Sequential addition: barium chloride (remove sulfate) → sodium hydroxide (remove magnesium chloride) → sodium carbonate (remove calcium chloride, barium chloride) → hydrochloric acid (neutralize sodium hydroxide, sodium carbonate)

folded filter paper with a glass rod dipped in water to moisten it close to the inner wall of the funnel and make the filter paper lower than the mouth of the funnel, the solution level is lower than the filter paper on the top edge of the beaker, the beaker of the liquid pouring to the mouth of the glass rod, the end of the glass rod is against one side of the three layers of filter paper. The end of the glass rod should be close to the side with three layers of filter paper, and the end of the funnel should be close to the inner wall of the beaker receiving the filtrate.

Pour the liquid slowly, and when there is no water in the filter paper, look carefully at what is left on the filter paper and the color of the filtrate. If the filtrate is still cloudy, it should be filtered again.

Expanded:

The angle at which the filter paper is folded should match the caliber of the inner wall of the funnel, so that the moist filter paper is close to the inner wall of the funnel without air bubbles, because if there are bubbles it will affect the filtration speed.

In the whole process of filtration should always be noted that the liquid level of the filtrate should be lower than the edge of the filter paper. This prevents impurities from flowing directly into the beaker unfiltered, so that the unfiltered liquid mixes with the filtrate and makes the filtrate cloudy, without achieving the purpose of filtration.

Baidu Encyclopedia - Coarse Salt Purification