METHOD FOR OBTAINING SODIUM SULFATE FROM PHOSPHOGYPSUM Russian patent published in 2021 - IPC C01D5/16 C01D5/18 B01D61/00 

FIELD: chemical industry; environmental protection.

SUBSTANCE: phosphogypsum (PG) is leached (101) using basic solution containing 0.1-0.8 M of a chelating agent selected from ethylenediaminetetraacetic acid (EDTA) and its sodium, potassium, calcium disodium, diammonium salt, triethanolamine salt (TEA-EDTA), hydroxyethylethylenediaminetetraacetic acid (GEDTA) and its trisodium salt and mixtures thereof. At the end of stage (101), the dissolution of sodium sulfate is 91-99%. Resulting solution (S) of sodium sulfate containing metal impurities, at least part of which forms complexes with the specified chelating agent, is treated (102) to remove solids (R), for example, by centrifugation and subsequent filtration. At the end of the specified treatment, solution (S) of sodium sulfate has solid particle content of less than 1%. Filtrate (F) is sent to first stage (103) of filtration using nanofiltration membrane (NF1), the cut-off point of which is 150-1000 g·mol^-1. Produced filtrate (P1) is sent to second stage (104) of filtration using nanofiltration membrane (NF2). Concentrates (C1, C2) containing the specified complexes are sent to stage (106) of returning to the chelating agent cycle by precipitation of these metal complexes. Filtrate (P2) produced in second stage (104) of filtration is sent to stage (105) of evaporation at a temperature of 200-250°C to obtain anhydrous sodium sulfate. Filtration (103, 104) using nanofiltration membrane (NF1, NF2) can be carried out once.

EFFECT: invention makes it possible to exclude waste streams that are harmful to the environment.

12 cl, 2 dwg, 2 tbl, 3 ex