Adding excessive barium hydroxide solution. Mainly removes magnesium ions and sulfate ions. In high school chemistry books, sodium hydroxide and barium chloride solution were added.

Add excess sodium carbonate solution. It is mainly to remove calcium ions and excess barium ions in the second step. In order not to add excessive sodium carbonate solution twice, it is required to add sodium carbonate solution later.

Filter. ? Remove the precipitate and precipitate produced by the reaction to avoid dissolving the precipitate when hydrochloric acid is added. That's what the high school book says. In fact, it should be filtered before the second step to prevent the precipitate from dissolving in the barium hydroxide solution.

Dropping an appropriate amount of hydrochloric acid. ? In the third step, excess carbonate ions are removed from the solution. Because the reaction will produce gas, when there is no gas, stop adding hydrochloric acid.

Evaporative crystallization

Washington state? The solute in the filtrate is mainly attached to the crystal. In our high school books, we thought that the impurities had been completely removed, but in fact there were a few other impurities.