PHOSPHOGYPSUM INTEGRATED PROCESSING METHOD Russian patent published in 2005 - IPC

FIELD: inorganic compounds technologies.

SUBSTANCE: invention relates to processing of phosphogypsum, large-scale side product of sulfuric acid-assisted phosphoric acid production process, containing valuable chemicals such as calcium and rare-earth elements. Method is characterized by that carbonization of phosphogypsum is first performed with 2.0-2.5 M sodium carbonate solution at 60-80°C for 30-45 min, at liquid-to-solids ratio 2.0-2.5 to form solid precipitate (insoluble precipitate 1: industrial-grade rare-earth element-contaminated calcium carbonate) and liquid phase, which is evaporated to produce sodium chloride as commercial product. Insoluble precipitate 1 is further calcined at 900-950°C, treated with ammonium chloride and resulting calcium chloride solution is separated from rare-earth element-containing insoluble precipitate (insoluble precipitate 2). The former is carbonized to produce commercial calcium carbonate and the latter is treated with 5-6% hydrochloric acid mixed with ascorbic acid at 80-90°C for 30-60 min, ascorbic acid-to-rare-earth elements weight ratio being (0.4-0.5):1. Thus formed solution containing rare-earth elements is separated from solid 30-32% strontium concentrate, recovered as commercial product, and then neutralized with ammonia to pH 9.0-9.5 to precipitate rare-earth elements. Precipitate is treated with sodium sulfate solution with pH between -0.3 and -0.5 at 80-90°C for 60-90 min to remove phosphates and sesquialteral oxides (R₂O₃) and to produce precipitate containing calcium sulfate and rare-earth elements, which is dried to give commercial product containing mixed calcium and rare-earth element sulfates. Insoluble precipitate 2 containing rare-earth elements is subjected to treatment with aqueous hydrochloric acid in presence of ascorbic acid, solid phase, which is strontium concentrate, is recovered as commercial product and liquid phase is treated with ammonia to pH 9.0-9.5. Resulting precipitate containing rare-earth elements is separated from liquid phase and treated with sodium sulfate solution, after which calcium sulfate and rare-earth elements are separated by known methods.

EFFECT: maximized recovery of valuable components as desired commercial products.

5 cl, 2 dwg, 4 tbl