Why does polyaluminum chloride have a different color after it dissolves?

Polyaluminium chloride (PAC) is a commonly used water treatment chemical used to purify and flocculate water. When polyaluminum chloride is dissolved in water, its color may change. The main reasons are related to the following factors:

1.Hydrolysis of aluminum ions

Polyaluminium chloride decomposes into aluminum ions and chloride ions in water. Aluminum ions can hydrolyze with water molecules to form aluminum hydroxide ions (AI(OH)n^3-n, where n is a value between 1 and 3). Different hydrolysis products may exhibit different colors in solution, ranging from clear to turbid or even colored.

2.Different degree of polymerization

Polyaluminium chloride is a mixture of aluminum skeletons with different degrees of polymerization. Polyaluminium chloride with different degrees of polymerization may have different colors, depending on its molecular structure and the number of aluminum polymerization ions formed.

3.Existence of impurities

There may be some impurities in the raw materials and manufacturing process of PAC, which can also cause the color of the liquid to change after dissolution.

4.Effect of pH

The pH value of the solution may also affect the hydrolysis reaction and color performance of PAC. The structure and concentration of the hydrolysate may change under different pH conditions, thus affecting the color of the liquid.

In general, the change of liquid color after the dissolution of PAC is the result of the hydrolysis reaction of aluminum ions contained therein, the degree of polymerization, impurities and pH value.