Abstract: A method for decomposing struvite comprises dissolving of a feed material comprising struvite in a mineral acid. Thereby a solution having an acid pH is formed. Magnesium is removed from the solution. The removing of magnesium comprises increasing a pH of the solution to a pH in the range of 4.5 to 6, precipitating magnesium compounds that do not comprise ammonium, and separating the precipitated magnesium compounds from the solution. Thereby, the solution, after the removing of magnesium, comprises an ammonium salt of the mineral acid. An arrangement for performing such a method is also disclosed. Also, a method and arrangement for recovering at least nitrogen from waste material, based on the decomposing of struvite are disclosed.

Abstract: A method for production of phosphate compounds comprises dissolving of a raw material comprising phosphorus, aluminium and iron, in a mineral acid. Insoluble residues from the dissolving step are separated. Iron hydroxide is added causing precipitation of phosphate compounds. The precipitated phosphate compounds are removed. The phosphate compounds are dissolved by an alkaline solution. Iron hydroxide is filtered out. Lime is added, causing precipitation of calcium phosphate. The precipitated calcium phosphate is separated. The leach solution after the separating of precipitated calcium phosphate is recycled to be used for dissolving phosphate compounds by an alkaline solution.

Abstract: A method for production of phosphate compounds comprises dissolving of a raw material comprising phosphorus, aluminium and iron, in a mineral acid. Insoluble residues from the dissolving step are separated. Iron hydroxide is added causing precipitation of phosphate compounds. The precipitated phosphate compounds are removed. The phosphate compounds are dissolved by an alkaline solution. Iron hydroxide is filtered out. Lime is added, causing precipitation of calcium phosphate. The precipitated calcium phosphate is separated. The leach solution after the separating of precipitated calcium phosphate is recycled to be used for dissolving phosphate compounds by an alkaline solution.

Abstract: A method for concentration of phosphate compounds comprises dissolving (205) of sludge ash in hydrochloric acid. Insoluble residues are separated (210), thereby forming a first leach solution. A mole ratio of phosphorus to a sum of ferric iron and aluminum in the first leach solution is controlled (215) to be larger than 1. A base is added (220) to the first leach solution in an amount causing precipitation of phosphate compounds. The precipitated phosphate compounds are removed (225) from the first leach solution. Sulphuric acid is added (240) to the first leach solution, causing precipitation of sulphate compounds. The precipitated sulphate compounds are separated (245) from the first leach solution. At least a part of the leach solution is recycled (248) as the hydrochloric acid used for the dissolving of sludge ash. Further methods for processing the precipitated phosphate compounds are presented as well as arrangements for performing the methods.

Abstract: An arrangement (100) for production of fully soluble, pure and well defined mono- or di-ammonium phosphates, comprises an extraction section (10), a stripping section (20) and end treatment arrangements (90). The extraction section performs a liquid-liquid extraction of phosphate between a feed liquid (1) comprising phosphoric acid and being essentially free from nitrate ions, and a solvent (5) having a solubility in water of less than 2%. The stripping section performs a liquid-liquid extraction of phosphate between solvent loaded with phosphate and a strip solution (4). The solvent depleted in phosphate is recirculated to the extraction section for further extraction of phosphate. The strip solution is an aqueous ammonium phosphate solution, wherein at least 80% of the ammonium phosphate is monoammonium phosphate and/or wherein the solvent is a water-immiscible alcohol.

Abstract: A method for concentration of phosphate compounds comprises dissolving (205) of sludge ash in hydrochloric acid. Insoluble residues are separated (210), thereby forming a first leach solution. A mole ratio of phosphorus to a sum of ferric iron and aluminium in the first leach solution is controlled (215) to be larger than 1. A base is added (220) to the first leach solution in an amount causing precipitation of phosphate compounds. The precipitated phosphate compounds are removed (225) from the first leach solution. Sulphuric acid is added (240) to the first leach solution, causing precipitation of sulphate compounds. The precipitated sulphate compounds are separated (245) from the first leach solution. At least a part of the leach solution is recycled (248) as the hydrochloric acid used for the dissolving of sludge ash. Further methods for processing the precipitated phosphate compounds are presented as well as arrangements for performing the methods.

Abstract: An arrangement (100) for production of fully soluble, pure and well defined mono- or di-ammonium phosphates, comprises an extraction section (10), a stripping section (20) and end treatment arrangements (90). The extraction section performs a liquid-liquid extraction of phosphate between a feed liquid (1) comprising phosphoric acid and being essentially free from nitrate ions, and a solvent (5) having a solubility in water of less than 2%. The stripping section performs a liquid-liquid extraction of phosphate between solvent loaded with phosphate and a strip solution (4). The solvent depleted in phosphate is recirculated to the extraction section for further extraction of phosphate. The strip solution is an aqueous ammonium phosphate solution, wherein at least 80% of the ammonium phosphate is monoammonium phosphate and/or wherein the solvent is a water-immiscible alcohol.