Abstract: In a process for producing a defluorinated product containing calcium, sodium and phosphorus, by calcination of a mixture of phosphate rock, with caustic soda, phosphoric acid and water, an improvement comprises maintaining the amount of phosphoric acid in the mixture such that the ratio of phosphorus in percentage by weight on a dry basis in said mixture-to-the phosphorus desired in percentage by weight in the calcined product is substantially equivalent to the ratio of the calcium in percentage by weight on a dry basis in the mixture-to-the calcium in percentage by weight in the calcined product. The process is especially useful where the phosphate rock has a bone phosphate of lime analysis of about 73% or less (e.g., about 71.5%), and also where the caustic soda is added to a mixture of phosphate rock and phosphoric acid prior to the addition of water.

Abstract: Phosphoric acids of significantly different content of soluble impurities, especially magnesium compounds, can be blended to produce a phosphoric acid with a decreased tendency for forming detrimental solids when converted to a liquid fertilizer or on storage, or during transportation as when the acid is transported by ocean vessel or railroad tank car. The blending can be effected either before or after a concentration step or steps (e.g., evaporation to "merchant grade" or to superphosphoric acid). For example, wet process phosphoric acid produced by a dihydrate or gypsum process can be blended with a phosphoric acid produced by a hemihydrate process.

Abstract: A process, for removing solid impurities from impure phosphoric acid containing solids, comprising:(a) passing said acid at an elevated temperature through a filter cake of a phosphoric acid-resistant filter aid supported on a porous medium, thereby to cause at least a portion of said solid impurities of said acid to be filtered therefrom and to be retained by said filter cake;(b) contacting at least a portion of said filter cake with a displacing liquid, maintained at a temperature and in an amount sufficient to cause at least a portion of the acid which remains in said filter cake to pass through said filter cake without fracturing said filter cake;(c) collecting said filtered acid which passes through said filter cake; and(d) removing an impurity-containing portion of said filter cake after contact with said acid and displacing liquid, thereby to present a fresh surface for subsequent filtration.

Abstract: In a multi-stage, multi-vessel phosphoric acid production system where a first reaction vessel contains a first slurry comprising calcium sulfate hemihydrate, monocalcium phosphate and phosphoric acid and a second reaction vessel contains a second slurry comprising calcium sulfate hemihydrate, sulfuric acid and phosphoric acid, in which the reaction slurry undergoes intra- and inter-vessel circulation, preferably through a draft tube, an improved start-up procedure involves filling the system with heated phosphoric acid having a P.sub.2 O.sub.5 analysis in the range of about 28 to about 38% (e.g. 31%), then feeding phosphate rock to the system, preferably in a separate reaction vessel, while phosphoric acid is recycled from a fourth, filter feed vessel, until the solids content in said slurry is in the range of 25-35% (e.g. about 30%) while the sulfate content in the first vessel is maintained at a negative level (e.g. excess calcium ion) and at a positive level in the second, crystallizer vessel.

Abstract: A system for the preparation of phosphoric acid from phosphate rock and sulfuric acid, includes in combination a first reaction vessel containing a first slurry comprising calcium sulfate hemihydrate, monocalcium phosphate and phosphoric acid, a second reaction vessel containing a second slurry comprising calcium sulfate hemihydrate, circulation means including a draft tube disposed centrally in each of said vessels and an agitator positioned axially in each of said vessels within said draft tube, a first conduit interconnecting said first and second reaction vessels for conducting said first slurry from said first reaction vessel to said second reaction vessel, a second conduit interconnecting said vessels for conducting said second slurry from said second reaction vessel to said first reaction vessel, an inlet pipe for introducing phosphate rock and phosphoric acid to said first reaction vessel, said inlet pipe connected with the interior of said draft tube in said first vessel and wherein a vent is connect

Abstract: A system for the preparation of phosphoric acid from phosphate rock and sulfuric acid, includes in combination a first reaction vessel containing a first slurry comprising calcium sulfate hemihydrate, monocalcium phosphate and phosphoric acid, a second reaction vessel containing a second slurry comprising calcium sulfate hemihydrate, circulation means including a draft tube disposed centrally in each of said vessels and an agitator positioned axially in each of said vessels within said draft tube, a first conduit interconnecting said first and second reaction vessels for conducting said first slurry from said first reaction vessel to said second reaction vessel, a second conduit interconnecting said vessels for conducting said second slurry from said second reaction vessel to said first reaction vessel, an inlet pipe for introducing phosphate rock and phosphoric acid to said first reaction vessel, and wherein a vent is connected to said inlet pipe to permit escape of gases and, thus, increasing the rate of fl

Abstract: Metal ion impurities are removed from phosphoric acid by adding to the acid a precipitant comprising ions of calcium and fluorine to cause precipitation of a magnesium-containing precipitate. A preferred precipitant is one containing calcium flouride, such as the sludge obtained by treating pond water from a phosphoric acid plant with a calcium-containing compound. Preferably, the soluble sulfate content of the phosphoric acid is maintained at at least about 2% by weight. An animal feed can be prepared from the precipitate by combining the precipitate with phosphate rock, water, and a sodium-containing compound, and then calcining the combination.

Abstract: Anhydrous hydrogen fluoride of high purity can be recovered from metallic fluoride salts containing phosphate values by digesting the metallic salts in an aqueous solution in a humid atmosphere at a sufficiently high temperature to release a gas containing hydrogen fluoride and negligible amount of P.sub.2 O.sub.5. The released gas is rectified in a rectification operation which includes a rectification zone in which the rectification occurs in the presence of sulfuric acid.

Abstract: Calcium fluoride is produced from pond waters resulting from phosphoric acid processing by treating the pond waters with calcium carbonate and/or calcium oxide in two stages to precipitate out the major part of the fluorine values from the waters as calcium fluoride. After removal of the calcium fluoride the filtrate is treated with calcium oxide to remove a substantial portion of the remaining fluorine values as calcium fluoride. After removal of these calcium fluoride solids, the filtrate is treated with another charge of calcium oxide to produce dicalcium phosphate (dical) which is separated from the aqueous phase. The aqueous phase is treated with an additional charge of calcium oxide to remove a substantial portion of the solids from the aqueous phase leaving waters that can be discharged as waste or recycled as process water.

Abstract: Metal ion impurities are removed from phosphoric acid by adding to the acid a precipitant comprising ions of calcium and fluorine to cause precipitation of a fluoride solid which contains ions of magnesium, and other metals (e.g., Al, N.sub.a) which were in the impure acid. A preferred precipitant comprises calcium fluoride, such as the sludge obtained by treating pond water from a phosphoric acid plant with calcium ions (e.g. lime and/or limestone).