The water purification equation of alum is Al3++3H2O?Al(OH)3+3H+.

Alum water purification mainly utilizes the principle of colloid coagulation. The coagulation of colloids is actually the process of destroying colloids, causing the colloid particles to aggregate into large particles and settle.

After alum is dissolved in water, aluminum hydroxide colloid is formed through hydrolysis. Since the aluminum hydroxide colloid is positively charged, while the suspended particles in natural water are generally negatively charged, the two will coagulate. At the same time, the impurities in the water will also sink together due to the adsorption of the aluminum hydroxide colloid, thereby purifying the water. purpose.

Physical properties of alum

Alum crystals are colorless or white octahedral crystals that are easily soluble in water. Its crystal structure belongs to the heteropolar trigonal crystal system. Its aqueous solution is acidic and can be used as an astringent. Adding sodium carbonate can produce "neutral alum".

When alum is heated, it will first dissolve in the crystal water it contains. If it continues to be heated, it will lose water and become anhydrous aluminum potassium sulfate white powder, which is called "burned alum" or "dried alum".