Patent GB-807057-A (GB)
Title: Improvements in or relating to a process for the preparation of water-soluble sulfates, phosphates or nitrates
IPC: C01B25/234
Abstract: A metal (including ammonium) chloride is reacted with sulphuric, phosphoric or nitric acid or with an acid sulphate or phosphate in an aqueous medium, the resultant hydrochloric acid is extracted with an organic solvent therefor which has limited miscibility with water and does not dissolve the salts present, the solvent phase is separated from the aqueous phase and the sulphate, phosphate, or nitrate contained in the latter is recovered in solid form.  Suitable solvents are monohydric alcohols having four or more carbon atoms (e.g. butanols and pentanols), ethers (e.g. diethyl and di-isopropyl ether) and ketones (e.g. methyl ethyl ketone).  Examples describe the preparation of potassium sulphate, sodium sulphate, potassium nitrate, disodium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate and other salts referred to are magnesium sulphate, zinc sulphate, ferrous sulphate, ferric sulphate and ammonium sulphate, phosphate and nitrate.  The extraction may be carried out in countercurrent or batchwise at ambient or elevated temperatures and can be repeated a number of times until the whole of the chloride or acid is used up; the extracted and separated aqueous phase is preferably continuously made up with acid and chloride and recycled.  Where the saturation concentration of the compound to be formed varies directly with the concentration of the hydrochloric acid, the concentration of the anion other than chloride may be made so high that the product salt precipitates during the process, but cooling, e.g. by 10 DEG  to 20 DEG  C., may be employed to separate a solid from the aqueous phase and in an example phosphoric acid is added to the separated aqueous phase after extraction to precipitate sodium dihydrogen phosphate.  The hydrochloric acid may be recovered from the solvent phase by the addition of a water-immiscible solvent such as petrol, hydrocarbons in the naphtha to gas oil range, benzene, toluene or xylene, which does not dissolve hydrochloric acid, sulphuric acid, phosphoric acid or nitric acid and is miscible with the first solvent, whereby a lower aqueous acid phase is formed which can be separated.  Where the process is applied to phosphates, the latter phase may be fractionally distilled to separate hydrochloric acid, leaving a residue of phosphoric acid. The mixed solvent phase can be resolved by fractional distillation and the solvents recycled to the appropriate stages of the process.  Where the solvent phase initially separated from the aqueous phase contains phosphoric and hydrochloric acids, distillation yields fractions of solvent and aqueous hydrochloric acid and a phosphoric acid residue; if the solvent phase contains phosphoric or nitirc acid it may be scrubbed with a concentrated aqueous chloride solution (preferably of the metal whose phosphate or nitrate is being prepared) whereby the phosphoric or nitric acid is removed and the hydrochloric acid may be separated by distillation of the scrubbed solvent or addition of a solvent thereto as indicated above.  The brine employed for scrubbing is used with other reactants in an example to make the aqueous phase to its original composition for the extraction.