A wet process phosphoric acid production method comprises digesting phosphate-containing ore in a slurry comprising sulfuric acid, whereby phosphoric acid and calcium sulfate crystals are formed; and separating the phosphoric acid from the calcium sulfate crystals; wherein a defoamer and a poly(carboxylic acid), or salt thereof, having a weight-average molecular weight of less than 1,000,000 grams per mole (g/mol), are added to the slurry. The poly(carboxylic acid) can be a poly(acrylic acid), or salt thereof, and the defoamer can be a dialkyl sulfosuccinate salt and an aliphatic alcohol or a fatty acid ester. The method enhances separation of phosphoric acid from calcium sulfate crystals in wet process phosphoric acid production by any one of increasing the volume average particle size of the calcium sulfate crystals, increasing filtration rate, and reducing foam formation.

A wet process phosphoric acid production method comprises digesting phosphate-containing ore in a slurry comprising sulfuric acid, whereby phosphoric acid and calcium sulfate crystals are formed; and separating the phosphoric acid from the calcium sulfate crystals; wherein a defoamer and a poly(carboxylic acid), or salt thereof, having a weight-average molecular weight of less than 1,000,000 grams per mole (g/mol), are added to the slurry. The poly(carboxylic acid) can be a poly(acrylic acid), or salt thereof, and the defoamer can be a dialkyl sulfosuccinate salt and an aliphatic alcohol or a fatty acid ester. The method enhances separation of phosphoric acid from calcium sulfate crystals in wet process phosphoric acid production by any one of increasing the volume average particle size of the calcium sulfate crystals, increasing filtration rate, and reducing foam formation.

The present invention refers to an improved process for recovering phosphoric acid from sewage sludge ash, said process comprising a leaching step; a transforming step for converting phosphate metallic salts into phosphoric acid; a solvent extraction of the phosphoric acid from the leached solution with an organic solvent; a washing step for removing sulfuric acid; and stripping of phosphoric acid to obtain an aqueous solution containing phosphoric acid.

The present invention refers to an improved process for recovering phosphoric acid from sewage sludge ash, said process comprising a leaching step; a transforming step for converting phosphate metallic salts into phosphoric acid; a solvent extraction of the phosphoric acid from the leached solution with an organic solvent; a washing step for removing sulfuric acid; and stripping of phosphoric acid to obtain an aqueous solution containing phosphoric acid.

A process may involve digesting raw phosphate with concentrated sulfuric acid and converting the raw phosphate to calcium sulfate in the form of dihydrate and/or hemihydrate, and phosphoric acid, separating off calcium sulfate as solid from a liquid phase of a suspension that is obtained, treating the calcium sulfate that is separated off or from a stockpile with an acid to give a suspension with purified calcium sulfate and P.sub.2O.sub.5-containing acid solution, separating off the purified calcium sulfate as solid from a liquid phase of a suspension obtained, using the P.sub.2O.sub.5-containing liquid phase as a portion of the sulfuric acid required for digesting the raw phosphate or as feedstock for treating phosphogypsum from the stockpile to give a suspension of purified calcium sulfate and P.sub.2O.sub.5-containing acid solution, which is thereafter processed.

A process may involve digesting raw phosphate with concentrated sulfuric acid and converting the raw phosphate to calcium sulfate in the form of dihydrate and/or hemihydrate, and phosphoric acid, separating off calcium sulfate as solid from a liquid phase of a suspension that is obtained, treating the calcium sulfate that is separated off or from a stockpile with an acid to give a suspension with purified calcium sulfate and P.sub.2O.sub.5-containing acid solution, separating off the purified calcium sulfate as solid from a liquid phase of a suspension obtained, using the P.sub.2O.sub.5-containing liquid phase as a portion of the sulfuric acid required for digesting the raw phosphate or as feedstock for treating phosphogypsum from the stockpile to give a suspension of purified calcium sulfate and P.sub.2O.sub.5-containing acid solution, which is thereafter processed.

A process may involve treating calcium sulfate separated from phosphoric acid with acid to obtain a suspension comprising purified calcium sulfate, separating the purified calcium sulfate in solid form from a liquid phase of the suspension, treating the purified calcium sulfate with water or with a salt- and/or chelate ligand-containing aqueous solution to leach rare earths out of the calcium sulfate, separating the further-purified calcium sulfate in solid form from the liquid phase of the suspension, mixing the purified calcium sulfate that is separated off with admixtures and reducing agents to obtain a raw meal mixture for cement clinker production, burning the raw meal mixture to obtain the cement clinker and thereby forming sulfur dioxide as offgas, and feeding the sulfur dioxide as raw material to sulfuric acid production to produce the sulfuric acid.

A process may involve treating calcium sulfate separated from phosphoric acid with acid to obtain a suspension comprising purified calcium sulfate, separating the purified calcium sulfate in solid form from a liquid phase of the suspension, treating the purified calcium sulfate with water or with a salt- and/or chelate ligand-containing aqueous solution to leach rare earths out of the calcium sulfate, separating the further-purified calcium sulfate in solid form from the liquid phase of the suspension, mixing the purified calcium sulfate that is separated off with admixtures and reducing agents to obtain a raw meal mixture for cement clinker production, burning the raw meal mixture to obtain the cement clinker and thereby forming sulfur dioxide as offgas, and feeding the sulfur dioxide as raw material to sulfuric acid production to produce the sulfuric acid.