Method of regenerating phosphoric acid extraction solvent

In a process of digesting phosphate rock with mineral acid to form an impure phosphoric acid solution, extracting phosphoric acid from the impure phosphoric acid solution using a substantially water immiscible solvent selected from the group consisting of alkyl phosphates, aryl phosphates and alkyl aryl phosphates, stripping the phophoric acid from the solvent, and washing the solvent with an aqueous solution to separate impurities from the solvent, the improvement which comprises conducting the washing with an aqueous alkali orthophosphate solution sufficient to maintain the pH of the solvent-aqueous mixture at from about 9.5 to about 12.5.

In a process of digesting phosphate rock with mineral acid to form an impure phosphoric acid solution, extracting phosphoric acid from the impure phosphoric acid solution using a substantially water immiscible solvent selected from the group consisting of alkyl phosphates, aryl phosphates and alkyl aryl phosphates, stripping the phosphoric acid from the solvent, and washing the solvent with an aqueous solution to separate impurities from the solvent, the improvement which comprises conducting the solvent wash with an aqueous alkali orthophosphate solution containing at least about 2 weight percent orthophosphate measured as P.sub.2 O.sub.5, and having a mole ratio of alkali to phosphorus of from about 2.5:1 to about 3.5:1.

In a process of digesting phosphate rock with mineral acid to form an impure phosphoric acid solution, extracting phosphoric acid from the impure phosphoric acid solution using a substantially water immiscible solvent selected from the group consisting of alkyl phosphates, aryl phosphates and alkyl aryl phosphates, stripping the phosphoric acid from the solvent, and washing the solvent with an aqueous solution to separate impurities from the solvent, the improvement which comprises conducting the solvent wash with an aqueous alkali orthophosphate solution containing from about 3 weight percent to about 4 weight percent orthophosphate measured as P.sub.2 O.sub.5, and having a mole ratio of alkali to phosphorus of from about 2.7:1 to about 3.2:1.

In a continuous process of producing phosphoric acid by digesting phosphate rock with mineral acid to form an impure phosphoric acid solution, extracting phosphoric acid from the impure phosphoric acid solution using a substantially water immiscible solvent selected from the group consisting of alkyl phosphates, aryl phosphates and alkyl aryl phosphates, stripping the phosphoric acid from solvent, and washing the solvent with an aqueous solution to separate impurities from the solvent, the improvement which comprises conducting the solvent wash with an aqueous alkali orthophosphate solution containing at least about 2 weight percent orthophosphate measured as P.sub.2 O.sub.5 and having a mole ratio of alkali to phosphorus of from about 2.5:1 to about 3.5:1, separating the resulting aqueous, solvent, and precipitated solid phases, recycling the solvent phase to the extraction step, and recycling from about 75 to about 95 weight percent of the aqueous phase to the washing step.

In a continuous process of digesting phosphate rock with sulfuric acid to form an impure phosphoric acid solution, extracting the phosphoric acid from the impure phosphoric acid solution using a substantially water immiscible organic phosphate solvent selected from the group consisting of alkyl phosphates, aryl phosphates, and alkyl aryl phosphates mixed with a substantially water immiscible organic diluent, stripping the phosphoric acid from the solvent, and washing the solvent with an aqueous solution to separate impurities from the solvent, the improvement which comprises recycling to the extraction step up to about 95 weight percent of the solvent prior to the washing step, conducting the washing step on the remaining solvent with an aqueous alkali orthophosphate solution containing from about 3 to about 4 weight percent orthophosphate measured as P.sub.2 O.sub.5 and having a mole ratio of alkali to phosphorus of from about 2.7:1 to about 3.2:1, centrifuging the resulting wash mixture to separate the resulting aqueous, solvent, and precipitated solid phases, treating the solvent phase with activated carbon, recycling the solvent phase to the extraction step, and recycling from about 75 to about 95 volume percent of the aqueous phase to the washing step.