Alum water purification mainly utilizes the principle of colloid aggregation and sinking. The aggregation and sinking of colloids is actually the process of destroying the colloids, making the colloidal particles gather into large particles and sink.

Alum dissolved in water, through the hydrolysis of aluminum hydroxide colloids. Because aluminum hydroxide colloid positively charged, and natural water suspended particles generally negatively charged, so the two occurring aggregation of sinking, while the impurities in the water will also be due to the adsorption of aluminum hydroxide colloid together with the sinking, so as to achieve the purpose of purifying water.

Chemical formula

For KAl(SO4)2-12H2O, is a kind of potassium sulfate and aluminum sulfate containing crystalline water of the complex salt. Soluble in water, insoluble in ethanol. Alum is sour and astringent, cold; antibacterial effect, astringent effect, etc., can be used to do traditional Chinese medicine, can also be used for the preparation of aluminum salts, baking powder, paint, tanning, clarifying agent, mordant, papermaking, waterproofing agent, etc., life is often used for water purification.

Because long-term consumption of aluminum-containing food additives is very harmful to the human body, especially for children's growth and development and intelligence will be affected, the country has banned its use in food additives.