BaCl2 is added, a white precipitate is produced, which is stopped when the white precipitate stops increasing, and the precipitate BaSO4 is considered to remove the impurity SO42-;

[Ba2+]+[SO42-]=BaSO4

Na2CO3 is added, a white precipitate is produced, which stops when the white precipitate stops increasing, and the precipitate CaCO3 is considered to remove the impurity Ca2+ and excess Ba2+

[CO32-]+[Ca2+]=CaCO3 [CO32-] +[Ca2+]=CaCO3 [CO32-] +[Ca2+]=CaCO3 [CO32-] +[CO32-] +[Ca2+] =CaCO3 Ca2+ and excess Ba2+

[CO32-]+[Ca2+]=CaCO3 [CO32-]+[Ba2+]=BaCO3

Add NaOH, produce a white precipitate, until the white precipitate is no longer increased when stop, consider the precipitate Mg(OH)2,;

[2OH-]+[Mg2+]=Mg(), and then add NaOH. OH)2

Finally HCl is added until the solution is neutral.

[OH-]+[H+]=H2O

.