What kinds of substances are added to purify the raw salt?

Impurities (Mg2+, Ca2+ and SO42-) were removed by purification of crude salt.

1, adding BaCL2 to generate BaSO4 precipitate-removing SO42-, leaving excess BaCL2.

2. Add NaOH to generate Mg(OH)2 precipitation-remove Mg2+. Excess NaOH remained.

3. Adding NaCO3 to generate precipitated CaCO3-removing Ca2+ and remaining Ba2+, filtering to remove precipitate, and leaving excess NaCO3 in the solution.

Then use dilute hydrochloric acid to remove excessive NaCO3 impurities, and finally heat and evaporate, because hydrochloric acid is volatile.